Electrocatalytic ammonia synthesis: Role of cathode materials and reactor configuration

Abstract

Ammonia was synthesized by reducing NO3-/NO2- over several bimetallic surfaces, supported on H+ conducting Nafion-117 polymer. When Pd was used alone as a cathode, the cent percent product was ammonia but the process was kinetically unfavorable (2.3 × 10−3 min−1) during nitrite reduction. Under the same experimental conditions, Pt–Pd, Ni–Pd, Ag–Pd and Cu–Pd cathodes were mainly selective to NH4+ (69–82%) but nitrite reduction activity was still low (⩽8.1 × 10−3 min−1). The Rh–Pd was only one cathode, which simultaneously enhanced nitrate (21.1 × 10−3 min−1) and nitrite (25.6 × 10−3 min−1) reduction yielding ca. 75% of NH4+. The cyclic voltammetric investigations as well as catalytic hydrogenation experiments indicated that the surface to substrate electron transfer reaction was the main reason of ammonia formation. It was noticed that multi functional roles of the Nafion membrane enhanced the ammonia synthesis performance of the electrolyte reactor.