Promoting nitrogen electroreduction to ammonia with bismuth nanocrystals and potassium cations in water

The electrochemical nitrogen reduction reaction (ENRR) can allow the production of ammonia from nitrogen and water under ambient conditions and is regarded as a sustainable alternative to the industrial Haber–Bosch process. However, electrocatalytic systems that selectively and efficiently catalyse nitrogen reduction remain elusive due to the strong competition with the hydrogen evolution reaction. Here, we report a strategy to simultaneously promote ENRR selectivity and activity using bismuth nanocrystals and potassium cations. Bismuth exhibits higher intrinsic ENRR activity than transition metals due to the strong interaction between the Bi 6p band and the N 2p orbitals. Potassium cations stabilize key nitrogen-reduction intermediates and regulate proton transfer to increase the selectivity. A high Faradaic efficiency of 66% and ammonia yield of 200 mmol g^–1 h^–1 (0.052 mmol cm^–2 h^–1) are obtained in aqueous electrolyte under ambient conditions. This strategy represents a general method to expand the library of catalysts and promoters for the selective electrochemical reduction of stable molecules.