TF-SOFC were produced starting from double-side polished (100) silicon wafers coated with 200 nm of low-stress silicon nitride. Free-standing silicon nitride square membranes arrays with 150 μm sidelength were fabricated using lithography, 12
reactive ion etching and KOH anisotropic etching. The fuel cells were then fabricated by sequentially sputtering the electrolyte 80 to 95 nm thick from a 8 mol % yttria-stabilized zirconia (YSZ) target, dry-etching the silicon nitride from the bottom side, depositing the vanadium oxide (VOx) and/or porous Pt anode on the bottom side and sputtering the porous Pt cathode through a stainless steel shadow mask. RF- sputtering of the oxide electrolyte and vanadium oxide anode were performed at 550 °C at pressures of 5 and 20 mTorr Ar and powers of 100 and 150 W, respectively. The composition of the vanadium oxide target was V2O5. DC-sputtering of Pt porous cathode and anode were performed without substrate heating at 75 and 85 mTorr, respectively. The fuel cells were tested in a custom-built environmental station.12 The anode- side was exposed to humidified 5% H2−Ar (specified purity of 99.999%) flowing at 30 mL min−1, while the cathode-side was exposed to ambient stationary air. As shown schematically in Figure 1a, fuel cells were fabricated with anodes consisting either of a porous Pt film, a VOx film, or a bilayer VOx/porous Pt film (further referred to as VOx/Pt). As we show later, the VOx/Pt anode has higher performance than the VOx anode due to lower anodic polarization losses.