An interesting energy storage twist on zero emission hydrogen fuel has been bubbling up under the CleanTechnica radar for a few years, and it’s time to play catch-up. The idea is to use liquid formic acid — HCO2H — to store hydrogen. That could be a significant development in terms of cutting costs and scaling up, compared to the use of compressed hydrogen gas. With the cost of renewable hydrogen already in steep decline, it looks like the “hydrogen society” unicorn might be real after all.
Hydrogen Energy Storage, Formic Acid Style
The allure of formic acid is pretty clear in terms of energy storage. Compared to storing hydrogen as a compressed gas, formic acid could potentially provide for improved energy density and efficiency. It also fares well against the solid-state hydrogen storage platforms that have begun to emerge as alternatives to compressed gas.
The potential for recycling carbon dioxide in formic acid production is another plus.
However, there is no such thing as a free energy storage lunch. One big challenge is cost.
The most recent development on the cost cutting score came out of Rice University in Texas just last week. A team of researchers there has been deploying electricity from renewable sources to generate formic acid directly in a reactor, without the need for additional — and expensive — purification steps.
For down-to-the-nanoscale details check out the research team’s article in the journal Nature. For those of you on the go, one key improvement is a new catalyst in the form of 2-D bismuth. The researchers credit it with providing more stability compared to conventional catalysts.
The researchers also shaved costs by using a solid-state electrolyte. Conventional formic acid reactors use salted water, which means that the salt has to be removed eventually. That’s where a lot of the expense and energy consumption come in.
The team’s reactor scored an fairly impressive energy conversion efficiency of 42%, and they are already plotting next steps to bump that up, including improvements to the catalyst.
Meanwhile, the researchers have a shoutout for the US Department of Energy’s Brookhaven National Laboratory all the way over in Long Island, New York. The lab lent out its Inner Shell Spectroscopy beamline at the National Synchrotron Light Source II for the research, which enabled the team to study the oxidation states of the bismuth catalyst in real time.
Next Steps For The Research
So, when will this new formic acid energy storage revolution happen? Who knows?
Progress appears to be moving along swiftly, though. Last year Switzerland’s EPFL (École polytechnique fédérale de Lausanne) announced a “world’s first” formic acid reactor, which deployed a relatively expensive catalyst based on ruthenium. As with the Rice team, those researchers are already casting about for opportunities to cut costs and improve catalyst performance.
Earlier this year, the Journal of Hydrogen Energy published a study by researchers from the Delft Institute of Technology that explores several major challenges for formic acid energy storage, including how to extract the hydrogen efficiently and economically.
The Long Road To Long Duration Energy Storage
Another interesting aspect to formic acid energy storage is the long duration energy storage angle.
As much as rechargeable battery technology has improved in recent years, the US Department of Energy is still in search of more efficient pathways for storing energy in bulk over long periods of time — like on the order of 10 to 100 hours.
Currently, hydroelectric dams and pumped storage are the only forms that fit the bill.
The Energy Department is looking into other next-generation storage pathways including flow batteries as well as a hydrogen peroxide approach to chemical storage for hydrogen.
Other long duration research in the works includes storing thermal heat in sand, carbon blocks or specialized materials. Many of these pathways leverage the availability of abundant, low cost renewable energy.
Stay tuned for an update on that hydrogen peroxide research, which is going on that the University of Tennessee in Knoxville. CleanTechnica is reaching out to the researchers for some insights on how their work compares to the formic acid approach.
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Schematic via Rice University: “This schematic shows the electrxolyzer developed at Rice to reduce carbon dioxide, a greenhouse gas, to valuable fuels. At left is a catalyst that selects for carbon dioxide and reduces it to a negatively charged formate, which is pulled through a gas diffusion layer (GDL) and the anion exchange membrane (AEM) into the central electrolyte. At the right, an oxygen evolution reaction (OER) catalyst generates positive protons from water and sends them through the cation exchange membrane (CEM). The ions recombine into formic acid or other products that are carried out of the system by deionized (DI) water and gas. Illustration by Chuan Xia and Demin Liu.”
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