How can nanotechnology be used to help limit climate change?

For decades, scientists have been warning about the potentially damaging effects of climate change, which is principally caused by the emission of greenhouse gases such as carbon dioxide into the atmosphere. Yet, in all that time, global emissions have continued their inexorable rise. It doesn’t take a climate scientist or policy expert to tell you that the first thing to do when you’re in a hole is to stop digging – and the difficulty in even slowing the climb of carbon dioxide concentrations shows the scale of the challenge ahead of us.

It is tempting for politicians and individuals to rely on technological innovation to rescue the climate situation without sacrificing economic growth – and it will have to be a part of the solution. At the same time, mainstream climate policy is already based on optimistic projections for how carbon dioxide removal technologies and renewable energy will develop in the future.

Could nanotechnology prove to be a gamechanger? After all, the industry has been projected to be worth $75bn+ by 2020. If you listen to the most optimistic futurists on this topic, they’ve been utterly seduced by Eric Drexler’s dream of nanorobots that can manipulate matter on the fundamental level – breaking apart and making molecular bonds at will. A new era of molecular manufacturing is ushered in, which leads to abundance for everyone. One can imagine that, if such nanobots did exist, they would be game-changing devices. If “utility fog” – nano-bots that can shape themselves into different devices on demand – were to be feasible, and become mainstream, then carbon emissions associated with manufacturing could be severely reduced. And if molecular manipulation in such a reliable way was possible, then one can also imagine artificial photosynthesis taking off – carbon dioxide emissions, and even individual molecules, pulled apart and converted into hydrocarbon fuels, with the chemistry powered by energy from the sun. (Of course, by then, climate hawks would hope that we would have stopped using fossil fuels in most applications.) The use of nanocatalysis as a means of transforming the industrial production of carbon dioxide has already been the subject of a great deal of scientific research – and while many promising candidates have been identified, scaling any of them up has its difficulties.

Stronger nanomaterials such as graphene may well have a role. Graphene itself, along with other 2D materials, have been implicated for use in battery cathodes – which might improve the energy storage capacities of lithium-ion batteries. And if these materials can be used in construction, or to bolster the strength of existing materials, it may well be possible to get by with less resource extraction, which can reduce the carbon footprint of industry.

Leaving these techno-utopias aside, how is nanotechnology helping to fight climate change in the nearer term? One answer lies in solar panels. Currently, solar panels are limited in efficiency by the Shockley-Queisser limit. The bandgap in the semiconductor silicon is not precisely aligned with the peak wavelength of the Sun’s incoming rays – although, by fortunate providence, it’s pretty close. Due to the way that light interacts with matter, if a photon arrives at the solar cell with insufficient energy to excite an electron across the bandgap, its energy is lost; excess energy, above the bandgap, is dissipated as heat in the solar panel.|Smallcreative

However, solar panel efficiency can be boosted yet further by replacing silicon with “quantum dots.” These are semiconductor crystals, built on the nanoscale, that have specific optical properties dependent on their size – allowing for a “tuneable bandgap” to be constructed. This means that a greater amount of energy from the Sun’s rays can be harnessed. It may be possible to combine this with ‘singlet fission’, a process which effectively “splits” energetic photons into two less energetic counterparts, to enhance the absorption of energy from the solar spectrum. And quantum dots used for LEDs allow for a reduction in power use, an extension in battery life, and a greater range of colours that can be produced by the system. Given that LEDs are more efficient than traditional lightbulbs, this is all good for the climate.

A system based on renewable energy, which is variable in nature, may rely on energy storage to make up for that intermittency. Some studies have indicated that if you have a system based on 100% renewable electricity, you may need 8-16 weeks of electricity consumption ready as storage as a backstop to guard against intermittent supply. Given that the world’s largest battery park currently in operation stores 129MWh – and world electricity consumption was around 21,000TWh in 2016 – if this is to be a reality, we would need vast amounts of energy storage and much better batteries. Nanotechnology can help by providing unprecedented levels of energy storage density; specially engineered materials can result in more compact batteries, which can reduce the scale of the energy storage plants required. Moving beyond the lithium-ion batteries that we use today could well require nanotechnology.

As a backstop technology for dealing with climate change, negative emissions technologies like direct air capture of carbon dioxide are receiving ever more attention. Many of these technologies rely on a “sorbent” material which absorbs the carbon dioxide that passes over it, and can then be “scrubbed” clean of the carbon dioxide with a simple application of water. The classic example is Klaus Lackner’s “artificial trees”. Such materials need to be compact and cheap to manufacture if direct air capture is going to be feasible at scale, and the chemical properties of the material are crucial to the amount of energy that negative emissions will require. Nanotechnology may allow for ever-more efficient sorbents to be designed for this purpose.

There are also ways that nanotechnology may be able to help that are slightly more indirect. A great deal of interest recently has focused around topological insulators, which could be used to create nanowires. A topological insulator is a substance which has virtually zero resistance on a small “surface layer” – effectively like a superconductor; the transmission of electrons is not impeded. With no resistance, the loss due to waste heat in circuitry can be dramatically reduced. This nanocircuitry may enable Moore’s Law to continue for a slightly longer time – and consequently, result in faster high-performance computers. This, in turn, will allow climate modellers to run higher-resolution models for longer times, and gain a deeper understanding of the processes that govern the climate. If we can understand the impacts of climate change using these models, then we will be able to help mitigate the effects of climate change – increasing preparedness in regions that might be vulnerable to extreme weather events like hurricanes, sea level rise, or droughts, for example.

Technology – and nanotechnology as a subset of that – cannot save us from climate change alone. We need to combine a strong political will to act with a great deal of effort and investment. But it may well prove to be a vital tool in our arsenal.

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