Multifunctional Na-enriched Ni–Fe/Ni–P plates for highly efficient photo- and electrocatalytic water splitting reactions

Abstract

In this work, we first report a novel sodium-enriched Ni–Fe mixed-oxide catalyst incorporated into a Ni–P electrode for photo and electrocatalytic water splitting. A one-pot special sol–gel method was adopted for the synthesis of sodium-enriched Ni–Fe mixed-oxide catalysts, and the parameters were optimized based on the electrode and characterized by suitable analytical techniques. The reported catalyst system has high solar water splitting activity with a high quantum efficiency of 53.89%. The functional electrode exhibited a very low overpotential of 198.3 mV at a current density of 10 mA cm⁻² during oxygen evolution reactions. Even though the oxygen evolution reaction is sluggish as it demands a high overpotential, the developed electrode system exhibited excellent OER characteristics by acting as a reversible electrode. Moreover, the LSV plots of electrodes before and after 1000 cycle CV revealed that the electrode possesses a high long-term electrochemical stability during the reversible OER. A high double-layer capacitance and a low charge transfer resistance value of the catalytic electrode are due to the high distribution of electroactive sites such as Na⁺, Ni²⁺, and Fe³⁺ on the surface and the combined effect of various functional components in the catalytic system. NaNiO₂ and Fe₂O₃ were preserved in the Z-scheme photo-catalyst, and it also enhanced the electron flow and conductivity which favours simultaneous oxidation and reduction. The developed electrode system exhibited excellent water splitting characteristics due to faster electron transfer reactions in sodium-incorporated catalysts. Furthermore, the coexistence of Ni²⁺ and Fe³⁺ would increase the electrical conductivity due to the synergic effect between Ni²⁺ and Fe³⁺. The photo- and electrocatalytic activity and stability of the catalytic electrode system is competent with the recently reported and comparable catalyst. The present work proposes an electrode system capable of large-scale water splitting with excellent activity and stability.