Disclosed are redox flow battery membranes, redox flow batteries incorporating the membranes, and methods of forming the membranes. The membranes include a densified polybenzimidazole gel membrane that is capable of incorporating a high liquid content without loss of structure that is formed according to a process that includes in situ hydrolysis of a polyphosphoric acid solvent followed by densification of the gel membrane. The densified membranes are then imbibed with a redox flow battery supporting electrolyte such as sulfuric acid and can operate at very high ionic conductivities of about 50 mS/cm or greater and with low permeability of redox couple ions, e.g. vanadium ions, of about 10.sup.−7 cm.sup.2/s or less. Redox flow batteries incorporating the membranes can operate at current densities of about 50 mA/cm.sup.2 or greater.

A proton-conducting polymer comprises a plurality of repeating units of formula (I) for electrochemical reactions. The polymer may be synthesized from a super acid catalyzed polyhydroxyalkylation reaction of monomers Ar.sub.1′, Ar.sub.2′, and X.sub.1′ followed by a nucleophilic substitution reaction or a grafting reaction, and optionally an acidification reaction.

##STR00001##

Proton-exchange membranes and membrane electrode assemblies made from the polymer are also described.

A new polyelectrolyte multilayer coated proton-exchange membrane for electrolysis and fuel cell applications has been developed for electrolysis and fuel cell applications. The polyelectrolyte multilayer coated proton-exchange membrane comprises: a cation exchange membrane, and a polyelectrolyte multilayer coating on one or both surfaces of the cation exchange membrane. The polyelectrolyte multilayer coating comprises alternating layers of a polycation polymer and a polyanion polymer. The polycation polymer layer is deposited on and is in contact with the cation exchange membrane. The top layer of the polyelectrolyte multilayer coating can be either a polycation polymer layer or a polyanion polymer layer.

A redox flow battery includes: a negative electrode; a positive electrode; a first liquid which is in contact with the negative electrode, and which contains a first nonaqueous solvent, a first redox species, and metal ions; a second liquid which is in contact with the positive electrode, and which contains a second nonaqueous solvent, a second redox species, and metal ions; and a metal ion-conducting membrane disposed between the first liquid and the second liquid. The metal ion-conducting membrane contains an organic polymer containing a plurality of hydroxy groups. The organic polymer contains a group formed by substituting at least a portion of the hydroxy groups with a metal sulfonate.

A redox flow battery includes: a negative electrode; a positive electrode; a first liquid which is in contact with the negative electrode, and which contains a first nonaqueous solvent, a first redox species, and metal ions; a second liquid which is in contact with the positive electrode, and which contains a second nonaqueous solvent, a second redox species, and metal ions; and a metal ion-conducting membrane disposed between the first liquid and the second liquid. The metal ion-conducting membrane contains an organic polymer containing a plurality of hydroxy groups. The organic polymer contains a group formed by substituting at least a portion of the hydroxy groups with a metal sulfonate.

To provide a proton conductive material which has high proton conductivity even under no humidification and does not elute into water. A proton conductive material comprising a proton-source-polymer and a proton-channel-polymer, wherein at least one selected from the group consisting of the proton-source-polymer and the proton-channel-polymer is a polymer containing an aromatic ring, and wherein at least a part of the polymer containing the aromatic ring has a stacked structure formed by n-n interactions, and a proton conductive material comprising a proton-source-crosslinked-polymer, wherein the proton-source-crosslinked-polymer is a polymer having a main skeleton which contains a proton source group and an aromatic ring, and a crosslinked structure which contains a proton channel, and wherein at least a part of the proton-source-crosslinked-polymer has a stacked structure formed by n-n interactions.

To provide a proton conductive material which has high proton conductivity even under no humidification and does not elute into water. A proton conductive material comprising a proton-source-polymer and a proton-channel-polymer, wherein at least one selected from the group consisting of the proton-source-polymer and the proton-channel-polymer is a polymer containing an aromatic ring, and wherein at least a part of the polymer containing the aromatic ring has a stacked structure formed by n-n interactions, and a proton conductive material comprising a proton-source-crosslinked-polymer, wherein the proton-source-crosslinked-polymer is a polymer having a main skeleton which contains a proton source group and an aromatic ring, and a crosslinked structure which contains a proton channel, and wherein at least a part of the proton-source-crosslinked-polymer has a stacked structure formed by n-n interactions.

A composite electrolyte membrane having a composite layer that is a composite of a hydrocarbon polymer electrolyte and a fluorine-containing polymer porous substrate, wherein a fractal dimension D exhibiting the distribution of the hydrocarbon polymer electrolyte and the fluorine-containing polymer porous substrate in the composite layer is 1.7 or more. An object of the present invention is to enable a composite electrolyte membrane composed of a hydrocarbon polymer electrolyte and a fluorine-containing polymer porous substrate to achieve high proton conduction ability and high mechanical durability.

A polymer including a hydrophilic block and a hydrophobic block, wherein the hydrophilic block includes a unit derived from a compound represented by Chemical Formula 1, and the hydrophobic block includes a unit derived from a fluorine-containing compound, a polymer separator including the same, and a membrane electrode assembly, a fuel cell and a redox flow battery including the same.

A polymer including a hydrophilic block and a hydrophobic block, wherein the hydrophilic block includes a unit derived from a compound represented by Chemical Formula 1, and the hydrophobic block includes a unit derived from a fluorine-containing compound, a polymer separator including the same, and a membrane electrode assembly, a fuel cell and a redox flow battery including the same.