New Developments February 2017

Surge in methane emissions threatens efforts to slow climate change

To save energy on heating and cooling, look at the shape of cities, not just their buildings  In North America and Europe, the greatest gains are likely to come from improving energy efficiency of buildings, especially retrofit of existing buildings. Efficiency gains matter relatively more in those regions that are already highly urban,” the researchers write. That’s because where cities are well established, their general form—compact or sprawling—is already set. Surprisingly, though, retrofitting buildings immediately doesn’t necessarily produce the greatest savings. Current technologies widely available for energy retrofits can save 20 to 40 percent of building energy use. But cutting-edge technologies could save 70 to 90 percent. Waiting five years or so for those new technologies to go mainstream and come down in cost could save more energy in the long term. And the picture is different in rapidly urbanizing regions like China, South Asia, Pacific Asia, the Middle East, North Africa, and Sub-Saharan Africa. There, changes in urban density will have the biggest effect on building energy use.

Technologies under development in NIMS: solar cell technology

In addition to batteries and fuel cells, another important technology helping society to reach 80% or more greenhouse gas emission reduction is photovoltaics or solar cells. At NIMS, a team lead by Kenjiro Miyano is researching the application of perovskites in solar cells to increase efficiency rates.

"Perovskite" is the name given to a structure whose elements can vary. Researchers are still discovering different combinations of elements that can function as perovskite structure and that have a high efficiency for solar power conversion. At NIMS one of the configurations under study is CH3NH3PbI3. You can learn more technical details about perovskites in this TEDX talk.

Perovskite CH3NH3PbI3 

(Image from https://www.nature.com/articles/ncomms8497)

Technologies under development in NIMS: fuel cells

A future technology enabling 80% or more greenhouse gas emission reduction is that of fuel cells. The difference between a fuel cell and a battery is that batteries have their energy stored inside, whereas fuel cells generate electricity from external fuel that can be refilled. At the moment hydrogen fuel cells are still under development, but their main advantage over current battery driven electric vehicles are their short refueling time. It takes several minutes to replace a hydrogen fuel tank, whereas charging batteries of electric vehicles regularly still takes several hours. Other advantages of fuel cells compared to batteries are their longer life time, their continued efficiency vs batteries whose efficiency decreases over time, and the reduced environmental impact in comparison with batteries that require more recycling processes. 

NIMS has two teams working on fuel cell developments. One is the  Polymer Electrolyte Fuel Cell Group led by Je-Deok Kim. This group is developing new conducting electrolyte membranes for alternate temperature fuel cells and new catalyst electrode materials. Another group is the Solid Oxide Fuel Cell Materials Design Group led by Toshiyuki Mori. Their goal is to increase fuel cell efficiency, by developing an optimum of materials on the active solid electrolyte/electrode interface and enable high speed ion diffusion pathways. 

The main difference in functioning of these two types of fuel cells is explained below: 

Technologies under development in NIMS: batteries

Our team has as task to help determine which future research directions and technology developments could be necessary and promising if we are to reach a society with 80% or more greenhouse gas emission reduction. To achieve this task, we coordinate with other GREEN team leaders and investigate current research projects at NIMS. Regarding energy storage, two types of batteries are being developed at NIMS, namely lithium air batteries, and all solid state batteries. 

You may have heard of rechargeable lithium-ion batteries that you find in mobile phones and laptop computers. They often rely on expensive metals like cobalt for the positive electrode and cheaper graphite for the negative electrode. A lithium air battery uses a simpler chemistry of lithium and oxygen and could be developed to be cheaper, and they have 5-15 times more energy per unit mass (also known as specific energy) than lithium ion batteries, which makes them highly sought out in the automobile industry. Under the leadership of Yoshimi Kubo, the lithium air battery team at NIMS is aiming to develop a battery with the highest energy density possible. 

Kazunori Takada leads the NIMS research team on all solid state batteries. They are developing batteries with higher energy densities than those obtainable with lithium ion batteries. Solid state batteries have a solid electrolyte and thus do not leak, and they can be made to be ultra thin, with finished products of only several mm thick. 

This short investigation in NIMS' technologies currently under development has taught me that batteries for mass storage of energy are nowhere near where we would like them to be. While there are billions of batteries in the world, they are often small, and have either little power stored in them (energy density) or a low capability of transferring energy (power density). For a sustainable energy supply, we need to develop more energy storage options with high energy and power density that allow capturing and transferring the intermittently produced energy from renewable sources such as solar, wind, and hydro.