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

Renewable electricity-powered nitrate (NO₃⁻) reduction reaction (NO₃RR) 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 NO₃RR 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 NO₃RR 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%.