Manipulating the Interface Relay Jumps of OH–ad Species to Accelerate the Anode Reaction Kinetics in Direct Ammonia Fuel Cells

Abstract

Ammonia is a hydrogen-dense, carbon-neutral energy carrier, but sluggish oxidation kinetics and catalyst toxicity limit its large-scale use in low-temperature alkaline direct ammonia fuel cells (DAFCs). Inspired by the “Grotthuss hopping” theory, we designed a hydroxyl group-modified membrane electrode catalyst system through the modification of interface key groups. This system can interact with adsorbed OH^– (hereafter, OH^–_ad), thus being similar to a “relay” that allows OH^–_ad to jump from one active site to another and then react with ammonia intermediates, injecting more impetus into the kinetic process of the orderly release of OH^–_ad. The results of molecular dynamics (MD) simulations and operando Fourier transform infrared spectroscopy (operando-FTIR) further demonstrated and confirmed that this process follows the Gerischer–Mauerer (G–M) mechanism. Consequently, the mass activity of the best membrane electrode catalyst in this series, PtNiNC@OH_0.05 (373 A g^–1_Pt), has been significantly enhanced in alkaline media, which is 3.2 times higher than that of the commercial 20% Pt/C (116 A g^–1_Pt) catalyst. Even more surprisingly, the DAFC of the membrane electrode catalyst as an anode achieves a peak power density of 17.4 mW cm^–2 at 60 °C, which is 9.89-fold higher than that of 20% Pt/C (1.76 mW cm^–2). The interface modification method based on the “relay” jumps proposed by us provides a way to fabricate DAFC membrane electrode catalysts.