Green Carbon Nanotubes: Reality or Good PR?
2023年8月16日 Dr Conor O'Brien
The market for nanomaterials, especially nanocarbons, continues to grow - reflecting the potential to unlock several next-generation technologies. Most notable for carbon nanotubes (CNTs) is incorporation in lithium-ion batteries, with production ramping up to fulfill demand, while major players are making acquisitions and expanding, leading to market consolidation. However, with environmentalism increasingly coming to the fore, the question remains; can CNTs be branded as a green material?
The new IDTechEx report, "Carbon Nanotubes 2023-2033: Market, Technology & Players", provides a comprehensive overview of the CNT market, including an assessment of the key application areas and major players, and also includes granular 10-year market forecasts for CNT demand (tpa) and market value (US$), segmented by application areas. IDTechEx project the market to grow in line with the booming lithium-ion battery market, given the utilization of CNTs as a conductive additive.
The three-pronged argument for the sustainable nature of CNTs. For further information on the carbon nanotube market, see the IDTechEx report "Carbon Nanotubes 2023-2033: Market, Technology, Players". Source: IDTechEx
When determining the green nature of a material, the first port of call is a comparison with alternative materials. As a (conductive) carbon additive, CNTs should be benchmarked against carbon black and the much-hyped two-dimensional material graphene. Carbon black typically has a higher CO2 footprint per kg than graphene and carbon nanotubes while also requiring higher loading in composites. Tires are a major use case for these materials, and a 2020 study by Michelin showed that nanoparticle release is lower for CNT-reinforced tires than alternative nanocarbons. "Top-down" production methods for graphene also have issues themselves - notably energy efficiency, high water requirements, and the utilization of harsh chemicals. In particular, the Hummer's method for making graphene faces significant challenges.
Traditional production processes for CNTs include laser ablation and arc discharge, while chemical vapor deposition (CVD) has become established as the dominant commercial process today. Modified catalytic-CVD methods include those with carbon monoxide as a feedstock. However, an emerging area for carbon nanotubes is the utilization of green or waste feedstocks. Electrolysis of captured CO2 in molten salts is the most common method to produce CNTs from green feedstocks; however, concerns exist regarding the quality of material produced in this process. Methane pyrolysis is the direct thermal decomposition of methane into hydrogen and solid carbon black (or nanocarbons, including CNTs). Several companies, such as CarbonMeta Technologies and Huntsman, are exploring the utilization of waste or by-product methane as feedstock, effectively locking the carbon emissions into a physical form factor rather than emitting greenhouse gases.
At the other end of the value chain, carbon nanotubes have the possibility to enable several green technologies. Application areas such as concrete, membranes, and even electronics all have green drivers and are exploring CNT-based solutions. However, the flagship market sector for CNTs in green technology is, without a doubt, lithium-ion batteries. As decarbonization drives the electrification of vehicles, the lithium-ion market is booming, with CNTs playing a key role as a conductive additive, primarily at the cathode, as part of a conductive slurry. Several academic studies have been published highlighting the role that single-walled carbon nanotubes (SWCNTs) can play in enabling next-generation batteries such as lithium-air or lithium-sulfur batteries, as well as lithium metal anodes.
So, can carbon nanotubes truly be considered to be a green material? Every aspect of the life cycle must be included in the discussion, from feedstock to production process and eventual utilization - while comparison with other conductive carbon additives is also required. The IDTechEx report provides coverage of each of these aspects relating to carbon nanotubes, including benchmarking of materials produced from various feedstocks and processes. Many companies are keen to emphasize the green credentials of their materials, but caution must be taken that performance, price point, or other metrics are comparable with traditional production methods.
For more details on the carbon nanotube market, please see the IDTechEx market report "Carbon Nanotubes 2023-2033: Market, Technology & Players".