Nano-Au-decorated hierarchical porous cobalt sulfide derived from ZIF-67 toward optimized oxygen evolution catalysis: Important roles of microstructures and electronic modulation

Enhancing both the number of active sites available and the intrinsic activity of Co-based electrocatalysts simultaneously is a desirable goal. Herein, a ZIF-67-derived hierarchical porous cobalt sulfide decorated by Au nanoparticles (NPs) (denoted as HP-Au@Co x S y @ZIF-67) hybrid is synthesized by low-temperature sulfuration treatment. The well-defined macroporous–mesoporous–microporous structure is obtained based on the combination of polystyrene spheres, as-formed Co x S y nanosheets, and ZIF-67 frameworks. This novel three-dimensional hierarchical structure significantly enlarges the three-phase interfaces, accelerating the mass transfer and exposing the active centers for oxygen evolution reaction. The electronic structure of Co is modulated by Au through charge transfer, and a series of experiments, together with theoretical analysis, is performed to ascertain the electronic modulation of Co by Au. Meanwhile, HP-Au@Co x S y @ZIF-67 catalysts with different amounts of Au were synthesized, wherein Au and NaBH 4 reductant result in an interesting “competition effect” to regulate the relative ratio of Co 2+ /Co 3+ , and moderate Au assists the electrochemical performance to reach the highest value. Consequently, the optimized HP-Au@Co x S y @ZIF-67 exhibits a low overpotential of 340 mV at 10 mA cm –2 and a Tafel slope of 42 mV dec –1 for OER in 0.1 M aqueous KOH, enabling efficient water splitting and Zn–air battery performance. The work here highlights the pivotal roles of both microstructural and electronic modulation in enhancing electrocatalytic activity and presents a feasible strategy for designing and optimizing advanced electrocatalysts.