The electrochemical synthesis of ammonia via N₂ reduction reaction (NRR) has received much attention in recent years due to its promising advantages of being more environmentally friendly and less energy consuming than conventional chemical synthesis. However, as the theoretical potentials of hydrogen evolution reaction (HER) and NRR are very close on most catalysts, H₂ is the dominant product due to the much faster reaction kinetics of HER, leading to low NRR Faradaic efficiency and ammonia formation rate. The DFT calculation indicates that the transition metal nitrides, such as VN, CrN, and ZrN, are promising candidates for NRR electrocatalysts.^1-2

In this study, chromium oxynitride (CrO_0.66N_0.56) was synthesized and its NRR performance was evaluated in a proton exchange membrane electrolyzer (PEMEL) under ambient conditions. The schematic illustration of the PEMEL employed in this study is shown in Figure 1a. The highest ammonia formation rate of 8.9×10^-11 mol s^-1 cm^-2 and Faradic efficiency of 6.7% were achieved, shown in Figure 1b, which is so far the best result reported among the non-noble metal-based electrocatalysts under similar conditions. Its performance is even higher than that of Pt/C and Pd/C.

Figure 1. a) The schematic illustration of the PEMEL device for the electrochemical synthesis of ammonia. b) The ammonia production rate and faradaic efficiency of chromium oxynitride at various potentials in a PEMEL device with ammonia water pretreated under room conditions.

References

(1) Abghoui, Y.; Skulason, E., J. Phys. Chem. C 2017, 121, 6141-6151.

(2) Abghoui, Y.; Garden, A. L.; Hlynsson, V. F.; Björgvinsdóttir, S.; Ólafsdóttir, H.; Skúlason, E., Phys. Chem. Chem. Phys. 2015, 17, 4909-4918.