Co₉S₈/CoTe₂ n‐n Type Heterojunction: A Heterogenic Interfacial Integration of Co₉S₈ and CoTe₂ Phases for Energy‐Efficient Hydrazine Oxidation Assisted Hydrogen Production

Controlled and optimized heterogenic interfacial coupling is the key to enhance the electrochemical performance. Herein, for the first time, telluride‐based Co₉S₈/CoTe₂ heterostructure is reported as a bifunctional catalyst for energy‐efficient H₂ generation. Detailed investigations suggest that the heterogenic interfacial coupling leads to superior bifunctional electrochemical performance of the Co₉S₈/CoTe₂ heterostructure. Furthermore, it displays excellent hydrazine oxidation reaction (HzOR) performance at industrial‐level current density (500 mA cm⁻² @ 338 mV) using an electrochemically neutral carbon paper substrate. The overall hydrazine electrooxidation‐assisted water splitting (OHzWS) cell performance of the Co₉S₈/CoTe₂ heterostructure couple is 10 mA cm⁻² @ 0.22 V, which is 1.60 V less than the conventional overall water splitting. Band energy profiles of Co₉S₈/CoTe₂ heterostructure reveal an n‐n type heterojunction formation between Co₉S₈ and CoTe₂ phases. The work function difference between the phases results in an impulsive electron flow from the CoTe₂ to the Co₉S₈ phase and the creation of a built‐in electric field. This prompts the electrochemical kinetics of HzOR and hydrogen evolution reaction (HER) by enabling faster charge transport at the interface. Furthermore, DFT supports the experimental findings, and Gibbs's free energy profile for HzOR studies indicate that the Co₉S₈/CoTe₂ heterostructure interface is favorable for HzOR compared to Co₉S₈ and CoTe₂.