Hollow PdCuCo Medium-Entropy Alloy on Reduced Graphene Oxide with Proton-Mediator Boosted Tandem Catalysis for High-Performance Nitrate Reduction

Electrocatalytic reduction of nitrate (NO3–) to ammonia (NH3) emerges as a sustainable approach for both wastewater treatment and NH3 synthesis. Herein, we report a hollow-structured PdCuCo medium-entropy alloy supported on reduced graphene oxide (HPdCuCo/RGO) as an efficient and robust electrocatalyst for nitrate reduction reaction (NO3–RR). A unique proton-mediator boosted tandem electrocatalysis toward NH3 production is established on the HPdCuCo/RGO, where Cu sites promote the NO3–-to-NO2– conversion, the Co sites facilitate the NO2–-to-NH3 conversion, and the Pd sites serve as proton mediators to further boost the tandem catalysis. As a result, the HPdCuCo/RGO exhibit high performance towards NO3–RR in Ar-saturated 0.5M K2SO4 electrolyte with 2,000 ppm NO3–, achieving a NH3-Faradaic Efficiency of ~100% and a corresponding NH3 yield of 36mgh–1 mg–1cat. at -0.5V versus reversible hydrogen electrode. This study showcases the significant potential of medium-entropy alloys as efficient catalysts for NO3–RR, motivating further exploration into the hitherto underexplored domain of medium-entropy alloys for NO3–RR.