Green chemical process for continuous production of high-purity 2,5-furandicarboxylic acid in anion exchange membrane flow electrolyzer

Domain: neuroscience
Published: 2026-01-28
Editorial outcome: major_revision

Abstract
The electrooxidation of biomass platform molecules to produce highly value-added chemicals represents a promising technology for biomass utilization and carbon emission reduction. However, low production capacity and the lack of well-established engineering paradigms have constrained the practical application of this technology. Here, a green chemical process for the anion-exchange membrane (AEM) electrocatalytic 5-hydroxymethylfurfural oxidation (AEM-HMFOR) is proposed and applied to 2,5-furandicarboxylic acid (FDCA) production, with subsequent separation and purification. We demonstrate an optimized hundred-watt-scale AEM-HMFOR stack (164.8 W) for continuous FDCA production, with a high Faradaic efficiency (94.6%) and FDCA yield (96.2%) at 100% single-pass conversion efficiency (SPCE). This stack operates stably for over 100 hours with a space-time yield (STY) of 367.2 mg h−1 cm−2. A membrane separation device is employed to purify FDCA with an overall purity of 99.8%. Techno-economic analysis (TEA) and life cycle assessment (LCA) have certified the economic viability and environmental sustainability of the proposed AEM-HMFOR technology. These findings represent a significant advancement in the practical application of large-scale AEM-HMFOR systems coupled to green H2 production.

Introduction
Global renewable biomass resources are abundant (Fig. 1a)1,2. In China, the forest area covered 221.9 million hectares in 2021, with a carbon stock associated with living biomass of 8,892.3 million tons3. The development of these resources has become increasingly important for reducing global carbon emissions4–6. 5-hydroxymethylfurfural (HMF) has been listed by the U.S. Department of Energy as a high-value, biomass-derived platform molecule suitable for the production of 2,5-furandicarboxylic acid (FDCA), a precursor for the synthesis of bio-based polymers7–10. Driven by environmental policies, the global FDCA market is gradually expanding11,12. Industry research analysis has identified China, the US, and Germany as substantial FDCA markets, estimated at 124.5, 71.9, and 20.5 million US$, respectively (Fig. 1a and Note S1). The development of biomass resources is an important driver for future economic growth. FDCA production technologies include electrooxidation, chemical oxidation, and thermal catalytic processes13–18. Electrochemical routes can be coupled with renewable energy, such as solar, wind, or tidal energy, to reduce carbon emissions. The estimated average value of global horizontal irradiance (GHI) in China is 1.50 × 103 MWh m−2 19, with 2.16 × 105 MW of newly installed photovoltaic (PV) capacity in 202320, representing an appreciable green electricity supply. Anion-exchange-membrane-based electrocatalytic HMF oxidation reaction (AEM-HMFOR) is an emerging technology to produce green hydrogen and FDCA (paired electrolysis), which can be used as a monomer for preparing polyethylene furanoate (PEF), polyamide, polycarbonate, etc. (Fig. 1b, c)18,21,22. This electrocatalytic process improves electron utilization efficiency and increases revenue potential compared to conventional AEM water electrolysis (AEM-WE)23–25. In addition, this approach, utilizing H2O as the green oxygen source, employs inexpensive catalysts, mild reaction conditions, and controllable reaction processes (Note S1)15–18,21,22,26. However, the FDCA productivity is markedly lower than the conventional routes, primarily due to the low HMF concentration (<200 mM) and working current densities (<200 mA cm−2) associated with the electrocatalytic route (Fig. 1d). Another obstacle is the impurities co-produced through electrooxidation, significantly affecting the quality of downstream products and limiting the commercial application.

Previous studies have focused on enhancing FDCA productivity by developing highly efficient electrocatalysts or suppressing non-Faradaic degradation at high HMF concentrations (>200 mM)15–17,27–33. A number of catalysts, including nickel oxide nanoparticles and nickel-based mixed oxides, have been investigated for potential application. The relationship between catalytic activity and stability, evaluated in batch experiments using small-scale electrolyzers, is not applicable to the AEM-HMFOR system under practical production conditions21,31–33. Differences will arise between small-scale studies and scale-up investigations regarding the distribution of organic compound concentrations, local pH in the electrolyzer, and the applied electrocatalytic parameters34,35. Some works have also developed alternative strategies for FDCA preparation, such as utilizing suspended NiOOH particles in place of electrodes and integrating fructose dehydration with HMFOR36,37. Although the AEM-HMFOR system shows great promise for application, long-term stability in large-scale electrolyzers (electrode area >100 cm2) under industrially relevant electrolysis conditions (≥200 mM HMF and ≥200 mA cm−2) has not been experimentally verified31–33,36,37, and even less so the consequent purification process of FDCA. A viable application of electrocatalytic FDCA production requires comprehensive evaluation at the industrial-relevant scenarios.

In this work, we demonstrate that the AEM-HMFOR system can be operated and maintained for over 400 h in single-pass mode with a stable-flow tank at HMF concentrations of 200 and 400 mM. Based on this, we have constructed a hundred-watt scale (164.8 W) AEM-HMFOR stack for continuous FDCA production, achieving a space-time yield (STY) of 367.2 mg h−1 cm−2 and 100% selectivity. The stack exhibits a current of 80 A (400 mA cm−2) at a cell voltage of 2.06 V, with 100% single-pass conversion of 500 mM HMF, demonstrating competitive performance metrics (Fig. 1d and Table S1). The significant improvement in FDCA productivity is attributed to the implementation of flow channels to enhance mass transfer efficiency, the use of highly active catalysts, and the optimization of feed types. We present a whole green chemical process comprising HMF purification, AEM-HMFOR, and subsequent membrane separation modules. An FDCA purity of 99.8% is established through proton nuclear magnetic resonance (1H NMR). Techno-economic analysis (TEA) and life cycle assessment (LCA) further demonstrate economic viability and environmental sustainability for this proposed FDCA production process. The findings of this work provide the basis for a practically feasible large-scale AEM-HMFOR system.

Results
Catalyst characterization and electrocatalytic performance evaluation
The first step in constructing a high-performance AEM-HMFOR system is to prepare high-activity electrocatalysts. The Ni-Co supported on Ni foam (Ni-Co/NF) for HMF oxidation was prepared using a two-step immersion strategy38,39, followed by aging in 1.0 M KOH solution (see “Methods”). The X-ray diffraction (XRD) pattern for Ni-Co/NF is consistent with Ni0.988Co0.012(OH)2 (PDF#00-059-0461) (Fig. S1). High-resolution transmission electron microscopy (HR-TEM) images showed that the lattice fringe spacing of 0.26 nm corresponds to the (100) plane of Ni0.988Co0.012(OH)2 as well (Fig. S2). Energy-dispersive X-ray (EDX) mapping demonstrates an even distribution of Ni, Co, and O elements (Fig. S3). High-resolution X-ray photoelectron spectroscopy (XPS) was conducted to determine the valence states of Ni and Co in Ni-Co/NF. The presence of Ni2+ (855.7/873.0 eV) and Co2+ (781.4/796.4 eV) species is confirmed in the Ni 2p and Co 2p spectra (Fig. S4)40,41. The O 1s spectra indicate the presence of three distinct oxygen species, including M–O at 530.8 eV, OH− at 531.5 eV, and adsorbed H2O at 533.3 eV, respectively. The oxidation states are comparable to those reported for nickel-cobalt hydroxides. Scanning electron microscopy (SEM) images have revealed a nanosheet structure for Ni-Co/NF (Fig. 2a), which may enhance the apparent catalytic activity33,42. In a three-electrode system containing 1.0 M KOH with 400 mM HMF, linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) analysis have revealed a high current density of 1,962 mA cm−2 at 1.65 V versus the reversible hydrogen electrode (RHE), with a small charge transfer resistance (Rct) (Fig. S5). Additionally, Ni-Co/NF outperforms Ni- or Co-based hydroxides for HMF oxidation (Fig. S6 and Note S2). These results demonstrate a high level of HMF oxidation activity for Ni-Co/NF.

Flow channel design of the electrolyzer
To increase the SPCE of HMF, it is necessary to enhance mass transfer efficiency in the flow channel. Drawing on microchannel reactor technology, flow channels with different widths were fabricated to achieve a high ratio of convective zone area (A) to electrolyte volume (V) in the electrolyzer (Fig. 2b and Fig. S7). The A/V values for 0.4, 0.6, and 0.8 mm width flow channels are 0.333, 0.468, and 0.588 mm–1, respectively. This microchannel structure, with a 0.8 mm width, increases A/V, thereby enhancing SPCE (Note S3)27,43. Achieving a high STY for practical production at elevated cell voltages may inevitably encounter the oxygen evolution reaction (OER). Hence, gas removal from the flow channels is critical21,31–33. OER was employed as a model reaction, and LSV and Nyquist plots indicated that the electrolyzer with a flow channel width of 0.8 mm delivers the highest current density and the lowest internal resistance (Fig. S8). In addition, pressure distribution over AEM was assessed using a flexible pressure sensor (Fig. 2c). Compared with the 0.4- and 0.6-mm-channel, the 0.8-mm-channel featured the lowest average fluid pressure without a steep pressure zone and a more uniform flow field as observed by pressure mapping in Fig. 2d. Based on this, larger flow channels (25 and 100 cm2) were fabricated to construct the AEM electrolyzers (Fig. S9).
We selected Ni-Co/NF, Ni-Mo/NF44, and PAP-TP-85 (a terphenyl-based poly(aryl piperidinium) polymer) as the anode, cathode, and AEM, respectively. In Fig. 2e and Fig. S10, a membrane electrode assembly (MEA) electrolyzer (1 cm2) was constructed for HMFOR coupled with hydrogen evolution reaction (HER). The purity and Faradaic efficiency of H2 were ~99.99% and ~99.8%, respectively. (Fig. S11). A current density of 366.8 mA cm⁻2 was achieved at a cell voltage of 1.60 V with 200 mM HMF (Fig. S12). The current density exhibited a positive correlation with HMF concentration below 200 mM and a negative dependence above 200 mM. This can be attributed to impurities produced by HMF degradation adhering to the AEM, blocking OH− transfer channels, and increasing internal resistance and ohmic losses (Fig. S13)45.
To boost the STYFDCA, a larger AEM-HMFOR electrolyzer (25 cm2) was constructed (Fig. S14). The current of this electrolyzer at 1.80 V (7,670 mA) was approximately 10-fold higher than that of the 1 cm2 electrolyzer (768 mA) (Fig. 3a, and Fig. S12). However, the current density (306.8 mA cm−2) was slightly lower. This may be ascribed to the amplification effect of the flow channel46,47, which results in a decrease in the A/V ratio (0.556 mm−1). In addition, a greater retention volume has a detrimental effect on reactant transfer from the bulk solution to the MEA catalytic interface, leading to a consequent reduction in mass transfer efficiency.

Effect of mass transfer on electrolyzer performance
When compared with the electrolyzer without a flow channel, the cell voltage of the electrolyzer with a flow channel was reduced by 190 mV at 3.5 A (Fig. 3a). The mass transfer overpotential (ηmass) and ohmic overpotential (ηohm) are 32 mV and 88 mV, respectively (Fig. S15 and Note S4). In the absence of flow channels, these values are 74 mV and 102 mV. The flow channel facilitates drainage and provides a uniform flow field (Fig. S16), improving the electrolyzer performance by enhancing mass transfer efficiency. Faradaic efficiency (FEFDCA), yieldFDCA, and STYFDCA were determined as a function of cell voltage using chronoamperometry (CA) tests in multi-batch mode (Fig. 3b). The concentrations of the organic compounds were analyzed through high-performance liquid chromatography (HPLC) (Fig. S17). The average FEFDCA and yieldFDCA are over 92.8% in the given potential window without obvious carbon loss, indicating that the competing OER had a minimal impact on HMFOR (Fig. S18a). The STYFDCA reached 30.2 ± 4.4 mg h–1 cm–2 at 1.50 V and increased significantly to 54.1 ± 4.8 mg h–1 cm–2 at 1.60 V. As shown in Fig. 3c, a faster flow rate led to a higher STY at the same charge passed (2000 C). An increase in the flow rate enhanced mass transfer, which shortened the reaction time required to achieve a comparable yield (Fig. S19 and Note S5), but did not exert a significant influence on FEFDCA, which was predominantly regulated by cell voltage. The reaction intermediates were 5-hydroxymethylfurancarboxylic acid (HMFCA) and 5-formyl-2-furancarboxylic acid (FFCA) instead of 2,5-diformylfuran (DFF), indicating that HMF oxidation followed the HMFCA pathway (Fig. S18b, c)31. In contrast, FEFDCA and yieldFDCA exhibited a significant drop for the electrolyzer without a flow channel. The O2 generated and the electrolyte were not effectively removed from the electrolyzer, which reduced mass transfer efficiency48,49. The STYFDCA decreased drastically to 32.5 mg h−1 cm−2 at 1.60 V (Fig. S20). The delayed completion of the reaction led to more impurities from the non-Faradaic process, contributing to increased carbon loss (Fig. S18a). Thus, the flow channel plays an essential role in enhancing mass transfer efficiency.
Ni-Co/NF catalyst was assessed by multi-batch electrolysis using CA tests, which showed good stability over 16 consecutive cycles for 480 minutes, with high FEFDCA and yieldFDCA (Fig. 3d), demonstrating appreciable potential for industrial applications. The performance of this non-precious-metal-based AEM electrolyzer exceeds that reported in recent publications (Fig. S21)21,27,30–32. However, the FE drops sharply above 1.60 V, reaching ~65% at 1.90 V due to the facilitated OER (Fig. S22). The STYFDCA increased with elevated voltage, as higher voltages boosted current, shortening the time required to transfer the same charge in the electrolyzer (Fig. 3e). At the onset of electrolysis, the electrolyzer exhibited a high initial STY that gradually decreased as HMF was continuously consumed under constant voltage. The HMF depletion and FDCA accumulation in the discontinuous model (multi-batch) result in current decay and increased separation costs, which limit applicability in industrial processes.

Chemical process optimization and watt-scale stack construction
To achieve continuous FDCA production, we have optimized the process by switching from a multi-batch to a single-pass operation (Fig. 4a, b)27,50. The KOH and HMF solution (in H2O) were separately placed in two tanks, rapidly mixed in the stable-flow tank, and then the electrolyte (HMF in KOH solution) was piped into the electrolyzer. It enables full mixing of the electrolyte in the required proportions (Fig. S23 and Note S6), effectively passivating the non-Faradaic reaction from HMF degradation and ensuring a stable electrocatalytic process. It is critical to increase the SPCE to maximize the advantages of single-pass operation. A parallel circuit AEM-HMFOR stack (P-stack, 25 cm2 × 5 units, Fig. 4c, d, and Fig. S24a) was designed and fabricated, and the performance was compared with that of a series circuit stack (S-stack, 25 cm2 × 5 units, Fig. S24b, S25), which serves as the conventional configuration for AEM-WE. The current of the P-stack reached 20.8 A for HMFOR at 1.80 V, and the cell voltage was reduced by 283 mV compared to OER at 16 A (Fig. S26). The internal resistance of the P-stack was lower than the S-stack. To evaluate stack performance under high SPCE (Fig. S27) using chronopotentiometry (CP), the flow rate applied to the S-stack was 1.33 mL min–1, and to the P-stack was 7.18 mL min–1. The power was measured at about 27 W (voltage of ~1.8 V, total current of 15 A) with 200 mM HMF, where the P-stack exhibited great stability, achieving 100% SPCE with high yieldFDCA (~98.5%), FEFDCA (~94.2%), and STYFDCA (~109.6 mg h–1 cm–2) (Fig. 4e, f). The parallel circuit ensured consistent voltage across each MEA, preventing excessive OER. The SPCE of the S-stack was only ~90.6% at ~27 W (voltage of ~9 V, total current of 3 A), with lower yieldFDCA (~89.7%), FEFDCA (~15.4%), and STYFDCA (~17.9 mg h–1 cm–2) (Fig. S28 and Fig. 4f). The significant difference in performance can be attributed to the flow sequence of electrolyte in the electrolyzer. In the P-stack, the fresh HMF solution was partially oxidized in the first MEA and subsequently flowed into the next assembly (Fig. S24a). The HMF concentration decreased stepwise from the first to the fifth MEA (Fig. S29 and Note S9). In the S-stack configuration, the electrolyte flowed through all MEAs before oxidation, ensuring an near-equivalent HMF concentration in each MEA (Fig. S24b). The P-stack enabled a cascade HMF oxidation with higher STY than the S-stack35,51. The electrolyte first passes through the polar plate with a flow channel and then the anode (Fig. 4d, similar to an individual electrolyzer with a flow channel). In the S-stack, the electrolyte flows through the anode and then the polar plates (Fig. S25a, similar to an individual electrolyzer without a flow channel). Consequently, the mass transfer efficiency of the P-stack is better than that of the S-stack, resulting in higher FEFDCA and yieldFDCA. In addition, the lower flow rate of the S-stack limited mass transfer. Nevertheless, the P-stack retains a performance advantage under the same conditions, including the same flow channels and flow rates (Fig. S30).
The performance of this P-stack was further investigated under harsh conditions by increasing the current to 25 A (200 mA cm−2) and HMF concentration to 400 mM, where the stack achieved 100% SPCE, with a yield of ~98.7%, FE of ~95.7%, and STY of ~185.7 mg h–1 cm–2. Long-term stability measurements over 400 h have demonstrated the high performance of the electrolyzer (Fig. 4e), yielding ~160 L of FDCA solution (Fig. S31). After electrolysis, the internal resistance of each cell remained stable (Fig. S32), and the morphology of Ni-Co/NF was maintained (Fig. S33). We have successfully separated 228.5 g of yellowish FDCA and 311.9 g of white K2SO4 from the electrolyte during 10 h of continuous electrolysis (Fig. S34a). The purity of the resultant crude FDCA was 99.2% (Fig. S34b), as determined by 1H NMR (Note S12). The impurities may result from the non-Faradaic reactions13,14. At higher HMF concentration (500 mM), the watt-scale electrolyzer achieved SPCE of ~99.5% (Fig. S35). A further reduction in flow rate (<6.75 mL min−1) to increase residence time can induce a gas-liquid countercurrent, destabilizing electrocatalysis. Although the yield remained high (~96.7%), impurities generated by the degradation of unreacted HMF and intermediates raised difficulties in FDCA purification.

Stack scale-up with FDCA purification and analyses of TEA and LCA
In terms of practical FDCA production, the stack was scaled up from watt-scale (48.7 W) to hundred-watt scale (164.8 W, Fig. 5a, inset) for HMF oxidation at higher concentration (500 mM). Thermal management is an important factor in the design and fabrication of large-scale electrolyzers. Thus, a heat exchanger was incorporated between each MEA (Fig. S36a). The performance and stability of the hundred-watt scale stack were assessed by the CP test at a current of 80 A. The maximum temperature of the MEA (63.8 °C) exhibited a slight increase compared to the watt-scale stack (58.7 °C) at 280 mA cm−2. The hundred-watt scale stack achieved a higher current density (400 mA cm−2) with an overall cell voltage increase by 110 mV than the watt-scale stack (200 mA cm−2). The yield (~96.2%) and FE (~94.6%) showed indiscernible change during the 100-h stability test with 100% SPCE and STY of ~367.2 mg h−1 cm−2 (32.2 t year−1 m−2, Fig. 5a), denoting its high durability. Based on the three electrolysis conditions involved in this work, a six-dimensional comparison is displayed in Fig. 5b and Table S2. The hundred-watt electrolyzer exhibits a favorable combination of all six parameters. Although the energy efficiency (EE, mass of FDCA produced per kilowatt-hour) is 0.45 kg kWh−1, which is only 6.25% lower than the watt-scale system (0.48 kg kWh−1), the STY has increased by 97.8%.
Because FDCA purity directly influences PEF quality, a nanofiltration membrane was used to continuously purify FDCA from soluble impurities (Fig. S36b). The electrolyte (pH of ~13.33) used 3 M H2SO4 to neutralize the unreacted KOH before entering the membrane separation device. A ~96% yield was achieved using integrated nanofiltration and reverse osmosis (RO) membranes with a gradient elution and concentration process. Waste liquids containing impurities can be treated by concentration, drying, and combustion. As the carbon content in the impurities originates from biomass, the carbon dioxide (CO2) generated during combustion does not contribute to additional carbon emissions12. The H2O obtained by the RO membrane has negligible FDCA content and can be recycled as a solvent (Fig. S37). The FDCA solution obtained in 8 h electrolysis was purified by membrane separation followed by acidification, yielding 553.3 g white FDCA powder (Fig. 5a, inset) with a purity of 99.8% (1H NMR, Fig. S38). The use of this high-purity FDCA as a monomer enables PEF polymerization with a shallower color and higher intrinsic viscosity (η) than low-purity FDCA (99.2%) (Fig. 5c and Note S16). Based on the above results, we propose a green chemical process for producing high-purity FDCA using the AEM-HMFOR technology. It encompasses the purification of crude HMF through active carbon, AEM-based HMF electrooxidation, and FDCA purification by membrane separation (Fig. 5c). Notably, this process employs H2O as the sole solvent, which can be recycled in the system, minimizing liquid waste for future scale-up production.
The economic feasibility of the AEM-HMFOR technology was evaluated using techno-economic analysis (TEA)4,52–54. A TEA model of this chemical process for FDCA production (Fig. S39, S40) was undertaken at industrially relevant manufacturing conditions (Fig. 5d, details in Supplementary TEA). Taking a local electricity cost of 0.042 US$ kWh−1 with a current density of 400 mA cm−2, and assuming HMF price to be 1390 US$ tonne−1 for academic analysis (detailed discussion in Supplementary), the production cost of FDCA is calculated to be 2224 US$ tonne−1, which is lower than the costs associated with conventional chemical routes, ranging from 2458 to 3157 US$ tonne−1 (Table S3). TEA has shown that the FDCA production costs comprise capital, chemicals (H2SO4, KOH, H2O, and HMF), and operating costs (Fig. 5e), with a detailed cost breakdown provided in Fig. S41 and S42. The material and capital costs, particularly for KOH and the electrolyzer, decrease sharply at higher current densities, resulting in lower FDCA costs. The cost of AEMs has decreased considerably over the past decade55. This trend is expected to continue as market penetration increases, driven by their application in fuel cells and water electrolysis. The impact of MEA replacement cost (AEM and catalysts) on the total FDCA cost is within ~1.5%, and this effect gradually diminishes with increasing current density (Fig. S43). Notably, the FDCA production cost is more sensitive to the HMF market price than to the KOH market price (Fig. S44). Furthermore, this cost can be substantially offset by the revenue from the by-products H2 and K2SO4 (Fig. S45). At current market prices, the AEM-HMFOR system achieves reasonable profits, highlighting its potential for scalable and cost-effective FDCA production (Fig. S46 and Table S5).
A lifecycle assessment (LCA) was conducted to assess the environmental sustainability of FDCA produced in the four cases in this work (Fig. 5f and Fig. S47, details in Supplementary LCA)56–58. Cases I and II involve operating currents of 15 and 25 A in 1.0 M KOH with 200 and 400 mM HMF, respectively. The global warming potential (GWP) of FDCA is primarily influenced by the constituent processes of production, purification, and waste treatment (Fig. 5f). Case III (current of 80 A, 500 mM HMF in 1.2 M KOH) shows a significant decrease in GWP relative to Case I, which can be attributed to the lower energy consumption in production and purification steps due to the reduced H2SO4, KOH, and H2O input, as well as the higher current density. The GWP of Case III is 21.69 kg CO2 eq kg–1, reflecting a reduction of ~64.7% compared to the value reported for the crystallization separation technique (Table S6). The electrooxidation parameters in Cases III and IV are identical except for the electrical energy sources. Case IV utilizes photovoltaic (PV) energy as green electricity, and the GWP of 5.40 kg CO2 eq kg−1 was estimated to be 75.1% lower than in Case III, indicating appreciable potential for coupling renewable electricity with the proposed technology. According to the sensitivity analysis of the GWP assumptions for feedstocks (HMF and KOH), KOH shows greater sensitivity than HMF, with a more pronounced change in magnitude from Case I to Case IV (Fig. S48). In all cases, the variations remained below 12%, underscoring the reliability of the LCA model. Other environmental impacts have been considered in the sustainability evaluation in Fig. S49. The use of renewable electricity has a negative impact on terrestrial ecotoxicity and mineral resources scarcity when considering Case III, mainly due to the use of heavy metals and chemicals in solar panel production59, and other environmental impacts have been greatly minimized. When cleaner wind energy and a larger separation system are taken (Case VI), the GWP could be further lowered (Fig. S50). As a result, the development of AEM-HMFOR systems directly coupled to PV or wind energy may be necessary. The integrated TEA and LCA results indicate that electrocatalytic FDCA production is both economically viable and environmentally sustainable.

Methods
Chemical materials
KOH (AR, 95%), Ni(SO4)·6H2O (AR, 98%), Ni(NO3)2·6H2O (AR, 98%), Fe(NO3)3·9H2O (AR, 98%), and Co(NO3)2·6H2O (AR, 99%) were purchased from Shanghai Hushi Company. (NH4)6Mo7O24·4H2O (AR, 99%), ethanol (C2H5OH, AR), and isopropanol (C3H8O, AR) were purchased from Shanghai Bide Pharm Company. Nickel foam was obtained from Suzhou Xingzhenghong Company. 5-hydroxymethylfurfural (HMF, 99%) was obtained from Zhejiang Sugar Energy Company, and 5-formyl-2-furancarboxylic acid (FFCA, 98%) was obtained from Shanghai Titan Company. 5-hydroxymethylfurancarboxylic acid (HMFCA, 98%) and 2,5-diformylfuran (DFF, 98%) were purchased from Thermo Fisher Scientific Inc. 2,5-furandicarboxylic acid (FDCA, 99%) was obtained from Shanghai Meryer Chemical Technology Co., Ltd. PAP-TP-85 (A40, a terphenyl-based poly(aryl piperidinium) polymer) was purchased from Suzhou Sinero Technology Co., Ltd.

Catalyst and polymer preparation
Preparation of Ni-Co/NF catalyst: a piece of Nickel foam (NF, 1.0 mm thickness, 5.0 × 5.2 cm2) was cut and washed in 3.0 M HCl for 30 minutes, followed by ultrasonication in ethanol and acetone for 30 minutes, respectively. After that, the NF was vertically immersed in a 100 mL aqueous solution (75 mL deionized H2O and 25 mL isopropanol), which consists of 17.55 mmol NiSO4·6H2O and 4.95 mmol Co(NO3)2·6H2O. The above solution containing NF was maintained at 40 °C for 24 h. Next, the catalyst was taken out and washed three times with deionized H2O and isopropanol. Then, it was aged in a 1.0 M KOH solution at 60 °C for 8 h. Finally, the catalyst was taken out and rinsed with deionized H2O three times, denoted as Ni-Co/NF. The mass loading of 2.7 ± 0.1 mg cm−2 was determined by measuring the NF weight before and after immersion. Preparation of Ni(OH)2/NF, Co(OH)2/NF and Co(OH)2/CF catalysts: NF (5.0 × 5.2 cm2) was immersed in the aqueous solutions containing 22.5 mmol of NiSO4·6H2O and Co(NO3)2·6H2O, respectively, to prepare Ni(OH)2/NF and Co(OH)2/NF via an impregnation strategy similar to that used for the Ni-Co catalyst (same preparation temperature and duration). The pretreatment method for cobalt foam (CF, 5.0 × 5.2 cm2) was consistent with that for NF, and the Co(OH)2/CF catalyst was also prepared by the identical impregnation method in a solution with 22.5 mmol Co(NO3)2·6H2O. Preparation of Ni-Fe/NF catalyst: 2.13 mmol Ni(NO3)2·6H2O and 0.71 mmol Fe(NO3)3·9H2O were dissolved in 30 mL deionized H2O with 10 mL ethanol. A washed NF (2.0 × 2.0 cm2) was immersed in the above solution at room temperature for 24 h. The catalyst was taken out and washed three times with ethanol and deionized H2O. After drying in an oven, the obtained catalyst on NF was denoted as Ni-Fe/NF. Preparation of Ni-Mo/NF catalyst: a washed NF (5.0 × 5.2 cm2) was immersed in 200 mL deionized H2O with 2.70 mmol (NH4)6Mo7O24·4H2O and 10.80 mmol Ni(NO3)2·6H2O. Next, the solution containing NF was transferred to a Teflon-lined autoclave at 150 °C for 6 h to obtain the catalyst precursor. The obtained precursor was washed with deionized H2O and ethanol, then dried under vacuum. Afterward, it was calcinated in an H2/Ar (v/v=5/95) atmosphere at 500 °C for 2 h to prepare the Ni-Mo/NF catalyst. Polymerization of polyethylene furanoate (PEF): 23.4 g of obtained FDCA (0.15 mol), 18.6 g of ethylene glycol (0.30 mol), and tetrabutyl titanate (TBT) as the catalyst (500 ppm of the total monomer mass), were vigorously stirred at 150 °C for 30 min in a 100 mL three-necked flask. Next, the temperature is raised to 180–200 °C for condensation polymerization. When the mass of collected water reached 95% of the theoretical water yield, the polycondensation process was complete. The reaction temperature was then increased to 210 °C for pre-polymerization, which lasted 1–1.5 h. Subsequently, the temperature was raised to 220–230 °C for terminal polymerization. When a pronounced pole-climbing phenomenon was observed, the reaction was finished.

Material and flow channel characterizations
Powder X-ray diffraction (PXRD) was performed with Cu Kα (0.154 nm) radiation on a Bruker D8 Advance X-ray diffractometer. High-resolution transmission electron microscopy (HR-TEM) images and Energy-dispersive X-ray (EDS) mappings were obtained on a Talos F200X G2 electron microscope operating at an accelerating voltage of 200 kV. Scanning electron microscopy (SEM) images were collected by an analytical field emission scanning electron microscope (ZEISS, Germini 450). X-ray photoelectron spectroscopy (XPS) measurements were performed on a Micro-focus X-ray photoelectron spectrometer (Thermo Scientific, Nexsa G2). Proton nuclear magnetic resonance (1H NMR) measurement was carried out on an NMR Spectrometer (Bruker BioSpin, AVANCE NEO). Three-dimensional images of the flow channel structure were collected by a confocal laser scanning microscope (ZEISS, LSM 900). The pressure distribution tests were conducted using a flexible pressure sensor (CNSCAN, G-Scan).

Electrochemical measurements
All three-electrode electrochemical tests were performed using an electrochemical workstation (Metrohm, Autolab PGSTAT302N with 10 A current booster) in a divided H-type cell at ambient temperature, unless otherwise stated. The prepared catalysts (1 × 1 cm2), Hg/HgO, and Pt mesh (2 × 2 cm2) were used as the working, reference, and counter electrodes (internal resistance obtained from the Nyquist plot). Both cathode and anode chambers were filled with 20 mL 1.0 M KOH (pH 13.67 ± 0.15) and separated by an anion exchange membrane (AEM, PAP-TP-85, 40 μm). AEM was pretreated with 1 M KOH for 12 h. Linear sweep voltammetry (LSV) was measured at a scan rate of 5 mV s−1 without iR correction. The electrochemical impedance spectroscopy (EIS) tests were performed with a frequency range from 100 kHz to 0.1 Hz with an amplitude of 10 mV. All potentials were converted to reversible hydrogen electrode (RHE) through the following equation: ERHE = Emeasured + 0.098 + 0.0591 × pH.

AEM-HMFOR electrolyzer performance tests
The AEM-HMFOR electrolyzer includes end plates (PEEK), polar plates (high-purity Ni, ≥99.99%), and MEA. The MEA takes Ni-Co/NF as the anode, Ni-Mo/NF as the cathode, and PAP-TP-85 as the membrane (internal resistance obtained from the Nyquist curve). For multi-batch electrolysis, the anolyte was fed 1.0 M KOH with 0.2 M HMF (20 mL), and the catholyte was fed 1.0 M KOH (20 mL). The HMF conversion efficiency of the AEM-HMFOR electrolyzer was evaluated by chronoamperometry (CA) tests at selected cell voltages. In single-pass mode, the stability of the stacks was investigated by chronopotentiometry (CP) using an electrochemical workstation (100 A current booster) at selected currents. All electrolyzer operating conditions are summarized in Table S14.

Product analysis
Quantitative and qualitative analyses of the products were determined by high-performance liquid chromatography (HPLC) with a C-18 column (Shim-pack GWS, 4.6 × 100 mm, 5 μm) and a UV-Vis detector set at 265 nm. The eluent consisted of 5 mM ammonium formate and methanol in a volume ratio of 4:1 at a flow rate of 0.5 mL min−1 for 10 min. The 100 μL electrolyte obtained during electrolysis was diluted 1000-fold (initial HMF concentration of 200 mM), 2000-fold (400 mM), and 4000-fold (500 mM) with ultrapure H2O for HPLC analysis. The single-pass conversion efficiency (SPCE) of HMF, space-time yield (STY) of FDCA, Faradaic efficiency (FE), specific energy consumption (SEC), and FDCA yield were calculated by the following equations:
SPCEHMF = mol of HMF consumed / mol of initial HMF × 100%
STYFDCA = mass of FDCA produced / (geometric area of anode × electrolysis time)
FEFDCA = mol FDCA produced × 6 × F / Q × 100%
YieldFDCA = mol of FDCA produced / mol of initial HMF × 100%
SEC = Ustack × Istack / FDCA productivity, (Unit: kWh kg−1)
where F refers to the Faraday constant (96,485 C mol−1) and Q is the passed charge.

Data availability
The data supporting the findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, the authors demonstrate the feasibilty and ecnomic viability for continuous production of industrial scale, high-purity FDCA using AEM- HMFOR technolgy. Such an attempt provides a paradigm for scientists engaged in fundamental research on HMFOR to scale up laboratory-scale research to industrial production. The paper was well present and could be accepted by Nature Commun once following issues could be answered.\n1.For the catalyst, Ni-Co/NF, the electronic conductivity is assumed to be inferior to those listed in Table S6. Did authors compare its electrocatalytic activities using traditional H-Cell with their sulfide or phosphide counterparts?\n2.In page 9, “ The purity of the resultant crude FDCA was 99.2%, as determined by 1H NMR.” Relevant reference or calculation method needs to be provided.\n3.In the flowing channel, how to tackle with the O2 generated as a result of OER.\n4.Is there any impurities produced by HMF degradation adhered to AEM after 400H running? If so, how much it is and how to reduce it?\n5.For TEA analysis, if produced H2 was collected, how much profit could be enhanced?", "reviewer_2": "This study proposes a green electrochemical process for producing FDCA from biomass-derived HMF via an anion-exchange membrane–based oxidation reaction (AEM-HMFOR), achieving a high Faradaic efficiency (94.6%) and FDCA yield (96.2%) with high purity. In addition, the authors demonstrate the techno-economic and environmental feasibility of the process through comprehensive TEA and LCA. Notably, the proposed system achieves a production cost of approximately $2,300/ton and significantly lower global warming potential compared to conventional FDCA production. Overall, this work offers a promising direction for replacing fossil-derived plastics with biomass-based alternatives. However, several issues must be addressed before this manuscript is suitable for publication in Nature Communications.\n1. The authors should clarify the specific advantages of the AEM-HMFOR process over conventional chemical-catalytic oxidation routes in terms of selectivity, operational conditions, environmental impacts, and potential for coupling with renewable electricity.\n2. While chemical oxidation processes typically benefit from economies of scale, the scalability of membrane-based systems such as AEM-HMFOR may face limitations due to membrane cost, durability, and stack integration complexity. The authors should discuss how such scale effects may impact the long-term competitiveness of the proposed system at commercial scale.\n3. The authors mentioned on page 11 that 3 M H₂SO₄ was used to neutralize unreacted KOH prior to membrane separation, whereas Figure 5c shows neutralization occurring after the RO membrane. This discrepancy should be clarified to avoid confusion regarding process flow.\n4. Given that HMF and KOH are the dominant contributors to both economic cost and environmental impact, a sensitivity analysis with respect to their price and GWP assumptions is recommended. This would enhance the robustness of the TEA and LCA conclusions.\n5. Since both input and output scales linearly with plant capacity, the claim that a larger separation system lowers GWP per kg of FDCA may not be fully justified. The authors should explain whether improved energy efficiency or other nonlinear effects contribute to the reduced GWP.\n6. The prices listed in Table S8 are mostly retail prices from chemical suppliers, which are not representative of bulk industrial pricing. The authors should provide or estimate wholesale prices for a fair comparison with their proposed production cost.\n7. The current TEA includes equipment and operating costs but omits overheads such as labor, financing, depreciation, and discount rate. These are crucial for realistic comparison with commercial FDCA prices and should at least be discussed as limitations.\n8. There appears to be a discrepancy between the purification cost fraction in the TEA and its environmental impact in the LCA. The authors should clarify whether this is due to energy consumption, solvent usage, or other factors.\n9. The environmental benefit of byproduct hydrogen is marginal in Fig. 5f. However, its actual value strongly depends on the reference hydrogen source it replaces (e.g., SMR-based, PEM electrolysis). The authors should specify this assumption or conduct scenario-based analysis.\n10. The reviewer cannot evaluate if the TEA and LCA results are correct or not because the detailed information is missing. For example, detailed process flow diagram, capital cost for equipment and corresponding size, variable and fixed operating costs considered for calculation, life cycle inventory data for all the materials and utilities considered in calculation, and system boundary are all missing. These information may be provided in Supplementary Material.\n11. How are impurities treated in the process? How did authors consider impurities in their TEA and LCA calculations?\n12. In the LCA calculation, how were byproducts considered? Did authors use allocation method or system expansion?\n13. According to Section 12 in Supplementary Material, the production rate is assumed to be 1,000 kg per day. This is not a commercial scale. The economic feasibility of the process should be evaluated at a commerical scale, assuming that the experimental data obtained at lab-scale experiments hold for a large scale process, so that the results provided in this paper can be directly compared to others presented in literatures (e.g., NREL). Moreover, the authors cannot achieve economic viability for such a small-scale because they cannot take advantages from economy of scale.\n14. Please also compare the TEA and LCA results to the values reported in literature (e.g., market price of FDCA, production cost reported in other literatures, GWP reported in other literatures).", "reviewer_3": "In the manuscript, the authors present a well-designed approach towards industrial scale FDCA synthesis, showcasing the route from HMF to PEF, and providing context in terms of LCA and TEA for the process. They increase the electrode area and stack design while providing inside into the engineering within the work. With the novelty in stack design in this application and product purification, the content of the article is worth publishing.\nYet, the manuscript lacks some details on experimental conditions and some aspects require revision and clarification prior to publication. As there are no line numbers, the following comments refer to figures, chapters, and counted lines on each page:\n1) Data transparency in introduction in reference to Figure 1:\nThe authors mention “industry research” (page 2 line 8) as their source for data and mention a report in the caption of Figure 1a) which for which there is no citation. It is advised to make the data source more available (citation with DOI or other unique references).\nThe data for Figure 1c) is even less traceable, with no specific report given, making verification and a validity check impossible. This should be remedied. Further, clarification in the caption is necessary, whether this is a projection (when, under what circumstances) or current market share of products.\n2) Relevance and clarity of Figure 1 b:\nWhile the authors include a TEA and an LCA within their work, there is no localization of production capacity and no coupling to solar energy supply. Therefore, Figure 1b adds little value to the content of the manuscript. Further, there is no explanation for the box on the bottom right corner, in which, additionally, the color scheme does not seem to be applied. This needs to be clarified.\n3) Missing data in Figure 1 d:\nThe focus in Figure 1d) on STY over concentration is a new interpretation of existing data, which is highly valuable from a scale-up point of view. The authors specified that the data collected is from recent publications without further specification. Yet, there appears to be some data missing (e.g. 10.1021/acsenergylett.4c03257 – 200mM HMF, 83 mg/cm²/h, or 10.1021/acssuschemeng.4c04754 – 1M HMF, 140mg/cm²/h.). It is advised to revisit the data included or specify the basis on which data was curated.\n4) Visibility of Data for Charge Transfer resistance (Rct)\nOn page 5 line one the authors describe the Rct from Figure S5. However, due to the large dots in Figure S5, it is hard to distinguish individual lines/data points. Revisiting and redesigning (e.g. smaller dots/excerpt) the figure is recommended.\n5) Missing Information/accessibility of methods:\nThe authors test different flow channel widths; however, the flowrate is not apparent, neither in the method section in the SI, nor in the manuscript. It could be the same as for Figure 3, but specification is needed.\nFurther, the “three-electrode system” (page 4 line 28) is not described in the methods, it needs to be specified if this is an H-cell, beaker or flow-cell.\nFor example, a table in the SI that links the results of the (sub) Figures to the experimental conditions (such as electrode are, CA or CP, current/voltage applied, flow rate, electrolyte, charge for evaluation, …) could increase accessibility.\n6) Inconsistency in data interpretation:\nOn page 6 line 11 and following, the authors claim that HMF concentrations above 200mM lead to AEM degradation and increasing ohmic losses. However, this is not apparent in Figure S5 and its interpretation on page 5 line 1. Further, this conclusion is not mentioned when regarding elevated concentrations for the 100cm2 electrolyzer and its implications for elevated HMF concentrations.\n7) Calculation of activation energy with reference to Figure 3a.\nThe authors show the resulting cell voltage in Figure 3a with and without flow channels. The general result is plausible. Yet, for the 200 mV difference (displayed in Figure 3a) the main single contributor is the higher activation potential in Figure S14, which is not specified in the manuscript. Clarification on why the activation potential changes with the addition of flow channels is required.\n8) Clarification on Error Bars in Figure 3b:\nFigure 3b is the only figure with error bars (for STY and FE) – clarification on what these display (and the absence of error bars on yield) is necessary.\n9) Missing current profile for Figure 3c:\nThe authors provide an STY for different flow rates after identical charge has passed through the electrode. The resulting STY (at roughly equal FE) can only result from increasing current. Since the difference is very high between 0.25 and 1 ml/min, displaying the current/time plots for these graphs in the SI would be beneficial as it is only implicitly given in the current form. Further, if the electrolyzer is “undersupplied” with HMF at low flow rates, this should be mentioned as, in this case, the reason would not be mass transfer limitations but the absence of HMF in the electrolyzer.\n10) Altering charge as basis for evaluation.\nThe authors evaluated the experiments in Figure 3b and Figure 3c after different charges (2000 C and 2300 C) in Figure 3. Clarification on why these points were chosen is necessary. Further, Figure 3c is the only such diagram that lacks the FDCA yield, which should be included.\n11) Voltage-Yield relation inconsistency/Electrical resistance in P-Stack:\nOn page 8 line 4, (Figure S20) the authors describe the lowered FE at elevated voltage (above 1.6V), which they attributed to OER, which is plausible. Yet, in Figure 4f, the authors describe, show how a cell voltage of 1.8 and ~2V produces a yield and FE of close to 100%. This inconsistency needs to be mentioned, and the phenomenon needs to be described. The “internal resistance” of the P-stack needs to be described and measured in more detail. Contact resistance needs to be accounted for at the elevated current and actual current distribution should be measured in the individual cells. This could give an indication of HMF conversion in the individual compartments.\n12) Clarification on differences and comparison between S-Stack and P-Stack:\nOn page 9 line 5 and following the authors describe how in the S-stack the electrolyte flows similar to an electrolyzer without a flow-channel, while in the P-stack, the electrolyte flowed as in an electrolyzer with a flow channel. However, the authors do not sufficiently make clear why this is the case. It should be clarified whether there are flow channels in both electrolyzers and why the flow is different (possibly via a sketch in the SI). If there are significant differences, they should be named. Furthermore, a fair comparison should be made.\nThe comparison is also hindered by the flow-velocity in both stacks. The flow rate in the P-stack is 5 times higher than in the S-stack (page 9 line 11). This would result in an actual flow velocity that is 27 times as high as in the S-stack (5*7,18/1,33) as there is a sequential flow in the P-stack while (as in a longer tube) than in the S-stack (as in a wider tube through parallel flow cells). This would result in vastly different mass transfer properties. Here, clarification and reevaluation of the comparison, especially in reference to the results in Figure 3c is necessary.\n13) Potentially misleading comparison on setups in Figure 5b):\nThe Spider-web diagram in Figure 5b is somewhat misleading in terms of SEC. For all other metrics, the favorable number are on the outside, while for the SEC, it would be more favorable to be at the center. This implies a superior performance of the 80A setup, while in terms of SEC, this is not the case. Therefore, this metric should be reconsidered and could be replaced by e.g. the amount of FDCA produced per kWh.\n14) Additional information required on lower flowrate threshold:\nOn page 9 line 23, the authors mention that a lower flowrate can destabilize electrocatalysis which is a highly interesting finding for practical application. If there is additional information on this (e.g. threshold value regarding current density), the scientific community would benefit much from sharing this information.\n15) Missing information on FDCA purification process:\nThe authors purified FDCA from the solution, which is highly relevant for industrial application. However, the manuscript lacks information on the purification procedure. To be able to reproduce the underlying data for the subsequent TEA and LCA, it is necessary to report on the membranes (pore size/MWCO and supplier) and membrane area used, the pressure difference, and the stage-cut of the individual stages (both NF and RO). This is highly relevant to judge whether water can be recycled and how energy-intense the separation would be. Further, the pH of the product solution should be measured, as close to 0.5M of FDCA (with two carboxylic acid groups) should have a substantial influence on the pH of the solution.\n16) Lack of discussion on PEF quality:\nThe authors report on the color of PEF when polymerized from purified FDCA (page 11 line 20). While it is clear that an extensive analysis of the PEF quality is beyond the scope of this work, the authors should include the necessity for future analysis, especially regarding critical impurities that might require different purification steps.\n17) TEA:\na. The authors state that even at current market prices, the AEM-HMFOR system would achieve reasonable profits (page 13 line 4). However, the products would remain in solution (in 1.2M KOH, according to the caption of Figure S34), which would not be the specification in Table S8. Here, clarification is needed. Further, the y-axis of Figure S34 does not match the numbers in Note S8 and the manuscript. This should be revised.\nb. While the authors design a system to purify FDCA, in the TEA the authors assume purification costs to be 30% of the electrolyzer costs. If there is a reason the authors do not refer to their purification system, it should be discussed, otherwhise, the designed system should be used as a basis for the TEA, as it is for the LCA.\nc. Additionally, other costs (such as that the MEA costs 3% of the electrolyzer and the MEA will run as long as the electrolyzer) are assumed without a reference indication. This would be necessary for clarification. Further, a discussion on the uncertainty of these assumptions is necessary.\nd. In the SI, the authors calculate an offset for H2 and K2SO4 price but do not specify whether this is included in the FDCA costs or if it is neglected. Especially the K2SO4 prices will have a significant influence. Yet, it can only be discussed in combination with the purification steps. Furthermore, paired electrolysis should be mentioned as a possibility to increase the economic perspectives (e.g. 10.1021/acssuschemeng.3c03144, 10.1021/acssuschemeng.4c04754 or 10.1039/D1GC00914A)\ne. The color choice in graph Figure 5e makes distinguishing between H2O and KOH costs fairly difficult, a line connecting KOH with the respective part in the diagram could assist.\n18) LCA:\nThe authors provide numbers on FDCA GWP and other factors which is highly relevant. In the discussion of these numbers, a comparison to similar products (e.g. Terephthalic acid as a precursor for PET) should be made to give a perspective to the numbers calculated.\n19) General lack of presentation of cathode side:\nIn all Figures except Figure 1c, there is no input of water on the cathode side on all diagrams. Additionally, there is a lack of data in the method section on the cathode side of the experiment. It is advised to clarify H2 production and the supply of water to the system, since OH- ions are supplied through the AEM. Furthermore, there is no mentioning of cation leakage through the AEM. If this was not measured, the possibility should at least be mentioned in the discussion.\n20) In the SI, Reference 6 and 7 appear to be identical.\nIf these comments can be satisfied, a publication can be recommended.\nKind regards", "reviewer_author_response": "Response letter to reviewers\nReviewer #1: In this manuscript, the authors demonstrate the feasibility and economic\nviability for continuous production of industrial scale, high-purity FDCA using AEM-\nHMFOR technology. Such an attempt provides a paradigm for scientists engaged in\nfundamental research on HMFOR to scale up laboratory-scale research to industrial\nproduction. The paper was well presented and could be accepted by Nature Commun once\nfollowing issues could be answered.\n1. For the catalyst, Ni-Co/NF, the electronic conductivity is assumed to be inferior to those\nlisted in Table S6. Did authors compare its electrocatalytic activities using traditional H-\nCell with their sulfide or phosphide counterparts?\nReviewer #1: I am satisfied with the authors' reply to my comments and would like to\nsuggest the acceptance of this work by Nature Communications.\nReviewer #3: The authors have substantially revised the manuscript. They have answered\nall points raised by the reviewer in detail and provided the necessary information. With\nthese changes, we believe the manuscript can be published as presented.\nReviewer #4: In this manuscript, the authors report the feasibility of continuous production\nof industrial-scale, high-purity FDCA via AEM-HMFOR technology. The work employs\nTEA and LCA to validate the economic viability and environmental sustainability of the\nproposed process, offering a valuable paradigm for the scale-up of biomass electrooxidation\ntechnologies from laboratory bench to industrial implementation. The manuscript is well-\nstructured and presented; however, the following revisions are suggested to further enhance\nits quality and clarity:\n1. Thermal management is critical for the design of large-scale electrolyzers, and the\nintegration of heat exchangers between MEAs constitutes a key structural configuration in\nthis work. We suggest supplementing the schematic diagrams to explicitly illustrate the\nconfiguration, layout, and connection mode of the heat exchangers."}, "author_response": ""}]

Decision letter