Fuel cell performance

A team of researchers will assess the performance of fuel cells using a suite of mapping sensors

Developing a detailed functional map of the inner workings of a fuel cell could help make future devices more efficient and longer lasting.

Dr Anthony Kucernak, a reader in physical chemistry at Imperial College, is leading research that will use sensors built into a working fuel cell to study how levels of reactants, products, pressure, heat and electrical chemical potential vary under a variety of conditions.

‘Macroscopically, fuel cells look like a two-terminal power device that you put air and fuel in and electrical power comes out,’ he said. ‘What actually happens inside a fuel cell is more complicated than that. The fuel and air gets depleted as it flows through the paths within the fuel cell and the amount of reaction and where it occurs within the fuel cell is not uniform.’

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, they will build an electrode partly composed of a printed circuit board (PCB), which then has the fuel-cell catalyst layers, electrolyte and other functional parts deposited on the surface. A suite of localised 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.

The 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 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.

Kucernak said 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 as good as it could be. The places that produce more current also create more heat and that can, in the long term, lead to degradation of materials.

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 in use.

‘A fuel cell in a car, for example, will operate in a dynamic range,’ said Kucernak. ‘You might start off relatively cold, it might be driven quite hard for a while, then steadily. It would encounter a whole range of different envelopes of temperature, flow rates of reactants and environmental humidities.’

The researchers will develop accelerated tests to mimic the degradation that occurs when fuel cells are in use. When an area shows signs of degradation, they will be able to examine previous readings and see if, for example, it was the site of a hot spot.

The project is funded by the Engineering and Physical Sciences Research Council and the National Physical Laboratory (NPL), which is contributing expertise in modelling and measurement of humidity in fuel cells.

University College London is also collaborating on the project, building a test facility for the bipolar plate, which is the part of a fuel cell that distributes reactants and collects the electrical current from the electrodes. It will develop models and approaches for testing a range of geometries for the channels stamped in metal or etched in graphite through which reactants flow.

Industrial Project partners Johnson Matthey and systems manufacturer Intelligent Energy are providing their know-how in return for an enhanced insight into how fuel cells work. Matthey will supply fuel-cell electrodes for the tests.

‘Both companies already have their own methods for examining what happens in fuel cells,’ said Kucernak. ‘We are not repeating their experiments, but aim to enhance what both companies have done previously.’

Among the reasons that the uptake of fuel cells has, to date, been slow are inconsistent performance and limited lifespan. The fundamental goal of the project, which runs until 2012, is to produce an operating instrument that NPL could use to help manufacturers test their components in and, in time, develop more efficient, longer-lasting fuel cells.

Berenice Baker