Quenching as a Route to Defect-Rich Ru-Pyrochlore Electrocatalysts toward the Oxygen Evolution Reaction

Quenching-induced anion defects and precise Ru doping on Co3O4/CoN heterostructures for efficient overall water splitting performance

The difficulty of nitride modification is to develop simple and efficient strategies to induce defects and efficiently capture Ru atoms. With these in mind, this work innovatively constructed a Ru-Co3O4/CoN-L catalyst with abundant anion defects (oxygen vacancies (VO) and nitrogen vacancies (VN)) using the nitridation-quenching-Ru doping strategy. Surprisingly, the porous structure provided more active sites, and the VN and VO were conducive to promoting the anchoring of Ru atoms. These significantly improved the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances of the Ru-Co3O4/CoN/NF-L catalyst. The density functional theory results showed that the anion defects optimized the hydrogen adsorption capacity of the Ru active sites for the HER. Furthermore, Ru dopants and anion defects reduced the OER energy barrier of the Co-active sites, accelerating the HER and OER kinetics. This study proposes a new concept for defect construction and nitride-structure optimization.

Role of MoOx Surficial Modification in Enhancing the OER Performance of Ru-Pyrochlore

Pyrochlore ruthenate (Y₂ Ru₂ O_7-δ ) is highlighted as a promising oxygen evolution reaction (OER) catalyst for water splitting in polymer electrolyte membrane electrolyzers. However, an efficient electronic modulation strategy for Y₂ Ru₂ O_7-δ is required to overcome its electrochemical inertness. Herein, a surface manipulation strategy involving implanting MoO_x moieties on nano Y₂ Ru₂ O_7-δ (Mo-YRO) using wet chemical peroxone method is demonstrated. In contrast to electronic structure regulation by intramolecular charge transfer (i.e., substitutional strategies), the heterogeneous Mo-O-Ru micro-interfaces facilitate efficient intermolecular electron transfer from [RuO₆ ] to MoO_x . This eliminates the bandgap by inducing Ru 4d delocalization and band alignment rearrangement. The MoO_x modifiers also alleviate distortion of [RuO₆ ] by shortening Ru-O bond and enlarging Ru-O-Ru bond angle. This electronic and geometric structure tailoring enhances the OER performance, showing a small overpotential of 240 mV at 10 mA cm^-2 . Moreover, the electron-accepting MoO_x moieties provide more electronegative surfaces, which serve as a protective "fence" to inhibit the dissolution of metal ions, thereby stabilizing the electrochemical activity. This study offers fresh insights into the design of new-based pyrochlore electrocatalysts, and also highlights the versatility of surface engineering as a way of optimizing electronic structure and catalytic performance of other related materials.

Oxygen Evolution Electrocatalysts for the Proton Exchange Membrane Electrolyzer: Challenges on Stability

Hydrogen generated by proton exchange membrane (PEM) electrolyzer holds a promising potential to complement the traditional energy structure and achieve the global target of carbon neutrality for its efficient, clean, and sustainable nature. The acidic oxygen evolution reaction (OER), owing to its sluggish kinetic process, remains a bottleneck that dominates the efficiency of overall water splitting. Over the past few decades, tremendous efforts have been devoted to exploring OER activity, whereas most show unsatisfying stability to meet the demand for industrial application of PEM electrolyzer. In this review, systematic considerations of the origin and strategies based on OER stability challenges are focused on. Intrinsic deactivation of the material and the extrinsic balance of plant-induced destabilization are summarized. Accordingly, rational strategies for catalyst design including doping and leaching, support effect, coordination effect, strain engineering, phase and facet engineering are discussed for their contribution to the promoted OER stability. Moreover, advanced in situ/operando characterization techniques are put forward to shed light on the OER pathways as well as the structural evolution of the OER catalyst, giving insight into the deactivation mechanisms. Finally, outlooks toward future efforts on the development of long-term and practical electrocatalysts for the PEM electrolyzer are provided.

Tensile-Strained RuO2 Loaded on Antimony-Tin Oxide by Fast Quenching for Proton-Exchange Membrane Water Electrolyzer

Future energy demands for green hydrogen have fueled intensive research on proton-exchange membrane water electrolyzers (PEMWE). However, the sluggish oxygen evolution reaction (OER) and highly corrosive environment on the anode side narrow the catalysts to be expensive Ir-based materials. It is very challenging to develop cheap and effective OER catalysts. Herein, Co-hexamethylenetetramine metal-organic framework (Co-HMT) as the precursor and a fast-quenching method is employed to synthesize RuO2 nanorods loaded on antimony-tin oxide (ATO). Physical characterizations and theoretical calculations indicate that the ATO can increase the electrochemical surface areas of the catalysts, while the tensile strains incorporated by quenching can alter the electronic state of RuO2 . The optimized catalyst exhibits a small overpotential of 198 mV at 10 mA cm-2 for OER, and keeps almost unchanged after 150 h chronopotentiometry. When applied in a real PEMWE assembly, only 1.51 V is needed for the catalyst to reach a current density of 1 A cm-2 .