Scientists at the Harvard School of Engineering and Applied Sciences (SEAS) have uncovered a way to make methane-powered laptops commercially viable.
Led by Shriram Ramanathan, the group has developed solid-oxide fuel cells (SOFCs), and it says it is optimistic about their use as a mobile technology. Most SOFCs are viewed as a potential eco-friendly alternative to fossil fuels, since they don’t leave behind much more waste than water. Reliability, temperature and cost have been the sticking points in using SOFCs for charging laptops, phones and next-generation cars and trucks, the group said.
An electric current is created when fuel cells convert chemical energy from hydrogen or a hydrocarbon fuel like methane. “Oxygen ions travel from the cathode through the electrolyte toward the anode, where they oxidize the fuel to produce a current of electrons back toward the cathode,” according to the SEAS group.
Now, Ramanathan’s group has developed stable and functional all-ceramic, thin-film SOFCs that don’t contain platinum, which can be unreliable and expensive. "If you use porous metal electrodes, they tend to be inherently unstable over long periods of time,” Ramanathan said in a statement. “They start to agglomerate and create open circuits in the fuel cells."
The platinum-free micro-SOFCs are more reliable and less expensive, he said.
The SEAS team also demonstrated what it said is a rare feat in this field: a methane-fueled micro-SOFC operating at less than 500 degrees Celsius. Traditional SOFCs have only been practical for stationary power generation since they operate at between 800 degrees and 1,000 degrees Celsius, making them less than ideal to power a smartphone. But in the past few years, materials scientists have reached a temperature range of about 300 degrees to 500 degrees Celsius, which Ramanathan referred to as the “sweet spot.”
Material reliability is less critical when fuel cells operate at lower temperatures and allows for the use of less expensive ceramics and metallic interconnects, as well as a shorter startup time, the SEAS group said.
"Low temperature is a holy grail in this field," Ramanathan said. "If you can realize high-performance solid-oxide fuel cells that operate in the 300 to 500 degrees Celsius range, you can use them in transportation vehicles and portable electronics, and with different types of fuels."
Another important finding was the use of methane gas, which is abundant and cheap, for SOFCs. Hydrogen has traditionally been the primary fuel source, but it requires more processing when it is in a pure state, according to the SEAS group. Ramanathan said that makes hydrogen more expensive to produce and hampers the applications in which it can be used. Methane is becoming the fuel of choice, and future SEAS research “will explore new types of catalysts for methane SOFCs, with the goal of identifying affordable, earth-abundant materials that can help lower the operating temperature even further," he said.