The ammonia oxidation reaction (AOR) is the key reaction in ammonia splitting for hydrogen production and wastewater treatment, in which N-H cleavage and N-N formation are the key steps. In this work, we demonstrate that the hydrogen-bond accepting effect from H2O to NH3 plays the pivotal role in accelerating the N-H cleavage, while the hydrogen-bond donating effect from H2O to NH3 inhibits the N-N formation of NH3 nucleophilic attack. Alkali metal cations are further applied to unbalance the hydrogen-bond accepting and -donating effects, among which the large-size cations assist in breaking the hydrogen bonds among H2O-H2O and H2O-NH3. The resulting isolated H2O and NH3 molecules promote the accepting effect and suppress the donating effect, which enhance the activity of photoelectrocatalytic AOR by 8 times on BiVO4 photoanodes. This study illustrates the molecular-level understanding of the hydrogen-bonding effect in AOR mechanisms and to develop efficient AOR systems.
Chen et al. (Wed,) studied this question.