Oxygen-Inserted Top-Surface Layers of Ni for Boosting Alkaline Hydrogen Oxidation Electrocatalysis

Metastable Phase Noble-Metal-Free Core-Shell Structure for Efficient Electrocatalytic Nitrobenzene Transfer Hydrogenation

In order to study the catalytic behavior of a metastable-phase catalyst in electrocatalytic hydrogenation, we report a new metastable-phase noble-metal-free core-shell catalyst with a metastable hexagonal closest packed (hcp) phase Ni as the shell and face-centered-cubic (fcc) phase Cu as the core (Cu@hcp Ni NPs) for electrocatalytic hydrogenation of nitrobenzene (Ph-NO2) to aniline (Ph-NH2). Using H2O as the hydrogen source, it achieves up to 99.63% Ph-NO2 conversion and ∼100% Ph-NH2 selectivity, with an improved activity turnover frequency (TOF: 6640 h-1), much higher than those of hcp Ni NPs (5183.7 h-1) and commercial Pt/C (3537.6 h-1). It can also deliver a variety of aminoarenes with outstanding selectivity and excellent functional group compatibility with several groups. Mechanistic studies have shown that the introduction of Cu enhances hcp Ni's ability to dissociate water in situ to produce H* and improves the hydrogenation rate, resulting in the rapid conversion of Ph-NO2 to the final product Ph-NH2.

Pd1Ni2 Trimer Sites Drive Efficient and Durable Hydrogen Oxidation in Alkaline Media

Anion-exchange membrane fuel cell (AEMFC) is a cost-effective hydrogen-to-electricity conversion technology under a zero-emission scenario. However, the sluggish kinetics of the anodic hydrogen oxidation reaction (HOR) impedes the commercial implementation of AEMFCs. Here, we develop a Pd single-atom-embedded Ni3N catalyst (Pd1/Ni3N) with unconventional Pd1Ni2 trimer sites to drive efficient and durable HOR in alkaline media. Integrating theoretical and experimental analyses, we demonstrate that dual Pd1Ni2 sites achieve a "*H on Pd1Ni2-HV + *OH on Pd1Ni2-HN" adsorption mode, effectively weakening the overstrong *H and *OH adsorptions on pristine Ni3N. Owing to the unique coordination mode and atomically dispersed catalytic sites, the resulting Pd1/Ni3N catalyst delivers a high intrinsic and mass activity together with excellent antioxidation capability and CO tolerance. Specifically, the HOR mass activity of Pd1/Ni3N reaches 7.54 A mgPd-1 at the overpotential of 50 mV. The AEMFC employing Pd1/Ni3N as the anode catalyst displays a high power density of 31.7 W mgPd-1 with an ultralow anode precious metal loading of only 0.023 mgPd cm-2. This study provides guidance for the design of high-performance alkaline HOR catalytic sites at the atomic level.

An Interstitial Boron Inserted Metastable Hexagonal Rh Nanocrystal for Efficient Hydrogen Oxidation Electrocatalysis

Constructing metastable phase structure plays an important role in changing the physicochemical properties and improving the catalytic performance of nanocrystals. Unfortunately, the synthesis of metastable phase metallic nanocrystals is highly challenging, mainly due to the thermodynamically unstable ground-state. Here, we report a synthesis of unconventional metastable hexagonal rhodium nanocrystal (Bint-Rhhcp/C) via interstitial boron insertion. The insertion of boron atoms into the interstitial sites of cubic Rh lattice not only induces the atomic arrangements from face-centered cubic (fcc) to hexagonal close-packed (hcp), but also stabilizes the metastable hexagonal Rh structure. Benefiting from the phase transition and interstitial boron doping, the Bint-Rhhcp/C catalyst exhibits remarkable catalytic performance toward hydrogen oxidation reaction (HOR) under alkaline media, with a mass activity of 1.413 mA μgPGM -1. Experimental measurements including in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations indicate that the strengthened adsorption of hydroxyl species on the electrode surface of Bint-Rhhcp/C is responsible for the reconstruction of interfacial water structure and increased water proportions in the gap region in the electric double layers. As a result, the increased water connectivity and hydrogen bond network facilitate high-efficiency hydrogen transfer across the interface, thereby boost the alkaline HOR performance.

Understanding the Roles and Regulation Methods of Key Adsorption Species on Ni-Based Catalysts for Efficient Hydrogen Oxidation Reactions in Alkaline Media

This review focuses on recent advancements in the development and understanding of nickel-based catalysts for the hydrogen oxidation reaction in alkaline media. Given the economic and environmental limitations associated with platinum group metals, nickel-based catalysts have emerged as promising alternatives due to their abundance, lower cost, and comparable catalytic properties. The review begins with an exploration of the fundamental HOR mechanisms, emphasizing the key roles of the reactive species in optimizing the catalytic activity of Ni-based catalysts. Thermodynamic and stability optimizations of nickel-based catalysts are thoroughly examined, focusing on alloying strategies, heteroatom incorporation, and the use of various support materials to enhance their catalytic performance and durability. The review also addresses the challenge of catalyst poisoning, particularly by carbon monoxide, and evaluates the effectiveness of different approaches to improve poison resistance. Finally, the review concludes by summarizing the key findings and proposing future research directions to further enhance the efficiency and stability of nickel-based catalysts for practical applications in anion exchange membrane fuel cells. The insights gained from this comprehensive analysis aim to contribute to the development of cost-effective and sustainable catalysts and facilitate the broader adoption of AEMFCs in the quest for clean energy solutions.

Hydroxyl-Binding Induced Hydrogen Bond Network Connectivity on Ru-based Catalysts for Efficient Alkaline Hydrogen Oxidation Electrocatalysis

Understanding the role of adsorbed intermediates at the polarized catalyst-electrolyte interface on the structure of electrical double layer (EDL) is essential for developing highly efficient electrocatalysts. Here, we prepared a series of unconventional face-centered-cubic (fcc) phase Ru-based catalysts (i.e. fcc-Ru, fcc-RuCr, and fcc-RuCrW) by rational tuning the binding energetics of hydroxyl intermediate to engineer the electrochemical interface and boost the performance of alkaline hydrogen oxidation reaction (HOR). The introduction of oxyphilic metals Cr and W can regulate the orbital occupation of Ru, promote the adsorption of hydroxyl species, resulting in an anomalous behavior that HOR performance under alkaline media exceeds acidic media. Experimental results and theoretical calculations unravel that the modulated adsorption of hydroxyl species on the electrode surface are responsible for the reconstruction of interfacial water structure and dynamic evolution of free water molecules from nearest to the electrode surface to above the gap region in the EDL, thereby leading to significantly increased water connectivity and hydrogen bond network. Our work reveals a new understanding of the surface intermediates in controlling the dynamic process of interfacial water and hydrogen bonding network in HOR electrocatalysis, and will guide rational design of advanced electrocatalysts through electrochemical interfacial engineering.

Exploiting Lattice Carbon-Induced Modulation Effect in Nickel towards Efficient Alkaline Hydrogen Oxidation

Doping with non-metallic heteroatom is an effective approach to tailor the electronic structure of Ni for enhancing its alkaline hydrogen oxidation reaction (HOR) catalytic performance. However, the modulation of HOR activity of Ni by lattice carbon (LC) atoms has rarely been reported, especially to reveal the rule between the doping effect and activity caused by the content of LC atoms. Here, hydrogen is proposed as a scavenger for LC atoms in the pyrolytic reduction process to finely control the content of LC atoms in Ni. With the removal of LC atoms in Ni lattice, the electronic structure changes from Ni3C-like electronic structure to quasi-Ni structure. Furthermore, a volcanic relationship between the LC content and HOR activity of Ni is established for the first time. The Cless-Ni (LC0.44-Ni) with optimized LC content shows the best activity owing to the weakened hydrogen binding energy (HBE) and optimal hydroxyl binding energy (OHBE). This work provides an inspiration for the design of high-performance catalysts by tailoring the electronic structure of the metal via LC atoms doping.

Rechargeable Hydrogen Gas Batteries: Fundamentals, Principles, Materials, and Applications

The growing demand for renewable energy sources has accelerated a boom in research on new battery chemistries. Despite decades of development for various battery types, including lithium-ion batteries, their suitability for grid-scale energy storage applications remains imperfect. In recent years, rechargeable hydrogen gas batteries (HGBs), utilizing hydrogen catalytic electrode as anode, have attracted extensive academic and industrial attention. HGBs, facilitated by appropriate catalysts, demonstrate notable attributes such as high power density, high capacity, excellent low-temperature performance, and ultralong cycle life. This review presents a comprehensive overview of four key aspects pertaining to HGBs: fundamentals, principles, materials, and applications. First, detailed insights are provided into hydrogen electrodes, encompassing electrochemical principles, hydrogen catalytic mechanisms, advancements in hydrogen catalytic materials, and structural considerations in hydrogen electrode design. Second, an examination and future prospects of cathode material compatibility, encompassing both current and potential materials, are summarized. Third, other components and engineering considerations of HGBs are elaborated, including cell stack design and pressure vessel design. Finally, a techno-economic analysis and outlook offers an overview of the current status and future prospects of HGBs, indicating their orientation for further research and application advancements.

Boosting Alkaline Hydrogen Oxidation Kinetics through Interfacial Environments Induced Surface Migration of Adsorbed Hydroxyl

Constructing bifunctional sites through heterojunction engineering to accelerate water formation has become a pivotal strategy to improve the alkaline hydrogen oxidation reaction (HOR) kinetics, which is mainly focused on the synergistic effect of neighboring sites and the energetics of the surface reaction steps. However, the roles of the surface migration of key intermediates that go beyond the bifunctional mechanism limited to neighboring atoms have usually been ignored. Using the heterostructured Ni3C-Ni catalyst as a model, we found that the rapid surface migration of OHad species from the positively charged Ni3C to the negatively charged Ni component played a decisive role in facilitating water formation. Such unprecedented surface migration of OHad is induced by the large discrepancy between the local surface charge densities and interfacial environments of the Ni3C and Ni components under operating conditions. Benefiting from this, the resultant Ni3C-Ni exhibited outstanding mass activity for the alkaline HOR, which was approximately 19-fold and 21-fold higher than those of Ni and Ni3C, respectively. These findings not only provide novel insights into the alkaline HOR mechanism of heterostructured catalysts but also open new avenues for developing advanced electrocatalysts for alkaline fuel cells.

The Roles of Surface Hydrogen and Hydroxyl in Alkaline Hydrogen Oxidation on Ni-Based Electrocatalysts

One important target for anion exchange membrane fuel cells (AEMFCs) is to enable the application of anode non-precious metal hydrogen oxidation reaction (HOR) catalyst. Nickel presents a promising candidate for alkaline HOR; yet, its practical application is hampered by the intrinsically sluggish activity and poor stability. Herein, a series of Ni-based metals (Ni5Mo, Ni25Co, Ni14W and Ni) are electrodeposited as model catalysts to systematically explore the alkaline HOR by considering the role of adsorbed hydroxyl (OHad). Spectroscopic studies together with density functional theory calculations shed light on the beneficial effect of transition metal M (M=Mo, Co, W) alloying/doping on HOR by introducing the charge transfer from M to Ni and down shifting Ni 3d band center. The HOR specific activities on Ni-based catalysts reveal a volcano-type relationship with the hydrogen binding energy (HBE). The strongly adsorbed OHad is proven to induce deactivation for Ni active sites, and the deactivation potential is OHad binding energy (OHBE) dependent. This study adds new insight into the HOR mechanism and stability of Ni-based electrocatalysts, providing a new avenue for the rational design of highly efficient and robust alkaline HOR catalysts.

Metal-Hydroxide Organic Frameworks for Aqueous Nickel-Zinc Batteries

Hydroxides exhibit a high theoretical capacity for energy storage by ion release and are often intercalated with anions to enhance the ion migration kinetics. In this study, a series of metal-hydroxide organic frameworks (MHOFs) are synthesized by intercalating aromatic organic linkers into hydroxides using I-M/Ni(OH)2 (where M = Co2+, Cu2+, Mg2+, Fe2+). The coordination environment and layer spacing (1.09 nm) of I-M/Ni(OH)2 are explored by X-ray absorption fine structure and cryo-electron microscopy. The intercalation nanostructure improves the conductivity of the hydroxides and facilitates Zn2+ migration by increasing the interlayer spacing, while enhancing the rate capability and cycling stability. Consequently, the I-Co/Ni(OH)2 material exhibites a satisfactory specific capacity of 0.35 mAh cm-2 at 3 mA cm-2 and a high peak power density of 6.78 mW cm-2. This study offers a novel perspective on the design of intercalated hydroxide and provides new insights into high-performance nickel-zinc batteres.

Deciphering Doping Effects in a V-Doped Ni Catalyst for Hydrogen Electrooxidation

The improved performance of soluble metal-doped Ni catalysts is perplexed by the evolvable surface structures in the alkaline electrolytes for hydrogen oxidation reaction (HOR). Herein, V-doped Ni nanoparticles, as a proof of concept, were carefully evaluated to explore the intrinsic function of the enthetic V-species in assisting the HOR kinetic improvement. As expected, it exhibits a mass-normalized kinetic current density of 50.34 mA mgNi-1, more than 12 times that of the Ni counterpart without the introduction of V. Systematic investigations prove that the surface V-species, including the V-oxides and the doped V atoms at the outmost layer, would be dissolved into the electrolytes during the alkaline HOR process. The remaining V-dopants inside the nanoparticles would rationally weaken the hydroxyl binding energy (OHBE) of the Ni-based surfaces, thereby accelerating the formation of water molecules. We also uncover that Ni is located at the overstrong branch of the OHBE-described volcano plot through theoretical calculations and alkali-metal cation probe experiments, and weakening the OHBE by internal V-doping can leave the activity to the volcanic apex.

Activating and Stabilizing Lattice Oxygen via Self-Adaptive Zn-NiOOH Sub-Nanowires for Oxygen Evolution Reaction

Efficient and durable catalysts for the oxygen evolution reaction are essential for realizing the large-scale application of water electrolysis technologies. Here, we report a novel Zn-doped NiOOH subnanowires (Zn-NiOOH SNWs) catalyst synthesized via the electrochemical reconstruction of Zn-NiMoO4 SNWs. The inclusion of Zn triggers a transition in the oxygen evolution reaction mechanism of NiOOH from the adsorbate evolution mechanism to the lattice oxygen mechanism, resulted from Zn's adaptive adjustment of coordination types, which also improves the reaction energetics, thereby enhancing the stability and activity. Furthermore, the subnanowire structure provides further stabilization of the lattice oxygen in Zn-NiOOH, preventing its destructive dissolution. Remarkably, Zn-NiOOH SNWs display a current density of 10 mA cm-2 with an overpotential of only 179 mV and maintain stable operation at 200 mA cm-2 for 800 h with minimal changes in overpotential, establishing them as one of the most effective catalysts involving lattice oxygen for the alkaline oxygen evolution reaction. When utilized as the anode in an alkaline water electrolyzer, our Zn-NiOOH SNWs catalyst demonstrates stability exceeding 500 h under a water-splitting current of 200 mA cm-2, indicating promising potential for practical applications.

The Role of Phosphorus on Alkaline Hydrogen Oxidation Electrocatalysis for Ruthenium Phosphides

Transition metal/p-block compounds are regarded as the most essential materials for electrochemical energy converting systems involving various electrocatalysis. Understanding the role of p-block element on the interaction of key intermediates and interfacial water molecule orientation at the polarized catalyst-electrolyte interface during the electrocatalysis is important for rational designing advanced p-block modified metal electrocatalysts. Herein, taking a sequence of ruthenium phosphides (including Ru2P, RuP and RuP2) as model catalysts, we establish a volcanic-relation between P-proportion and alkaline hydrogen oxidation reaction (HOR) activity. The dominant role of P for regulating hydroxyl binding energy is validated by active sites poisoning experiments, pH-dependent infection-point behavior, in situ surface enhanced infrared absorption spectroscopy, and density functional theory calculations, in which P could tailor the d-band structure of Ru, optimize the hydroxyl adsorption sites across the Ru-P moieties, thereby leading to improved proportion of strongly hydrogen-bonded water and facilitated proton-coupled electron transfer process, which are responsible for the enhanced alkaline HOR performance.

Unconventional hcp/fcc Nickel Heteronanocrystal with Asymmetric Convex Sites Boosts Hydrogen Oxidation

Developing non-platinum group metal catalysts for the sluggish hydrogen oxidation reaction (HOR) is critical for alkaline fuel cells. To date, Ni-based materials are the most promising candidates but still suffer from insufficient performance. Herein, we report an unconventional hcp/fcc Ni (u-hcp/fcc Ni) heteronanocrystal with multiple epitaxial hcp/fcc heterointerfaces and coherent twin boundaries, generating rugged surfaces with plenty of asymmetric convex sites. Systematic analyses discover that such convex sites enable the adsorption of *H in unusual bridge positions with weakened binding energy, circumventing the over-strong *H adsorption on traditional hollow positions, and simultaneously stabilizing interfacial *H2O. It thus synergistically optimizes the HOR thermodynamic process as well as reduces the kinetic barrier of the rate-determining Volmer step. Consequently, the developed u-hcp/fcc Ni exhibits the top-rank alkaline HOR activity with a mass activity of 40.6 mA mgNi -1 (6.3 times higher than fcc Ni control) together with superior stability and high CO-tolerance. These results provide a paradigm for designing high-performance catalysts by shifting the adsorption state of intermediates through configuring surface sites.

Promoting OH* adsorption by defect engineering of CuO catalysts for selective electro-oxidation of amines to nitriles coupled with hydrogen production

Developing a high-efficiency benzylamine oxidation reaction (BOR) to replace the sluggish oxygen evolution reaction (OER) is an attractive pathway to promote H2 production and concurrently realize organic conversion. However, the electrochemical BOR performance is still far from satisfactory. Herein, we present a self-supported CuO nanorod array with abundant oxygen vacancies on copper foam (Vo-rich CuO/CF) as a promising anode for selective electro-oxidation of benzylamine (BA) to benzonitrile (BN) coupled with cathodic H2 generation. In situ infrared spectroscopy demonstrates the selective conversion of BA into BN on Vo-rich CuO. Furthermore, in situ Raman spectroscopy discloses a direct electro-oxidation mechanism of BA driven by electroactive hydroxyl species (OH*) over the Vo-rich CuO catalyst. Theoretical and experimental studies verify that the presence of oxygen vacancies is more favorable for the adsorption of OH* and BA molecules, enabling accelerated kinetics for the BOR. As expected, the Vo-rich CuO/CF electrode delivers outstanding BOR activity and stability, giving a high faradaic efficiency (FE) of over 93% for BN production at a potential of 0.40 V vs. Ag/AgCl. Impressively, almost 100% FE for H2 production can be further achieved at the NiSe cathode by integrating BA oxidation in a two-electrode electrolyzer.

Unraveling Stoichiometry Effect in Nickel-Tungsten Alloys for Efficient Hydrogen Oxidation Catalysis in Alkaline Electrolytes

Anion-exchange membrane fuel cells provide the possibility to use platinum group metal-free catalysts, but the anodic hydrogen oxidation reaction (HOR) suffers from sluggish kinetics and its source is still debated. Here, over nickel-tungsten (Ni-W) alloy catalysts, we show that the Ni : W ratio greatly governs the HOR performance in alkaline electrolyte. Experimental and theoretical studies unravel that alloying with W can tune the unpaired electrons in Ni, tailoring the potential of zero charge and the catalytic surface to favor hydroxyl adsorption (OHad). The OHad species coordinately interact with potassium (K+) ions, which break the K+ solvation sheath to leave free water molecules, yielding an improved connectivity of hydrogen-bond networks. Consequently, the optimal Ni17W3 alloy exhibits alkaline HOR activity superior to the state-of-the-art platinum on carbon (Pt/C) catalyst and operates steadily with negligible decay after 10,000 cycles. Our findings offer new understandings of alloyed HOR catalysts and will guide rational design of next-generation catalysts for fuel cells.

KIr4O8 Nanowires with Rich Hydroxyl Promote Oxygen Evolution Reaction in Proton Exchange Membrane Water Electrolyzer

The sluggish kinetics for anodic oxygen evolution reaction (OER) and insufficient catalytic performance over the corresponding Ir-based catalysts are still enormous challenges in proton exchange membrane water electrolyzer (PEMWE). Herein, it is reported that KIr4O8 nanowires anode catalyst with more exposed active sites and rich hydroxyl achieves a current density of 1.0 A cm-2 at 1.68 V and possesses excellent catalytic stability with 1230 h in PEMWE. Combining in situ Raman spectroscopy and differential electrochemical mass spectroscopy results, the modified adsorbate evolution mechanism is proposed, wherein the rich hydroxyl in the inherent structure of KIr4O8 nanowires directly participates in the catalytic process for favoring the OER. Density functional theory calculation results further suggest that the enhanced proximity between Ir (d) and O (p) band center in KIr4O8 can strengthen the covalence of Ir-O, facilitate the electron transfer between adsorbents and active sites, and decrease the energy barrier of rate-determining step from OH* to O* during the OER.

Multidimensional Electrochemistry Decodes the Operando Mechanism of Hydrogen Oxidation

Being an efficient approach to the utilization of hydrogen energy, the hydrogen oxidation reaction (HOR) is of particular significance in the current carbon-neutrality time. Yet the mechanistic picture of the HOR is still blurred, mostly because the elemental steps of this reaction are rapid and highly entangled, especially when deviating from the thermodynamic equilibrium state. Here we report a strategy for decoding the HOR mechanism under operando conditions. In addition to the wide-potential-range I-V curves obtained using gas diffusion electrodes, we have applied the AC impedance spectroscopy to provide independent and complementary kinetic information. Combining multidimensional data sources has enabled us to fit, in mathematical rigor, the core kinetic parameter set in a 5-D data space. The reaction rate of the three elemental steps (Tafel, Heyrovsky, and Volmer reactions), as a function of the overpotential, can thus be distilled individually. Such an undocumented kinetic picture unravels, in detail, how the HOR is controlled by the elemental steps on polarization. For instance, at low polarization region, the Heyrovsky reaction is relatively slow and can be ignored; but at high polarization region, the Heyrovsky reaction will surpass the Tafel reaction. Additionally, the Volmer reaction has been the fastest within overpotentials of interest. Our findings not only offer a better understanding of the HOR mechanism, but also lay the foundation for the development of improved hydrogen energy utilization systems.

Atomically dispersed Iridium on Mo2C as an efficient and stable alkaline hydrogen oxidation reaction catalyst

Hydroxide exchange membrane fuel cells (HEMFCs) have the advantages of using cost-effective materials, but hindered by the sluggish anodic hydrogen oxidation reaction (HOR) kinetics. Here, we report an atomically dispersed Ir on Mo2C nanoparticles supported on carbon (IrSA-Mo2C/C) as highly active and stable HOR catalysts. The specific exchange current density of IrSA-Mo2C/C is 4.1 mA cm-2ECSA, which is 10 times that of Ir/C. Negligible decay is observed after 30,000-cycle accelerated stability test. Theoretical calculations suggest the high HOR activity is attributed to the unique Mo2C substrate, which makes the Ir sites with optimized H binding and also provides enhanced OH binding sites. By using a low loading (0.05 mgIr cm-2) of IrSA-Mo2C/C as anode, the fabricated HEMFC can deliver a high peak power density of 1.64 W cm-2. This work illustrates that atomically dispersed precious metal on carbides may be a promising strategy for high performance HEMFCs.

Oxygen Radical Coupling on Short-Range Ordered Ru Atom Arrays Enables Exceptional Activity and Stability for Acidic Water Oxidation

The discovery of efficient and stable electrocatalysts for oxygen evolution reaction (OER) in acid is vital for the commercialization of the proton-exchange membrane water electrolyzer. In this work, we demonstrate that short-range Ru atom arrays with near-ideal Ru-Ru interatomic distances and a unique Ru-O hybridization state can trigger direct O*-O* radical coupling to form an intermediate O*-O*-Ru configuration during acidic OER without generating OOH* species. Further, the Ru atom arrays suppress the participation of lattice oxygen in the OER and the dissolution of active Ru. Benefiting from these advantages, the as-designed Ru array-Co3O4 electrocatalyst breaks the activity/stability trade-off that plagues RuO2-based electrocatalysts, delivering an excellent OER overpotential of only 160 mV at 10 mA cm-2 in 0.5 M H2SO4 and outstanding durability during 1500 h operation, representing one of the best acid-stable OER electrocatalysts reported to date. 18O-labeled operando spectroscopic measurements together with theoretical investigations revealed that the short-range Ru atom arrays switched on an oxide path mechanism (OPM) during the OER. Our work not only guides the design of improved acidic OER catalysts but also encourages the pursuit of short-range metal atom array-based electrocatalysts for other electrocatalytic reactions.

Revealing the role of a bridging oxygen in a carbon shell coated Ni interface for enhanced alkaline hydrogen oxidation reaction

Encapsulating metal nanoparticles inside carbon layers is a promising approach to simultaneously improving the activity and stability of electrocatalysts. The role of carbon layer shells, however, is not fully understood. Herein, we report a study of boron doped carbon layers coated on nickel nanoparticles (Ni@BC), which were used as a model catalyst to understand the role of a bridging oxygen in a carbon shell coated Ni interface for the improvement of the hydrogen oxidation reaction (HOR) activity using an alkaline electrolyte. Combining experimental results and density functional theory (DFT) calculations, we find that the electronic structure of Ni can be precisely tailored by Ni-O-C and Ni-O-B coordinated environments, leading to a volcano type correlation between the binding ability of the OH* adsorbate and HOR activity. The obtained Ni@BC with a optimized d-band center displays a remarkable HOR performance with a mass activity of 34.91 mA mgNi-1, as well as superior stability and CO tolerance. The findings reported in this work not only highlight the role of the OH* binding strength in alkaline HOR but also provide guidelines for the rational design of advanced carbon layers used to coat metal electrocatalysts.

Enhancing photocatalytic H2O2 production with Au co-catalysts through electronic structure modification

Gold-based co-catalysts are a promising class of materials with potential applications in photocatalytic H2O2 production. However, current approaches with Au co-catalysts show limited H2O2 production due to intrinsically weak O2 adsorption at the Au site. We report an approach to strengthen O2 adsorption at Au sites, and to improve H2O2 production, through the formation of electron-deficient Auδ+ sites by modifying the electronic structure. In this case, we report the synthesis of TiO2/MoSx-Au, following selective deposition of Au onto a MoSx surface which is then further anchored onto TiO2. We further show that the catalyst achieves a significantly increased H2O2 production rate of 30.44 mmol g-1 h-1 in O2-saturated solution containing ethanol. Density functional theory calculations and X-ray photoelectron spectroscopy analysis reveal that the MoSx mediator induces the formation of electron-deficient Auδ+ sites thereby decreasing the antibonding-orbital occupancy of Au-Oads and subsequently enhancing O2 adsorption. This strategy may be useful for rationally designing the electronic structure of catalyst surfaces to facilitate artificial photosynthesis.

Graphitic Armor: A Natural Molecular Sieve for Robust Hydrogen Electroxidation

Carbon coating layers have been found to improve the catalytic performance of transition metals, which is usually explained as an outcome of electronic synergistic effect. Herein we reveal that the defective graphitic carbon, with a unique interlayer gap of 0.342 nm, can be a highly selective natural molecular sieve. It allows efficient diffusion of hydrogen molecules or radicals both along the in-plane and out-of-plane direction, but sterically hinders the diffusion of molecules with larger kinetic diameter (e.g., CO and O2) along the in-plane direction. As a result, poisonous species lager than 0.342 nm are sieved out, even when their adsorption on the metal is thermodynamically strong; at the same time, the interaction between H2 and the metal is not affected. This natural molecular sieve provides a very chance for constructing robust metal catalysts for hydrogen-relevant processes, which are more tolerant to chemical or electrochemical oxidation or CO-relevant poisoning.

CO-Tolerant Hydrogen Oxidation Electrocatalysts for Low-Temperature Hydrogen Fuel Cells

The severe performance degradation of low-temperature hydrogen fuel cells upon exposure to trace amounts of carbon monoxide (CO) impurities in reformate hydrogen fuels is one of the challenges that hinders their commercialization. Despite significant efforts that have been made, the CO-tolerance performance of electrocatalysts for the hydrogen oxidation reaction (HOR) is still unsatisfactory. This Perspective discusses the path forward for the rational design of CO-tolerant HOR electrocatalysts. The fundamentals of the CO-tolerant mechanisms on commercialized platinum group metal (PGM) electrocatalysts via either promoting CO electrooxidation or weakening CO adsorption are provided, and comprehensive discussions based on these strategies are presented with typical examples. Given the recent progress, some emerging strategies, including blocking CO diffusion with a barrier layer and developing non-PGM HOR catalysts, are also discussed. We conclude with a discussion of the strengths and limitations of these strategies along with the perspectives of the major challenges and opportunities for future research on CO-tolerant HOR electrocatalysts.

Symmetry-Broken Ru Nanoparticles with Parasitic Ru-Co Dual-Single Atoms Overcome the Volmer Step of Alkaline Hydrogen Oxidation

Efficient dual-single-atom catalysts are crucial for enhancing atomic efficiency and promoting the commercialization of fuel cells, but addressing the sluggish kinetics of hydrogen oxidation reaction (HOR) in alkaline media and the facile dual-single-atom site generation remains formidable challenges. Here, we break the local symmetry of ultra-small ruthenium (Ru) nanoparticles by embedding cobalt (Co) single atoms, which results in the release of Ru single atoms from Ru nanoparticles on reduced graphene oxide (Co1 Ru1,n /rGO). In situ operando spectroscopy and theoretical calculations reveal that the oxygen-affine Co atom disrupts the symmetry of ultra-small Ru nanoparticles, resulting in parasitic Ru and Co dual-single-atom within Ru nanoparticles. The interaction between Ru single atoms and nanoparticles forms effective active centers. The parasitism of Co atoms modulates the adsorption of OH intermediates on Ru active sites, accelerating HOR kinetics through faster formation of *H2 O. As anticipated, Co1 Ru1,n /rGO exhibits ultrahigh mass activity (7.68 A mgRu -1 ) at 50 mV and exchange current density (0.68 mA cm-2 ), which are 6 and 7 times higher than those of Ru/rGO, respectively. Notably, it also displays exceptional durability surpassing that of commercial Pt catalysts. This investigation provides valuable insights into hybrid multi-single-atom and metal nanoparticle catalysis.

Building Feedback-Regulation System Through Atomic Design for Highly Active SO2 Sensing

Reasonably constructing an atomic interface is pronouncedly essential for surface-related gas-sensing reaction. Herein, we present an ingenious feedback-regulation system by changing the interactional mode between single Pt atoms and adjacent S species for high-efficiency SO2 sensing. We found that the single Pt sites on the MoS2 surface can induce easier volatilization of adjacent S species to activate the whole inert S plane. Reversely, the activated S species can provide a feedback role in tailoring the antibonding-orbital electronic occupancy state of Pt atoms, thus creating a combined system involving S vacancy-assisted single Pt sites (Pt-Vs) to synergistically improve the adsorption ability of SO2 gas molecules. Furthermore, in situ Raman, ex situ X-ray photoelectron spectroscopy testing and density functional theory analysis demonstrate the intact feedback-regulation system can expand the electron transfer path from single Pt sites to whole Pt-MoS2 supports in SO2 gas atmosphere. Equipped with wireless-sensing modules, the final Pt1-MoS2-def sensors array can further realize real-time monitoring of SO2 levels and cloud-data storage for plant growth. Such a fundamental understanding of the intrinsic link between atomic interface and sensing mechanism is thus expected to broaden the rational design of highly effective gas sensors.

Tuning the apparent hydrogen binding energy to achieve high-performance Ni-based hydrogen oxidation reaction catalyst

High-performance platinum-group-metal-free alkaline hydrogen oxidation reaction catalysts are essential for the hydroxide exchange membrane fuel cells, which generally require high Pt loadings on the anode. Herein, we report a highly active hydrogen oxidation reaction catalyst, NiCuCr, indicated by the hydroxide exchange membrane fuel cell with a high peak power density of 577 mW cm-2 (18 times as high as the Ni/C anode) and a stability of more than 150 h (a degradation rate slower by 7 times than the Ni/C anode). The spectroscopies demonstrate that the alloy effect from Cu weakens the hydrogen binding, and the surface Cr2O3 species enhance the interfacial water binding. Both effects bring an optimized apparent hydrogen binding energy and thus lead to the high hydrogen oxidation reaction performance of NiCuCr. These results suggest that the apparent hydrogen binding energy determines the hydrogen oxidation reaction performance and that its tuning is beneficial toward high electrocatalytic performance.

A Highly-Efficient Boron Interstitially Inserted Ru Anode Catalyst for Anion Exchange Membrane Fuel Cells

Developing high-performance electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is crucial for the commercialization of anion exchange membrane fuel cells (AEMFCs). Here, boron interstitially inserted ruthenium (B-Ru/C) is synthesized and used as an anode catalyst for AEMFC, achieving a peak power density of 1.37 W cm-2 , close to the state-of-the-art commercial PtRu catalyst. Unexpectedly, instead of the monotonous decline of HOR kinetics with pH as generally believed, an inflection point behavior in the pH-dependent HOR kinetics on B-Ru/C is observed, showing an anomalous behavior that the HOR activity under alkaline electrolyte surpasses acidic electrolyte. Experimental results and density functional theory calculations reveal that the upshifted d-band center of Ru after the intervention of interstitial boron can lead to enhanced adsorption ability of OH and H2 O, which together with the reduced energy barrier of water formation, contributes to the outstanding alkaline HOR performance with a mass activity of 1.716 mA µgPGM -1 , which is 13.4-fold and 5.2-fold higher than that of Ru/C and commercial Pt/C, respectively.

Enhanced Hydroxyl Adsorption in Ultrathin NiO/Cr2 O3 In-Plane Heterostructures for Efficient Alkaline Methanol Oxidation Reaction

The exploration of advanced nickel-based electrocatalysts for alkaline methanol oxidation reaction (MOR) holds immense promise for value-added organic products coupled with hydrogen production, but still remain challenging. Herein, we construct ultrathin NiO/Cr2 O3 in-plane heterostructures to promote the alkaline MOR process. Experimental and theoretical studies reveal that NiO/Cr2 O3 in-plane heterostructures enable a favorable upshift of the d-band center and enhanced adsorption of hydroxyl species, leading to accelerated generation of active NiO(OH)ads species. Furthermore, ultrathin in-plane heterostructures endow the catalyst with good charge transfer ability and adsorption behavior of methanol molecules onto catalytic sites, contributing to the improvement of alkaline MOR kinetics. As a result, ultrathin NiO/Cr2 O3 in-plane heterostructures exhibit a remarkable MOR activity with a high current density of 221 mA cm-2 at 0.6 V vs Ag/AgCl, which is 7.1-fold larger than that of pure NiO nanosheets and comparable with other highly active catalysts reported so far. This work provides an effectual strategy to optimize the activity of nickel-based catalysts and highlights the dominate efficacy of ultrathin in-plane heterostructures in alkaline MOR.

Construction of Heterostructure between Ni17W3 and WO2 to Boost the Hydrogen Oxidation Reaction in Alkaline Medium

The inferior intrinsic performance of Ni-based catalysts for the hydrogen oxidation reaction (HOR) in an alkaline medium seriously restricts the utilization of emerging anion-exchange membrane fuel cells (AEMFCs). This is because the hydrogen and hydroxyl binding energies on Ni need to be optimized. Although electrocatalysts obtained by alloying Ni with Mo or W reportedly exhibit enhanced activity, they are still far from industrial requirements based on unbalanced HBE and OHBE. Herein, we report to further enhance alkaline HOR activity by constructing a heterostructure between NiW alloy and metal oxide (Ni17W3/WO2), which is synthesized through solvothermal treatment combined with annealing. The as-fabricated reduced graphene oxide (rGO)-supported Ni17W3/WO2 (Ni17W3/WO2/rGO) exhibits state-of-the-art catalytic activity (current density of 2.9 mA cm-2 at 0.1 V vs RHE), faster kinetics (geometric kinetics current density of 4.0 mA cm-2 that can be comparable to Pt/C), and high stability (maintaining the current density for more than 80 h) toward HOR in alkaline media. The detailed characterizations reveal that the charge transfer across the boundary arising from constructing the as-prepared heterostructure tunes the electronic structures, ultimately facilitating the HOR process.

Unveiling the Electrolyte Cations Dependent Kinetics on CoOOH-Catalyzed Oxygen Evolution Reaction

The electrolyte cations-dependent kinetics have been widely observed in many fields of electrocatalysis, however, the exact mechanism of the influence on catalytic performance is still a controversial topic of considerable discussion. Herein, combined with operando X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), we verify that the electrolyte cations could intercalate into the layer of pristine CoOOH catalyst during the oxygen evolution reaction (OER) process, while the bigger cations lead to enlarged interlayer spacing and increased OER activity, following the order Cs+ >K+ >Na+ >Li+ . X-ray absorption spectroscopy (XAS), in situ Raman, in situ Ultraviolet-visible (UV/Vis) spectroscopy, in situ XAS spectroscopy, cyclic voltammetry (CV), and theoretical calculations reveal that the intercalation of electrolyte cations efficiently modify the oxidation states of Co by enlarging the Co-O bonds, which in turn enhance the d-band center of Co, optimize the adsorption strength of oxygen intermediates, facilitate the formation of OER active Co(IV) species, and reduce the energy barrier of the rate-determing step (RDS), thereby enhancing the OER activity. This work not only provides an informative picture to understand the complicated dependence of OER kinetics on electrolyte cations, but also sheds light on understanding the mechanism of other electrolyte cation-targeted electrocatalysis.

High Flux and Stability of Cationic Intercalation in Transition-Metal Oxides: Unleashing the Potential of Mn t2g Orbital via Enhanced π-Donation

Transition-metal oxides (TMOs) often struggle with challenges related to low electronic conductivity and unsatisfactory cyclic stability toward cationic intercalation. In this work, we tackle these issues by exploring an innovative strategy: leveraging heightened π-donation to activate the t2g orbital, thereby enhancing both electron/ion conductivity and structural stability of TMOs. We engineered Ni-doped layered manganese dioxide (Ni-MnO2), which is characterized by a distinctive Ni-O-Mn bridging configuration. Remarkably, Ni-MnO2 presents an impressive capacitance of 317 F g-1 and exhibits a robust cyclic stability, maintaining 81.58% of its original capacity even after 20,000 cycles. Mechanism investigations reveal that the incorporation of Ni-O-Mn configurations stimulates a heightened π-donation effect, which is beneficial to the π-type orbital hybridization involving the O 2p and the t2g orbital of Mn, thereby accelerating charge-transfer kinetics and activating the redox capacity of the t2g orbital. Additionally, the charge redistribution from Ni to the t2g orbital of Mn effectively elevates the low-energy orbital level of Mn, thus mitigating the undesirable Jahn-Teller distortion. This results in a subsequent decrease in the electron occupancy of the π*-antibonding orbital, which promotes an overall enhancement in structural stability. Our findings pave the way for an innovative paradigm in the development of fast and stable electrode materials for intercalation energy storage by activating the low orbitals of the TM center from a molecular orbital perspective.

Catalytic Structure Design by AI Generating with Spectroscopic Descriptors

Generative artificial intelligence has depicted a beautiful blueprint for on-demand design in chemical research. However, the few successful chemical generations have only been able to implement a few special property values because most chemical descriptors are mathematically discrete or discontinuously adjustable. Herein, we use spectroscopic descriptors with machine learning to establish a quantitative spectral structure-property relationship for adsorbed molecules on metal monatomic catalysts. Besides catalytic properties such as adsorption energy and charge transfer, the complete spatial relative coordinates of the adsorbed molecule were successfully inverted. The spectroscopic descriptors and prediction models are generalized, allowing them to be transferred to several different systems. Due to the continuous tunability of the spectroscopic descriptors, the design of catalytic structures with continuous adsorption states generated by AI in the catalytic process has been achieved. This work paves the way for using spectroscopy to enable real-time monitoring of the catalytic process and continuous customization of catalytic performance, which will lead to profound changes in catalytic research.

Stabilizing Low-Valence Single Atoms by Constructing Metalloid Tungsten Carbide Supports for Efficient Hydrogen Oxidation and Evolution

Designing novel single-atom catalysts (SACs) supports to modulate the electronic structure is crucial to optimize the catalytic activity, but rather challenging. Herein, a general strategy is proposed to utilize the metalloid properties of supports to trap and stabilize single-atoms with low-valence states. A series of single-atoms supported on the surface of tungsten carbide (M-WCx , M=Ru, Ir, Pd) are rationally developed through a facile pyrolysis method. Benefiting from the metalloid properties of WCx , the single-atoms exhibit weak coordination with surface W and C atoms, resulting in the formation of low-valence active centers similar to metals. The unique metal-metal interaction effectively stabilizes the low-valence single atoms on the WCx surface and improves the electronic orbital energy level distribution of the active sites. As expected, the representative Ru-WCx exhibits superior mass activities of 7.84 and 62.52 A mgRu -1 for the hydrogen oxidation and evolution reactions (HOR/HER), respectively. In-depth mechanistic analysis demonstrates that an ideal dual-sites cooperative mechanism achieves a suitable adsorption balance of Had and OHad , resulting in an energetically favorable Volmer step. This work offers new guidance for the precise construction of highly active SACs.

Programmable Synthesis of High-Entropy Nanoalloys for Efficient Ethanol Oxidation Reaction

Controllable synthesis of nanoscale high-entropy alloys (HEAs) with specific morphologies and tunable compositions is crucial for exploring advanced catalysts. The present strategies either have great difficulties to tailor the morphology of nanoscale HEAs or suffer from narrow elemental distributions and insufficient generality. To overcome the limitations of these strategies, here we report a robust template-directed synthesis to programmatically fabricate nanoscale HEAs with controllable compositions and structures via independently controlling the morphology and composition of HEA. As a proof of concept, 12 kinds of nanoscale HEAs with controllable morphologies of zero-dimension (0D) nanoparticles, 1D nanowires, 2D ultrathin nanorings (UNRs), 3D nanodendrites, and vast elemental compositions combining five or more of Pd/Pt/Ag/Cu/Fe/Co/Ni/Pb/Bi/Sn/Sb/Ge are synthesized. Moreover, the as-prepared HEA-PdPtCuPbBiUNRs/C demonstrates the state-of-the-art electrocatalytic performance for the ethanol oxidation reaction, with 25.6- and 16.3-fold improvements in mass activity, relative to commercial Pd/C and Pt/C catalysts, respectively, as well as greatly enhanced durability. This work provides a myriad of nanoscale HEAs and a general synthetic strategy, which are expected to have broad impacts for the fields of catalysis, sensing, biomedicine, and even beyond.

Embedding oxophilic rare-earth single atom in platinum nanoclusters for efficient hydrogen electro-oxidation

Designing Pt-based electrocatalysts with high catalytic activity and CO tolerance is challenging but extremely desirable for alkaline hydrogen oxidation reaction. Herein we report the design of a series of single-atom lanthanide (La, Ce, Pr, Nd, and Lu)-embedded ultrasmall Pt nanoclusters for efficient alkaline hydrogen electro-oxidation catalysis based on vapor filling and spatially confined reduction/growth of metal species. Mechanism studies reveal that oxophilic single-atom lanthanide species in Pt nanoclusters can serve as the Lewis acid site for selective OH^- adsorption and regulate the binding strength of intermediates on Pt sites, which promotes the kinetics of hydrogen oxidation and CO oxidation by accelerating the combination of OH^- and *H/*CO in kinetics and thermodynamics, endowing the electrocatalyst with up to 14.3-times higher mass activity than commercial Pt/C and enhanced CO tolerance. This work may shed light on the design of metal nanocluster-based electrocatalysts for energy conversion.

Improving the Hydrogen Oxidation Reaction Rate of Ru by Active Hydrogen in the Ultrathin Pd Interlayer

Enhancing the catalytic activity of Ru metal in the hydrogen oxidation reaction (HOR) potential range, improving the insufficient activity of Ru caused by its oxophilicity, is of great significance for reducing the cost of anion exchange membrane fuel cells (AEMFCs). Here, we use Ru grown on Au@Pd as a model system to understand the underlying mechanism for activity improvement by combining direct in situ surface-enhanced Raman spectroscopy (SERS) evidence of the catalytic reaction intermediate (OH_ad) with in situ X-ray diffraction (XRD), electrochemical characterization, as well as DFT calculations. The results showed that the Au@Pd@Ru nanocatalyst utilizes the hydrogen storage capacity of the Pd interlayer to "temporarily" store the activated hydrogen enriched at the interface, which spontaneously overflows at the "hydrogen-deficient interface" to react with OH_ad adsorbed on Ru. It is the essential reason for the enhanced catalytic activity of Ru at anodic potential. This work deepens our understanding of the HOR mechanism and provides new ideas for the rational design of advanced electrocatalysts.

Mn-Incorporation-Induced Phase Transition in Bottom-Up Synthesized Colloidal Sub-1-nm Ni(OH)2 Nanosheets for Enhanced Oxygen Evolution Catalysis

Sub-1-nm structures are attractive for diverse applications owing to their unique properties compared to those of conventional nanomaterials. Transition-metal hydroxides are promising catalysts for oxygen evolution reaction (OER), yet there remains difficulty in directly fabricating these materials within the sub-1-nm regime, and the realization of their composition and phase tuning is even more challenging. Here we define a binary-soft-template-mediated colloidal synthesis of phase-selective Ni(OH)₂ ultrathin nanosheets (UNSs) with 0.9 nm thickness induced by Mn incorporation. The synergistic interplay between binary components of the soft template is crucial to their formation. The unsaturated coordination environment and favorable electronic structures of these UNSs, together with in situ phase transition and active site evolution confined by the ultrathin framework, enable efficient and robust OER electrocatalysis. They exhibit a low overpotential of 309 mV at 100 mA cm^-2 as well as remarkable long-term stability, representing one of the most high-performance noble-metal-free catalysts.

Heterostructural Ni-Ni0.2 Mo0.8 N Interface Engineering Boosts Alkaline Hydrogen Electrocatalysis

Exploring efficient and low-cost bifunctional catalysts for hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) is highly desirable for the achievement of unitized regenerative fuel cells. Herein, a facile method to prepare hetero-interfacial Ni-Ni_0.2 Mo_0.8 N nanosheets with tailored d-band for efficient alkaline hydrogen electrocatalysis is presented. Mechanism studies indicate that interface engineering can downshift the d-band center of Ni-Ni_0.2 Mo_0.8 N nanosheets due to the electron transfer from Ni to Ni_0.2 Mo_0.8 N, which weakens the binding strength of reaction intermediates, thereby boosting the catalytic performance. Relative to pure Ni, Ni-Ni_0.2 Mo_0.8 N nanosheets show a lower overpotential of 83 mV at -10 mA cm^-2 and good stability during 2,000 cycles for HER. Meanwhile, Ni-Ni_0.2 Mo_0.8 N nanosheets exhibit an improved exchange current density for HOR with a 10.2-fold enhancement in comparison with that of pure Ni. This work provides valuable insight into the reasonable design of efficient energy-related electrocatalysts based on the tailoring of d-band center by interface engineering.

Band engineering in heterostructure catalysts to achieve High-Performance Lithium-Oxygen batteries

The electronic structure of cathode catalysts dominates the electrochemistry reaction kinetics in lithium-oxygen batteries. However, conventional catalysts perform inferior intrinsic activity due to the low d-band level of the active sites makes it difficult to bond with the reaction intermediates, which results in poor electrochemical performance of lithium-oxygen batteries. Herein, NiFe₂O₄/MoS₂ heterostructures are elaborately constructed to reach an electronic state balance for the active sites, which realizes the upper shift of the d-band level and enhanced adsorption of intermediates. Density functional theory calculation suggests that the d-band center of Fe active sites on the heterostructure moves toward the Fermi level, demonstrating the heterointerface engineering endows Fe active sites with high d-band level by the transfer and balance of electron. As a proof of concept, lithium-oxygen battery catalyzed by NiFe₂O₄/MoS₂ exhibits a large specific capacity of 21526 mA h g^-1 and an extended cycle performance for 268 cycles. Moreover, NiFe₂O₄/MoS₂ with strong adsorption to intermediates promotes the uniform growth of discharge products, which is favor of the reversible decomposition during cycling. This work presents the energy band regulation of the active sites in heterostructure catalysts has great feasibility for enhancing catalytic activities.

Hydroxyl-Binding Energy-Induced Kinetic Gap Narrowing between Acidic and Alkaline Hydrogen Oxidation Reaction on Intermetallic Ru3 Sn7 Catalyst

Developing highly efficient catalysts toward alkaline hydrogen oxidation reaction (HOR) and narrowing the kinetic gap between acidic and alkaline electrolytes are of great importance for the practical application of alkaline exchange membrane fuel cell . Herein, ordered Ru₃ Sn₇ /C intermetallic compound has been developed for the HOR under alkaline and acidic conditions. The authors demonstrate that the ordered intermetallic Ru₃ Sn₇ /C shows much enhanced HOR activity, stability, and CO-tolerance compared with its disordered RuSn solid solution alloy counterpart. More importantly, the authors find that the kinetic gap of HOR between acidic and alkaline media is significantly narrowed in the as-synthesized intermetallic Ru₃ Sn₇ /C catalysts. Combined experiment results and theoretical calculations, the authors understand that promoted hydroxyl-binding energy on Ru₃ Sn₇ /C derived from the intermetallic-induced strong electron interaction is responsible for the accelerated alkaline HOR performance and narrowed kinetic gap.

Interface Metal Oxides Regulating Electronic State around Nickel Species for Efficient Alkaline Hydrogen Electrocatalysis

Heterogeneous electrocatalysis typically depends on the surface electronic states of active sites. Modulating the surface charge state of an electrocatalysts can be employed to improve performance. Among all the investigated materials, nickel (Ni)-based catalysts are the only non-noble-metal-based alternatives for both hydrogen oxidation and evolution reactions (HOR and HER) in alkaline electrolyte, while their activities should be further improved because of the unfavorable hydrogen adsorption behavior. Hereto, Ni with exceptional HOR electrocatalytic performance by changing the d-band center by metal oxides interface coupling formed in situ is endowed. The resultant MoO₂ coupled Ni heterostructures exhibit an apparent HOR activity, even approaching to that of commercial 20% Pt/C benchmark, but with better long-term stability in alkaline electrolyte. An exceptional HER performance is also achieved by the Ni-MoO₂ heterostructures. The experiment results are rationalized by the theoretical calculations, which indicate that coupling MoO₂ with Ni results in the downshift of d-band center of Ni, and thus weakens hydrogen adsorption and benefits for hydroxyl adsorption. This concept is further proved by other metal oxides (e.g., CeO₂ , V₂ O₃ , WO₃ , Cr₂ O₃ )-formed Ni-based heterostructures to engineer efficient hydrogen electrocatalysts.

The Role of Discrepant Reactive Intermediates on Ru-Ru2 P 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-Ru₂ P/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 H₂ O* 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.