Ru nanoclusters confined on α/β cobalt hydroxide nanosheets as efficient bifunctional oxygen electrocatalysts for Zn–air batteries

Abstract

Rational regulation of the coordination environment of Ru active sites by employing layered transition metal hydroxides as the substrate could achieve high catalytic performance towards the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). However, it is still challenging to clarify the interactions between the Ru catalysts and the layered transition metal hydroxides in different phases and also to unveil the mechanism responsible for the boosted performance. Herein, we report novel Ru nanocluster-decorated few-layer Co(OH)₂ nanosheets, which are employed as a model to investigate the structure–property relationship between zero-dimensional (0D) noble metal catalysts and two-dimensional (2D) substrates toward electrochemical reactions. The obtained α-Co(OH)₂-Ru catalyst exhibits a very low potential difference (ΔE) of 0.557 V between the half-wave potential towards the ORR and the potential at 10 mA cm⁻² towards the OER, which is smaller than those of β-Co(OH)₂-Ru (0.614 V), α-Co(OH)₂ (0.774 V) and β-Co(OH)₂ (0.897 V). Density functional theory (DFT) calculations further reveal that the reaction energy barrier of the rate-determining step of α-Co(OH)₂-Ru is much smaller than those of β-Co(OH)₂-Ru and Ru, implying that the strong electronic interactions between Ru nanoclusters and layered α-Co(OH)₂ nanosheets contribute majorly to the enhanced catalytic performance. Furthermore, the optimized α-Co(OH)₂-Ru nanohybrid is employed as the air electrode to assemble rechargeable Zn–air batteries, which possesses a power density of 187.8 mW cm⁻² and a long-term durability of 400 cycles without obvious attenuation.