Biomimetic design of monolithic fuel cell electrodes with hierarchical structures

Despite the significant improvement of polymer electrolyte membrane fuel cell catalyst activities, a cost-effective and stable membrane electrode assembly is still lacking, which greatly inhibits the commercialization of this efficient and environmental friendly technology in stationary and transportation applications. The main reason is that the engineering of different components of an electrode, such as catalytically active metals, electron transport and reactant diffusion paths in a compatible way is very challenging. Here we show the design and preparation of a monolithic fuel cell electrode with a compatible wire on wire structure that mimics the configuration of a pine tree. We developed a procedure to make a flexible carbon thin film composed of porous nanofibers with a thickness of $ 100 nm and centimeter scale lengths. Platinum nanowires (ca. 3 nm diameter) were deposited on these microscale carbon nanofiber films, resulting in a hierarchical structure. The platinum nanowires were then decorated with a porous bismuth coating to modulate the atomic structure and induce catalytic activity toward formic acid electrooxidation. The end result is a monolithic structure used as a fuel cell electrode that combines microscale diffusive pathways and nanoscale catalyst structures. Prepared by a process that is readily scalable, this design strategy offers a new way to tailor catalytic functions at a system level.