Large scale storage technologies are vital to increase the share of renewable electricity in the global energy mix.

Obtaining high power density at low operating temperatures has been an ongoing challenge in solid oxide fuel cells (SOFC), which are efficient engines to generate electrical energy from fuels. Here we report successful demonstration of a thin-film three-dimensional (3-D) SOFC architecture achieving a peak power density of 1.3 W/cm(2) obtained at 450 °C. This is made possible by nanostructuring of the ultrathin (60 nm) electrolyte interposed with a nanogranular catalytic interlayer at the cathode/electrolyte interface. We attribute the superior cell performance to significant reduction in both the ohmic and the polarization losses due to the combined effects of employing an ultrathin film electrolyte, enhancement of effective area by 3-D architecture, and superior catalytic activity by the ceria-based interlayer at the cathode. These insights will help design high-efficiency SOFCs that operate at low temperatures with power densities that are of practical significance.

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Structural and microstructural properties as well as the fuel cell performance of anhydrous proton conducting yttria-doped barium zirconate (BYZ) membranes were investigated. The membranes were nominally about 100 nm thick and were fabricated by both atomic layer deposition (ALD) and pulsed laser deposition (PLD) techniques on micromachined Si substrates. Electrochemical cells (H 2 , Pt/BYZ/Pt, air) were fabricated using porous platinum electrodes deposited by sputtering. The cells were tested in the temperature regime 200-450 °C. Power densities of 136 mW/cm 2 at 400 °C employing a BYZ membrane fabricated by ALD and 120 mW/cm 2 at 450 °C employing a BYZ fabricated by PLD clearly represent the highest reported values in the literature at these temperatures. The difference in the cell performances for the ALD BYZ versus PLD BYZ membranes is attributed to differences in their surface morphology and interfacial microstructure.

The proton conductivity of yttrium-doped barium zirconate (BYZ) films epitaxially grown on MgO(100) has been studied in the range of 140–290°C as a function of film thickness (60–670nm) in relation to their crystal and morphological structure at the nanoscale. Highly textured 60nm BYZ film epitaxially grown on MgO(100) showed high ionic conductivity, close to its bulk value. In contrast, thicker polycrystalline samples with rougher surfaces, caused by grain boundary formation, exhibited lower conductivity.