Doped nanotubes beat heavy metal for CO2 reduction

Avoiding the use of fossil fuels in energy production is high on the sustainability agenda and the likes of wind and solar power have come to the fore as viable alternatives. But, liquid and gas fuels are still needed for many applications. Instead of using fossil fuels, what if we could extract the greenhouse gas carbon dioxide from the atmosphere and convert it into organic fuels in a process driven by wind or solar?

US researchers  are developing nitrogen-doped carbon nanotube that can efficiently reduce carbon dioxide electrochemically, thus driving the waste product of fossil fuel combustion back up the energy chain and giving the carbon another lease of life to drive the engines of both vehicles and industry on days when the wind dies down and the sun is behind the clouds. The reduction of carbon dioxide to carbon monoxide allows the more energy-rich methane or methanol to be generated, which can then be further processed to other forms or can itself be used as is. [Sharma et al, Angew Chem, 2015; DOI: 10.1002/anie.201506062]

Pranav Sharma and Jingjie Wu of Rice University and their colleagues suggest that their catalyst with the potential to convert carbon dioxide is both efficient and inexpensive, based as it is on nitrogen-doped carbon nanotubes, thus avoiding rare and costly heavy metals. Moreover, the material is also more stable than previously reported metal-based catalysts used for this electrochemical reaction.

The team has used transmission electron microscopy (TEM) and other techniques to characterize the microstructure of their nitrogen-doped carbon nanotube array and to help them understand the role of defects and defect density on efficacy, efficiency and selectivity. Importantly, they reveal the pyridinic structure, as opposed to the graphitic structure, to be the most effective as an electrocatalyst, better still than precious metal catalysts. Density functional theory (DFT) calculations lend computational support to the team's experimental results in terms of the mechanism of catalysis.

 “We are working in conjunction with other institutions, and they are developing the other side, the water side, using photovoltaics to split water, and eventually we want to couple those two reactions together,” team member Xiao-Dong Zhou of the University of South Carolina explains. “So one side will be water splitting, generating protons from the anode that travel through the electrolyte to reach the cathode side and then react with carbon dioxide and with incoming electrons to convert carbon dioxide to fuels. Carbon monoxide is one kind of fuel you can produce, and methane and methanol are other fuels that can be produced. There’s still a long way to go, but it’s a start.”

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".