In the global effort to combat climate change, researchers worldwide are actively seeking ways to extract carbon dioxide from the atmosphere or power plant emissions and convert it into useful materials. One promising approach involves turning carbon dioxide into a stable fuel that can replace fossil fuels in various applications. However, most conversion processes face challenges such as low carbon efficiency, toxicity, flammability, or difficulty in handling the produced fuels.
Addressing these limitations, a team of researchers from MIT and Harvard University has developed an efficient process to convert carbon dioxide into formate, a liquid or solid material that can be utilized as an alternative to hydrogen or methanol in fuel cells for electricity generation. Potassium or sodium formate, which is already produced at industrial scales and commonly used as a de-icer, is non-toxic, nonflammable, easy to store and transport, and can remain stable in steel tanks even after months or years of production.
Described in the journal Cell Press Physical Sciences, the new process was demonstrated at a small laboratory scale, encompassing the capture of carbon dioxide and its electrochemical conversion to a solid formate powder. The researchers believe that the process is scalable and could potentially provide emissions-free heat and power to individual homes, as well as industrial or grid-scale applications.
Unlike other carbon dioxide conversion methods that involve a two-stage process with low efficiency, the new process achieves a conversion rate of over 90% without the need for inefficient heating. Instead, the carbon dioxide is first converted into an intermediate form called liquid metal bicarbonate, which is then electrochemically transformed into liquid potassium or sodium formate in an electrolyzer using low-carbon electricity from renewable sources.
The highly concentrated liquid formate solution can be dried to produce a stable solid powder that can be stored in regular steel tanks for extended periods. This shelf-stable characteristic sets it apart from hydrogen storage, where significant leakage occurs over time, hindering year-long storage. Additionally, unlike methanol, which is toxic and poses a health hazard in case of leakage, formate is widely used and considered safe according to national safety standards.
The significant improvement in efficiency is attributed to several optimizations. First, the design of the membrane materials and their arrangement prevents a shift in acidity over time, ensuring a steady-state conversion process. The researchers also introduced a buffer layer of bicarbonate-enriched fiberglass wool to block unwanted side reactions that produce non-useful chemical products.
To utilize the formate fuel, the team constructed a fuel cell specifically optimized for this purpose. The solid formate particles are dissolved in water and fed into the fuel cell as needed. Although the solid fuel is heavier than pure hydrogen, the weight and volume of high-pressure hydrogen gas tanks required for storage offset the difference, resulting in electricity output comparable to hydrogen for a given storage volume.
The researchers envision various applications for the formate fuel, ranging from household units to large-scale industrial and grid-scale storage systems. For household use, an electrolyzer unit about the size of a refrigerator could capture and convert carbon dioxide into formate, which can be stored in an underground or rooftop tank. When required, the powder can be mixed with water and fed into a fuel cell to provide power and heat. This technology not only has the potential to transform homes but also to be employed in factories or integrated into the existing grid infrastructure.
1. Source: Coherent Market Insights, Public sources, Desk research
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