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,
reactive ion etching and KOH anisotropic etching.12 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. RFsputtering
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 anodeside
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.