Hydrogen Electrode Research Articles

Electron Deficiency is More Important than Conductivity in C-N Coupling for Electrocatalytic Urea Synthesis.

The electrocatalytic C-N coupling from CO2 and nitrate emerges as one of the solutions for waste upgrading and urea synthesis. In this work, we constructed electron-deficient Cu sites by the strong metal-polymer semiconductor interaction, to boost efficient and durable urea synthesis. In situ Raman spectroscopy identified the existence of electron-deficient Cu sites and was able to withstand electrochemical reduction conditions. Operando synchrotron-radiation Fourier transform infrared spectroscopy and theoretical calculations disclosed the vital role of electron-deficient Cu in adsorption and C-N coupling of oxygen-containing species. The electron-deficient Cu displayed a high urea yield rate of 255.0 mmol h-1 g-1 at -1.4 V versus the reversible hydrogen electrode and excellent electrochemical durability, superior than that of non-electron-deficient counterpart with conductive carbon material as the support. It can be concluded that the regulation of site electronic structure is more important than the optimization of catalyst conductive properties in the C-N coupling reactions.

Tailoring the electron redistribution of RuO2 by constructing a Ru-O-La asymmetric configuration for efficient acidic oxygen evolution

Stabilizing the highly active RuO2 electrocatalyst for the oxygen evolution reaction (OER) is critical for the application of proton exchange membrane water electrolysis, but this remains challenging due to the inevitable over-oxidation of Ru in harsh oxidative environments. Herein, we describe constructing Ru-O-La asymmetric configurations into RuO2 via a facile sol-gel method to tailor electron redistribution and thereby eliminate the over-oxidation of Ru centers. Specifically, the as-prepared optimal La0.1Ru0.9O2 shows a low overpotential of 188 mV at 10 mA cm–2, a high mass activity of 251 A at 1.6 V vs. reversible hydrogen electrode (RHE), and a long-lasting durability of 63 hours, far superior to the 8 hours achieved by standard RuO2. Experiments and density functional theory calculations jointly reveal that the Ru-O-La asymmetric configuration could trigger electron redistribution in RuO2. More importantly, electron transfer from La to Ru via the Ru-O-La configuration could lead to increased electron density around Ru, thus preventing the over-oxidation of Ru. In addition, electron redistribution tunes the Ru 4d band center’s energy level, which optimizes the adsorption and desorption of oxygen intermediates. This work offers an effective strategy for regulating electronic structure to synergistically boost the activity and stability of RuO2-based acidic OER electrocatalysts.

Preparation of Porous Ni-W Alloys Electrodeposited by Dynamic Hydrogen Bubble Template and Their Alkaline HER Properties

Nickel–tungsten (Ni-W) alloys are gaining significant attention due to their superior hardness, wear resistance, anti-corrosion and electrochemical hydrogen evolution reaction (HER) activity. In this work, porous and crack Ni-W alloys with different W contents were prepared in a pyrophosphate bath. The key to forming a porous structure is a very high current density over 300 mA cm−2. The HER activity of porous and crack Ni-W alloys was studied by means of electrochemical technologies of linear sweep voltammetry (LSV), Tafel curves (Taf) and electrochemical impedance spectroscopy (EIS). Compared with the crack Ni-W alloy, the porous Ni-W alloy exhibits improved alkaline electrochemical HER performances, which can deliver a current density of 10 mA cm−2 at 166 mV (η10) vs. RHE (reversible hydrogen electrode).

Cascade Electrocatalytic Reduction of Nitrate to Ammonia Using a Heterobimetallic Covalent Organic Framework Composed of Cu-Porphyrin and Co-Bipyridine.

The electrocatalytic reduction of nitrate (NO3-) to ammonia (NH3) not only offers an effective solution to environmental problems caused by the accumulation of NO3- but also provides a sustainable alternative to the Haber-Bosch process. However, the conversion of NO3- to NH3 is a complicated process involving multiple steps, leading to a low Faradaic efficiency (FE) for NH3 production. The structural designability of covalent organic frameworks (COFs) renders feasible and precise modulation at the molecular level, facilitating the incorporation of multiple well-defined catalytic sites with different reactivities into a cohesive entity. This promotes the efficiency of the overall reaction through the coupling of multistep reactions. Herein, heterobimetallic CuP-CoBpy was prepared by postmodification, involving the anchoring of cobalt ions to the CuP-Bpy structure. As a result of the cascade effect of the bimetallic sites, CuP-CoBpy achieved an outstanding NH3 yield of 13.9 mg h-1 mgcat.-1 with a high FE of 96.7% at -0.70 V versus the reversible hydrogen electrode and exhibited excellent stability during catalysis. A series of experimental and theoretical studies revealed that the CuP unit facilitates the conversion of NO3- to NO2-, while the CoBpy moiety significantly prompts the reduction of NO2- to NH3. This study demonstrates that tailoring the structural units for the construction of COFs based on each step in the multistep reaction can enhance both the catalytic activity and product selectivity of the overall process.

Metal–Organic Framework Supported Low‐Nuclearity Cluster Catalysts for Highly Selective Carbon Dioxide Electroreduction to Ethanol

AbstractIt is still a great challenge to achieve high selectivity of ethanol in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials and lower energy barrier of possible other C2+ products. Here, we report a MOF‐based supported low‐nuclearity cluster catalysts (LNCCs), synthesized by electrochemical reduction of three‐dimensional (3D) microporous Cu‐based MOF, that achieves a single‐product Faradaic efficiency (FE) of 82.5 % at −1.0 V (versus the reversible hydrogen electrode) corresponding to the effective current density is 8.66 mA cm−2. By investigating the relationship between the species of reduction products and the types of catalytic sites, it is confirmed that the multi‐site synergism of Cu LNCCs can increase the C−C coupling effect, and thus achieve high FE of CO2–to–ethanol. In addition, density functional theory (DFT) calculation and operando attenuated total reflectance surface‐enhanced infrared absorption spectroscopy further confirmed the reaction path and mechanism of CO2–to–EtOH.

Metal-Organic Framework Supported Low-Nuclearity Cluster Catalysts for Highly Selective Carbon Dioxide Electroreduction to Ethanol.

It is still a great challenge to achieve high selectivity of ethanol in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials and lower energy barrier of possible other C2+ products. Here, we report a MOF-based supported low-nuclearity cluster catalysts (LNCCs), synthesized by electrochemical reduction of three-dimensional (3D) microporous Cu-based MOF, that achieves a single-product Faradaic efficiency (FE) of 82.5 % at -1.0 V (versus the reversible hydrogen electrode) corresponding to the effective current density is 8.66 mA cm-2. By investigating the relationship between the species of reduction products and the types of catalytic sites, it is confirmed that the multi-site synergism of Cu LNCCs can increase the C-C coupling effect, and thus achieve high FE of CO2-to-ethanol. In addition, density functional theory (DFT) calculation and operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy further confirmed the reaction path and mechanism of CO2-to-EtOH.

Modulating Surface Oxygen Valence States via Interfacial Potential in BiVO4/CoOx/Au Photoanode for Enhanced Selective Photoelectrochemical Oxidation of Glycerol to Dihydroxyacetone

AbstractThe concept of photoelectrochemical conversion of biomass into industrially valuable chemicals presents a compelling strategy to supplant the lower‐value oxygen evolution typically associated with photoanodes. Here, a surface potential manipulation method by regulating the surface oxygen valence states is put forward, which is demonstrated to be effective in enhancing the selective photoelectrochemical oxidation of glycerol to dihydroxyacetone (DHA). This involves the concurrent establishment of a BiVO4/CoOx heterojunction and a BiVO4/Au Schottky junction, aiming to fine‐tune the BiVO4 photoanode's surface potential and improve both its charge carrier separation and interfacial transfer kinetics. The BiVO4/CoOx/Au photoanode exhibits a photocurrent density of 6.15 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE). Meanwhile, selective glycerol oxidation efficiency achieves a DHA evolution rate of 339.74 mmol m−2 h−1 and a selectivity exceeding 60%. Experiments and theoretical analysis underscore the pivotal role played by the surface potential in mediating glycerol and DHA adsorption and desorption processes. Additionally, the diminished surface potential attributed to the CoOx and Au amendments is responsible for the decreased Gibbs free energy of the dehydrogenation's rate‐limiting step involving the intermediate carbon species. This work demonstrates a method to design glycerol oxidation catalysts by modulating the interfacial molecular adsorption/desorption by surface potential regulation.

Hydrogen Peroxide Spillover on Platinum-Iron Hybrid Electrocatalyst for Stable Oxygen Reduction.

Iron-nitrogen-carbon (Fe-N-C) catalysts, although the most active platinum-free option for the cathodic oxygen reduction reaction (ORR), suffer from poor durability due to the Fe leaching and consequent Fenton effect, limiting their practical application in low-temperature fuel cells. This work demonstrates an integrated catalyst of a platinum-iron (PtFe) alloy planted in an Fe-N-C matrix (PtFe/Fe-N-C) to address this challenge. This novel catalyst exhibits both high-efficiency activity and stability, as evidenced by its impressive half-wave potential (E1/2) of 0.93 V versus reversible hydrogen electrode (vs RHE) and minimal 7 mV decay even after 50,000 potential cycles. Remarkably, it exhibits a very low hydrogen peroxide (H2O2) yield (0.07%) at 0.6 V and maintains this performance with negligible change after 10,000 potential cycles. Fuel cells assembled with this cathode PtFe/Fe-N-C catalyst show exceptional durability, with only 8 mV voltage loss at 0.8 A cm-2 after 30,000 cycles and ignorable current degradation at a voltage of 0.6 V over 85 h. Comprehensive in situ experiments and theoretical calculations reveal that oxygen species spillover from Fe-N-C to PtFe alloy not only inhibits H2O2 production but also eliminates harmful oxygenated radicals. This work paves the way for the design of highly efficient and stable ORR catalysts and has significant implications for the development of next-generation fuel cells.

One-pot hydrothermal synthesis of transition metal sulfides-decorated CuS microflower-like structures for electrochemical CO2 reduction to CO

Electrochemical CO2 reduction (ECR) to value-added products is regarded as a sustainable strategy to mitigate global warming and energy crisis, and designing highly efficient and robust catalysts is essential. In this work, transition metal sulfides (TMS)-decorated CuS microflower-like structures were prepared via the one-pot hydrothermal synthesis method for ECR to CO, and the influence of TMS doping on ECR performance was demonstrated. Characterization of the catalysts was performed using XRD, FESEM-EDS, N2 physisorption, and XPS, revealing the successful loading of TMS, the formation of microflower-like architectures and the generation of sulfur vacancies. Electrochemical tests demonstrated that doping ZnS, Bi2S3, CdS and MoS2 improved the intrinsic CO2 reduction activity of the CuS catalyst. Particularly, the MoS2-CuS composite catalyst with imperfect petal-like structure showed uniform distribution of edge Mo sites, which worked synergistically with the formed grain boundaries (GBs) and undercoordinated S vacancy sites in promoting CO2 activation, stabilizing *COOH adsorption, facilitating *CO desorption, and lowering the energy barrier of the potential-limiting step for improved CO selectivity. The MoS2-CuS catalyst achieved a maximum CO selectivity of 83.2% at –0.6 V versus the reversible hydrogen electrode (RHE) and a high CO cathodic energetic efficiency of 100%. At this potential, the catalyst maintained stable catalytic activity and CO selectivity during a 333-min electrolysis process. The findings will offer a promising avenue for the development of efficient and stable catalysts for CO production from ECR.

Green light all the way: Triple modification synergistic modification effect to enhance the photoelectrochemical water oxidation performance of BiVO4 photoanode

The recombination of photogenerated electron-hole pairs of the photoanode seriously impairs the application of bismuth vanadate (BiVO4) in photoelectrochemical water splitting. To address this issue, we prepared a Yb:BiVO4/Co3O4/FeOOH composite photoanode by employing drop-casting and soaking methods to attach Co3O4/FeOOH cocatalysts to the surface of ytterbium-doped BiVO4. The prepared Yb:BiVO4/Co3O4/FeOOH photoanode demonstrates a high photocurrent density of 4.89 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE), which is 5.1 times that of bare BiVO4 (0.95 mA cm−2). Detailed characterization and testing demonstrated that Yb doping narrows the band gap and significantly enhances the carrier density. Furthermore, Co3O4 serves as a hole transfer layer to expedite hole migration and diminish recombination, while FeOOH offers additional active sites and minimizes surface trap states, thus boosting stability. The synergistic effects of Yb doping and Co3O4/FeOOH cocatalyst significantly improved the reaction kinetics and overall performance of PEC water oxidation. This work provides a strategy for designing efficient photoanodes for PEC water oxidation.

MOF˗derived sulfur˗doped iron˗nickel bimetallic phosphide nanowires: A bifunctional electrode for hydrogen and oxygen evolution reactions

Creating affordable and efficient bifunctional electrocatalysts is crucial for producing clean hydrogen energy through complete water splitting. We describe a way to make S-doped carbon-encapsulated iron-nickel phosphide nanowires (S/FeNiP@C) using metal-organic frameworks. These nanowires exhibit exceptional electrocatalytic performance for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions. The optimized S/FeNiP@C nanowires exhibit low overpotentials of 53 mV and 270 mV at a current density of 10 mA cm˗2 for HER and OER, respectively. They also have tiny Tafel slopes of 159 mV dec˗1 for HER and 50 mV dec˗1 for OER. The water electrolyzer uses S/FeNiP@C nanowires as both the anode and the cathode to reach a current density of 10 mA cm˗2 at a voltage of 1.61 V and stays very stable for 48 h. The great catalytic performance is mostly due to the simple carbon framework and low sulfur integration. This creates a large surface area for the catalyst and electrolyte to interact, allowing charge and mass to move quickly, and a lot of active sites that last a long time.

Single atom catalyst induced by redox reaction between iron ion and aniline monomer

The effective design of a low-cost, efficient, and stable non-noble metal electrocatalyst to substitute the noble metal electrocatalyst for oxygen reduction reaction is highly significant. Even though atomically dispersed metal catalyst shows excellent catalytic activity with maximized atom efficiency, the challenge often lies in achieving uniform distribution for single-atom catalysts owing to their tendency to aggregate. In this work, we present a sequential method that involves the reduction of iron (Fe) mediated by aniline (anchored on support), followed by pyrolysis to fabricate the Fe-Nx moieties and achieve the high density of single atom active sites. The resulting Fe SA 900 catalyst exhibited a half-wave potential of 0.84 V vs. reversible hydrogen electrode (RHE) for oxygen reduction reaction and outstanding stability in alkaline condition. Using various analysis techniques and electrochemical analysis, we demonstrated that the electrocatalytic activity of the catalyst arises from Fe single atom. To validate the practical applicability of Fe-N-C catalysts, we conducted an anion exchange membrane fuel cell (AEMFC) test, which demonstrated a high performance of 212 mW cm−2 at maximum power density. This study proves that the effectiveness of a sequential strategy adopting redox reaction and following pyrolysis for precise synthesis of a single atom Fe catalyst.

Hexavalent iridium boosts oxygen evolution performance

Proton exchange membrane water electrolysis (PEMWE) involves the oxygen evolution reaction (OER) at the anode to produce O2 and the hydrogen evolution reaction (HER) at the cathode to produce H2. Although hydrogen is the desired product of PEMWE, the main challenge lies on the anode side, as the OER is kinetically more sluggish and thus requires a more efficient catalyst and higher overpotential (>1.3V vs. reversible hydrogen electrode, RHE) than the HER (>0V vs. RHE). Recently, Nakamura et al. developed a new atomically dispersed hexavalent iridium oxide catalyst (IrVI-ado) with a much lower Ir loading and higher specific activity than traditional IrO2. This breakthrough offers hope for advancing PEMWE technology.

Zn-Cu bimetallic gas diffusion electrodes for electrochemical reduction of CO2 to ethylene

The application of renewable energy to drive the electroreduction of carbon dioxide (CO2) into valuable compounds serves as a means of energy storage and simultaneously aids in the mitigation of climate change. In this study, a bimetallic catalyst consisting of Zinc and Copper is synthesized using the Zinc-doped HKUST-1 metal-organic framework. The catalyst is then fabricated on gas diffusional electrode and investigated in both H-Cell and Flow cell configurations for electrochemical CO2 reduction reaction (ECO2RR). In the H-Cell, the catalysts that have been developed exhibit an ethylene faradaic efficiency (FE) up to 40 % when operated at a potential of −0.8 V relative to the reversible hydrogen electrode (RHE). The Zn-Cu bimetallic gas diffusion electrodes (GDE) exhibit an impressive ethylene FE up to 45 % when operating at a current density of −200 mA cm−2 at −1.0 V versus RHE in the flow cell. This research offers valuable insights into the strategic development of copper-based bimetallic catalysts with the aim of enhancing the efficiency of electrochemical reduction of CO2 to yield multicarbon compounds.

Low-temperature fabrication of morphology-controllable Cu2O for electrochemical CO2 reduction

Cu2O has been successfully synthesized in different morphologies/sizes (nanoparticles and octahedrons) via a low-temperature chemical reduction method. Trapping metal ions in an ice cube and letting them slowly melt in a reducing agent solution is the simplest way to control the nanostructure. Enhancement of charge transfer and transportation of ions by Cu2O nanoparticles was shown by cyclic voltammetry and electrochemical impedance spectroscopy measurements. In addition, nanoparticles exhibited higher current densities, the lowest onset potential, and the Tafel slope than others. The Cu2O electrocatalyst (nanoparticles) demonstrated the Faraday efficiencies (FEs) of CO, CH4, and C2H6 up to 11.90, 76.61, and 1.87%, respectively, at −0.30 V versus reference hydrogen electrode, which was relatively higher FEs than other morphologies/sizes. It is mainly attributed to nano-sized, more active sites and oxygen vacancy. In addition, it demonstrated stability over 11 h without any decay of current density. The mechanism related to morphology tuning and electrochemical CO2 reduction reaction was explained. This work provides a possible way to fabricate the different morphologies/sizes of Cu2O at low-temperature chemical reduction methods for obtaining the CO, CH4, and C2H6 products from CO2

Boron-Doped Ti3C2Tx MXene for Effective and Durable High-Current-Density Ammonia Synthesis.

Ammonia (NH3) synthesis via the nitrate reduction reaction (NO3RR) offers a competitive strategy for nitrogen cycling and carbon neutrality; however, this is hindered by the poor NO3RR performance under high current density. Herein, it is shown that boron-doped Ti3C2Tx MXene nanosheets can highly efficiently catalyze the conversion of NO3RR-to-NH3 at ambient conditions, showing a maximal NH3 Faradic efficiency of 91% with a peak yield rate of 26.2mgh-1mgcat. -1, and robust durability over ten consecutive cycles, all of them are comparable to the best-reported results and exceed those of pristine Ti3C2Tx MXene. More importantly, when tested in a flow cell, the designed catalyst delivers a current density of ‒1000mAcm-2 at a low potential of ‒1.18V versus the reversible hydrogen electrode and maintains a high NH3 selectivity over a wide current density range. Besides, a Zn-nitrate battery with the catalyst as the cathode is assembled, which achieves a power density of 5.24mWcm-2 and a yield rate of 1.15mgh-1mgcat. -1. Theoretical simulations further demonstrate that the boron dopants can optimize the adsorption and activation of NO3RR intermediates, and reduce the potential-determining step barrier, thus leading to an enhanced NH3 selectivity.

Studying impact of cobalt content on electrocatalytic activity of Cu-Co-P coating with dendrite-like architectures for hydrogen production

The aim of this study was to enhance the electrocatalytic performance of the electrodeposited Cu-Co-P coating by adjusting the Co content. SEM images revealed that the presence of Co contributed to the formation of a nano/micro dendritic morphology. The electrocatalyst performance improved as the Co content increased. Specifically, the Cu-Co-P/60@NF electrode only required an overpotential of 102 mV (versus reversible hydrogen electrode (RHE)) at a current density of −10 mA/cm2. This electrode exhibited the lowest charge transfer resistance, promoting faster charge transfer at the electrocatalyst/electrolyte interface. The increase in electroactivity for the hydrogen evolution reaction (HER) with a higher Co content can be attributed to two factors: the construction of the porous nano/micro dendritic structure and the synergistic effect between P, Cu, and Co elements, which is influenced by their amounts in the coating. Moreover, this electrode demonstrated satisfactory stability for 14 hours of electrolysis at −100 mA/cm2. In a two-electrode system, it only required a cell voltage of 1.57 V to achieve a current density of 10 mA/cm2. As a result, the Cu-Co-P/60@NF electrode could hold promise as a cost-effective alternative to noble metal-based electrocatalysts.

Bismuth Iron Oxide Catalysts for Efficient CO2 Electroreduction to Formate.

Renewable energy-driven electrocatalytic CO2 reduction reaction (CO2RR) over bismuth-based catalysts shows great promise for converting CO2 into formic acid and formate while closing the carbon cycle. Herein, we report a high-performance BiFeO3/Bi25FeO40 precatalyst, which delivers a formate partial current density of 359.8 mA cm-2 and a formate formation rate of 6.71 mmol h-1 cm-2 in a flow cell at -0.75 V versus reversible hydrogen electrode (vs RHE). Furthermore, it shows stable formate production for 88 h at -0.64 V vs RHE with a total current density of 160 mA cm-2. The impressive electrocatalytic performance toward CO2RR to formate is likely ascribed to the synergistic effect of single Bi atoms and bimetallic BiFe nanoparticles present in close proximity after in situ electrochemical reconstruction of the BiFeO3/Bi25FeO40 precatalyst. This work presents new insights into the development of highly efficient Bi-based catalysts for the CO2RR.

A Solid Electrolyte RHE for Electrode Diagnosis of Proton Exchange Membrane Water Electrolyzers.

Reference electrode is the foundation of electrochemical study; thus, most electrode materials are tested in a three-electrode mode to acquire potential-dependent kinetics. However, it is difficult to directly use conventional reference electrodes to detect potential information in solid electrolyte devices due to their compact assembly structure. Therefore, the kinetic study of an electrochemical device faces challenges in precise identification of specific problems originating from the anode or cathode. Here, focusing on proton exchange membrane water electrolysis, we design a solid electrolyte reversible hydrogen electrode (SE-RHE), which can be used for electrode diagnosis under various operating conditions. Compared to the reference electrodes reported in the literature, which are mainly based on liquid electrolyte, the SE-RHE is highly sensitive and compatible, as well as easy to assemble. The potential deviation is less than ±0.5 mV, and the cell voltage derived from the electrode potential well reproduces the value that was directly measured with a deviation less than 0.2%. The reference electrode developed in this work enables the kinetic study of a specific electrode rather than the entire cell. For instance, an interesting observation is that the cathode shows distinct stability under stable and fluctuating operations. Differing from the high stability under stable operation, the cathode degrades significantly under fluctuating operations.

High-efficiency electrochemical nitrate reduction to ammonia via boron-doped hydroxyl oxide cobalt induced electron delocalization

Electrochemical nitrate reduction to ammonia is a promising alternative strategy for producing valuable ammonia. This prospective route, however, is subject to a slow electrocatalytic rate, which resulted from the weak adsorption and activation of intermediate species, and the low density electron cloud of active centers. To address this issue, we developed a novel approach by doping boron into metal hydroxyl oxides to adjust the electronic structure of active centers, and consequently, led a significant improvement in the Faraday efficiency upto approaching 100 %, as well as an impressive ammonia yield upto approximately 23 mg/h mgcat−1 at −0.6 V vs. reversible hydrogen electrode (RHE). Experimental data in mechanism demonstrate that the doped boron play a crucial role in modulating the local electronic environment surrounding the active sites Co. In situ Raman and FTIR spectra provide evidences that boron facilitates the formation of deoxidation and hydrogenation intermediates. Additionally, density functional theory (DFT) calculations support the notion that boron doping enhances the adsorption capability of intermediates, reduces the reaction barrier, and facilitates the desorption of NH3.