5  US 7,118,821 B2  6  An approach to produce an effective PCM is based on  organic-inorganic materials generated by sol-gel and has  recently gained increasing interest in view of obtaining new  composite compounds with unique properties that result  from intimate mixing of various components on a molecular  level. In the sol-gel process organic groups are introduced by  co-condensation of alkoxides (of silicon, aluminum, tita› nium, zirconium, tin, etc.) with reactive organic functional› ities followed by organic cross-liuking reactions, thus pro› viding the advantages of the polymers, while the inorganic  network gives an amorphous structure and good thermal,  mechanical and chemical stability. Some of the membranes  investigated so far are: 1) NAFION/alkoxide composite  membranes, such as, NAFION/SiO$_{2}$-P  $_{2}$O$_{5}$-ZrO$_{2 }$ [M.  Aparicio, F. Damay,  L.  C. Klein, "Characterization of SiO2- P2O5-Zr02 sol-gel/NAFION composite membranes",  Jour› nal of Sol-Gel Science and Technology,  26(1/2/3) (2003), p.  1055-1059 and Aparicio, M.; Klein,  L.  C.; Adjemian, K. T.;  Bocarsly, A. B., "SiO2-P2O5-Zr02 sol-gel/NAFION com› posite membranes for PEMFC",  Ceramic Transactions,  127  (2002), p. 167-176], NAFION/silicon oxide [Jung, D. H.;  Cho, S.  Y.; Peck, D. H.; Shin, D. R.; Kim, J. S., "Perfor› mance evaluation of a Nafion/silicon oxide hybrid mem› brane for direct methanol fuel cell",  Journal of Power  Sources,  106 (2002), p. 173-177 and Kim, Haekyoung; Lim,  C.; Chang, H., "Fabrications and direct methanol fuel cell  applications ofNafion based organic-inorganic hybrid mem› brane",  Proceedings-Electrochemical  Society  (2001 ),  2001-4(Direct Methanol Fuel Cells), p14-28], NAFION/  glass [Nogami, M.; Usui,  Y.; Kasuga, T., "Proton conducting  organic-glass  composites",  Fuel Cells,  1  (2001 ),  p.  181-185], NAFION/silica [Miyake, N.; Wainright, J. S.;  Savinell, R. F., "Evaluation of a sol-gel derived Nafion/silica  hybrid membrane for polymer electrolyte membrane fuel  cell applications 11. Methanol uptake and methanol perme› ability",  Journal of the Electrochemical Society,  148 (2001),  A905-A909 and Miyake, N.; Wainright, J. S.; Savinell, R.  F., "Evaluation of a sol-gel derived Nafion/silica hybrid  membrane for proton electrolyte membrane fuel cell appli- Hence, in the subject invention the host polymer, such as  PVP, has a strong interaction with the selected acid, such as  H$_{3}$PO$_{4}$ ,  thus having a large intake of the acid. The acid is  immobilized in the interpenetrating network formed by  condensation of silica in the membrane to avoid leaching  out. The membrane is flexible, transparent, and ductile.  Because of a large amount of acid, such as H$_{3}$PO$_{4}$ ,  already  imbedded in the membrane, a small amount of water can  significantly facilitates the proton conduction, thus leading  to a high conductivity under a low humidity. The conduction  mechanism is a proton being transferred between acid  molecules or between an acid molecule and a water mo!- ecule or between water molecules in a combination of a  Grotthus-type mechanism (i.e., the protons are transferred  within adjacent hydrogen bonds) and a vehicular mecha› msm.  In relation to Chen et al. [Chen, N.; Hong,  L.  Solid State  Ionics,  2002, 146, 377], the subject invention uses H$_{3}$PO$_{4 }$ as  an extra proton carrier to facilitate the proton conduction and  H$_{3}$PO$_{4 }$ is imbedded in the silica network.  cations  1.  Proton conductivity and water content",  Journal  of the Electrochemical Society,  148 (2001), A898-A904],  NAFION/TiO$_{2 }$ [Uchida, Hiroyuki; Ueno, Yoshihiko; Hagi- hara, Hiraki; Watanabe, Masahiro, "Self-humidifying elec› trolyte membranes for fuel cells",  Journal of the Electro› chemical Society,  150 (2003), A57-A62], NAFION/Cs+ ions  [V. Tricoli, "Proton and methanol transport in poly(perfluo› rosulfonate) membranes containing Cs+ and H+ cations",  J.  Electrochem.  Soc.  145  (1998),  p.  3798-3801],  and  NAFION/alkoxides of Ti, Al, Zr and organoalkoxysilanes  [V. Tricoli, "Proton and methanol transport in poly(perfluo› rosulfonate) membranes containing Cs+ and H+ cations",  J.  Electrochem. Soc.  145 (1998), p. 3798-3801]. It was found  that the incorporation of inorganic phase in NAFION led to  improvements in its thermal stability, reduction of methanol  crossover, and higher performance at elevated temperature.  However, the proton conductivity in the hybrid membrane  was lower than, or equal to, that in unmodified NAFION  membranes if the inorganic phase was not P$_{2}$O$_{5 }$ [M. Apari- cio, F. Damay,  L.  C. Klein, "Characterization ofSiO2-P2O5- Zr02 sol-gel/NAFION composite membranes",  Journal of  Sol-Gel Science and Technology,  26(1/2/3) (2003), p.  1055-1059, Nogami, M.; Usui,  Y.; Kasuga, T., "Proton  conducting organic-glass composites",  Fuel Cells,  1 (2001),  p. 181-185, and Miyake, N.; Wainright, J. S.; Savinell, R.  F.,  "Evaluation of a sol-gel derived Nafion/silica hybrid mem- brane for proton electrolyte membrane fuel cell applications  1. Proton conductivity and water content",  Journal of the  Electrochemical Society,  148 (2001), A898-A904], which  favored proton migration based on the Grotthus-type mecha› nism [T. Yajima and H. Iwahara H. Uchida, "Protonic and  oxide ionic conduction in BaCeO$_{3}$-based ceramics---effect  of partial substitution for Ba in BaCe$_{0}$ _ $_{9}$O$_{3}$ - with Ca",  Solid  State Ionics,  47 (1991), p. 117-124, N. Bonanos, B. Ellis, K.  S. Knight and M. N. Mahmood, "Ionic conductivity of  gadolinium-doped barium cerate perovskites",  Solid State  Ionics,  35 (1989), p. 179-188, and H. Iwahara, H. Uchida,  K. Morimoto, "High temperature solid electrolyte fuel cells  using perovskite-type oxide based on barium cerium oxide  (BaCeO$_{3}$ )",  J. Electrochem. Soc.,  137 (1990), p. 462-465].  The studies suggested that inorganic network led to  increased close "channel" in film formation, thus decreased  the ionic conductivity. 2) Polymer/heteropolyacid composite  membranes [Chu, Young-Hwan; Lim, Jung-Eun; Kim,  Hyun-Jong; Lee, Chang-Ha; Han, Hak-Soo; Shu!, Yong› Gun, "Proton conducting silica mesoporous/heteropolyacid› PVA/SSA nano-composite membrane for polymer electro› lyte membrane fuel cell",  Studies in Surface Science and  Catalysis,  146 (2003), (Nanotechnology in Mesostructured  Materials), p. 787-790, Honma,  I.;  Nakajima, H.; Nish› ikawa, O.; Sugimoto, T.; Nomura, S., "Family of High› Temperature Polymer-Electrolyte Membranes Synthesized  from Amphiphilic Nanostructured Macromolecules",  Jour› nal of the Electrochemical Society,  150 (2003), A616-A619,  Honma, Itaru; Nakajima, Hitoshi; Nishikawa, Osamu; Sug› imoto, Toshiya; Nomura, Shigeki, "Proton conducting elec› trolyte  membranes  synthesized  through  amphiphilic  organic/inorganic hybrid macromolecules",  Electrochemis› try  (Tokyo, Japan), 70 (2002), p. 920-923, Honma, Itaru;  Nakajima, Hitoshi; Nomura, Shigeki, "High temperature  proton conducting hybrid polymer electrolyte membranes",  Solid State Ionics,  154-155 (2002), p. 707-712, Honma,  I.;  Nakajima, H.; Nishikawa, O.; Sugimoto, T.; Nomura, S.,  "Amphiphilic organic/inorganic nanohybrid macromol- ecules for intermediate-temperature proton conducting elec› trolyte membranes",  Journal of the Electrochemical Society,  149 (2002), A1389-A1392, Honma,  I.;  Nishikawa, O.; Sug- The subject hybrid membrane has higher conductivity  than the prior arts. This is because the subject membrane has  a different host polymer, PVP, which is a more desirable host  polymer for H$_{3}$PO$_{4 }$ due to PVP’s extreme high affinity to the  acid, thus having a higher uptake of H$_{3}$PO$_{4}$ ,  leading to a 5  higher conductivity even under low humidity. Also, it forms  a very transparent, well dispersed membrane with very few  pores. 