The extensive implementation of hydrogen-powered technology today is limited by a number of fundamental problems related to materials research. Fuel-cell hydrogen conversion technology requires proton-conducting materials with high conductivity at intermediate temperatures up to 120 °C. The development of such materials remains challenging because the proton transport of many promising candidates is based on extended microstructures of water molecules, which deteriorate at temperatures above the boiling point. Here we show the impregnation of the mesoporous metal-organic framework (MOF) MIL-101 by nonvolatile acids H(2)SO(4) and H(3)PO(4). Such a simple approach affords solid materials with potent proton-conducting properties at moderate temperatures, which is critically important for the proper function of on-board automobile fuel cells. The proton conductivities of the H(2)SO(4)@MIL-101 and H(3)PO(4)@MIL-101 at T = 150 °C and low humidity outperform those of any other MOF-based materials and could be compared with the best proton conductors, such as Nafion.

Copper(II) oxide nanopowders exhibit a high catalytic activity in CO oxidation at low temperatures. The combination of in situ XPS, XRD, and HRTEM methods was applied to investigate initial steps of CuO nanoparticles reduction, to identify oxygen and copper species and to revealed structural features in the dependence on reducing power of reaction medium. At the oxygen deficient surface of CuO nanopowders the metastable Cu4O3 oxide was formed under the mild reducing conditions −10–5 mbar CO or CO + O2 mixture with oxygen excess. Destruction of Cu4O3 structures in strong reducing medium (P(CO) ≥ 10–2 mbar) or under UHV conditions resulted in the formation of Cu2O which was epitaxially bounded with initial CuO particle. The reversible bulk reduction of CuO nanopowder to Cu2O at temperatures ∼150 °C can be explained by effortless propagation of Cu2O∥CuO epitaxial front inside the nanoparticle. The model of the surface restructuring along the {−111}CuO → {202}Cu4O3 → {111}Cu2O planes under the reduction of CuO nanopowders is proposed. The initial surface of CuO nanopowders is probably distorted and resembles Cu4O3-like structures that facilitates the CuO x ↔ Cu4O3 transition in mild reducing conditions. Such restructuring results in a unique electronic Cu4O3 structure with high oxygen deficiency and low-valence Cu1+ sites stimulating the formation of highly reactive CO and O2 adsorbed species. It was shown that the most active oxygen species on the surface of CuO x is stabilized as O–, which was previously reported in papers by Roberts and Madix in their study of the copper–oxygen systems.

Strong toluenesulfonic and triflic acids were incorporated into a MIL-101 chromium(III) terephthalate coordination framework, producing hybrid proton-conducting solid electrolytes. These acid@MIL hybrid materials possess stable crystalline structures that do not deteriorate during multiple measurements or prolonged heating. Particularly, the triflic-containing compound demonstrates the highest 0.08 S cm(-1) proton conductivity at 15% relative humidity and a temperature of 60 °C, exceeding any of today's commercial materials for proton-exchange membranes. The structure of the proton-conducting media, as well as the long-range proton-transfer mechanics, was unveiled, in a certain respect, by Fourier transform infrared and (1)H NMR spectroscopy investigations. The acidic media presumably constitutes large separated droplets, coexisting in the MIL nanocages. One component of proton transfer appears to be related to the facile relay (Grotthuss) mechanism through extensive hydrogen-bonding interactions within such droplets. The second component occurs during continuous reorganization of the droplets, thus ensuring long-range proton transfer along the porous structure of the material.

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The effect of thermal strain on the rate of photoisomerization is qualitatively different from the effect of strain generated by elastic loading.

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