Evaluation of Pt–Rh Nanoparticle–Based Electrodes for the Electrochemical Reduction of Nitrogen to Ammonia

Abstract

Ammonia (NH3) is one of the most used chemicals. Industrially, ammonia is produced by hydrogenation of N2 through the Haber–Bosch process, a process in which enormous amounts of CO2 are released and requires a huge energy consumption (~ 2% of the total global energy). Therefore, it is of paramount importance to explore more sustainable and environmentally friendly routes to produce NH3. The electrochemical nitrogen reduction reaction (NRR) to ammonia represents a promising alternative that is receiving great attention but still needs to be significantly improved to be economically competitive. In this work, the NRR is studied on Pt–Rh nanoparticle–based electrodes. Carbon-supported Pt–Rh nanoparticles (2–4 nm) with different Pt:Rh atomic compositions were synthesized and subsequently airbrushed onto carbon Toray paper to fabricate electrodes. The electrochemical NRR experiments were performed in a H-cell in 0.1 M Na2SO4 solution. The results obtained show interesting faradaic efficiencies (FE) towards NH3 which range between 5 and 23% and reasonable and reliable NH3 yield values of about 4.5 µg h−1 mgcat−1, depending on the atomic composition of the electrocatalysts and the metal loading. The electrodes also showed good stability and recyclability (constant FE and NH3 yield in five consecutive experiments).