Interface enables faster surface reconstruction in a heterostructured Co–Ni–S electrocatalyst towards efficient urea oxidation

Abstract

The electrocatalytic urea oxidation reaction (UOR) can be utilized as an alternative anodic reaction for water electrolysis to provide more economic electrons and high-efficiency H₂ production. Nonetheless, electrocatalytic urea oxidation still suffers from its high energy barrier, sluggish kinetics and intricate reaction mechanism. Low-cost and efficient electrocatalysts towards the UOR with satisfactory activity and long lifespan are still lacking, and the underlying electrochemical mechanisms are not fully understood yet. Herein, an electrocatalyst of heterostructured cobalt-and-nickel-based-sulfides anchored on nickel foam (Co–Ni–S@NF) with a designed interface between Ni₃S₂ and Co₉S₈ was designed and synthesized via a one-step solvothermal method, exhibiting excellent urea electrooxidation activity (100 mA cm⁻² at 1.35 V vs. reversible hydrogen electrode) and stability (100 h at 100 mA cm⁻²). Detailed structural and compositional characterization, along with electrochemical measurements reveals that the interface induced charge transfer between the strongly coupled Ni₃S₂ and Co₉S₈ could enhance the catalytic activity and stability of the hybrid material. In situ Raman and in situ Fourier transform infrared measurements clarify the voltage-driven self-reconstruction process based on different catalyst surfaces and help to understand the reaction pathway on the basis of the detected intermediated species. The ultrahigh UOR performance of Co–Ni–S@NF can be attributed to the incorporated Co element accelerating the structural evolution of Ni₃S₂ and facilitating the formation of high-valent Ni species, which are highly relevant to urea decomposition efficiency. The Co–Ni–S@NF electrode contributes to the improved C–N and N–H bond cleavage in urea and achieves a high-speed production of CO₂, resulting in a higher activity upon the UOR. DFT calculations indicate sufficient charge exchange and defect formation at the heterointerface which boost the urea oxidation reaction. This work opens a new avenue to develop efficient electrocatalysts with a designed heterostructure and interface for electrochemical hydrogen production.