Ally Winning, European Editor, PSD
The electrification of the automotive industry is continuing at pace as governments attempt to meet the commitments that they have made towards the environment. The majority of governments in the developed world see the move to EVs as an easy way to slash emissions, and as such, have set tough to meet schedules for the phase out of internal combustion engine vehicles. For normal passenger vehicles, the technology and infrastructure is almost there and improving all the time. However, for vehicles, such as aeroplanes and cranes and other heavy plant equipment, batteries may not be able to supply their needs, or if they can, the size and weight of the battery pack would be detrimental to their operation.
Hydrogen fuel cells have been proposed as an alternative for these types of application. Fuel cells are generally more efficient than combustion engines, converting chemical energy to electrical energy at over 60% efficiency in some cases, almost twice the conversion efficiency of a normal ICE engine. This conversion is normally clean with no environmentally damaging emissions, depending on how the hydrogen is extracted.
In this type of application, the fuel cell acts like a battery and it produces electricity and heat as long as it is supplied with fuel. Like batteries, the fuel cell also consists of an anode and a cathode separated by an electrolyte. The fuel is fed to the anode, and air is fed to the cathode. In a hydrogen fuel cell, the catalyst at the anode separates the hydrogen molecules into protons and electrons, which take different paths to the cathode. Electrons use an external circuit, creating an electrical current. Protons move through the electrolyte to the cathode, where they unite with oxygen and the electrons to produce water and heat. The main reason that fuel cells are not more widely adopted is there are some issues with cost, performance and durability.
Michigan Technological University researcher Yun Hang Hu and two graduate students, Hanrui Su and Wei Zhangmay have solved some of those issues by changing the conventional path of a fuel cell. The research team created an interface between the electrolyte and melted carbonate as an ultrafast channel for oxygen ion transfer. The new type of fuel cell has been named carbonate-superstructured solid fuel cell (CSSFC) by the researchers. Most fuel cells are powered by hydrogen — typically produced from hydrogen-containing compounds, most often methane — via an expensive process called reforming. But the CSSFC can directly use both methane and other hydrocarbon fuels.
The new fuel cell provides electrochemical performance at lower operating temperatures and offers several other advantages. Conventional solid oxide fuel cells usually operate at 800 degrees Celsius or higher, because ion transfer in a solid electrolyte is very slow at a lower temperatures. The CSSFC’s superstructured electrolyte can provide a fast ion transfer as low as 470 degrees Celsius. This low operating temperature also offers high theoretical efficiency and lower cell manufacturing costs. It could also potentially be safer to operate than other solid fuel cells. Tests on the CSSFC showed a high open circuit voltage (OCV), which indicates no current leakage loss and high energy conversion efficiency. It is estimated that CSSFC fuel efficiency could reach 60%.
Lower operating temperatures with hydrocarbon fuels are suually problematic because they result in slow fuel oxidation and cause coking due to the strong carbon-hydrogen bonds. Carbon deposition also deactivates the electrodes by covering their catalytic sites.
The researchers fabricated a device in the lab. The CSSFC exhibited ultrahigh oxygen ionic conductivity at 550 degrees Celsius, achieving rapid oxidation of hydrocarbon fuel. This led to an unprecedented high open-circuit voltage of 1.041 volts and a very high peak power density of 215 milliwatts per square centimetre, along with excellent coking resistance using dry methane fuel.
Hu, Su and Zhang had their findings, “Carbonate-superstructured solid fuel cells with hydrocarbon fuels,” published in the Proceedings of the National Academy of Sciences journal.