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

Ammonia (NH3) is one of the most used chemicals. Industrially, ammonia is produced by hydrogenation of N-2 through the Haber-Bosch process, a process in which enormous amounts of CO2 are released and requires a huge energy consumption (similar to 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 mu g h(-1) mg(cat)(-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).