Light-powered process could convert carbon dioxide into fuel
Nickel-based photocatalyst a step towards making high-value multi-carbon fuels using solar energy.
In what could well be described as a win-win outcome, a team of scientists from the US Department of Energy's Lawrence Berkeley National Laboratory and Singapore’s Nanyang Technological University have developed a light-activated process that turns carbon dioxide into carbon monoxide with no toxic by-products.
The achievement is being hailed as an important step in the quest to deploy solar-powered methods to reduce global greenhouse gas concentrations while simultaneously creating useable fuel.
The researchers, co-led by Haimei Zheng from the Berkeley lab, created a nickel-organic photocatalyst, fashioned into a kind of matrix broadly similar to a metal-organic framework, or MOF – a three-dimensional structure comprising metal ions and polymers that can be used for hydrogen or carbon dioxide storage.
The team’s nickel-based structure differs from standard MOFs in one significant way. While MOFs are rigid, the new material contains many “soft” linkages, giving it sponge-like characteristics. This substantially improves its ability to convert one gas to another in a highly efficient way.
"We show a near 100% selectivity of CO production, with no detection of competing gas products like hydrogen or methane," Zheng says. "That's a big deal. In carbon dioxide reduction, you want to come away with one product, not a mix of different things. Complete suppression of the competing hydrogen evolution during a photocatalytic CO2-to-CO conversion had not been achieved before our work."
To create their nickel-organic catalyst, Zheng and colleagues first dissolved nickel precursors in a solution of triethylene glycol. The result was then exposed to an unfocused red laser, causing the metal to absorb the light.
The team found that changing the wavelength of the laser resulted in different composites being produced. From this, the researchers were able to determine which reactions were catalysed by heat, and which by light.
Measuring the behaviour of the chosen nickel-composite using gas chromatography and mass spectrometry, they found that one gram of the material – held at room temperature for one hour – was able to produce 400 millilitres of carbon monoxide.
The material was not only highly efficient and selective in its operation but also showed signs of considerable robustness – indicating that when scaled up it will endure long periods of high-volume use.
The team’s work potentially brings the world one step closer to the urgent goal of being able to mitigate climate change in ways that are both efficient and profitable.
Converting carbon dioxide into carbon monoxide is a popular research target in the field. In 2015, for instance, a team from the University of California, Berkeley, unveiled a way of making the conversion using electrified cobalt porphyrins.
Converting carbon dioxide into a tradeable commodity is seen as a key driver for tackling global warming in some quarters. The potential benefit is indicated by the sponsorship of the Carbon X Prize, which is offering a total of $US 20 million, including a $US 7.5 million grand prize purse, to promote research into solutions to effectively convert carbon dioxide from problem to profit.
"The world right now is in need of innovative ways to create alternatives to fossil fuels, and to stem the levels of excessive CO2 in the atmosphere," says Zheng. "Converting CO2 to fuels using solar energy is a global research endeavor. The spongy nickel-organic photocatalyst we demonstrated here is a critical step toward practical production of high-value multi-carbon fuels using solar energy."