Electrified Plants from Stanford; Grid-scale Batteries from MIT
In an electrifying first, Stanford scientists have plugged into algae cells to harness a tiny electric current that could be a first step toward generating “high efficiency” bioelectricity that doesn’t give off CO2 as a by product, while at MIT researchers have come up with a battery able to match the output of those used in cellphones from 1/20th of their electrode area. Its inventors hope it will provide much-needed storage capacity for electricity grids.
Released by Stanford University (13 April 2010):
Stanford researchers find electrical current stemming from plants
In an electrifying first, Stanford scientists have plugged in to algae cells and harnessed a tiny electric current. They found it at the very source of energy production – photosynthesis, a plant’s method of converting sunlight to chemical energy. It may be a first step toward generating “high efficiency” bioelectricity that doesn’t give off carbon dioxide as a byproduct, the researchers say.
“We believe we are the first to extract electrons out of living plant cells,” said WonHyoung Ryu, the lead author of the paper published in the March issue of Nano Letters. Ryu conducted the experiments while he was a research associate for mechanical engineering professor Fritz Prinz.
The Stanford research team developed a unique, ultra-sharp nanoelectrode made of gold, specially designed for probing inside cells. They gently pushed it through the algal cell membranes, which sealed around it, and the cell stayed alive. From the photosynthesizing cells, the electrode collected electrons that had been energized by light and the researchers generated a tiny electric current.
“We’re still in the scientific stages of the research,” said Ryu. “We were dealing with single cells to prove we can harvest the electrons.”
Plants use photosynthesis to convert light energy to chemical energy, which is stored in the bonds of sugars they use for food. The process takes place in chloroplasts, the cellular powerhouses that make sugars and give leaves and algae their green color. In the chloroplasts, water is split into oxygen, protons and electrons. Sunlight penetrates the chloroplast and zaps the electrons to a high energy level, and a protein promptly grabs them. The electrons are passed down a series of proteins, which successively capture more and more of the electrons’ energy to synthesize sugars until all the electron’s energy is spent.
In this experiment, the researchers intercepted the electrons just after they had been excited by light and were at their highest energy levels. They placed the gold electrodes in the chloroplasts of algae cells, and siphoned off the electrons to generate the tiny electrical current.
The result, the researchers say, is electricity production that doesn’t release carbon into the atmosphere. The only byproducts of photosynthesis are protons and oxygen.
“This is potentially one of the cleanest energy sources for energy generation,” Ryu said. “But the question is, is it economically feasible?”
Ryu said they were able to draw from each cell just one picoampere, an amount of electricity so tiny that they would need a trillion cells photosynthesizing for one hour just to equal the amount of energy stored in a AA battery. In addition, the cells die after an hour. Ryu said tiny leaks in the membrane around the electrode could be killing the cells, or they may be dying because they’re losing out on energy they would normally use for their own life processes. One of the next steps would be to tweak the design of the electrode to extend the life of the cell, Ryu said.
Harvesting electrons this way would be more efficient than burning biofuels, as most plants that are burned for fuel ultimately store only about 3 to 6 percent of available solar energy, Ryu said. His process bypasses the need for combustion, which only harnesses a portion of a plant’s stored energy. Electron harvesting in this study was about 20 percent efficient. Ryu said it could theoretically reach 100 percent efficiency one day. (Photovoltaic solar cells are currently about 20-40-percent efficient.)
Possible next steps would be to use a plant with larger chloroplasts for a larger collecting area, and a bigger electrode that could capture more electrons. With a longer-lived plant and better collecting ability, they could scale up the process, Ryu said. Ryu is now a professor at Yonsei University in Seoul, South Korea.
Other authors of the paper are Prinz, the senior author,; Seoung-Jai Bai, Tibor Fabian, Rainer J. Fasching, Joong Sun Park, and Zubin Huang, all researchers in the Rapid Protoyping Laboratory at Stanford University; and Jeffrey Moseley and Arthur Grossman, both researchers in the Department of Plant Biology at the Carnegie Institution and Department of Biological Sciences.
By David C. Holzman in New Scientist (9 April 2010):
A BATTERY able to match the output of those used in cellphones from 1/20th of their electrode area may have you dreaming of more talk time.
But putting it in your pocket would be a bad idea – it’s full of molten metal. Instead, its inventors hope it will provide much-needed storage capacity for electricity grids.
Grid-scale batteries would boost efficiency by allowing solar energy to be used at night, for example, or excess power from a nuclear plant to be stored for later.
Engineers led by Donald Sadoway at the Massachusetts Institute of Technology were inspired by the way aluminium is smelted using electricity. They created a similar but reversible process that can either consume or release energy.
Their batteries are simply tanks filled with three separate layers of liquid at 700 °C that float on top of one another: the top one is molten magnesium, the bottom antimony and the one in between a salt containing magnesium antimonide, a dissolved compound of the two metals.
When the battery is being charged, magnesium antimonide in the middle layer breaks down into the pure elements and so the upper and lower layers deepen. Discharging the battery reverses the process and releases electrons to provide power. Once heated up to its operating temperature, the battery generates enough heat on its own to keep the liquids molten.
A small prototype provided up to 20 times as much current as a lithium-ion battery – the kind used in portable devices and electric cars – from the same area of electrode, says team member Luis Ortiz. The materials used are much cheaper than lithium, making scaling to up to grid scale feasible, he says.
“Cost-effective storage is the holy grail of the electricity grid,” says Matthew Nordan, a specialist in clean technology at venture-capital firm Venrock in Cambridge, Massachusetts, who has not invested in the technology.
The MIT team calculates that a battery the size of a shipping container could deliver a megawatt of electricity – enough to power 10,000 100-watt light bulbs – for several hours.
A battery the size of a shipping container could deliver a megawatt of electricity.