Electrocatalytic nitrate reduction on bimetallic Palladium-Copper Nanowires: Key surface structure for selective dinitrogen formation

Selective electrocatalytic nitrate reduction reaction (NO3RR) to dinitrogen (N-2) is essential to nitrogen-cycle management and environmental sustainability. Palladium-based nanomaterials were extensively studied as NO3RR catalysts, but only delivered limited N2 selectivity (< 50%, NH3 dominated the product). Here we report that, by tuning bimetallic composition of CuPd alloy nanowires, the Cu28Pd72 nanowires deliver a near-unit conversion of NO3--N and an unprecedented N-2 product selectivity of 75.9 +/- 5.2% in treating 22.5 mg L-1 NO3--N solution at-0.80 V vs. Ag/AgCl. Combining in-situ spectrometric measurements and theoretical calculations, we demonstrate that the contiguous Pd ensemble with a specific size at catalyst surface is essential to the N-2 formation via a kinetically-favored pathway of NO2*->* NO*->* N*->* N-2*. Alloying Pd with Cu is indispensable as Cu contributes to the N*-N* pairing by initiating the NO3--NO2* conversion and lowering the Hads coverage on catalyst. This work discloses the key surface atomic structure for N-2 formation, and provides a guideline for the design of efficient NO3RR catalyst that enables selective NO3--N-2 conversion.