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 & AP;450 mA cm(-2) is achieved, a Faradaic efficiency of >97% for the formation of NH3, and an unprecedented half-cell EE of & AP;42%.

Automated summary

Renewable electricity-powered nitrate reduction reaction (NO3RR) offers a net-zero carbon route to high ammonia (NH3) productivity. However, this route suffers from low energy efficiency due to the need for high overpotentials. A rational catalyst design strategy involving the assembly of Cu/Co nanophases into nanoribbons is suggested to alleviate this issue. Experimental studies show that the Cu-Co nanoribbons enable strong NO3- adsorption and rapid catalysis of NO3- to NH3, achieving a stable NO3RR with high current density and Faradaic efficiency.