Providing a new ray of hope for hydrogen fuel cell fans, researchers at Eindhoven University of Technology have developed a more efficient way to produce the fuel needed to keep fuel cells going — namely, hydrogen. We’ve been giving hydrogen the stinkeye because it is sourced primarily from fossil natural gas, but the Eindhoven solution works on solar energy and water, and gallium phosphide aka GaP.
The Allure Of Hydrogen
Hydrogen is a very energy dense fuel and hydrogen fuel cells are emissionless. They are also quick to refuel, which accounts for the growing use of hydrogen fuel cell electric vehicles (FCEVs) in warehouse logistics.
Auto manufacturers are also starting to dabble in FCEVs, but currently there are a few huge catches. Aside from the fracking issues related to fossil natural gas sources, the process of producing hydrogen from natural gas is energy-intensive.
One solution is to use renewable energy, so if the hydrogen from solar energy and water thing sounds familiar, that’s because the field of solar “water splitting” research has been expanding and progressing in recent years.
There are a couple of ways to go about using solar energy for water splitting, one of which is to use the solar energy from photovoltaic cells.
A more direct pathway is the use of photoelectrochemical cells. There have been quite a few developments on that front in recent years, including a low-cost, small-scale “artificial leaf” designed for undeveloped communities, and an advanced “bionic leaf” system that integrates liquid fuel production.
The New Solar Fuel Cell
The folks at Eindhoven have taken the photoelectrochemical approach, which they are calling a “solar fuel cell.”
Their new twist on the research is an array of nanowires based on gallium phosphide, which is a semiconductor commonly used to manufacture some types of light emitting diodes.
According to the team, gallium phosphide was their “dream candidate” because of its strong electrical properties, but apparently the material has escaped notice in the water splitting field because it is not an especially efficient material for conventional solar cells.
The solution was to create a grid of gallium phosphide nanowires rather than arraying the material on a flat surface. The wires are pretty small, even for nanowires — 500 nanometers long and 90 thick.
The result was a vastly increased surface area, which increased the hydrogen yield by a factor of 10, to 2.9%. That actually doesn’t sound like much compared to the 15% hydrogen yield attainable with a silicon solar cell/battery system, but the research is still in the initial phases and, according to Eindhoven, “there is still a lot of scope for improvement.”
The relatively low efficiency of the new system could also be balanced out by its extremely low cost. Here’s the explainer from the research team:
For the nanowires we needed ten thousand less precious GaP material than in cells with a flat surface. That makes these kinds of cells potentially a great deal cheaper. In addition, GaP is also able to extract oxygen from the water — so you then actually have a fuel cell in which you can temporarily store your solar energy. In short, for a solar fuels future we cannot ignore gallium phosphide any longer.
More details are available at Nature Communications under the title “Efficient water reduction with gallium phosphide nanowires.”
Photo credit: Array of nanowires gallium phosphide made with an electron microscope via Eindhoven University of Technology.
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