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.     

Rational Design of Pt−Pd−Ni Trimetallic Nanocatalysts for Room-Temperature Benzaldehyde and Styrene Hydrogenation

Nanostructures of the multimetallic catalysts offer great scope for fine tuning of heterogeneous catalysis, but clear understanding of the surface chemistry and structures is important to enhance their selectivity and efficiency. Focussing on a typical Pt−Pd−Ni trimetallic system, we comparatively examined the Ni/C, Pt/Ni/C, Pd/Ni/C and Pt−Pd/Ni/C catalysts synthesized by impregnation and galvanic replacement reaction. To clarify surface chemical/structural effect, the Pt−Pd/Ni/C catalyst was thermally treated at X=200, 400 or 600 °C in a H₂ reducing atmosphere, respectively termed as Pt−Pd/Ni/C−X. The as-prepared catalysts were characterized complementarily by XRD, XPS, TEM, HRTEM, HS-LEIS and STEM-EDS elemental mapping and line-scanning. All the catalysts were comparatively evaluated for benzaldehyde and styrene hydrogenation. It is shown that the “PtPd alloy nanoclusters on Ni nanoparticles” (PtPd/Ni) and the synergistic effect of the trimetallic Pt−Pd−Ni, lead to much improved catalytic performance, compared with the mono- or bi- metallic counterparts. However, with the increase of the treatment temperature of the Pt−Pd/Ni/C, the catalytic performance was gradually degraded, which was likely due to that the favourable nanostructure of fine “PtPd/Ni” was gradually transformed to relatively large “PtPdNi alloy on Ni” (PtPdNi/Ni) particles, thus decreasing the number of noble metal (Pt and Pd) active sites on the surface of the catalyst. The optimum trimetallic structure is thus the as synthesised Pt−Pd/Ni/C. This work provides a novel strategy for the design and development of highly efficient and low-cost multimetallic catalysts, e. g. for hydrogenation reactions.     

Pd-Enriched-Core/Pt-Enriched-Shell High-Entropy Alloy with Face-Centred Cubic Structure for C1 and C2 Alcohol Oxidation

High-entropy alloy nanoparticles (HEA NPs) have aroused great interest globally with their unique electrochemical, catalytic, and mechanical properties, as well as diverse activity and multielement tunability for multi-step reactions. Herein, a facile low-temperature synthesis method at atmospheric pressure is employed to synthesize Pd-enriched-HEA-core and Pt-enriched-HEA-shell NPs with a single phase of face-centred cubic structure. Interestingly, the lattice of both Pd-enriched-HEA-core and Pt-enriched-HEA-shell enlarge during the formation process of HEA, with tensile strains included in the core and shell of HEA. The as-obtained PdAgSn/PtBi HEA NPs show excellent electrocatalytic activity and durability for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The specific (mass) activity of PdAgSn/PtBi HEA NPs for MOR is 4.7 mA cm⁻² (2874 mA mg_(Pd+Pt)⁻¹), about 1.7 (5.9) and 1.5 (4.8) times higher than that of commercial Pd/C and Pt/C catalysts, respectively. Additional to high-entropy effect, Pt sites and Pd sites on the interface of the HEA act synergistically to facilitate the multi-step process towards EOR. This study offers a promising way to find a feasible route for scalable HEA manufacturing with promising applications.     

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...     

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.     

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics

The key issue in the 5-hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co-doped Ni(OH)₂ support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm² at only 1.38 V. Compared to unmodified Ni(OH)₂, the Pd/NiCo achieved an 8.3-fold increase in peak current density. DFT calculations and in situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO₆ octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni³⁺−O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni³⁺−O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni³⁺−O.     

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.     

Atomically Dispersed Cobalt/Copper Dual-Metal Catalysts for Synergistically Boosting Hydrogen Generation from Formic Acid

The development of practical materials for (de)hydrogenation reactions is a prerequisite for the launch of a sustainable hydrogen economy. Herein, we present the design and construction of an atomically dispersed dual-metal site Co/Cu−N−C catalyst allowing significantly improved dehydrogenation of formic acid, which is available from carbon dioxide and green hydrogen. The active catalyst centers consist of specific CoCuN₆ moieties with double-N-bridged adjacent metal-N₄ clusters decorated on a nitrogen-doped carbon support. At optimal conditions the dehydrogenation performance of the nanostructured material (mass activity 77.7 L ⋅ g_metal⁻¹ ⋅ h⁻¹) is up to 40 times higher compared to commercial 5 % Pd/C. In situ spectroscopic and kinetic isotope effect experiments indicate that Co/Cu−N−C promoted formic acid dehydrogenation follows the so-called formate pathway with the C−H dissociation of HCOO* as the rate-determining step. Theoretical calculations reveal that Cu in the CoCuN₆ moiety synergistically contributes to the adsorption of intermediate HCOO* and raises the d-band center of Co to favor HCOO* activation and thereby lower the reaction energy barrier.     

Understanding the high activity of a nanostructured catalyst obtained by a deposit of Pd on Ni: first principle calculations

The catalytic activity of a 4 monolayer deposit of Pd on a Ni(110) surface toward the hydrogenation of ethylene is investigated by using gradient-corrected periodic density functional calculations. The Pd/Ni(110) surface is strongly nanostructured, due to the anisotropic stress induced by the Ni(110) substrate on the Pd layer. A kinetic analysis, based on the investigation of the optimal reaction pathway for the hydrogenation of ethylene to ethane, is presented, allowing a comparison between Pd/Ni(110) and pure Pd(110) surfaces. The calculated activation energies allow one to reproduce the experimental result, which shows that the Pd/Ni(110) surface is about 30 times more active than the pure Pd(110) surface. This marked increase of the catalytic activity is a consequence of the specific nanostructure of the Pd/Ni(110) surface. By examining the structure of the adsorbed species and of the transition states and by analyzing the electronic properties, we show that this rate increase can be associated to the fact that the ethylene adsorption energy in the first hydrogenation step and the ethyl-hydrogen coadsorption energy in the second step are both much lower on Pd/Ni(110) than on pure Pd(110).     

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.     

Adsorption and Decarbonylation Reaction of Furfural on the Pd(111) and M/Pd(111)(M=Ni,Cu and Ru) Surfaces

By performing with density functional theory(DFT) method, the detailed adsorption process and the catalytic decarbonylation mechanisms of furfural over Pd(111) and M/Pd(111)(M = Ni, Cu, Ru) surfaces toward furan were clarified. The results of atomic size factor, formation energy and d-band center showed that Ru/Pd(111) surface was the most stable and active. The adsorption energies of furfural on the different surfaces followed the order Ru/Pd(111) Cu/Pd(111) Pd(111) Ni/Pd(111). After analyzing Mulliken atomic charge population and the deformation density, we can find that on Ru/Pd(111) surface, the number of charge transfer was the most and the interaction was the strongest. Therefore, its adsorption energy was the highest. Furthermore, the furfural decarbonylation pathway is more kinetically feasible on bimetallic surface, and the reaction is the most likely to occur on Ru/Pd(111).     

Tuning the hydrogen and hydroxyl adsorption on Ru nanoparticles for hydrogen electrode reactions via size controlling

Controlling the particle size of catalyst to understand the active sites is the key to design efficient electrocatalysts toward hydrogen electrode reactions including hydrogen oxidation and evolution (HOR/HER). Herein, the hydrogen and hydroxyl adsorption on Ru/C could be effectively tuned for HOR/HER by simple controlling the particle sizes. It is found that the metallic Ru (Ru⁰) is the active site for HOR/HER, while oxidized Ru (Ru^x+) will hinder the adsorption and desorption of hydrogen on the catalyst. For the HOR, catalyst with small particles is more efficient, due to it is a three-phase interface reaction of gas on the surface of the catalyst. For the HER, the metallic state of Ru is crucial. The deconvolution of hydrogen peaks indicates that the catalytic sites with low hydrogen binding energy (HBE) shoulder the majority of the HOR activity. CO stripping curve further demonstrates that the stronger hydroxyl species (OH_ad) affinity is beneficial to promote the HOR performance. The results indicate that the design of efficient HOR/HER catalyst should focus on the balance between particle size and metallic states.     

Understanding the Reactivity of Supported Late Transition Metals on a Bare Anatase (101) Surface: A Periodic Conceptual DFT Investigation

The rapidly growing interest for new heterogeneous catalytic systems providing high atomic efficiency along with high stability and reactivity triggered an impressive progress in the field of single-atom catalysis. Nevertheless, unravelling the factors governing the interaction strength between the support and the adsorbed metal atoms remains a major challenge. Based on periodic density functional theory (DFT) calculations, this paper provides insight into the adsorption of single late transition metals on a defect-free anatase surface. The obtained adsorption energies fluctuate, with the exception of Pd, between −3.11 and −3.80 eV and are indicative of a strong interaction. Depending on the considered transition metal, we could attribute the strength of this interaction with the support to i) an electron transfer towards anatase (Ru, Rh, Ni), ii) s-d orbital hybridisation effects (Pt), or iii) a synergistic effect between both factors (Fe, Co, Os, Ir). The driving forces behind the adsorption were also found to be strongly related to Klechkowsky's rule for orbital filling. In contrast, the deviating behaviour of Pd is most likely associated with the lower dissociation enthalpy of the Pd−O bond. Additionally, the reactivity of these systems was evaluated using the Fermi weighted density of states approach. The resulting softness values can be clearly related to the electron configuration of the catalytic systems as well as with the net charge on the transition metal. Finally, these indices were used to construct a model that predicts the adsorption strength of CO on these anatase-supported d-metal atoms. The values obtained from this regression model show, within a 95 % probability interval, a correlation of 84 % with the explicitly calculated CO adsorption energies.     

Oxygen reduction reaction on carbon supported Palladium–Nickel alloys in alkaline media

Carbon supported Palladium–Nickel alloys with various compositions (Pd–Ni/C) were synthesized by chemical reduction of the co-precipitated Pd and Ni hydroxides on carbon. The structure of these alloys was characterized using X-ray diffraction (XRD) analysis. The catalytic activity of Pd–Ni/C for oxygen reduction reaction (ORR) in alkaline media was studied using a glassy carbon rotating disk electrode (RDE). Pd/C showed ORR activity close to that of Pt/C. The activities of Pd–Ni (3:1)/C and Pd–Ni (1:1)/C were found unchanged compared with that of Pd/C. Ni/C showed about 175 mV lower onset potential than Pt/C, and the activity of Pd–Ni (1:3)/C was observed to be between that of Pd/C and Ni/C.     

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.