Control of the micro/nano structure of cathode catalyst layers for polymer electrolyte membrane fuel cells

Abstract

In the most hydrocarbon membrane based PEMFCs, hydrocarbon binders are favorably considered in the catalyst layers because these membrane-binder combinations prevent the interfacial delamination problem. However, hydrocarbon binders form dense layers so that catalytic reactions in the electrodes, especially on the cathode side, are easily impaired. Because the oxygen reduction reaction (ORR) and water flooding is typically a major bottleneck in the overall fuel cell performance, this additional problem represents a serious limitation in the entire cell operation. Although large capacity Li-ion battery for electric vehicle (EV) has accelerated as plug-in hybrid vehicles and ultimately pure EVs are developed, its energy density is still the insufficient storage capacity by the positive electrode. Different from conventional Li-ion batteries, the air electrode of Li-air batteries can reduce $O_2$ from air to deliver capacity. If the inexhaustible $O_2$ in air can be continuously utilized to provide capacity, the Li-air battery potentially has much higher gravimetric energy storage density compared to all other energy storage devices. Then, further developed by many scientists over the world. In Chapter Ⅱ, A new concept of in-situ pore generation to reduce water flooding in cathode catalyst layer (CCL) of polymer electrolyte membrane fuel cell(PEMFC) is proposed with the introduction of water soluble poly(ethylene glycol) (PEG) as a porogen to CCL based on sulfonated poly(ether ether ketone) (sPEEK). In this new type of CCL, PEG is directly removed by water produced during the cathode reaction. The new CCL exhibited much higher cell performance especially in mass transport limitation region compared to the pristine sPEEK CCL. In addition, the presence of PEG in the new CCL lowered the glass transition temperature of the sPEEK binder, and it could improve the transference of catalyst layer onto the polymer electrolyte membrane. In Chapter Ⅲ, The electrochemical acti...