Tuning surficial atomic configuration of Pt–Ir catalysts for efficient ammonia oxidation and low-temperature direct ammonia fuel cells

Abstract

Low-temperature direct ammonia fuel cell via ammonia oxidation reaction (AOR) is one of the most attractive ways for ammonia utilization. The Pt–Ir alloyed catalysts have been proven greatly efficient in AOR to overcome the sluggish kinetics and complex multi-electron processes; however, it still remains challenging for further improvement because of the complexity of alloyed types and unclear fundamental understanding. Herein, we systematically fabricated a series of PtxIry/XC-72 catalysts via tuning the Pt/Ir compositions and these catalysts demonstrate significant composition-dependent behaviours in AOR, whereas the Pt favours increasing current densities and the Ir facilitates reducing onset potentials. Importantly, the actual surface Pt/Ir atomic configuration is totally different with the classic view for homogeneous alloys by combining catalytic and characteristic analyses. The Pt prefers to be segregated on the topmost surface. Then the quantified correlations between current density/onset potential and Pt composition in Pt − Ir nanoparticles (NPs) were further established and discussed. The onset potential of AOR is significantly reduced by Ir incorporation while it is insensitive to Ir contents. Accordingly, the well-studied Pt5Ir5/XC-72 catalyst was further employed in an alkaline exchange membrane fuel cell, exhibiting a peak power density (230.0 mW cm−2). Our work provides insights into the effect of Pt/Ir compositions on AOR, with the goal of catalysts engineering for AOR and ammonia fuel cells.