Sulphur edge and vacancy assisted nitrogenphosphorus co- doped exfoliated tungsten disulfide: a superior electrocatalyst for hydrogen evolution reaction

Currently, transition metal disulfides are used as promising non-noble metal-based electrocatalysts for the hydrogen evolution reaction (HER) from water splitting in quest for alternative renewable and clean energy sources. In view of this, the present study reports the fabrication of N and P co-doped exfoliated tungsten disulphide (PNEWS2) as a superior electrocatalyst for HER. The high performance of PNEWS2 imparts a significantly low potential (59 mV), which corresponds to a geometrical current density of 10 mA cm(-2) and Tafel slope of 35 mV per decade. This could be attributed to the presence of highly active sites in the exfoliated single-layered porous 1T-WS2 network and synergistic effect of N and P doping. Furthermore, evaluation of durability tests suggested excellent stability of the PNEWS2 catalyst. Our multifaceted strategy for the formation of a flake-like 1T (metallic) phase with expanded interlayer spacings in the PNEWS2 catalyst compared with that in WS2 results in an increase in S active edges and presence of sulphur vacancies, facilitating extremely high electrochemically active surface area (C-dl = 37.1 mF cm(-2)) and high turnover frequency (0.791 s(-1)). Furthermore, the downshift in the d band, high lifetime (0.239 ms) and low Gibbs free energy (-0.26 eV) of PNEWS2 account for its excellent mass transport properties. We also established that the electrochemical performance of PNEWS2 is not associated with the dissolution/redeposition of platinum from the counter electrode (Pt). In summary, the superior performance of the nonprecious, promising N-P-co-doped WS2 provides an alternative substitute for Pt-based electrocatalysts.