Fuel cells: Engineering methods

Five fuel cell types, named by what carries the ions

What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.

Fuel cells are named after their electrolyte, which sets the temperature, the catalyst and the fuels accepted. Efficiencies are electrical, LHV. Packaged power units (stack plus compressor, humidifier, cooling and DC/DC converter) are covered under Equipment.

Comparison

Method	Efficiency	Scale	Economics	Limitations	Reliability
Proton-exchange membrane (PEM)¹⁶	About 60% on pure hydrogen (DOE); 56% rated, 64.5% peak for a truck system	Under 1 kW to about 300 kW per system	155 USD/kW modelled at mass volume; about 282 at today's volumes	Needs pure hydrogen and platinum; heat comes out too cool to be very useful	Designed for 25,000 hours in trucks
Methanol fuel cells¹⁰	About 25% for a commercial direct methanol unit (calculated from 0.9 litres of methanol per kWh)	Tens of watts to a few kW	Niche: valued for unattended off-grid power, not energy cost	Methanol crosses the membrane and oxidises slowly; emits CO2 unless the methanol is renewable	Warranty 4,500 operating hours (SFC Energy)
Phosphoric acid (PAFC)⁶⁹	About 40% typical (DOE); 50% for a current 440 kW hydrogen unit, up to 90% with heat use	100-440 kW modules	Competes with engines for on-site power	Still needs platinum; acid is corrosive	10-year cell-stack life claimed by maker
Molten carbonate (MCFC)⁶⁸	Up to 50%, 47% average; over 80% with heat use	1.25 MW blocks; plants up to 58.8 MW	Utility and industrial baseload	Corrosive salt limits life; modules replaced every 5-7 years	25-30 year plant design life with module swaps
Solid oxide (SOFC)²³⁴⁶	About 60% (DOE); 65% falling to 53% over cell life on gas; about 60% on hydrogen	325 kW modules combined into multi-MW sites	Fuel about USD 23-29/MWh at USD 4 per million Btu gas (calculated)	Slow start; ceramics dislike repeated heating and cooling	Fleet availability about 99.9% (company figure)

PEM wins where fast starts, compact size and varying loads matter, but needs pure hydrogen and platinum. Solid oxide is the most efficient and takes natural gas, biogas or hydrogen, but suits steady round-the-clock loads. Carbonate and phosphoric acid plants are older stationary options at 40-50%. Direct methanol trades efficiency for an easy liquid fuel. On any fuel the cost of the fuel, not the efficiency, decides most cases.

How each method works

Proton-exchange membrane (PEM)

A thin polymer membrane carries protons between platinum electrodes below about 100 C. Starts in seconds and follows load well, which suits vehicles.

Methanol fuel cells

Liquid methanol is oxidised directly at the anode (direct methanol cell) or reformed on board into hydrogen for a high-temperature PEM. Easy fuel storage suits off-grid and portable power.

Phosphoric acid (PAFC)

Liquid phosphoric acid held in a porous matrix, with platinum electrodes, at 150-200 C. A mature design for buildings and combined heat and power.

Molten carbonate (MCFC)

Molten lithium, sodium and potassium carbonates in a matrix at 600-700 C. The heat lets natural gas be reformed inside the stack.

Solid oxide (SOFC)

A zirconia ceramic carries oxide ions at 500-1,000 C, reforms natural gas inside the cell and needs no platinum.

Sources

Hydrogen Program Record 26002: Heavy-Duty Fuel Cell System Cost - 2024 US Department of Energy, Hydrogen and Fuel Cell Technologies Office, 2026
Bloom Energy Server 6.5 datasheet Bloom Energy (company data), 2025
Bloom Energy Corp Form 10-K for fiscal year 2025 Bloom Energy / US SEC, 2026
Bloom Energy announces hydrogen solid oxide fuel cell with 60% electrical efficiency and 90% combined heat and power efficiency (company press release) Bloom Energy via Business Wire, 2024
Comparison of Fuel Cell Technologies (fact sheet) US Department of Energy, Fuel Cell Technologies Office, 2016
FuelCell Energy Form 10-K for fiscal year 2025 FuelCell Energy / US SEC, 2025
PureCell Model 400 Hydrogen data sheet (HyAxiom, a Doosan Fuel Cell company) Doosan (company data), 2024
EFOY Pro 800 direct methanol fuel cell specifications SFC Energy (company data), 2025