Bifunctional Transition Metal Hydroxysulfides: Room-Temperature Sulfurization and Their Applications in Zn-Air Batteries

Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable metal-air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn-air batteries. By simply immersing Co-based hydroxide precursor into solution with high-concentration S2-, transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as-obtained Co-based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm(-2) OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half-wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co3FeS1.5(OH)(6) hydroxysulfides are employed in the air electrode for a rechargeable Zn-air battery with a small overpotential of 0.86 V at 20.0 mA cm(-2), a high specific capacity of 898 mAh g(-1), and a long cycling life, which is much better than Pt and Ir-based electrocatalyst in Zn-air batteries.