Optimizing nitrogen doping in graphene oxide for superior WS2-based hydrogen evolution catalysts

Abstract

The electrocatalytic performance of WS2 in the hydrogen evolution reaction (HER) can be significantly improved by employing graphene oxide (GO) as the substrate. Incorporating non-metals (such as N, S, P, etc.) into graphene oxide (GO) sheets has the potential to enhance the electrocatalytic activity even further. In this study, the initial step involved tuning GO through the doping of varying amounts of nitrogen (25, 35, and 45 w/w%), introduced from urea. Subsequently, WS2 was synthesized on nitrogen-doped reduced graphene oxide (NrGO) to create the WS2-NrGO nanocomposite using a two-step hydrothermal process. The formation of tuned NrGO was confirmed through FTIR, Raman, and SEM imaging techniques. The FTIR spectra validated the incorporation of nitrogen into GO, evidenced by the presence of pyridinic and pyrrolic nitrogen in all three NrGOs. Additionally, the intensity of these bonds increased with the rising amount of nitrogen doping. Raman analysis indicated that NrGOs exhibit a lower ID/IG ratio in comparison to GO, implying an enhancement in the size of C sp2 atom clusters due to the simultaneous reduction of GO. Voltammetry was employed to assess the electrocatalytic performance of the WS2- NrGO nanocomposite. The polarization curve shows that WS2- 35%NrGO exhibits the lowest overpotential of -382.65 mV at a current density of -10 mA cm-2 , along with the lowest Tafel slope of 105.01 mV dec-1 . WS2-35%NrGO exhibits the highest electrochemical active surface area (ECSA) of 63.5 cm2 . The findings suggest that an optimal nitrogen doping level of 35% into GO significantly improves the electrocatalytic activity for hydrogen evolution reactions.