Unveiling the Reactive Sites for Electrocatalytic Conversion of Nitrate to High-Value-Added Chemicals

CuZn catalysts with various structures were synthesized for electrocatalyzing the NO3– and CO2. Among them, CuZn supported on nitrogen-doped carbon exhibited the capability for directly producing urea, while after being treated at higher temperatures, it presents the highest yield of ammonia. X-ray absorption fine structure (XAFS) analysis revealed that in the optimized sample, Zn existed as the single atom and Cu contained Cu–O(N) and Cu–Cu coordination structures. The Cu–O(N) species promoted the C–N coupling, while the Cu–Cu component played a crucial role in the reduction of nitrate to ammonia. Cuδ+ (1 < δ < 2) in the catalyst contributed to the C–N coupling. In addition, in situ XAFS data indicated that under the optimal potential of −0.89 V, the valence state of Cuδ+ decreased slightly but remained within the range of 1 < δ < 2. After 8 h stability tests, the catalyst maintained a stable coordination structure. This study reveals that the Cu coordination environment is a crucial parameter for selectively producing ammonia or urea.