One-dimensional platinum-based hybrid nanostructures for high performance electrodes in proton exchange membrane fuel cells

To reduce the required high loading of Pt to catalyse the sluggish oxygen reduction reaction (ORR) at cathodes in proton exchange membrane fuel cells (PEMFC), much development has been made on increasing the efficiency of the catalyst material. However, there is big challenge to fully translate catalytic enhancements into higher performance catalyst electrodes in PEMFCs. Pt nanowire (NW) array gas diffusion electrodes (GDEs) matches the promise of higher PEMFC performances. Alloying of Pt with a non-noble metal such as Ni, and using alternative carbonaceous supports such as carbon nanotubes (CNTs) are known methods of increasing ORR catalytic activity. This study applies both methods to improve the performance of the Pt NW array system and to better understand the mechanisms that influence real performance of PEMFC catalyst materials. Herein, a facile method for the preparation of PtNi NWs supported on carbon is developed by an impregnation and annealing approach. The optimal PtNi NW/C catalyst is achieved at an annealing temperature of 150°C with a duration of 24 hrs, showing 1.78-fold mass activity enhancement with respect to the pure Pt NWs. However, very poor power performance is observed for the PtNi NW/C GDE in PEMFCs. This is ascribed to the increased mass transport resistance resulting from ionomer contamination within the catalyst layer caused by severe Ni dissolution from the PtNi NWs. An acid leaching step is therefore introduced in the fabrication of PtNi NW array GDEs and an optimised GDE gave a 1.07-fold of power density with respect to the Pt NW array GDE. Finally, nitrogen-doped CNT arrays are fabricated directly onto the GDL surface by plasma enhanced chemical vapour deposition (PECVD) and active screen plasma treatment (ASP). These act as the catalyst support for Pt NW arrays where much enhanced power performance as compared to Pt NW array and Pt/C GDEs is attributed to an increase in macropores with a diameter range of 315-360 nm, concluding that mass transport properties are the key to translating effective ORR catalysts into high performance PEMFC electrodes