Synergy electrocatalysis between palladium and cobalt aligned on carbon nanosheet architectures for nitrate-to-ammonia conversion coupled with sulfur ion oxidation.

The integration of the electrochemical nitrate reduction reaction (eNORR) and sulfur oxidation reaction (SOR) represents an effective strategy for the removal of harmful nitrates and sulfides from wastewater. However, the development of a cost-effective and high-performance bifunctional electrocatalyst remains a significant challenge. In this study, a trace amount of Pd is introduced into Co, N-doped carbon nanosheet arrays anchored on carbon cloth (Pd-Co@NC/CC), serving as a bifunctional electrocatalyst for cathodic eNORR and anodic SOR. This catalyst achieves a maximum ammonia (NH) yield of 500.1 ± 0.8 μmol h cm with a Faraday efficiency of 93.1 ± 1.4 % under alkaline conditions. Theoretical calculations indicate that the cooperative interaction between Pd and Co in Pd-Co@NC/CC facilitates NO adsorption through Co sites, while Pd sites accelerate NH desorption, thereby enhancing eNORR performance. Furthermore, the potential for SOR with Pd-Co@NC/CC is only 0.22 V at 10 mA cm, which is substantially lower than that of the oxygen evolution reaction (OER). Additionally, the Pd-Co@NC/CC||Pd-Co@NC/CC configuration achieves a potential of only 0.20 V at 10 mA cm for cathodic eNORR and anodic SOR, markedly lower than the coupling of eNORR with OER (0.99 V). This study provides a viable strategy for the resource utilization of nitrate/sulfide-containing wastewater.