Fuel for thought

UK

industry and academics are to collaborate on a £2.1m research project to investigate potential barriers to the introduction of fuel cells for vehicles and power generation.

The EPSRC-funded project will examine the obstacles that must be overcome before fuel cells can be fully exploited, including key issues like durability and power density. The research will also investigate the potential of new fuels like ethanol and innovative materials that could allow cells to operate at a wider range of temperatures.

The programme includes four UK universities, and is backed by DSTL, Rolls-Royce, Johnson Matthey and ImperialCollegespin-off Ceres Power.

Prof Nigel Brandon, leading the research at ImperialCollege, said the project is the first in the UK to bring together work on low-temperature fuel cells used in cars with the high-temperature fuel cells being developed for gas turbines. This means research efforts can be combined, he said, so for example electrode design improvements could enhance the performance of both high and low-temperature fuel cells.

High-temperature solid oxide fuel cells (SOFCs) with ceramic membranes operate at around 1,000°C. Rolls Royce is backing this area of the research, which will focus on reducing operating temperatures, because SOFCs are slow to start up, require heavy shielding and can use only high-temperature parts.

‘There are system benefits and efficiency gains to be won by putting the air and fuel in at a lower temperature, and so reducing the necessary cooling systems for the stack,’ said Brandon.

The research at NewcastleUniversity will focus on low-temperature polymer electrolyte membrane (PEM) fuel cells for vehicles, which operate around 80°C. The researchers hope to find a new polymer membrane material capable of operating at higher temperatures to increase durability and fuel flexibility.

Prof Keith Scott, heading the PEM research at Newcastle, said today’s polymer membrane needs water to operate, and dries out and loses conductivity at higher temperatures. ‘We’re hoping to get the fuel cells to operate at 200°C or more,’ he said. ‘This will give a much better tolerance to impurities such as carbon monoxide from the fuel, for example.’

Fuel type is also a challenge for PEM cell development. Hydrogen is bulky and difficult to store, and so fuels like ethanol would prove more suitable if its power efficiency can be improved.

In addition, the researchers aim to reduce the operating temperature of metallic membrane SOFCs in collaboration with Ceres Power.

How fuel cells work

On one side (the anode side) of the fuel cell is fuel in the form of hydrogen gas, and on the other side (the cathode side) is oxygen (in air). Sandwiched between the anode and cathode is the very thin, gas tight, electrically insulating but ion conducting, electrolyte layer. An electrical circuit connects the anode to the cathode and provides the mechanism to power electrical devices.

The combination of the materials used to make the fuel cell components, the type of fuel used and the operating temperature allow electricity to be generated via a chemical reaction rather than burning the fuel. The reaction starts with the oxygen on the cathode side being ionised at the cathode and generating negatively charged oxygen ions that then flow through the cathode and across the electrolyte.

At the anode side the oxygen ion combines with a positively charged hydrogen ion and releases an electron that then, because of the charge imbalance and the electron-impermeable electrolyte, flows around the electrical circuit to the cathode side generating direct current. This direct current will continue to be produced as long as there is a supply of fuel and air to the fuel cell. – courtesy Ceres Power.