Deng and his research team got around those challenges by altering the chemistry to allow an outside energy source to activate the fuel cell's oxidation-reduction reaction.
In the new system, the biomass is ground up and mixed with a polyoxometalate (POM) catalyst in solution and then exposed to light from the sun or heat. A photochemical and thermochemical catalyst, POM functions as both an oxidation agent and a charge carrier. The POM oxidizes the biomass under photo or thermal irradiation, and delivers the charges from the biomass to the fuel cell's anode. The electrons are then transported to the cathode, where they are finally oxidized by oxygen through an external circuit to produce electricity.
"If you mix the biomass and catalyst at room temperature, they will not react," said Deng. "But when you expose them to light or heat, the reaction begins. The POM introduces an intermediate step because biomass cannot be directly accessed by oxygen."
The system provides major advantages, including combining the photochemical and solar-thermal biomass degradation in a single chemical process, leading to high solar conversion and effective biomass degradation. It also does not use expensive noble metals as anode catalysts because the fuel oxidation reactions are catalyzed by the POM in solution. Finally, because the POM is chemically stable, the hybrid fuel cell can use unpurified polymeric biomass without concern for poisoning noble metal anodes.
The system can use soluble biomass, or organic materials suspended in a liquid. In experiments, the fuel cell operated for as long as 20 hours, indicating that the POM catalyst can be re-used without further treatment.
In their paper, the researchers reported a maximum power density of 0.72 milliwatts per square centimeter, which is nearly
|Contact: John Toon|
Georgia Institute of Technology