Composite Noble-Metal Films/H+-Conducting Solid-Polymer Electrolyte Assemblies: The Nitrate-Reduction Activity in an Asymmetric Sandwich-Type Reactor

Asymmetric (Pt|Nafion|Pt–Pd–Cu) assemblies were fabricated to study the nitrate-reduction reaction (NRR) at the cathode surface. The influence of the material composition, supplied current, and applied potential on the reactivity, kinetics, and product selectivity were thoroughly investigated. The cathode assembly consisting of 54 atom % Pt showed enhanced reactivity both in binary (Pt–Pd; k1≈10.7×10−3 min−1) and ternary (Cu–Pt–Pd; k1≈28.6×10−3 min−1) states. This composition was found to be highly nitrite-selective (80 % in the binary state and 53 % in the ternary state). The mechanistic studies revealed that the reduction of nitrate ions to ammonia proceeded through a catalytic hydrogenation reaction followed by electrochemical hydrogen generation.