Modulation of cationic vacancies in Co3O4 for promoted photocatalytic nitrogen fixation and electrocatalytic nitrate reduction to ammonia

Defect engineering offers a powerful approach to tune the local surface microstructure, electron band structure and chemistry of photo- and electro-catalysts, to thereby enhancing their performance in nitrogen reduction reaction (NRR) and electrocatalytic nitrate reduction to ammonia (NO3-RR). The present study has successfully synthesized cobalt-rich vacancy (VCo) Co3O4 through a two-step method, allowing for controlled manipulation of the concentration of cobalt vacancies through heat treatment. The impact of varying concentrations of cobalt vacancies on the performance of photocatalytic nitrogen reduction reaction and electrocatalytic nitrate ammonia production was investigated. Remarkably, the catalysts heat-treated at 500 °C, exhibited a significantly enhanced photocatalytic nitrogen fixation performance with a rate of 67.5 μmol·g-1·h-1. The catalysts heat-treated at 300 °C, exhibited an ammonia yield of 339.05 mmol·g-1·h-1 at -1.1 V (vs. RHE), while achieving a maximum Faraday efficiency of 84.3% at -0.9 V (vs. RHE). The enhanced activity can be attributed to the presence of cobalt vacancies, which synergistically modulate both the structural and electronic properties. This dual functionality of cobalt-rich vacancy Co3O4 not only underscores its potential as a highly efficient photocatalyst for NRR and an electrocatalyst for NO3-RR but also highlights the intricate interplay between defect engineering, microstructural tuning, and electronic structure in promoting diverse catalytic activities. Our findings not only advance the fundamental understanding of defect-induced enhancements but also pave the way for the rational design of multifunctional catalysts capable of excelling in both photo- and electro-catalytic applications.