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The new fuel cells can help store electricity generated from renewable energy sources, such as wind farms, by converting it into a chemical fuel for long-term storage, and then transforming it. in electricity as needed.
iStock.com/Ron_Thomas
By Robert F. Service
If we want to try to switch to renewable energies, we need one crucial thing: technologies that convert electricity produced by wind and sun into a chemical fuel for storage, and vice versa. The commercial devices that are part of it exist, but most of them are expensive and represent only half of the equation. Now researchers have created lab gadgets that do both tasks. If larger versions work as well, they would help make it possible – or at least more affordable – to manage the world from renewable energies.
The market for these technologies has increased in parallel with renewable energies: in 2007, solar and wind energy provided only 0.8% of total energy in the United States; in 2017, this number was 8%, according to the US Energy Information Administration. But the demand for electricity often does not match that of solar and wind. For example, under the California sun, solar panels regularly produce more energy than needed in the middle of the day, but not at night, after the return of most workers and students.
Some utilities are starting to install huge batteries in hopes of storing excess energy and fueling their balance sheets. However, batteries are expensive and only store enough power to back up the network for a few hours at most. Another option is to store energy by converting it to hydrogen fuel. To do this, appliances called electrolysers use electricity – ideally solar and wind – to split water into oxygen and hydrogen, a carbon-free fuel. A second set of devices called fuel cells can then reconvert hydrogen into electricity to power cars, trucks and buses, or to power the grid.
But commercial electrolysers and fuel cells use different catalysts to speed up both reactions, which means that one device can not do both tasks at once. To solve this problem, researchers have experimented with a new type of fuel cell, called the Proton Conductively Conductive Conductive Fuel Cell (PCFC), which converts fuel into fuel or reconverts it into electricity using a single set of catalysts.
The PCFCs consist of two electrodes separated by a membrane allowing the protons to pass through. On the first electrode, called the air electrode, steam and electricity are introduced into a ceramic catalyst, which separates the water molecules from the vapor into positively charged hydrogen ions (protons), electrons and oxygen molecules. The electrons pass through an external wire to the second electrode, the fuel electrode, where they encounter protons crossing the membrane. There, a nickel-based catalyst assembles them to produce hydrogen (H2). In previous PCFCs, nickel catalysts gave good results, but ceramic catalysts were inefficient and used less than 70% of electricity to split water molecules. Much of the energy has been lost as heat.
Two research teams made decisive progress to improve this efficiency. Both focused on the improvements to be made to the air electrode because the nickel – based fuel electrode did a good job. In January, researchers led by chemist Sossina Haile of Northwestern University in Evanston, Illinois, reported Energy and environmental science that they have developed a ceramic alloy fuel electrode containing six elements, which used 76% of its electricity to split water molecules. And in today's issue of Nature EnergyRyan O'Hayre, a chemist at the Colorado School of Mines in Golden, reports that his team has done better. The five-element ceramic alloy electrode uses up to 98% of the energy supplied to the water division.
When both teams perform their settings in reverse, the fuel electrode divides H2 molecules in protons and electrons. The electrons pass through an external wire to the air electrode, thus providing electricity to the devices. When they reach the electrode, they combine with oxygen from the air and protons that have returned to the membrane to produce water.
O'Hayre's latest work is "impressive," says Haile. "The electricity you put in H2 and do not heat your system. They did a great job with that. Nevertheless, she warns, her new device and the O'Hayre lab are small demonstrations in the lab. For technology to have a societal impact, researchers will need to develop button-sized devices, a process that typically reduces performance. If engineers can make it happen, the cost of storing renewable energy could drop precipitously, helping utilities get rid of their fossil fuel dependency.
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