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 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).

Graphical Abstract

Pt–Rh nanoparticle–based electrodes were employed for the NRR to NH₃ in 0.1 M Na₂SO₄. Interesting FE towards NH₃ and reasonable and reliable NH₃ yield values were observed depending on atomic composition and metal loading. Good stability and recyclability (constant FE and NH₃ yield in five consecutive experiments) were also observed.