A novel phosphotungstic acid-supported single metal atom catalyst with high activity and selectivity for the synthesis of NH3 from electrochemical N2 reduction: a DFT prediction

The electrochemical reduction of N-2 to generate NH3 (NRR) under ambient conditions is a promising alternative to the industrial Haber-Bosch process which requires high temperature and pressure. NRR electrocatalysts are needed to overcome the slow kinetics due to the high energy barrier for N & xe002;N bond cleavage. Another main challenge is suppressing the competing hydrogen evolution reaction (HER) which results in poor NRR selectivity. Here, we report the development of a novel and cost-efficient electrocatalyst-a phosphotungstic acid (PTA)-supported single metal (M) atom (M-PTA, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, and Cd) which exhibits substantial stability-via a comprehensive theoretical screening formula of over 20 different d-block metals (M-PTA, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, and Cd). It is interesting to mention that this class of catalysts has a greatly suppressed HER selectivity with 17 of the 20 candidates falling in the N-2-dominant region. Further study demonstrates that Mo-PTA, Tc-PTA and Ru-PTA only demand an energy input of 0.42 eV, 0.24 eV and 0.34 eV for the first hydrogenation step of N-2. Detailed analysis of NRR mechanisms show that it follows the distal mechanism with an overpotential of 0.26 V on Mo-PTA. This work provides DFT guidelines for developing stable electrocatalysts through experiments for catalyzing the NRR with high reactivity and selectivity.