Ir/g-C3N4/Nitrogen-Doped Graphene Nanocomposites as Bifunctional Electrocatalysts for Overall Water Splitting in Acidic Electrolytes

Recent Development of Ir- and Ru-Based Electrocatalysts for Acidic Oxygen Evolution Reaction

Proton exchange membrane (PEM) water electrolyzers are one type of the most promising technologies for efficient, nonpolluting and sustainable production of high-purity hydrogen. The anode catalysts account for a very large fraction of cost in PEM water electrolyzer and also determine the lifetime of the electrolyzer. To date, Ir- and Ru-based materials are types of promising catalysts for the acidic oxygen evolution reaction (OER), but they still face challenges of high cost or low stability. Hence, exploring low Ir and stable Ru-based electrocatalysts for acidic OER attracts extensive research interest in recent years. Owing to these great research efforts, significant developments have been achieved in this field. In this review, the developments in the field of Ir- and Ru-based electrocatalysts for acidic OER are comprehensively described. The possible OER mechanisms are first presented, followed by the introduction of the criteria for evaluation of the OER electrocatalysts. The development of Ir- and Ru-based OER electrocatalysts are then elucidated according to the strategies utilized to tune the catalytic performances. Lastly, possible future research in this burgeoning field is discussed.

Regulation of Electron and Mass Transport Pathways in Efficient and Stable Low-Loading PEM Water Electrolyzers

Improving the utilization of iridium in proton exchange membrane (PEM) water electrolyzer is critical in reducing their cost for future development. Titanium dioxide (TiO2) has notable electrochemical stability at high operating potential and has been developed as a promising support of iridium-based OER nano-catalysts. However, limited by insufficient conductivity, the iridium content on TiO2 support catalysts is normally above 50 wt.%. Herein, support is provided for iridium on conductivity-enhanced TiO2 for low-iridium-loading PEMWE, successfully reducing the iridium content to 28 wt.% by the regulation of electron transport pathway. A new ionomer distribution strategy is then applied to the Ir@Pt@TiO2 catalyst layer to release the iridium sites and regulate the local mass transport pathways in the anode. This work reveals that the catalyst-ionomer interface played an important role in activity and stability in the anode of PEMWE. Building a thin and uniform ionomer distribution on supports with iridium exposure can result in continuous proton and electron transport pathways, promoting bubble escape, and exposing more effective active sites during reaction situations. This work provides a novel perspective for future research on the catalyst-ionomer interface and mass transport in PEMWEs.

Organic pollutant degradation for micro-molecule product emission over SiO2 layers-coated g-C3N4 photocatalysts

In this study, a SiO2 layer-coated g-C3N4 catalyst was prepared by a sol-gel method to overcome the poor adsorption ability and high recombination rate of charge carriers of pristine g-C3N4. SEM and TEM images indicated that SiO2 nanoparticles were coated on the surface of g-C3N4 nanoparticles with a layered structure and the layers were tightly contacted with g-C3N4. XRD patterns, FTIR spectra, UV-vis spectra and XPS spectra revealed that the structure of g-C3N4 was not destroyed and its photoelectric catalytic properties were not suppressed by the coating of SiO2 layers. Adsorption experiments revealed that the SiO2 layers improved the adsorption performance of g-C3N4 and their ratios were adjusted. The molecular weights of the final products of the degradation of RhB and antibiotics were at the micro-molecule level while the amount of g-C3N4 reached 1.2% of the mass fraction, which were more suitable for pollutant degradation compared with those of g-C3N4 due to its poor adsorption ability. The reason for this was likely that the SiO2 layers were not only beneficial for the adsorption of pollutants and intermediate products but also for prolonging the life time of the separated electrons and holes. Finally, active trapping experiments confirmed that both the holes and superoxide radicals were the main factors in the degradation of RhB and antibiotics, with the superoxides being the most active species.

Ru nanoclusters anchored on boron- and nitrogen-doped carbon for a highly efficient hydrogen evolution reaction in alkaline seawater

Electrochemical seawater splitting is an intriguing strategy for green hydrogen production. Constructing advanced electrocatalysts for the hydrogen evolution reaction (HER) in seawater is extremely demanded for accelerating the sluggish kinetic process. Herein, a Ru nanocluster anchored on boron- and nitrogen-doped carbon (Ru/NBC) catalyst was successfully synthesized for the HER in alkaline/seawater electrolytes. Remarkably, Ru/NBC exhibits outstanding activity and durability, delivering low overpotentials@10 mA cm-2 in 1.0 M KOH (30 mV) and 1.0 M KOH + seawater electrolyte (35 mV), outperforming Pt/C, Ru/NC, Ru/BC and Ru/C. Additionally, Ru/NBC also provides a high specific activity of 0.093 mA cm-2ECSA at an overpotential of 150 mV, which is higher than those of Ru/NC, Ru/BC and Ru/C, respectively. Density functional theory calculation results demonstrate that the Ru-B formed interfacial chemical bond can regulate the electronic structure of Ru active sites of Ru/NBC, which can facilitate the adsorption of water and hydrogen in alkaline media. This work provides a feasible strategy to fabricate outstanding electrocatalysts for the HER in alkaline/alkaline seawater electrolytes.

Low Ruthenium Content Confined on Boron Carbon Nitride as an Efficient and Stable Electrocatalyst for Acidic Oxygen Evolution Reaction

To date, only a few noble metal oxides exhibit the required efficiency and stability as oxygen evolution reaction (OER) catalysts under the acidic, high-voltage conditions that exist during proton exchange membrane water electrolysis (PEMWE). The high cost and scarcity of these catalysts hinder the large-scale application of PEMWE. Here, we report a novel OER electrocatalyst for OER comprised of uniformly dispersed Ru clusters confined on boron carbon nitride (BCN) support. Compared to RuO2 , our BCN-supported catalyst shows enhanced charge transfer. It displays a low overpotential of 164 mV at a current density of 10 mA cm-2 , suggesting its excellent OER catalytic activity. This catalyst was able to operate continuously for over 12 h under acidic conditions, whereas RuO2 without any support fails in 1 h. Density functional theory (DFT) calculations confirm that the interaction between the N on BCN support and Ru clusters changes the adsorption capacity and reduces the OER energy barrier, which increases the electrocatalytic activity of Ru.

Recent advances in proton exchange membrane water electrolysis

Proton exchange membrane water electrolyzers (PEMWEs) are an attractive technology for renewable energy conversion and storage. By using green electricity generated from renewable sources like wind or solar, high-purity hydrogen gas can be produced in PEMWE systems, which can be used in fuel cells and other industrial sectors. To date, significant advances have been achieved in improving the efficiency of PEMWEs through the design of stack components; however, challenges remain for their large-scale and long-term application due to high cost and durability issues in acidic conditions. In this review, we examine the latest developments in engineering PEMWE systems and assess the gap that still needs to be filled for their practical applications. We provide a comprehensive summary of the reaction mechanisms, the correlation among structure-composition-performance, manufacturing methods, system design strategies, and operation protocols of advanced PEMWEs. We also highlight the discrepancies between the critical parameters required for practical PEMWEs and those reported in the literature. Finally, we propose the potential solution to bridge the gap and enable the appreciable applications of PEMWEs. This review may provide valuable insights for research communities and industry practitioners working in these fields and facilitate the development of more cost-effective and durable PEMWE systems for a sustainable energy future.

In Situ Electroplating of Ir@Carbon Cloth as High-Performance Selective Oxygen Evolution Reaction Catalyst for Direct Electrolytic Recovery of Lead

The hydrometallurgical technology provides an efficient and sustainable green lead recovery process from lead acid batteries. Methanesulfonic acid has been widely considered as a green solvent for lead electrolytic recovery. However, the competitive precipitation of PbO2 at anode and higher overpotential for OER limit the lead recovery efficiency. In this work, an anodic oxygen evolution reaction (OER) catalyst with a low Ir mass fraction of 7.2% is obtained by electroplating iridium on carbon cloth (CC), exhibiting a lower overpotential of 256 mV, longer lifetime of 10 h, and better stability in the 0.5 M MSA solution. When CC-Ir is used as an anodic catalyst for lead recovery in the lead methanesulfonate electrolyte, only a lesser Pb precipitation product with Pb atom mass fraction of 1.42% is found after electrolysis of 10 h, demonstrating the suppression effect of CC-Ir for a PbO2 side reaction. This work proves that the anodic catalyst plays an important role in the lead electrolytic recovery process, which can inhibit the side reaction, reduce the energy consumption, and increase recovery efficiency.

Supported Iridium-based Oxygen Evolution Reaction Electrocatalysts - Recent Developments

The commercialization of acidic proton exchange membrane water electrolyzers (PEMWE) is heavily hindered by the price and scarcity of oxygen evolution reaction (OER) catalyst, i. e. iridium and its oxides. One of the solutions to enhance the utilization of this precious metal is to use a support to distribute well dispersed Ir nanoparticles. In addition, adequately chosen support can also impact the activity and stability of the catalyst. However, not many materials can sustain the oxidative and acidic conditions of OER in PEMWE. Hereby, we critically and extensively review the different materials proposed as possible supports for OER in acidic media and the effect they have on iridium performances.

Cobalt Incorporated Graphitic Carbon Nitride as a Bifunctional Catalyst for Electrochemical Water-Splitting Reactions in Acidic Media

Non-noble metal-based bifunctional electrocatalysts may be a promising new resource for electrocatalytic water-splitting devices. In this work, transition metal (cobalt)-incorporated graphitic carbon nitride was synthesized and fabricated in electrodes for use as bifunctional catalysts. The optimum catalytic activity of this bifunctional material for the hydrogen evolution reaction (HER), which benefitted at a cobalt content of 10.6 wt%, was promoted by the highest surface area and conductivity. The activity achieved a minimum overpotential of ~85 mV at 10 mA/cm² and a Tafel slope of 44.2 mV/dec in an acidic electrolyte. These values of the HER were close to those of a benchmark catalyst (platinum on carbon paper electrode). Moreover, the kinetics evaluation at the optimum catalyst ensured the catalyst flows (Volmer-Heyrovsky mechanism), indicating that the adsorption step is rate-determining for the HER. The activity for the oxygen evolution reaction (OER) indicated an overpotential of ~530 mV at 10 mAcm^-2 and a Tafel slope of 193.3 mV/dec, which were slightly less or nearly the same as those of the benchmark catalyst. Stability tests using long-term potential cycles confirmed the high durability of the catalyst for both HER and OER. Moreover, the optimal bifunctional catalyst achieved a current density of 10 mAcm^-2 at a cell voltage of 1.84 V, which was slightly less than that of the benchmark catalyst (1.98 V). Thus, this research reveals that the present bifunctional, non-noble metallic electrocatalyst is adequate for use as a water-splitting technology in acidic media.

Highly Active Visible Light-Promoted Ir/g-C3N4 Photocatalysts for the Water Oxidation Reaction Prepared from a Halogen-Free Iridium Precursor

A combination of the exceptional stability of fac-[Ir(H₂O)₃(NO₂)₃] together with thermolability of nitro and aqua ligands and high solubility in various solvents makes it promising as a brand-new chlorine-free precursor of iridium for the preparation of heterogeneous catalysts. In the current work, a new technique of fac-[Ir(H₂O)₃(NO₂)₃] preparation based on hydrothermal treatment of (NH₄)₃[Ir(NO₂)₆] was developed. For this purpose, the influence of reaction parameters such as the reaction time, temperature, and pH of the solution on the process of hexanitroiridate salt hydrolysis was investigated. The synthesized fac-[Ir(H₂O)₃(NO₂)₃] solution in this optimized way was used for the preparation of the series of Ir/g-C₃N₄ catalysts, which were evaluated in the water oxidation reaction with NaIO₄ utilized as a sacrificial reagent. A 20-fold enhancement of the oxygen evolution reaction (OER) activity was found to take place under visible light (λ = 411 nm) illumination of the systems. The highest rate of the photoinduced OER per iridium center was achieved by the Ir_0.005/g-C₃N₄ (air, 400°C) catalyst with an exceptional turnover frequency value of 967 min^-1 approaching the activity of known homogeneous iridium OER catalysts. The leaching experiments have shown that aquated Ir species are generated in a solution after prolonged functioning of the catalysts. Despite this, in the closed system the photodriven OER activity persists at a steady-state level evidencing an equilibrium achieved between dissolved and anchored Ir species forming catalytic tandem with the g-C₃N₄.

Synergistic catalysis of graphitic carbon nitride supported bimetallic sulfide nanostructures for efficient oxygen generation

Herein, a series of g-C₃N₄ supported bimetallic sulfide nanostructures (Ni₃S₂/MoS₂/ng-C₃N₄, n = 10, 20 and 30) was prepared by a hydrothermal method and subsequently a thermal annealing approach. Ni₃S₂/MoS₂/20g-C₃N₄ with controlled composition exhibits efficient OER activity with a low overpotential of 183 mV at 10 mA cm^-2, which outperforms the vast majority of sulfide OER electrocatalysts reported previously.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

TiO2-CeO2/g-C3N4 S-scheme heterostructure composite for enhanced photo-degradation and hydrogen evolution performance with combined experimental and DFT study

The g-C₃N₄/TiO₂ nanocomposites (NCs) are fabricated by optimization of calcination and subsequent hydrothermal technique decorated with CeO₂ nanoparticles (NPs) to build the g-C₃N₄/TiO₂-CeO₂ hybrid NCs. The chemical and surface characterizations of structural, morphological, elemental composition, optical, photo-degradation, HER performance and the DFT computation has been efficiently analyzed. The g-C₃N₄/TiO₂-CeO₂ composite photocatalysts (PCs) exhibit photocatalytic improved performance (∼97 %) for MB aqueous dye related to pristine g-C₃N₄ and g-C₃N₄/TiO₂ composite PCs. The obtained k value of the g-C₃N₄/TiO₂/CeO₂ heterostructure composite PCs has around 0.0262 min^-1 and 6.1, 2.6 and 1.5 times higher than to g-C₃N₄ (0.0043 min^-1), g-C₃N₄/CeO₂ (0.0099 min^-1) and g-C₃N₄/TiO₂ (0.0180 min^-1) PCs respectively. Likewise, the synergistic probable S-scheme charge separation mechanism based on scavengers' tests and other values, which leads to effective separation of photo-excited (e^--h⁺) pairs, whereas high degradation and more H₂O molecules have photo-reduction to H₂. The H₂ evolution reaction (HER) and the electrochemical impedance spectroscopy (EIS) of the as-obtained samples were explored via electrochemical study. This exertion recommends that the rational strategy and building of g-C₃N₄/TiO₂-CeO₂ nano-heterostructures were beneficial for developing visible-light-driven recyclable PCs for ecological refinement.

A novel bifunctional catalyst for overall water electrolysis: nano IrxMn(1-x)Oy hybrids with L12-IrMn3 phase

A nano Ir_xMn_(1-x)O_y hybrid electrode with a L1₂-IrMn₃ phase was used as a bifunctional catalyst with ultra-low iridium loading for overall water electrolysis in an acid solution for the first time. The HER activity of the Ir_xMn_(1-x)O_y hybrid electrode not only exceeded that of IrO₂, but also exceeded that of Pt/C. The OER activity of the Ir_xMn_(1-x)O_y hybrid electrode also exceeded that of IrO₂.

Electrocatalytic Oxygen Evolution Reaction in Acidic Conditions: Recent Progress and Perspectives

The electrochemical oxygen evolution reaction (OER) is an important half-cell reaction in many renewable energy conversion and storage technologies, including electrolyzers, nitrogen fixation, CO₂ reduction, metal-air batteries, and regenerative fuel cells. Among them, proton exchange membrane (PEM)-based devices exhibit a series of advantages, such as excellent proton conductivity, high durability, and good mechanical strength, and have attracted global interest as a green energy device for transport and stationary sectors. Nevertheless, with a view to rapid commercialization, it is urgent to develop highly active and acid-stable OER catalysts for PEM-based devices. In this Review, based on the recent advances in theoretical calculation and in situ/operando characterization, the OER mechanism in acidic conditions is first discussed in detail. Subsequently, recent advances in the development of several types of acid-stable OER catalysts, including noble metals, non-noble metals, and even metal-free OER materials, are systematically summarized. Finally, the current key issues and future challenges for materials used as acidic OER catalysis are identified and potential future directions are proposed.

Atomic-Scale Tailoring and Molecular-Level Tracking of Oxygen-Containing Tungsten Single-Atom Catalysts with Enhanced Singlet Oxygen Generation

The local coordination structure of metal atoms in single-atom catalysts (SACs) greatly influences their catalytic performance. And for most SACs, single metal atoms were anchored on carbon materials with N or C coordination. However, the rational design of oxygen-containing SACs and analyzing its structure-performance relationship remain challenging. Herein, we used amino-rich compounds to tailor the metatungstate and fix the W atoms and finally obtained the oxygen-containing W-SACs. The structural evolution of tungsten and its coordination atoms were tracked by electrospray ionization high-definition mass spectrometry. Furthermore, aberration-corrected transmission electron microscopy, X-ray absorption fine-structure spectroscopy, and first-principles calculation results revealed that different from the traditional SACs, the WO₂N₂ moiety (W coordinated with two O atoms and two N atoms) may be the favored structure for W species. This special structure promoted the energy transfer for enhancing singlet oxygen generation. This work presents an efficient way to prepare more high-efficiency SACs by atomic-scale tailoring and structural evolution tracking at the molecular level.

Electrocatalysis for the Oxygen Evolution Reaction in Acidic Media: Progress and Challenges

The oxygen evolution reaction (OER) is the efficiency-determining half-reaction process of high-demand, electricity-driven water splitting due to its sluggish four-electron transfer reaction. Tremendous effects on developing OER catalysts with high activity and strong acid-tolerance at high oxidation potentials have been made for proton-conducting polymer electrolyte membrane water electrolysis (PEMWE), which is one of the most promising future hydrogen-fuel-generating technologies. This review presents recent progress in understanding OER mechanisms in PEMWE, including the adsorbate evolution mechanism (AEM) and the lattice-oxygen-mediated mechanism (LOM). We further summarize the latest strategies to improve catalytic performance, such as surface/interface modification, catalytic site coordination construction, and electronic structure regulation of catalytic centers. Finally, challenges and prospective solutions for improving OER performance are proposed.

Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment

The proton exchange membrane (PEM) water electrolysis is one of the most promising hydrogen production techniques. The oxygen evolution reaction (OER) occurring at the anode dominates the overall efficiency. Developing active and robust electrocatalysts for OER in acid is a longstanding challenge for PEM water electrolyzers. Most catalysts show unsatisfied stability under strong acidic and oxidative conditions. Such a stability challenge also leads to difficulties for a better understanding of mechanisms. This review aims to provide the current progress on understanding of OER mechanisms in acid, analyze the promising strategies to enhance both activity and stability, and summarize the state-of-the-art catalysts for OER in acid. First, the prevailing OER mechanisms are reviewed to establish the physicochemical structure-activity relationships for guiding the design of highly efficient OER electrocatalysts in acid with stable performance. The reported approaches to improve the activity, from macroview to microview, are then discussed. To analyze the problem of instability, the key factors affecting catalyst stability are summarized and the surface reconstruction is discussed. Various noble-metal-based OER catalysts and the current progress of non-noble-metal-based catalysts are reviewed. Finally, the challenges and perspectives for the development of active and robust OER catalysts in acid are discussed.

Ir-based bifunctional electrocatalysts for overall water splitting

The recent progress on Ir-based bifunctional electrocatalysts in enhancing the overall water splitting performance is reviewed mainly from the aspects of optimizing the composition and morphology.

Investigation of polymer-derived Si-(B)-C-N ceramic/reduced graphene oxide composite systems as active catalysts towards the hydrogen evolution reaction

Hydrogen Evolution Reaction (HER) is an attractive technology for chemical conversion of energy. Replacement of platinum with inexpensive and stable electrocatalysts remains a major bottleneck hampering large-scale hydrogen production by using clean and renewable energy sources. Here, we report electrocatalytically active and ultra-stable Polymer-Derived Ceramics towards HER. We successfully prepared ultrathin silicon and carbon (Si–C) based ceramic systems supported on electrically conducting 2D reduced graphene oxide (rGO) nanosheets with promising HER activity by varying the nature and the composition of the ceramic with the inclusion of nitrogen, boron and oxygen. Our results suggest that oxygen-enriched Si-B-C-N/rGO composites (O-SiBCN/rGO) display the strongest catalytic activity leading to an onset potential and a Tafel slope of − 340 mV and ~ 120 mV dec⁻¹ respectively. O-SiBCN/rGO electrodes display stability over 170 h with minimal increase of 14% of the overpotential compared to ~ 1700% for commercial platinum nanoparticles. Our study provides new insights on the performance of ceramics as affordable and robust HER catalysts calling for further exploration of the electrocatalytic activity of such unconventional materials.

Fundamental understanding of the acidic oxygen evolution reaction: mechanism study and state-of-the-art catalysts

The oxygen evolution reaction (OER), as the anodic reaction of water electrolysis (WE), suffers greatly from low reaction kinetics and thereby hampers the large-scale application of WE. Seeking active, stable, and cost-effective OER catalysts in acidic media is therefore of great significance. In this perspective, studying the reaction mechanism and exploiting advanced anode catalysts are of equal importance, where the former provides guidance for material structural engineering towards a better catalytic activity. In this review, we first summarize the currently proposed OER catalytic mechanisms, i.e., the adsorbate evolution mechanism (AEM) and lattice oxygen evolution reaction (LOER). Subsequently, we critically review several acidic OER electrocatalysts reported recently, with focus on structure-performance correlation. Finally, a few suggestions on exploring future OER catalysts are proposed.

Rhodium/graphitic-carbon-nitride composite electrocatalyst facilitates efficient hydrogen evolution in acidic and alkaline electrolytes

Exploring the highly efficient and durable electrocatalysts for hydrogen evolution reaction (HER) is vitally necessary for sustainable energy conversion and storage system. Herein, we fabricate an interfacial engineered Rh-carbon nitride as advanced electrocatalysts for HER in the acidic and alkaline electrolytes. The interface between Rh nanocrystals and carbon nitride may adjust the electronic structure of Rh, which results in high activity for HER. The optimal Rh-carbon nitride shows low overpotential at current density of -10 mA·cm^-2 and small Tafel slope (13 mV and 25.0 mV dec^-1 in 0.5 M H₂SO₄, 46 mV and 42.0 mV dec^-1 in 1.0 M KOH, respectively), which is superior to that of commercial Pt/C (21 mV and 28.5 mV dec^-1 in 0.5 M H₂SO₄, 55 mV and 44.0 mV dec^-1 in 1.0 M KOH, respectively). Importantly, this composite also exhibits long-term stability in 0.5 M H₂SO₄ and 1.0 M KOH. The excellent HER performances can be attribute to the interface between Rh and carbon nitride, which downshifts their d-band center positions, tuning the adsorption ability for hydrogen and accelerating the HER kinetics. This work may open up an efficient method to design metal/carbon hybrid for electrocatalysis.

IrCo alloy nanoparticles supported on N-doped carbon for hydrogen evolution electrocatalysis in acidic and alkaline electrolytes

Designing efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is of great importance to advance water splitting technology towards practical applications. Herein, we report the preparation of IrCo nanoparticles supported on nitrogen-doped carbon (IrCo/NC) as a HER electrocatalyst in acidic and alkaline electrolytes. The IrCo/NC composite is obtained by pyrolyzing an Ir-doped Co(OH)2 precursor on g-C3N4, and is endowed with N-doped carbon and uniform IrCo alloy nanoparticles via a crystal confinement resulting from the Ir-doping into the Co(OH)2 layer. Electrocatalytic analysis shows that the IrCo/NC electrode requires low overpotentials of 32 mV at 10 mA cm-2 in 0.5 M H2SO4 and 33 mV in 1 M KOH, which are superior to those of the Co/NC and IrCo alloys that are free of Ir-doping or N-doped carbon. The results provide a strategy for designing and preparing active noble-transition bimetallic alloy electrocatalysts as efficient HER catalysts.

Atomic and electronic modulation of self-supported nickel-vanadium layered double hydroxide to accelerate water splitting kinetics

Herein, ruthenium (Ru) and iridium (Ir) are introduced to tailor the atomic and electronic structure of self-supported nickel-vanadium (NiV) layered double hydroxide to accelerate water splitting kinetics, and the origin of high hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities are analyzed at atomic level. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectroscopy studies reveal synergistic electronic interactions among Ni, V, and Ru (Ir) cations. Raman spectra and Fourier and wavelet transform analyses of the extended X-ray absorption fine structure indicate modulated local coordination environments around the Ni and V cations, and the existence of V vacancies. The Debye–Waller factor suggests a severely distorted octahedral V environment caused by the incorporation of Ru and Ir. Theoretical calculations further confirm that Ru or Ir doping could optimize the adsorption energy of intermediates in the Volmer and Heyrovsky steps for HER and accelerate the whole kinetic process for OER.

While water-splitting affords a renewable means to store energy, expensive catalysts are often required to achieve high performances. Here, authors modulate nickel-vanadium double hydroxide properties by noble-metal doping to accelerate electrocatalytic water splitting kinetics.

Robust noble metal-based electrocatalysts for oxygen evolution reaction

The oxygen evolution reaction (OER) is a kinetically sluggish anodic reaction and requires a large overpotential to deliver appreciable current. Despite the fact that non-precious metal-based alkaline water electrocatalysts are receiving increased attention, noble metal-based electrocatalysts (NMEs) applied in proton exchange membrane water electrolyzers still have advantageous features of larger current and power densities with lower stack cost. Engineering NMEs for OER catalysis with high efficiency, durability and utilization rate is of vital importance in promoting the development of cost-effective renewable energy production and conversion devices. In this tutorial review, we covered the recent progress in the composition and structure optimization of NMEs for OER including Ir- and Ru-based oxides and alloys, and noble-metals beyond Ir and Ru with a variety of morphologies. To shed light on the fundamental science and mechanisms behind composition/structure-performance relationships and activity-stability relationships, integrated experimental and theoretical studies were pursued for illuminating the metal-support interaction, size effect, heteroatom doping effect, phase transformation, degradation processes and single-atom catalysis. Finally, the challenges and outlook are provided for guiding the rational engineering of OER electrocatalysts for applications in renewable energy-related devices.

Silver encapsulated copper salen complex: efficient catalyst for electrocarboxylation of cinnamyl chloride with CO2

An active catalyst, [Cu]@Ag composite, was synthesized for the first time and used as a cathode for electrocarboxylation of cinnamyl chloride with CO₂. β,γ-Unsaturated carboxylic acids were obtained with excellent yield and moderate selectivity. Moreover, reasonable yields and selectivities of carboxylic acids were also achieved with several allylic halides and aryl halides.

An active catalyst, [Cu]@Ag composite, was synthesized for the first time and used as a cathode for electrocarboxylation of cinnamyl chloride with CO₂.