Role of electrons and H* in electrocatalytic nitrate reduction to ammonium for CuNi alloy

Electrocatalytic reduction of nitrate (NO 3 - ) to ammonium (NH 4 + ) is an environment friendly approach for treating nitrogen-containing wastewater. Consequently, electrocatalysts capable of effectively and selectively reducing NO 3 - to NH 4 + receives growing attention. However, Cu-based catalysts demonstrate limited efficiency and the drawback of generating toxic NO 2 - though it is prevalent in the field of electrocatalytic reduction of NO 3 - (NO 3 RR). In this work, a CuNi alloy was synthesized on a Co foil through electrodeposition (marked as CuNi@Co) and its electrocatalytic performance for NO 3 RR was evaluated. XRD, EDS mapping and XPS characterization indicate CuNi exists with alloy state. Electrocatalytic experiments demonstrate that CuNi@Co exhibits an exceptional FE NH3 of 99.12% at -0.64 V (vs. RHE). Importantly, no detrimental NO 2 - generated during NO 3 RR process because the reduction rate from NO 2 - to NH 4 + is faster than that from NO 3 - to NO 2 - . Mechanistic analysis suggests that Cu serves as a ‘reservoir’ to provide electrons to facilitate the reduction of NO 3 - to NO 2 - during NO 3 RR process and the synergistic effect of Ni and Cu promotes more active hydrogen (H*) to participate the reduction process of NO 2 - to NH 4 + not H 2 generation, ultimately improving FE NH3 . This work elucidates the role of electrons and H* in electrocatalytic nitrate reduction to ammonium for CuNi alloy, providing new insights into the reduction process of NO 3 RR for Cu-based materials.