Effect of heat treatment on the surface structure of Pd@Pt–Ni core-shell catalysts for the oxygen reduction reaction

Highlights: • We design an efficient and green batch preparation method for high-performance core-shell catalysts. • Suitable heat treatment temperature can effectively promote the formation of core-shell structure. • The MEA prepared by the core-shell Pd@Pt-Ni catalyst shows an increase of 2.2% in the maximum power density compared with the commercial Pt/C catalyst. -- Abstract: To promote the commercialization of fuel cells by reducing cost, it is essential to reduce the amount of Pt in the catalyst and apply the low-Pt catalysts to the membrane electrode assembly (MEA). In this work, the high-performance Pd@Pt-Ni/C catalysts are prepared by a simple and effective method and applied in MEAs successfully. The particle size of the core-shell structure catalyst (Pd@Pt–Ni/C-200 °C) is around 4.5 nm and the particles are evenly dispersed on the carbon support. By optimizing the heat treatment temperature, it is found that the reduction of Pt on the surface of the catalyst can be achieved and the uniform distribution of the Pt-Ni shell can also be promoted to enhance the catalyst activity at 200 °C. Besides, the heat treatment at 200 °C can not only extend the stability of the catalyst but also avoid excessive particle size growth. The mass activity (MA) is nearly 5.1 times higher than that of commercial Pt/C catalysts (JM). After the accelerated degradation testing (ADT), the half-wave potential of Pd@Pt–Ni/C-200 °C only shifted 6 mV and MA could maintain 85.5%. In single-cell tests, the MEA prepared by Pd@Pt-Ni/C-200 °C has a maximum power density of 0.92 W/cm², which is 2.2% higher than that of Pt/C. Besides, the oxygen mass transfer resistance of MEA-Pd@Pt-Ni/C (23.0 s/m) is lower than that of MEA-Pt/C (26.2 s/m), indicating that the catalyst layer prepared by Pd@Pt–Ni/C is more conducive to oxygen transmission. It indicates that the Pd@Pt-Ni/C core-shell catalyst can be the promising catalyst to be applied to proton exchange membrane fuel cells (PEMFC).