Electrooxidation of hydrazine utilizing high-entropy alloys: assisting the oxygen evolution reaction at the thermodynamic voltage

Abstract

Hydrazine electrooxidation is an important reaction as it assists in decreasing the OER overvoltage. Herein, we report the utilization of a high-entropy nanocatalyst alloy for the electrooxidation of hydrazine. The high-entropy nanocatalyst comprising five elements (Ag, Au, Pt, Pd, Cu) shows profound activity toward this molecule at a low overvoltage. An intriguingly high-entropy nanocatalyst prepared by the casting-cum-cryomilling method is endowed with the unique catalytic activity for the HzOR. A detailed analysis of gaseous product points to the formation of nitrogen as well as oxygen as the oxidation product, a sign of accompanying the oxygen evolution reaction (OER). Interestingly, a significant amount of oxygen is detected at 1.13 V (reversible hydrogen electrode (RHE)) in a neutral buffered medium, confirming that the OER is functional at a voltage near the thermodynamic voltage of 1.23 V (RHE). The quantitative contribution of each hydrazine and OER is ascertained, which explains a vital insight into this reaction. Density functional theory calculations showed that both HzOR and OER assist each other where the electron-donating effect of H2O to the surface can reduce the endothermicity of the HzOR. However, the electron acceptance of *NHNH2 helps in a favorable overlap of the HEA Fermi level and vacant states with the HOMO of H2O.