Provided are a method for producing a liquid composition which is capable of eliminating clouding of a liquid with cerium (IV) hydroxide particles in a relatively short time, and methods for producing a polymer electrolyte membrane, a catalyst layer and a membrane/electrode assembly, each having excellent durability, in a relatively short time. A method for producing a liquid composition containing a fluoropolymer having sulfonic acid groups, trivalent cerium ions and water, which comprises (1) irradiating a solution containing at least one cerium compound selected from the group consisting of cerium carbonate, cerium hydroxide and cerium oxide, the fluoropolymer and the water, with light at least partially in a wavelength region from 300 to 400 nm so that the ultraviolet irradiance on the surface of the solution is at least 0.1 mW/cm.sup.2 or (2) adding a reducing agent to a solution containing at least one cerium compound selected from the group consisting of cerium carbonate, cerium hydroxide and cerium oxide, the fluoropolymer and the water.

The present invention provides a method of operating a fuel cell, which method enables a polymer electrolyte membrane to be humidified sufficiently under high-temperature conditions, and can obtain excellent power generation performance. The present invention is a method of operating a fuel cell including a membrane electrode assembly containing an electrolyte membrane, catalyst layers, and gas diffusion layers, the method including a step of setting the operating temperature of the fuel cell at 100° C. or more, wherein, in the step, the relative humidity of supply gas to be supplied to the fuel cell is 70% or more, and the back pressure of the supply gas is 330 kPa or more.

The present invention provides a method of operating a fuel cell, which method enables a polymer electrolyte membrane to be humidified sufficiently under high-temperature conditions, and can obtain excellent power generation performance. The present invention is a method of operating a fuel cell including a membrane electrode assembly containing an electrolyte membrane, catalyst layers, and gas diffusion layers, the method including a step of setting the operating temperature of the fuel cell at 100° C. or more, wherein, in the step, the relative humidity of supply gas to be supplied to the fuel cell is 70% or more, and the back pressure of the supply gas is 330 kPa or more.

The present invention relates to new anion exchange polymers and (blend) membranes made from polymers containing highly fluorinated aromatic groups by means of nucleophilic substitution and processes for their production by means of nucleophilic aromatic substitution and their areas of application in membrane processes, in particular in electrochemical membrane processes such as fuel cells, electrolysis and redox flow batteries.

The invention relates to a membrane which contains crosslinked phosphonated pentafluorostyrene. The invention also relates to the use of a membrane or membrane electrodes containing crosslinked phosphonated pentafluorostyrene in an electrochemical cell at a temperature of 0 to 380° C. The invention also describes the use of a membrane or membrane electrodes containing non-crosslinked phosphonated pentafluorostyrene in an electrochemical cell at a temperature of 0 to 380° C. In addition, the invention discloses a nonwoven fabric containing phosphonated polypentafluorostyrene. The invention also relates to the use of the nonwoven fabric in a membrane or in a membrane electrode unit in electrochemical applications at temperatures up to 380° C.

A coated electrode assembly (CEA) comprising: i) a gas diffusion layer (GDE); and ii) a coating. The GDE comprises a gas diffusion layer (GDL) and a catalyst layer. The catalyst layer is disposed between the coating and the GDL. The catalyst layer comprises a hydrophobic polymer and/or an ionomeric polymer and the coating comprises a hydrophobic polymer and/or an ionomeric polymer. A method for making a CEA is provided. The CEA may have improved performance and stability compared to a membrane electrode assembly (MEA).

An anion exchange polymer includes aryl ether linkage free polyarylenes having aromatic/polyaromatic rings in polymer backbone and a tethered alkyl quaternary ammonium hydroxide side groups. This anion exchange polymer may be utilized in an anion exchange process and may be made into a thin anion transfer membrane. An ion transfer membrane may be mechanically reinforced having one or more layers of functional polymer based on a terphenyl backbone with quaternary ammonium functional groups and an inert porous scaffold material for reinforcement. An anion exchange membrane may have multilayers of anion exchange polymers which each containing varying types of backbones, varying degrees of functionalization, or varying functional groups to reduce ammonia crossover through the membrane.

An anion exchange polymer includes aryl ether linkage free polyarylenes having aromatic/polyaromatic rings in polymer backbone and a tethered alkyl quaternary ammonium hydroxide side groups. This anion exchange polymer may be utilized in an anion exchange process and may be made into a thin anion transfer membrane. An ion transfer membrane may be mechanically reinforced having one or more layers of functional polymer based on a terphenyl backbone with quaternary ammonium functional groups and an inert porous scaffold material for reinforcement. An anion exchange membrane may have multilayers of anion exchange polymers which each containing varying types of backbones, varying degrees of functionalization, or varying functional groups to reduce ammonia crossover through the membrane.

Disclosed is an antioxidant for a polymer electrolyte membrane of a fuel cell including cerium hydrogen phosphate (CeHPO.sub.4). The presence of cerium hydrogen phosphate in the antioxidant enhances the dissolution stability of cerium and improves the ability to capture water, leading to an increase in proton conductivity. In addition, the cerium hydrogen phosphate has a crystal structure composed of smaller cerium particles. This crystal structure greatly improves the ability of the antioxidant to prevent oxidation of the electrolyte membrane. Also disclosed are an electrolyte membrane including the antioxidant, a fuel cell including the electrolyte membrane, a method for preparing the antioxidant, a method for producing the electrolyte membrane, and a method for fabricating the fuel cell.

The present disclosure relates to a polymer electrolyte membrane comprising a polymer membrane containing an ion conductor, and a plurality of composite fibers, wherein the composite fiber comprises a core portion continuously formed in the longitudinal direction of the composite fiber and a matrix portion surrounding the core portion, and the core portion contains an ion exchange functional group.