Polymer Electrolyte Fuel Cells (PEFCs) -- Materials and Operating Physics Principles
Polymer Electrolyte Fuel Cells (PEFCs) -- Materials and Operating Physics Principles
Polymer electrolyte fuel cells (PEFCs), also known as proton exchange membrane fuel cells (PEMFCs), are electrochemical devices that
convert hydrogen and oxygen into electricity, water, and heat with high efficiency and low emissions. Their operation relies on advanced
materials and fundamental electrochemical and transport phenomena.
1. Key Materials in PEFCs
(1) Polymer Electrolyte Membrane (PEM)
- Function: Conducts protons (H⁺) while blocking electrons and gases.
- Materials:
- Perfluorosulfonic acid (PFSA) membranes (e.g., Nafion®, Aquivion®):
- Hydrophobic fluorocarbon backbone with hydrophilic sulfonic acid (–SO₃H) groups.
- Proton conduction occurs via water-mediated Grotthuss mechanism (hopping mechanism).
- Alternative membranes: Hydrocarbon-based (for cost reduction), phosphoric acid-doped (for high-temperature PEMFCs).
-Requirements: High proton conductivity (>0.1 S/cm), low gas crossover, chemical/thermal stability.
(2) Catalyst Layers (Anode & Cathode)
- Function: Accelerate hydrogen oxidation (HOR) and oxygen reduction (ORR).
- Materials:
-Platinum (Pt) nanoparticles (2–5 nm) dispersed on carbon supports (e.g., Vulcan XC-72, Ketjenblack).
-Alloy catalysts(Pt-Co, Pt-Ni) for improved ORR kinetics.
-Non-precious metal catalysts (NPMCs) under research (e.g., Fe-N-C).
-Challenges: Pt cost, carbon corrosion, catalyst poisoning (CO, sulfur).
(3) Gas Diffusion Layers (GDLs)
-Function: Distribute reactant gases, conduct electrons, and manage water.
-Materials:
-Porous carbon paper/cloth(e.g., Toray TGP-H) coated with a hydrophobic microporous layer (MPL) (carbon + PTFE).
-Key Properties: High electrical conductivity, gas permeability, and water management.
(4) Bipolar Plates
-Function: Distribute gases, collect current, and provide mechanical support.
-Materials:
-Graphite composites (lightweight, corrosion-resistant).
-Metallic plates (stainless steel, titanium) with protective coatings.
2. Operating Physics Principles
(1) Electrochemical Reactions
(2) Proton and Electron Transport
-Protons (H⁺): Move through the hydrated PEM via vehicular (water drag) and Grotthuss (hopping) mechanisms.
-Electrons (e⁻): Flow through the external circuit, generating electricity.
(3) Mass Transport (Gas & Water Management)
-Reactant Gases (H₂, O₂): Diffuse through GDL and catalyst layers.
-Water Management:
-Liquid water must be removed to prevent flooding (cathode).
-Membrane hydration is critical for proton conductivity (too dry → high resistance; too wet → flooding).
(4) Heat Generation & Thermal Management
- Heat is produced due to:
-Ohmic losses (resistance in membrane, contacts).
-Activation losses (slow ORR kinetics).
- Entropic heat from the electrochemical reactions.
- Cooling methods: Air/liquid cooling, heat exchangers.
(5) Voltage Losses (Polarization)
-Activation polarization (kinetic limitations, especially at cathode).
-Ohmic polarization (resistance in membrane, contacts).
-Concentration polarization (gas diffusion limitations at high current).
3. Challenges & Advancements
|Challenge | Current Research Focus |
| High Pt cost | Ultra-low Pt, Pt alloys, NPMCs |
| Membrane degradation | Chemically stable alternatives (e.g., PFSA modifications) |
| Water management | Advanced GDLs, flow field optimization |
| Cold start capability | Ice formation mitigation strategies |
| Durability | Degradation-resistant materials, accelerated stress tests |
Conclusion
PEFCs rely on a delicate balance of materials (membrane, catalysts, GDLs) and physics (electrochemistry, transport phenomena). Advances
in catalyst design, membrane durability, and system integration are driving their adoption in automotive, stationary power, and portable
applications.
Would you like a deeper dive into any specific aspect (e.g., catalyst design, membrane physics)?
-
A&S Power 553640 3.7v 850mAh Lithium Polymer BatteryAug,06,2023
-
Lithium Polymer Batteries in Aerospace ApplicationsDec,05,2023
-
Application areas of lithium polymer batteriesOct,23,2023
-
Lithium Polymer Battery: The Heart of Portable PowerOct,20,2023
-
Discover the Power of the Lithium Polymer Battery Model 401230 3.7v 120mAh 3.7v 120mAhOct,30,2023