Novel electrode could convert CO2 into useful products

Activation of carbon dioxide – converting it into useful carbon-based fuels and chemicals – is a subject of much interest in recent years, as it may be away to reduce the levels of the gas in the atmosphere and therefore combat its greenhouse effect that contributes to climate change. However, it has always been a difficult goal, because CO2 is so stable that most methods to reduce the carbon atom to a more reactive state have had poor yields and reaction mechanisms that are hard to determine and understand. Many researchers have attempted to mimic the way that carbon dioxide is activated in nature: electrochemically. Plants achieve this feat through photosynthesis, converting carbon into sugars.

Physicists and chemists from the University of Bath, collaborating with two Chinese institutions – Fudang University, Shanghai and the Shanghai Institute of Pollution Control and Ecological Security – have devised a novel type of electrode that they claim performs much better than previous versions. The key to its performance is its shape: rather than being flat, it is bowl-shaped.

The researchers explain, in the Journal of Materials Chemistry A, that the shape they have used, technically known as an inverse opal, concentrates electric field on the rim of the bowl, which in use is hot. The reaction they studied employs potassium as a catalyst, and the "hot edges" of the bowl concentrates the potassium ions onto the active sites of the reaction, which takes place on the indium-copper alloy from which the electrode is made.

The researchers claim that the bowl-shaped electrode converts carbon dioxide six times faster than a conventional planar electrode. Moreover, the copper-indium construction allows Raman spectroscopy to be used to study the reaction progress.

As with all processes which use electricity for environmentally-significant purposes, the source of the power needed for the reaction is crucial, stressed Prof Liwu Zhang. "By using clean electricity, we can convert CO2 into chemical fuels, which can be used again. This builds a cycle of CO2, with no increment of CO2 concentration and will help save our world. However, to improve the efficiency of transforming CO2 into chemical fuels, it is extremely important to know the reaction pathway, and find the most suitable catalyst. Just as plants transform CO2 into sugar we are finding suitable electrochemical 'leaf' for CO2 conversion."

Bath research leader Prof Ventsislav Valev is keen to stress the importance of this research. "There is no more pressing human need than breathing. Yet for hundreds of million people this most basic activity is a source of anxiety over lowering life expectancy, rising child mortality and climate change. There is evidence that CO2 increases surface ozone, carcinogens, and particulate matter, thereby increasing death, asthma, hospitalisation, and cancer rates. It is therefore crucial to keep researching new ways for lowing the CO2 levels in the atmosphere."

Future stages of the research will focus on optimising the catalyst to produce the most useful products.