Amorphous MoSx developed on Co(OH)2 nanosheets generating efficient oxygen evolution catalysts

Abstract

Exploration of high-efficiency and inexpensive electrocatalysts for the oxygen evolution reaction (OER) is of great importance for the design of renewable energy storage and conversion devices. Herein, we prepared amorphous MoS_x-encapsulated Co(OH)₂ nanosheets (aMoS_x/Co(OH)₂ NSs) as strongly robust and active OER electrocatalysts via a three-step procedure: first, Co(OH)₂ nanosheets with catalytically active octahedral MO₆ structures were synthesized by the hydrothermal process; second, violent ultrasonication was applied to exfoliate individual nanosheets from stacked Co(OH)₂ sheets and break them down into smaller sheets and attach MoS₄²⁻ ions uniformly on the nanosheets; third, MoS₄²⁻ ions were thermally decomposed into amorphous MoS_x on the Co(OH)₂ nanosheets. The role of the incorporation of the amorphous MoS_x nanostructure was to enhance the surface hydrophilicity for the availability of H₂O and accelerate the electron transport capability for kinetic activities. Furthermore, the interaction between MoS_x and Co(OH)₂ is proposed to induce electron transfer from amorphous MoS_x to Co(OH)₂, which will promote the basic environment for cobalt sites, break the Co–O bond, favor the release of O₂ molecules, and thus enhance the OER process. Optimization of the Co/Mo molar ratio demonstrated that aMoS_x/Co(OH)₂ NSs with the Co/Mo molar ratio of 8 had the best OER activity and delivered the overpotential of 350 mV at the current density of 10 mA cm⁻² and the Tafel slope of 65.4 mV dec⁻¹ in 0.1 M KOH. This study enriches the research on non-first-row (3d) metal incorporation for high-efficient OER catalysts and offers an alternative to noble metal catalysts.