No abstract

High-efficient electrocatalysts are crucial for fuel cell applications; however, the whole cell performance is generally restricted by the anodic part because of the sluggish kinetics involved in the oxygen evolution reaction (OER) process. Herein, a hierarchical hollow (Co,Ni)­Se2@NiFe layered double hydroxide (LDH) nanocage was synthesized by deriving from the metal–organic framework (MOF) of ZIF-67. Concretely, it involves first fabrication of hollow rhombic (Co,Ni)­Se2 nanocages and then deposition of NiFe LDH nanosheets on the surface of nanocages. Notably, the incorporation of Ni into Co-based ZIF-67 (via ion-exchange) could tail the atomic arrangement of the MOF, exposing more additional active sites in the following selenization treatment. The as-synthesized (Co,Ni)­Se2@NiFe LDH demonstrates splendid OER performance with a small overpotential of 277 mV (to launch a current density of 10 mA cm–2), a small Tafel slope of 75 mV dec–1, and robust durability (a slight stability decay of 5.1% after 17 h of continuous test), not only surpassing the commercial RuO2 but also being comparable/superior to most reported nonprevious metal-based catalysts. Upon analysis, the outstanding OER performance is attributed to the optimized adsorption/desorption nature of iron and nickel/cobalt toward the oxygenated species and partial delocalization of spin status at the interface via the bridging O2–. This work represents a solid step toward exploration of advanced catalysts with deliberate experimental design and/or atom tailoring.

Real bifunctional electrocatalysts for hydrogen evolution reaction and oxygen evolution reaction have to be the ones that exhibit a steady configuration during/after reaction without irreversible structural transformation or surface reconstruction. Otherwise, they can be termed as “precatalysts” rather than real catalysts. Herein, through a strongly atomic metal–support interaction, single-atom dispersed catalysts decorating atomically dispersed Ru onto a nickel–vanadium layered double hydroxide (LDH) scaffold can exhibit excellent HER and OER activities. Both in situ X-ray absorption spectroscopy and operando Raman spectroscopic investigation clarify that the presence of atomic Ru on the surface of nickel–vanadium LDH is playing an imperative role in stabilizing the dangling bond-rich surface and further leads to a reconstruction-free surface. Through strong metal–support interaction provided by nickel–vanadium LDH, the significant interplay can stabilize the reactive atomic Ru site to reach a small fluctuation in oxidation state toward cathodic HER without reconstruction, while the atomic Ru site can stabilize the Ni site to have a greater structural tolerance toward both the bond constriction and structural distortion caused by oxidizing the Ni site during anodic OER and boost the oxidation state increase in the Ni site that contributes to its superior OER performance. Unlike numerous bifunctional catalysts that have suffered from the structural reconstruction/transformation for adapting the HER/OER cycles, the proposed Ru/Ni3V-LDH is characteristic of steady dual reactive sites with the presence of a strong metal–support interaction (i.e., Ru and Ni sites) for individual catalysis in water splitting and is revealed to be termed as a real bifunctional electrocatalyst.