Electrocatalytic oxidation of ammonia on Pt: Mechanistic insights into the formation of N2 in alkaline media

Electrochemical ammonia oxidation reaction (AOR) is one of the most effective methods to utilize ammonia. Currently, the favorable coupling process during AOR and most important intermediates are still under debate. Herein we used ab initio molecular dynamics (AIMD) method combined with deliberately designed free-energy calculations to thoroughly study the energetics of elementary steps during AOR. The main pathway of N2 formation during AOR is initiated by the dehydrogenation of NH3 to NH2, and subsequent NH2 + NH2 coupling to form N2H4, followed by stepwise dehydrogenation of N2H4 to N2. The Gerischer-Mauerer mechanism was found to be favored in the process. The dehydrogenation of NH3 to NH2 was determined to be the rate-limiting step, and NH2 is the most important intermediate. Through this work, the overall reaction network and corresponding energetics of AOR is revealed, which may enlighten the understanding of AOR and further accelerate corresponding catalyst innovation.