The nitrogen reduction reaction (N2RR) to produce ammonia (NH3) is one of the most important chemical transformation processes. Electrochemical N2RR using electricity generated from renewable sources can offer an attractive alternative to the conventional Haber-Bosch (HB) process because it produces NH3 using water as the hydrogen source instead of H2 gas and can also be performed at ambient temperature and pressure. Decreasing costs of electricity produced by renewable sources further encourages the development of efficient electrochemical N2RR processes. The primary current limitation of electrochemical N2RR is its low Faradaic efficiency (FE) because the standard reduction potential of N2 to NH3 is very close to that of water to hydrogen. Since the N2RR is kinetically much slower than the hydrogen evolution reaction (HER), N2RR cannot effectively compete with HER. To date, catalysts that have achieved a FE for NH3 production greater than 10% mostly utilize noble metals that are relatively inactive for HER such as Au and Pd. In this study, we will present multiple effective strategies that can be used to modify the surface of non-noble metal-based catalysts to significantly increase the FE for NH3 production. We will discuss in detail how each of the surface modification processes we perform alters the surface properties of the catalysts and affects the catalytic properties for N2RR in terms of the required overpotential, current density, and FE for NH3 production.

Strategies to enhance electrochemical ammonia production on the surfaces of non-noble metal electrocatalysts

2019 Fall National Meeting

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