The use of oxide fuel cells and other solid-state ionic devices in energy applications is limited by their requirement for elevated operating temperatures, typically above 800°C (ref. 1). Thin-film membranes allow low-temperature operation by reducing the ohmic resistance of the electrolytes. However, although proof-of-concept thin-film devices have been demonstrated, scaling up remains a significant challenge because large-area membranes less than ~ 100 nm thick are susceptible to mechanical failure. Here, we report that nanoscale yttria-stabilized zirconia membranes with lateral dimensions on the scale of millimetres or centimetres can be made thermomechanically stable by depositing metallic grids on them to function as mechanical supports. We combine such a membrane with a nanostructured dense oxide cathode to make a thin-film solid-oxide fuel cell that can achieve a power density of 155 mW cm⁻² at 510 °C. We also report a total power output of more than 20 mW from a single fuel-cell chip. Our large-area membranes could also be relevant to electrochemical energy applications such as gas separation, hydrogen production and permeation membranes.

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The electric-field-induced evolution of the recently discovered periodic 180 degree nanostripe domain structure is predicted in epitaxial Pb(Zr0.5Ti0.5)O3 ultrathin films from first principles. This evolution involves (1) the lateral growth of majority dipole domains at the expense of minority domains with the overall stripe periodicity remaining unchanged, (2) the creation of surface-avoiding nanobubbles, and (3) the formation of a single monodomain state. Analogies and differences (i) with ferroelectric thin films made of BaTiO3 and (ii) with ferromagnetic thin films under magnetic field are discussed.

Using a first-principles-based scheme, we determine the qualitative and quantitative effects of surface∕interface, thickness and electrical boundary conditions on the temperature-misfit strain phase diagrams of epitaxial (001) BaTiO3 ultrathin films. The microscopic reasons leading to such effects are also revealed.

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Thin film micro-solid oxide fuel cells (mSOFCs) utilizing nanoporous ruthenium (Ru) anodes were fabricated and investigated for direct methane operation for the first time. The mSOFCs consist of 8 mol % yttria-stabilized zirconia (YSZ) thin film electrolytes, porous platinum (Pt) cathodes and porous Ru anodes, fabricated on silicon platforms by physical vapor deposition. The fuel cells, tested with methane as the fuel and air as the oxidant, exhibited an open circuit voltage (OCV) of 0.71 V and a peak power density of 450 mW cm À2 at 500 C without visually detectable carbon deposition. Structural investigations revealed that the morphology evolution in nanoporous Ru anodes was strongly dependent on the fuels (namely, methane or hydrogen) used, and possible mechanisms leading to the observations are discussed. Results presented here project insights to enable direct use of hydrocarbons with high performance, and are of potential relevance to advancing low temperature micro-fuel cell technology for portable power.

A first-principles-derived method is used to study the morphology and electricfield-induced evolution of stripe nanodomains in ( which is associated with a single monodomain. Such evolution differs from that of PZT ultrathin films for which neither Region I nor zigzagged domain walls exist, and for which the bubbles contract along [100]. Discussion about such differences is provided.

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