---
title: "SOFC versus PEMFC"
subject: "Energy Environment and Society"
chapter: 3
key: "semester_7/energy_environment_and_society:sofc-pemfc-comparison"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/sofc-pemfc-comparison
site: BCT Engineering
---

# SOFC versus PEMFC

Energy Environment and Society · Chapter 3: Renewable Energy Sources

- Asked in: year not given
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/sofc-pemfc-comparison
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3

## Question

What are the similarities and differences between SOFC and PEMFC?

## Short answer

Both convert hydrogen and oxygen into electricity, heat, and water without combustion, using anode, cathode, and electrolyte. SOFC uses solid ceramic electrolyte, operates at 600–1000°C, transports O²⁻, and can use various fuels; PEMFC uses polymer membrane, operates at 60–80°C, transports H⁺, and requires pure hydrogen.

## Answer

Both are electrochemical devices that convert hydrogen-rich fuel and oxygen into electricity, heat and water without combustion.

#### Similarities
- Both consist of anode, cathode and electrolyte, and cells are stacked to get higher voltage.
- Overall reaction with hydrogen is the same: H₂ + ½O₂ → H₂O.
- Both are efficient and quiet, produce low emissions, and have no moving parts in the cell.
- Both give DC power and use catalysts at electrodes.

#### Differences
| Point | SOFC | PEMFC |
|---|---|---|
| Electrolyte | Solid ceramic (YSZ) | Solid polymer membrane (Nafion) |
| Ion transported | Oxide ion O²⁻ (cathode to anode) | Proton H⁺ (anode to cathode) |
| Operating temperature | 600–1000 °C | 60–80 °C |
| Water produced at | Anode | Cathode |
| Catalyst | Nickel / ceramic, no platinum | Platinum |
| Fuel | H₂, CO, natural gas, biogas (internal reforming) | Pure H₂ (CO poisons it) |
| Efficiency | 50–60% (up to 85% with CHP) | 40–60% |
| Start-up | Slow (hours) | Fast (seconds) |
| Application | Stationary power, CHP | Vehicles, portable and backup power |
| Cost issue | Materials and thermal stress | Platinum and membrane |
| Anode reaction | H₂ + O²⁻ → H₂O + 2e⁻ | H₂ → 2H⁺ + 2e⁻ |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which pair correctly gives the ion carried through the electrolyte?
   A. SOFC: H+; PEMFC: O2-
   B. Both: H+
   C. Both: O2-
   D. SOFC: O2-; PEMFC: H+
   Answer: D. SOFC carries oxide ions from cathode to anode; PEMFC carries protons from anode to cathode. (Key point: Ion transported)

2. Where is water produced in SOFC and PEMFC respectively?
   A. SOFC at the anode; PEMFC at the cathode
   B. SOFC at the cathode; PEMFC at the anode
   C. Both at the cathode
   D. Both at the anode
   Answer: A. In SOFC, H2 + O2- -> H2O + 2e- at the anode; in PEMFC water forms at the cathode. (Key point: Water location)

3. Which is correct?
   A. SOFC runs at 60-80 °C and starts fast
   B. SOFC runs at 600-1000 °C and starts slowly; PEMFC runs at 60-80 °C and starts fast
   C. Both run at about 80 °C
   D. PEMFC runs at 600-1000 °C and starts slowly
   Answer: B. The high-temperature ceramic SOFC suits stationary power and CHP; PEMFC suits vehicles. (Key point: Operating temperature and start-up)

4. Why can SOFC use natural gas or biogas but PEMFC cannot?
   A. SOFC uses platinum, which tolerates CO
   B. PEMFC works at higher temperature
   C. High temperature allows internal reforming and CO can be used as fuel; PEMFC's platinum is poisoned by CO
   D. Both are poisoned by CO equally
   Answer: C. SOFC uses nickel/ceramic catalysts and internal reforming; PEMFC needs pure H2. (Key point: Fuel flexibility)

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