Fuel cells are electrochemical devices that produce usable electricity by the catalyzed combination of a fuel such as hydrogen and an oxidant such as oxygen. In contrast to conventional power plants, such as internal combustion generators, fuel cells do not utilize combustion. As such, fuel cells produce little hazardous effluent. Fuel cells convert hydrogen fuel and oxygen directly into electricity, and can be operated at higher efficiencies compared to internal combustion generators.
A fuel cell such as a proton exchange membrane (PEM) fuel cell typically contains a membrane electrode assembly, which consists of a catalyst coated membrane disposed between a pair of gas diffusion layers. The catalyst coated membrane itself typically includes an electrolyte membrane disposed between a pair of catalyst layers. The respective sides of the electrolyte membrane are referred to as an anode portion and a cathode portion. In a typical PEM fuel cell, hydrogen fuel is introduced into the anode portion, where the hydrogen reacts and separates into protons and electrons. The electrolyte membrane transports the protons to the cathode portion, while allowing a current of electrons to flow through an external circuit to the cathode portion to provide power. Oxygen is introduced into the cathode portion and reacts with the protons and electrons to form water and heat.
Another type of electrochemical device is an electrolysis cell, which uses electricity to produce chemical changes or chemical energy. An example of an electrolysis cell is a chlor-alkali membrane cell where aqueous sodium chloride is electrolyzed by an electric current between an anode and a cathode. The electrolyte is separated into an anolyte portion and a catholyte portion by a membrane subject to harsh conditions. In chlor-alkali membrane cells, caustic sodium hydroxide collects in the catholyte portion, hydrogen gas is evolved at the cathode portion, and chlorine gas is evolved from the sodium chloride-rich anolyte portion at the anode.
Due to their ionic properties, fluorinated ionomers are suitable for forming electrolyte membranes in fuel cells, electrolysis cells, and other electrochemical devices. Fluorinated ionomers are typically prepared by free-radical polymerization of fluorinated ionic monomers or precursors. The free-radical polymerization, however, also produces carbonyl end groups (e.g., —COOH end groups, —COO− end groups, —COF end groups, and —CONH2 end groups) on the resulting fluorinated ionomers. The carbonyl end groups are vulnerable to peroxide radical attacks, which reduce the oxidative stability of the fluorinated ionomers. During operation of a fuel cell, electrolysis cell, or other electrochemical cell, peroxides can be formed. This degrades the fluorinated ionomers, and correspondingly reduces the operational life of the given electrolyte membrane.