This post is part of a series examining the connections between nanotechnology and the top 10 trends facing the world, as described in the Outlook on the Global Agenda 2015. All authors are members of the Global Agenda Council on Nanotechnology.
The late Richard Smalley, often considered to be one of the fathers of nanotechnology following his Nobel Prize-winning work on fullerenes, had a keen interest in energy. In many presentations he would ask the audience to call out what they considered to be the most pressing issues facing humanity. The answers were often similar to those identified in the World Economic Forum’s Global Risks Report, including persistent worries such as disease, clean water, poverty, inequality and access to resources. Smalley would then rearrange the list to put energy at the top and proceed to explain how a happy, healthy world of 9 billion could be achieved if we could only fix the problem of providing cheap and abundant clean energy.
Back in the early 2000s, most of the imagined solutions to the energy challenge involved novel materials such as carbon nanotubes for lossless electricity transmission, or hydrogen storage to enable fuel-cell vehicles. While novel materials like nanotubes never quite lived up to their promise, 15 years later many nanotechnologies, including the latest carbon-based material graphene, are now promising to deliver huge leaps in the way that we generate, store and use energy.
But these advances are not enabled by nanotechnologies in isolation. Many of the technologies identified in the Forum’s top 10 emerging technologies list for the past three years, from gene editing to additive manufacturing, also play a role, supporting our ability to understand the nanoscale processes in nature, generating new insights into how to move beyond conventional solar cells and copy some of nature’s tricks, such as photosynthesis.
The problem is that conventional silicon-based solar cells, while effective, have many drawbacks. They are brittle, which means that they need to be fixed to a rigid support, and they only harvest a small amount of the spectrum of light generated by the sun. For instance, silicon is transparent to infrared light, which means a lot of potential energy available is not harvested.
Researchers at the University of California, Riverside, are helping to solve this by working with hybrid material combining inorganic semiconductor nanoparticles with organic compounds. These first capture two infrared photons that would normally pass right through a solar cell without being converted to electricity, then add their energies together to make one higher energy photon.
An alternative approach is the use of quantum dots. These are nanoscale particles where the response to different wavelengths can be tuned by altering their sizes. Because of their unique optical properties, they are finding increasing uses in lighting and televisions, but these properties are also useful in solar cells. While the efficiency of quantum-dot solar cells reported in recent studies is increasing to as high as 9%, the real breakthrough is that the new devices can be produced at room temperature and in an atmosphere, rather than an expensive and hard-to-maintain vacuum. Perhaps the most exciting aspect of quantum-dot solar cells, though, is that the quantum dots can be dispersed in other materials, leading to “spray on” low-cost and large-area solar cells that can be applied to buildings or vehicles.
A leaf out of nature’s book
But the big prize in advanced photovoltaics will come with achieving artificial photosynthesis. The aim is to enable the production of useful chemicals and fuels directly from sunlight and carbon dioxide, just as plants do. By combining nanotechnology and biology, researchers are mimicking the processes that occur in the leaf of a plant to produce fuels such as butanol and biodegradable plastics. Once combined with synthetic biology to precisely engineer the bacteria, the possibilities are endless.
Generating energy is only half the solution, though. It also has to be stored for later use. This is an addressable issue for energy utilities, who balance peaks and troughs in demand by using techniques such as pumping water uphill into hydro-electric dams. But such large-scale engineering solutions are not an option for off-grid communities in much of the developing world. Local energy use requires a cheap and efficient way of storing energy, as do electric vehicles and smartphones.
Nanomaterials, and graphene in particular, have been attracting significant interest as potential game-changers for energy storage. One driver for this is the high surface area of many nanomaterials, which increases the ability to store charge within a given volume. Graphene – which is formed from layers of carbon a single atom thick – has a tremendous surface area for a given amount of material, and has created a lot of excitement about graphene-based supercapacitors and anodes for lithium ion batteries.
One of the biggest problems with the lithium ion batteries is the amount of charge that can be stored in the conventional graphite-based anodes they use. Lithium is added to the graphite when the battery is charging and removed as it discharges, but the low capacity of graphite means that the anode is limited in the amount of energy it can store. Researchers have been looking at silicon anodes that promise 10 times better capacity for the best part of decade, but the constant stresses on the material results in a short lifetime. One way of addressing this issue has been to place the silicon in cage of fullerenes, nanotubes or nanowires. Companies such as XG Sciences and California Lithium Battery are developing graphene-coated silicon, or “silicon-graphene nano-composite anode material”.
Taking a more bio-inspired approach, the Israeli company StoreDot is combining nanotechnology and biology to create nanoscale peptide crystals to produce a battery that will charge in less than a minute, while researchers in Singapore have recently developed a nanotube-based battery that could last more than 10 times as long as normal ion batteries and can also charge in minutes.
In the meantime, while we wait for current nanotechnology research to bear fruit, the biggest contribution that nanotechnology can make today is simply to reduce the amount of energy required to perform common tasks, such as heating and cooling.
The UK company Xefro, for instance, is making use of graphene to create a smart home-heating system which promises savings of up to 70%. The heaters make use of the high surface area of what is effectively a two-dimensional material to create an efficient heating material which is then applied as an ink. The ink can be printed on a variety of materials and in just about any shape, including water heaters. In a two-dimensional material, energy isn’t wasted in heating up the heater, so the heat can be turned on and off quickly. This both reduces energy use and makes the system ideal for use with smart thermostats.
Meanwhile, another UK start-up called Inclusive Designs is addressing the problem of keeping things cool by combining nanomaterials and fractals with 3D printing. The company prints 3D fractal structures designed to absorb infrared (heat) and then removes the heat by making use of the high thermal conductivity of graphene, creating a cooling system with no liquids or moving parts.
Since Richard Smalley’s untimely death in 2005, the energy situation has improved, with an increasing number of countries now generating the majority of their power from renewable sources; electric vehicles are now a common sight. But cheap, efficient renewable-energy production – together with its storage and transmission – remains a challenge. The combination of nanotechnology, with a wide range of other emerging and transformative technologies, promises to make Smalley’s dream of a world of abundant, cheap, clean energy a reality over the coming decade.
Author: Tim Harper, CEO G2O Water International and co-founder of Xefro
Image: Solar panels are seen in the Palm Springs area, California April 13, 2015. REUTERS/Lucy Nicholson