In a recent report in The Engineer, Kucernak, a reader in physical chemistry, says that while fuel cells look like simple two-terminal power devices on a macroscopic level – with fuel and air going in and electricity coming out – what actually happens inside them is more complicated. The fuel and air become depleted as they flow through the paths within the fuel cell, and the amount of reaction and where it occurs within the fuel cell is not uniform.
Kucernak is leading research that will use sensors built into a working fuel cell to study how levels of reactants, products and electrical chemical potential vary under a variety of conditions. The key variables that the researchers will measure are temperature, electrical potential, electrical flow, pressure, humidity and conductivity, including contact resistance between the fuel cell electrode and the electrical contact that takes the current away.
To do this the researchers will build an electrode that is partly composed of a printed circuit board (PCB), onto to which has been deposited the fuel cell catalyst layers, electrolyte and other functional parts. A set of localized sensors will be attached to the PCB to monitor the adjacent electrode. Most of the sensors will be off-the-shelf, but the team will develop a suite to measure local electrical potential.
These sensors will help to build a model of why some parts of a fuel cell might not perform as well as other parts, as a function of their position within the fuel cell. This could be as a result of a number of factors, such as depleted reactants at that point or the presence of water, one of the by-products of the fuel cell reaction that can hinder the flow of reactants. Places that produce more current also generate more heat which, in the long term, can lead to degradation of materials.
Kucernak says that the ideal situation would be to achieve uniform rates of reaction throughout the fuel cell, as unequal rates of reaction mean that the overall efficiency of the system is not optimized.
The researchers will develop a 2D image that shows the distribution of current, pressure and temperature as a function of position within fuel cells. The various factors will be measured over a variety of conditions that might be encountered by a fuel cell while it is running. They will use tests to mimic the degradation that occurs when fuel cells are in use.
The project is funded by the UK’s Engineering and Physical Sciences Research Council and the National Physical Laboratory, which is contributing expertise in modeling and measurement of humidity in fuel cells. Industrial project partners Johnson Matthey – which is supplying the fuel cell electrodes for the tests – and systems manufacturer Intelligent Energy are providing their practical knowledge and expertise in return for an enhanced insight into how fuel cells work.