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article imageEssential Science: Creating carbon neutral fuels from waste

By Tim Sandle     Sep 23, 2019 in Science
A new study demonstrates how carbon-neutral re-use of carbon dioxide is emerging as an alternative to burying the greenhouse gas underground. This could lead to cleaner fuels for aircraft as well as greener plastics.
Scientists are working on an efficient means for converting carbon dioxide into sustainable liquid fuels. This includes fuels that can be used with the types of transportation that are likely to be difficult to electrify, such as airplanes, ships, and freight trains. This has come about as a collaboration between researchers based at Stanford University, U.S., and the Technical University of Denmark.
In addition, the new approach, based on the artificial electrochemical re-use of carbon dioxide, obviates the need to bury the greenhouse gas underground.
Australia is one of the world's worst per capita greenhouse gas polluters
Australia is one of the world's worst per capita greenhouse gas polluters
Paul Crock, AFP/File
Research process
To develop their method, the scientists took stock of how earlier devices succeeded and failed in carbon dioxide electrolysis. Building on earlier success stories was key to the current research. This showed, for example, how the efficiency of electrocatalysts can be maximized by offsetting the well-known mismatch of optimal conditions for electrocatalysts between the anode (normally alkaline) and the cathode (generally acidic).
Electrocatalysts
The surface of a nanostructured copper catalyst that converts CO2 into ethylene. (The Canadian Light...
The surface of a nanostructured copper catalyst that converts CO2 into ethylene. (The Canadian Light Source is a national research facility of the University of Saskatchewan).
© Canadian Light Source
Electrocatalysts are a specific form of catalysts that function at electrode surfaces or may be the electrode surface itself. This means, an electrocatalyst is like a catalyst but it involves some electrical current. The flow of electric charge is through a conductor. A key example is a fuel cell, where engineers can essentially burn hydrogen and oxygen and make electricity.
Research outcomes
The research demonstrates how electricity and an Earth-abundant catalyst can convert carbon dioxide into energy-rich carbon monoxide, in a way that is more efficient than is possible with any conventional method (using nickel-based catalysts). The new method relies on a catalyst called cerium oxide (an oxide of the rare-earth metal cerium), and it is the catalyst that drives the efficiency in that the catalyst is far more resistant to breaking down.
Carbon dioxide levels are increasing faster than at any time since the end of the dinosaurs.
Carbon dioxide levels are increasing faster than at any time since the end of the dinosaurs.
US - DOE
The role of the catalyst is with stripping oxygen from carbon dioxide to produce carbon monoxide gas. The produce carbon monoxide can then be converted into a range of liquid fuels. This includes a form of synthetic diesel and a type of jet fuel. Other products can also be produced, such as synthetic gas and plastics. Each of these is carbon-neutral.
Commenting on the research, lead scientist William Chueh (Stanford) said: “We showed we can use electricity to reduce carbon dioxide into carbon monoxide with 100 percent selectivity and without producing the undesired byproduct of solid carbon.”
The efficiency of the new method, which stands at over fifty percent, was assessed using X-ray photoelectron spectroscopy (a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand range).
Key advantages
An airplane flies over Detroit  Michigan
An airplane flies over Detroit, Michigan
The advantage of developing processes to manufacture sustainable liquid fuels is that this uses the existing gasoline and diesel infrastructure, such as engines, pipelines, and petrol stations. This type of fuel also provides an alternative path to the consideration of electrification of aircraft, which brings with it a big complication in terms of the high weight of batteries.
Research paper
The new research has been published in the journal Nature Energy. The research paper is titled “Selective high-temperature CO2 electrolysis enabled by oxidized carbon intermediates.”
Essential Science
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we looked at U.S. Food and Drug Administration (FDA) phase 1 trial shows that a new hydrogel designed to repair the heart is safe to inject in humans. This represents the first application of this type of medical technology.
The week before we considered new research into soft drinks, both sugar and ‘diet’ varieties and the impact on human health. There is data connecting soft drink consumption and the risk of early mortality.
More about Carbon neutral, Carbon dioxide, Carbon monoxide, green fuels, Fuel
 
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