Enhanced alkaline ammonia oxidation reaction activity using PtW alloy catalysts with tungsten as built-in competitor reservoir

Abstract

Direct ammonia anion exchange membrane fuel cells (DA-AEMFCs) have drawn great attention recently with the recognition that liquid ammonia (NH3), as a carbon-free hydrogen storage medium, is easy to store, transport, and distribute. However, its practical application is significantly limited by the anodic ammonia oxidation reaction (AOR), which not only is kinetically sluggish, but also suffers from competitive adsorption of oxidizing agent, OH–. Herein, we tackle the above challenges simultaneously by alloying the highly active platinum with electron-deficient tungsten. The W sites would preferentially adsorb *OH to serve as the reservoir and supply for the dehydrogenation of NH3. The Pt sites are thus liberated and free for the targeting adsorption of NH3. Moreover, density functional theory calculations suggest that, with the pre-adsorption of *OH, the d band center of PtW alloy experiences a positive shift toward the Fermi level, which would contribute to stronger adsorption of the reaction intermediates and thus benefit the whole AOR process. As expected, the synthesized alloy with the optimum ratio exhibits a low onset potential of 0.46 V versus reversible hydrogen electrode and a large peak current density of 11.70 mA cm−2. When subjected to practical application, the DA-AEMFCs assembled with such electrocatalyst deliver an excellent peak power density of 22.47 mW cm−2, indicating its potential feasibility in the next-generation energy devices.