Spatial-confined effect of CuOx microneedles bundles on TiO2 nanotubes: Reinforcing the adsorption and enrichment of ultralow concentration nitrate for efficient NH3 electrosynthesis

Nitrate (NO 3 − ) Electroreduction to produce NH 3 offers an alternative approach to sustainable production of NH 3 . Yet it remains challenging to simultaneously improve the adsorption and enrichment of low-concentration NO 3 − . Here, bundles of CuO x microneedles on TiO 2 nanotubes (NTs) were developed by a spatial-confined electrodeposition strategy, achieving 87.7 % or 98.4 % NH 3 FE at −0.25 V or −0.45 V vs RHE in 2 or 10 mM NO 3 − electrolytes, respectively. Both in-situ spectroscopy and finite element analysis simulation demonstrated that CuO x microneedle bundles and its interface between TiO 2 NTs not only greatly improve the enrichment of low concentration NO 3 − and its derived-NO 2 − and the diffusion of NH 3 product, but also enhance the adsorption of NO 2 − and H 2 O to facilitate the hydrodeoxygenation of NO 3 − as well as inhibit hydrogen evolution reaction competition. This work will provide a promising avenue to develop electrocatalysts to realize efficient catalytic conversion of reactants at low concentrations.