Effective collective value-added recycling of nitrate and sulfion in wastewater via synergistic electrocatalysis of dual-active sites on copper-cobalt oxides
Donglin Zhao, Song Wu, Yihan Zhang, Dongxu Cao, Ruizhi Li, Long Yan, Guangyin Fan
Abstract
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.