Computational prediction and experimental evaluation of nitrate reduction to ammonia on rhodium

Abstract We predicted the reaction energetics for nitrate reduction on rhodium surfaces in alkaline media using the density functional theory (DFT) in combination of implicit continuum solvation model. The study covered three typical facets including (1 1 1), (1 1 0) and (1 0 0) of Rh crystal, as well as the surface adsorption of five major chemical species (i.e., NO2−, NO, N2O, N2 and NH3) involved in nitrate reduction. Our calculation results reveal that Rh (1 1 0) exhibits activity for nitrate reduction towards ammonia with the widest potential range below 0.06 V, and Rh (1 0 0) has the best activity and selectivity towards ammonia above −0.57 V with the highest onset potential up to 0.15 V, the lowest activation energy at the rate-determining step from *N to *NH and the preferable configuration of nitrate adsorption at low surface coverage to suppress nitrogen formation. The optimal potential range for nitrate reduction towards ammonia on Rh (1 0 0) was predicted to be from 0.15 V to 0.09 V, which was further verified by our experimental evaluation of ammonia yield on commercial Rh/C electrocatalysts. The peak of ammonia yield rate of 34.4 μg·h−1·cm−2 as well as the faradic efficiency of 20.8% on the experimental sample exactly lie in the as-predicted potential range of Rh (1 0 0), hence consistently matching our computational predictions. Our study not only provides a detailed mechanistic understanding of nitrate reduction with quantified experimental detection of ammonia yield on rhodium, but also demonstrates reliable predictions via DFT in combined with implicit continuum solvation model for electrocatalysts.