Ru Colloidosome Catalysts for the Hydrogen Oxidation Reaction in Alkaline Media

Crystalline-dependent surface reconstruction at low applied potential region for enhanced oxygen evolution reaction

Alkaline water electrolysis is apreferred technology for large-scale green hydrogen production. For most active transition metal-based catalysts during anodic oxygen evolution reaction (OER), the atomic structure of the anodic catalysts' surface often undergoes reconstruction to optimize the reaction path and enhance their catalytic activity. The design and maintenance of highly active sites during this reconstruction process remain critical and challenging for most OER catalysts. In this study, we explored the effects of crystal structures in pre-catalysts on surface reconstruction at low applied potential. Through experimental observation and theoretical calculation, we found out that catalysts with specific crystal structures exhibit superior surface remodeling ability, which enables them to better adapt to the conditions of the oxygen evolution reaction and achieve efficient catalysis. The discharge process enables the formation of abundant phosphorus vacancies on the surface, which in turn affects the efficiency of the entire oxygen evolution reaction. The optimized crystal structure of the catalyst results in an increase as high as 58.5 mA/cm2 for Ni5P4, which is twice as high as that observed for Ni2P. These results provide essential theoretical foundations and technical guidance for designing more efficient catalysts for oxygen evolution reactions.

In-Situ Derived Defective Ru Particles Anchored on Ru-Ni Layered Double Hydroxides for Enhanced Alkaline Hydrogen Evolution

Developing active, stable, and cost-efficient electrocatalysts to replace platinum for the alkaline hydrogen evolution reaction (HER) is highly desirable yet represents a great challenge. Here, it is reported on a facile one-pot synthesis of RuxNi layered double hydroxides (RuxNi-LDHs) that exhibit remarkable HER activity and stability after an in-situ activation treatment, surpassing most state-of-the-art Ru-based catalysts as well as commercial Ru/C and Pt/C catalysts. The structural and chemical changes triggered by in-situ activation are systematically investigated, and the results clearly show that the pristine, less-active RuxNi-LDHs are transformed into a highly active catalyst characterized by raft-like, defect-rich Ru° particles decorated on the surface of RuxNi-LDHs. Density functional theory (DFT) calculations reveal that the defective Ru sites can effectively optimize the reaction pathway and lower the free energies of the elemental steps involved, leading to enhanced intrinsic activity. This work highlights the importance of the currently understudied strategy of defect engineering in boosting the HER activity of Ru-based catalysts and offers an effective approach involving in-situ electrochemical activation for the development of high-performance alkaline HER catalysts.

Regulation of hydrogen binding energy via oxygen vacancy enables an efficient trifunctional Rh-Rh2O3 electrocatalyst for fuel cells and water splitting

Developing multi-functional electrocatalysts is of great practical significance for fuel cells and water splitting. Herein, Rh-Rh2O3 nanoclusters are prepared and the surface oxygen vacancy content is regulated elaborately by post-treatment. The optimized Rh-Rh2O3/C-400 exhibits superior trifunctional catalytic activity for hydrogen oxidation reaction (HOR), hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), i.e., the mass activity for HOR is 2.29 mA μgRh-1, and the overpotential for HER and HzOR at 10 mA cm-2 is as low as 12 mV and 31 mV, respectively, superior to the benchmark Pt/C. Rh-Rh2O3/C-400 also displays promising performance in practical devices, with the H2-O2 anion-exchange-membrane fuel cell delivering a peak power density of 0.66 W cm-2, and the hydrazine-assisted water splitting electrolyzer requiring a low electrolysis voltage of 0.161 V at 0.1 A cm-2. The experimental and theoretical investigations discover that the hydrogen binding energy (HBE) is linearly depended on surface oxygen vacancy contents, and the HBE directly determines the catalytic activity for HOR, HER and HzOR. This work not only innovates an efficient Rh-based nanocluster tri-functional electrocatalyst, but also eludicates the intrinsic relationship of surface structure-intermediate adsorption-catalytic activity.

Porous Ruthenium-Tungsten-Zinc Nanocages for Efficient Electrocatalytic Hydrogen Oxidation Reaction in Alkali

With the rapid development of anion exchange membrane technology and the availability of high-performance non-noble metal cathode catalysts in alkaline media, the commercialization of anion exchange membrane fuel cells has become feasible. Currently, anode materials for alkaline anion-exchange membrane fuel cells still rely on platinum-based catalysts, posing a challenge to the development of efficient low-Pt or Pt-free catalysts. Low-cost ruthenium-based anodes are being considered as alternatives to platinum. However, they still suffer from stability issues and strong oxophilicity. Here, we employ a metal-organic framework compound as a template to construct three-dimensional porous ruthenium-tungsten-zinc nanocages via solvothermal and high-temperature pyrolysis methods. The experimental results demonstrate that this porous ruthenium-tungsten-zinc nanocage with an electrochemical surface area of 116 m2 g-1 exhibits excellent catalytic activity for hydrogen oxidation reaction in alkali, with a kinetic density 1.82 times and a mass activity 8.18 times higher than that of commercial Pt/C, and a good catalytic stability, showing no obvious degradation of the current density after continuous operation for 10,000 s. These findings suggest that the developed catalyst holds promise for use in alkaline anion-exchange membrane fuel cells.

Unveiling the nature of Pt-induced anti-deactivation of Ru for alkaline hydrogen oxidation reaction

While Ru owns superior catalytic activity toward hydrogen oxidation reaction and cost advantages, the catalyst deactivation under high anodic potential range severely limits its potential to replace the Pt benchmark catalyst. Unveiling the deactivation mechanism of Ru and correspondingly developing protection strategies remain a great challenge. Herein, we develop atomic Pt-functioned Ru nanoparticles with excellent anti-deactivation feature and meanwhile employ advanced operando characterization tools to probe the underlying roles of Pt in the anti-deactivation. Our studies reveal the introduced Pt single atoms effectively prevent Ru from oxidative passivation and consequently preserve the interfacial water network for the critical H* oxidative release during catalysis. Clearly understanding the deactivation nature of Ru and Pt-induced anti-deactivation under atomic levels could provide valuable insights for rationally designing stable Ru-based catalysts for hydrogen oxidation reaction and beyond.

N-Coordinated Iridium-Molybdenum Dual-Atom Catalysts Enabling Efficient Bifunctional Hydrogen Electrocatalysis

Achieving effective hydrogen evolution/oxidation reaction (HER/HOR) across a wide pH span is of critical importance in unlocking the full potential of hydrogen energy but remains intrinsically challenging. Here, we engineer the N-coordinated Ir-Mo dual atoms on a carbon matrix by ultrafast high-temperature sintering, creating an efficient bifunctional electrocatalyst for both HER and HOR in both acidic and alkaline electrolytes. The optimized catalyst, Ir-Mo DAC/NC, demonstrates exceptional performance, with a significantly reduced HER overpotential of 11.3 mV at 10 mA/cm2 and a HOR exchange current (i0,m) of 3972 mA/mgIr in acidic conditions, surpassing the performance of Pt/C and Ir/C catalysts. In alkaline conditions, Ir-Mo DAC/NC also outperforms Pt/C, as evidenced by its low HER overpotential of 23 mV at 10 mA/cm2 and a high i0,m of 1308 mA/mgIr. Furthermore, our catalyst exhibits remarkable stability in both acidic and alkaline environments. DFT calculations results reveal that the superior electrochemical performance of Ir-Mo DAC/NC arises from the electronic synergy between Ir and Mo pairs, which regulates the interaction between the intermediates and active sites. These findings present a promising strategy for the development of dual-atom catalysts (DACs), with potential applications in the polymer fuel cells and water electrolyzers.

Boosting Alkaline Hydrogen Oxidation Activity of Ru Single-Atom Through Promoting Hydroxyl Adsorption on Ru/WC1- x Interfaces

The sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline conditions continue to pose a significant challenge for the practical implementation of anion-exchange membrane fuel cells. Developing single-atom catalysts can accelerate the pace of new HOR catalyst discovery for highly cost-effective and active HOR performance. However, single-atom catalysts (SACs) for the alkaline HOR have rarely been reported, and fundamental studies on the rational design of SACs are still required. Herein, the design of Ru SAC supported on the tungsten carbide (Ru SA/WC1- x ) via in situ high-temperature annealing strategy is reported. The resulting Ru SA/WC1- x catalyst exhibits remarkably enhanced HOR performance in alkaline media, a level of activity that can not be achieved with carbon-supported Ru SAC. Electrochemical results and density functional theory demonstrate that promoting the hydroxyl adsorption on Ru SA/WC1- x interfaces, which is derived from the low potential of zero charge of WC1- x support, has a significant effect on enhancing the HOR performance of SACs. This enhancement leads to 5.8 and 60.1 times higher Ru mass activity of Ru SA/WC1- x than Ru nanoparticles on carbon and Ru single-atom on N-doped carbon, respectively. This work provides new insights into the design of highly active SACs for alkaline HOR.

Nanotip-Induced Electric Field for Hydrogen Catalysis

Local electric field induced by the lightning-rod effect attracts great attention for regulating the local microenvironment and electronic properties of active sites. Nevertheless, local electric-field-assisted applications are mainly limited to metals with strong surface plasmonic resonance properties (e.g., Au, Ag, and Cu). Herein, we fabricate RuCu snow-like nanosheets (SNSs) with high-curvature nanotips for enhancing the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER). Theoretical simulations show that RuCu SNSs can induce a strong local electric field around the sharp nanotips, which favors the accumulation of OH- for HOR and H+ for HER. Cu incorporation can modulate the binding strength of OH* and H*, leading to significantly enhanced HOR and HER performance. Impressively, the mass activity of RuCu SNSs for alkaline HOR is 31.3 times higher than that of RuCu nanocrystals without sharp tips. Besides, the required overpotential for reaching 10 mA cm-2 during HER over RuCu SNSs is 14.0 mV.

Directional electronic tuning of Ni nanoparticles by interfacial oxygen bridging of support for catalyzing alkaline hydrogen oxidation

Metallic nickel (Ni) is a promising candidate to substitute Pt-based catalysts for hydrogen oxidation reaction (HOR), but huge challenges still exist in precise modulation of the electronic structure to boost the electrocatalytic performances. Herein, we present the use of single-layer Ti3C2Tx MXene to deliberately tailor the electronic structure of Ni nanoparticles via interfacial oxygen bridges, which affords Ni/Ti3C2Tx electrocatalyst with exceptional performances for HOR in an alkaline medium. Remarkably, it shows a high kinetic current of 16.39 mA cmdisk-2 at the overpotential of 50 mV for HOR [78 and 2.7 times higher than that of metallic Ni and Pt/C (20%), respectively], also with good durability and CO antipoisoning ability (1,000 ppm) that are not available for conventional Pt/C (20%) catalyst. The ultrahigh conductivity of single-layer Ti3C2Tx provides fast transmission of electrons for Ni nanoparticles, of which the uniform and small sizes endow them with high-density active sites. Further, the terminated -O/-OH functional groups on Ti3C2Tx directionally capture electrons from Ni nanoparticles via interfacial Ni-O bridges, leading to obvious electronic polarization. This could enhance the Nids-O2p interaction and weaken Nids-H1s interaction of Ni sites in Ni/Ti3C2Txenabling a suitable H-/OH-binding energy and thus enhancing the HOR activity.

Carbon-Doped Nickle Via a Fast Decarbonization Route for Enhanced Hydrogen Oxidation Reaction in Alkaline Media

Nickel (Ni) based materials with non-metal heteroatom doping are competitive substitutes for platinum group catalyst toward alkaline hydrogen oxidation reaction (HOR). However, the incorporation of non-metal atom into the lattice of conventional fcc phase Ni can easily trigger a structural phase transformation, forming hcp phase nonmetallic intermetallic compounds. Such tangle phenomenon makes it difficult to uncover the relationship between HOR catalytic activity and doping effect on fcc phase Ni. Herein, taking trace carbon doped Ni (C-Ni) nanoparticles as an example, a new nonmetal doped Ni nanoparticles synthesized by a simple fast decarbonization route using Ni3 C as precursor is presented, which provides an ideal platform to study the structure-activity relationship between alkaline HOR performance and non-metal doping effect toward fcc phase Ni. The obtained C-Ni exhibits an enhanced alkaline HOR catalytic activity compared with pure Ni, approaching to commercial Pt/C. X-ray absorption spectroscopy confirms that the trace carbon doping can modulate the electronic structure of conventional fcc phase nickel. Besides, theoretical calculations suggest that the introducing of C atoms can effectively regulate the d-band center of Ni atoms, resulting in the optimized hydrogen absorption, thereby improving the HOR activity.

Enriched Fe Doped on Amorphous Shell Enable Crystalline@Amorphous Core-Shell Nanorod Highly Efficient Electrochemical Water Oxidation

The rational design of efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER) with sluggish kinetics, is imperative to diverse clean energy technologies. The performance of electrocatalyst is usually governed by the number of active sites on the surface. Crystalline/amorphous heterostructure has exhibited unique properties and opens new paradigms toward designing electrocatalysts with abundant active sites for improved performance. Hence, Fe doped Ni-Co phosphite (Fe-NiCoHPi) electrocatalyst with cauliflower-like structure, comprising crystalline@amorphous core-shell nanorod, is reported. The experiments uncover that Fe is enriched in the amorphous shell due to the flexibility of the amorphous component. Further density functional theory calculations indicate that the strong electronic interaction between the enriched Fe in the amorphous shell and crystalline core host at the core-shell interface, leads to balanced binding energies of OER intermediates, which is the origin of the catalyst-activity. Eventually, the Fe-NiCoHPi exhibits remarkable activity, with low overpotentials of only 206 and 257 mV at current density of 15 and 100 mA cm-2 . Unceasing durability over 90 h is achieved, which is superior to the effective phosphate electrocatalysts. Although the applications at high current remain challenges , this work provides an approach for designing advanced OER electrocatalysts for sustainable energy devices.

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.

Kinetic-Modulated Crystal Phase of Ru for Hydrogen Oxidation

Crystal-phase-engineering provides a powerful strategy for regulating the catalytic performance yet remains great challenge. Herein, the kinetic-modulated crystal-phase-control of Ru nanosheet assemblies (Ru NAs) is demonstrated by simply altering the concentration of citric acid (CA). Detailed experimental results reveal that high concentration of CA retards the growth kinetics and thus leads to the formation of metastable face-centered cubic (fcc) Ru NAs, while low concentration of CA results in the fast growth kinetics and the preferential formation of Ru NAs with stable hexagonal close packed (hcp) phase. Moreover, Ru NAs with different phases are used as catalyst for hydrogen oxidation reaction (HOR) to evaluate the effects of crystal phase on catalytic performance. Impressively, Ru NAs with fcc phase display a mass activity of 2.75 A mg_Ru ^-1 at 50 mV, which is much higher than those of Ru NAs with fcc/hcp (1.02 A mg_Ru ^-1 ) and hcp (0.74 A mg_Ru ^-1 ) phases. Theoretical calculations show that fcc Ru NAs display weaker adsorption toward ^* H and lower energy barrier toward the rate-determining step (RDS) during HOR. This work provides a facile strategy for regulating the crystal phase of Ru nanocrystals, which may attract rapid interests of researchers in materials, chemistry, and catalysis.

Tuning Electron Transfer in Atomic-Scale Pt-Supported Catalysts for the Alkaline Hydrogen Oxidation Reaction

Developing efficient atomic-scale metal-supported catalysts is of great significance for energy conversion technologies. However, the precise modulation of electron transfer between the metal and supporter in atomic-scale metal-supported catalysts to further improve the catalytic activity is still a major challenge. Herein, we show tunable electron transfer between atomic-scale Pt and tungsten nitride/oxide supports (namely, Pt/WN and Pt/W₁₈O₄₉). Pt/WN with modest electron exchange and Pt/W₁₈O₄₉ with aggressive electron exchange exhibit notably different catalytic activities for the alkaline hydrogen oxidation reaction (HOR), in which Pt/WN shows a 5.7-fold enhancement in HOR intrinsic catalytic performance in comparison to Pt/W₁₈O₄₉. Additionally, the tunable electronic transfer at the interface of Pt/WN and Pt/W₁₈O₄₉, as proven by the theoretical calculation, resulted in the discrepancy of the adsorption free energy of the reaction intermediates, as well as catalytic activity, for the HOR process. Our work provides new insights into the design of advanced atomic-scale metal-supported catalysts for electrocatalysis.

Ligand Hybridization for Electro-reforming Waste Glycerol into Isolable Oxalate and Hydrogen

The electro-reforming of glycerol is an emerging technology of simultaneous hydrogen production and biomass valorization. However, its complex reaction network and limited catalyst tunability restrict the precise steering toward high selectivity. Herein, we incorporated the chelating phenanthrolines into the bulk nickel hydroxide and tuned the electronic properties by installing functional groups, yielding tunable selectivity toward formate (max 92.7 %) and oxalate (max 45.3 %) with almost linear correlation with the Hammett parameters. Further combinatory study of intermediate analysis and various spectroscopic techniques revealed the electronic effect of tailoring the valence band that balances between C-C cleavage and oxidation through the key glycolaldehyde intermediate. A two-electrode electro-reforming setup using the 5-nitro-1,10-phenanthroline-nickel hydroxide catalyst was further established to convert crude glycerol into pure H₂ and isolable sodium oxalate with high efficiency.

Facet Control of Nickel Nitride Nano-Framework for Efficient Hydrogen Evolution Electrocatalysis via Auxiliary Cooling Assisted Plasma Engineering

The precise facet modulation of transition metal nitrides (TMNs) has been regarded as an essential issue in boosting electrocatalytic H₂ production. Compared to thermal nitridation, the plasma technique serves as a favorable alternative to directly achieve TMNs, but the apparent surface heating effect during plasma treatment inevitably causes the thermally stabilized nitride formation, resulting in the deterioration of the highly reactive facet. To optimize the hydrogen evolution reaction (HER) behavior, an auxiliary cooling assisted plasma system to selectively expose Ni₃ N (2-10) with favorable activity by controlling surface heating during plasma nitridation is designed. The resultant nickel nitride (cp-Ni₃ N) nano-framework delivers exceptional catalytic performance, evidenced by its low overpotential of 58 and 188 mV at the current density of 10 and 100 mA cm^-2 for HER, in stark comparison with that of normal plasma and thermally fabricated Ni₃ N. Operando plasma diagnostics along with numerical simulation further confirm the effect of surface heating on typical plasma parameters as well as the Ni₃ N nanostructure, indicating the key factor responsible for the high-performance nitride electrocatalyst.

Reconstruction of Highly Dense Cu−N 4 Active Sites in Electrocatalytic Oxygen Reduction Characterized by Operando Synchrotron Radiation

The emerging star of single atomic site (SAS) catalyst has been regarded as the most promising Pt-substituted electrocatalyst for oxygen reduction reaction (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the metal loading in SAS directly affects the whole device performance. Herein, we report a dual nitrogen source coordinated strategy to realize high dense Cu-N₄ SAS with a metal loading of 5.61 wt% supported on 3D N-doped carbon nanotubes/graphene structure wherein simultaneously performs superior ORR activity and stability in alkaline media. When applied in H₂ /O₂ AEMFC, it could reach an open-circuit voltage of 0.90 V and a peak power density of 324 mW cm^-2 . Operando synchrotron radiation analyses identify the reconstruction from initial Cu-N₄ to Cu-N₄ /Cu-nanoclusters (NC) and the subsequent Cu-N₃ /Cu-NC under working conditions, which gradually regulate the d-band center of central metal and balance the Gibbs free energy of *OOH and *O intermediates, benefiting to ORR activity.