Abstract
Hydrogen is one of the most promising sustainable energy among numerous new energy resources. Electrocatalytic water splitting for H2 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/Co1-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.
Highlights
In the past decades, huge efforts have been dedicated to the substitution of precious metal catalysts with cheaper transition metal based materials
For the first time, we presented a facile one-step sulfurization/ carbonization approach to produce bimetallic tungsten-cobalt sulfide-based on heteroatom doped porous carbon (WS2/ Co1-xS@N, S co-doped porous carbon) nanocomposites utilizing the in-situ synthesized phosphotungstic acid (PTA)@Zeolitic imidazolate frameworks (ZIFs)-67 as precursors, where the PTA can provide abundant tungsten source, metal ion in ZIF-67 acts as cobalt source while the organic linker in ZIF-67 is the source of carbon substrate
3.1 Characterization of as-made PTA@Z67 PTA@Z67 hybrids were first synthesized through an in-situ self-assembly of 2
Summary
Huge efforts have been dedicated to the substitution of precious metal catalysts with cheaper transition metal based materials. The active site density of the catalyst can usually be increased by the formation of nanoscale structures or dispersion of the active components in highly porous supports,[8, 9] while the electronic conductivity of the catalyst can normally be enhanced via the combination of the catalytic active components with electronic conductive substrates such as carbon nanotubes, graphene and so on.[10, 11] On the other hand, cobalt sulfide is a typical kind of transition metal chalcogenide which is earth abundant and frequently exhibits good OER activities.[12] It is, anticipated that a composite containing cobalt sulfide and tungsten sulfide as well as conducting carbon substrate is potential bifunctional electrocatalysts towards both HER and OER Such a complex composite is difficult to generate via conventional material process methods, not to mention the desire of homogeneous nanostructures that could expose more catalytic active sites and enable better mass transport for the reactions of interest. The resulting bimetallic Co-W sulfides/porous carbon composites exhibit the prominent improvement in electrocatalytic activities towards both HER and OER, and show increased stability in electrocatalytic performance due to the effective prevention of the agglomeration of metal sulfide particles via the in-situ formed porous carbon matrix
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