Effective collective value-added recycling of nitrate and sulfion in wastewater via synergistic electrocatalysis of dual-active sites on copper-cobalt oxides

The well-engineered bifunctional CuCo 2 O 4 @CC enhances the electrochemical purification of wastewater rich in NO 3 − and S 2− , while simultaneously enabling the effective recovery of valuable NH 3 and S. • Copper-cobalt bimetallic oxide (CuCo 2 O 4 @CC) catalyzes both NO 3 RR and SOR. • CuCo 2 O 4 @CC achieves a FE of 98.5 % at − 0.4 V and NH 3 yield of 445.6 μmol h −1 cm −2 . • CuCo 2 O 4 @CC shows SOR performance with an overpotential of 0.504 V at 100 mA cm −2 . • The system coupled with NO 3 RR and SOR achieves 50 mA cm −2 current density at 0.31 V. • The study offers a green synthetic method for valuable chemicals from NO 3 − and S 2− . The development of an advanced electrocatalytic system that integrates the nitrate reduction reaction (NO 3 RR) with the sulfion oxidation reaction (SOR) to enable the simultaneous valorization of nitrate (NO 3 − ) and sulfion-rich (S 2− ) wastewater remains a significant challenge. In this study, we present a hybrid electrolysis system that couples cathodic NO 3 RR with anodic SOR, utilizing CuCo 2 O 4 nanowire assemblies grown on carbon cloth (CuCo 2 O 4 @CC) as the electrode. The resulting CuCo 2 O 4 @CC catalyst, characterized by synergistic catalysis between Cu and Co and a three-dimensional architecture assembled from nanowires, not only provides abundant surface-active centers but also facilitates mass and electron transfer, thereby demonstrating bifunctional catalytic activity for NO 3 RR to ammonia (NH 3 ) and SOR to polysulfide. The catalyst achieves a maximum Faraday efficiency of 98.5 ± 0.8 % at − 0.4 V versus the reversible hydrogen electrode, with an NH 3 yield rate of 445.6 ± 21.2 μmol h −1 cm −2 , significantly surpassing that of CuO@CC and Co 3 O 4 @CC. Additionally, CuCo 2 O 4 @CC exhibits strong stability during a 50-hour continuous electrolysis test. Moreover, CuCo 2 O 4 @CC demonstrates robust SOR performance, with a potential of only 0.51 V at 100 mA cm −2 , which is considerably lower than that of Co 3 O 4 @CC (0.94 V) and CuO@CC (0.67 V). Furthermore, as a bifunctional catalyst coupling NO 3 RR with SOR, CuCo 2 O 4 @CC achieves 100 mA cm −2 at 0.45 V, notably lower than the 1.68 V required for coupling NO 3 RR with oxygen evolution reaction. This work provides a promising green strategy for synthesizing high-value products from NO 3 − and S 2− wastewater at low electrolysis potential under mild conditions.