Solar-induced hybrid fuel cell produces electricity directly from biomass

Feb 18, 2014
A new solar-induced direct biomass-to-electricity hybrid fuel cell can operate on a variety of fuels. The fuel cell, shown on the right, relies on a polyoxometalate (POM) catalyst (shown in the vials) which changes color as it reacts with light. Credit: John Toon

Although low temperature fuel cells powered by methanol or hydrogen have been well studied, existing low temperature fuel cell technologies cannot directly use biomass as a fuel because of the lack of an effective catalyst system for polymeric materials.

Now, researchers at the Georgia Institute of Technology have developed a new type of low-temperature fuel cell that directly converts to electricity with assistance from a catalyst activated by solar or thermal energy. The hybrid fuel cell can use a wide variety of biomass sources, including starch, cellulose, lignin – and even switchgrass, powdered wood, algae and waste from poultry processing.

The device could be used in small-scale units to provide electricity for developing nations, as well as for larger facilities to provide power where significant quantities of biomass are available.

"We have developed a new method that can handle the biomass at room temperature, and the type of biomass that can be used is not restricted – the process can handle nearly any type of biomass," said Yulin Deng, a professor in Georgia Tech's School of Chemical and Biomolecular Engineering and the Institute of Paper Science and Technology (IPST). "This is a very generic approach to utilizing many kinds of biomass and organic waste to produce electrical power without the need for purification of the starting materials."

The new solar-induced direct biomass-to-electricity hybrid fuel cell was described February 7, 2014, in the journal Nature Communications.

The challenge for cells is that the carbon-carbon bonds of the biomass – a natural polymer – cannot be easily broken down by conventional catalysts, including expensive precious metals, Deng noted. To overcome that challenge, scientists have developed microbial fuel cells in which microbes or enzymes break down the biomass. But that process has many drawbacks: power output from such cells is limited, microbes or enzymes can only selectively break down certain types of biomass, and the microbial system can be deactivated by many factors.

This schematic shows the solar-induced direct biomass-to-electricity hybrid fuel cell. Electrons in the biomass can be transferred to polyoxometalate under sunlight irradiation, and reduced POM can deliver the charges to the anode. These electrons are then captured by oxygen in the cathode. Credit: Yulin Deng

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 100 times higher than cellulose-based microbial fuel cells, and near that of the best . Deng believes the output can be increased five to ten times when the process is optimized.

"I believe this type of fuel cell could have an energy output similar to that of in the future," he said. "To optimize the system, we need to have a better understanding of the chemical processes involved and how to improve them."

The researchers also need to compare operation of the system with solar energy and other forms of input energy, such as waste heat from other processes. Beyond the ability to directly use biomass as a fuel, the new cell also offers advantages in sustainability – and potentially lower cost compared to other types.

"We can use sustainable materials without any chemical pollution," Deng said. "Solar energy and biomass are two important sustainable energy sources available to the world today. Our system would use them together to produce electricity while reducing dependence on fossil fuels."

Explore further: Robotic EcoMow cuts and uses grass as fuel

More information: Wei Liu, et al., "Solar-induced direct biomass-to-electricity hybrid fuel cell using polyoxometalates as photocatalyst and charge carrier," Nature Communications, 2014. www.dx.doi.org/10.1038/ncomms4208

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MR166
not rated yet Feb 18, 2014
Forget it bad post.

MR166
not rated yet Feb 18, 2014
New Post

Lets say they get to the 10X output level. That is only 72 watts per square meter. A solar cell produces twice the amount of power. So this device wastes 1/2 the solar power it receives and needs biomass to do this.

Perhaps the numbers work better with waste heat but I am willing to bet that you are better of burning the biomass directly to produce steam.
Osiris1
not rated yet Feb 18, 2014
Think anywhere you have heat to waste, this process can work. Back it up with some kind of energy storage such as some of the new batteries, and the system is complete. For instance, central air conditioning systems are huge sources of waste heat.
MR166
not rated yet Feb 18, 2014
There are a lot of waste heat sources that are available 24/7 so battery backup is not needed. That makes the power much more valuable. But a lot more must be disclosed about the economics of the whole system before any judgement can be made about it's usefulness.
Caliban
not rated yet Feb 18, 2014
There are a lot of waste heat sources that are available 24/7 so battery backup is not needed. That makes the power much more valuable. But a lot more must be disclosed about the economics of the whole system before any judgement can be made about it's usefulness.


"We can use sustainable materials without any chemical pollution," Deng said. "Solar energy and biomass are two important sustainable energy sources available to the world today. {{ Our system would use them together to produce electricity while reducing dependence on fossil fuels.}}"

The bracketed part of the quoted passage is what gives such "skeptical" pause to mr166.

In the near future, fossil fuels will again be --literally-- just that.

Howhot
not rated yet Feb 18, 2014
Brilliant engineering idea, although I don't like the CO2 waste product. The CO2 waste is a big red flag to me.
Restrider
not rated yet Feb 19, 2014
Brilliant engineering idea, although I don't like the CO2 waste product. The CO2 waste is a big red flag to me.

The CO2 "waste" would be coming from the biomass, which in order to become biomass had to sequestrate the CO2 from the atmosphere during photosynthesis.
So, all in all it should be CO2 neutral (not counting any other effects that may produce it, though).
MR166
not rated yet Feb 19, 2014
It is great to be able to take biomass out of the waste stream and convert it into energy but growing it and harvesting it solely for energy production has some problems. Eventually you deplete the soils on which it is grown and destroy them. Done on a large scale this does more harm than good to the environment.

There are many areas where large tidal ponds could be created using existing land masses. Perhaps tide generators could be and answer.
SantaBJ
5 / 5 (1) Feb 19, 2014
There is no need to grow biomass solely for energy production. We produce an insane amount of waste biomass which would be useful for energy production purposes if technologies like this one can be perfected. And even if we do grow biomass solely for energy production, we are learning more and more about how we can grow crops without depleting the soil (or at least minimizing the depletion). It is a problem that can be fixed, and as biomass production becomes more important for things other than materials and food, finding a solution becomes increasingly important.

The search for alternative energy sources is not a matter of this or that, it's a matter of this *and* that. One of the most important paths in the search is finding inefficiencies and untapped sources of energy in our existing systems of production and consumption and turning them to our advantage. That is what this technology does.