Effect of the Pt surface shell in PtNi alloy catalysts on ammonia electrooxidation
The sluggish kinetic processes of the anode and the poisoning characteristics of *NH 3 intermediates in the direct ammonia fuel cell paradigm necessitate bespoke electrocatalyst engineering. Given the fundamental traits of surface reactions in electrochemical ammonia oxidation reaction (AOR) and the high efficiency of alloy catalysts, PtNi nanowires, nanorods, and nanoparticles with a Pt shell structure were developed as surface-engineered model catalysts to clarify how the microarchitecture of nanocatalysts affects the adsorption of NH 3 and intermediates, along with AOR activity. PtNi nanowires exhibit significantly improved activity compared to PtNi nanorods, nanoparticles, and commercial Pt/C, due to the higher proportion of the Pt(100) facet and their unique thin Pt shell layer structure. The peak current density of PtNi nanowires reaches 0.63 mA cm −2 , 2.52 times higher than that of commercial Pt/C. Furthermore, the incorporation of Ni into Pt can effectively bolster the electrochemical durability via electronic effects on the Pt surfaces. Upon conversion from ambient temperature to 60 °C, PtNi nanowires still demonstrate superior AOR activity and durability compared to commercial Pt/C. Density functional theory calculations have elucidated that the thin Pt shell structure can effectively augment the adsorption of NH 3 and diminish the activation energy of the AOR process. This seminal work provides a conceptual framework for the design of efficacious AOR catalysts.
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