Abstract: A substrate for a composite membrane includes a microporous polyolefin membrane for carrying a hydrophilic resin compound within the pores of the microporous membrane wherein: the average pore diameter is 1 nm to 50 nm; the porosity is 50% to 78%; the membrane thickness is 1 ?m to 12 ?m; and, when a mixed solution of ethanol and water (volume ratio 1/2) is dripped onto a surface of the microporous polyolefin membrane which has not undergone hydrophilization treatment, the contact angle ?1 between the droplet and the surface is 0 to 90 degrees 1 second after the dripping, and the contact angle ?2 between the droplet and the surface is 0 to 70 degrees 10 minutes after the dripping, and the rate of change of the contact angle ((?1??2)/?1×100) is 10 to 50%.

Abstract: A substrate for a composite membrane includes a microporous polyolefin membrane for carrying a hydrophilic resin compound within the pores of the microporous membrane wherein: the average pore diameter is 1 nm to 50 nm; the porosity is 50% to 78%; the membrane thickness is 1 ?m to 12 ?m; and, when a mixed solution of ethanol and water (volume ratio 1/2) is dripped onto a surface of the microporous polyolefin membrane which has not undergone hydrophilization treatment, the contact angle ?1 between the droplet and the surface is 0 to 90 degrees 1 second after the dripping, and the contact angle ?2 between the droplet and the surface is 0 to 70 degrees 10 minutes after the dripping, and the rate of change of the contact angle ((?1??2)/?1×100) is 10 to 50%.

Abstract: To provide an electrolyte membrane that exhibits high proton conductivity even at low humidity, the electrolyte membrane includes a composite membrane including: a microporous polyolefin membrane that has an average pore diameter of 1 to 1000 nm and a porosity of 50 to 90% and that can be impregnated with a solvent having a surface free energy of 28 mJ/m2 or more, and an electrolyte containing a perfluorosulfonic acid polymer having an EW of 250 to 850 loaded into the pores of the microporous polyolefin membrane, wherein the membrane thickness of the composite membrane is 1 to 20 ?m.

Abstract: A substrate for a composite membrane includes a microporous polyolefin membrane for carrying a hydrophilic resin compound within the pores of the microporous membrane wherein: the average pore diameter is 1 nm to 50 nm; the porosity is 50% to 78%; the membrane thickness is 1 ?m to 12 ?m; and, when a mixed solution of ethanol and water (volume ratio ½) is dripped onto a surface of the microporous polyolefin membrane which has not undergone hydrophilization treatment, the contact angle ?1 between the droplet and the surface is 0 to 90 degrees 1 second after the dripping, and the contact angle ?2 between the droplet and the surface is 0 to 70 degrees 10 minutes after the dripping, and the rate of change of the contact angle ((?1??2)/?1×100) is 10 to 50%.

Abstract: To provide an electrolyte membrane that exhibits high proton conductivity even at low humidity, the electrolyte membrane includes a composite membrane including: a microporous polyolefin membrane that has an average pore diameter of 1 to 1000 nm and a porosity of 50 to 90% and that can be impregnated with a solvent having a surface free energy of 28 mJ/m2 or more, and an electrolyte containing a perfluorosulfonic acid polymer having an EW of 250 to 850 loaded into the pores of the microporous polyolefin membrane, wherein the membrane thickness of the composite membrane is 1 to 20 ?m.