New Catalytic Reactors Convert Greenhouse Gases Into Industrial Fuels

• Researchers develop a new method to reduce carbon dioxide into carbon monoxide, using renewable electricity. 
• It can decrease the amount of carbon dioxide released into the atmosphere every year. 
• In fact, industries can capture these gases and convert it into useful products. 

The intensive consumption of fossil fuels and excessive emission of greenhouse gases such as carbon dioxide (CO₂) are increasing environmental problems every year. Now, it has become necessary to address these issues and find some effective solutions.

Recently, researchers at Harvard University came up with an enhanced technique to reduce CO₂ into CO (carbon monoxide), using renewable electricity. It seems a promising method to restrict CO₂ emission while producing value-added chemicals and fuels.

CO has a huge market compatibility and a variety of applications in medicine and chemical manufacturing. The reduction of CO₂ into CO is the most promising approach (compared to various carbon dioxide reduction reactions) due to its large current density, relatively high selectivity, and its potential to separate gas product from liquid water.

A Dramatic Step Forward From The Last Year’s Technique

This new technique is based on a previous system that relied on two electrolyte-filled chambers, each holding one electrode (anode and cathode). This one is less expensive and relies on high-concentration of water vapor and carbon dioxide gas to work more efficiently.

The new system is relatively small (10*10 cm) compared to the previous one and can generate up to 4 liters of carbon monoxide every hour. Basically, it addresses 2 main issues that were limiting the initial methodology: 1) Cost and 2) Scalability.

In the previous system, researchers were using catalysts made of a single nickel atom to reduce CO₂ to CO. However, the cost of synthesizing these materials was quite high.

Since these single nickel atoms were associated with graphene, it was very hard for them to scale up the process for feasible use in the future. That’s why they switched to a product (carbon black) that is thousand times more economical than graphene.

They were able to effectively capture positively charged single Ni atoms into negatively charged defects in carbon black particles, using an electrostatic-attraction-like process. This yielded a highly selective, low-cost substance suitable for carbon dioxide reduction.

Reference: Cell | doi:10.1016/j.joule.2018.10.015 | Harvard University

With the previous system, researchers could only create in milligram-scales per batch, but now the maximum they can generate is grams. This end product is only limited by the instruments: if they had access to a bigger tank, they could produce kilograms of this catalyst.

Another big advantage of this system is that it can work with water vapor (instead of liquid water, which is used in the previous system) and feed in high-concentration of carbon dioxide.

Single nickel atoms on commercial carbon black were synthesized in large quantities | Courtesy of researchers 

Now, researchers can pump 97% of CO₂ and 3% water vapor into the system, compared to the older system’s 99% water and 1% CO₂ ratio. Furthermore, vapor functions as ion exchange membranes to help ions move around, which is a better alternative to ion conductors in the system.

As a result, researchers can provide higher current density: a year before, they were operating at 10 milliamps/cm², but now they can go up to 100 milliamps with almost 100% selectivity for CO₂ to CO conversion.

What’s Next?

In order to make the system work in a real-world environment, they need to make it continuously work for thousands of hours. As of now, it operates for only tens of hours. So there is still a lot of work to do.

Researchers believe that they can achieve this feat by analyzing both the water oxidation catalyst and the CO₂ reduction catalyst. They are pretty sure that one day industries will be capturing CO₂ instead of releasing it into the atmosphere and converting it into useful end-products.

Read: Proposed US Pipeline Network For Capturing 30 Million Metric Tons of Carbon Dioxide Every Year

Also, they plan to test various copper-based catalysts that can efficiently reduce carbon dioxide into more valuable products (other than carbon monoxide).