Boosting Hydrogen Oxidation Activity of Ni in Alkaline Media through Oxygen‐Vacancy‐Rich CeO2/Ni Heterostructures

The search for highly efficient platinum group metal (PGM)‐free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline electrolytes remains a great challenge in the development of alkaline exchange membrane fuel cells (AEMFCs). Here we report the synthesis of an oxygen‐vacancy‐rich CeO₂/Ni heterostructure and its remarkable HOR performance in alkaline media. Experimental results and density functional theory (DFT) calculations indicate the electron transfer between CeO₂ and Ni could lead to thermoneutral adsorption free energies of H* (ΔG_H*). This, together with the promoted OH* adsorption strength derived from the abundance of oxygen vacancies in the CeO₂ species, contributes to the excellent HOR performance with the exchange current density and mass activity of 0.038 mA cm_Ni^?2 and 12.28 mA mg_Ni^?1, respectively. This presents a new benchmark for PGM‐free alkaline HOR and opens a new avenue toward the rational design of high‐performance PGM‐free electrocatalysts for alkaline HOR.     

Efficient Hydrogen Oxidation Catalyzed by Strain‐Engineered Nickel Nanoparticles

The hydroxide‐exchange membrane fuel cell (HEMFC) is a promising energy conversion device. However, the development of HEMFC is hampered by the lack of platinum‐group‐metal‐free (PGM‐free) electrocatalysts for the hydrogen oxidation reaction (HOR). Now, a Ni catalyst is reported that exhibits the highest mass activity in HOR for a PGM‐free catalyst as well as excellent activity in the hydrogen evolution reaction (HER). This catalyst, Ni‐H₂‐2 %, was optimized through pyrolysis of a Ni‐containing metal‐organic framework precursor under a mixed N₂/H₂ atmosphere, which yielded carbon‐supported Ni nanoparticles with different levels of strains. The Ni‐H₂‐2 % catalyst has an optimal level of strain, which leads to an optimal hydrogen binding energy and a high number of active sites.     

Insight into the hydrogen oxidation electrocatalytic performance enhancement on Ni via oxophilic regulation of MoO_2

Exploring platinum-group-metal(PGM)free electrocatalysts for hydrogen oxidation reaction(HOR)in alkaline media is essential to the progress of anion exchange membrane fuel cells(AEMFCs).In this work,a Ni/MoO₂ heterostructure catalyst with comparable HOR activity in alkaline electrolyte with PGM catalyst was prepared by a simple hydrothermal-reduction method.Remarkably,the Ni/MoO₂ presents a mass kinetic current density of 38.5 mA mgNi^-1 at the overpotential of 50 mV,which is higher than that of the best PGM free HOR catalyst reported by far.Moreover,the HOR performance of Ni/MoO₂ under 100 ppm CO shows negligible fading,together with the superior durability,render it significant potential for application in AEMFCs.A particular mechanistic study indicates that the excellent HOR performance is ascribed to the accelerated Volmer step by the incorporation of MoO₂.The function of MoO₂ was further confirmed by CO striping experiment on Pt/C-MoO₂ that MoO₂ can facilitated OH adsorption thus accelerate the HOR process.On account of the high performance and low cost,the Ni/MoO₂ electrocatalyst encourages the establishment of high performance PGM free catalyst and shows significant potential for application in AEMFCs.     

Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel‐Based Metal–Organic Framework

The sluggish hydrogen oxidation reaction (HOR) under alkaline conditions has hindered the commercialization of hydroxide‐exchange membrane hydrogen fuel cells. A low‐cost Ni/NiO/C catalyst with abundant Ni/NiO interfacial sites was developed as a competent HOR electrocatalyst in alkaline media. Ni/NiO/C exhibits an HOR activity one order of magnitude higher than that of its parent Ni/C counterpart. Moreover, Ni/NiO/C also shows better stability and CO tolerance than commercial Pt/C in alkaline media, which renders it a very promising HOR electrocatalyst for hydrogen fuel cell applications. Density functional theory (DFT) calculations were also performed to shed light on the enhanced HOR performance of Ni/NiO/C; the DFT results indicate that both hydrogen and hydroxide achieve optimal binding energies at the Ni/NiO interface, resulting from the balanced electronic and oxophilic effects at the Ni/NiO interface.     

A Pd/C‐CeO2 Anode Catalyst for High‐Performance Platinum‐Free Anion Exchange Membrane Fuel Cells

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM‐FCs). The anion exchange membrane fuel cell (AEM‐FC) has long been proposed as a solution as non‐Pt metals may be employed. Despite this, few examples of Pt‐free AEM‐FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt‐free AEM‐FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt‐free AEM‐FC that employs a mixed carbon‐CeO₂ supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM‐FC tests run on dry H₂ and pure air show peak power densities of more than 500 mW cm^?2.     

Efficient Hydrogen Oxidation Catalyzed by Strain-Engineered Nickel Nanoparticles

The hydroxide-exchange membrane fuel cell (HEMFC) is a promising energy conversion device. However, the development of HEMFC is hampered by the lack of platinum-group-metal-free (PGM-free) electrocatalysts for the hydrogen oxidation reaction (HOR). Now, a Ni catalyst is reported that exhibits the highest mass activity in HOR for a PGM-free catalyst as well as excellent activity in the hydrogen evolution reaction (HER). This catalyst, Ni-H₂-2 %, was optimized through pyrolysis of a Ni-containing metal-organic framework precursor under a mixed N₂/H₂ atmosphere, which yielded carbon-supported Ni nanoparticles with different levels of strains. The Ni-H₂-2 % catalyst has an optimal level of strain, which leads to an optimal hydrogen binding energy and a high number of active sites.     

The Role of Discrepant Reactive Intermediates on Ru-Ru2P Heterostructure for pH-Universal Hydrogen Oxidation Reaction

Developing highly efficient electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline media is essential for the commercialization of alkaline exchange membrane fuel cell (AEMFC). However, the kinetics of HOR in alkaline media is complicated, resulting in orders of magnitude slower than that in acid, even for the state-of-the-art Pt/C. Here, we find that Ru-Ru₂P/C heterostructure shows HOR performance with a non-monotonous variation in a whole pH region. Unexpectedly, an inflection point located at pH≈7 is observed, showing an anomalous behavior that HOR activity under alkaline media surpasses acidic media. Combining experimental results and theoretical calculations, we propose the roles of discrepant reactive intermediates for pH-universal HOR, while H* and H₂O* adsorption strengths are responsible for acidic HOR, and OH* adsorption strength is essential for alkaline HOR. This work not only sheds light on fundamentally understanding the mechanism of HOR but also provides new designing principles for pH-targeted electrocatalysts.     

Reversible Electrocatalytic Activity of Carbon‐Supported PtxNi1−x in Hydrogen Reactions

Hydrogen oxidation and evolution reactions (HOR and HER) are studied on Pt_xNi_1?x/C materials synthesized by the bromide anion exchange method. Physicochemical characterization shows that this surfactant‐free method enables the preparation of well‐dispersed and effective catalysts for the processes involved in the anode of H₂/O₂ fuel cells (HOR) and the cathode of water electrolyzers (HER). The Pt‐based materials are modified with different Ni contents to decrease the amount of costly precious metal in the electrode materials. These modified Pt‐based materials are found to be electroactive for both reactions without additional overpotential. Kinetic parameters such as the Tafel slope, exchange (j₀) and kinetic current densities, and the rate‐determining steps of the reaction mechanisms are determined for each Pt–Ni catalyst and compared to those obtained at the Pt/C surface in alkaline medium. The high j₀ values that are obtained indicate a probable contribution of the surface structure of the catalysts due to their roughness and the presence of oxygenated Ni species even at low potentials.     

Pb-Modified Ultrathin RuCu Nanoflowers for Active,Stable, and CO-resistant Alkaline Electrocatalytic Hydrogen Oxidation

CO poisoning of Pt group metal (PGM) catalysts is a chronic problem for hydrogen oxidation reaction (HOR), the anodic reaction of hydroxide exchange membrane fuel cell (HEMFC) for converting H₂ to electric energy in sustainable manner. We demonstrate here an ultrathin Ru-based nanoflower modified with Pb (PbRuCu NF) as an active, stable, and CO-resistant catalyst for alkaline HOR. Mechanism studies show that the presence of Pb can weaken the adsorption of *H, strengthen *OH adsorption to facilitate CO oxidation, as a result of significantly enhanced HOR activity and improved CO tolerance. Furthermore, in situ electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) suggests that Pb acts as oxygen-rich site to regulate the behavior of the linear CO adsorption. The optimized Pb_1.04-Ru₉₂Cu₈/C displays a mass activity and specific activity of 1.10 A mg_Ru⁻¹ and 5.55 mA cm⁻², which are ≈10 and ≈31 times higher than those of commercial Pt/C. This work provides a facile strategy for the design of Ru-based catalyst with high activity and strong CO-resistance for alkaline HOR, which may promote the fundamental researches on the rational design of functional catalysts.     

Interfacial Engineering of Ni/V2O3 Heterostructure Catalyst for Boosting Hydrogen Oxidation Reaction in Alkaline Electrolytes

Alkaline fuel cells can permit the adoption of platinum group metal-free (PGM-free) catalysts and cheap bipolar plates, thus further lowering the cost. With the exploration of PGM-free hydrogen oxidation reaction (HOR) catalysts, nickel-based compounds have been considered as the most promising HOR catalysts in alkali. Here we report an interfacial engineering through the formation of nickel-vanadium oxide (Ni/V₂O₃) heterostructures to activate Ni for efficient HOR catalysis in alkali. The strong electron transfer from Ni to V₂O₃ could modulate the electronic structure of Ni sites. The optimal Ni/V₂O₃ catalyst exhibits a high intrinsic activity of 0.038 mA cm⁻² and outstanding stability. Experimental and theoretical studies reveal that Ni/V₂O₃ interface as the active sites can enable to optimize the hydrogen and hydroxyl bindings, as well as protect metallic Ni from extensive oxidation, thus achieving the notable activity and durability.     

碱性介质中氢氧化反应电催化剂的开发:从机理认识到材料设计

阴离子交换膜(AEM)燃料电池因具有使用非贵金属作为催化剂的优点而受到广泛关注.然而,在碱性体系中,AEM燃料电池中氢氧化反应(HOR)的反应动力学比在酸性介质中的慢两个数量级.针对HOR在碱中动力学缓慢的问题,有两种主要的理论来解释,(1)pH相关的氢结合能作为主要影响因素来控制HOR动力学的理论;(2)质子和氢氧根离子的吸附共同作为影响因子来控制HOR在碱性条件下的动力学的双功能理论.本文首先讨论了在碱性电解质中可能的HOR反应机理及其Tafel性能变化.除了传统的Tafel-Volmer和Heyrovsky-Volmer-HOR机理外,还讨论了最新提出的氢氧根离子吸附参与的HOR机理来说明在酸性和碱性介质中HOR机理的差异.然后,总结了具有代表性的碱性HOR催化剂(如贵金属、合金、金属间化合物、镍基合金、碳化物、氮化物等),简要介绍了它们相应的HOR反应机理,从而进一步理解在碱性介质中不同基元反应步骤给HOR性能带来的差异.最后,提出了一种未来设计HOR碱性催化剂的可行性方案,为今后碱性环境下的HOR催化剂设计提供参考.     

碳载合金 IrM（M = Fe，Ni，Co）纳米颗粒催化酸性与碱性介质中氢氧化反应

质子交换膜燃料电池(PEMFC)因能量转化率高、电流密度大、对负荷响应快及环境友好等优点而应用前景广阔.然而, Pt基催化剂的大量使用使得 PEMFC成本居高不下,阻碍了其商业化进程.金属 Ir具有良好的稳定性和相比 Pt较低的成本,可替代金属 Pt催化燃料电池阳极氢氧化反应.但是, Ir基催化剂的催化活性比 Pt低,难以满足商业化要求.通过合金调控 Ir纳米晶的电子结构和几何结构是降低 Ir用量、提高 Ir催化剂氢氧化活性的有效方法.
　　本文研究了 Ir基合金纳米晶中合金元素(Fe, Ni, Co)所产生的合金效应在酸碱性介质中对催化氢氧化的影响.采用溶剂蒸发-氢气还原法合成了具有相近合金度且平均粒径小于5 nm的 IrFe, IrNi和 IrCo纳米合金催化剂.电化学测试表明, IrNi合金催化剂具有最高的催化氢氧化活性.在酸性介质中, IrNi合金催化剂的质量比活性达到152 A/gIr (@0.1 V vs RHE),高于 IrFe (146 A/gIr)和IrCo (133 A/gIr)合金催化剂以及商业化 Pt/C催化剂(116 A/gPt).而在碱性介质中, Ir基合金催化剂活性较酸性介质中低,各合金催化剂优劣次序与酸性介质中一致.结构分析表明,合金化致使 Ir晶格收缩,收缩程度以 IrFe, IrNi和 IrCo的顺序依次降低. IrNi合金催化剂中 Ni合金元素诱导 Ir发生晶格收缩适中,使催化剂与中间物种(Had, OHad)的相互作用适度,从而获得最优的催化性质.另外,合金效应在不同 pH介质中影响不一：在酸性介质中,由合金元素(Fe, Ni, Co)导致的 Ir–Had相互作用弱化是提高氢氧化活性的主要原因;在碱性介质中,催化剂表面的亲氧效应决定了电极表面的 OHad吸/脱附性质和 Had表面覆盖度,从而影响催化氢氧化活性.     

The Solid‐Phase Synthesis of an Fe‐N‐C Electrocatalyst for High‐Power Proton‐Exchange Membrane Fuel Cells

The environmentally friendly synthesis of highly active Fe‐N‐C electrocatalysts for proton‐exchange membrane fuel cells (PEMFCs) is desirable but remains challenging. A simple and scalable method is presented to fabricate Fe^II‐doped ZIF‐8, which can be further pyrolyzed into Fe‐N‐C with 3 wt % of Fe exclusively in Fe‐N₄ active moieties. Significantly, this Fe‐N‐C derived acidic PEMFC exhibits an unprecedented current density of 1.65 A cm^?2 at 0.6 V and the highest power density of 1.14 W cm^?2 compared with previously reported NPMCs. The excellent PEMFC performance can be attributed to the densely and atomically dispersed Fe‐N₄ active moieties on the small and uniform catalyst nanoparticles.     

Blending Cr2O3 into a NiO–Ni Electrocatalyst for Sustained Water Splitting

The rising H₂ economy demands active and durable electrocatalysts based on low‐cost, earth‐abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over‐coated by a Cr₂O₃‐blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr₂O₃ triphase material exhibits superior activity and stability similar to Pt for the hydrogen‐evolution reaction in basic solutions. The chemically stable Cr₂O₃ is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen‐evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm^?2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. The non‐precious metal catalysts afford a high efficiency of about 15 % for light‐driven water splitting using GaAs solar cells.     

Enhanced catalytic activity of Ru through N modification toward alkaline hydrogen electrocatalysis

Exploring highly efficient electrocatalysts and understanding the reaction mechanisms for hydrogen electrocatalysis,including hydrogen oxidation reaction （HOR） and hydrogen evolution reaction （HER） in alkaline media are conducive to the conversion of hydrogen energy.Herein,we reported a new strategy to boost the HER/HOR performances of ruthenium （Ru） nanoparticles through nitrogen （N） modification.The obtained N-Ru/C exhibit remarkable catalytic performance,with normalized HOR exchange current d...     

Remarkably Enhanced Hydrogen Oxidation Reaction Activity of Carbon-supported Pt by Facile Nickel Modification

Developing high activity catalysts for hydrogen oxidation reaction(HOR)under alkaline condition remains a challenge in the exchange membrane fuel cell(AEMFC).Herein,we report that the activity of carbon-supported platinum(Pt/C)towards the hydrogen oxidation reaction(HOR)in alkaline media can be remarkably enhanced by simple immersion of Pt/C in nickel chloride solution.The adsorption of hydrogen on the catalyst surface is weakened by modification of nickel.The HOR activity on the Pt/C after immersion possesses an excellent mass current density of 33.4 A/gmetal,which is 18%higher than that(28.3 A/gmetal)on Pt/C.     

Heteroatom‐doped MoSe2 Nanosheets with Enhanced Hydrogen Evolution Kinetics for Alkaline Water Splitting

Electrochemical water splitting for hydrogen generation is a vital part for the prospect of future energy systems, however, the practical utilization relies on the development of highly active and earth‐abundant catalysts to boost the energy conversion efficiency as well as reduce the cost. Molybdenum diselenide (MoSe₂) is a promising nonprecious metal‐based electrocatalyst for hydrogen evolution reaction (HER) in acidic media, but it exhibits inferior alkaline HER kinetics in great part due to the sluggish water adsorption/dissociation process. Herein, the alkaline HER kinetics of MoSe₂ is substantially accelerated by heteroatom doping with transition metal ions. Specifically, the Ni‐doped MoSe₂ nanosheets exhibit the most impressive catalytic activity in terms of lower overpotential and larger exchange current density. The density functional theory (DFT) calculation results reveal that Ni/Co doping plays a key role in facilitating water adsorption as well as optimizing hydrogen adsorption. The present work paves a new way to the development of low‐cost and efficient electrocatalysts towards alkaline HER.     

The Comparability of Pt to Pt‐Ru in Catalyzing the Hydrogen Oxidation Reaction for Alkaline Polymer Electrolyte Fuel Cells Operated at 80 °C

The Pt‐catalyzed hydrogen oxidation reaction (HOR) for alkaline polymer electrolyte fuel cells (APEFCs) has been one of the focus subjects in current fuel‐cell research. The Pt catalyst is inferior for HOR in alkaline solutions, and alloying with Ru is an effective promotion strategy. APEFCs with Pt‐Ru anodes have provided a performance benchmark over 1 W cm^?2 at 60 °C. The Pt anode is now found to be in fact as good as the Pt‐Ru anode for APEFCs operated at elevated conditions. At 80 °C with appropriate gas back‐pressure, the cell with a Pt anode exhibits a peak power density of about 1.9 W cm^?2, which is very close to that with a Pt‐Ru anode. Even by decreasing the anode Pt loading to 0.1 mg cm^?2, over 1.5 W cm^?2 can still be achieved at 80 °C. This finding alters the previous understanding about the Pt catalyzed HOR in alkaline media and casts a new light on the development of practical and high‐power APFEC technology.     

S‐Doping of an Fe/N/C ORR Catalyst for Polymer Electrolyte Membrane Fuel Cells with High Power Density

Fe/N/C is a promising non‐Pt electrocatalyst for the oxygen reduction reaction (ORR), but its catalytic activity is considerably inferior to that of Pt in acidic medium, the environment of polymer electrolyte membrane fuel cells (PEMFCs). An improved Fe/N/C catalyst (denoted as Fe/N/C‐SCN) derived from Fe(SCN)₃, poly‐m‐phenylenediamine, and carbon black is presented. The advantage of using Fe(SCN)₃ as iron source is that the obtained catalyst has a high level of S doping and high surface area, and thus exhibits excellent ORR activity (23 A g^?1 at 0.80 V) in 0.1 M H₂SO₄ solution. When the Fe/N/C‐SCN was applied in a PEMFC as cathode catalyst, the maximal power density could exceed 1 W cm^?2.     

High‐Performance Bismuth‐Doped Nickel Aerogel Electrocatalyst for the Methanol Oxidation Reaction

Low‐cost, non‐noble‐metal electrocatalysts are required for direct methanol fuel cells, but their development has been hindered by limited activity, high onset potential, low conductivity, and poor durability. A surface electronic structure tuning strategy is presented, which involves doping of a foreign oxophilic post‐transition metal onto transition metal aerogels to achieve a non‐noble‐metal aerogel Ni₉₇Bi₃ with unprecedented electrocatalytic activity and durability in methanol oxidation. Trace amounts of Bi are atomically dispersed on the surface of the Ni₉₇Bi₃ aerogel, which leads to an optimum shift of the d‐band center of Ni, large compressive strain of Bi, and greatly increased conductivity of the aerogel. The electrocatalyst is endowed with abundant active sites, efficient electron and mass transfer, resistance to CO poisoning, and outstanding performance in methanol oxidation. This work sheds light on the design of high‐performance non‐noble‐metal electrocatalysts.