Hollow PdCuCo medium-entropy alloy on reduced graphene oxide with proton-mediator boosted tandem catalysis for high-performance nitrate reduction

Electrocatalytic reduction of nitrate (NO 3 – ) to ammonia (NH 3 ) emerges as a sustainable approach for both wastewater treatment and NH 3 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 (NO 3 – RR). A unique proton-mediator boosted tandem electrocatalysis toward NH 3 production is established on the HPdCuCo/RGO, where Cu sites promote the NO 3 – -to-NO 2 – conversion, the Co sites facilitate the NO 2 – -to-NH 3 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 NO 3 – RR in Ar-saturated 0.5 M K 2 SO 4 electrolyte with 2000 ppm NO 3 – , achieving a NH 3 -Faradaic Efficiency of ∼100 % and a corresponding NH 3 yield of 36 mg h –1 mg –1 cat. at −0.5 V versus reversible hydrogen electrode. This study showcases the significant potential of medium-entropy alloys as efficient catalysts for NO 3 – RR, motivating further exploration into the hitherto underexplored domain of medium-entropy alloys for NO 3 – RR.