Polyoxometallates@zeolitic-imidazolate-framework derived bimetallic tungsten-cobalt sulfide/porous carbon nanocomposites as efficient bifunctional electrocatalysts for hydrogen and oxygen evolution

Hydrogen is one of the most promising sustainable energy among numerous new energy resources. Electrocatalytic water splitting for H-2 generation is a clean and sustainable approach due to the use of widely existed water as resource. The searching for efficient and low-cost non-precious metal based electrocatalysts for water splitting, including both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), still remains a great challenge. In this work we report a simple method that utilizes the one-pot in-situ synthesized POMs@ZIFs (POMs = Polyoxometallates, ZIFs = Zeolitic imidazolate frameworks) as precursor for the production of WS2/Ca1-xS/N, S co-doped porous carbon nanocomposite as efficient electrocatalysts. These precursors POMs@ZIFs can effectively prevent the agglomeration of metal compound particles during heat treatment and lead to homogeneous dispersion of metal active sites within carbon matrix. The resulting bimetallic Co-W sulfide/heteroatom doped porous carbon composites show significant improvement in electrocatalytic activity towards both OER (Tafel slop of 53 mV dec(-1) with overpotential of 0.365 V @10 mA cm(-2) current density in 1 M KOH solution) and HER (Tafel slop of 64 mV dec(-1) with overpotential of -0.250 V @-10 mA cm(-2) current density in 0.5 M H2SO4 solution). This work opens up a new way to obtain low cost bifunctional electrocatalysts towards both OER and HER in water splitting. (C) 2019 The Authors. Published by Elsevier Ltd.