bluuebunny/crossref_metadata_2025 huggingface dataset:
Colloidal Synthesis and Photoluminescence Properties of Near-IR-Responsive Ag8GeS6 Quantum Dots
Authors: Rismaningsih Nurmanita , Kubo Junya , Akiyoshi Kazutaka , Kameyama Tatsuya , Yukawa Hiroshi , Baba Yoshinobu , Torimoto Tsukasa
Published: December 2024

Near-infrared (NIR)-responsive quantum dots (QDs) hold immense promise for a range of applications, such as photovoltaics, photocatalysts, and biomedical imaging. Their unique optoelectronic properties, including tunable photoluminescence (PL) peaks and high PL quantum yields (QY), originate from the quantum confinement effect. In biomedical imaging, QDs offer superior photostability and enhanced biocompatibility compared to traditional organic fluorophores. Although binary QDs, such as CdTe, CdSe, PbS, and HgTe, have been extensively explored, their practical use is limited by the content of heavy metals with high toxicity. Here, we report the first synthesis of Ag8GeS6 QDs emitting a NIR PL peak at 920 nm and their potential as luminescent probes for in vivo bioimaging.

Ge(gly)2(H2O)2 was prepared by the modified method described in previous study, as a germanium precursor resistant to air and moisture.[1] Precursor powders of Ge(gly)2(H2O)2, silver(I) diethyldithiocarbamate, and thiourea were dispersed in a mixture solvent containing 1-dodecanethiol and oleylamine, followed by the heat treatment at 423 K for 20 min. The obtained Ag8GeS6 QDs were surface-coated with a ZnS shell layer with different shell thicknesses.

Spherical Ag8GeS6 QDs were formed with the average size of 4.2–4.6 nm. XRD diffraction patterns showed that the obtained QDs had an orthorhombic Ag8GeS6 crystal structure. The absorption spectra were broad and structureless, with an onset wavelength at around 850 nm. The energy gap was almost constant at 1.48-1.48 eV, regardless of the Ge/(Ag+Ge) ratio in the precursors. The Ag8GeS6 QDs prepared with Ge/(Ag+Ge) = 0.82 exhibited a broad PL peak at 920 nm with a PLQY of 11%. The surface coating with a ZnS shell enhanced the PLQY to 40–42%. The ligand exchange of the QDs with 3-mercaptopropionic acid (MPA) enabled uniform dispersion in an aqueous solution for the application to in vivo bioimaging. The resulting MPA-modified Ag8GeS6@ZnS QDs maintained similar size distribution but the PL QY was slightly decreased to ca. 23%. These QDs were successfully applied for in vivo bioimaging by injecting them into the back of mouse, in which a clear PL image was obtained and the detected PL intensity was proportional to the concentration of injected QDs.In conclusion, the present Ag8GeS6@ZnS QDs seem promising as a probe for bio-imaging, marking a significant advancement in the field and opening avenues for safer and more effective NIR-responsive QDs.

[1] A.S.R. Chesman, et al., Chem. Mater, 26, 5726 (2014).
Synthesis and Photoelectrochemical Properties of Copper Titanate for Pollutant Removal
Authors: de Almeida Juliana , Rajeshwar Krishnan , Rodrigues Christiane de Arruda
Published: December 2024

Copper species are considered one of the materials capable of converting pollutants in add-products values. However, its stability is a challenge when applied in photoelectrocatalytic (PEC) processes. A promissory alternative is to couple copper species with other materials improving their chemical stability, such as TiO2, an p-type semiconductor with excellent charge transfer. The insertion of Cu atoms into the titanium crystal lattice can promote the formation of stable binary copper oxides and/or the production of ternary/quaternary oxides by sharing oxygen between the species1,2. In addition, the presence of TiO2 on CO2 conversion may lead to the reactions for methanol and ethanol formation due to its property to favor the generation of hydroxyl radicals (OH•) and H+ from the oxidation of water. Then, in the present work carried out the preparation of n-type ternary oxide semiconductor based in copper and titanium oxides. Cu–O–Ti was synthesized by a time-efficient, arc-melting method from TiO2 and Cu2O. The particulate product showed in its composition mixture between TiCu2O3 / TiCu3O5 and high crystalline phase. These ternary oxides presented a broad-band absorption in the UV−visible spectral region with absorbance coefficient located at 675 nm. Also, the material showed thermal stability up to ∼475 °C, and cathodic photoelectrochemical activity. Controlled thermal oxidation of copper from the Cu (I) to Cu (II) oxidation state showed that the crystal lattice could accommodate Cu2+ cations up to ∼475 °C, beyond which the compound was converted to CuO and TiCuO3. This process was monitored by powder X-ray diffraction and X-ray photoelectron spectroscopy. The mott-Schottky plots for this ternary oxide exhibited a decrease of capacitance indicating an increase of CO2 absorbing active sites. The efficiency of photocatalyst was evaluated by PEC experiments to CO2 conversion into alcohols. The experiments were carried out bubbling CO2 in 1.0 Mol L-1 NaHCaO3. The ternary oxide favored the ethanol and propane formation, as the final product, exhibiting high selectivity and concentration.

Keywords: ternary copper oxide, copper titanate, arc synthesis, p-type semiconductor, photoelectrochemistry, CO2 conversion, C2 products formation.
Synthesis of (9-Triptycyl)Tin Halides for Application in Perovskite Solar Cells
Authors: Hasegawa Akio , Chen Chien-Yu , Nakamura Tomoya , Truong Minh Anh , Murdey Richard , Wakamiya Atsushi
Published: December 2024

Solar cells using ABX3-type perovskite semiconductors are attracting attention due to their high photoelectric conversion efficiency. However, since most of them use lead (Pb), there is a need to develop Pb-free perovskite solar cells from the viewpoint of environmental impact. Perovskites using tin (Sn) have shown promise as an alternative material for Pb-based perovskites, but many challenges remain in achieving high performance because Sn2+ is more susceptible to oxidation than Pb2+. We have previously improved the quality of Sn-based perovskite films by scavenging the Sn4+ ions1 and applying different surface passivation methods.2,3 Most of the materials used for surface passivation have ammonium groups that can bind to the A-site of the perovskite lattice, or thiocyanate or carboxyl groups that can bind to the X-site. In this work, we present a novel modification method using halometallylene, a highly reactive chemical species that is expected to replace the metal at the B-site of the perovskite structure. For this purpose, we designed a series of halostannylenes, (Trp)XSn: (Trp = 9-triptycyl group, X = F, Cl, Br, and I). These compounds can be added to the precursor solution or applied to the surface of the perovskite layer.

The reaction of 9-triptycyl lithium, which was generated by a lithiation of 9-bromotriptycene with n-BuLi, with SnX2 (X = Cl, Br) gave thermally stable yellow crystals of the product (Figure 1a). The crystals were determined to have a novel five-membered ring structure, {(Trp)XSn}5 (Figure 1b). In a coordinating solvent (dimethyl sulfoxide (DMSO) or pyridine), the compounds transformed into monomeric halostannylene complexes. From cyclic voltammetry (CV) measurements of (Trp)XSn: in DMSO solutions, the shift of the oxidation potential below any tin halide (SnX2, X = F, Cl, Br, and I) confirms that reaction active Sn2+ species, which can reduce Sn4+, were obtained. When (Trp)ClSn: was added to the solution of SnI4 in DMSO-d
6, in the 119Sn NMR spectra, a peak at –2030 ppm corresponding to SnI4 disappeared, and a new peak at –685 ppm was observed corresponding to SnI2. From these results, it’s expected that the compound will function as a reductant for Sn4+ generated in the perovskite precursor solution. In the presentation, we will further discuss the characteristics of (Trp)XSn: and its application to tin perovskite solar cells.

1) T. Nakamura, A. Wakamiya et al, Nat. Commun.
2020, 11, 3008. 2) T. Nakamura, A. Wakamiya et al., ACS Appl. Mater. Interfaces
2022, 14, 56290. 3) S. Hu, A. Wakamiya et al., Adv. Mater.
2023, 35, 2208320.

Figure 1
Aspect Ratio-Dependent Charge Carrier Dynamics in CdSe/CdS Dot-in-Rod Nanoheterostructures and the Application in Photocatalytic Hydrogen Evolution
Authors: Wei Yu Chen , Pu Ying-Chih , Hsu Yung-Jung
Published: December 2024

Hydrogen (H2) evolution reaction from photoreduction of water is a technology that converts solar energy into chemical fuel by charge carriers (electron-hole pairs) in semiconductor photocatalysts under sunlight illumination, which has been received considerable attention in the development of renewable energy. In this study, aspect ratio (AR)-tunable CdSe/CdS dot-in-rod (DiR) nanoheterostructures (NHSs) were synthesized by hot injection method. The quasi-type Ⅱ band structure of CdSe/CdS DiR was confirmed by ultraviolet photoelectron spectroscopic characteristics. When the AR of CdSe/CdS DiR was tuned from 9.8 to 37.0, the exciton localization efficiency decreased from 57.9 % to 15.1 % and the H2 evolution rate enhanced from 0.40 to 2.11 mmol g-1 h-1. In-situ transient absorption spectroscopy was employed to study the interfacial charge carrier dynamics of CdSe/CdS DiRNSs during the photocatalytic H2 evolution. The results indicated that the half-life of photoexcited electrons in CdSe/CdS DiRNS increases from 11.5 μs to 20.1 μs as the AR increased. These outcomes suggest that the AR-dependent charge carrier dynamics dominates the efficiency of photocatalytic H2 evolution in CdSe/CdS DiR. This research provides the important and novel insights into the mechanism of semiconductor heterostructures for efficiency improvement in renewable energy generation.
(Invited) Design of Durable OER Catalyst for Water Splitting
Authors: Huang Yu
Published: December 2024

Developing durable catalysts for the acidic oxygen evolution reaction (OER) is critical for advancing the hydrogen economy. Here, we reported OER catalyst based on cobalt spinel oxide with ultrahigh activity and remarkable durability for the acidic OER. Specifically, the as-prepared NiCo2O4 displayed a low overpotential of 310 mV at 10 mA/cm2 in 0.5 M H2SO4, respectively. More importantly, at a high current density of 100 mA/cm2, NiCo2O4 also delivered a low overpotential of 395 mV and a high mass stability of 384 h/mg, demonstrating its exceptional durability. Furthermore, as X-ray absorption spectroscopy studies revealed that Ni mainly occupied the octahedral site in the NiCo2O4 spinel structure. With Ni in the lattice, the structural integrity was maintained during the OER, which led to its outstanding durability. Density functional theory calculations showed that the acidic OER on the NiCo2O4 spinel structure underwent a direct O-O coupling mechanism on the (001) facet rather than the traditional adsorbate evolution mechanism. Our calculation demonstrated that the metal vacancy formation is significantly suppressed with Ni in the structure. Ni can also prevent surface electronic relaxation during the OER cycles, consistent with the superior durability provided by NiCo2O4. This study demonstrated a promising and cost-effective approach to producing nickel cobalt spinel oxides with outstanding acidic OER performance. The markedly improved OER activity and durability in acidic media promise an attractive catalyst material for proton exchange membrane water electrolyzers and renewable chemical fuel generation.
Near Real-Time Evaluation of Hydroxyl Radical Generation on Photocatalytic Electrodes Using Flow-Type Electron Spin Resonance Method
Authors: Suzuki Souta , Amano Fumiaki
Published: December 2024

Tungsten trioxide (WO3) and titanium oxide are known as photocatalysts that oxidize and decompose organic compounds. Hydroxyl radicals (•OH) generated during water oxidation not only decompose organic substances but also cause other selective oxidation reactions. However, the behavior of •OH production under different reaction conditions is not completely understood. The purpose of this study is to quantitatively analyze the •OH generated during the photoanodic reaction on photocatalyst electrodes. Herein, we developed a novel electrolyte flow-type electron spin resonance (ESR) method using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping agent to analyze the Faraday efficiency of •OH production in near real-time response. The WO3 photoanode was prepared by a dip coating method using Ti felt as the conductive substrate. When the WO3 electrode was irradiated with ultraviolet light at 1.2 V vs. RHE, four ESR signals were observed, and the formation of •OH (•DMPO-OH) was confirmed from the g value and hyperfine coupling constant. The amount of •OH produced was quantified every minute by comparing the double-integrated intensity of this signal with that of a standard sample. The results showed that the Faraday efficiency of the total amount of •OH in WO3 was low, less than 1%, and most of the photocurrent was used for oxygen evolution reaction. In the presentation, we will also report on the dependence of •OH formation on applied potential and incident light intensity.

Figure 1
Photocatalytic CO2 Reduction to Formic Acid (HCOOH) By an Organocobalt Catalyst - Two Different Mechanisms with Temporal Evolution of Catalysis, Effectuated by Second Coordination Sphere Interactions
Authors: Agarwala Hemlata
Published: December 2024

The photocatalytic reduction of CO2 to formic acid (HCOOH) using molecular transition metal complexes as catalysts is believed to proceed via two mechanisms: CO2 insertion into metal hydride bonds, or hydrogenation of CO2. We present herein CO2 reduction photocatalysis by a mononuclear organocobalt catalyst with second coordination sphere interactions, which uniquely demonstrates both pathways for the conversion of CO2 to HCOOH. This dual functionality is attributed to distinct active forms of the catalyst at different temporal stages of irradiation. We employ in-situ NMR spectroscopy to monitor potential catalytic intermediates during irradiation. These observed states align closely with the kinetic profiles of product evolution, proving to be a valuable method for an informed design of molecular photocatalytic CO2 reduction catalysts.

Figure 1
Alternating Substrate-Ligand Coordination Provides a Lower Energy C-O Bond Cleavage Pathway for Electrochemically Driven Catalytic CO2 Reduction
Authors: Agarwala Hemlata
Published: December 2024

Large-scale employment of electrocatalysts requires diving deep into their structure and operative mechanism. My talk will focus on the ruthenium-polypyridyl class of electrocatalysts for CO2 reduction to CO, improved over time to reduce the overpotential of electrochemical CO2-reduction. Focus will be on the bottleneck C-O bond-breaking step. Often Brønsted or Lewis acidic metal ions are employed to facilitate C-O bond cleavage. The former usually lead to loss in product selectivity, H2 being a co-product, while the latter usually form insoluble carbonates in anhydrous conditions. We present herein a mechanism with the aforementioned catalyst framework, selective for CO production at a low overpotential, without necessarily requiring an additional acid or base.
1,2
This pathway embodies a metallacyclic intermediate promoting C-O bond cleavage with lower activation barrier compared to C-O cleavage in the acyclic intermediate (Figure 1). Detailed computational studies (DFT), corroborated with FT-IR spectroscopy, substantiate the involvement of the metallacyclic intermediate in the catalytic cycle. Two principal factors dictate the formation of the metallacycle: (1) the flexible
denticity of the polypyridyl ligands, (2) the choice of metal center: one that can exhibit optimal electronic coupling with the ligands and bound CO2, hence functioning as a Lewis base (donates electrons to the incoming CO2) as well as a Lewis acid (accepts electrons from the bound CO2, hence forming the metallacycle), in a single catalytic cycle. Solvation of the intermediates also play a critical role.

References:

1
Agarwala, H.;* Chen, X.; Lyonnet, J. R.; Johnson, B. A.; Ahlquist, M.; Ott, S. Angew. Chem. Int. Ed.
2023, 62, e202218728.

2
Agarwala, H.;* Lyonnet, J. R.; Ott, S. Influence of π-π stacking on electroreduction of CO2. (Manuscript in preparation)

Figure 1. Energetics of two different catalytic pathways for C-O bond cleavage

Figure 1
Development of Organic Electrocatalysts for the Production of Solar Fuels
Authors: Torres Méndez Carlos Enrique , Tian Haining
Published: December 2024

Solar fuels produced by electrocatalysis have a great potential to reduce the concentration of atmospheric CO2 and make the production of fuels and chemicals more sustainable. The composition of an electrocatalyst employed for the production of solar fuels is key, ideally the catalyst should be made of abundant elements that can be found anywhere in the world. In this sense, organic molecules composed of light elements such as C, H, O, N, P and S fulfill this requirement. In addition, the extensive advances in the field of organic synthesis make possible to study the active sites, tune them at molecular level, synthesize them and scale the process with ease. In recent years, a handful of nitrogenated heterocycles have been reported for water oxidation, hydrogen evolution and carbon dioxide reduction. Special interest exists in our group on the study of benzothiadiazole based electrocatalysts for reduction reactions due to their favorable redox properties and their affinity towards different chemical species (H+ and CO2) relevant for the production of solar fuels. In this talk we will present recent efforts of our group to employ benzothiadiazoles in reactions relevant for electrocatalytic production of fuels.
Solid Oxide Cell Tests inside a Transmission Electron Microscope
Authors: Simonsen Soren Bredmose , Ma Zhongtao , Mølhave Kristian Speranza , Chatzichristodoulou Christodoulos
Published: December 2024

Simultaneous electrochemical and nano-scale structural/compositional analyses allow for a direct link between a material’s properties and its electrochemical performance. We present a method that merges high-temperature solid-state electrochemical analysis with transmission electron microscopy (TEM)1-3. This method can be important for the further development of solid oxide electrolysis and fuel cells (SOEC/SOFC), and may be applicable to other solid-state electrochemical technologies, such as solid-state batteries and thermoelectric devices.

The presentation shows how to conduct high-temperature electrochemical operando TEM experiments, including electrochemical impedance spectroscopy (EIS) analysis by using an environmental TEM (ETEM) and a MEMS chip-based heating-biasing TEM holder connected to a potentiostat (Fig. 1). The capability of executing electrochemical cell tests in the TEM is validated for both single materials1-2 and full solid oxide cells3 at temperatures up to 800 ˚C in gases such as O2 and H2/H2O, with applied electrical polarization. EIS analysis in the TEM will be showcased. Furthermore, we present results from experiments of polarization-induced degradation at an SOEC electrode-electrolyte interface.

Acknowledgements

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 850850)”

References

Ma, W.L. Dacayan, C. Chatzichristodoulou, K.S. Mølhave, F.M. Chiabrera, W. Zhang, S.B. Simonsen, “Electrochemical Impedance Spectroscopy integrated with Environmental Transmission Electron Microscopy” Small Methods 7 (2023) 2201713. doi.org/10.1002/smtd.202201713

Ma, C. Chatzichristodoulou, W.L. Dacayan, K.S. Mølhave, F.M. Chiabrera, T.E.L. Smitshuysen, C.D. Damsgaard, S.B. Simonsen, “Experimental requirements for high temperature solid state electrochemical TEM experiments”, Small Methods (2024) 2301356, DOI:10.1002/smtd.202301356

Ma, C. Chatzichristodoulou, F.M. Chiabrera, K.S. Mølhave, S.B. Simonsen, “Operando electron microscopy and impedance analysis of solid oxide electrolysis/fuel cells”, ACS Energy Letters, 9 (2024) 2007-2012, DOI: 10.1021/acsenergylett.4c00671

Fig. 1: Heating-biasing MEMS chip for temperature control and electrical polarization; TEM image over symmetric model solid oxide cell mounted on the chip; Nyquist plot of EIS data recorded at OCV at 800 ˚ C from the symmetric model cell in the TEM in a gas mixture of H2 and H2O.

Figure 1
In Operando Diagnosis of Site Density and Turnover Changes of Fe-N-C Cathodes in Oxygen Electroreduction
Authors: Bae Geunsu , Kim Minho M. , Han Man Ho , Cho Junsic , Kim Dong Hyun , Sougrati Moulay-Tahar , Kim Jinjong , Lee Kug-Seung , Joo Sang Hoon , Goddard William A , Oh Hyung-Suk , Kim Hyungjun , Jaouen Frederic , Choi Chang Hyuck
Published: December 2024

Fe-N-C catalysts have shown promising initial activity, but continue to struggle with stability issues in acidic environments, a critical barrier to replacing Pt in fuel cell cathodes. The complex interactions within fuel cells obscure the deactivation pathways of Fe-N-C cathodes, hindering the development of more durable solutions. In this study, we use an innovative online analytical system for a quantitative, time- and potential-resolved diagnosis that identifies the rapid performance degradation of Fe-N-C cathodes in the early stages of fuel cell operation. Our results reveal a strong dependence of Fe leaching from active Fe-N4 moieties on operating variables such as temperature and gas atmosphere, which not only trigger Fe dissolution but also influence the fate of dissolved Fe ions. This operando study distinguishes real-time changes in active site density (SD) and turnover frequency (TOF) from apparent decreases in oxygen reduction reaction (ORR) activity. A lifetime-dependent stability plot is presented that highlights a critical shift in the primary deactivation pathway from SD loss to TOF decrease under realistic fuel cell operating conditions. Furthermore, the introduction of site-isolated Pt ions on the Fe-N-C catalyst emerges as a synthetic solution to prevent Fe demetallation, thereby enhancing fuel cell stability. Supported by theoretical calculations and inspired by previous work, this approach not only mitigates the rapid performance degradation observed during initial operation, but also proposes a pathway for the development of synthetic routes involving non-precious group metal stabilizers of Fe-N4 sites.

Figure 1
Immobilization of Dimethylferrocene-Modified Linear Poly(ethylenimine) on Epoxy-Terminated Supports for in-Situ Confocal Raman Microscopy
Authors: Koh Miharu , Baiarashov Egor , Kitt Jay P. , Korzeniewski Carol , Harris Joel M. , Minteer Shelley D.
Published: December 2024

Dimethylferrocene-modified linear poly(ethylenimine) (DMFc-LPEI) has been widely studied as a redox-mediating polymer for biosensor and biofuel cell applications. An increasing number of studies have shown the potential for DMFc-LPEI to immobilize oxidoreductase enzymes and to mediate electron transfer at electrode supports, making DMFc-LPEI a promising high current density bioanode material. Herein, we introduce the immobilization of DMFc-LPEI on 3-glycidoxypropyltrimethoxysilane-modified glass substrates. The epoxy-terminated functional groups on the substrate are used to covalently attach the polymer chains to the substrate by a simple nucleophilic substitution reaction, while a crosslinker, ethylene glycol diglycidyl ether, stabilizes a network of polymer chains using the same chemistry. Confocal Raman spectroscopy reveals that the vibrational bands of immobilized linear poly(ethylenimine) (LPEI) broaden compared to those of free solid-phase LPEI, suggesting that immobilized polymer film exists in an amorphous phase. The Raman spectra of DMFc-LPEI showed prominent vibrations corresponding to CH3 wagging mode at 1037 cm-1 and NH || bending mode at 1451 cm-1 of dimethylferrocene (DMFc) and LPEI, respectively. In the future, this chemistry will be extended to in-situ confocal Raman microscopy investigations of DMFc-LPEI on optically-transparent indium tin oxide electrodes to unravel the structural and conformational changes associated with varying the redox state of the DMFc mediator.
Operando X-Ray Absorption Spectroscopy Investigation of Molybdenum (IV) Oxo Benzene 1,2 Dithiolate [MoIV O(bdt)2] 2- Electrocatalyst Toward Oxygen Atom Transfer Reaction
Authors: Rathnayake Rathnayake Mudiyanselage Kumuditha Anjala , Cabana Jordi
Published: December 2024

Electrocatalytic Oxygen Atom Transfer (E-OAT) reactions are vital in chemical manufacturing, notably in fields such as pharmaceuticals. Inspired by the efficiency of Molybdoenzymes in oxygen atom transfer within biological systems, various Molybdenum compounds have been synthesized to understand chemical oxygen atom transfer. This study employed a bio-inspired Molybdenum(IV) oxo benzene 1,2 dithiolate [MoIV O(bdt)2]2- catalyst for E-OAT, utilizing Triphenylphosphine (PPh3) as the substrate and water as the oxygen donor. Notably, a significant enhancement was achieved, with a 46% conversion of triphenylphosphine into triphenylphosphine oxide over 4 hours at ambient temperature, surpassing traditional methods. To further optimize processes, such as epoxide formation, a deeper understanding of catalytically active species at low overpotential is essential. Operando X-ray Absorption Spectroscopy (XAS) investigations at Mo K-edge and S K-edge provided insights into electronic structure changes during homogeneous catalysis of Phosphine oxidation and catalyst stability. The challenge posed by the limited concentration of active metal, which results in low X-ray Absorption Spectroscopy signals, was addressed by employing Operando Grazing Incidence XAS. Through this approach, the evolution of pre-edge features was observed, indicating the formation of Mo-O binding in the active states. Moreover, Operando S K-edge analysis revealed the catalyst's chemical and structural evolution mediated by electrochemically induced sulfur vacancies, elucidating the active state.
Importance of Charge Transfer Descriptor for the Computational Screening of Electrocatalysts
Authors: Ringe Stefan
Published: December 2024

Electrochemistry has become a key player in establishing a global sustainable energy landscape. Unfortunately, most electrochemical processes are limited in their efficiency and selectivity which has prevented them from replacing carbon-intensive industrial processes. Computational simulations have the potential to conquer the vast chemical space and reveal so far unconsidered new electrocatalysts and boost the performance of these devices. This, however, requires the knowledge of computationally accessible activity and selectivity descriptors. In this work, and by the example of electrochemical CO2 reduction, it is shown that the conventionally considered adsorption energy descriptor is not enough to distinguish product selectivity among catalysts. Including specifically the electrochemical environment in the quantum chemical calculations, we find that a charge-transfer descriptor is separately re- quired, such as the work function or the potential of zero charge. With this, experimental trends in product selectivity can be well described, thus providing a new set of descriptors for high-throughput screening of electrocatalysts.
Decoding Electrochemical Interfaces with Computational Approaches: The Case of NiOOH Catalyst
Authors: Kowalski Piotr M. , Ting Yin-Ying , Price Conor , Tipp Fabian , Eikerling Michael
Published: December 2024

Fundamental understanding of electrochemical interfaces is a prerequisite for designing well performing and economically viable electrocatalyst materials. The rapid increase in supercomputing power accompanied by methodical improvements in atomistic simulations enables an accelerated computer-aided materials design process. Our research in this context integrates theory and advanced simulation methods to decipher the relations between structure, properties and performance of electrochemical interfaces [1-4]. The presentation emphasizes the necessity of combining novel computational schemes [1,2,5,6] with knowledge from solid state chemistry and computational mineralogy in order to be able to rationalize the tremendous enhancement in the activity for the oxygen evolution reaction (OER) under alkaline conditions that is achieved upon Fe-doping of NiOOH [4,7]. Significant research has been dedicated to understanding the enhanced electrocatalytic activity of this material with different, often contradicting mechanisms proposed [7-11]. On the computational side, we identified the severe overestimation of the occupancy of d-orbitals by the widely used DFT+U computational approach as the origin of the problem and corrected it by employing localized Wannier functions as projectors for calculating the occupations of d-orbitals [4,2]. This approach allowed us to correctly compute the band gap of NiOOH and to reveal a realistic electronic structure of Fe-doped NiOOH. It occurred that Fe exists in the low-spin state for Fe contents below the solubility limit in Fe:NiOOH solid solution. The low-spin state of Fe dopant is responsible for lowering the OER overpotential relative to the value for pure NiOOH by ~300 mV, which agrees with the measured decrease [7] . The discovered state allows for the consistent explanation of measured data on ionic and electronic structure as well as magnetic and electrochemical properties. We will show that the miscibility of Fe in NiOOH is related to the sizes of Ni3+ and Fe3+ cations and that it is the closely matching cation radii of Ni and Fe in the low spin state that enable the formation of a mixed phase. Our results reconcile catalyst composition and structure with the mixing behavior in solid solution and the electrocatalytic activity.

[1] Tesch, Kowalski & Eikerling, J. Phys.: Condens. Matter 33, 444004 (2021)

[2] Ting & Kowalski, Electrochim. Acta 443, 141912 (2023)

[3] He et al., Angewandte Chemie 136, e202315371 (2023)

[4] He et al., Nat, Commun. 14, 3498 (2023)

[5] Nishihara & Otani Phys. Rev. B 96 115429 (2017)

[6] Kowalski et al. Front. Energy Res. 10, 1096190 (2023)

[7] Friebel et al., J. Am. Chem. Soc. 137, 1305 (2015)

[8] Conesa, J. Phys. Chem. C 120, 18999 (2016)

[9] Martirez & Carter, Chem. Mater. 30, 5205 (2018)

[10] Tkalych et al., Phys. Chem. Chem. Phys., 20, 19525 (2018)

[11] Rajan et al., J. Am. Chem. Soc. 142, 3600 (2020)
Multiscale Modeling Reveals Mass Transport-Controlled Product Selectivity in Electrochemical CO2 Reduction on Cu
Authors: Ramakrishnan Velmurugan Adith , Ringe Stefan
Published: December 2024

Electrochemical CO2 reduction is one of the most promising processes for a sustainable closure of the artificial carbon cycle. A severe limitation for wide-scale industrial applicability has been the absence of an efficient and selective electrocatalyst for the reduction of CO2 to higher-reduced valuable chemicals and fuels. Cu is the only catalyst found to produce considerable amount of multicarbon products, albeit at high overpotentials. The mechanism of the conversion process is unclear, with different active sites and rate-determining steps being proposed. In addition, the mass transport of CO2 has been suggested to have a significant impact on the product selectivity1,2. Gas-diffusion-layer(GDL)-based electrolyzers have become a state-of-the-art solution to provide a high concentration of CO2 to the active sites to circumvent these mass transport limitations. In this work, we present a new multi-scale model based on first-principles kinetics3, and a modification of a recently reported gas diffusion electrode model4. We use this to generate a digital twin of experimental electrode systems and show that even in GDL systems, mass transport is the limiting factor governing all experimentally observed trends in product selectivity, irrespective of reaction mechanism or product pathway. We further find indications of C2 products being predominantly formed in wider, accessible pores, while C1 products are generated in deeper and thinner pores with less access to CO2. This work provides strong evidence for the importance of mass transport in designing CO2 electrolyzers.

References:

Watkins, N. B. et al. Hydrodynamics Change Tafel Slopes in Electrochemical CO2 Reduction on Copper. ACS Energy Lett.
8, 2185–2192 (2023).

Ringe, S. et al. Double layer charging driven carbon dioxide adsorption limits the rate of electrochemical carbon dioxide reduction on Gold. Nat. Commun.
11, 33 (2020).

Liu, X. et al. pH effects on the electrochemical reduction of CO(2) towards C2 products on stepped copper. Nat. Commun.
10, 1–10 (2019).

Weng, L.-C., Bell, A. T. & Weber, A. Z. Modeling gas-diffusion electrodes for CO2 reduction. Phys. Chem. Chem. Phys.
20, 16973–16984 (2018).
Exploring the Role of Interfacial Water and Adsorbed Hydroxide in Oxygen Reduction Reaction (ORR) Transients
Authors: Spaulding Carolyn , Snyder Joshua David
Published: December 2024

Recently, Caffeine has been shown to improve the kinetics of the oxygen reduction reaction (ORR)[1], [2]. This activity improvement has been attributed to the adsorption geometry of caffeine at the electrode interface. To better understand this phenomena, fundamental studies of the impact of interfacial water and adsorbed hydroxide species must be conducted. We will examine the transient behavior of ORR on a well-defined Pt(111) electrode to achieve this.

While transient current decay has been discussed regarding membrane electrode assemblies (MEAs), transients are rarely considered for rotating disk electrode (RDE) experiments [3]. We have found that Pt(111) transients in the ORR potential window last in the order of hundreds of seconds, notably longer than what is typically observed for polycrystalline electrodes. During these transients, initially slow current decay occurs until a critical point, where an inflection point indicates the transition to more rapid decay. We hypothesize that these dynamic transients are caused by 2D nucleation and growth of adsorbed spectator hydroxide islands. We will present our understanding of the surface processes occurring during ORR transients, gained from experiments in conjunction with microkinetic and kinetic Monte Carlo modeling. Understanding the kinetics of these surface processes will inform the development of small molecule interface modifiers, such as caffeine, that must balance ORR activity with transient behavior.

References

[1] R. Gawas, “Modifying Interface Solvation to Improve the Oxygen Reduction Reaction Electrocatalysis,” Doctor of Philosophy, Drexel University, Philadelphia, Pennsylvania, United States, 2023. doi: 10.17918/00001760.

[2] N. Hoshi, M. Nakamura, R. Kubo, and R. Suzuki, “Enhanced oxygen reduction reaction on caffeine-modified platinum single-crystal electrodes,” Commun Chem, vol. 7, no. 1, p. 23, Feb. 2024, doi: 10.1038/s42004-024-01113-6.

[3] J. Dang, F. Yang, Y. Li, X. Deng, and M. Ouyang, “Transient behaviors and mathematical model of proton exchange membrane electrolyzer,” Journal of Power Sources, vol. 542, p. 231757, Sep. 2022, doi: 10.1016/j.jpowsour.2022.231757.
(Invited) Influence of Electric Double Layer Rigidity on CO Adsorption and Electroreduction Rate on Cu
Authors: Lu Qi
Published: December 2024

Understanding the structure of the electric double layer (EDL) is critical for designing efficient electrocatalytic process. However, the interplay between reactant adsorbates and the concentrated ionic species within the EDL remains an aspect that has yet to be fully explored. In the present study, we employ electrochemical CO reduction on Cu as a model reaction to reveal the significant impact of EDL structure on CO adsorption. By altering the sequence of applying negative potential and elevating CO pressure, we discern two distinct EDL structures with varying cation density and CO coverage. Our findings demonstrate that the EDL comprising densely packed cations substantially hinders CO adsorption on the Cu as opposed to the EDL containing less compact cations. These two different EDL structures remained stable over the course of our experiments, despite their identical initial and final conditions, suggesting an insurmountable kinetic barrier present in between. Moreover, we show that the size and identity of cations play decisive roles in determining the properties of the EDL in CO electroreduction on Cu. This study presents a refined adaptation of the classical Gouy-Chapman-Stern model and highlights its catalytic importance, which bridges the mechanistic gap between the EDL structure and cathodic reactions.

Figure 1
Co-Ion Identity Affects Double Layer Structure and Reactivity Trends in the Hydrogen Evolution Reaction
Authors: Anderson Seth R. , Johnstone Samuel G. , Dent Aaron M. , Liu Beichen , Guo Wenxiao , Gebbie Matthew A.
Published: December 2024

The formation of an electric double layer is ubiquitous in electrolytes undergoing electrochemical reactions. Currently, models for the double layer rely on the assumptions of dilute electrolyte theory where ions in solution do not interact. Dilute electrolyte theory predicts that solely hydrated counterions, or ions opposing the surface charge, occupy the near surface region and impact reactivity. Since this theory does not account for conditions like high applied potentials and high ion concentrations, understanding the relationship between double layer structure and electrochemical reactivity is critical for opening new domains for electrochemical modulation.

Notably, our recent work shows that co-ions, or ions with the same charge as the surface, can also have a definitive influence on reaction rates, particularly under conditions of high applied potential and large bulk ion concentrations. In this talk, I will discuss how to use the hydrogen evolution reaction as a model system to explore co-ion effects in electrocatalytic reactions. In our work, we systematically vary co-ion identity and track hydrogen evolution reactivity as a function of concentration to highlight how the co-ion becomes increasingly relevant in the concentrated regime. In particular, we highlight the unique ability of the tetrafluoroborate co-ion to undergo dynamic ligand exchange between hydroxide and fluoride. This allows tetrafluoroborate to act as a hydroxide sink to stabilize the hydrogen evolution byproduct. Furthermore, I will discuss our use of Raman spectroscopy to describe how co-ions impact interfacial hydrogen bonding networks, which can have a significant impact on aqueous electrochemistry. Our results highlight how co-ions influence double layer structures and have significant implications for tuning other aqueous reactions such as carbon dioxide and nitrate electroreduction.
Understanding Water Dissociation Physics through Controlled Oxide Surface Chemistry
Authors: Stovall Timothy Nathan , Bui Justin C. , Boettcher Shannon W. , Weber Adam Z.
Published: December 2024

Bipolar membranes (BPMs) provide a platform for the interconversion between electric and chemical potential gradients and the precise control over local ion concentrations and fluxes, making BPMs attractive materials for many electrochemical processes. In reverse bias charge carriers must be generated via heterolytic water dissociation (WD, 2H2O → OH- + H3O+), and which must be accomplished at high rates and low overpotentials to realize scalable BPM applications. It is hypothesized that WD is driven by a combination of electric field and catalytic effects within the bipolar junction. However, the extent to which each contributes to observed rates, and the possible interplay between the two, is yet to be resolved.

Here, we explore the interfacial physics within the BPM to understand the kinetics and mechanisms of water dissociation on TiO2 and graphene oxide (GO) derivative catalysts. Using a membrane-potential-sensing testbed we isolate the WD polarization signature in a BPM water electrolyzer. We find that neat-GO exhibits an anomalous exponential current response as a function of WD overpotential, contrary to the linear polarization response of TiO2 (and other metal oxides, reported previously). Similarly, the rates were independent of GO loading, contrasting the typical U-shaped loading dependence on WD performance using metal oxide catalysts. We hypothesize the unique behavior of GO can be linked to the double layer profile within the bipolar junction, which can be screened and localized to the catalyst/AEL interface via the acidic carboxylate moieties on the GO surface. We validate this framework by controlling the degree of hydroxyl/carboxylation on the graphene-oxide surface, and thus the electric double layer profile, to control the polarization response. Using temperature-dependent measurements at varying potentials and a simple Arrhenius-type equation we decouple the apparent enthalpic and entropic driving forces for WD within a confined and polarized heterojunction. Broadly, this work advances our understanding of the interplay between catalyst surface chemistry and electric double layer formation under confinement, and how this effect can be leveraged in (electro)chemical transformations.

Figure 1. A large electric field within the catalyst layer increases the WD rate within the BPM

Figure 1
Importance of the Cation-Water Interaction on Water Dissociation for Hydrogen Evolution
Authors: Choi Hansol , Choi Chang Hyuck
Published: December 2024

The solid-liquid interface models are generally concentrated on understanding either covalent interactions between adsorbates and solid surfaces or long-range liquid electrolyte–solid electrode electrostatic interactions. Recently, the focus of interfaces shifts to the cation-water interaction, which is not included in the conventionally pondered. This interaction reportedly plays a pivotal role in water-involved reactions because it affects the intramolecular O-H bond of water molecules. Herein, we demonstrate a correlation between the thermodynamics of water dissociation and the cation species using hydrogen evolution as a probing reaction. Surprisingly, a significantly improved onset potential of water reduction is observed by using multivalent cations, especially, the lowest solubility product (Ksp) towards metal hydroxide, Al3+. It infers that the metal cations interact directly or indirectly with water molecules to form the metal hydroxide, subsequently providing sufficient reactant, i.e., H+, at the electrode surface in the more positive potential region. By correlating electrochemical and spectroscopic results, we surmise that the presence of cations in weak acid conditions causes the formation of metal hydroxide compared to the absence of cations, resulting in a promoted onset potential of water reduction.
Cation Effect on the Product Selectivity of Electrochemical CO Reduction
Authors: Ni Weiyan , Liang Yongxiang , Cao Yufei , Chen Zhu , Sargent Edward H.
Published: December 2024

Renewable electricity-powered reduction of CO2 (CO2R) is a promising route to upgrade CO2 to ethylene, an industrial feedstock in high demand. Compared with direct CO2 electroreduction to ethylene, CO2-CO-C2H4 tandem electrolysis is more carbon efficient, circumventing CO2 crossover and carbonate formation. However, current CO electroreduction produces a mixture of multi-carbon products (ethylene, ethanol, acetate, and propanol), and the mechanism underlying this dispersion of selectivity remains unclear.

We studied the role of the microenvironment of the electrode in selectivity among C2+ products, and hypothesized that destabilizing the oxygen-containing intermediates would direct the reaction pathway toward the sole oxygen-free C2+ product, ethylene. When we explore the cations in electrolyte, we find the one with the most robust hydration shell (Li) promotes ethylene production, among C2+ products, compared to weakly hydrated cations (e.g. K). This is a distinctive trend compared to studies of activity that found reverse cation trend in jc2+. A combined study of operando Raman spectroscopy, MD simulation, and DFT calculation suggests that the strongly hydrated Li+ on the electrode surface has the greatest H2O-Ointermediate interaction and the least cation-Ointermediate interaction. This increases the difference in activation energy of the selectivity-determining step between ethylene pathway and oxygenates pathway, and hence leads to the preference of Li for hydrocarbons over oxygenates.

Figure 1
Reactive Capture and Conversion of CO2 with Functionalized Ionic Liquid Electrolytes: A Case Study Showcasing Structural Design and Key Considerations for Performance Evaluation
Authors: Dongare Saudagar , Coskun Oguz Kagan , Gurkan Burcu E
Published: December 2024

This work presents the functional design of an ionic liquid (IL) for reactive capture and conversion of CO2 (RCC) where enhanced Faradic efficiencies, stable electrolysis, and lowered overpotentials were obtained toward CO and C2+ products on Ag and Cu electrodes, respectively. Critical experimental factors that impact the evaluation of such electrolytes for RCC including the cosolvent selection, working electrode construction, reference electrode choice, and the cell design are discussed. As the IL chemisorbs CO2, the changes in the bulk viscosity and conductivity as well as the speciation (e.g, ion-CO2 adducts and newly formed hydrogen bonded species) near the electrode surface alter RCC activation overpotential, thus impacting conversion reaction outcomes as well as the interpretation of results. We showcase the utilization of in-situ surface enhanced Raman spectroscopy (SERS) in the characterization of the electrode-electrolyte interface in corroboration of the mechanisms proposed for the RCC products obtained from constant potential electrolysis. This study serves as a basis for the understanding of RCC mechanism in the presence of reactive ILs, which could lead to the development of more efficient and selective CO2 reduction electrolytes.
Mechanistic Insights into the Electrochemical Oxidation of 5-Hydroxymethylfurfural on a Thin Film Ni Anode
Authors: Prajapati Aditya , Govindarajan Nitish , Sun Wenyu , Jeong Huiyun , Feaster Jeremy , Akhade Sneha A , Bucci Giovanna , Hahn Christopher
Published: December 2024

Oxygen evolution reaction (OER) in ambient electrolyzers consumes a significant amount of energy and yields oxygen, an inherently low-value product. Therefore, it is imperative to choose anodic reactions that can make efficient use of the supplied energy to the electrolyzer when paired with a desired cathodic reaction such as CO2 reduction into value-added commodities. Utilizing biomass oxidation offers a promising avenue to reduce the overall energy input by >50% while producing high-value chemicals, and address the critical requirements for biomass conversion, a crucial 21st-century non-fossil carbon resource. In this work, we demonstrate the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) as an alternative to OER. This reaction not only reduces the theoretical overall energy input into the electrolyzer but also generates FDCA, a significant building block for the sustainable polyester PEF, which has a global market size of more than 30 Mt/yr. We present an experimental and computational approach to understand HMF oxidation on Ni-based catalysts. Our experimental investigation involves evaluating the effect of microenvironment on thin-film (5nm) Ni-catalyst in a pH range of 11-13 to understand the intrinsic kinetics of HMF oxidation. In addition, we compare the reaction energetics of OER and the hydride transfer reaction of the HMF oxidation using density functional theory to understand the competing reaction pathways on the anode. Using the experimental data, we also develop a Multiphysics model to evaluate the electrode kinetics and species concentration distribution near the catalyst surface to understand the implications of mass transport limitations in this electrochemical system. This comprehensive analysis could potentially provide new guidelines to design more energy-efficient anodes for upgrading sustainable alcohols.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.