Scientists and researchers across the globe are tirelessly exploring methods to harness carbon dioxide from the atmosphere or power plant emissions and transform it into a valuable resource. Amongst these endeavors, MIT and Harvard engineers transformed CO2 into efficient fuel capable of replacing fossil fuels in various applications. Earlier conversion methods faced challenges such as low carbon efficiency and the production of dangerous fuels. The new process is expected to be more efficient on a larger scale.
Researchers from MIT and Harvard University have made a significant breakthrough by creating an efficient process capable of transforming carbon dioxide into formate. This remarkable achievement opens the door to utilizing formate as a versatile material in liquid or solid form that can be used like methanol or hydrogen to fuel cells and generate electricity.
Sodium formate or popularly known as potassium is already produced on an industrial scale. They are most commonly used as a de-icer for sidewalks and roads. It is non-flammable and non-toxic, plus it can be easily stored and transported. Moreover, it has the ability to remain stable in ordinary steel tanks from where it can be used for months. Sometimes, the material is used even after years after its production.
About the Process
The entire process is about capturing and electrochemical conversion of the gas to a solid formate powder. On a small scale in the laboratory, the team demonstrated the process where this powder was transferred into a fuel cell to generate electricity.
According to Professor Li, other approaches to convert carbon dioxide into fuel involve a two-stage process. They are:
- To capture and convert the gas into calcium carbonate, a solid form. Then later the material is heated and in this process carbon dioxide is removed. After this it is converted into a fuel feedstock like carbon monoxide.
- The second step is not very efficient. It usually converts less than 20% of the gaseous carbon dioxide into the desired product.
Carbon capture and conversion is a process that starts with capturing carbon dioxide using an alkaline solution. This solution concentrates the carbon dioxide from different sources, like power plants or even the air, into a liquid metal-bicarbonate form.
Through the utilization of a cation-exchange membrane electrolyzer, bicarbonate is transformed electrochemically into solid formate crystals. The carbon efficiency of over 96 percent has been validated through rigorous lab-scale experiments conducted by the team.
According to Professor Li, the crystals do not expire and can be stored for many years without any loss. In contrast, even the best hydrogen storage tanks currently available let the gas leak at a rate of about 1 percent per day. This makes it impossible to use them for long-term storage purposes.
Also See: All About Fuel Cell Advantages
High Conversion Rate
In contrast, the new process achieves a conversion rate of over 90 percent, surpassing the previous method. Additionally, it eliminates the need for the inefficient heating step by transforming carbon dioxide into a highly efficient intermediate form known as liquid metal bicarbonate.
The liquid is subsequently transformed into liquid potassium or sodium formate through electrochemical conversion in an electrolyzer powered by low-carbon electricity, such as nuclear, wind, or solar power.
Different Forms of Formate
According to Prof. Li, the solution of potassium or sodium formate, which is highly concentrated, can be subsequently dried to create a solid powder. This process can be achieved through methods like solar evaporation. The resulting powder is exceptionally stable and can be safely stored in standard steel tanks for extended periods, spanning years or even decades.
MIT and Harvard engineers transformed CO2 into efficient fuel and the success of this process inspired the researchers to make it scalable so that it can produce emission-free heat along with powering individual homes. Furthermore, it can be used for grid-scale operations or in industries.
According to Professor Li, the team’s development of numerous optimization techniques played a pivotal role in transforming an ineffective chemical-conversion process into a viable solution. Prof. Li, who holds positions in both the departments of Nuclear Science and Engineering and Materials Science and Engineering, emphasizes the significant impact achieved through these steps of optimization.
Subsequently, when necessary, the solid powder would be blended with water and introduced into a fuel cell for the purpose of delivering both power and heat. “This is for community or household demonstrations, but we believe that also in the future it may be good for factories or the grid,” Zhang said.
While methanol is a toxic substance that presents challenges in terms of safety, formate emerges as a viable and safer alternative for transforming carbon dioxide into a fuel suitable for fuel cells. National safety standards acknowledge formate as a widely used and harmless option, providing a reliable solution without compromising the well-being of individuals in cases of potential leakage.
Steps Leading to Success
The efficiency of this process has greatly improved due to several enhancements.
- Firstly, a well-thought-out design of the membrane materials and their arrangement has solved a problem faced by previous attempts at this system.
- In those cases, the accumulation of specific chemical by-products would alter the pH, resulting in a gradual decline in efficiency over time.
Zhang says, “Traditionally, it is difficult to achieve long-term, stable, continuous conversion of feedstocks. The key to our system is to achieve a pH balance for steady-state conversion.”
In order to accomplish this, the researchers conducted thermodynamic modeling in order to devise a new process that maintains chemical equilibrium and a stable pH without any fluctuations in acidity. By doing so, the system can operate with optimal efficiency for extended durations.
The system was tested for over 200 hours and the output did not significantly decrease. The process can be carried out at ambient temperatures and relatively low pressures, about five times atmospheric pressure.
An additional problem was the production of chemical by-products that were not useful due to unwanted side reactions. However, the team solved this issue by introducing an extra layer, made of bicarbonate-enriched fiberglass wool, which prevented these reactions.
Additionally, the team has developed a fuel cell that is specifically designed to efficiently utilize this formate fuel for electricity generation. The formate particles that are stored are easily dissolved in water and then seamlessly injected into the fuel cell whenever required.
According to Li, even though solid fuel is significantly heavier than pure hydrogen, when we take into account the weight and size of the high-pressure gas tanks required to store hydrogen, the overall result is an electricity output that is almost equal for a given storage volume.
Various Potential Applications of Formate
According to the researchers, the formate fuel has the potential to be customized for a wide range of purposes, from small-scale home units to large industrial applications or grid-scale storage systems. At the household level, a refrigerator-sized electrolyzer unit could be used to capture and convert carbon dioxide into formate, which can then be stored in an underground or rooftop tank.
MIT and Harvard engineers transformed CO2 into efficient fuel and a professor of chemistry and of electrical and computer engineering at Northwestern University, Ted Sargent, who is not a part of this study, said, “The formate economy is an intriguing concept because metal formate salts are very benign and stable, and a compelling energy carrier. The authors have demonstrated enhanced efficiency in liquid-to-liquid conversion from bicarbonate feedstock to formate, and have demonstrated these fuels can be used later to produce electricity.”