Transforming CO2 into industrial fuels

Turning tide on greenhouse gases.

"The most promising idea may be to connect these devices with coal-fired power plants or other industry that produces a lot of CO2,” said Haotian Wang of his latest research. Rose Lincoln/Harvard file photo

An individual at the Rowland Institute at Harvard, Haotian Wang and associates have built up an enhanced framework to utilize sustainable power to diminish carbon dioxide into carbon monoxide (CO) — a key item utilized in various mechanical procedures.

About 20 percent of those gases are CO2, so pumping them into the cell and combine it with clean electricity, then we can potentially produce useful chemicals out of these wastes in a sustainable way, and even close part of that CO2 cycle.

The system represents mainly relies on high concentrations of CO2 gas and water vapor to operate more efficiently. Just one 10-by-10-centimeter cell, it can produce as much as four liters of CO per hour.

Wang said, “In that earlier work, we had discovered the single nickel atom catalysts which are very selective for reducing CO2 to CO … but one of the challenges we faced was that the materials were expensive to synthesize. The support we were using to anchor single nickel atoms was based on graphene, which made it very difficult to scale up if you wanted to produce it at the gram or even kilogram scale for practical use in the future.”

“To address that problem, we turned to a commercial product that’s thousands of times cheaper than graphene as an alternative support — carbon black.”

“Using a process similar to electrostatic attraction, we were able to absorb single nickel atoms (positively charged) into defects (negatively charged) in carbon black nanoparticles, with the resulting material being both low-cost and highly selective for CO2 reduction.”

“Right now, the best we can produce is grams, but previously we could only produce milligrams per batch. But this is only limited by the synthesis equipment we have; if you had a larger tank, you could make kilograms or even tons of this catalyst.”

The other test Wang and associates needed to defeat was fixing to the way that the first system just worked in a liquid solution.

The underlying system worked by utilizing a terminal in one chamber to split water particles into oxygen and protons. As the oxygen gurgled away, protons directed through the liquid solution would move into the second chamber, where — with the assistance of the nickel impetus — they would tie with CO2 and break the particle separated, leaving CO and water. That water could then be encouraged once more into the primary chamber, where it would again be part, and the procedure would begin once more.

Wang said, “The problem was that the CO2 we can reduce in that system are only those dissolved in water; most of the molecules surrounding the catalyst were water. There was only a trace amount of CO2, so it was pretty inefficient.”

“While it may be tempting to simply increase the voltage applied on the catalyst to increase the reaction rate, that can have the unintended consequence of splitting water, not reducing CO2.”

“If you deplete the CO2 that’s close to the electrode, other molecules have to diffuse to the electrode, and that takes time. But if you’re increasing the voltage, it’s more likely that the surrounding water will take that opportunity to react and split into hydrogen and oxygen.”

“We replace that liquid water with water vapor and feed in high-concentration CO2 gas. So if the old system was more than 99 percent water and less than 1 percent CO2, now we can completely reverse that and pump 97 percent CO2 gas and only 3 percent water vapor into this system. Before those, liquid water also functioned as ion conductors in the system, and now we use ion exchange membranes instead to help ions move around without liquid water.”

“If you want to use this to make an economic or environmental impact, it needs to have a continuous operation of thousands of hours. Right now, we can do this for tens of hours, so there’s still a big gap, but I believe those problems can be addressed with more detailed analysis of both the CO2 reduction catalyst and the water oxidation catalyst.”

“Carbon monoxide is not a particularly high-value chemical product. To explore more possibilities, my group has also developed several copper-based catalysts that can further reduce CO2 into products that are much more valuable.”

Wang credited the freedom he enjoyed at the Rowland Institute with helping lead to breakthroughs like the new system.

The system is described in a Nov. 8 paper published in Joule, a newly launched sister journal of Cell Press.