Light-activated catalyst turns CO₂ to CO

RESEARCHERS at Lawrence Berkeley National Laboratory in the US have developed a “spongy” nickel-based, light-activated catalyst which can convert CO₂ to CO with near 100% efficiency.

The researchers, led by materials scientist Haimei Zheng, say that it is the first time a catalyst has been developed which produces only CO from CO₂ without unwanted byproducts. Being able to generate carbon-neutral fuel and other chemicals from atmospheric CO₂ rather than fossil fuels is one of many important research strands in the fight against climate change. CO is more chemically reactive than CO₂ and can be turned more easily into useful products. Zheng says that the new catalyst is a critical step on the road to generating fuels from CO₂ using solar energy.

The researchers made the metal-organic photocatalyst, Ni (TPA/TEG), through a light-catalysed reaction. Solutions of TEG, TPA and nickel ions were irradiated with an unfocussed infrared laser for around three hours. This creates a catalyst with a crystalline architecture but with a significant number of defects. The catalyst is similar in structure to a metal organic framework, with the metal ions connected with rigid organic linkers, however in this case, the linkers are flexible.

The team tested the catalyst in a sealed reactor. After one hour at room temperature, 1 g of the catalyst produced 400 ml of CO. The reaction reduces CO₂ using electrons from water to make CO. The reaction would normally also produce H₂ gas, but this was undetectable with the use of the new catalyst. The researchers believe that the architecture of the catalyst suppresses the alternate reaction by favouring the binding of CO₂ anions, leaving no space for hydrogen.

The researchers also tested the catalyst after enriching it with silver and rhodium nanocrystals. The silver-enriched catalyst produced acetic acid, with the rhodium-enriched catalyst produced formic acid. Both of these chemicals are widely used in industry, but more importantly, the researchers point out that it shows the catalysts can generate carbon-carbon links, which is important in the generation of liquid fuels.

Zheng and the team now plan to look at a tandem catalyst system which could use visible light, and developing more advanced metal-organic heterogeneous photocatalysts, which can use a broader spectrum of light and better fix CO₂.

Science Advances doi.org/b95d