Nanofilms of Y‐doped zirconium pyrophosphate, with a molar composition of Y0.95/Y0.05/P2.64, exhibit high proton conductivities with an area‐specific resistance of 0.085 Ω cm2. The films are very stable, even when operating in the flow of dry air at 340 °C for a prolonged period of time (see figure).

Fuel cells that operate at intermediate temperatures between 200 and 400 8C are of particular interest, since this temperature range allows for the use of less precious metal catalysts and alcohol fuel, enables in situ reforming of hydrocarbon fuels, and facilitates simpler module assembly. Unfortunately, these advantages are not available with electrolyte membranes of conventional organic polymers due to limited thermal stability. Although certain inorganic crystalline materials show satisfactory ion conductivity at high temperatures, only a few examples of proton-conductive inorganics that show promising conduction within this temperature range have been reported. [1][2][3][4] The advantage of using thermally stable inorganic electrolytes is not restricted to fuel cells; they should be valuable in the development of electrochemical pump devices, membrane reactors, and electrochemical sensors. Therefore, there is a strong motivation to develop suitable electrolyte materials that can operate at intermediate temperatures. [5] We discovered that silica-based, nanometer-thick films gave enhanced ionic conduction at 100-400 8C due to the formation of stable Brønsted acid sites in the silicate framework when doped with 13 other metal ions. Among these double oxides, Al, Zr, Ti, and Hf-doped membranes showed practically usable levels of area-specific resistance at 300-400 8C, and the determination of electromotive force (EMF) indicated that the Al-, Zr-, and Ce-doped membranes gave predominant proton conductivity without apparent permeation of H 2 gas. The development of membrane materials for fuel cells and related applications may be divided into the following three stages: i) development of efficient ion-conductive materials with negligible electron conduction, ii) fabrication of materials such as gas-tight (defect-free) membranes (the thinner the better), and iii) fabrication of working devices: membraneelectrode assembly in the case of fuel cells. Previously, we successfully fabricated void-free, uniform ultrathin films of various metal oxides by the surface sol-gel process. [6][7][8] This process involves stepwise film growth composed of the reaction of metal alkoxides on the surface hydroxyl group of solid substrates and subsequent hydrolysis of the ultrathin alkoxide layer. We recently applied this method to preparation of amorphous aluminosilicate nanofilm and found that this nanometer-thick film is a practically useful proton conductor with area-specific resistance of 0.2 V cm 2 at 400 8C in dry atmosphere. [9] In order to evaluate such unique proton conductivity, it is important to see if similar proton conductivity is observed with other silica-based metal oxides. These materials would be useful as electrolyte membranes if they could be fabricated into ultrathin membranes that are nonpermeable toward neutral gas molecules; hydrogen and oxygen, since silica is one of the most stable matrix under electrochemical conditions.[10] Here, we report that protonic conduction is, in fact, a common feature of amorphou...

No abstract

Amorphous aluminosilicate nanofilms as prepared by a sol-gel process and post-annealing exhibit proton conduction at a wide temperature range in dry air with a lowest area specific resistance of 0.24 omega cm2 at 400 degrees C.

We report herein the fabrication of ferritin-embedded self-supporting silica nanofilms via a simple spin-coating process. Ferritin was employed as a template molecule, and solutions of ferritin and silica were spread on a polymer-coated silicon substrate, in this order. After dissolving the polymer underlayer by simply immersing ethanol, a centimeter-sized self-supporting nanofilm of ferritin/silica composite with a thickness of 15 nm was successfully transferred onto an alumina membrane without the film breaking. Ozone and hydrochloric acid solution treatment removed the template ferritin molecules from the composite film to produce corresponding transmembrane nanoholes. The reported method is very simple, and the fabrication of a protein-embedded self-supporting nanofilm enables the design of biomembrane-mimetic devices.