21 Sep 2015
The scientists are using cellulose, an organic compound found in plants, bacteria, algae and trees, to build more efficient and longer-lasting energy storage devices or capacitors. This development paves the way toward the production of lightweight, flexible, and high-power electronics, such as wearable devices, portable power supplies and hybrid and electric vehicles.
“Ultimately the goal of this research is to find ways to power current and future technology with efficiency and in a sustainable way,” says Cranston, whose joint research was recently published in Advanced Materials. “This means anticipating future technology needs and relying on materials that are more environmentally friendly and not based on depleting resources.
Cellulose offers the advantages of high strength and flexibility for many advanced applications; of particular interest are nanocellulose-based materials. The work by Cranston, an assistant chemical engineering professor, and Zhitomirsky, a materials science and engineering professor, demonstrates an improved three-dimensional energy storage device constructed by trapping functional nanoparticles within the walls of a nanocellulose foam.
The foam is made in a simplified and fast one-step process. The type of nanocellulose used is called cellulose nanocrystals and looks like uncooked long-grain rice but with nanometer-dimensions. In these new devices, the ‘rice grains’ have been glued together at random points forming a mesh-like structure with lots of open space, hence the extremely lightweight nature of the material. This can be used to produce more sustainable capacitor devices with higher power density and faster charging abilities compared to rechargeable batteries.
Lightweight and high-power density capacitors are of particular interest for the development of hybrid and electric vehicles. The fast-charging devices allow for significant energy saving, because they can accumulate energy during braking and release it during acceleration.
“I believe that the best results can be obtained when researchers combine their expertise,” Zhitomirsky says. “Emily is an amazing research partner. I have been deeply impressed by her enthusiasm, remarkable ability to organize team work and generate new ideas.”
Explore further: Engineers craft new material for high-performing ‘supercapacitors’
More information: Cellulose Nanocrystal Aerogels as Universal 3D Lightweight Substrates for Supercapacitor Materials, DOI: 10.1002/adma.201502284
By Michael Berger – Nanowerk. During 2002 and 2003, Nobel laureate Richard E. Smalley developed a list of the Top Ten Problems Facing Humanity over the next 50 years. The Richard E. Smalley Institute for Nanoscale Science and Technology at Rice University (which in May 2015 has been merged with the Rice Quantum Institute into a new entity: the Smalley-Curl Institute) has identified 5 of these problems as society’s Grand Challenges – and energy tops the list.
Since then, researchers around the world have demonstrated the potential for nanotechnology to be a key technology on the path to a sustainable energy future. Against the double-whammy backdrop of an energy challenge – the world’s appetite for energy keeps growing1 – plus a climate challenge – climate goals (2°C target) require substantial reduction in greenhouse gases (see: Climate change: Action, trends and implications for business. pdf) – it is the role of innovative energy technologies to provide socially acceptable solutions through energy savings; efficiency gains; and decarbonization.
Why is nanotechnology relevant here? Many effects important for energy happen at the nanoscale: In solar cells, for instance, photons can free electrons from a material, which can then flow as an electric current; the chemical reactions inside a battery or fuel cell release electrons which then move through an external circuit; or the role of catalysts in a plethora of chemical reactions. These are just a few examples where nanoscale engineering can significantly improve the efficiency of the underlying processes.
The working principle of a solar cell. (Image: University of Massachusetts Amherst)
Nanotechnologies are not tied exclusively to renewable energy technologies. While researchers are exploring ways in which nanotechnology could help us to develop energy sources, they also develop techniques to access and use fossil fuels much more efficiently. Corrosion resistant nanocoatings, nanostructured catalysts, and nanomembranes have been used in the extraction and processing of fossil fuels and in nuclear power. There is no silver bullet – nanotechnology applications for energy are extremely varied, reflecting the complexity of the energy sector, with a number of different markets along its value chain, including energy generation, transformation, distribution, storage, and usage. Nanotechnology has the potential to have a positive impact on all of these – albeit with varying effects.
Nanomaterials could lead to energy savings through weight reduction or through optimized function:
- In the future, novel, nano-technologically optimized materials, for example plastics or metals with carbon nanotubes (CNTs), will make airplanes and vehicles lighter and therefore help reduce fuel consumption;
- Novel lighting materials (OLED: organic light-emitting diodes) with nanoscale layers of plastic and organic pigments are being developed; their conversion rate from energy to light can apparently reach 50 % (compared with traditional light bulbs = 5%);
- Nanoscale carbon black has been added to modern automobile tires for some time now to reinforce the material and reduce rolling resistance, which leads to fuel savings of up to 10%;
- Self-cleaning or “easy-to-clean”-coatings, for example on glass, can help save energy and water in facility cleaning because such surfaces are easier to clean or need not be cleaned so often;
- Nanotribological wear protection products as fuel or motor oil additives could reduce fuel consumption of vehicles and extend engine life;
- Nanoparticles as flow agents allow plastics to be melted and cast at lower temperatures;
- Nanoporous insulating materials in the construction business can help reduce the energy needed to heat and cool buildings.
Nanomaterials could improve energy generation and energy efficiencies:
- Various nanomaterials can improve the efficiency of photovoltaic facilities;
- Dye solar cells (‘Grätzel cells’) with nanoscale semiconductor materials mimic natural photosynthesis in green plants;
- Plastics with carbon nanotubes as coatings on the rotor blades of wind turbines make these lighter and increase the energy yield;
- Nano optimized lithium-ion batteries have an improved storage capacity as well as an increased lifespan and find use in electric vehicles for example;
- Fuel cells with nanoscale ceramic materials for energy production require less energy and resources during manufacturing;
- The effectiveness of catalytic converters in vehicles can be increased by applying catalytically active precious metals in the nanoscale size range.
We have compiled an overview of Nanotechnology in Energy that shows how nanotechnology innovations could impact each part of the value-added chain in the energy sector – energy sources; energy conversion; energy distribution; energy storage; and energy usage.
The European GENNESYS project identified a range of nanomaterial application and requirements for future energy applications3. (click on image to enlarge) In the short term, energy nanotechnology is likely to have the greatest impact in the areas of efficiency of photovoltaics (among renewables, solar has by far the biggest global energy potential) and energy storage where it can help overcome current performance barriers and substantially improve the collection and conversion of solar energy. Nanotechnology for Solar Energy Collection and Conversion is one of the five Signature Initiatives funded by the U.S. National Nanotechnology Initiative. The goals are to enhance understanding of conversion and storage phenomena at the nanoscale, improve nanoscale characterization of electronic properties, and help enable economical nanomanufacturing of robust devices. The initiative has three major thrust areas:
- – improve photovoltaic solar electricity generation;
- – improve solar thermal energy generation and conversion; and
- – improve solar-to-fuel conversions.
The thermodynamic limit of 80% efficiency is well beyond the capabilities of current photovoltaic technologies, whose laboratory performance currently approaches only 43% 2. Nanomaterials even make it possible to raise light yield of traditional crystalline silicon solar cells. By using cheaper, nanoscale materials than the current dominant technology (single-crystal silicon, which uses a large amount of fossil fuels for production), the cost of solar cells could be brought down. Numerous research labs are working on nanotechnology-enabled batteries to increase their efficiencies for electric vehicles, home, or grid storage systems. Improving the efficiency/storage capacity of batteries and supercapacitors with nanomaterials will have a substantial economical impact.
Graphene has already been demonstrated to have many promising applications in energy-related areas. (read more: “Graphene materials for energy storage applications“). Nanotechnology also has the potential to deliver the next generation lithium-ion batteries with improved performance, durability and safety at an acceptable cost (“The promise of nanotechnology for the next generation of lithium-ion batteries“).
A major push on basic research for energy technologies is coming from the U.S. Department of Energy, which since 2009 has invested nearly $800m as part of the Energy Frontier Research Center (EFRC) program. For example, the Joint Center for Artificial Photosynthesis (JCAP) has developed a nanowire-based design that incorporates two semiconductors to enhance absorption of light; or the Nanostructures for Electrical Energy Storage (NEES) EFRC Center has demonstrated that precise nanostructures can be constructed to test the limits of 3-D nanobatteries by designing billions of tiny batteries inside nanopores.
Against the double-whammy backdrop of an energy challenge and a climate challenge it is the role of innovative energy technologies to provide socially acceptable solutions through energy savings; efficiency gains; and decarbonization.
So where does that leave ‘nanotechnology’? It may not be the silver bullet, but nanomaterials and nanoscale applications will have an important role to play.
Notes 1) Energy demand grows by 37% to 2040 on planned policies, an average rate of growth of 1.1%. World electricity demand increases by almost 80% over the period 2012-2040. 1.6bn people still without access to electricity, thereof 950 million in sub-Saharan Africa. (Source: IEA World Energy Outlook 2014) 2) Source: NSI Solar White Paper (pdf) 3) Source: GENNESYS White paper