Published on March 4th, 2015 | by Tina Casey54
Supersonic “Solar Fuel Cell” Could Churn Out Sustainable Hydrogen
March 4th, 2015 by Tina Casey
A while back, we introduced you to the artificial leaf and the bionic leaf. Now, check out this supersonic leaf. An international team of researchers headed up by Sweden’s Lund University is developing a thing they’re calling a supersonic “solar fuel cell.” Like its bionic cousin, the solar fuel cell mimics the chemical reactions in photosynthesis to produce sustainable fuel, namely hydrogen.
Right now the fuel of choice for fuel cell electric vehicles (FCEVs) is hydrogen sourced from natural gas, which comes with a huge load of environmental baggage, so if the Lund work pays off, that’s good news for all you FCEV fans out there.
The Inevitable March Of The Fuel Cell
We were just talking about the inevitable march of the fuel cell the other day, and here comes another indication that despite its critics, the fuel cell electric vehicle might find a solid niche in the personal mobility market, one way or another.
Actually, we’ve had a number of lively discussions about the pros and cons of FCEVs here at CleanTechnica, but there doesn’t seem to be any doubt over at the US Energy Department.
Earlier, the Energy Department followed up with yet another multimillion-dollar fuel cell research funding opportunity, to the tune of $35 million. In its open call for new fuel cell ideas, the agency is particularly looking for hydrogen production through microbial biomass conversion.
We’re especially interested in the agency’s interest in using fuel cells as a range extender for light duty hybrid electric vehicles — since we were already wondering if the electric vehicle of the future might one day embrace a battery and a fuel cell in peaceful coexistence, but we digress. Let’s get back to that new supersonic solar fuel cell from the Lund University.
A Supersonic Solar Fuel Cell
The Lund team is calling its effort “artificial photosynthesis.” The reasoning goes that since plants use sunlight to convert water and carbon dioxide to energy-rich molecules, so can we.
Until now, we’ve been focusing on harnessing solar energy by converting it to electricity through photovoltaic cells, or converting it to heat in the form of from rooftop water heaters and utility-scale concentrating solar power plants.
Both of these systems lose energy as heat along the way. A solar fuel cell, on the other hand, could theoretically store all of its solar energy in the form of chemical energy within molecules. All you need is light-collecting molecules and a catalyst to do the work for you.
For their solar fuel cell, the Lund team has developed a molecule with two metal atoms at its heart. One is for collecting solar energy, and the other mimics the catalyst that produces hydrogen (and potentially, in this case, methane).
Study of the new molecule has revealed that electrons “cross the bridge” between the two atoms in half a picosecond (check out the illustration above for a summary of the time scale). That rounds out to about 4 kilometers per second or about 10 times the speed of sound, hence the name “supersonic solar fuel cell.”
That’s nothing. The team also found that you can change up speeds depending on which kind of bridge you use, and another study using a different type of bridge reached a speed 100 times higher than the first bridge.
ET Come Home!
The press materials were a little thin on detail but you can find the study online at Nature Communications under the somewhat mysterious title, “Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses.”
For those of you on the go, the double-hearted molecule studied by the team was based on ruthemium and cobalt. Fancyspeak for the process is ET, short for photoinduced electron transfer:
The bimetallic complex studied in this work consists of a light-harvesting, ruthenium (Ru)-based chromophore linked to an optically dark cobalt (Co) electron sink by a bridge that mediates ultrafast ET. This prototypical dyad exemplifies the wide class of synthetic and natural photocatalysts for which the coupled electronic and structural dynamics are only partially understood…
So, now that the Lund team has converted a partial understanding to a more fleshed out picture, it’s on to the next stage of R&D. In other words, don’t hold your breath for abundant solar-sourced hydrogen just yet, but things are certainly heading in that direction.
For the record, the international team included the US as well as Denmark, Germany, Hungary, and Japan.
Also for the record, the artificial leaf refers to Harvard (formerly MIT) researcher Daniel Nocera’s low cost, palm-sized photoelectrochemical cell, designed to get solar-generated hydrogen from water — even dirty water — for use in small household fuel cells.
Based partly on that work, earlier this year Harvard introduced a “bionic leaf” that combines ET with bacteria in an integrated system that produces liquid fuel, specifically isopropanol (that’s fancyspeak for rubbing alcohol).
The bionic leaf moniker actually first crossed our radar last year when the folks at Lawrence Berkeley National Laboratory used it to describe a revved-up photoelectrochemical cell using gallium phosphide (a semiconductor that absorbs visible light), and a hydrogen-producing catalyst called cobaloxime.
Image Credit (screenshot): Courtesy of Lund University.