Storing Electricity In Chemical Form

Researchers in Japan have created a device that stores excess electrical energy using glycolic acid, which has a much greater energy capacity than hydrogen, one of the more popular energy-storage chemicals.

AsianScientist (Jan. 10, 2018) – In a study published in Scientific Reports, Japanese scientists have created a device to store excess electrical energy in chemical form through continuous electrolysis.

Interest in renewable energy continues to burgeon. Many renewables, however, can be frustratingly intermittent—when the sun stops shining, or the wind stops blowing, the power flickers. The fluctuating supply can be partly smoothed-out by energy storage during peak production times. However, storing electricity is not without its challenges either.

In this study, a research group at the International Institute for Carbon-Neutral Energy Research (I2CNER), within southern Japan’s Kyushu University, investigated the use of glycolic acid (GC) for energy storage. The researchers noted that GC has a much greater energy capacity than hydrogen, one of the more popular energy-storage chemicals. GC can be produced by four-electron reduction of oxalic acid (OX), a widely available carboxylic acid.

The team devised an electrolytic cell based on a novel membrane-electrode assembly. Sandwiched between two electrodes are an iridium oxide-based anode and a titanium dioxide (TiO2)-coated titanium (Ti) cathode, linked by a polymer membrane.

“In our device, by using a solid polymer electrolyte in direct contact with the electrodes, we can run the reaction as a continuous flow. The OX solution can effectively be thought of as a flowable electron pool,” said Dr. Masaaki Sadakiyo of Kyushu University who is the lead author of the study.

The team’s other consideration was cathode design. The reaction at the cathode is catalyzed by TiO2. To ensure a solid connection between catalyst and cathode, the team ‘grew’ TiO2 directly on Ti in the form of a mesh or felt.

Electron microscope images revealed the TiO2 structure as a wispy fuzz, clinging to the outside of the Ti rods like a coating of fresh snow. In fact, its job is to catalyze the electro-reduction of OX to GC. Meanwhile, at the anode, water is oxidized to oxygen.

The team found that the reaction accelerated at higher temperatures. However, turning the heat up too high encouraged an unwanted by-process: the conversion of water to hydrogen. The ideal balance between these two effects was at 60°C. At this temperature, the device could be further optimized by slowing the flow of reactants while increasing the amount of surface area available for the reaction.

Interestingly, even the texture of the fuzzy TiO2 catalyst made a major difference. When TiO2 was prepared as a felt, by growing it on thinner and more densely packed Ti rods, the reaction occurred faster than on the mesh. The researchers attributed this to the greater surface area of the felt structure. The felt also discouraged hydrogen production by blanketing the Ti surface more snugly than the mesh, preventing the exposure of bare Ti.

“Under the right conditions, our cell converts nearly 100 percent of OX, which we find very encouraging,” said study co-author Professor Miho Yamauchi of Kyushu University. “We calculated that the maximum volumetric energy capacity of the GC solution is around 50 times that of hydrogen gas. To be clear, the energy efficiency, as opposed to capacity, still lags behind other technologies. However, this is a promising first step to a new method for storing excess current.”



The article can be found at: Sadakiyo et al. (2017) Electrochemical Production of Glycolic Acid from Oxalic Acid Using a Polymer Electrolyte Alcohol Electrosynthesis Cell Containing a Porous TiO2 Catalyst.

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Source: Kyushu University; Photo: Sadakiyo et al.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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