Abstract

Herein, we report a pulsed-laser-engineered Cu-incorporated rock-salt FeCoO (Cu–FeCoO) catalyst with efficient bifunctional electrocatalytic activity for sulfide oxidation reaction (SOR) and nitrate reduction reaction (NO₃RR). Cu incorporation modulates the electronic structure of FeCoO, enabling efficient sulfide oxidation to polysulfides at a low potential of 0.29 V versus the reversible hydrogen electrode (RHE) at 10 mA·cm⁻². Under cathodic NO₃RR conditions, Cu–FeCoO undergoes in situ reconstruction into a Cu–FeCo alloy, achieving a high ammonia (NH₃) yield rate of 10.42 mg·h⁻¹·cm⁻² with a Faradaic efficiency of 92.16% at −0.4 V vs. RHE. Remarkably, a coupled NO₃RR||SOR electrolyzer using Cu–FeCoO as both anode and cathode enables simultaneous NH₃ and polysulfide production at a low cell voltage, with stable operation over 500 h. In situ Raman spectroscopy and post-reaction characterizations indicate that Cu–FeCoO retains its rock-salt structure during SOR but reconstructs into a Cu–FeCo alloy under NO₃RR conditions. Furthermore, density functional theory calculations suggest that Cu incorporation optimizes the electronic structure of FeCoO to accelerate SOR, whereas the reconstructed alloy lowers the free-energy requirements for NO₃RR by tuning the adsorption of key intermediates. These findings support pulsed-laser engineering of rock-salt oxides as a strategy for energy-efficient integrated waste-to-chemical conversion.