Electrochemical Nitrogen Reduction Reaction from Ab Initio Thermodynamics: Single versus Dual Atom Catalysts

The electrochemical nitrogen reduction reaction (NRR) is a key process for the energy transition. Transition metal atoms atomically dispersed on a solid support represent a promising approach to the design of new catalytic materials. The interest for single- (SACs) and dual-atom catalysts (DACs) is steadily growing. In general, DACs are considered more active than SACs for NRR. In this work, the complex chemistry behind NRR is investigated on a set of SACs and DACs by means of density functional theory (DFT) calculations. The results indicate that self-interaction corrected exchange-correlation functionals must be adopted, at variance with several studies in the literature. Furthermore, it is not possible to extrapolate results obtained on conventional extended catalytic surfaces to SACs and DACs, due to a richer scenario of possible reaction paths. In general, the results show a positive effect on the catalytic activity moving from 3d to 5d metals, and from SACs and DACs. However, if the two effects work together, that is, 5d metals in DACs, the reaction intermediates may be too strongly bound, thus resulting in reduced catalytic activity. In this respect, the fact that DACs are expected to be superior to SACs in NRR is not always verified.