Hierarchical, Nature-Inspired Nanomaterials for Electrochemical Energy Conversion/Storage Devices

摘要

Several studies on polymer electrolyte fuel cell (PEFC) durability have shown that the components of the central membrane electrode assembly (MEA), especially the polymer electrolyte membrane (PEM) and electrocatalyst, deteriorate during long term operation. PEM chemical degradation as well as electrocatalyst dissolution are reported to be the major contributors to PEFC lifetime limitations. The chemical degradation of the PEM occurs in a two step process: (i) formation of reactive oxygen species (ROS) such as hydroxyl (OH*) and hydroperoxyl (HOO*) radicals (OH* are far more reactive); and (ii) reaction of ROS with the PEM leading to chain scission. Additionally, loss of electrochemically active area is observed under long term operation due to nanoparticle growth by Ostwald ripening where large Pt particles grow at the expense of small ones via interparticle transport of single atoms. In order to mitigate those degradation mechanisms, the efficacy of rare earth metal oxide nanoparticles on reducing the membrane degradation rate as a function of their microstructure, redox properties and location within the fuel cell is presented. On the catalyst dissolution front, the investigation of the effect of uniform particle size distribution on catalyst stability is presented via theoretical and in-situ experimental studies. To further improve the design of highly stable hierarchical electrocatalysts, in-depth research on the effect of nano-architecture on reaction/transport kinetics is necessary. Inspiration can be derived from nature as it is full of hierarchical designs that are intrinsically scaling. Developing fundamental understanding of how such desired properties of biological systems are related to their architecture and self-assembly dynamics can guide the development of novel hierarchical catalytic nanomaterials and nature-inspired electrochemical devices.