A solar-energy storage cell that works at night

July 3, 2015

A UT Arlington team has developed a new energy cell that is more efficient and can store solar energy even at night (credit: UT Arlington)

A University of Texas at Arlington materials science and engineering team has developed a new “photoelectrochemical” energy cell that can efficiently store solar energy and deliver electrical power 24 hours a day. It can also be scaled up to provide large amounts of energy, limited only by the size of its chemical storage tanks, according to Fuqiang Liu, an assistant professor in the Materials Science and Engineering Department who led the research team.

The innovation is based on an all-vanadium photoelectrochemical flow cell that allows for storage of electrons in the cell — an advance over the most common solar energy systems, which are restricted to using sunlight immediately as a power source. The team is now working on a larger prototype.

Photoelectrochemical energy storage system (credit: Fuqiang Liu/University of Texas at Arlington)

“The ability to store solar energy and use it as a renewable alternative provides a sustainable solution to the problem of energy shortage as renewable energy becomes more prevalent,” Liu said.

The research is detailed in the journal ACS Catalysis. The work was funded by a 2013 National Science Foundation $400,000 Faculty Early Career Development grant awarded to Liu.

UPDATE July 6, 2015: Follow-up Q&A with Prof. Liu

KurzweilAI: Regarding your statement, “Compared to battery, this cell is more efficient and offers much higher capacity.” Could you quantify the efficiency and capacity comparison?

Liu: Our system is different to existing solar energy storage systems; therefore, a precise comparison is difficult to make. However, our system has already demonstrated ~95% Faradaic efficiency and more than 10x higher in peak IPCE (Incident photon-to-current efficiency) compared to conventional photo-generation of hydrogen, a widely accepted approach for solar energy storage.

KurzweilAI: How does your system compare to conventional lithium ion batteries?

Liu: We do not have solid data to compare our system to conventional lithium ion batteries.

KurzweilAI: One of our readers asked how the CellCube energy storage system relates to your technology.

Liu: Our approach mimics a redox flow battery (the CellCube energy storage system)in the discharge direction. Besides, our monolithic approach, with an internally integrated photoelectrochemical system and a redox flow battery, obviates the need for externally hooking up a (solid-state) PV system with a battery. In this regard, and it shares much of the same logic behind a photoelectrochemical water splitting device as opposed to a hybrid PV-water electrolyzer combination.

Abstract of Reversible Electron Storage in an All-Vanadium Photoelectrochemical Storage Cell: Synergy between Vanadium Redox and Hybrid Photocatalyst

Colossal solar energy conversion and storage studies using photoelectrochemical cells (PECs) have been undertaken in the past four decades; however, how to efficiently utilize solar energy despite the intermittent nature of sunlight still remains a challenge. In this paper, a WO3/TiO2 hybrid photoelectrode was coupled with our newly developed all-vanadium photoelectrochemical cell (PEC) with the aim of implementing photoelectrochemical solar energy conversion and storage. Zero-resistance ammetry (ZRA) and electrochemical impedance spectroscopy (EIS) were employed to study the photoelectrochemical response of this system in the conversion and storage of solar energy both under illumination and in the dark. The preliminary results proved the feasibility of this approach to store/release solar energy, even under dark conditions and showed that hydrogen tungsten bronze was responsible for the storage and release of photogenerated electrons from the semiconductor. The results also indicated an important synergy between electron storage and the all-vanadium electrolytes, which potentially offers great reversibility, high-capacity electron storage, and significant improvement in the photocurrent. To better understand the observed photoelectrochemical and electrochemical impedance behavior of our system, a model that unfolds the WO3 electron storage mechanism and photogenerated charge carrier pathways in the all-vanadium PEC is proposed.