Electrochemical Hydrogen Evolution Research Articles

Novel sensing signal mode constructed by dual responsive silence layer combined with catalytic hydrogen evolution

For electrochemical assays, to obtain sensing signals, the redox of the modified electrochemical signal substance to provide a detectable signal is commonly required. However, during the process of assembly and sensing, the loss of signal substance caused by multiple steps of modification, incubation, and washing would lead to non-negligible fluctuation of signal and lack of reproducibility. To overcome this issue, a novel sensing signal mode without electrochemical signal substance was developed. By introducing electrochemical catalytic hydrogen evolution into the sensing scheme, and taking the overpotential as the detectable signal, the sensing system was constructed in the absence of electrochemical signal substance. As a proof of concept, the sensor was used to quantify squamous cell carcinoma antigen, a model analyte, and exhibited an excellent analytical performance with a wide linear range from 0.100 ng mL−1 to 100 ng mL−1 and a low detection limit of 52.4 fg mL−1. As envisioned, the sensor exhibited excellent long-term stability and reproducibility due to the avoidance of signal substance. This method provided a new way for the design of electrochemical sensors.

Corrolato(oxo)antimony(V) Dimer with Hydrogen-Bond Donor Groups in Secondary Coordination Sphere as a Catalyst for Hydrogen Evolution Reaction.

The focus is on developing alternative molecular catalysts using main-group elements and implementing strategic improvements for sustainable hydrogen production. For this purpose, a FB corrole with a (2-(2-((4-methylphenyl)sulfonamido)ethoxy)phenyl) group inserted into the meso position (C-10) of the corrole, along with its high-valent (corrolato)(oxo)antimony(V) dimer, was synthesized. In the crystal structure analysis of the FB corrole and the (corrolato)(oxo)antimony(V) dimer complex, it was noted that the sulfonamido group in the ligand periphery sits atop the corrole ring. The electrochemical hydrogen evolution reaction (HER) of the (corrolato)(oxo)antimony(V) dimer was studied and compared with a previously reported (corrolato)(oxo)antimony(V) complex, which lacks hydrogen-bond donor groups in the secondary coordination sphere. The newly designed molecules, featuring hydrogen-bond donor groups in the secondary coordination sphere, demonstrated clear superiority in the electrochemical HER. Controlled potential electrolysis was employed to evaluate the charge accumulation associated with hydrogen generation in a homogeneous three-electrode system in the presence of 50 mM TFA. The produced hydrogen exhibits a Faradaic efficiency of approximately 80.96%, a turnover frequency (TOF) of 0.44 h-1, and a production rate of 52.83 μL h-1, highlighting the effective catalytic activity of the (corrolato)(oxo)antimony(V) dimer in hydrogen evolution.

Tobacco stem-derived porous carbon-supported Ru catalysts for efficient electrochemical hydrogen evolution

Tobacco stem-derived porous carbon-supported Ru catalysts for efficient electrochemical hydrogen evolution

The Key Role of Proton‐Responsive Groups in Electrochemical Hydrogen Evolution Reaction

AbstractThe much‐needed global shift from fossil fuels to sustainable energy is driving significant attention towards hydrogen (H2) as a promising alternative. Proton reduction, a process central to H2 production, is a key area of research for this transition. Naturally‐occurring [FeFe] and [NiFe]‐hydrogenase enzymes play vital roles in the reversible production and oxidation of H2. These enzymes feature a proton‐relay unit comprising of pendant amine and thiol groups in the secondary coordination sphere at the active site. This unit accelerates the rate of H2 production/oxidation, making it a focal point for scientific exploration. Efforts are concentrated on mimicking the active sites of these enzymes both structurally and functionally. In this pursuit, many synthetic transition metal complexes with proton‐responsive units at the secondary coordination sphere of the active site mimic the enzyme's behavior. These units facilitate intramolecular metal‐hydride (M−H) generation and H2‐elimination via H+/H−s coupling, leveraging the proton from the pendant functional group and the hydride from the M−H intermediate. This review delves into electrocatalysts featuring pendant proton‐responsive units and their roles in the electrochemical hydrogen evolution reaction (eHER).

Hydrogen evolution reaction catalyzed by Co-based metal-organic frameworks and their derivatives

In this study, Co-bearing Metal-Organic Frameworks (MOFs) are grown via a facile solvothermal process on the surface of two kinds of conductive substrates – titanium dioxide nanotubes (TiO2NT) and fluorine-doped tin oxide (FTO) glass and tested as electrodes in the electrochemical hydrogen evolution reaction (HER). The materials derived from three organic linkers - terephthalic acid (Co-BDC), 2-aminoterephthalic acid (Co-BDCNH2), and trimesic acid (Co-BTC) are characterized by FTIR, Raman, XRD, SEM-EDS, BET, and XPS. Among the layers on FTO without post-synthesis treatment, Co-BTC shows the highest activity (overpotential of HER 1.72 V vs. Ag/AgCl/KCl). The effects of substrate change on TiO2NT and annealing of Co-BTC layers in air and argon on their electrocatalytic properties are also studied. Using TiO2 nanotubes as a substrate and annealing the material in air results in a reduction of the hydrogen evolution overpotential to 1.44 V vs. Ag/AgCl/KCl and a significant reduction in the exchange current density.

Cross‐Scale Process Intensification of Spindle CuO Supported Tungsten Single‐Atom Catalysts toward Enhanced Electrochemical Hydrogen Production

AbstractProcess intensification engineering of electrocatalysts is crucial to facilitate electrocatalytic reaction, while its cross‐scale modulation is of great challenge. Herein, the spindle CuO supported tungsten single‐atom catalysts (W SACs) with tunable mesoscale electric field and atomic‐scale coordination structure are reported toward enhanced electrochemical hydrogen evolution process. Finite element analysis indicates the mesoscale electric field can be enhanced by tailoring the tip angle of spindle configuration from 74° to 27°, enhancing hydrogen production rate by 5 times. Based on the density functional theory calculations, the configuration regulation also triggers the increase of coordination number of W–O, which increases charge transfer and downshifts d‐band center, stabilizing W sites and optimizing hydrogen desorption process. The optimized WSA/CuO‐27 exhibits much better hydrogen evolution activity (η100 = 94 mV) and stability (200 mA cm−2 for 120 h) than as‐prepared WSA/CuO‐56 and WSA/CuO‐74 analogues. Impressively, the anion exchange membrane electrolyzer fabricated with the WSA/CuO‐27 presents excellent activity comparable to that of commercial electrocatalysts, and also delivers an ultra‐low attenuation of 0.085 mA cm−2 h−1 at 300 mA cm−2 after continuous electrocatalysis for 120 h. This work inspires the design of high‐efficiency supported metal catalysts for electrochemical synthesis via the cross‐scale process intensification engineering.

Tailoring Electrocatalytic Hydrogen Evolution Activity in Topological Triangular Metal–Organic Frameworks

AbstractMetal–organic frameworks (MOFs) have attracted considerable attention in catalysis due to their exceptional structural and chemical tunability. However, high electrical conductivity is rare in MOFs, hindering their practical applications toward catalytic reactions. Recently, 2D topological MOFs stand out for the unique topologically nontrivial electronic structures. Particularly, their high electrical conductivity and chemical tunability make them promising candidates as high‐performance catalysts. In this study, theoretical investigations are conducted into the intrinsic electronic properties and chemical activity of a 2D topological Cu‐1,3,5‐tris(pyridyl)benzene (Cu‐TPyB) framework. It is found that the coordination environment of Cu with pyridyl groups plays a crucial role in modulating the electron density around the Fermi level, thereby enhancing the catalytic activity of Cu‐TPyB toward electrochemical hydrogen evolution reaction (HER). Furthermore, substituting the single embedded Cu atom with Cu3 and Cu4Bi3 clusters further increases the electron density around the Fermi level. Specifically, the Cu4Bi3‐TPyB framework exhibits superior HER activity, which is attributed to its high electron density contributed by the p orbitals of Bi and the d orbitals of Cu. This work introduces a novel approach for optimizing the catalytic activity of 2D MOFs and developing high‐performance catalysts.

Design of NiPS3/MoS2/rGO hybrid electrocatalyst for electrochemical hydrogen evolution

The design and development of efficient electrocatalysts for hydrogen evolution reaction is presently a pressing task to overcome future energy demands. In the present study a hybrid layered compound NiPS3/MoS2/rGO (NMR) is investigated as an electrocatalyst for hydrogen evolution reaction (HER). The metal trichalcogenidophosphates (MTPs), transition metal dichalcogenides and reduced graphene oxide materials based electrocatalysts are promising material for HER. The hybrid layered compound NMR displays good electrocatalytic activity in acidic medium in comparison to its counterparts MoS2/rGO and NiPS3/rGO with an overpotential and Tafel slope of 152 mV vs RHE and 75 mV/dec, whereas MoS2/rGO and NiPS3/rGO shows an overpotential of 206 mV and 223 mV vs RHE with a Tafel slope value of 146 mV/dec and 154 mV/dec respectively. The hybrid electrocatalyst exhibited high stability up to 1000 cycles with a stable current. The high HER activity of NMR is attributed to synergistic effect of electrocatalysts where P and S of NiPS3 acts as an appropriate hydrogen adsorption sites and catalytically active Mo edge sites of MoS2 with high charge carrier property of rGO contributed to enhanced hydrogen evolution reaction.

Transition-metal atoms embedded MoTe2 single-atom catalyst for efficient electrocatalytic hydrogen evolution reaction

As an attractive catalyst for the electrochemical hydrogen evolution reaction(HER), MoTe2 has attracted great interest. However, scarce catalytic sites and unsatisfactory catalytic activity of pristine MoTe2 basal plane impeded its practical application. The incorporation of single metal atom into 2D-substrate have been demonstrated as an effective strategy to tune HER activity of materials. Herein, we systematically investigated a series of transition-metal atoms(Fe, Co, Ni, Cu, Ru, Rh, Pd and Ag) embedded MoTe2 plane and edge single-atom catalysts(SAC, TM-MoTe2) for HER performance by employing density functional theory calculations. All TM-MoTe2 catalysts exhibit good thermodynamically and electrochemical stability. Compared with pristine MoTe2, HER catalytic activity of TM-MoTe2 are significantly enhanced due to effective modulation of charge transfer on embedded metal, which attribute to synergy interaction between embedded TM and surrounding Mo atoms. Specially, 2 candidate catalysts with Ru-MoTe2 plane and Fe-MoTe2 edge are found to show higher HER catalytic performance with low overpotential of only 10 mV and 60 mV, respectively. Furthermore, we found a key descriptor Δdd′ to well predict HER-activity trend of MoTe2-based material, which is closely correlated with H adsorption energy(ΔEH). This work provides in-depth theoretical insights for understanding active sites and designing high-efficiency MoTe2-based HER catalysts.

Accelerated Electrons Transfer and Synergistic Interplay of Co and Ge Atoms (111 Crystal Plane) Activated by Anchoring Nano Spinel Structure Co2GeO4 onto Carbon Cloth Composite Electrocatalyst for Highly Enhanced Hydrogen Evolution Reaction

The electrochemical hydrogen evolution reaction (HER) was considered to be a promising strategy for future clean energy. In this work, a composite electrocatalyst (designated as CGO36@CC) was synthesized through anchoring of nano spinel structure Co2GeO4 onto carbon cloth fibers and exhibited outstanding electrocatalytic performance for HERs in an alkaline medium. The characterization outcome established that, after 36 h of hydrothermal reaction, nano spinel structure Co2GeO4 particles (exposed abundant 111 crystal planes) were stably loaded onto a carbon cloth fiber surface, and this structural configuration facilitated the electrons transferring between each other. In addition, the electrochemical analysis revealed that the incorporation of nano spinel structure Co2GeO4 and carbon cloth significantly augmented the electrochemical activity value of the composite and efficiently enhanced the HER performance. Notably, the overpotential was merely 96 mV at 10 mA·cm−2 current density, and the Tafel slope was only 48.9 mV·dec−1. Moreover, CGO36@CC displayed remarkable catalytic activity and sustained HER catalytic stability. The theoretical catalytic prowess of CGO36@CC stemmed from the collaborative influence of germanium and cobalt atoms within the exposed 111 crystal plane of the Co2GeO4 molecular framework. The amalgamation of Co2GeO4 with carbon cloth fiber conferred upon the composite electrocatalyst both superior theoretical catalytic activity and enhanced electron transfer capability. This work provides a novel strategy for exploring a highly efficient composite electrocatalyst combined transition metal with carbon material to accelerate the HER activity.

Deliberate Amorphization of Co-MOF for Constructing Crystalline-Amorphous Heterostructures Toward High-Performance Water Electrolysis.

The endowment of metal organic frameworks (MOF) with superior electrocatalytic performance without compromising their structural/compositional superiorities is of great significance for the development of renewable energy devices, yet remains a grand challenge. Herein, a deliberate partial amorphization strategy is developed to construct a heterostructured electrocatalyst consisting of crystalline Co-MOF and amorphous Co-S nanoflake arrays aligned on the carbon cloth (CC) substrate (abbreviated as Co-MOF/Co-S@CC hereafter) through a rapid sulfuration method. The simultaneous implement of crystalline-amorphous (c-a) heterostructure and nanoflake arrayed architecture on CC substrate renders the Co-MOF/Co-S@CC with abundant and tight active sites, accelerated charge transfer rate, regulated electronic structures, and reinforced structural stability. As such, the obtained Co-MOF/Co-S@CC electrode demonstrates outstanding electrochemical hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances with the overpotentials of 64 and 217mV at 10mA cm-2, respectively. Moreover, a two-electrode electrolyzer assembled by Co-MOF/Co-S@CC electrodes exhibits the lower cell voltages and larger current densities than those of Pt/C and RuO2 counterparts, excellent reversibility and prominent long-term stability, representing a great prospect for feasible H2 production. This adopted concept of c-a heterostructure for electronic regulation may bring about insightful inspiration for designing high-performance electrocatalysts for sustainable energy systems.

Organocatalytic Hydrogen Evolution Reaction by Diazaphospholenes.

The electrochemical hydrogen evolution reaction (HER) is currently recognized as a prospective way to obtain clean energy. The electrocatalysts used currently are dominantly based on transition metals. In this work, we have demonstrated a diazaphospholene (N-heterocyclic phosphine (NHP))-type small molecular organocatalyst that can catalyze the HER with a maximum current density of 130 mA·cm-2, an overpotential of 354 mV, and a faradaic efficiency of 90%. Mechanistic studies verify a Heyrovsky-type process with NHP, whereas its hydricity and aromaticity favor hydrogen release and catalyst regeneration.

Facile hydrothermal synthesis of Sb2S3 thin-film photo-cathodes for green hydrogen energy production

Semiconducting characteristics of antimony-based chalcogenides in the recent past gained the utmost attention for photovoltaic (PV) cells and photo electrochemical (PEC) hydrogen evolution. In the current research endeavour, a simple hydrothermal route has been employed to prepare polycrystalline Sb2S3 thin films. Under ideal temperature conditions of 120 °C, Sb2S3 films were prepared in an autoclave, varying the reaction times between 10:00 and 14:30 h with an interval of 30 min. Further heat treatment of the as-synthesized Sb2S3 thin films was carried out on an electric hot plate at 200 °C for 90 min. XRD analysis of heat-treated Sb2S3 films unveiled an orthorhombic crystal structure with (310) predominant plane. Consequently, the crystallite sizes, displayed improvement from ∼ 33 to 77 nm, with reaction periods for 10:00 to 13:30 h and decreased after that. The five distinct Raman modes were spotted at 155, 190, 236, 280, and 305 cm−1, further confirming the single-phase formation of Sb2S3 thin films. SEM and EDS analysis indicated conspicuous variations in surface morphology and stoichiometric ratios of antimony and sulfur elements. The Sb2S3 thin films deposited at 120 °C for 13:30 h are found to be nearly stoichiometric (Sb and S are 42.61 and 57.39 at. %). The resultant oxidation states were demonstrated to be (+3) and (−2) for antimony and sulfur respectively. All the thin films exhibited an optical absorption coefficient greater than 104 cm−1 with a direct energy band gap ranging between 1.43 and 1.61 eV. The Sb2S3 thin films deposited for 13:30 h have unveiled the highest photocurrent density of −0.27 mA/cm2, indicating a potential photocathode for hydrogen production.

Nitrogen-doping engineering in two-dimensional transition-metal carbides for electrochemical hydrogen evolution

Developing electrocatalysts with the trade-off between overall electrocatalytic performance and economic cost towards hydrogen evolution reaction (HER) is crucial for producing green hydrogen fuels. Although theoretical studies have reported the potential of two-dimensional (2D) MXenes for the HER, their electrocatalytic performance is still unsatisfactory for the particular application due to their low intrinsic active and MXene stacking. To address this problem, we herein modify the electronic structure and increase the interlayer spacing between 2D Ti3C2Tx MXenes through ammonia (NH3)-assisted hydrothermal approach. The effect of synthesis temperature on the nitrogen doping mechanism and electrochemical behaviors for the HER is systemically explored. As a result, the nitrogen (N)-doped Ti3C2Tx MXene fabricated at 160 °C exhibits the highest HER activity among all 2D N-doped Ti3C2Tx nanosheets with the overpotential/Tafel slope of 186.91 mVRHE/115.94 mVRHE dec−1 in an acidic solution. Due to the synergistic contribution of nitrogen, the N-doped Ti3C2Tx-160 °C has mass activity of 337.95 mA mg−1 at 0.3 VRHE, being 27.50-fold higher than that of pristine Ti3C2Tx. This work indicated that heteroatom doping is a facile but efficient approach for modulating the electronic structure and intrinsic activity of MXene-based materials for electrochemical reactions.

Pt nanoparticles loaded on three-dimensional porous carbon as electrocatalysts for hydrogen evolution reaction

The electrochemical catalytic hydrogen evolution reaction (HER) holds significant potential for the sustainable production of environmentally friendly hydrogen energy. Currently, the precious metal Pt is widely acknowledged as the most superior electrocatalyst. However, its limited availability and exorbitant cost impede its extensive application. In this study, low Pt-loaded three-dimensional (3D) porous carbon composites were successfully synthesized as catalysts using a template-free method and a high-temperature pyrolysis method. By evaluating the HER performance of different Pt concentrations of the catalysts Pt/C-X (X=0, 0.05, 0.1, 0.2, 0.4, 0.7 mmol) in acid solution, it was observed that the overpotential of Pt/C-0.2 reached as low as 17 mV with a significantly low Tafel slope value of 48 mV cm−2. Meanwhile, the Bilayer capacitance (Cdl) reached an impressively high value of 247.5 mF cm−2. Consequently, this also provides a promising way to enhance the catalytic performance of the loaded catalysts.

Ambipolar Nature Accelerates Dual‐Functionality on Ni/Ni3N@NC for Simultaneous Hydrogen and Oxygen Evolution in Electrochemical Water Splitting System

AbstractMetal nitrides with extraordinary electrochemical characteristics established widespread applications in energy devices. Inspired by the recent research on promising heterostructured catalysts, the preparation of a nitride‐based heterostructure via a facile approach involving a one‐step nitridation process is revisited. An innovative Ni/Ni3N is decorated on nitrogen‐doped carbon (NC) and evaluated for its dual‐functionality as a catalyst in the electrochemical hydrogen evolution reaction (EHER) and the electrochemical oxygen evolution reaction (EOER). In contrast to Ni@NC and pristine NC, Ni/Ni3N@NC with the well‐constructed NC significantly enhanced its catalytic performance toward EHER and EOER in a water electrolyzer. The water electrolyzer consists of Ni/Ni3N@NC as both the anode and cathode achieve a current density of 10 mA cm−2 with a remarkably low voltage of 1.52 V. The designed catalyst takes full advantage of its heterostructure and ambipolar behavior leading to the presence of active sites for EOER and EHER, as confirmed by in‐situ Raman analysis. These results provide important guidance on designing an efficient and cost‐effective heterostructured dual‐functional catalyst as well as revealing the mechanism at the interface between the surface of an ambipolar catalyst and electrolyte.

Perspective—Concerning a New Mechanistic Model Toward the Catalytic Ammonia Synthesis

A reasonable catalytic mechanistic model should refer to a widely range of catalytic reaction. We believe that all types of catalytic reaction on heterogeneous catalysis should follow a general mechanism, and it is our opinion that with the hall-filled valence orbitals, the atom of catalysts could convert the reactant into reactive radical and/or support the formation of new chemical bond between two reactants via radical dimerization. In our recent publications this new mechanistic model on the catalytic Fischer-Tropsch reaction (the conversion of CO and H<sub>2</sub> to hydrocarbons), electrochemical hydrogen evolution reactions, and hydrogen combustion in various metal catalysts is discussed, and which seems to provide a reasonable interpretation to those catalytic reactions. In the present work it is discussed that this new mechanistic model is suitable to the Haber-Bosch process (catalytic ammonia synthesis) on various transition metal catalysts, and a reasonable explanation is provided on the catalytic property of various transition metal for ammonia synthesis.

An Efficient and Stable MXene-Immobilized, Cobalt-Based Catalyst for Hydrogen Evolution Reaction

Hydrogen (H2) is considered to be the best carbon-free energy carrier that can replace fossil fuels because of its high energy density and the advantages of not producing greenhouse gases and air pollutants. As a green and sustainable method for hydrogen production, the electrochemical hydrogen evolution reaction (HER) has received widespread attention. Currently, it is a great challenge to prepare economically stable electrocatalysts for the HER using non-precious metals. In this study, a Co/Co3O4/Ti3C2Tx catalyst was synthesized by supporting Co/Co3O4 with Ti3C2Tx. The results show that Co/Co3O4/Ti3C2Tx has excellent HER activity and durability in 1 mol L−1 KOH, and the overpotential and Tafel slope at 10 mA·cm−2 were 87 mV and 61.90 mV dec−1, respectively. The excellent HER activity and stability of Co/Co3O4/Ti3C2Tx can be explained as follows: Ti3C2Tx provides a stable skeleton and a large number of attachment sites for Co/Co3O4, thus exposing more active sites; the unique two-dimensional structure of Ti3C2Tx provides an efficient conductive network for rapid electron transfer between the electrolyte and the catalyst during electrocatalysis; Co3O4 makes the Co/Co3O4/Ti3C2Tx catalyst more hydrophilic, which can accelerate the release rate of bubbles; Co/Co3O4 can accelerate the adsorption and deionization of H2O to synthesize H2. This study provides a new approach for the design and preparation of low-cost and high-performance HER catalysts.

Electrodeposition strategies for synthetic highly dispersed Ru-decorated Co(OH)2 nanoneedles as advanced hydrogen evolution reaction catalysts

Ru-based nanomaterials have a lot of potential as electrochemical hydrogen evolution reaction (HER) catalysts; however, achieving a uniform dispersion of Ru nanoparticles on substrate materials remains a key challenge. To achieve this, in the current study, we formed NF/Co(OH)2/Ru by electrodepositing Ru nanoparticles onto Co(OH)2 nanoneedles. The Co and O vacancies in the sample promoted water decomposition and the cleavage of O-H bonds, while the high surface energies at the apexes of the Co(OH)2 nanoneedles supported the even growth and attachment of Ru nanoparticles. In addition, the electron-rich Ru nanoparticles aided in the desorption of hydrogen intermediates. Compared to recently published Ru-based HER materials, the NF/Co(OH)2/Ru material created in this study shown improved electrochemical characteristics, with an overpotential of 20 mV at 10 mA·cm−2 and a Tafel slope of 35.43 mV·dec−1. Therefore, this material and the findings of this study are expected to contribute to HER research.

Nitrogen-Tungsten Oxide Nanostructures on Nickel Foam as High Efficient Electrocatalysts for Benzyl Alcohol Oxidation.

Electrocatalytic alcohol oxidation (EAO) is an attractive alternative to the sluggish oxygen evolution reaction in electrochemical hydrogen evolution cells. However, the development of high-performance bifunctional electrocatalysts is a major challenge. Herein, we developed a nitrogen-doped bimetallic oxide electrocatalyst (WO-N/NF) by a one-step hydrothermal method for the selective electrooxidation of benzyl alcohol to benzoic acid in alkaline electrolytes. The WO-N/NF electrode features block-shaped particles on a rough, inhomogeneous surface with cracks and lumpy nodules, increasing active sites and enhancing electrolyte diffusion. The electrode demonstrates exceptional activity, stability, and selectivity, achieving efficient benzoic acid production while reducing the electrolysis voltage. A low onset potential of 1.38 V (vs. RHE) is achieved to reach a current density of 100 mA cm-2 in 1.0 M KOH electrolyte with only 0.2 mmol of metal precursors, which is 396 mV lower than that of water oxidation. The analysis reveals a yield, conversion, and selectivity of 98.41%, 99.66%, and 99.74%, respectively, with a Faradaic efficiency of 98.77%. This work provides insight into the rational design of a highly active and selective catalyst for electrocatalytic alcohol oxidation.