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

• Published in: Advanced materials (Weinheim) Vol. 35; no. 32; pp. e2303050 - n/a
• Main Authors: He, Wenhui, Chandra, Shubhadeep, Quast, Thomas, Varhade, Swapnil, Dieckhöfer, Stefan, Junqueira, João R. C., Gao, Huimin, Seisel, Sabine, Schuhmann, Wolfgang
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.08.2023
• Subjects: Ammonia; Catalysis; Chemical reduction; Copper; CuCo nanoribbons; Efficiency; energy efficiency; linear assembly; Materials science; Nanoribbons; nitrate reduction; Nitrogen dioxide; Raman spectroscopy; redox polymers; tandem catalysis; CuCo nanoribbons; linear assembly; nitrate reduction; redox polymers; energy efficiency; tandem catalysis
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202303050

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%. Electrochemical redox‐driven linear assembly of sub‐5 nm CuCo nanocrystals, coupled with a specifically designed protective redox polymer, is first reported for designing an inorganic‐organic hybrid catalyst with enzyme‐like properties, which enables enhanced nitrate (NO3−) adsorption and tandem catalysis of NO3− to ammonia (NH3) with a Faradaic efficiency of >97% at low overpotentials, leading to a record‐high half‐cell energy efficiency of ≈42.0%.