Electrochemical dechlorination and hydrocarbon valorization by cobalt phthalocyanine with non-proton-coupled redox property

Domain: physics
Published: 2025-12-21
Editorial outcome: major_revision

Abstract
Electrochemical dechlorination provides a sustainable method to treat chlorinated volatile organic compounds polluted water with producing value-added hydrocarbon. However, dechlorination of dichloromethane (CH2Cl2) generates *CH3 and *CH2Cl intermediates, which are highly unstable due to lack of efficient hyperconjugation from neighboring carbon sites. Herein, we report that cobalt phthalocyanine (CoPc) grafts onto sulfur-doped graphene toward efficient electrocatalysis of CH2Cl2 dechlorination at moderate potentials. It reveal that sulfoxide groups within graphene linked to Co sites by an axial coordination, resulting in an electron donation effect to decrease the barriers of elemental dechlorination step. While in situ electrochemically generates [Co1+Pc]⁻ species mediated the electron transfer from Co sites to CH2Cl2. The production rate of CH4 is significantly enhanced compares to the current level, and an additional case of producing C2H4 and C2H6 is achieved. For potential practical application, the electrochemical dechlorination of a diluted CH2Cl2 solution is validated in an electrofiltration module setup by an efficient flow-through mode.

Introduction
Dichloromethane (CH2Cl2) represents one of the most significant chlorinated volatile organic compounds (CVOCs) with low molecular weights that have been widely used as solvents or cleaning agents in various fields of paint strippers, metal degreaser and the pharmaceutical industry, etc.1–3. However, CH2Cl2 is of high toxicity, which can be persistent in the ecological environment to seriously threaten life health4,5. To degrade CH2Cl2 is mainly realized by thermal and advanced oxidation6–10. While these approaches are operative to completely mineralize CH2Cl2, they require significant energy input and complicated systems to prevent the formation of harmful byproducts (e.g., dioxins and furans)6,11,12. Alternatively, electrochemical dechlorination reduction (EDR) in water powered by renewable energy provides a sustainable approach to degrade CH2Cl2 through cleaving C-Cl bonds and simultaneously generates value-added hydrocarbon compounds through water-enabled protonation13–15. However, EDR in water needs to compete with the hydrogen evolution reaction (HER) for overlapped working potentials, resulting in decreased Faradaic efficiencies (FEs) of cleaving C-Cl bonds and protonating CH2Cl216–19. Such an issue is highly detrimental to the EDR performance, limiting broad-scale up applications.

Metalphthalocyanines (MPcs) represent a type of well-established molecular catalysts, which contain planar macrocyclic geometry to exhibit low steric hindrance for chemisorbing a variety of small molecules20–22. Both the macrocyclic planes and axial positions of MPcs can be systematically regulated to optimize the chemisorption of substrates for the appropriate substrate activation22–25. In addition, the metal sites of MPcs generally exhibit relatively weak chemisorption toward H+/*H species, causing sluggish HER kinetics26–28. These dominant characters make MPcs highly potential for selective EDR. For instance, Wang et al. demonstrated that CoPc loaded on carbon nanotubes efficiently electrocatalyzed dechlorination of 1,2-dichloroethane, competing with trivial HER events14,15,29. However, the *CH3 or *CH2Cl intermediate30,31, which potentially emerges in the EDR of CH2Cl2, is unstable due to lack of efficient hyperconjugation from neighboring carbon sites. This leads to relatively high barriers in the dechlorination of CH2Cl2 compared to cases of treating CVOCs with longer carbon chains. In addition, the elemental pathway of dechlorination has not yet been fully clarified, especially lacking insights into the dynamic interfacial electron transfer from catalysts to CH2Cl2. Thus, it requires further investigations of MPcs-based EDR electrocatalysts with tailored electronic states to stabilize reactive *CH3 and *CH2Cl intermediates, thereby enhancing EDR selectivity and activity of CH2Cl2 together with elucidating the reaction pathway.

On the basis of the aforementioned considerations, we report that CoPc grafted onto sulfur-doped graphene (CoPc-SG) at a mild condition functioned as an efficient electrocatalyst for the EDR of CH2Cl2. The binding of CoPc is accomplished by sulfoxide groups doped in graphene, providing an axial coordination environment to the Co sites. Such an axial binding resulted in an electron donation effect to Co sites that facilitated EDR. It identified that the electron transfer from Co sites to CH2Cl2 was realized through electrochemical generation of [Co1+Pc]⁻ species serving as the electron media. It afforded a production rate (PR) of CH4 significantly enhanced compared to the current reported level, as well as an additional case of C2H4 and C2H6 production. For potential practical application, the EDR process was examined toward diluted CH2Cl2 solution by an electrofiltration module setup in an efficient flow-through operation mode. In one single-pass filtration, 98% of CH2Cl2 was removed with CH4 conversion efficiency of 32.7%.

Results
Synthesis of CoPc-based catalysts
Graphene oxide (GO) was first synthesized following a modified Hummers’ method32. The GO aqueous solution was reacted with thioacetamide under hydrothermal conditions to generate a sulfur-doped graphene (SG, Table S1). Then CoPc complex was linked to SG under a mild condition (80 °C, 12 h, N,N-dimethylformamide)25, and the as-derived sample was denoted as CoPc-SG (all details have been provided in the Supplementary information, SI). The loading amounts of CoPc on SG were approximately 6.62×10−7 mol mg−1 by inductively coupled plasma optical emission spectroscopy (ICP-OES, Table S2). Scanning and transmission electron microscopic (SEM/TEM, Figs. 1a and S1, S2) images revealed the typical graphene characteristics of CoPc-SG without observable metal-based nanostructures or bulk aggregates. Energy-dispersive X-ray (EDX, Fig. S3) mapping images showed a homogeneous distribution of Co elements across those carbon layers. Raman spectra revealed that CoPc-SG contained both the bonding characters of CoPc and SG (Fig. S4)33–35, which verified the successful linking between the two components. X-ray photoelectron spectra (XPS, Figs. 1b and S5 also presented the CoPc characters of CoPc-SG according to the dominant Co 2p3/2 (780.3 eV), Co 2p1/2 (795.8 eV) and N 1s signals. The S sites remained as two forms of carbonized (163.4 eV) and oxidized (167.7 eV) sulfur species, ongoing from SG to CoPc-SG (Fig. 1c)36–38.

Ultraviolet-visible (UV-Vis, Fig. 1d) spectra presented the characteristic B and Q bands of CoPc-SG. The Q band at 663 nm is attributed to the a1u (π)-eg (π*) transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), showing a significant redshift compared to the transition of pristine CoPc. This suggests a ligand modification occurring at the axial position of Co sites24,39. X-ray absorption spectroscopy was employed to analyze the oxidation states and coordination spheres of Co sites, referring to the Co foil, CoO, Co3O4 and CoPc standards. In the normalized X-ray absorption near-edge spectra (XANES, Fig. 1e), CoPc-SG exhibited a discernible shift to a lower energy compared to the pristine CoPc, which is consistent with the shift in the corresponding electron paramagnetic resonance (EPR, Fig. S6) data. According to the Fourier-transformed k3-weighted extended X-ray absorption fine structure (FT-EXAFS, Fig. 1f), the intensity of the first sphere is enhanced going from CoPc to CoPc-SG. Such a result reflected the increased coordination number of Co sites upon interacting with SG. Moreover, the wavelet transform (WT) contour plots (Fig. 1h, i) exhibited a positive shift of k value from the maximum intensity at 7.45 Å−1 in CoPc-SG to 7.05 Å−1 in CoPc, suggesting the tuned coordination of Co sites by the support of SG40,41. As examined by the least squares EXAFS fitting (Fig. 1g, Figs. S7, S8 and Table S3) it revealed that the Co site of CoPc-SG is made of four Co-N scattering paths (1.87 Å) by the planar Pc ligation, and one Co-O scattering path with slightly prolonged distance (1.88 Å), while the pristine CoPc only contains the four Co-N paths. This supports the axial modification of Co sites in CoPc-SG, which is consistent with the UV-Vis data.

Electrocatalytic measurements
The EDR performance was evaluated in a gas-tight H-type cell using a three-electrode setup. An Ar carried CH2Cl2 vapor was continuously fed into 0.1 M KH2PO4 (pH=8.8) at the ambient condition. The high ionic conductivity and buffering capability of the electrolyte ensured durable electrochemical measurement conditions (all potentials refer to the reversible hydrogen electrode, RHE, if not specified). As a main control sample, a reduced OG was synthesized from GO by the same hydrothermal method without introducing any dopants, which linked to CoPc (denoted as CoPc-OG, Figs. S9–S12), following the same procedures as the synthesis of CoPc-SG. A series of chronoamperometric curves presented that CoPc-SG afforded reduced overpotentials with enhanced currents compared to CoPc-OG (Fig. 2a). In-line gas chromatographic (GC) analysis identified the reduction products of EDR as CH4, C2H4 and C2H6 with a fraction of methyl chloride (CH3Cl) (Figs. 2b, c and S13). Apparently, CoPc-SG afforded higher dechlorination efficiency than CoPc-OG by FECH4 and FEC2 up to 62.3% and 13.2%, while a minimal fraction of competent H2 was detected. Correspondingly, CoPc-SG increased the PRs of CH4 and C2 products by more than 6-fold compared to the cases of CoPc-OG at a typical potential of −0.68 V, which reached 53.9 mmol g−1 h−1 and 10.08 mmol g−1 h−1, respectively (Fig. 2d, e). Note that compared to previous works, we reported that the PR of CH4 was significantly enhanced, and an additional case of emerging C2 products (Fig. 2f and Table S4). In the meantime, a quantitative analysis of chloride ions released into the electrolyte was conducted by ion chromatography (IC), verifying that CoPc-SG afforded higher FEs of dechlorination ions compared to CoPc-OG (Fig. S14). Under the same condition, the pristine SG barely showed any EDR activity, indicating the active sites originated from CoPc (Fig. S15). The pristine CoPc without the carbon supports also exhibited significantly degraded FEs and currents of EDR, suggesting that the molecular dispersion of CoPc on the carbon supports is critical to achieve such high EDR performance42. By normalizing the partial reduction currents with the amounts of CoPc exposed on the electrode surfaces (Fig. 2g and Table S5), the TOFs for CH4 and C2 production were assessed. At −0.68 V, the TOFs were enhanced by more than 8-fold for CH4 production, and 7-fold C2 production transiting from CoPc-OG to CoPc-SG, revealing the intrinsically improved dechlorination activity of CoPc by the SG linkage (Fig. 2h, i).

In order to verify the EDR process on CoPc-SG, an in situ attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was conducted under the same conditions as set in the H-type electrolytic cell (Fig. S16). At an open circuit potential (OCP), the emerged IR peaks at 744 cm−1 and 1258 cm−1 are attributed to the C-Cl symmetric stretching and C-H bending vibration of CH2Cl229,43,44. As the potential was made more negative on the CoPc-SG catalyst, a new band appeared at 1448 cm−1. This band, which is absent on the pristine SG support, can be attributed to the C-H deformation vibration of *CH345. Meanwhile, doublet bands emerged at 2989/3008 cm−1 corresponding to the asymmetric stretching vibration of CH3, indicating the dechlorination process46. In contrast, on the pristine SG that only afforded HER events, the peak intensities of C-Cl and C-H vibration are relatively weak, which even decreased with applying reduction potentials, suggesting very weak chemisorption of CH2Cl2 in the absence of CoPc. Correspondingly, there are no vibrations of CH4 being observed. We further conducted EPR spin-trapping experiments using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to probe the EDR intermediates (Fig. S17). The electrolyte exhibited a characteristic six-line pattern with the electrocatalysis of EDR. The hyperfine splitting constants (AN=16.1 G, AH=23 G) agree with the literature values of the DMPO-•CH3 adduct47,48, indicating the generation of *CH3 intermediate. Besides, note that the EDR processes involved the formation of CH3Cl, which should be realized through the protonation of *CH2Cl intermediate49,50.

An insight into dechlorination mechanism
We conducted the density functional theory (DFT) calculations to gain an insight into the CoPc-based EDR process (the atomic coordinates of the optimized computational models are provided in Supplementary Data 1). According to previous studies25, sulfoxide (-SO)/sulfone (-SO2)/sulfonic (-SO3) groups of SG, and carboxyls (-CO2) of OG were considered as typical groups that can link to CoPc, and established the heterogeneous structures of CoPc in CoPc-SG and CoPc-OG, respectively. In the case that CoPc is immobilized onto carbon supports through the Vander Waals force, which does not affect the intrinsic activity in the DFT calculation, a free-standing CoPc is considered51,52. As revealed by the differential charge distribution, CoPc-SO exhibited a prominent electron transfer region at the molecule-graphene interface, which is broader than that in CoPc-CO2 (Fig. 3a). A clear change in Bader charges for CoPc in CoPc-SO was +1.62 e−, which turned to be −0.48 e− in CoPc-CO2. Thus, the sulfoxide group generally exhibited an electron-donating effect to CoPc, which is consistent with the energy shift observed in the XANES data. While the carboxyl group had the inverse effect of electron withdrawing. Based on partial density of state (PDOS, Fig. 3b), the low-to-medium spin transition ongoing from CoPc-CO2 to CoPc-SO facilitated the d orbital filling of Co sites that enhanced the Co-O bond energy. Correspondingly, the interaction energies of the molecule-graphene interface were calculated to be −0.96 eV for CoPc-SO and 0.42 eV for CoPc-CO2 (Fig. 3c). Note that in the cases of CoPc-SO2 and CoPc-SO3 (Fig. S18), the interaction energies of the molecule-graphene interface significantly increased to 2.10 eV and 2.88 eV, suggesting that the formation of CoPc-SO2 and CoPc-SO3 is relatively difficult.

Toward the EDR pathway, it involves multiple elemental steps of dechlorination and protonation to generate *CH2Cl and *CH3 intermediates (Figs. 3d and S19–S21). The cleavage of the C–Cl bond is identified as a potential-limiting step. For the dechlorination of either CH2Cl2 or CH3Cl, the energy barriers on CoPc-SO are significantly lower than those on CoPc-CO2, as well as those on the free-standing CoPc by reducing 0.5–0.7 eV. For CoPc-SO2 and CoPc-SO3, the dechlorination processes are even more difficult than the free-standing CoPc and CoPc-CO2. Accordingly, among those various models, the electron donation ability of linkages exhibits a negative correlation with the Gibbs free energy of the elemental dechlorination steps (Fig. 3e). These results are highly consistent with the experimental results and demonstrate that the linkage of sulfoxides resulted in electron donation to the Co sites, which facilitates C-Cl bond cleavage and thus enhances the EDR performance. In addition, we presented the complete Gibbs free energy changes for the pathways of EDR into CH4, C2H4 and C2H6 products based on the proposed CoPc-SO configuration (Figs. S22, S24, S25). For C2 products, the DFT calculations revealed that the involved C-C coupling elemental steps followed the Eley-Rideal mechanism, where surface-bound intermediates (*CH2Cl or *CH3) reacted with solvated CH2Cl2 molecules (Fig. S23)53,54. In all cases, CoPc-SO exhibited consistently lower energy barriers than both pristine CoPc and CoPc-CO2 samples, underscoring the pivotal role of the sulfoxide axial coordination in facilitating the EDR processes.

In the DFT calculations, it is found that both CH2Cl2 and CH3Cl cannot directly chemisorb onto CoPc, as the distance between Co (CoPc) and C (CH2Cl2/CH3Cl) sites is more than 3.6 Å. The onset potential of EDR on CoPc-SG approaches −0.28 V. Prior to this catalytic potential, the Co2+/1+Pc redox was observed (Fig. S26). Thus, CoPc should electrochemically evolve by generating Co1+ sites to commence EDR55,56. To validate such an assumption, an in situ Raman spectroscopic measurement was conducted in an electrochemical cell set with a transparent quartz window. CoPc-SG exhibited distinct peaks at 1145 and 754 cm−1 at OCP, corresponding to the A1g (Co-N and C-H vibrations) and B1g (in-plane ring symmetric Co-N pyrrole stretch) modes of CoPc, respectively (Fig. 4a). As the potential passed across the CoPc redox range, the A1g and B1g modes gradually shifted to 1125 cm−1 and 746 cm−1, respectively, signifying the Co2+ to Co1+ reduction prior to the EDR events (Fig. 4b, c). However, the redox of CoPc contains two different pathways that have either H+ coupling or H+ non-coupling character to generate different structures57. We then examined the pH dependence of Co2+/1+ redox in a broad pH range in various PBS buffers, and established the Pourbaix diagram (Fig. S27). The Pourbaix slope of Co2+/1+Pc-SG redox is only −4.3 mV pH−1, indicating that the redox event is barely coupled with H+ transfer. The Co2+ to Co1+ reduction should generate [Co1+Pc]⁻ species instead of the possible [Co1+PcH] species as previously reported57, which commenced EDR and the competent HER events (Fig. 4d, e). As the DFT calculation showed an intermediate state in which the *CH2Cl species bonded with CoPc, it indicated that the [Co1+Pc]⁻ sites should bond to CH2Cl2, and the additional electrons transferred to the bonded CH2Cl2 for commencing the dechlorination elemental step (Fig. 4f, g).

Besides, the Pourbaix slope of HER on CoPc-SG was fitted to be −58.1 mV pH−1 for the typical one H+ and one electron coupled transfer process (Fig. S28). Upon the EDR event involving into HER, the Pourbaix slope significantly turned to be a positive value of +21.6 mV pH−1, which approaches the Co2+/1+Pc redox potential with increasing pH. Such a phenomenon is observed in our previous result, indicating that the alkaline environment could facilitate the chemisorption of CH2Cl2 on the [Co1+Pc]− sites. In the case of CoPc-OG, it follows the same evolution process of CoPc (Figs. S29, S30). While the Laviron analysis showed that the redox kinetics of Co2+/1+Pc in CoPc-SG is more rapid than that in CoPc-OG (Fig. S31)58, suggesting the tuned electron communication between CoPc and carbon supports by the S-based linkages, and should reflect the above DFT calculation results.

Electrochemical membrane performance
For the scale up application, CoPc-SG was integrated into a self-made electrofiltration module setup to assess its performance in treating the CH2Cl2-contaminated wastewater in a flow-through operation mode (Fig. 5a). The module comprises a feed chamber with a commercial RuO2-IrO2/Ti mesh anode (top), and a permeate chamber featuring a CoPc-SG coated carbon paper (CP) supported by a polyvinylidene difluoride (PVDF) membrane as the cathode (CoPc-SG@CP, bottom). The feeding solution is 0.1 M KH2PO4 with 3 mM CH2Cl2. The as-derived CoPc-SG@CP exhibited a lower water permeability of 100.5 L m−2 h−1 compared to 135 L m−2 h−1 of the pristine CP, which allowed extended residence time for dealing with water purification (Fig. S32). In one single-pass filtration (details in SI), 98% of total CH2Cl2 was removed at a constant current density of 75 mA cm−2 for 300 mL 3 mM CH2Cl2 solution (Figs. 5b–d and S33), including 32.7% of CH2Cl2 converted into CH4, 1.64% of CH2Cl2 converted into C2 products, 63% of CH2Cl2 converted into the incompletely dechlorinated byproduct of CH3Cl and some CH2Cl2 might be physically adsorbed (under the same condition, we indeed detected that the CP electrode without the loading CoPc-SG removed 59% of CH2Cl2 without generating CH4, C2 products and CH3Cl). In addition, the process remained highly energy-efficient, achieving a relatively low electrical energy consumption per order (EEO) of 0.062 kWh m−3 under 75 mA cm−2 (Fig. 5e), which is substantially lower than the EEO value of 0.42 kWh m−3 reported in an analogous cross-flow system treating another typical chlorinated organic compound of 1,2-dichloroethane14. The performance degradation at 100 mA cm−2 could be ascribed to the overly limited mass transport of CH2Cl2 reactant by increasing the applied currents. To provide a more complete picture of the system’s performance, we also calculated the FE for these products (Fig. S34). The concentrations of released Cl− ions showed a consistent variation trend (Fig. S35). Particularly, the vertical flow mode is more effective for enriching and treating trace or low concentrations of CH2Cl2 compared to the traditional lateral flow mode (Fig. S36). To assess the durability of the device, the flow-through electrofiltration was continuously operated for 10 cycles, which maintained the high PRs of CH4 and C2 production, and Cl− ions release (Figs. 5f and S37).

Methods
Materials
Dichloromethane (DCM; 99%), N,N-dimethylformamide (DMF; 99.5%), Phthalocyanine (HPc; 99.5%), K3PO4 (99%), KH2PO4 (99.7%) and K2HPO4 (99.7%) were purchased from Sigma-Aldrich. Co(NO3)2·6H2O (99%), Graphite powder (99%), K2S2O8 (99.5%), P2O5 (99.99%), thioacetamide (98%) were purchased from Macklin Biochemical Technology. The RuO2-IrO2/Ti mesh was purchased from Hangzhou Saiao Technology. Deionized water (18.2 MΩ cm at 25 °C) from a Millipore water purification system was used throughout the experiments. Unless otherwise noted, all the commercial chemicals were used without purification. All solutions in this work were prepared using ultrapure water.

Synthesis of CoPc-SG and CoPc-OG
GO was synthesized based on a modified Hummers’ method. Firstly, 2 g graphite powders, 1 g K2S2O8 and 1.2 g P2O5 were added into 20 mL 98% H2SO4, and were heated at 100 °C for 10 h. The resultant solids were washed with water to neutrality and dried to obtain a pre-oxidized product. Afterwards, the pre-oxidized product was transferred into 50 mL 98% H2SO4 in an ice bath, and 6.5 g of KMnO4 was slowly added. The mixture was heated in an oil bath at 50 °C for 6 h to further react with KMnO4. Finally, 5 mL of H2O2 was added under ice bath conditions, and the final product was bright yellow. The final solid was washed with 3.7% HCl and plenty of water, centrifuged and dialyzed for 7 days to obtain GO.

To obtain a sulfur-doped graphene (SG), thioacetamide was used as the dopant, and mixed with GO aqueous solution (1 mg mL−1) (mass ratio 1:50). Then the suspension was transferred into a polytetrafluoroethylene-lined stainless autoclave for heat treatment at 150 °C for 3 h. After the reaction, the resultant solids were washed with water and ethanol to obtain the desired SG. As a control sample, the oxygen-doped graphene (OG) was synthesized from GO following the same hydrothermal conditions without using any dopants.

To obtain heterogeneous cobalt complexes, the as-synthesized SG or OG (4 mg) was dispersed in 20 mL DMF and mixed with 2 mg of cobalt phthalocyanine (CoPc). The resultant dispersion was heated at 80 °C for 12 h, and washed with ethanol to remove excess CoPc. The final solid was dispersed in isopropanol with a concentration of 2 mg mL−1 to obtain the catalyst ink, which was denoted as CoPc-SG and CoPc-OG, respectively.

Electrochemical measurements
All electrochemical measurements were conducted using a CHI1140 potentiostat in a three-electrode setup at room temperature (25 °C). A gas-tight H-type cell was employed with a cathode chamber (50 mL) and an anode chamber (50 mL) separated by a proton exchange membrane (Nafion-117, 183 μm in thickness). Prior to use, the Nafion-117 membrane was pretreated by sequential 80 °C boiling steps in 5 wt% H2O2, deionized water, 1.0 M H2SO4. All potentials were measured against a Hg/HgO electrode, unless indicated otherwise. A graphite electrode was used as the counter electrode. The supporting electrolyte was 0.1 M K2HPO4 solutions (pH=8.8 ± 0.1, stored in a sealed container at 25 °C). (CPs, 1×1 cm2) With casting, 140 μL catalyst inks were used as the working electrodes, the covered area was 2 cm2, giving a catalyst mass loading of 0.14 mg cm−2.

For the electrocatalysis of EDR, Ar was flown at 20 ccm through a pure CH2Cl2 liquid to carry CH2Cl2 vapor into the cathode chamber for at least 30 min to obtain a CH2Cl2 aqueous solution before each electrolysis. All the electrochemical CH2Cl2 dechlorination measurements were conducted with stirring at 300 rpm. The Ar carried the CH2Cl2 vapor was kept bubbling into the electrolyte during the electrolysis. Gaseous products from the cathodic chamber were analyzed in real-time by in-line (GC, Agilent Technologies 8890) equipped with Hayesep D/N and Molsieve 5A columns, a thermal conductivity detector (for H2 detection) and a flame ionization detector (for hydrocarbons detection). All the reported current density was normalized to the geometric area of CP without iR compensation. All recorded potentials (E) were converted to the reversible hydrogen electrode (RHE) scale with the Eq. (1),

E(vs. RHE) = E(vs. Hg/HgO) + 0.098 + 0.592 × (pH) (1)

The Faradaic efficiency for products was calculated using the Eq. (2),

FE(%) = (n × F × M) / Q (2)

where n is the number of electron transfer, M is the relative molecular mass, F is the Faraday constant, Q is the quantity of applied electricity.

Turnover frequency and production rate analysis
Turnover frequency (TOF) was calculated based on Eq. (3),

TOF = (J × A) / (n × F × M) (3)

where J is the cathodic current density, A is the geometric surface area of the electrode, F is Faraday’s constant, and M is the molar amount of Co sites on the surface of the electrode. The molar amount of Co sites was quantified by ICP-OES. In brief, the electrodes coated with catalysts were immersed in 0.5 mL HNO3 (65%) for 3 min, and the resultant acidic solutions containing Co2+ ions were diluted to 5 mL, and then were tested by ICP-OES. The PR was calculated as the molar amounts of CH4 or C2 produced per gram of catalyst per hour.

In situ attenuated total reflectance Fourier transform infrared spectra
In situ ATR-FTIR spectra were performed on a Thermo Fisher Scientific Nicolet iS50 FTIR spectrometer, equipped with a diamond crystal and a DLaTGS detector cooled with liquid nitrogen. A customized three-electrode electrochemical single-cell was used for tests. Graphite rod and Ag/AgCl were used as the counter and reference electrodes, respectively, and CoPc-SG coated CP were used as the working electrodes. For ATR-FTIR measurement, 64 scans were collected with a spectral resolution of 1 cm−1. The potential-dependent spectra were collected by applying the working potential from 0.28 to 0.78 V vs. RHE in 0.1 M K2HPO4 with steps and durations of 0.1 V and 120 s, respectively.

In situ Raman spectra
In situ Raman measurements were conducted on an electrochemical cell quartz window in 0.1 M K2HPO4. An Ag/AgCl wire (soaked in saturated KCl) and a carbon rod were used as the reference and counter electrode, respectively. Glassy carbon electrodes coated with catalysts were used as the working electrodes. Raman spectral window was set as 200–1200 cm−1, and the acquisition time was set as 90 s with a 638 nm laser.

Electrochemical membrane
The filtration module consists of upper and lower chambers with gas collection and inlet and outlet ports, a CoPc-SG@CP/PVDF/Ti mesh and a commercial RuO2-IrO2/Ti mesh was applied as the cathode and anode, respectively, and were connected with a DC power supply (UNI-T, UTP136S). The size of the CP coated with the catalyst was 32 cm−2. Typically, in one single-pass filtration, the feeding solution of 3 mM CH2Cl2 dissolved in 300 mL 0.1 M K2HPO4 was circulated utilizing a constant-current pump (Rongbai, BT100-2J) under a constant current density of 25/50/75/100 mA cm−2. After 1 h of operation, any gaseous products generated from EDR in the upper chamber were collected through a gas collection port, and the anodic gas was collected in the lower chamber. The collected gases were quantitatively analyzed by gas chromatography, the Cl- ions released into the solutions were measured by IC, and the amounts of residual CH2Cl2 were measured by 1H NMR.

Computational details
Spin-polarized DFT calculations were performed by the Vienna ab initio simulation package (VASP) with the projector augmented method to describe the interaction between atomic cores and valence electrons59–61. The exchange-correlation functional is treated with the generalized gradient approximation in the form of Perdew-Burke-Ernzerhof62 CoPc, CoPc-OG, and CoPc-SG slab models were employed to simulate the surface properties. The vacuum layer was set around 15 Å in the z-direction to avoid interaction between neighboring images. The Van der Waals interaction is considered using the DFT-D3 method. An energy cutoff for the plane wave basis expansion was set to 480 eV, and the force on each atom less than 0.03 eV/Å was set as the convergence criterion for geometry relaxation. The k-points in the Brillouin zone were sampled by a 1×1×1 grid63. The electronic energy was considered self-consistent with the energy change less than 10–5 eV. VASPsol was used to simulate the solvent effect in the experimental environment64.

The energy differences (ΔE) for the reactions were calculated according to the approach proposed by Nørskov and coworkers, ΔE=ΔE0+ΔEU, where ΔE0 is the computed reaction energy, ΔEU is the externally applied potential. In the dechlorination process, ΔEU = −e(U − UθCl), where UθCl is the standard potential of the reversible chlorine electrode, UθCl = 1.36 V at 298 K. In the hydrogenation process, ΔEU = −eUH, where UH is the electrode potential relative to the standard hydrogen electrode, UH = 0 V at 298 K.

Electrical energy consumption
Electrical energy consumption per order (EEO, kWh m−3 order−1) for CH2Cl2 reduction during electrofiltration was evaluated using the Eq. (4),

EEO = (Ucell × I) / (Q × log(C0 / C)) (4)

where Ucell (V) is the applied voltage, I (A) is the current, Q is the permeate flow rate, C0 and C are the initial and timely measured contaminant concentrations, respectively.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study reports that cobalt phthalocyanine (CoPc) grafted onto sulfur-doped graphene (CoPc-SG) under mild conditions\nserves as an efficient electrocatalyst for the electrochemical dechlorination reduction (EDR) of CH₂Cl₂. The production rate\n(PR) of methane (CH₄) is enhanced by more than one order of magnitude compared to reported levels, with simultaneous\nsynthesis of ethylene (C₂H₄) and ethane (C₂H₆) achieved for the first time. The research demonstrates significant innovation\nand publication potential, and specific comments on details are provided as follows:\n1. The authors only calculated the free energy diagrams for the elementary dechlorination reactions of CoPc, CoPc-SO and\nother systems, but did not present the free energy changes for the complete reaction pathways. It is recommended to\nsupplement the free energy profiles for the entire reaction processes, which will be more helpful for in-depth understanding\nof the dechlorination mechanism.\n2.The authors claim that sulfoxide groups in SG are linked to Co sites through axial coordination. Could the authors provide\nmore experimental evidence?\n3.In the computational part, the authors failed to account for the role of water, which might render the results less plausible. It\nis strongly suggested that the authors explicitly incorporate solvent effects into their calculations to enhance the accuracy\nand reliability of the computational outcomes.", "reviewer_2": "In this manuscript, Wang et al. reported that CoPc grafted onto sulfur-doped graphene (CoPc-SG) could serve as an efficient\nelectrocatalyst for the electrochemical dechlorination of CH2Cl2. Additionally, the study revealed that axial coordination of\nsulfoxide groups in graphene facilitated electron donation to lower the barriers of dichlorination step, and demonstrated\npractical applicability using flow-through electrofiltration of diluted CH2Cl2 solution. However, several critical issues remain\nto be addressed regarding mechanistic elucidation, experimental validation, and demonstration of innovation. Addressing\nthese issues, outlined in the detailed comments below, is essential before the work can be considered for publication in\nNature Communications.\n1. In the mechanistic study, the authors primarily used theoretical calculations to illustrate how axial ligands facilitate C-Cl\nbond cleavage, but failed to provide experimental evidence for key intermediates in the reaction pathway (such as *CH2Cl\nor *CH3). It is suggested that the authors supplement their reaction pathway analysis with more convincing experimental\nevidence, such as using probe molecules combined with EPR to capture and characterize potential adsorbed intermediates.\n2. The formation of C2 coupling products following C-Cl bond cleavage is particularly intriguing. Given that CoPc is\nuniformly monodispersed on the SG support, the substantial size of the ligand framework keeps adjacent Co sites relatively\ndistant from each other. Therefore, it appears mechanistically puzzling how the CH2Cl2-derived intermediates could\nsubsequently couple to form C2 products. The authors need to provide further analysis and explanation for this\nphenomenon.\n3. The authors' interpretation of some experimental evidence may involve overanalysis: (1) in the Wavelet transform (WT)-\nEXAFS analysis, the claimed Co-O scattering path (1.88 Å) is hardly identifiable from the presented data; (2) the assignment\nof the weak 3007 cm⁻¹ signal in FTIR spectra to C-H vibration of CH4 appears questionable due to its negligible intensity.\n4. The data and the corresponding analysis presented in the wastewater treatment application section appear limited in\nseveral aspects: (1) At 98% CH2Cl2 conversion, besides 32.7% CH4 and minor C2 products, the identity of other major\nproducts remains unclear (potentially incomplete dechlorination byproducts like CH3Cl?); (2) The Faradaic efficiency (FE)\nof the wastewater treatment system was not reported; (3) The significant performance degradation at higher current density\n(100 mA/cm²) lacks mechanistic explanation (possibly due to HER dominance?). We recommend the authors provide\nadditional analysis on these aspects.\n5. The electrofiltration module setup employed in the wastewater treatment section appears similar to those previously\nreported for wastewater remediation (e.g., nitrate (Nat. Chem. Eng. 2025, 2, 379) and CVOC removal (Nat. Nanotechnol.\n2023, 18, 160)). We are curious whether the current configuration presents any substantive differences from these prior\nsystems. Furthermore, since the Introduction highlights the high energy input associated with industrial pollutant degradation\nmethods, it would be valuable to include a comparative analysis of energy consumption or economic feasibility for this\nsystem to enable comprehensive assessment of its practical potential.", "reviewer_3": "Y. You presented a work dedicated to the electrocatalytic dechlorination of dichloromethane to produce methane and minor\nC2 products. A CoPc-based catalyst supported by Sulfur-doped graphene was employed, which is claimed to be capable of\nstabilizing the CH2Cl and the CH3 intermediates, key to the production of methane. The work has performed a good variety,\nand amount, of characterizations, attempting to provide insights on the reaction mechanism.\nWhile I appreciate the amount and quality of the data in general, I regret to say that I cannot support publication of the work in\nNature Communications at the moment, because I question the techno-economic feasibility, as well as the advancement in\nperformance, of the work. I have the following specific questions and comments.\n1. The major performance advancement, as claimed by the authors, is the high-selectivity production of methane, and the\nproduction of trace amount of C2 products. However, it seems that similar achievements have been reported by Ref. 13 cited\nby the authors. Ref. 13 reports similar products and selectivity (FE) with much higher reaction rate in terms of current density\nand TOF.\n2. Along this thread, the authors compared their performance with other works in Table S4, but they only listed works\nperformed in DMF solvent. Why did they not list other works performed in water as solvent? I also encourage the authors to\nlist other performance factors: FE and current density are more important than the specific production rate to me. The specific\nproduction rate, which is obtained by normalizing to the loading of catalyst, is more important if the catalyst is very\nexpensive.\n3. Is the production of specific feedstock important to the dechlorization of dichloromethane? If the authors claim so then they\nshould support that claim with a techno-economic analysis. In turn, if they do not expect to make profit from the products, they\ncan just reduce the dichloromethane (as a pollutant) all the way down to CO2 and Cl ion.\n4. Can the in-situ Raman resolve any peak for the CH2Cl intermediate which is supposed to be the most critical for the\nwork?\n5. If the authors claim the production of C2 products as a major advancement, they should add discussions (with appropriate\nexperimental data) on the C-C coupling mechanism."}, "author_response": "Response to Reviewer #1\nThis study reports that cobalt phthalocyanine (CoPc) grafted onto sulfur-doped\ngraphene (CoPc-SG) under mild conditions serves as an efficient electrocatalyst for the\nelectrochemical dechlorination reduction (EDR) of CH Cl . The production rate (PR)\n2 2\nof methane (CH ) is enhanced by more than one order of magnitude compared to\n4\nreported levels, with simultaneous synthesis of ethylene (C H ) and ethane (C H )\n2 4 2 6\nachieved for the first time. The research demonstrates significant innovation and\npublication potential, and specific comments on details are provided as follows:\nResponse: We sincerely thank the reviewer for the positive recommendation and\nconstructive feedback, which are highly valuable to improve the quality of our\nmanuscript. Based on these comments, we have accordingly provided the point-by-\npoint responses as presented below, and revised our work with the best efforts. All the\nchanges in the revised manuscript and revised SI appendix have been highlighted in\nblue for clarity.\n1. The authors only calculated the free energy diagrams for the elementary\ndechlorination reactions of CoPc, CoPc-SO and other systems, but did not present the\nfree energy changes for the complete reaction pathways. It is recommended to\nsupplement the free energy profiles for the entire reaction processes, which will be more\nhelpful for in-depth understanding of the dechlorination mechanism.\nResponse: We sincerely thank the reviewer for the valuable advice. We have analyzed\nthe comprehensive free energy diagrams for the whole pathways of electrochemical\ndechlorination of CH Cl into the experimentally observed products, including CH ,\n2 2 4\nC H and C H . Our initial calculations and XPS surveys have implied that the\n2 4 2 6\nsulfoxide (-SO) group of SG functioned to link CoPc with enhancing the Co sites based\nEDR electrocatalysis. Accordingly, such a core immobilized molecular configuration\nwas investigated and compared with the free standing CoPc and CoPc linked to the\ntypical carboxyls (-CO ) group of OG as discussed in the initial manuscript.\n2 2 4\nsequential elemental steps of dechlorination and protonation (J. Phys. Chem. C 2025,\n129, 9356; ACS Appl. Mater. Interfaces 2023, 15, 12915). For the CH Cl -to-C\n2 2 2\nproducts pathways, our calculations indicate that the Eley-Rideal mechanism is\noperative, where a surface-bound intermediate (*CH Cl or *CH ) coupled with a\n2 3\nsolvated CH Cl molecule to realize the C-C coupling elemental step (J. Am. Chem.\n2 2\nSoc. 2025, 147, 21764; J. Am. Chem. Soc. 2024, 146, 13949). Note that the CH Cl -to-\n2 2\nC products pathways generally quired higher barriers compared to the CH Cl -to-CH\n2 2 2 4\npathway, which thus should lead to the inferior selectivity of C production compared\n2\nto that of CH production being consistent with our experimental results of EDR\n4\nmeasurements. Nevertheless, toward the production of C H (Figure R2), the pathway\n2 4\ninvolves the critical coupling of *CH Cl with CH Cl followed by dechlorination\n2 2 2\nelemental steps to form a *CH CH Cl intermediate, which underwent further\n2 2\ndechlorination to generate C H . Toward the production of C H (Figure R3), it is both\n2 4 2 6\nthermodynamically feasible that *CH Cl or *CH can couple with CH Cl to realizethe\n2 3 2 2\ncritical C-C coupling for the further dechlorination and hydrogenation.\nAcross the pathways of CH and C production, the established CoPc-SO moiety\n4 2\nconsistently exhibited lower energy barriers compared to the pristine CoPc (black lines)\nand CoPc-CO (blue lines). This result reinforces our conclusion that the axial\n2\ncoordination of sulfoxide groups on SG exhibited electron donation effect to Co sites,\nthereby lowering the barriers of C-Cl bond cleavage throughout the entire reactions.\nIn the revised SI appendix, we have added Figures R1-R3 as Figures S22-S24,\nrespectively. Correspondingly, we have added the following discussion in the revised\nmanuscript, “In addition, we presented the complete Gibbs free energy changes for the\npathways of EDR into CH , C H and C H products based on the proposed active\n4 2 4 2 6\nCoPc-SO configuration (Figures S22-S24). For C products, the DFT calculations\n2\nrevealed that the involved C-C coupling elemental steps followed the Eley-Rideal\nmechanism, where surface-bound intermediates (*CH Cl or *CH ) reacted with\n2 3\nsolvated CH Cl molecules (Figure S25).52,53 In all cases, CoPc-SO exhibited\n2 2\nconsistently lower energy barriers than both pristine CoPc and CoPc-CO samples,\n2\nunderscoring the pivotal role of the sulfoxide axial coordination in facilitating the EDR\nprocesses.”\nFigure R1. Free energy diagrams of CH formation including dichlorination and\n4\nprotonation steps on free-standing CoPc, CoPc-SO and CoPc-CO .\n2 4\nprotonation and C-C coupling steps on free-standing CoPc, CoPc-SO and CoPc-CO .\n2 6\nprotonation and C-C coupling steps on free-standing CoPc, CoPc-CO and CoPc-SO in\n2\ntwo different pathways.\n2. The authors claim that sulfoxide groups in SG are linked to Co sites through axial\ncoordination. Could the authors provide more experimental evidence?\nResponse: We sincerely thank the reviewer for the valuable comment. We\nacknowledge that providing direct, atomically resolved experimental proof of a specific\naxial Co-O linkage between the sulfoxide group and the Co site is exceptionally\nchallenging with available characterization techniques. While we have established\nindirect but solid experimental and theoretical investigations to support this assignment.\nFirstly, the presence of sulfoxide groups in SG was suggested by the XPS S 2p survey.\nThe S 2p signal emerged at 167.7 eV (Figure R4a), which is well matched with the\nreported binding energies of sulfoxide (-SO) groups (Phys. Scr. 1970, 1, 286, Figure\nR4b).\nSecondly, grafting CoPc onto the SG support induced a significant red-shift of the\nQ-band as gained in the UV-Vis spectra (Figure R4c), which has been considered as a\nwell-established character of axial ligand modification in phthalocyanine based\ncomplexes (Angew. Chem. Int. Ed. 2020, 59, 19162; ACS Catal. 2021, 11, 21, 13203).\nEXAFS fitting of CoPc-SG revealed an additional Co-O scattering path that is absent\nin pristine CoPc, providing experimental evidence for the presence of an axial Co-O\ncoordination (Figure R4d).\nFinally, our DFT calculation confirmed that the sulfoxide group is the effective\nanchoring site, stabilizing CoPc via the axial Co-O bond. The interaction energies of\nmolecule-graphene interface were calculated to be -0.96 eV for CoPc-SO (Figure R4e).\nWhile in the potential cases of CoPc-SO and CoPc-SO , the interaction energies of\n2 3\nmolecule-graphene interface significantly increased to 2.10 eV and 2.88 eV, suggesting\nthat the formation of CoPc-SO and CoPc-SO isrelatively difficult.\n2 3\nFigure R4. (a) XPS S 2p core levels of SG and CoPc-SG. (b) S 2p electron binding\nenergies for S based compounds (Phys. Scr. 1970, 1, 286). (c) UV-Vis spectra of CoPc,\nSG and CoPc-SG. (d) FT-EXAFS fitting curves of CoPc-SG in R space. (e) Interaction\nenergy of CoPc-SO, CoPc-SO and CoPc-SO .\n2 3\n3. In the computational part, the authors failed to account for the role of water, which\nmight render the results less plausible. It is strongly suggested that the authors explicitly\nincorporate solvent effects into their calculations to enhance the accuracy and reliability\nof the computational outcomes.\nResponse: We sincerely thank the reviewer for this crucial suggestion. Following this\ncomment, we have also calculated the Gibbs free energy profile of dechlorination and\nhydrogenation steps based on the reduction of CH Cl to the CH product using an\n2 2 4\nimplicit solvent model (VASPsol). It directly compared the complete reaction pathway\nof CH formation in vacuum versus in water (Figure R5). The results showed that the\n4\ninclusion of solvent model has very slight impact shifting on the free energy of\nelemental steps, and the overall energetic trends, including the identification of the C-\nCl bond cleavages as the rate-determining step, as well as the relatively lower EDR\nbarrier of CoPc-SO moiety compared to those of control samples (CoPc-CO and\n2\npristine CoPc) remained unchanged.\nFigure R5. Free energy diagrams of dechlorination and protonation process to generate\nCH on CoPc-SG without (a) and with (b) the solvent model.\nIn this manuscript, Wang et al. reported that CoPc grafted onto sulfur-doped graphene\n(CoPc-SG) could serve as an efficient electrocatalyst for the electrochemical\ndechlorination of CH Cl . Additionally, the study revealed that axial coordination of\n2 2\nsulfoxide groups in graphene facilitated electron donation to lower the barriers of\ndichlorination step, and demonstrated practical applicability using flow-through\nelectrofiltration of diluted CH Cl solution. However, several critical issues remain to\n2 2\nbe addressed regarding mechanistic elucidation, experimental validation, and\ndemonstration of innovation. Addressing these issues, outlined in the detailed\ncomments below, is essential before the work can be considered for publication in\nNature Communications.\nResponse: We sincerely thank the reviewer for the valuable and constructive feedback,\nwhich has prompted us to carefully reconsider several aspects of our work. Based on\nthese comments, we have revised the manuscript thoroughly to address the concerns\nraised. We have done our best to incorporate the suggested improvements, and the\nspecific point-by-point responses are provided below. All revisions in the manuscript\nand SI appendix have been highlighted in blue for clarity.\n1. In the mechanistic study, the authors primarily used theoretical calculations to\nillustrate how axial ligands facilitate C-Cl bond cleavage, but failed to provide\nexperimental evidence for key intermediates in the reaction pathway (such as *CH Cl\n2\nor *CH ). It is suggested that the authors supplement their reaction pathway analysis\n3\nwith more convincing experimental evidence, such as using probe molecules combined\nwith EPR to capture and characterize potential adsorbed intermediates.\nResponse: We sincerely thank the reviewer for this insightful suggestion. We fully\nagree that providing experimental evidence for key intermediates is critical to\nstrengthen the proposed reaction pathway. Following this advice, we performed EPR\nspin-trapping experiments using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a\nradical-trapping agent.\nThe electrolyte with adding DMPO exhibited flat EPR signals before the EDR\nelectrolysis, whereas after the electrolysis, it emerged a characteristic six-line signals\n(Figure R6). The hyperfine splitting constants (A = 16.1 G, A = 23 G) match with\nN H\nthe literature values for DMPO-•CH adduct (A = 15.9 G, A = 22.8 G, Water Res.\n2022, 221, 118747). According to the in situ ATR-FTIR spectra (Figure R7), a distinct\nband exclusively emerged at 1448 cm-1 on CoPc-SG, corresponding to the C-H\ndeformation vibration of *CH (Nat. Commun. 2025, 16, 2831; ACS Catal. 2025, 15,\n3\n11, 9717). This data provides the additional experimental evidence for the generation\nof *CH intermediate. These should provide straightforward experimental proofs for\n3\nthe formation of *CH species during the CH Cl dechlorination.\n3 2 2\nToward the *CH Clspecies, we have thoroughly searched for the relevant literature\n2\nbut did not find reliable detection methods of •CH Cl radical. Nevertheless, we obtained\n2\nsolid indirect evidence of its formation. Since CH Cl was detected as a reduction\n3\nproduct in our experiments of EDR, the only plausible pathway to the CH Cl formation\n3\nis via protonation of the •CH\nJ. 2023, 470, 144040). Take together with our DFT calculations, these results should\nestablish a convincing picture of the dechlorination pathway involving both *CH Cl\n2\nand *CH intermediates.\nas Figure S16. Correspondingly, we have added the following discussion in the revised\nmanuscript.\n“We further conducted EPR spin-trapping experiments using 5,5-dimethyl-1-\npyrroline N-oxide (DMPO) to probe the EDR intermediates (Figure S17). The\nelectrolyte exhibited a characteristic six-line pattern with the electrocatalysis of EDR.\nThe hyperfine splitting constants (A = 16.1 G, A = 23 G) agree with the literature\nN H\nvalues of the DMPO-•CH adduct,47,48 indicating the generation of *CH intermediate.\n3 3\nBesides, note that the EDR processes involved the formation of CH Cl, which should\n3\nbe realized through the protonation of *CH Cl intermediate.49,50”\nCoPc-SG using DMPO as the spin-trapping agent.\nFigure R7. In situ ATR-FTIR measurements of CoPc-SG (a) and SG (b) in 0.1 M\nK HPO in the presence of CH Cl vapor. The potentials applied on CoPc-SG and SG\n2 4 2 2\nranged from OCP to -0.78 V vs. RHE.\n2. The formation of C coupling products following C-Cl bond cleavage is particularly\n2\nintriguing. Given that CoPc is uniformly monodispersed on the SG support, the\nsubstantial size of the ligand framework keeps adjacent Co sites relatively distant from\neach other. Therefore, it appears mechanistically puzzling how the CH Cl -derived\n2 2\nintermediates could subsequently couple to form C products. The authors need to\n2\nprovide further analysis and explanation for this phenomenon.\nResponse: We sincerely thank the reviewer for raising this insightful comment, which\nguides us to have a systematic investigation of EDR elemental steps on CoPc.\nAccording to the literature (J. Am. Chem. Soc. 2025, 147, 21764; J. Am. Chem. Soc.\n2024, 146, 13949), the C-C coupling process can be realized through two potential\npathways, i) the Langmuir-Hinshelwood (L-H) pathway, where two intermediates react\non two adjacent active sites, and ii) the Eley-Rideal (E-R) pathway, where a surface-\nbound intermediate on one active site couples with a solution-phase molecule (Figure\nR8). The reviewer has pointed out that the L-H pathway is very difficult on the\nmonodispersed CoPc on graphene surface. Alternatively, our additional DFT\ncalculations suggests the E-R pathway that enabled the C-C coupling on CoPc. During\nthe EDR process, the *CH Cl and *CH intermediates can respectively couple with a\n2 3\nfree-standing CH Cl molecule followed by dechlorination elemental steps to form the\n2 2\n*CH CH Cl or *+CH CH Cl intermediate. In these ways, the C-C coupling was\n2 2 3 2\nrealized, which further led to the generation of C H and C H , respectively.\n2 4 2 6\nNote that the CH Cl -to-C products pathways generally require higher barriers\n2 2 2\ncompared to the CH Cl -to-CH pathway (Figures R9, R10), which thus should lead\n2 2 4\nto the inferior selectivity of C production compared to that of CH production.\n2 4\nNevertheless, across the pathways of CH and C production, the established CoPc-SO\n4 2\nmoiety consistently exhibited significantly lower energy barriers compared to the\npristine CoPc (black lines) and CoPc-CO (blue lines). Such results are highly\n2\nconsistent with our experimental results of product distribution analysis.\nIn the revised SI appendix, we have added Figures R8-R10 as Figures S23-S25,\nrespectively. Correspondingly, we have added the following discussion in the revised\nmanuscript, “In addition, we presented the complete Gibbs free energy changes for the\npathways of EDR into CH , C H and C H products based on the proposed active\n4 2 4 2 6\nCoPc-SO configuration (Figures S22, S24, S25). For C products, the DFT calculations\n2\nrevealed that the involved C-C coupling elemental steps followed the Eley-Rideal\nmechanism, where surface-bound intermediates (*CH Cl or *CH ) reacted with\n2 3\nsolvated CH Cl molecules (Figure S23).52,53 In all cases, CoPc-SO exhibited\n2 2\nconsistently lower energy barriers than both pristine CoPc and CoPc-CO samples,\n2\nunderscoring the pivotal role of the sulfoxide axial coordination in facilitating the EDR\nprocesses.”\nFigure R8. An illustration of the Langmuir-Hinshelwood type (a) and Eley-Rideal type\n(b) C-C coupling mechanism for EDR.\nFigure R9. Free energy diagrams of C H formation including dichlorination,\n2 4\nprotonation and C-C coupling steps on free-standing CoPc, CoPc-SO and CoPc-CO .\n2 6\nprotonation and C-C coupling steps on free-standing CoPc, CoPc-CO and CoPc-SO in\n2\ntwo different pathways.\n3. The authors’ interpretation of some experimental evidence may involve overanalysis:\n(1) in the Wavelet transform (WT)-EXAFS analysis, the claimed Co-O scattering path\n(1.88 Å) is hardly identifiable from the presented data; (2) the assignment of the weak\n3007 cm-¹ signal in FTIR spectra to C-H vibration of CH appears questionable due to\n4\nits negligible intensity.\nResponse: We sincerely thank the comment of the reviewer. We apologize for this\noversight and have carefully revised our data to present only well-supported arguments.\nFor the WT-EXAFS analysis, we have re-analyzed the data (Figure R11). Ranging\nfrom CoPc to CoPc-SG, the WT contour exhibited a discernible positive shift of k\nvalue from 7.05 Å-1 to 7.45 Å-1, suggesting the tuned coordination of Co sites by the\nsupport of SG (J. Am. Chem. Soc. 2018, 140, 12, 4218; Nat. Commun. 2025, 16, 8276;\nAdv. Mater. 2023, 35, 2209552). This observation is consistent with the assignment of the\nEXAFS fitting.\nIn the revised manuscript, we have replaced Figure 1h, i with Figure R11 with\nincluding the above discussion. “Moreover, the wavelet transform (WT) contour plots\n(Figures 1h, i) exhibited a positive shift of k value from the maximum intensity at 7.45\nÅ-1 in CoPc-SG to 7.05 Å-1 in CoPc, suggesting the tuned coordination of Co sites by\nthe support of SG.40,41”\nFigure R11. The WT-EXAFS plots of CoPc (a) and CoPc-SG (b).\n(2) For the in situ ATR-FTIR spectra, we have re-conducted the measurement to\noptimize the quality of data (Figure R12). It clearly showed doublet IR bands at\n2989/3008 cm-1 on CoPc-SG (Figure R12a), which were ascribed to the asymmetric\nstretching vibration of CH (Kinet. Catal. 2002, 43, 419; J. Am. Chem. Soc. 2025,\n4\n10.1021/jacs.5c13767). This feature is absent in the SG sample (Figure R12b). Besides,\nanother distinct band exclusively emerged at 1448 cm-1 on CoPc-SG, corresponding to\nthe C-H deformation vibration of *CH (Nat. Commun. 2025, 16, 2831; ACS Catal.\n3\n2025, 15, 11, 9717). This data provides the additional experimental evidence for the\ngeneration of *CH intermediate.\nrevised manuscript, we added this detailed discussion, “At an open circuit potential\n(OCP), the emerged IR peaks at 744 cm-1 and 1258 cm-1 are attributed to the C-Cl\nsymmetric stretching and C-H bending vibration of CH Cl .29,43,44 As the potential was\n2 2\nmade more negative on the CoPc-SG catalyst, a new band appeared at 1448 cm-1. This\nband, which is absent on the pristine SG support, can be attributed to C-H deformation\nvibration of *CH .45 Meanwhile, doublet bands emerged at 2989/3008 cm-¹\n3\ncorresponding to the asymmetric stretching vibrationof CH , indicating the\n4\ndechlorination process.46”\nFigure R12. In situ ATR-FTIR measurements of CoPc-SG (a) and SG (b) in 0.1 M\nK HPO in the presence of CH Cl vapor. The potentials applied on CoPc-SG and SG\n2 4 2 2\nranged from OCP to -0.78 V vs. RHE.\n4. The data and the corresponding analysis presented in the wastewater treatment\napplication section appear limited in several aspects: (1) At 98% CH Cl conversion,\n2 2\nbesides 32.7% CH and minor C products, the identity of other major products remains\n4 2\nunclear (potentially incomplete dechlorination byproducts like CH Cl?); (2) The\nsignificant performance degradation at higher current density (100 mA/cm²) lacks\nmechanistic explanation (possibly due to HER dominance?). We recommend the\nauthors provide additional analysis on these aspects.\nResponse: We sincerely thank the reviewer for the careful assessment and constructive\ncomments. For these concerns, we have listed the following revisions with providing\nthe detailed discussions.\n(1) Products distribution. As shown in Figure R13, at 75 mA cm-2, in one single-pass\nconversion, 98% of CH Cl was removed. Specifically, 32.7% of the initial CH Cl was\n2 2 2 2\nconverted to CH , 1.64% of the initial CH Cl was converted to C products, 63% of\n4 2 2 2\nthe initial CH Cl was converted to the incompletely dechlorinated byproduct of CH Cl,\n2 2 3\nand some CH Cl might be physically adsorbed (under the same condition, we indeed\n2 2\ndetected that the CP electrode without the loading CoPc-SG removed 59% of CH Cl\n2 2\nwithout generating CH , C products and CH Cl).\n4 2 3\nIn the revised SI appendix, we have added Figure R13 as Figure S33.\nCorrespondingly, in the revised manuscript, we have added the claim, “In one single-\npass filtration (details in SI), 98% of total CH Cl was removed at a constant current\n2 2\ndensity of 75 mA cm-2 for 300 mL 3 mM CH Cl solution (Figures 5b-d, S33), including\n2 2\n32.7% of CH Cl converted into CH , 1.64% of CH Cl converted into C products, 63%\n2 2 4 2 2 2\nof CH Cl converted into the incompletely dechlorinated byproduct of CH Cl and some\n2 2 3\nCH Cl might be physically adsorbed (under the same condition, we indeed detected\n2 2\nthat the CP electrode without the loading CoPc-SG removed 59% of CH Cl without\n2 2\ngenerating CH , C products and CH Cl).”\n4 2 3\nFigure R13. Single-pass conversion efficiency of all dechlorination products on CoPc-\nSG@CP in the vertical flow cell.\n(2) Faradaic efficiencies. The FEs for CH , C products and CH Cl were calculated at\n4 2 3\nthe different current densities (Figure R14). It showed that the FEs of dechlorination is\nthe electrofiltration module setup are relatively low. In this device setup, our primary\ntarget is to demonstrate a high treatment rate of waste water under a relatively high flux\nand a relatively low concentration of CH Cl that approaches the concentration level of\n2 2\nreal wastewater, which should result in the low FEs of dechlorination.\nBecause of the low concentrated CH Cl (3 mM) and the high flux (100.5 L m-2 h-1),\n2 2\nthe mass transport of CH Cl to catalyst surface would be affected that significantly\n2 2\ncompetes with the H O diffusion. Our system was operated at a flux of 100.5 L m-2 h-1,\n2\na value over 2-fold larger than that of other electrified membrane setups (e.g., Sci. Adv.\n2025, 11, eads6943, operated at approximately 48 L m-2 h-1). Such a high flux resulted\nin a short residence time of CH Cl within the catalysts layer. To have a high reduction\n2 2\nkinetics of CH Cl , it was thus operated at current densities of 25-75 mA cm-2 that is\n2 2\none order of magnitude higher than that reported in those studies (Sci. Adv. 2025, 11,\neads6943). Under the high current densities, the CH Cl diffusion layer gradually\n2 2\nbecame thick, while the amount of water was significant. The confluence of high flux\nand low substrate concentration established a regime dominated by mass transport\nlimitations for the target dechlorination reaction. The competing hydrogen evolution\nreaction (HER) became the dominant electrochemical pathway, which accounts for the\nobserved low FE. This is an anticipated trade-off for demonstrating the system’s\ncapacity for rapid pollutant removal at a high throughput as a key performance indicator\nfor practical applications.\nIn the revised SI appendix, we have added Figure R14 as Figure S34.\nCorrespondingly, in the revised SI appendix, we have the added the above claim.\nFigure R14. Single-pass FE of all dechlorination products on CoPc-SG@CP in the\nvertical flow cell.\n(3) Performance degradation at 100 mA cm-2. The degradation of performance at 100\nmA cm-2 might be ascribed to the overly limited mass transport. In our viewpoint, the\nEDR kinetics increased with increasing currents at the range of 25-75 mA cm-2, where\nthe interfacial electron transfer can still affect the EDR kinetics. Above the applied\ncurrent of 75 mA cm-2, the EDR kinetics should be determined by the mass transport of\nCH Cl , and the diffusion layer of CH Cl became over thick, where the CH Cl supply\n2 2 2 2 2 2\nto the catalyst surface is insufficient. Indeed, the concentration of CH Cl is relatively\n2 2\nlow of 3 mM for approaching the concentration level of real wastewater. Instead, water\nsupply kept sufficient in the aqueous solutions that made HER become dominant. This\ncould degrade the EDR performance (Chem. Rev. 2015, 115, 13362-13407;\nChemosphere 2018, 208, 159-175).\nIn the revised manuscript, we have added the claim, “The performance degradation\nat 100 mA cm-2 could be ascribed to the overly limited mass transport of CH Cl\n2 2\nreactant by increasing the applied currents.”\n5. The electrofiltration module setup employed in the wastewater treatment section\nappears similar to those previously reported for wastewater remediation (e.g., nitrate\n(Nat. Chem. Eng. 2025, 2, 379) and CVOC removal (Nat. Nanotechnol. 2023, 18, 160)).\nWe are curious whether the current configuration presents any substantive differences\nfrom these prior systems. Furthermore, since the Introduction highlights the high energy\ninput associated with industrial pollutant degradation methods, it would be valuable to\ninclude a comparative analysis of energy consumption or economic feasibility for this\nsystem to enable comprehensive assessment of its practical potential.\nResponse: We sincerely thank the reviewer for the comment. The major difference\nbetween our system and the prior systems is the flow mode. As shown in Figure R15,\nfor those reported systems of nitrate reduction (Nat. Chem. Eng. 2025, 2, 379) and\nCVOC removal (Nat. Nanotechnol. 2023, 18, 160), they adopted the cross-flow mode\nthat the bulk solutions only circulate in the anode chamber, and the influent-to-effluent\ndirection is parallel to the membrane surface. The solutions in the anode chamber pass\nthrough the membrane to the cathode by gravity or permeation, and then the reduction\nof wastes occur.\nIn contrast, our system is configured with a vertical flow-through mode. The\nsolutions circulate in the both anode and cathode chambers. The influent is set at the\ncathode, and the effluent is set at the anode, so that the solutions are forced to flow\nthrough the catalyst membrane by pumps, and the influent-to-effluent direction is\nvertical to the membrane. In such a flow-through mode, the waste water flux can be\nproportional to the treatment rate of waste water, which can be easily scale up. This is\nconsidered as the main advantage of our flow-through mode compared to the reported\nones (i.e., Nat. Chem. Eng. 2025, 2, 379; Nat. Nanotechnol. 2023, 18, 160), where the\ntreatment rate of waste water should mainly depend on the permeation properties of\nmembranes between anodes and cathodes.\nWe also agree that a quantitative energy analysis is essential for the practical\nassessment. We therefore calculated the electrical energy per order (E ) at different\nEO\ncurrent densities (Figure R16). The results show that the removal efficiency and energy\nconsumption are optimized at 75 mA cm-2. A rough estimation indicated an optimal\noperating condition at 75 mA cm-2, where a high removal efficiency of ~98% was\nachieved with a corresponding E value of 0.062 kWh m-3. This energy consumption\nEO\nis lower than the E value of 0.42 kWh m-3 reported in an analogous cross-flow system\nEO\ntreating another typical chlorinated organic compound of 1,2-dichloroethane (Nat.\nNanotechnol. 2023, 18, 160). It is also noteworthy that our level of energy efficiency\nwas attained toward treating a CH Cl stream that its concentration (3 mM) is 6-fold\n2 2\nhigher than that of above 1, 2-dichloroethane stream (i.e., 0.5 mM), a condition that can\nbe more representative of industrial effluents. This analysis suggests that our system is\ncapable of energy-efficient operation.\nIn the revised manuscript, we have added Figure R16b as Figure 5e this detailed\ndiscussion, “In addition, the process remained highly energy-efficient, achieving a\nrelatively low electrical energy consumption per order (E ) of 0.062 kWh m-3 under\nEO\n75 mA cm-2 (Figure 5e), which is substantially lower than the E value of 0.42 kWh\nEO\nm-3 reported in an analogous cross-flow system treating another typical chlorinated\norganic compound of 1,2-dichloroethane.14”\n[FIGURE REDACTED]\nFigure R15. Schematic illustration of two different flow modes. (a) The reported cross-\nflow systems (i.e., Nat. Chem. Eng. 2025, 2, 379; Nat. Nanotechnol. 2023, 18, 160). (b)\nThe vertical flow-through system in this work.\nFigure R16. (a) Residual concentrations and removal efficiency of CH Cl in one\n2 2\nsingle-pass filtration at different current densities. (b) E in one single-pass filtration\nEO\nat different current densities.\nResponse to Reviewer #3\nY. You presented a work dedicated to the electrocatalytic dechlorination of\ndichloromethane to produce methane and minor C products. A CoPc-based catalyst\n2\nsupported by Sulfur-doped graphene was employed, which is claimed to be capable of\nstabilizing the CH Cl and the CH intermediates, key to the production of methane. The\n2 3\nwork has performed a good variety, and amount, of characterizations, attempting to\nprovide insights on the reaction mechanism. While I appreciate the amount and quality\nof the data in general, I regret to say that I cannot support publication of the work in\nNature Communications at the moment, because I question the techno-economic\nfeasibility, as well as the advancement in performance, of the work. I have the following\nspecific questions and comments.\nResponse: We sincerely thank the reviewer for the valuable comments that let us\nreconsider several aspects of our work, which are very helpful to improve its quality.\nAccording to these valuable comments, we have accordingly improved the manuscript\nand SI appendix with our best efforts. The point-by-point responses to the specific\ncomments are provided as below. All the changes are highlighted in blue color in the\nrevised manuscript and SI appendix.\n1. The major performance advancement, as claimed by the authors, is the high-\nselectivity production of methane, and the production of trace amount of C products.\nauthors. Ref. 13 reports similar products and selectivity (FE) with much higher reaction\nrate in terms of current density and TOF.\nResponse: We sincerely thank the reviewer for this insightful comment. We agree that\nRef. 13 represents a landmark study in electrocatalytic CH Cl reduction, reporting high\n2 2\nFEs for CH and C products together with high current densities. Nevertheless, our\n4 2\nwork presents several critical and distinct advances.\n(1) Performance comparison. Compared to the mentioned work, the developed\ncatalyst of CoPc-SG exhibited the following advantages. i) CoPc-SG was conducted\nEDR at a lower onset potential of -0.28 V vs. RHE that started to achieve high FE of\nhydrocarbon production (versus -0.48 V vs. RHE, CuT2 catalyst in the mentioned\nwork). ii) CoPc-SG exhibited minimal FE for the competitive HER (~2-3%, -0.28 to -\n0.58 V vs. RHE), while the CuT2 consistently showed about 25% FE for HER.\nIt indicated that CoPc-SG is more catalytically selective for the CH Cl degradation.\n2 2\nDespite that some portion of incompletely dechlorinated byproduct CH Cl was\n3\ngenerated on CoPc-SG, it is generally considered to be less toxic than the parent CH Cl ,\n2 2\nand it is gaseous to be removed from the wastewater.\nThe TOF comparison is not fair since the calculation methods of the number of active\nsites are fundamentally different. In the mentioned work, it utilized an estimation from\nelectrochemical double-layer capacitance, while in our calculation, the number of\nactive sites on the electrode surface was measured by the ICP-OES method, which\nshould be more precise to reflect the intrinsic activity of active sites. Besides, the\nobserved difference in current density could be attributed to the loading amount of\nmetal center. Our system employed the metal loading of approximately 0.24 µmol cm-\n2, which is four times lower than that in the mentioned work of 1.0 µmol cm-2.\n(2) A novel mechanistic insight. As known, immobilization of molecular catalysts\nonto solid supports to generate heterogeneous molecular catalysts is a prerequisite for\nthe practical application of molecular catalysis. Our work provides a novel insight into\nthe support effect that is important to enhance the heterogeneous molecular catalysis,\nwhich is absent in the mentioned work. Namely, we identified that the sulfoxide groups\non SG can have an axial coordination to the Co centers of CoPc, which exhibited an\nelectron donation effect to CoPc enhancing its EDR performance. In addition, we also\nidentified a state of active site under the turnover condition that the non-proton-coupled\ngeneration of a [Co1+Pc]- active species commenced EDR, providing additional novel\nmechanistic insight into the phthalocyanine-based catalysts.\n(3) Practical application. Our work demonstrated a crucial step approaching the\npractical application of EDR by implementing the CoPc-SG catalyst in a flow-through\nelectrofiltration system. This represents a significant advance in technological readiness\ncompared to the conventional H-cell setup used in the mentioned work. By enabling\ncontinuous operation, our system demonstrates a viable pathway for scalable water\ntreatment, achieving 98% pollutant removal in a single pass treatment.\n2. Along this thread, the authors compared their performance with other works in Table\nS4, but they only listed works performed in DMF solvent. Why did they not list other\nworks performed in water as solvent? I also encourage the authors to list other\nperformance factors: FE and current density are more important than the specific\nproduction rate to me. The specific production rate, which is obtained by normalizing\nto the loading of catalyst, is more important if the catalyst is very expensive.\nResponse: We sincerely thank the reviewer for this valuable suggestion and apologize\nfor the omission of aqueous-phase comparisons in the initial submission. Following this\nadvice, we have conducted an extensive literature survey and revised the comparison\ntable accordingly. The updated table (Table R1) have included the reported CH Cl\n2 2\nelectroreduction catalysts operating in aqueous electrolytes, alongside those in DMF, to\nenable a more comprehensive comparison. In addition, we have expanded the listed\nperformance metrics beyond the specific production rate to include FE and current\ndensity.\nIn the revised SI appendix, we have replaced Table S4 with Table R1.\nTable R1. Comparison of electrocatalysis performances of various EDR catalysts.\nCurrent\nFE FE FE PR PR PR\nCH4 C2 CH3Cl CH4 C2 CH3Cl\nCatalysts Potential Solvent density\n(%) (%) (%) (mmol g-1 h-1) (mmol g-1 h-1) (mmol g-1 h-1)\n(mA cm−2)\nCoPc-SG -0.68 V vs. RHE H O 1.77 45.84 13.2 25.07 53.9 10.08 44.95\n12 2\n-2.98 V vs.\nNCO /C9 DMF \\ 17 \\ \\ 3.53 \\ \\\n4-β\nAg/AgCl/Me NCl\n2 4\n-2.98 V vs.\nCu /Co O 11 DMF 14.5 mA \\ \\ \\ \\ \\ 2.93\n0.30 3 4-β\nAg/AgCl/Me NCl\n4\n-3.03 V vs.\nP -NMHTNFs12 DMF \\ \\ \\ \\ \\ \\ 11.66\n1.0\nAg/AgCl/Me NCl\n2 4\n3. Is the production of specific feedstock important to the dechlorization of\ndichloromethane? If the authors claim so then they should support that claim with a\ntechno-economic analysis. In turn, if they do not expect to make profit from the\nproducts, they can just reduce the dichloromethane (as a pollutant) all the way down to\nCO and Cl‾ ion.\nthe techno-economic feasibility of our strategy. The central motivation of this work is\nto couple environmental remediation with the sustainable valorization of pollutants into\nuseful chemical feedstocks. In this context, the production of CH and C hydrocarbons\n4 2\nis considered as a valuable secondary benefit rather than the primary economic driver\nat this stage.\nFollowing the advice of the reviewer, we have conducted a preliminary cost analysis\nfor our system and compared with several other wastewater treatment systems (Table\nR2, Figure R17). The preliminary analysis suggests that our system could be more\neconomical than other capital-intensive technologies. For instance, its total cost is less\nthan half that of nanofiltration with BDD electrochemical oxidation and nearly six times\nlower than reduction with zero-valent palladium. It also demonstrates a clear cost\nadvantage over in situ chemical oxidation using coupled magnetite nanoparticles-\npersulfate.\nFurthermore, our approach is more energy-efficient to the complete\nmineralization strategies. Note that methods like BDD oxidation consume energy to\ndestroy the pollutant into valueless byproducts like CO , while it also would generate\n2\nmore hazardous byproducts (e.g., perchlorates). Thus, the reductive route of\nvalorization strategy not only aligns with circular economy principles by preserving\nresources, but also creates a potential revenue stream that is entirely absent in\nmineralization-based treatments.\nIn addition, to provide a preliminary quantitative perspective, we have calculated the\nelectrical energy consumption per order (E ) of our system (Figure R18). The results\nEO\nshow that the removal efficiency and energy consumption are optimized at 75 mA cm-\n2. The rough estimation indicated an optimal operating condition at 75 mA cm-2, where\na high removal efficiency of ~98% was achieved with a corresponding E value of\nEO\n0.062 kWh m-3. This energy consumption is lower than the E value of 0.42 kWh m-3\nEO\nreported in an analogous cross-flow system treating another typical chlorinated organic\ncompound of 1, 2-dichloroethane (Nat. Nanotechnol. 2023, 18, 160). It is also\nnoteworthy that our level of energy efficiency was attained toward treating a CH Cl\n2 2\nstream that its concentration (i.e., 3 mM) is 6-fold higher than that of above 1,2-\ndichloroethane stream (i.e., 0.5 mM), a condition that can be more representative of\nindustrial effluents. This analysis suggests that our system is capable of energy-efficient\noperation.\nIn the revised manuscript and SI appendix, we have added, Figure R18b as Figure\n5e. In the revised manuscript, we have added this detailed discussion, “In addition, the\nprocess remained highly energy-efficient, achieving a relatively low electrical energy\nconsumption per order (E ) of 0.062 kWh m-3 under 75 mA cm-2 (Figure 5e), which is\nEO\nsubstantially lower than the E value of 0.42 kWh m-3 reported in an analogous cross-\nEO\nflow system treating another typical chlorinated organic compound of 1,2-\ndichloroethane.14”\nTable R2. Comparison of the cost for halogenated organic compound (HOC)\ncontaminated wastewater treatment (1 ton) by different methods.\nCost for 1 ton HOC\nUnit price Quality\nMaterial contaminated wastewater\n(US dollar) required\n(US dollar)\nElectrochemical reduction by CoPc/SG (This work)\nSG 1.2 g-1 0.6 g 0.7\nCoPc 29.4 g-1 0.6 g 17.6\nK HPO 4.4 kg-1 17.4 kg 76.5\n2 4\nRuO -IrO /Ti mesh\n2 2\n0.2 (cm2)-1 16 (cm2) 3.2\nelectrode\nCarbon paper 0.1 (cm2)-1 3 (m2) 300\nPVDF membrane 7.0 (m2)-1 1 (m2) 7\nTotal cost 422.64\nElectrochemical reduction by CoPc/CNT\n(Nat. Nanotechnol. 2023, 18, 160)\nCNTs 1.2 g-1 84 g 100.8\nCoPc 46.24 g-1 4.2 g 194.2\nNa SO 4.5 kg-1 1.4 kg 6.3\n2 4\nRuO -IrO /Ti mesh\n2 2\n0.2 (cm2)-1 100 (cm2) 20\nelectrode\nCeramic membrane 116.8 (m2)-1 0.7 (m2) 81.8\nTotal cost 403.1\nNanofiltration electrochemical oxidation by Boron-doped diamond\n(Environ. Sci. Technol. 2019, 53, 12602)\nFILMTEC NF90\n836.48 (column)-1 1 836.48\nmembrane\nBoron-doped\nultrananocrystalline 4.5 (cm2)-1 44 (cm2) 198\ndiamond (UNCD)\nNa SO 4.5 kg-1 0.5 kg 2.3\n2 4\nNaCl 3.8 kg-1 0.1 kg 0.4\nTotal cost 1037.2\nChemical reduction by palladium nanoparticles\n(Water Res. 2025, 268, 122574)\nIron nanoparticles 138.9 kg-1 4.2 kg 583.4\nNa O S 24.9 kg-1 3.3 kg 82.2\n2 4 2\nK PdCl 28.6 g-1 64.4 g 1841.8\n2 6\nTotal cost 2507.4\nChemical oxidation by magnetite nanoparticles with in situ activated persulfate\n(Chem. Eng. J. 2018, 342, 281-292)\nMagnetite\n10.4 kg-1 41.5 kg 431.6\nnanoparticles\nNa S O 11.2 kg-1 2.4 kg 26.9\n2 2 8\nSilica sand 0.03 kg-1 2145.7 kg 64.2\nTotal cost 522.7\nFigure R17. Estimation of cost for the treatment of 1 ton of halogenated organic\ncompound contaminated wastewater by CoPc-SG@CP and other reported systems.\nFigure R18. (a) Residual concentrations and removal efficiency of CH Cl in one\n2 2\nsingle-pass filtration at different current densities. (b) E in one single-pass filtration\nEO\nat different current densities.\n4. Can the in-situ Raman resolve any peak for the CH Cl intermediate which is\n2\nsupposed to be the most critical for the work?\nResponse: We sincerely thank the reviewer for this valuable comment. We fully agree\nthat providing experimental evidence for key intermediates is critical to strengthen the\nproposed reaction pathway. Following this advice, we performed EPR spin-trapping\nexperiments using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a radical-trapping\nagent.\nThe electrolyte with adding DMPO exhibited flat EPR signals before the EDR\nelectrolysis, whereas after the electrolysis, it emerged a characteristic six-line signals\n(Figure R19). The hyperfine splitting constants (A = 16.1 G, A = 23 G) match with\nN H\nthe literature values for DMPO-•CH adduct (A = 15.9 G, A = 22.8 G, Water Res.\n2022, 221, 118747). According to the in situ ATR-FTIR spectra (Figure R20), a distinct\nband exclusively emerged at 1448 cm-1 on CoPc-SG, corresponding to the C-H\ndeformation vibration of *CH (Nat. Commun. 2025, 16, 2831; ACS Catal. 2025, 15,\n3\n11, 9717). This data provides the additional experimental evidence for the generation\nof *CH intermediate. These should provide straightforward experimental proofs for\n3\nthe formation of *CH species during the CH Cl dechlorination.\n3 2 2\nToward the *CH Clspecies, we have thoroughly searched for the relevant literature\n2\nbut did not find reliable detection methods of •CH Cl radical. Nevertheless, we obtained\n2\nsolid indirect evidence of its formation. Since CH Cl was detected as a reduction\n3\nproduct in our experiments of EDR, the only plausible pathway to the CH Cl formation\n3\nis via protonation of the •CH\nJ. 2023, 470, 144040). Take together with our DFT calculations, these results should\nestablish a convincing picture of the dechlorination pathway involving both *CH Cl\n2\nand *CH intermediates.\nCorrespondingly, we have added the following discussion in the revised manuscript.\n“We further conducted EPR spin-trapping experiments using 5,5-dimethyl-1-pyrroline\nN-oxide (DMPO) to probe the EDR intermediates (Figure S17). The electrolyte\nexhibited a characteristic six-line pattern with the electrocatalysis of EDR. The\nhyperfine splitting constants (A = 16.1 G, A = 23 G) agree with the literature values\nN H\nof the DMPO-•CH adduct,47,48 indicating the generation of *CH intermediate. Besides,\n3 3\nnote that the EDR processes involved the formation of CH Cl, which should be realized\n3\nthrough the protonation of *CH Cl intermediate.49,50”\nCoPc-SG using DMPO as the spin-trapping agent.\nFigure R20. In situ ATR-FTIR measurements of CoPc-SG (a) and SG (b) in 0.1 M\nK HPO in the presence of CH Cl vapor. The potentials applied on CoPc-SG and SG\n2 4 2 2\nranged from OCP to -0.78 V vs. RHE.\n5. If the authors claim the production of C products as a major advancement, they\n2\nshould add discussions (with appropriate experimental data) on the C-C coupling\nmechanism.\nResponse: We thank the reviewer for this important suggestion. According to the\nliterature (J. Am. Chem. Soc. 2025, 147, 21764; J. Am. Chem. Soc. 2024, 146, 13949),\nthe C-C coupling process can be realized through two potential pathways, i) the\nLangmuir-Hinshelwood (L-H) pathway, where two intermediates react on two adjacent\nactive sites, and ii) the Eley-Rideal (E-R) pathway, where a surface-bound intermediate\non one active site couples with a solution-phase molecule (Figure R21). The\nreviewer#2 has pointed out that the L-H pathway is very difficult on the\nmonodispersed CoPc on graphene surface. Alternatively, our additional DFT\ncalculations suggests the E-R pathway that enabled the C-C coupling on CoPc. During\nthe EDR process, the *CH Cl and *CH intermediates can respectively couple with a\n2 3 2 2\nfree-standing CH Cl molecule followed by dechlorination elemental steps to form the\n2 2\n*CH CH Cl or *+CH CH Clintermediate. In these ways, the C-C coupling was\n2 2 3 2\nrealized, which further led to the generation of C H and C H , respectively.\n2 4 2 6\nNote that the CH Cl -to-C products pathways generally require higher barriers\n2 2 2\ncompared to the CH Cl -to-CH pathway (Figures R22, R23), which thus should lead\n2 2 4\nto the inferior selectivity of C production compared to that of CH production.\n2 4\nNevertheless, across the pathways of CH and C production, the established CoPc-SO\n4 2\nmoiety consistently exhibited significantly lower energy barriers compared to the\npristine CoPc (black lines) and CoPc-CO (blue lines). Such results are highly\n2\nconsistent with our experimental results of product distribution analysis.\nIn the revised SI appendix, we have added Figures R21-R23 as Figures S23-S25,\nrespectively. Correspondingly, we have added the following discussion in the revised\nmanuscript, “In addition, we presented the complete Gibbs free energy changes for the\npathways of EDR into CH , C H and C H products based on the proposed active\n4 2 4 2 6\nCoPc-SO configuration (Figures S22, S24, S25). For C products, the DFT calculations\n2\nrevealed that the involved C-C coupling elemental steps followed the Eley-Rideal\nmechanism, where surface-bound intermediates (*CH Cl or *CH ) reacted with\n2 3\nsolvated CH Cl molecules (Figure S23).53,54 In all cases, CoPc-SO exhibited\n2 2\nconsistently lower energy barriers than both pristine CoPc and CoPc-CO samples,\n2\nunderscoring the pivotal role of the sulfoxide axial coordination in facilitating the EDR\nprocesses.”\nFigure R21. An illustration of the Langmuir-Hinshelwood type (a) and Eley-Rideal\ntype (b) C-C coupling mechanism on the Co active site belonging to a CH Cl EDR\n2 2\nreaction intermediate.\nFigure R22. Free energy diagrams of C H formation including dichlorination,\n2 4\nprotonation and C-C coupling steps on free-standing CoPc, CoPc-SO and CoPc-CO .\n2 6\nprotonation and C-C coupling steps on free-standing CoPc, CoPc-CO and CoPc-SO in\n2\ntwo different pathways."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed each of my questions one by one, and I currently have no further inquiries.", "reviewer_2": "The authors have well addressed the comments from me and other reviewers. I think the revised manuscript is suitable for\npublication.", "reviewer_3": "I appreciate that Y. You et al. have attempted to answer every one of my questions,\nwhich indeed improved the clarity of the work. However, there are still remaining\nquestions hindering the work from qualifying for Nature Comm.\n1. Continuing the discussion of Q1 and Q2: Table R1 is indeed much more informative,\nbut it also clearly shows that the authors’ work did not achieve a significant\nbreakthrough to the performance. Comparing the authors’ CoPc-SG with CuT2 (Ref. 7),\nthe present work operates at a much (at least one order of magnitude) lower current\ndensity, with a lower FE for methanol, at an over-potential that is not that much lower\n(-0.68 V as compared to est. -0.9V, both with respected to RHE, assuming that Ref. 7\noperates at a similar pH). Here I would like to emphasize that lowering the operational\npotential should not be considered as a major breakthrough since electricity expenditure\nis usually a small portion in any techno-economic analysis. Selectivity and throughput\nis much more important.\n2. The authors claims that the use of, what they call, a flow-though electrofiltration\nsystem as a major advancement. As depicted in Fig. 5a, the scheme looks like a flow-\ncell that is already widely used in three-phase interface electrochemical reactions.\nI would like to ask: 1) In what aspects does the authors’ system bring a significant\nadvancement to a conventional flow-cell? 2) Why did this system not bring a significant\nboost to the performance, especially the throughput?\n3. Regarding my Q3, I feel that the question has not been answered to full. How does\nthe profit of producing chemical feedstock compare to the profit of pollutant\ndegradation? That is the techno-economic analysis that I would like to see, even\nthough the feedstock profit might be secondary. Furthermore, if the feedstock profit is\nindeed secondary, then the production of methanol and C product should not be\n2\nconsidered a major breakthrough of the work. In that case the discussion may loop\nback to my original question: why did the authors not choose to degrade CH2Cl2 all\nthe way to CO2 and Cl- so that they do not have to worry about selectivity and may\ndesign more active catalyst?"}, "author_response": "Reviewer #3 (Remarks to the Author):\nI appreciate that Y. You et al. have attempted to answer every one of my questions,\nwhich indeed improved the clarity of the work. However, there are still remaining\nquestions hindering the work from qualifying for Nature Comm.\n1. Continuing the discussion of Q1 and Q2: Table R1 is indeed much more informative,\nbut it also clearly shows that the authors’ work did not achieve a significant\nbreakthrough to the performance. Comparing the authors’ CoPc-SG with CuT2 (Ref. 7),\nthe present work operates at a much (at least one order of magnitude) lower current\ndensity, with a lower FE for methanol, at an over-potential that is not that much lower\n(-0.68 V as compared to est. -0.9V, both with respected to RHE, assuming that Ref. 7\noperates at a similar pH). Here I would like to emphasize that lowering the operational\npotential should not be considered as a major breakthrough since electricity expenditure\nis usually a small portion in any techno-economic analysis. Selectivity and throughput\nis much more important.\nResponse: We sincerely thank the valuable comments of the reviewer that let us re-\nconsider the significance of our work. By the careful consideration of the raised\nconcerns and further literature investigations, we respectfully argue that our claims\nshould be appropriate, and the detailed discussions have been listed below.\ni. Regarding the concern on the selectivity\nWe consider that it is a prerequisite demand of EDR that the preliminary target is to\ndegrade CH Cl under the competition of hydrogen evolution reaction (HER) in water.\n2 2\nThis necessitates high selectivity of catalysis against HER. As we discussed in the 1st\nround response, CoPc-SG demonstrated nearly complete suppression of HER, and thus\nexhibited 97%-98% Faradaic efficiency (FE) for degrading CH Cl (-0.28 V to -0.58 V\n2 2\nvs. RHE), while the CuT2 consistently showed about 75% FE for degrading CH Cl ,\n2 2\nand the other events were the competitive HER. CoPc-SG has higher selectivity toward\nthe target CH Cl degradation. Despite that some portion of incompletely dechlorinated\n2 2\nbyproduct CH Cl was generated on CoPc-SG, it is generally considered to be less toxic\n3\nthan the parent CH Cl ,and it is gaseous that can be removed from the wastewater.\n2 2\nii. The significance of overpotential\nAccording to the literature (Sustainable Energy Fuels, 2024, 8, 1806; J. Mater. Chem.\nA, 2023, 11, 21694), the economic viability of aqueous electrolytic processes depends\non the cost of electricity since it occupies a large portion of the total cost of electrolysis.\nFor instance, for the significantly developed water electrolysis, the electricity cost\noccupies 36%-57% of total cost (Energy Storage Sci. Technol. 2020, 9, 688). Even for\nthe chlor-alkali electrolysis that has been largely applied in industry, the electricity cost\nis 30%-50% of total production cost (J. Appl. Electrochem., 1984, 14, 403; Euro\nChlor, The electrolysis process and the real costs of production, www.eurochlor.org).\nThe relationship of overpotential and current density of each electrochemical process\nobeys the well-established Butler-Volmer equation,\nα zF α zF\na c\nj = j ∙ {exp[ (E−E )]− exp[− (E−E )]}\nwhere j is electrode current density, j is exchange current density, α is charge-transfer\n0\ncoefficient, E is electrode potential, E is equilibrium potential and T is absolute\n0\ntemperature.\nAccording to the above Butler-Volmer equation, it is known that the overpotential\nintrinsically determines the current density, and thus is considered as one of the most\ncritical parameters defining the energy efficiency of each electrochemical process.\nAccordingly, significant literature provided the claims on the significance of decreasing\nthe overpotential (in other words, decreasing electricity input), and some instances were\nprovided as followings.\nBy Niu et al. for crucial energy conversion reactions, “electrocatalysts are of great\nsignificance to effectively promote the reaction efficiency. In most cases,\noverpotential (η)... is selected as the primary parameter to evaluate the activity of\nan electrocatalyst”. (ACS Energy Lett. 2020, 5, 1083)\nAs explicitly stated by Appel and Helm in their authoritative viewpoint on evaluating\nmolecular electrocatalysts, “To become competitive with current electrocatalytic\nenergy conversion technologies, new catalysts must be robust, fast, and energy-\nefficient. This last feature, the energy-efficiency, is dependent upon the\noverpotential”. A lower overpotential directly translates to reduced energy\nconsumption and is often the primary parameter used to evaluate catalyst activity.\n(ACS Catal. 2014, 4, 630)\nAs highlighted by Han et al. in their work on nitrate reduction, “Large\noverpotentials will not only lead to energy loss, but also promote the competitive\nhydrogen evolution reaction (HER) and reduce the Faradaic efficiency (FE)...\nresulting in an unsatisfactory energy efficiency”. (Nat Catal 2023, 6, 402)\nThe reviewer also considers that the decrease in overpotential is not meaningful (i.e.,\n~220 mV). We looked into some literature for typical electrochemical reactions. For\ninstance, toward electrochemical oxygen reduction reaction (Science, 2016, 354, 1414),\nthe authors studied Pt based catalysts and claimed a decrease in overpotential in 75 mV.\nFor electrochemical water oxidation (Nat. Catal. 2022, 5, 414: Table S2), the authors\nstudied molecular Co based catalysts and claimed a decrease in overpotential less than\n100 mV. Actually, based on the above Butler-Volmer equation, the overpotential has\nthe exponential-like relationship on the current density.\nThe overpotential governs the current density that precisely reflects the intrinsic\nactivity of catalyst. Except for the overpotential, the current density also depends on\nother parameters, such as catalyst loadings (e.g., the electrode loading of mentioned\nCuT2 is 4-fold higher than that of CoPc), surface areas and porosity of electrodes, and\nthese parameters can all be optimized by electrode engineering. While we consider that\nour main effort is to investigate the electrochemical evolution of EDR on the CoPc\nbased the electrocatalyst, and the study of electrode engineering has beyond the scope\nof this work.\n2. The authors claims that the use of, what they call, a flow-through electrofiltration\nsystem as a major advancement. As depicted in Fig. 5a, the scheme looks like a flow-\ncell that is already widely used in three-phase interface electrochemical reactions. I\nwould like to ask: 1) In what aspects does the authors’ system bring a significant\nadvancement to a conventional flow-cell? 2) Why did this system not bring a significant\nboost to the performance, especially the throughput?\nResponse: We sincerely thank the valuable comments of the reviewer. For the raised\nconcerns, the detailed discussions have been provided below.\ni. Distinction from the conventional flow cell\nOur electrochemical membrane filtration system is configured with a vertical flow-\nthrough mode (Figure R2), where the contaminated influent is forced to vertically\nflow through the catalytic membrane (CoPc-SG@CP). Reactants are delivered to the\ncatalytic sites throughout the entire electrode volume via the convection. This contrasts\nwith the traditional flow-cell that commonly operate in a lateral flow mode, where the\nreactants transport relies on the diffusion from bulk streams flowing parallel to the\nelectrode surfaces (Figure R3). Accordingly, our vertical flow-through mode optimizes\nthe utilization efficiency of the entire catalyst volume, maximizes the contact between\nreactions and catalytic layers, and minimizes diffusional limitations through forced\nconvection.\nFigure R2. Scheme illustration of an electrofiltration module setup with a vertical flow.\nFigure R3. Schematic illustration of a conventional flow cell with a lateral flow.\nii. Regarding the concerns on performance\nIf the reviewer refers to the performance comparison between electrochemical\nmembrane filtration system and conventional flow cell, we did achieve the performance\nimprovement (i.e., variation from the vertical flow-through mode to the lateral flow\nmode). Such performance improvement is presented in Figure R4. At the optimal\ncurrent density of 75 mA cm-2, the single-pass conversion efficiency to methane is much\nhigher in the vertical flow cell configuration versus the lateral flow cell. Likewise, the\nconversion efficiency towards C products is elevated in the vertical flow setup across\n2\nthe investigated range of current densities. These results indicate that the process\nthroughput, defined in this context as the efficiency of reactant conversion per pass at\na given current density, is significantly augmented by the vertical flow-through\narchitecture.\nIf the reviewer refers to the performance comparison between electrochemical\nmembrane filtration system and H-cell, it is essential to highlight the significant\ndifferences in operating conditions and objectives. H-cell experiments (both ours and\nin Ref. 7) are typically conducted in a saturated CH Cl solution (e.g., >80 mM) to\n2 2\nensure the catalyst’s intrinsic kinetics are the only limiting factor. In contrast, our\nelectrofiltration system was purposefully challenged with a dilute 3 mM solution, which\nis far more representative of a practical wastewater treatment setting. Therefore, the\nperformance of the flow-through system should not be directly compared to an H-cell\noperating at saturation (>80 mM), as the reaction limitations are different.\nFigure R4. (a) Single-pass conversion efficiency of CH production on CoPc-SG@CP\n4\nin vertical and lateral flow cells. (b) Single-pass conversion efficiency of C production\n2\non CoPc-SG@CP in vertical and lateral flow cells.\n3. Regarding my Q3, I feel that the question has not been answered to full. How does\nthe profit of producing chemical feedstock compare to the profit of pollutant\ndegradation? That is the techno-economic analysis that I would like to see, even\nthough the feedstock profit might be secondary. Furthermore, if the feedstock profit is\nindeed secondary, then the production of methanol and C product should not be\n2\nconsidered a major breakthrough of the work. In that case the discussion may loop\nback to my original question: why did the authors not choose to degrade CH Cl all\n2 2\nthe way to CO and Cl- so that they do not have to worry about selectivity and may\n2\ndesign more active catalyst?\nResponse: We sincerely thank the reviewer’s careful question about techno-economic\ntradeoffs between producing chemical feedstocks and pure pollutant degradation.\nRegarding such a raised concern, we would like to response by clarifying the following\nthree points, i) technical reasons not pursuing oxidative mineralization to CO + Cl⁻,\n2\nii) quantitative techno-economic summary based on experimental/reported data, and iii)\nour viewpoints on “value” and “profit”.\ni. Technical reasons not pursing oxidative mineralization to CO + Cl⁻\nvarying from of -1, 0, +1, +3, +4, +5 to +7. As gained from these various valance states,\nit would infer that oxidation of Cl based species is much complicated than reduction of\nCl based species.\nOn the one side, if the reviewer refers to the electrochemical oxidation method, we\nlisted a group of electrochemical equations that involve the evolution of Cl element as\nfollowings (J. Phys. Chem. Ref. Data 1988, 18, 1).\nCl (g) + 2e- ⇌ 2Cl- Eϴ = 1.360\n2 2\nClO - + H O + 2e-⇌ ClO- + 2OH- Eϴ = 0.681\n2 2\nClO - + 3H O + 6e-⇌ Cl- + 6OH- Eϴ = 0.614\n3 2\nClO - + 4H O + 8e-⇌ Cl- + 8OH- Eϴ = 0.560\n4 2\nClO - + 2H O + 4e-⇌ ClO- + 4OH- Eϴ = 0.476\n3 2\n2ClO - + 6H O + 10e-⇌ Cl (g) + 12OH- Eϴ = 0.465\n3 2 2\n2ClO - + 8H O + 14e-⇌ Cl (g) + 16OH- Eϴ = 0.446\n4 2 2\nClO- + 2H O + 2e-⇌ Cl (g) + 4OH- Eϴ = 0.420\n2 2\nClO - + H O + 2e-⇌ ClO - + 2OH- Eϴ = 0.398\n4 2 3\nClO - + H O + 2e-⇌ ClO - + 2OH- Eϴ = 0.271\n3 2 2\nMany of these reactions have close standard potentials, and it can infer that the during\nthe oxidative processes, the produced Cl⁻ species can be further oxidized through\nseveral routes, potentially forming Cl (g), HOCl/ClO⁻, ClO ⁻, ClO ⁻, or even ClO ⁻\n2 2 3 4\nspecies depending on the potentials and pH. Besides, the water oxidation (1.23 V vs\nRHE, standard potential) would also involve into the oxidative processes. All these\nreactions significantly affect the selectivity of oxidative mineralization to CO +\npresents a significant electrochemical challenge.\nOn the other side, if the reviewer refers to the oxidative mineralization (AOPs or\nelectrochemical oxidation) by highly reactive species (i.e., •OH), we listed a group of\nreactions that involve the evolution of Cl element as followings (Environ. Sci. Technol.\n2021, 55, 1, 689, Environ. Sci.: Water Res. Technol., 2020, 6, 2416).\n•OH + Cl- ⇌ •OHCl- k = 4.3×109 M-1·s-1\n•Cl + Cl- ⇌ Cl •- k = 8.5×109 M-1·s-1\n2\n•OHCl- + Cl- ⇌ Cl •- + OH- k = 1.0×105 M-1·s-1\n•ClO +•ClO + H O ⇌ HClO + HClO k = 2.5×109 M-1·s-1\n2 2\n•OH + ClO - ⇌ •ClO + OH- k = 6.3×109 M-1·s-1\n2 2\n•OH + •ClO ⇌ ClO - + H+ k = 4.0×109 M-1·s-1\n2 3\n•OH + •ClO ⇌ ClO - + H+ k = 1.0×106 M-1·s-1\n3 4\nBased on the above equations, it can infer that •OH radicals can be rapidly scavenged\nby Cl⁻ species to give reactive chlorine species. These species would engage in\nuncontrolled secondary chlorination, producing disinfection byproducts, such as\nhalogenated acids, and chlorate/perchlorate (Water Res. 2006, 40, 10, 2033, Environ.\nSci. Technol. 2017, 51, 12, 6918). Due to the high reaction kinetics (k), these chain\nreactions are kinetically fast and difficult to steer, leading to poor selectivity and\nformation of toxic, persistent organochlorine by-products, plus possible generation of\ninorganic oxidized chlorine species (ClO ⁻, ClO -) under strong electrochemical\n3 4\noxidation. In the meantime, the water oxidation would also involve into the oxidative\nprocesses since •OH radicals are known as a main intermediate of water oxidation.\nii. Quantitative techno-economic analysis\n1. Product yields and revenues (per ton wastewater):\n CH 4 yield = 32.7% → moles CH 4 = 3 × 0.327 = 0.981 mol → mass = 0.981 ×\n16.04 g/mol = 15.74 g = 0.01574 kg.\nRevenue (price = $421.19/ton = $0.42119/kg) = 0.01574 kg × $0.42119/kg ≈\n$0.0066.\n CH 3 Cl yield = 63% → moles CH 3 Cl = 3 × 0.63 = 1.89 mol → mass = 1.89 ×\n50.487 g/mol = 95.42 g = 0.09542 kg.\nRevenue (price = $912.58/ton = $0.91258/kg) = 0.09542 kg × $0.91258/kg ≈\n$0.0871.\n Total product revenue ≈ $0.094 per ton wastewater.\n2. Energy consumption (experiment parameters used):\n j = 75 mA·cm-², electrode area A = 32 cm2 → I = j·A = 2.4 A.\n Cell voltage V in average = 7.48 V → P = I·V = 2.4 A × 7.48 V = 17.952 W =\n0.017952 kW.\n Processing time (for 1000 L at the given throughput) = 1000 L / 0.1608 L·h-1 =\n6219 h.\n Energy = 0.017952 kW × 6219 h ≈ 111.7 kWh. At electricity price $0.03/kWh\n→ electricity cost ≈ $3.35 per ton.\n3. Revenue of wastewater treatment: market benchmark for disposal/treatment =\n$350.99 per ton.\n4. Net economic balance (per ton wastewater):\nProduct revenue ($0.094) − Electricity ($3.35) + Revenue of wastewater treatment\n($350.99) ≈ $347.73 per ton.\niii. Our viewpoints on “value” and “profit”\nBased on the above techno-economic analysis, we showed that our EDR results\nshould imply a profitable technique. And the conversion of CH Cl (unit price, $304.66\n2 2\nper ton) into CH (unit price, $421.19 per ton) or even the side product of CH Cl (unit\n4 3\nprice, $912.58 per ton) is a valorization process.\nAs implied by the reviewer, the feedstock profit is inferior to the profit of wastewater\ntreatment. Even our main product claiming on CH , its revenue is lowest compared to\n4\nthose of wastewater treatment, as well as the side product of CH Cl. However, we keep\n3\nemphasizing on CH product since we consider that its generation process is valuable\n4\nfor the global carbon cycle. As known, CH occupies a uniquely foundational position\n4\nin C chemical cycle, which serves as the starting feedstock for the vast majority of C\n1 1\nsynthesis (e.g., methanol, formaldehyde) mainly via conversion to synthesis gas (CO +\nH ). It is also a major global energy fuel used directly for power generation, heating,\n2\nand transportation. For chemical and energy industry, we consider that the value of\nCH far exceeds its relatively low market price as a bulk commodity. However, as\n4\nfar as we know, the chemical cycle of CH has not been widely investigated, especially\n4\nthe fundamental insights remain not sufficient. Thus, to preliminarily provide the\nmechanism investigations into this cycle should be meaningful toward advancing this\ncycle to approach the practical demands, which is the main target of our work."}, {"round": 3, "reviewer_comments": {"reviewer_3": "The authors have answered all my questions and I am delighted to recommend publication of the manuscript."}, "author_response": "Response: We sincerely thank the reviewer for the positive comments, which helped\nto improve the quality of our work."}]

Decision letter