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Reduced Surface Area for the Oxygen Reduction Reaction in Porous Electrode via Electrical Conductivity Relaxation
Hairui Han1, Guanwei Guo1, Shaowei Zhang1
1CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, No. 96 Jinzhai Road, Hefei, Anhui, 230026, P. R. China.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|August 29, 2024
Summary
Gas diffusion significantly impacts oxygen reduction reaction (ORR) in solid oxide fuel cell (SOFC) electrodes. Optimizing electrode structure for faster gas transport is crucial for enhanced ORR performance.
Area of Science:
- Electrochemistry
- Materials Science
- Chemical Engineering
Background:
- Oxygen reduction reaction (ORR) performance in porous electrodes is vital for solid oxide fuel cells (SOFCs).
- Gas diffusion effects on ORR in porous media require further investigation.
- Nonthermal surface oxygen exchange issues have been linked to gas diffusion limitations.
Purpose of the Study:
- To investigate the impact of gas diffusion on ORR in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) electrodes with varying porosity and permeability.
- To quantify the influence of gas diffusion on the effective surface area available for ORR.
- To propose a new metric, 'reduced surface area,' to represent gas diffusion effects in electrode performance.
Main Methods:
- Utilizing the electrical conductivity relaxation method to study LSCF electrodes.
- Applying the distributed of characteristic time (DCT) model for data analysis.
- Investigating electrodes with controlled porosity, pore radii, and gas permeability.
Main Results:
- ORR in porous electrodes exhibits three characteristic times: gas diffusion, small-pore surface exchange, and large-pore surface exchange.
- Gas diffusion demonstrably slows the oxygen surface exchange reaction, reducing the effective chemical oxygen surface exchange coefficient.
- A 'reduced surface area' metric was defined, increasing with gas permeability, to quantify gas diffusion effects.
Conclusions:
- Gas diffusion significantly hinders ORR kinetics in porous SOFC electrodes.
- Electrode engineering for enhanced gas transport is essential for improving SOFC performance.
- The 'reduced surface area' metric is proposed as a more accurate parameter than specific surface area for calculating electrode polarization impedance using the ALS model.
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