In response to the energy needs of modern society and emerging ecological concerns, the pursuit of novel, low-cost, and environmentally friendly energy conversion and storage systems has raised significant interest. Among these systems, proton exchange membrane fuel cells (PEMFCs), have gained much attentions for their high efficiency, high power density, with low greenhouse gas emission. In conventional PEMFCs, Nafion^® is used as the electrolyte, which however brings many drawbacks such as high production cost, environmental incompatibility, and low operation temperature (< 80 ºC). These bottlenecks hindered the development and commercialization of PEMFCs. Alternative types of PEMs thereby were adopted, such as hydrocarbon polymers and hybrid membranes. In the case of hybrid PEMs, many different types of fillers have been adopted into the polymer matrix to fabricate hybrid membranes with different methods. The composite method has proved to be an effective route to improve the practical properties of PEMs and offer the opportunity to operate PEMFCs at higher temperatures. However, severe problems still exist to limit their practical use in PEMFCs. Firstly, a vast majority of fillers with little protogenic groups were used as the additives of PEMs. The adoption of these fillers greatly decreased the ionic sites for proton transport and thus the conductivity. Furthermore, the natural conflict between high content of fillers and particle agglomeration makes it difficult to select a proper concentration for fillers that can not only be well dispersed in PEMs, but also construct inorganic pathways for improved proton conductivity. These shortcomings would greatly limit the implementation of hybrid PEMs. New strategies to form uniformly dispersed filler materials that can form continuous proton pathway are appreciated.

In this dissertation, the fabrication of novel hybrid PEMs, in which fibers with surface sulfonic acid groups were incorporated, is demonstrated. Electrospinning and post-electrospinning treatments, such as sulfonation, calcinations, et al., were applied to fabricate the filler materials. Chemical or physical methods were applied to prepare the hybrid PEMs with ionomer matrices. In the novel hybrid PEMs, sulfonic acid groups surrounding the interconnected fibers help build a network of long-range ionic pathways on the interfaces of fibers and ionic polymer matrix for fast proton transport. Compared with conventional composite PEMs as well as Nafion, the novel hybrid PEMs possess much higher proton conductivity. Furthermore, the newly developed hybrid PEMs are easy to fabricate, highly controllable, and can be used in practical fuel cell systems. Therefore, this new technology offers a potential strategy on the rational design of advanced PEMs, and opens up new opportunities for high-perfomance PEMFCs, which are one of the promising power sources for consumer devices and electric vehicles, and will play a critical role in solving the worldwide critical energy issue.