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.

Electrocatalytic nitrate-to-ammonia conversion on CoO/CuO nanoarrays using Zn–nitrate batteries

“…The appearance of O in CF may be due to surface oxidation when it is exposed to air. 55 Fig. 1f shows the Cu 2p XPS spectra of CF, CuO-NA/CF, and CoO/CuO-NA/CF.…”

“…The binding energy of Cu 2p 3/2 and Cu 2p 1/2 of CoO/CuO-NA/CF have a shift of about 0.2 eV compared to that of CuO-NA/CF, which is possibly attributed to the interaction between CoO and Cu components in CoO/CuO-NA/CF. 55 Fig. 1g shows the Co 2p XPS spectra of CoO/CuO-NA/CF.…”

Cu/NiO nanorods for efficiently promoting the electrochemical nitrate reduction to ammonia

“…1–3 At present, the Haber–Bosch process is the main method to produce NH 3 in an industry under high temperature and pressure conditions, which not only requires harsh reaction conditions, but also causes a large amount of fossil energy consumption and high CO 2 emissions. 4–6 Therefore, in view of increasingly depleted fossil fuels and serious environmental pollution issues, there is an urgent need to explore new technologies to replace the Haber–Bosch ammonia production process. 7 Recently, ammonia production by the electrochemical nitrogen reduction reaction (NRR) under environmental conditions has been extensively studied and greatly developed.…”