Polymer electrolyte membrane, method for producing the same, and proton conductivity evaluation method for polymer electrolyte membrane

Abstract

The present invention provides a polymer electrolyte membrane with excellent proton conductivity in its thickness direction. Preferably, the polymer electrolyte membrane contains a polymer compound comprising an ionic segment having an ionic functional group and a nonionic segment having substantially no ionic functional group, and the phase containing ionic segments as a main component and the phase containing nonionic segments as a main component are phase-separated, and in the surface region thereof, the change in the amount of the ionic segment from the surface toward the interior substantially decreases monotonically.

1 . A polymer electrolyte membrane containing a polymer compound comprising an ionic segment having an ionic functional group and a nonionic segment having substantially no ionic functional group, wherein
 a phase containing the ionic segments as a main component and a phase containing the nonionic segments as a main component are phase-separated, and   when the intensity of a specific signal selected from signals originating in the ionic segment is assigned value A and the intensity of a specific signal selected from signals originating in the nonionic segment is assigned value B for performing X-ray photoelectron spectroscopy, a change in value represented by A/(A+B) substantially decreases monotonically from the surface toward the interior in the surface region of at least one surface thereof.   
     
     
         2 . The polymer electrolyte membrane according to  claim 1 , wherein the change in value represented by A/(A+B) is expressed as the change in value of A/(A+B) plotted against sputtering time t when sputtering using C 60  ions and measurement of the value represented by A/(A+B) are repeatedly performed. 
     
     
         3 . The polymer electrolyte membrane according to  claim 2 , wherein, in the surface region, when the value of A/(A+B) is measured, from the start of sputtering, at each elapsed time point in which the depth in terms of SiO 2  is between 0.1 nm and 0.5 nm, and the correlation coefficients between t and the value represented by A/(A+B), which are obtained by taking measurements from the 1st measurement up to an arbitrary nth measurement, are calculated, all correlation coefficients obtained thereby are negative when n is 4 or more. 
     
     
         4 . The polymer electrolyte membrane according to  claim 1 , wherein the specific signal selected from the signals originating in the ionic segment is a signal that is not observed from the main nonionic segment. 
     
     
         5 . The polymer electrolyte membrane according to  claim 1 , wherein the specific signal selected from the signals originating in the nonionic segment is a signal that is not observed from the main ionic segment. 
     
     
         6 . A polymer electrolyte membrane containing a polymer compound comprising an ionic segment having an ionic functional group and a nonionic segment having substantially no ionic functional group, wherein
 a phase containing the ionic segments as a main component and a phase containing the nonionic segments as a main component are phase-separated, and in a surface region said membrane does not have a layer in which the concentration of the nonionic segments is essentially higher than the mean concentration of the nonionic segments throughout the entirety thereof.   
     
     
         7 . A method for producing a polymer electrolyte membrane containing a polymer electrolyte comprising a polymer compound having an ionic segment having an ionic functional group and a nonionic segment having substantially no ionic functional group; said method comprising the steps of:
 applying a solution containing the polymer electrolyte to a substrate having a surface comprising a metal or a metal oxide; and   evaporating the solvent from the solution, wherein   in the evaporation step, the time from the start of solvent evaporation until completion thereof is 60 minutes or less.   
     
     
         8 . A proton conductivity evaluation method for a polymer electrolyte membrane containing a polymer compound comprising an ionic segment having an ionic functional group and a nonionic segment having substantially no ionic functional group,
 said method comprising:   a first step of performing sputtering in use of C 60  ions from the surface toward the interior, and by performing X-ray photoelectron spectroscopy on the surface at sputtering elapsed time t for each time point, obtaining the intensity A of a specific signal selected from signals originating in the ionic segment and the intensity B of a specific signal selected from signals originating in the nonionic segment for each time point t; and   a second step of determining a change in value represented by A/(A+B) plotted against t is whether substantially monotonically decreasing or not.   
     
     
         9 . The evaluation method according to  claim 8 , wherein in the first step, A/(A+B) is measured from the start of sputtering for each elapsed time in which the depth in terms of SiO 2  is between 0.1 nm and 0.5 nm, and in the second step, and the correlation coefficient between t and the value represented by A/(A+B), which are obtained by taking measurements from the 1st measurement up to an arbitrary nth measurement, is obtained and judged to be negative or positive for all correlation coefficients obtained when n is 4 or more.