A study from researchers in the UK and New Zealand has revealed an ambient-energy-driven membrane that could advance carbon dioxide (CO2) capture technology. Published in Nature Energy on Friday, this breakthrough could reshape the future of direct air capture, crucial in combating climate change.
CO2 is the main greenhouse gas, with about 40 billion tonnes released annually. Its low air concentration—around 0.04%—makes separation and capture challenging. Traditional methods need substantial energy inputs, like heat or pressure, to overcome these hurdles. The new membrane technology developed by an international team of scientists offers a promising alternative by using natural humidity differences.
Dr. Greg Mutch from the Royal Academy of Engineering highlights the significance of this advancement: “Direct air capture will be crucial for the future energy system. In our work, we demonstrate the first synthetic membrane to capture carbon dioxide from the air and increase its concentration without traditional energy input like heat or pressure. A helpful analogy might be a water wheel on a flour mill. Whereas a mill uses the downhill water transport to drive milling, we use it to pump carbon dioxide out of the air.”
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The membrane uses humidity gradients to drive CO2 through the material. When one side has higher humidity, the device pumps CO2 from the air into that stream. This approach eliminates the need for external energy sources for CO2 capture.
The research team, collaborating with institutions like Victoria University of Wellington, Imperial College London, Oxford University, Strathclyde University, and UCL, faced two primary challenges: overcoming slow reaction kinetics due to low CO2 concentration and addressing high energy demands of concentration processes.
Prof. Ian Metcalfe, Royal Academy of Engineering Chair in Emerging Technologies at Newcastle University, explains, “Dilute separation processes are the most challenging separations to perform for two key reasons. First, due to the low concentration, the kinetics (speed) of chemical reactions targeting the removal of the dilute component are very slow. Second, concentrating the dilute component requires a lot of energy.”
The researchers used ambient energy from humidity differences to tackle these challenges. The membrane’s structure was characterized using X-ray micro-computed tomography, in collaboration with UCL and the University of Oxford. This analysis allowed for performance comparisons with existing membranes.
Density-functional-theory calculations modeled the membrane’s behavior at the molecular level. The calculations identified specific ‘carriers’ within the membrane that uniquely transport both CO2 and water. This dual transport mechanism allows the membrane to use the energy from humidity differences to pump CO2 from lower to higher concentrations.
Dr. Evangelos Papaioannou, Senior Lecturer in the School of Engineering at Newcastle University, further elaborates on the membrane’s operation: “In a departure from typical membrane operation, and as described in the research paper, the team tested a new carbon dioxide-permeable membrane with a variety of humidity differences applied across it. When the humidity was higher on the output side of the membrane, the membrane spontaneously pumped carbon dioxide into that output stream.”
The importance of this development extends beyond just capturing CO2. Direct air capture is anticipated to play a critical role in achieving global climate targets, including the 1.5 °C goal set by the Paris Agreement. As the world moves towards a circular economy, such technologies could also enable CO2 to be used as a feedstock for producing hydrocarbon products, potentially creating a carbon-neutral or even carbon-negative cycle.
Prof. Metcalfe underscores the collaborative nature of this achievement: “This was a real team effort over several years. We are very grateful for the contributions from our collaborators, and for the support from the Royal Academy of Engineering and the Engineering & Physical Sciences Research Council.”
The membrane’s ability to bypass traditional energy inputs represents a significant step forward in direct air capture technology. By making CO2 removal more energy-efficient and feasible, this breakthrough could prove instrumental in mitigating climate change and advancing towards a sustainable future
