One-Step Synthesis and Operando Electrochemical Impedance Spectroscopic Characterization of Heterostructured MoP-Mo₂N Electrocatalysts for Stable Hydrogen Evolution Reaction

This study presents a novel synthesis of self-standing MoP and Mo₂N heterostructured electrocatalysts with enhanced stability and catalytic performance. Facilitated by the controlled phase and interfacial microstructure, the seamless structures of these catalysts minimize internal resistivity and prevent local corrosion, contributing to increased stability. The chemical synthesis proceeds with an etching step to activate the surface, followed by phosphor-nitriding in a chemical vapor deposition chamber to produce MoP-Mo₂N@Mo heterostructured electrocatalysts. X-ray diffraction analyses confirmed the presence of MoP, Mo₂N, and Mo phases in the electrocatalyst. Morphology studies using scanning electron microscopy characterize the hierarchical growth of structures, indicating successful formation of the heterostructure. X-ray photoelectron spectroscopy (XPS) analyses of the as-synthesized and postcatalytic activity samples reveal the chemical shift in terms of the binding energy (BE) of the Mo 3d XPS peak, especially after catalytic activity. The XPS BE shifts are attributed to changes in the oxidation state, electron transfer, and surface reconstruction during catalysis. Electrochemical evaluation of the catalysts indicates the superior performance of the MoP-Mo₂N@Mo heterostructured catalyst in hydrogen evolution reactions (HER), with lower overpotentials and enhanced Tafel slopes. The stability tests reveal changes in double layer capacitance over time, suggesting surface reconstruction and an increased active surface area during catalysis. Operando electrochemical impedance spectroscopy (EIS) further elucidates the dynamic changes in resistance and charge transfer during HER. Overall, a comprehensive understanding of the synthesis, characterization, and electrochemical behavior of the developed MoP-Mo₂N@Mo heterostructured electrocatalyst, as presented in this work, highlights its potential utilization in sustainable energy applications.