Enhanced Nitrate‐to‐Ammonia Efficiency over Linear Assemblies of Copper‐Cobalt Nanophases Stabilized by Redox Polymers
Wenhui He, Shubhadeep Chandra, Thomas Quast, Swapnil Varhade, Stefan Dieckhöfer, João R. C. Junqueira, Huimin Gao, Sabine Seisel, Wolfgang Schuhmann
Abstract
Abstract Renewable electricity‐powered nitrate (NO 3 − ) reduction reaction (NO 3 RR) offers a net‐zero carbon route to the realization of high ammonia (NH 3 ) 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 NO 3 − binding affinity and sluggish NO 3 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 NO 3 − adsorption and rapid tandem catalysis of NO 3 − to NH 3 , 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 (NO 2 ). As a result, a stable NO 3 RR with a current density of ≈450 mA cm −2 is achieved, a Faradaic efficiency of >97% for the formation of NH 3 , and an unprecedented half‐cell EE of ≈42%.