A photoelectrochemical cell (PEC) is a special type of solar cell that gathers the Sun's energy and transforms it into either electricity or chemical energy used to split water and produce hydrogen for use in fuel cells. In an advance that could help this clean energy source play a stronger role within the smart grid, researchers at the University of Texas, Arlington have found a way to store the electricity generated by a PEC cell for extended periods of time and allow electricity to be delivered around the clock.

Currently, the electricity generated by a PEC cell could not be stored effectively, as the electrons would quickly "disappear" into a lower-energy state. This meant that these cells were not a viable solution for a clean-energy grid, as the electricity had to be used very shortly after being produced. That is, on sunny days, at a time when standard PV panels would already be producing energy at full tilt.

Now, researchers Fuqiang Liu and colleagues have created a PEC cell that includes a specially designed photoelectrode (the component that converts incoming photons into electrons). Unlike previous designs, their hybrid tungsten trioxide/titanium dioxide (WO3/TiO2) photoelectrode can store electrons effectively for long periods of time, paving the way for PEC cells to play a bigger role within a smart energy grid.

The system also includes a vanadium redox-flow battery (VRB). This is an already established type of energy storage cell that is very well-suited for the needs of the electrical grid as it can stay idle for very long times without losing charge, is much safer than a lithium-ion cell (though less energy-dense), is nearly immune to temperature extremes, and can be scaled up very easily, simply by increasing the size of its electrolyte tanks.

According to the researchers, the vanadium flow battery works especially well with their hybrid electrode, allowing them to boost the electric current, offering great reversibility (with 95 percent Faradaic efficiency) and allowing for high-capacity energy storage.

"We have demonstrated simultaneously reversible storage of both solar energy and electrons in the cell," says lead author of the paper Dong Liu. "Release of the stored electrons under dark conditions continues solar energy storage, thus allowing for continuous storage around the clock."

The team is now working on building a larger prototype, with the hope that this technology could be used to better integrate photoelectrochemical cells within the smart grid.

A paper describing the advance appears in the latest edition of the journal ACS Catalysis.

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