Theory-Directed Designing of an Intrinsic-Activity-Modulated Metal-Doped Copper Oxide Electrode for Nitrate to Ammonia Synthesis

Abstract

Synthesis of ammonia via electrochemical reduction of nitrate is one of the most sustainable routes both for environmental protection as well as energy saving initiatives. However, this process is limited to the development of high-performance free-standing catalytic electrodes with improved selectivity and Faradaic efficiency. Herein, we report theory-guided designing and fabrication of free-standing non-noble metal (Mn, Fe, and Co)-doped copper oxide (CuO) electrodes by using a simple and scalable electrode preparation method. The density functional theory (DFT)-based calculations show that the doped-Co sites in the Cu surface facilitate the generation and supply of H+ to the adsorbed NO3– during the reduction process; as a result, the Co–CuO catalyst displays higher selectivity toward nitrate reduction. The Co-doped Cu electrode (Co–CuO) delivers a higher NH3 yield (5492 μg cm–2) at a reduction potential of −0.91 V vs RHE while maintaining a Faradaic efficiency of >95%. The alloying of Co to the copper metal not only facilitates the proton donation to the adsorbed reactant (NO3–) but also tunes the Cu d-center, resulting in the active site modulation responsible for the activation of catalysts.