Enhanced Nitrate-to-Ammonia Efficiency over Linear Assemblies of Copper-Cobalt Nanophases Stabilized by Redox Polymers

Renewable electricity-powered nitrate (NO₃ ^- ) reduction reaction (NO₃ RR) offers a net-zero carbon route to the realization of high ammonia (NH₃ ) productivity. However, this route suffers from low energy efficiency (EE, with a half-cell EE commonly <36%), since high overpotentials are required to overcome the weak NO₃ ^- binding affinity and sluggish NO₃ RR kinetics. To alleviate this, a rational catalyst design strategy that involves the linear assembly of sub-5 nm Cu/Co nanophases into sub-20 nm thick nanoribbons is suggested. The theoretical and experimental studies show that the Cu-Co nanoribbons, similar to enzymes, enable strong NO₃ ^- adsorption and rapid tandem catalysis of NO₃ ^- to NH₃ , owing to their richly exposed binary phase boundaries and adjacent Cu-Co sites at sub-5 nm distance. In situ Raman spectroscopy further reveals that at low applied overpotentials, the Cu/Co nanophases are rapidly activated and subsequently stabilized by a specifically designed redox polymer that in situ scavenges intermediately formed highly oxidative nitrogen dioxide (NO₂ ). As a result, a stable NO₃ RR with a current density of ≈450 mA cm^-2 is achieved, a Faradaic efficiency of >97% for the formation of NH₃ , and an unprecedented half-cell EE of ≈42%.