Platinum-Nickel Nanowires and Nanotubes Arrays as Carbon-Free Cathodes for the Polymer Electrolyte Membrane Fuel Cell

The cathode is the most crucial component of the polymer electrolyte membrane fuel cell (PEMFC) because it is the most limiting in terms of performance, durability, and cost. Regarding the performance, the main losses are due to the cathode because of the negative coupling between a sluggish oxygen reduction reaction (ORR) and H+ and O2 transport loss issues. Therefore, many efforts have been conducted on the one hand to increase the kinetic of the ORR by developing a catalyst with improved activity and stability. On the other hand, attempts have been made to reduce mass transport losses in the cathode by tuning its nanostructure. This paper describes a multistep process to nanostructure the electrocatalyst in the view of simultaneously benefiting from enhanced activity toward the ORR and reduced O2 transport limitations. Thus, original carbon-free electrode's architectures made of organized and well-ordered and oriented PtNi nanowires (PtNiNWs) and nanotubes (PtNiNTs) directly embedded onto a Nafion membrane were developed. Here, the nanotubes were templated from Ni nanowires grown on an anodic aluminum oxide (AAO) template. The fabrication process was optimized to improve the quality of the nanotubes and their integration into the membrane: the process includes thermal treatment in a H2/Ar environment and an acid leaching step as key steps to obtain the desired structure. After the electrodes were integrated in a complete membrane-electrode assembly (MEA), we tested the performance and durability of these nanostructures under real operating conditions. We compared the results to a Pt/C conventional electrode at low Pt loading (similar to 35 mu gPt/cm2) exhibiting a roughness factor close to that of PtNiNWs and PtNiNTs electrodes. Results have shown a great improvement in the mass activity and stability of PtNiNTs electrodes in an accelerated stress test. Also, they have shown a significant sensitivity toward relative humidity variation.