A Georgia Tech-led research team has developed a self-cleaning method utilizing barium oxide nanoparticles. The method will enable coal gas to power solid oxide fuel cells directly at low operating temperatures, the minimum level being 750°C.
The technology could offer a highly effective and cleaner option to traditional power facilities using coal. According to the scientists, a combination of fuel cells and gas turbines could convert 80% of the energy produced from traditional coal-fired facilities. However, to achieve that conversion efficiency, the fuel cells should operate for longer times on coal gas, but coal gas causes the anodes to get deactivated after just 30 minutes.
The research team’s carbon removal system utilizes a vapor deposition method to deposit the barium oxide nanoparticles over the electrode produced from nickel and yttria-stabilized zirconia (YSZ), a ceramic material. The nanoparticles with sizes ranging between 10 and 100 nm create islands on the nickel, which allows the flow of electrons through the electrode surface.
The water vapor brought into the stream of coal gas is adsorbed by the barium oxide and then dissociated into hydroxide (OH) and protons. The OH ions, which moves towards the surface of the nickel, forms the intermediate COH by combining with the carbon atoms deposited on the surface. The COH is then dissociated into hydrogen and carbon monoxide, which are used to power the fuel cells through oxidation, eventually generating water and CO2. Nearly 50% of the CO2 is then reused for the gasification of coal to produce coal gas.
The scientists also investigated the utilization of propane as a power source for solid oxide fuel cells utilizing the Ni-YSZ. This eliminates the introduction of water vapor, as water is produced by the oxidation of the hydrogen molecule in the propane. The normal operating temperatures of solid oxide fuel cells are more than 850°C and carbon deposition is less. But such high temperatures require the fluid cells to be fabricated from special materials, which is not cost-effective. One of the objectives of the research work is to decrease the operating temperatures down to 700 or 750°C, which enables the utilization of cheaper materials for interlinks and other important components.
The formation of the barium oxide structures does not need additional methods and can be performed as part of the production processes for traditional anodes. The scientists have successfully evaluated their method for a shorter period, which showed no proof of carbon formation. The actual challenge in front of them is to assess the system’s durability for longer period for fuel cells, which are developed to function for five years. They should also investigate the risk of potential fuel contaminants on the Ni-YSZ electrode.
Source: http://www.gatech.edu