Efforts to combat climate change may find a surprising ally in carbon itself. A recent review published in the journal Science Advances highlights the potential for transforming carbon emissions into innovative catalysts. This shift could significantly impact the energy and chemical industries by paving the way for effective decarbonisation while mitigating reliance on critical minerals often associated with high costs and geopolitical risks.
Researchers from the ARC Centre of Excellence for Carbon Science and Innovation (COECSI) have conducted extensive studies on converting carbon dioxide (CO2) into non-volatile carbon products. While this approach alone may not fully offset carbon emissions at a large scale, it presents a promising avenue for innovation. The team argues for a more practical method: converting CO2 into high-value catalysts that can be utilized to produce fuels and chemicals.
Professor Liming Dai, Director of COECSI and corresponding author of the review, states, “Achieving this will advance climate goals, material innovation and contribute to a circular carbon economy.”
The Role of Carbon as a Catalyst
Carbon’s unique properties make it a strong candidate for use in catalysis. It is stable and conductive even in the demanding environments of electrocatalytic cells, though it remains catalytically inactive in its natural state. Professor Dai’s team has made significant strides in engineering carbon into effective catalysts for energy conversion.
By employing techniques such as heteroatom doping and defect engineering, researchers can create catalytic active centres (CACs) within carbon. This process alters the electron symmetry in carbon’s aromatic rings, enhancing its catalytic capabilities. For example, researchers have developed bifunctional porous graphene catalysts co-doped with nitrogen and phosphorus for zinc-air batteries, achieving energy capacities nearing theoretical limits.
The structure of the carbon substrate also plays a critical role in the efficacy of the CACs. A novel three-dimensional carbon nanotube-graphene pillar configuration has demonstrated marked improvements in both ion and electron transfer, as well as an increased number of accessible CACs.
Innovative Methods for CO2 Conversion
Various methods have been explored to convert CO2 into an array of carbon-based nanostructures, including graphene and carbon nanoparticles. One straightforward approach involved thermally reducing CO2 with magnesium, resulting in hollow mesoporous carbon cubes. These cubes show promise as alternatives to traditional platinum-carbon catalysts in fuel cells.
Additionally, a COECSI team has successfully converted CO2 into edge-doped graphene electrocatalysts through a co-ball milling process with dry ice. While traditional electrocatalytic conversion of CO2 is energy-intensive, a recent breakthrough using a cerium-containing liquid metal electrocatalytic converter has enabled the conversion of CO2 into carbonaceous products at ambient temperatures.
Despite the challenges associated with each method, the review’s authors note the significant techno-economic potential for synthesizing carbon materials from CO2. According to Professor Zhenhai Xia, “The market price for carbon nanotubes (CNTs) currently exceeds $100,000 per ton, highlighting economically attractive methods for converting CO2 into carbon catalysts.”
The transition to a circular economy means previously discarded carbon could now hold market value, reducing the environmental penalties associated with carbon waste.
Challenges Ahead for Scalability and Efficiency
While the research holds promise, challenges remain regarding the efficiency and scalability of these technologies. Professor Shizhang Qiao emphasizes the need to improve catalytic efficiency and yields. One potential solution may lie in the development of metal-free and metal-doped carbon catalysts.
For example, a metal-free carbon catalyst utilizing nitrogen-doped graphene quantum dots has shown success in converting CO2 into higher-order hydrocarbons such as ethylene and ethanol. These carbon catalysts are also being explored for their ability to convert nitrogen waste into ammonia and urea, vital components for fertilizers and pharmaceuticals.
Integrating CO2 capture, conversion, and material synthesis into a cohesive and cost-effective system is technically complex. Nevertheless, CO2-derived carbon materials present distinct advantages over those sourced from fossil fuels, offering a sustainable and renewable carbon supply while potentially lowering production costs.
With ongoing research and innovation, the vision of utilizing carbon emissions as a resource rather than a liability could become a reality, advancing both environmental sustainability and economic growth in the process.
