Anodic Oxygen Evolution Reaction Research Articles

Trimetallic Ni-CuCoN0.6 Ohmic junction for the enhanced oxidation of methanol and urea

Methanol oxidation reaction (MOR) and urea oxidation reaction (UOR) can be utilized as effective alternatives to the anodic oxygen evolution reaction (OER) in overall water-splitting. Nevertheless, the development of cost-effective, highly efficient and durable electrocatalysts for MOR and UOR remains a significant challenge. Herein, the Ohmic junction (Ni-CuCoN0.6@CC) comprising CuCoN0.6 nanosheets and Ni nanoparticles anchored on carbon cloth (CC) was successfully synthesized via a two-step hydrothermal process followed by pyrolysis. The Ni-CuCoN0.6@CC demonstrates exceptional performance in both MOR (1.334 V@10 mA cm−2) and UOR (1.335 V@10 mA cm−2), coupled with outstanding durability, maintaining 88.70 % current density for MOR and 88.92 % for UOR after a rigorous 50-h stability test. Furthermore, the Ni-CuCoN0.6@CC demonstrates a high selectivity for oxidizing methanol to formic acid, achieving Faraday efficiencies exceeding 90 % at various current densities in the context of MOR. The outstanding performance of Ni-CuCoN0.6@CC in terms of MOR and UOR either surpasses or closely approaches the levels reported in previous literature, primarily due to the synergistic effect resulting from the Ohmic junction: in this system, Ni serves as the principal active component, Co augments catalytic activity and diminishes onset potential, while Cu enhances long-term durability. Moreover, CuCoN0.6 nanosheets effectively modulate electronic structure and optimize the morphology of Ni, leading to the exposure of numerous defects that provide a wealth of active sites for the reaction. Additionally, the exceptional hydrophilic and aerophobic surface promotes enhanced mass transfer. Density functional theory (DFT) calculations show that Ni-CuCoN0.6@CC enhances reactant adsorption and product desorption, reducing energy barriers and expediting MOR and UOR kinetics.

Recent Development of Transition Metal‐based Amorphous Electrocatalysts for Water Splitting

AbstractElectrochemical water splitting, including the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), is a promising hydrogen production technology. However, in practice, the high overpotentials and sluggish reaction kinetics associated with the anode OER process are the major obstacles to the smooth progress of electrocatalytic water splitting. Amorphous electrocatalysts, a crucial family of functional materials, exhibit unexpected performance due to their special short‐range ordered and long‐range disordered atom arrangement, abundant defect sites and adjustable composition. To date, while numerous recent publications showcase promising results for transition metal‐based amorphous electrocatalysts, including amorphous metal phosphide and metal hydroxide electrocatalysts with remarkable HER and OER properties respectively, the utilization of single‐function HER or OER catalysts tends to augment system complexity for water electrolysis, thereby escalating the cost of hydrogen production. In this regard, amorphous HER/OER bifunctional electrocatalysts are desired. In this review, we summarize the recent development on transition metal‐based amorphous catalysts for electrochemical water splitting. The design strategies for constructing HER/OER bifunctional transition‐metal‐based amorphous electrocatalysts are highlighted here, also including the exploration of relationship between catalyst structures and their remarkably improved performance. Finally, the possibilities of amorphous bifunctional catalysts for practical industrial applications are evaluated and future research direction are suggested.

Oxyanion Engineering on RuO2 for Efficient Proton Exchange Membrane Water Electrolysis

In proton exchange membrane water electrolysis (PEMWE), the anode oxygen evolution reaction (OER) catalysts rely heavily on the expensive and scarce iridium‐based materials. Ruthenium dioxide (RuO2) with lower price and higher OER activity, has been explored for the similar task, but has been restricted by the poor stability. Herein, we developed an anion modification strategy to improve the OER performance of RuO2 in acidic media. The designed multicomponent catalyst based on sulfate anchored on RuO2/MoO3 displays a low overpotential of 190 mV at 10 mA cm‐2 and stably operates for 500 hours with a very low degradation rate of 20 μV h‐1. When assembled in a PEMWE cell, this catalyst as an anode shows an excellent stability at 500 mA cm‐2 for 150 h. Experimental and theoretical results revealed that MoO3 could stabilize sulfate anion on RuO2 surface to suppress its leaching during OER. Such MoO3‐anchored sulfate not only reduces the formation energy of *OOH intermediate on RuO2, but also impedes both the surface Ru and lattice oxygen loss, thereby achieving the high OER activity and exceptional durability.

Correlating crystallinity regulation in spinel oxides and catalytic activity in electrocatalytic water oxidation

Recently, the electro-Fenton (EF) process by coupling cathodic two-electron oxygen reduction reaction (2e- ORR) with anodic oxygen evolution reaction (OER) has emerged as a potentially viable technology, while the sluggish OER is the main bottleneck. As promising OER catalysts, the amorphous and crystal phases of spinel oxides display high activities and electrical conductivity, respectively. Efforts to produce amorphous/crystal spinel oxides have progressed slowly, and how an amorphous/crystal structure benefits the catalytic performances remains elusive. Herein, Fe-doped NiCo2O4 (Fe-NiCo2O4) was used as a model catalyst to explore the effect mechanism of crystallinity controlled by annealing temperature on OER performance. The results display that the Fe-NiCo2O4 obtained at 300 ℃ shows amorphous/crystal structure, which facilitates the active site exposure and the charge transfer, leading to superior OER activity and catalytic stability. Based on the crystallinity regulation of OER catalysts, we propose an anodic optimized strategy to upgrade the EF-related processes by effectively providing O2 produced in the anode.

Transition Metal Oxide/Sulfide on the Ni Foam for Electrocatalytic UOR & OER

Water electrolysis is an important technology related to the energy conservation, is a promising technology. Currently, one of the key efforts is to improve the efficiency and reduce the cost of water electrolysis, in particular, the anodic oxygen evolution reaction (OER). Nobel-metal free OER catalyst or alternative urea oxidation reaction (UOR) is thus favored. Due to the advantages of enhance charge transfer and desirable charge redistribution, we have investigated nobel-metal free transition metal oxide/sulfide heterostructure UOR electrocatalyst. Co-Ni based metal heterostructure is synthesized using a simple two-step hydrothermal method. The resulting samples are examined using X-ray diffractometer, Scanning electron microscopy, X-ray photoelectron spectroscopy and the Inductively coupled plasma will used as the material analysis. Electrochemical performance is evaluated using linear sweep voltammetry, electrochemical impedance spectroscopy, cyclic voltammetry, and electrochemical active surface area. Moreover, the electrocatalyst is also evaluated as OER catalysts. The relation between the material characteristics and the electrochemical performance is discussed.

Electronic Structure Investigation of BSCF Catalysts during Electrochemical Water Electrolysis by Using Time Zero Analysis and Advanced Operando X-Ray Absorption Spectroscopy

The rapid increase in global energy demands and environmental awareness regarding the excessive use of fossil fuel has spurred significant academic interest in the development of alternative energy conversion and storage technologies that prioritize both efficiency and environmental sustainability. Among all kinds of renewable energy, hydrogen energy holds the potential to create a carbon free clean society, and a possible solution to the environmental issues.1 Electrochemical water splitting is considered as a greener approach for pure H2, which involved cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). The anodic OER is kinetically sluggish and considered as a rate determining step of the water splitting reaction. Therefore, it is necessary to develop OER catalysts with high activities.Perovskite oxides knows as a promising oxygen electrode catalyst due to their low cost, flexibility, and tailorable properties. However, most perovskite oxides possess poor electrical conductivity at room temperatures, and this limits their oxygen catalytic activity. In our work Ba0.5Sr0.5CoxFe1-xO3-δ (BSCF) catalysts with different cobalt and iron amounts where X=0, 0.2, 0.8, 1 were synthesized and investigated by time zero analysis and flow rate infinitization analysis which are electrochemical testing method that uses pressure to remove generated oxygen gas bubbles and provides accurate activity of the catalyst.2We find the volcano plot of the Fe amount and the OER activities, showing samples with X=0.8 have the best OER activities as Figure 1. Electronic structure of B-Site transition metal elements, oxygen vacancies, crystal structures and electrical conductivity are the key factors for determining the activities of Perovskite catalysts in OER.3Also it is quite important to determine the real active sites during the OER process by using advance operando techniques.Therefore, in order to investigate the in-depth mechanism of OER activities of Perovskite catalysts, the newly designed operando soft X-ray Absorption Spectroscopy (XAS) cells was utilized to analyze the subtle change as shown in Figure 2 on the oxygen K-edge (531 eV - 532 eV). Ba0.5Sr0.5Co0.8Fe0.2O3-δ has the most obvious changes in integral surface area at the O K-edge pre-edge region, which leads to the best activity among other BSCF samples. According to the Energy Dispersive X-ray Spectroscopy and Lattice Oxygen Evolution Mechanism, ions on the A sites (Ba2+,Sr2+) tend to dissolve and ions on the B sites (Co, Fe) are forming hydroxides (BOOH).Keywords: oxygen evolution reaction, BSCF catalysts, Time zero analysis, operando X-ray absorption spectroscopy Acknowledgements This work is based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. Reference: (1) Rose, P. K.; Neumann, F. Hydrogen refueling station networks for heavy-duty vehicles in future power systems. Transportation Research Part D: Transport and Environment 2020, 83, 102358.(2) Nagasawa, K.; Matsuura, I.; Kuroda, Y.; Mitsushima, S. A Novel Evaluation Method of Powder Electrocatalyst for Gas Evolution Reaction. Electrochemistry 2022, 90 (1), 017012-017012.(3) Zhu, Y.; Zhou, W.; Shao, Z. Perovskite/carbon composites: applications in oxygen electrocatalysis. Small 2017, 13 (12), 1603793. Figure 1

Application of Bifunctional Layered Double Hydroxide Electrocatalysts to Water Splitting

Water splitting is an area of research which is of pressing interest in addressing climate change. Water splitting provides oxygen and hydrogen as products, with hydrogen finding use as a potential high-density fuel to replace fossil fuels. Water splitting manifests as two half-cell reactions, namely the anodic oxygen evolution reaction and the cathodic hydrogen evolution reaction. The purpose of this project is to synthesise a bifunctional electrocatalyst to use in the water splitting reaction, replacing the rare and expensive transition metals catalysts currently in use such as platinum and ruthenium. The ideal material would exhibit strong performance for both the oxygen evolution reaction and the hydrogen evolution reaction.In this project, Layered Double Hydroxides (LDHs) have been synthesised for use in water splitting. LDHs are a group of ionic compounds characterised by their layered structure of positively charged sheets and an interlayer region consisting of the corresponding anions. LDHs typically contain a bivalent and a trivalent metal as part of the generic formula [M2+ 1–xM3+ x(OH)2][An–]x/n·zH2O. In this project the bivalent metal in use is typically cobalt and the trivalent metal is typically iron. The synthesis developed is a simple, one pot hydrothermal synthesis which can be seen in Figure 1. In this synthesis, the process begins with the precursor materials dissolved in solution. These solutions are mixed and stirred until homogenous. The resultant solution is then heated to form an impure product. Following washing steps and centrifugation a purified powder product is obtained. A variety of metallic salts have been tested for their use in these LDHs with the optimum LDHs selected for further study. The metallic salts used to provide the metals for the LDHs are typically hydrated transition metal nitrates.The LDHs have been characterised and their structure confirmed by a variety of analytical techniques including X-Ray Diffraction and Scanning Electron Microscopy. Simple qualitative analysis has been performed with FTIR spectroscopy. These LDHs have been immobilised on a variety of porous, high surface area materials, including nickel foam and copper foam, to enhance the properties seen in the screening study. These materials allow synthesis of high surface area, reactive electrocatalysts. To enhance the stability of the LDHs, carbon materials have been integrated with the LDHs. Examination of a variety of carbon materials involved post-synthesis mixing of the carbon material and the LDH product or inclusion of the carbon material in the LDH synthesis to form a composite. A variety of carbon materials have been analysed including graphene oxide, carbon black and carbon nanotubes. Figure 1

(Invited) Fundamentals of Plasmon-Induced Charge Transfer in Semiconducting Materials: Showcasing OER Catalysis

Using Localized Surface Plasmon Resonance Effect for Enhancing Electrochemical reactions has been reported earlier both in terms of direct electron injection/transfer (DET) in outer-sphere reductive processes as well as charge injection into semiconductors via plasmon-induced resonant electron transfer processes (PIRE). While the former (DET) is mainly influenced by the lifetimes of the ejected hot electrons and their rapid cooling at the interface. For inner sphere reductive processes via the LSPR phenomenon, direct charge injection into the LUMO states of the adsorbed species is required. In this regard, it is imperative to distinguish between the inter-band charge transfer of the adsorbed species because of exposure to photons.In contrast to these charge injections into semiconductors via plasmon-induced resonant electron transfer processes (PIRE), they must be more understood and complex. In this presentation, we will use the well-known endothermic anodic oxygen evolution reaction (OER) in alkaline pH to showcase the fundamental aspects of charge injection and its effect on the hole-driven OER mechanism. For this well-known OER catalyst, layered double hydroxides of Ni with Fe and Co dopants will be used. The electrochemical enhancement of OER will be explained based on detailed structural motifs of the semiconductors, its band structure, and the resonance effect of Au induced by the LSPR effect. Direct and indirect bandgaps will be discussed in the context of three possible mechanisms: (i) Charge carriers are directly injected into the semiconductor via LSPR. The semiconductor's conduction band is usually (-0.1 to 0.0 eV vs. NHE), and the valence band is between (2.00 and 3.5 eV), corresponding to electron energy between -2.00 to 3.5 eV vs. NHE. For LSPR nanoparticles, SPR energy is between 1.0 and 4.0 eV. Also, the Fermi energy of LSPR is usually 0.0 vs. NHE. Hence, LSPR only enables energetic electrons to be transferred from metals to semiconductors. It is the interface between LSPR and the semiconductor which is important. Charge injection is more prevalent when metal LSPR is of lower energy than the semiconductor—direct electron transfer (DET). (ii) Transfer does not involve direct electron injection but via (a) near-field electromagnetic and (b) resonant photon scattering mechanism. This has been shown to work by adding a thin dielectric material between the LSPR and the semiconductor. This would be most likely in the case of OER, where surface-localized plasmons will be the most important determinant instead of recombination events in the bulk of the semiconductor. This is most important for OER as it depends on the surface hole concentration. It should be noted that larger nanoparticles (>50 nm) have increased resonant photon scattering. Such a mechanism is more prevalent when we overlap metal LSPR and semiconductor bands, leading to plasmon-induced resonant electron transfer (PIRET). (iii) When metal LSPR is in direct contact with the semiconductor, all three phenomena could be active.

Structure–Activity–Stability Relationship of Ru-Ir-Ti Electrocatalysts for the Oxygen Evolution Reaction

Environmentally friendly strategies for energy conversion and storage are urgently needed to account for natural intensity variations of power generation by renewables and to ensure a stable electrical grid. Green hydrogen, produced by water electrolysis, can be considered as one of the most promising energy carriers since it can balance the energy demand in multiple energy sectors. Proton exchange membrane water electrolyzers (PEMWE) are state of the art devices for on-site hydrogen production. Still, their upscaling is challenged by the corrosive acidic environment and sluggish anodic oxygen evolution reaction (OER), which demand using noble metal based catalysts [1, 2]. Currently, Ir-based oxides are employed as OER catalysts in commercial PEMWE as they provide the best balance between activity and stability. Yet, the scarcity and high market price of Ir lead to poor cost-benefit factors. In the last years, Ir-Ru mixed oxides have attracted significant attention of the community due to their improved electrocatalytic activity [2, 3]. However, Ru degradation during the OER becomes challenging in conditions of long-term operation of the electrolyzer. Therefore, balancing stability and activity towards the OER at reduced Ir loading remains a significant challenge in PEMWE.Here, we examine the effect of low additions of Ti (1 to 6 at. %) on the catalytic activity and stability of Ru-Ir alloys towards the OER [4]. The catalysts are synthesized as ternary Ru-Ir-Ti thin film material libraries with Ir contents below 50 at. %. After the high-throughput screening of these libraries for desired electrocatalytic properties by online inductively coupled plasma mass spectrometry (ICP-MS), the most promising alloy compositions are selected and tested in conditions of long-term electrolysis (Figure 1). The observed activity-stability trends are correlated with the electronic structure of the Ru-Ir-Ti catalysts derived from X-ray photoelectron (XPS) and X-ray absorption spectroscopies (XAS). Furthermore, the structural changes in the near-surface regions of these catalysts induced by the OER, are investigated with the aid of atom probe tomography (APT). Our data reveal formation of Ir-Ru hydrous oxide layers in the course of the OER, providing high catalytic activity, while Ti additions promote stabilization of these reactive oxides in the near surface region. Our multidisciplinary approach of combining advanced electrochemical, spectroscopic and atomic-scale characterization methods provides insights on structure-function relationships in electrocatalysis, guiding the rational design of active and stable electrocatalysts.[1.] Carmo, M., et al., A comprehensive review on PEM water electrolysis. International journal of hydrogen energy, 2013. 38(12): p. 4901-4934.[2.] Kasian, O., et al., On the Origin of the Improved Ruthenium Stability in RuO2-IrO2 Mixed Oxides. Journal of the Electrochemical Society, 2016. 163(11): p. F3099-F3104.[3.] Saveleva, V.A., et al., Uncovering the stabilization mechanism in bimetallic ruthenium–iridium anodes for proton exchange membrane electrolyzers. The journal of physical chemistry letters, 2016. 7(16): p. 3240-3245.[4.] Lahn, L., et al. Low Ti Additions to Stabilize Ru‐Ir Electrocatalysts for the Oxygen Evolution Reaction. ChemElectroChem, 2023, e202300399. DOI: https://doi.org/10.1002/celc.202300399. Figure 1

High‐efficient electrocatalytic CO2 reduction to HCOOH coupling with 5‐hydroxymethylfurfural oxidation using flow cell

AbstractAmong various products from electrocatalytic CO2 reduction (CO2ER), HCOOH is highly profitable one. However, the slow kinetics of anodic oxygen evolution reaction lowers overall energy efficiency, which can be replaced by an electro‐oxidation reaction with low thermodynamic potential and fast kinetics. Herein, we report an electrolysis system coupling CO2ER with 5‐hydroxymethylfurfural oxidation reaction (HMFOR). A BiOCl–CuO catalyst was designed to sustain CO2ER to HCOOH at partial current density of 500 mA/cm2 with FEHCOOH above 90% and 700 mA/cm2 with FEHCOOH above 80%. In situ and ex situ x‐ray absorption fine structure was used to capture the structure transform of BiOCl–CuO into metallic Bi and Cu during CO2ER process, and the presence of CuO will promote this transformation which are supported by DFT calculations. Coupling HMFOR with CO2ER, we realize both FEHCOOH and FEFDCA above 95% simultaneously, providing new prospects vista for the electrosynthesis of value‐added products from paired system.

Unveiling the Enhancement of Electrocatalytic Oxygen Evolution Activity in Ru-Fe2O3/CoS Heterojunction Catalysts.

The development of highly efficient electrocatalysts for the sluggish anodic oxygen evolution reaction (OER) is crucial to meet the practical demand for water splitting. In this study, an effective approach is proposed that simultaneously enhances interfacial interaction and catalytic activity bymodifyingFe2O3/CoS heterojunctionusing Ru doping strategy to construct an efficient electrocatalytic oxygen evolution catalyst. The unique morphology of Ru doped Fe2O3 (Ru-Fe2O3) nanoring decorated by CoS nanoparticles ensures a large active surface area and a high number of active sites. The designed Ru-Fe2O3/CoS catalyst achieves a low OER overpotential (264mV) at 10mAcm-2 and demonstrates exceptional stability even at high current density of 100mAcm-2, maintaining its performance for an impressive duration of 90h. The catalytic performance of this Ru-Fe2O3/CoS catalyst surpasses that of other iron-based oxide catalysts and even outperforms the state-of-the-art RuO2. Density functional theory (DFT) calculation as well as experimental in situ characterization confirm that the introduction of Ru atoms can enhance the interfacial electron interaction, accelerating the electron transfer, and serve as highly active sites reducing the energy barrier for rate determination step. This work provides an efficient strategy to reveal the enhancement of electrocatalytic oxygen evolution activity of heterojunction catalysts by doping engineering.

Modulation strategies of electrocatalysts for 5-hydroxymethylfurfural oxidation-assisted water splitting

To address energy shortages and environmental issues, prioritizing renewable energy development and usage is crucial. Employing renewable sources for water electrolysis offers a sustainable method for hydrogen generation. Reducing the water electrolysis potential is vital for efficient clean energy conversion and storage. Substituting the anodic oxygen evolution reaction in conventional hydrogen production from water electrolysis with the more thermodynamically favorable 5-hydroxymethylfurfural (HMF) oxidation reaction can greatly decrease overpotential and yield the valuable product 2,5-furan dicarboxylic acid. The key to this process is developing effective electrocatalysts to minimize the potential of the HMF electrooxidation-hydrogen production system. Therefore, this review provides a comprehensive introduction to the modulation strategies that affect the electronic and geometric structure of electrocatalysts for HMF oxidation-assisted water splitting. The strategies encompass heteroatom doping, defect projection, interface engineering, structural design, and multi-metal synergies. The catalysts are assessed from various angles, encompassing structural characterization, reaction mechanisms, and electrochemical performance. Finally, current challenges in the catalyst design and potential development of this promising field are proposed.

A Cu doped RuO2 catalyst for efficient and durable acidic water oxidation

AbstractProducing hydrogen by water electrolysis in acidic system is essential for advancing the proton‐exchange membrane water electrolyzer (PEMWE) and maintaining the global sustainability. However, excavating highly active and durable catalysts for anodic oxygen evolution reaction (OER) in acid medium remains a great challenge due to the sluggish kinetics of OER and the severe catalyst dissolution. In this work, we developed a Cu doped RuO2 catalyst (Cu‐RuO2@CP) through simple drop casting and low temperature pyrolysis procedures. The incorporation of Cu into RuO2 executes complicated responsibilities: improving OER activity by raising more oxygen vacancies and accelerating the charge transfer between solid‐liquid interface; strengthening the long‐term durability via suppressing the over‐oxidation of RuO2 into soluble RuO4; lowering the catalyst cost by replacing with less expensive Cu. Hence, the Cu‐RuO2@CP exhibits excellent activity and stability in 0.5 M H2SO4 electrolyte, requiring a low overpotential of 200 mV to achieve 10 mA cm−2 and preserving stability for almost 500 h. Moreover, the overpotential is as low as 397 mV even when operating under an industrial‐level current density of 1000 mA cm−2, paving a new way to develop high performance OER electrocatalyst in acidic environment to promote the large‐scale utilization of PEMWE.

Lanthanum‐Nickel‐Based Mixed‐Oxide‐Coated Nickel Electrodes for the OER Electrocatalysis

ABSTRACTThe anodic oxygen evolution reaction (OER) remains a bottleneck for electrocatalytic water splitting due to its sluggish kinetics and, thus, high overpotentials. This limits water electrolysis as a key technology for the generation of hydrogen as a sustainable alternative to fossil fuels. For alkaline water splitting, perovskite phases (ABO3) with earth‐abundant first‐row transition‐metals have emerged as a promising material class for OER electrocatalysts. Among these, LaNiO3 has been found to exhibit high intrinsic OER activity. To increase catalyst utilization, a high surface area of the catalyst is desirable and can be achieved by impregnation of porous templates. In this work, La–Ni‐based oxides were prepared via impregnation of activated carbon and subsequent heating, combining precursor calcination and template removal into one step. The phase structure of the samples is analyzed via powder X‐ray diffractometry, and the morphology is determined by scanning electron microscopy. The synergistic effect of B‐site mixing iron as well as A‐site mixing strontium into LaNiO3 is studied and found to increase its OER activity, confirming the activity‐enhancing effect of Fe in Ni‐based OER electrocatalysts. To allow for facile technical application of the catalysts, the electrodes are prepared by coating a perovskite ink onto Ni‐metal as industrially relevant substrates, followed by calcination.

Unlocking Efficient Hydrogen Production: Nucleophilic Oxidation Reactions Coupled with Water Splitting.

Electrocatalytic water splitting driven by sustainable energy is a clean and promising water-chemical fuel conversion technology for the production of high-purity green hydrogen. However, the sluggish kinetics of anodic oxygen evolution reaction (OER) pose challenges for large-scale hydrogen production, limiting its efficiency and safety. Recently, the anodic OER has been replaced by a nucleophilic oxidation reaction (NOR) with biomass as the substrate and coupled with a hydrogen evolution reaction (HER), which has attracted great interest. Anode NOR offers faster kinetics, generates high-value products, and reduces energy consumption. By coupling NOR with hydrogen evolution reaction, hydrogen production efficiency can be enhanced while yielding high-value oxidation products or degrading pollutants. Therefore, NOR-coupled HER hydrogen production is another new green electrolytic hydrogen production strategy after electrolytic water hydrogen production, which is of great significance for realizing sustainable energy development and global decarbonization. This review explores the potential of nucleophilic oxidation reactions as an alternative to OER and delves into NOR mechanisms, guiding future research in NOR-coupled hydrogen production. It assesses different NOR-coupled production methods, analyzing reaction pathways and catalyst effects. Furthermore, it evaluates the role of electrolyzers in industrialized NOR-coupled hydrogen production and discusses future prospects and challenges. This comprehensive review aims to advance efficient and economical large-scale hydrogen production.

Grain Boundary Defect Engineering in Rutile Iridium Oxide Boosts Efficient and Stable Acidic Water Oxidation.

Proton exchange membrane water electrolysis (PEMWE) is considered a promising technology for coupling with renewable energy sources to achieve clean hydrogen production. However, constrained by the sluggish kinetics of the anodic oxygen evolution reaction (OER) and the acidic abominable environment render the grand challenges in developing the active and stable OER electrocatalyst, leading to low efficiency of PEMWE. Herein, we develop the rutile-type IrO2 nanoparticles with abundant grain boundaries and the continuous nanostructure through the joule heating and sacrificial template method. The optimal candidate (350-IrO2) demonstrates remarkable electrocatalytic activity and stability during the OER, presenting a promising advancement for efficient PEMWE. DFT calculations verified that grain boundaries can modulate the electronic structure of Ir sites and optimize the adsorption of oxygen intermediates, resulting in the accelerated kinetics. 350-IrO2 affords a rapid OER process with 20 times higher mass activity (0.61 A mgIr -1) than the commercial IrO2 at 1.50 V vs. RHE. Benefiting from the reduced overpotential and the preservation of the stable rutile structure, 350-IrO2 exhibits the stability of 200 h test at 10 mA cm-2 with only trace decay of 11.8 mV. Moreover, the assembled PEMWE with anode 350-IrO2 catalyst outputs the current density up to 2 A cm-2 with only 1.84 V applied voltage, long-term operation for 100 h without obvious performance degradation at 1 A cm-2.

Coupling methanol oxidation with CO2 reduction: A feasible pathway to achieve carbon neutralization

The energy consumption of up to 90 % of the total power input in the anodic oxygen evolution reaction (OER) slows down the implementation of electrochemical CO2 reduction reaction (CO2RR) to generate valuable chemicals. Herein, we present an alternative strategy that utilizes methanol oxidation reaction (MOR) to replace OER. The iron single atom anchored on nitrogen-doped carbon support (Fe-N-C) use as the cathode catalyst (CO2RR), low-loading platinum supported on the composites of tungsten phosphide and multiwalled carbon nanotube (Pt-WP/MWCNT) use as the anode catalyst (MOR). Our results show that the Fe-N-C exhibits a Faradaic selectivity as high as 94.93 % towards CO2RR to CO, and Pt-WP/MWCNT exhibits a peak mass activity of 544.24 mA mg−1Pt, which is 5.58 times greater than that of PtC (97.50 mA mg−1Pt). The well-established MOR||CO2RR reduces the electricity consumption up to 52.4 % compared to conventional OER||CO2RR. Moreover, a CO2 emission analysis shows that this strategy not only saves energy but also achieves carbon neutrality without changing the existing power grid structure. Our findings have crucial implications for advancing CO2 utilization and lay the foundation for developing more efficient and sustainable technologies to address the rising atmospheric CO2 levels.

Recent Advances in High‐Performance Direct Seawater Electrolysis for “Green” Hydrogen

Electrocatalytic water splitting through the electrolyzer is the most promising strategy for hydrogen production. Recently, water electrolysis is mainly based on high‐purity freshwater, which not only consumes a large number of freshwater resources but also improves the overall cost due to the extra water purification system. Hence, direct electrolysis of seawater is more desirable for large‐scale hydrogen generation. As is known, the dominant rate‐determining step of overall water splitting is the anodic oxygen evolution reaction (OER), which involves four‐electron transfer and owns a much larger overpotential than cathodic hydrogen evolution reaction. The large challenge for the design of OER catalysts in the seawater media is the competition reaction between OER and chloride oxidation reaction, which greatly influences energy efficiency. Hence, except for the activity and stability, selectivity is another key point for seawater splitting. Herein, after a brief introduction of two half reactions for water splitting, the latest metal hydr(oxide) electrocatalysts with different crystalline structures are summarized according to the previous reports. Moreover, the advantages and disadvantages of three common water electrolyzers are compared. Finally, the perspectives of seawater electrolysis for hydrogen production are outlined for practical applications.

Reaction engineering for high yield electrosynthesis: Unraveling the impact of reaction conditions and conversion on methanol oxidation to formate

Electrochemical processes offer defossilized alternatives to conventional routes. Key processes, such as hydrogen evolution and electrochemical CO2 reduction, are typically paired with the anodic oxygen evolution reaction (OER). However, the generated oxygen holds little value and the electrical costs associated with energy-intensive OER pose a significant economic barrier. The methanol oxidation reaction (MOR) to formate is a promising alternative to OER, requiring less energy and providing a value-added product. Extensive research focuses on MOR regarding high Faraday efficiencies, but conversion and product yields are mostly neglected. However, high conversion with sufficient yield is a prerequisite to transition from lab-scale catalysis towards feasible industrial applications. In this work, we investigated the selectivity of MOR to formate with progressing conversion at high current densities of up to 200mA/cm2 on hierarchically structured copper(II) oxide electrodes. We assessed the impact of the reaction conditions, including current density, temperature, flow rate, electrolyte composition, and membrane type. We found a positive influence of low current density and high temperature on the FE. Through tailored reaction conditions, we achieved a formate yield of 70% at 100mA/cm2 with an anodic potential of 1.33V vs. RHE. The anodic potential remained below typical OER potentials even at high conversion. For the first time, we demonstrated that MOR can achieve significant formate yields at high current density. Our results reveal the impact of conversion, reaction conditions and ion balance on selectivity and provide valuable insights for operating MOR at high yield in paired processes, e.g., with hydrogen evolution or CO2 reduction.

Superior electrocatalytic nitrate-to-ammonia conversion activity on CuCo bimetals in neutral media

Electrocatalytic recycling of waste nitrate (NO3-) to valuable ammonia (NH3) has been regarded as a sustainable and promising alternative to the unfriendly Haber-Bosch process. Nevertheless, it is still a challenge to achieve high production rate in a neutral media due to the multi-step electron and proton transfer process. Herein, a nonprecious CuCo tandem catalyst is facilely fabricated and the cooperative active sites enable efficient cascade NO3--to-NH3 conversion with outstanding Faradaic efficiency (FE) and high-rate NH3 generation (95 %, 710 μmol h−1 cm−2 at −0.65 VRHE) in neutral media. In-situ Fourier transform infrared spectroscopy (FTIR) is implemented to identify the reaction intermediates to figure out the tandem pathway. Further combined the density functional theory (DFT) calculations, the structure-activity relationship is unveiled. The introduction of Cu regulates the electronic structure of Co to boost the adsorption capacity of nitrate and shifts the d-band to lower the energy barrier. Moreover, the presence of Cu plays a vital role in inhibiting the binding of H*, which ensures the superior FE. To further maximize the energy utilization efficiency, a two-electrode electrolyzer (Cu45Co55||CuNi) is assembled by replacing the anodic oxygen evolution reaction (OER) with thermodynamically favored 5-hydroxymethylfurfural (HMF) oxidation to produce value-added 2,5-furandicarboxylic (FDCA), an important intermediate in the synthesis of bioplastics. These findings might guide the rational design of efficient and inexpensive electrocatalysts to produce value-added chemicals and hold the promise for contributing to carbon peaking and neutrality goals.