Mechanistic insights into the promotional effect of Ni substitution in non-noble metal carbides for highly enhanced water splitting

Real time mechanistic analyses through operando studies reveals that the synergistic electronic interactions through in-situ charge transfer between Ni and active centres of WC/MoC@NGC catalysts promotes the overall water splitting activity and stability. [Display omitted] •Ni-substituted WC/MoC on N-doped graphitic carbon (NGC) prepared by facile method.•Ni-MoC@NGC exhibits best HER activity and stability in the entire pH range.•Ni-MoC@NGC exhibits excellent water splitting activity on par with PtǁIrO2 pair.•Operando XAS confirms enhanced HER kinetics via synergistic electronic interaction.•Ni plays an active role in OER through the formation of Ni-oxyhydroxide species. We elucidate real-time mechanistic insights into the promotional effect of Ni substitution on the bifunctional overall water splitting (OWS) activity of molybdenum and tungsten carbides (Ni-MoC/WC@NGC) supported on N-doped graphitic carbon (NGC). Ni substitution yields multi-fold improvement in OWS over the pristine systems that are comparable to commercial Pt/C for hydrogen evolution reaction (HER) and better than IrO2 for oxygen evolution reaction (OER). Ni-MoC@NGC champions in HER activity exhibiting an onset overpotential of 65 mV and current density of 140 mA/cm2 at −370 mV (v RHE) in acidic media. An H2O electrolyzer constructed with Ni-MoC@NGC shows a comparable cell voltage to the PtǁIrO2 pair and could split water aided by 1.5 V AAA commercial battery. First principle calculations and in-situ probing through quick-XAS during electrochemical processes provide valuable insights into how the adsorption energies of intermediates and reaction kinetics are modulated at different catalytic sites with the promotional electronic effect of Ni.