Operando Analyses of Highly Enhanced Water Splitting by Electronically Modulated Non-noble Metal Carbides

Designing non-noble metal based electrocatalysts for efficient overall water splitting (OWS) solves a critical bottleneck of sustainable water electrolyzer technology. Here, we elucidate real-time mechanistic insights into the promotional effect of Ni substitution on the bifunctional OWS activity of N-doped graphite carbon (NGC) supported molybdenum and tungsten carbides (Ni-MoC/WC@NGC). Ni substitution yields multi-fold improvement in water splitting activity over the pristine systems that are comparable to commercial Pt/C for HER and better than IrO2 in case of 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. Their excellent OWS activity in alkaline media prompted us to construct a H2O electrolyzer where the bifunctional Ni-MoC@NGC system shows a comparable cell voltage to the PtǁIrO2 pair and could split water aided by a 1.5V AAA commercial battery. First principle calculations and in-situ probing of the local Ni and W sites 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 substitution.