Confining intermediates within a catalytic nanoreactor facilitates nitrate-to-ammonia electrosynthesis

Electrocatalytic nitrate reduction reaction (NitRR) has gained attention because of its potential to mitigate environmental nitrogen pollution and recycle artificial nutrients. NitRR produces ammonia through complicated pathways that involve multistep electron transfer, while the formation of byproducts, e.g. toxic nitrite (NO 2 ˉ), leads to lower energy efficiency and recontamination. In this work, we report the incorporation of CuO x active species into a TiO 2 -nanotube reactor (TiO 2 NTs/CuO x ) for the highly selective NitRR. In particular, the NO 2 ˉ intermediate is diminished due to the hindered diffusion within the nanoconfined space. Thus, the CuO x modified nanoreactor performs a maximum faradaic efficiency of 92.23% and a yield rate of 1241.81 μg h −1 cm −2 for nitrate-to-ammonia conversion. Theoretical insights further support a fundamental understanding of a cross-scale interaction over the surface and interface. The findings suggest a promising approach for enhancing reaction activity and selectivity enabled by rationally designed active sites coupled with geometrically regulated structures. • A CuO x integrated TiO 2 nanoreactor exhibits an impressive performance for nitrate-to-ammonia electroreduction. • Endowed with nanoconfinement and surface-active species, the nanoreactor gains promotion in selectivity and efficiency. • The proof-of-concept research advances knowledge of catalytic nanoreactors for ammonia electrosynthesis.