Regulating d-p band center with selenium vacancy in iron diselenide nanoarrays towards sulfion-assisted seawater electrolysis for chlorine-free hydrogen production

Defect engineering is considered one of the most powerful strategies for regulating the catalytic activity of electrocatalysts. A deep understanding of the defect-involved mechanism in electrocatalytic process is of great importance but remains a challenging task. In this study, an anionic Se-vacancy (V_Se) was introduced into iron diselenide (FeSe₂) nanoarrays, enabling the catalyst to exhibit improved electrocatalytic performance for sulfion oxidation reaction (SOR). The Se vacancy incorporated can modulate surface electronic structure and optimize the proximity of the d-p band center, strengthening the interaction between FeSe₂-V_Se and S atom. This endows the FeSe₂/IF-V_Se catalyst with the excellent electrocatalytic activity for SOR. As an alternative reaction to oxygen evolution reaction (OER), the low-potential SOR enables an ultralow electricity consumption in SOR-hydrid seawater electrolysis, avoiding detrimental chlorine electrochemistry. A proof-of-concept self-powered system based on FeSe₂-V_Se electrodes was constructed by integrating Zn-nitrite battery and SOR-hybrid seawater electrolyzer to produce high-value hydrogen, sulfur and ammonia. This work offers a fascinating strategy for the construction of an advanced energy system to produce hydrogen while utilizing seawater and wastewater.