Modulating Single-Atom Pt Coordination for Enhanced Low-Temperature Ammonia Fuel Cell Electrocatalysis

Low-temperature direct ammonia fuel cells (DAFCs) can be used for the on-demand generation of clean electricity. However, such systems have low efficiency due to the kinetically sluggish ammonia oxidation reaction (AOR) and oxygen reduction reaction (ORR). Prior reports have largely focused on Pt-based electrocatalysts, however, their high cost motivates the need for simultaneously increasing activity whilst reducing the metal loading. Here, the design of a bifunctional Pt single-atom catalyst (SAC) is reported, with enhanced catalytic activities compared to commercial Pt/C for both reactions. Notably, by modulating the Pt SAC coordination, the optimal catalyst (Pt-DG-1) displayed a high AOR mass activity of 1.23 A mg_Pt ^-1 and ORR mass activity of 7.98 A mg_Pt ^-1. This is then integrated into a DAFC as both the cathode and anode, achieving a peak power density of 21.8 mW cm^-2 and low Pt mass loading of only 0.034 mg cm^-2. In situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) experiments on Pt-DG-1 indicate a lower ^*OH coverage under ORR conditions and suppressed formation of poisoning species ^*NO_x under AOR conditions as additional reasons for its enhanced bifunctional catalytic activity. Importantly, the study demonstrates how SACs can be rationally designed for DAFC electrocatalysis.