Physics / mechanism
Solid oxide fuel cells convert chemical energy directly to electricity via oxygen-ion conduction through a ceramic electrolyte (typically yttria-stabilised zirconia, YSZ) at 600–1000°C. At the cathode, O₂ is reduced to O²⁻; ions migrate through the dense electrolyte; at the anode, H₂ or reformate is oxidised. No combustion. Electrical efficiency reaches 55–65% (LHV, standalone), rising to >85% in combined heat-and-power configurations. Stack degradation runs ~0.5–1% per 1000 h; thermal cycling tolerance is the dominant reliability constraint. Current SoA: Bloom Energy (250 kW–multi-MW), Ceres Power (steel-cell intermediate-temperature SOFC, ~550°C), Elcogen. Key material bottleneck is cathode mixed ionic-electronic conductors (MIEC) — LSCF composites dominating, but chromium poisoning limits lifetime.
Competitive landscape
PEM fuel cells (Ballard, Plug Power) operate at 60–80°C, faster start, better for mobile/transport; SOFC wins on efficiency and fuel flexibility but loses on cold-start and cost-per-kW. Molten carbonate fuel cells (Fuel Cell Energy) compete in stationary >1 MW but are being displaced by SOFC economics. Solid-state batteries share electrolyte ceramics science but different ion carrier and application. Adjacent: electrolysis (SOEC, reverse SOFC operation — same stack, Sunfire), thermal batteries, advanced gas turbine hybrids.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.