Coupling post-modification with reconstruction over Co-based metal–organic frameworks for electrochemical collective value-added recycling of nitrate and sulfion in wastewater

Abstract

Integrating electrochemical nitrate reduction to ammonia (NRA) and the sulfion oxidation reaction (SOR) to construct a coupled electrolysis system is expected to realize the collective value-added recycling of nitrate and sulfion wastes. In this study, we developed a dimethylamineborane (DMAB)-involved post-modification strategy to convert pre-synthesized Co-MOF/NF into DMAB–Co-MOF/NF, which could serve as a bifunctional precatalyst and in situ reconstructed into heterogeneous CoOOH/Co(OH)₂/NF (for NRA) and amorphous B–Co–S/NF (for SOR) as active phases under electrocatalytic conditions, respectively. With demonstrated excellent nitrate-to-ammonia activity over the reconstructed CoOOH/Co(OH)₂/NF (NH₃ yield rate: 0.238 mmol h⁻¹ cm⁻² and NH₃ faradaic efficiency: 94.16%) and enhanced sulfion recycling capability over the reconstructed B–Co–S/NF (100 mA cm⁻² of the SOR@0.268 V vs. the reversible hydrogen electrode), coupling NRA to the SOR based on these two electrocatalysts could realize energy-efficient collective value-added recycling of nitrate and sulfion into ammonia and sulfur (50 mA cm⁻²@1.062 V cell voltage).