Reassessment of the catalytic activity of bismuth for aqueous nitrogen electroreduction

Electrochemical conversion of dinitrogen to give ammonia in aqueous electrolyte solutions at a high selectivity and rate requires a catalyst with unique properties. In particular, the surface of such a catalyst should exhibit a higher affinity for nitrogen, as opposed to that for hydrogen, to facilitate the nitrogen reduction reaction (NRR) and suppress the hydrogen evolution reaction. Detailed density functional theory studies by Skúlason and co-workers1 suggest that this is hardly possible with most metals traditionally considered in electrocatalytic research. One metal not included in the analysis in ref. 1 and long known to be a very poor hydrogen evolution reaction catalyst2 is bismuth, which was recently introduced by Hao et al.3 as an efficient NRR catalyst in their article in Nature Catalysis. The density functional theory data reported in that publication clearly indicate that N2 adsorption on various bismuth surfaces is highly thermodynamically unfavourable with an essentially insurmountable energy barrier of more than 2.7 eV.