Fuel cell technology has powered ahead in recent years, but difficulties remain in translating this clean energy source into mainstream use. Professor Peter Slater is one of several Birmingham scientists working to overcome some of the obstacles.
Peter is collaborating with academics at Nanyang Technological University in Singapore on solid oxide fuel cell (SOFC) research. Earlier this year, a paper they co-wrote with colleagues from Spain, Australia and Germany, entitled ‘Interstitial Oxide Ion Distribution and Transport Mechanism in Aluminum-Doped Neodymium Silicate Apatite Electrolytes’, was published in the Journal of the American Chemical Society. It also won Peter the College’s Paper of the Month award.
‘The fuel cells that attract news headlines tend to be polymer fuel cells used in transport applications,’ says Peter, who is Professor of Materials Chemistry. ‘Although those work well, the problem has always been the lack of hydrogen infrastructure. That is why SOFCs, which use natural gas rather than hydrogen to produce electrical energy, are starting to be commercialised. You get the efficiency of the fuel cell and you also have the associated fuel infrastructure. A number of companies in the US have SOFCs powering their headquarters, and research is being done into using SOFCs as replacements for gas boilers.’
But, as with polymer fuel cells, SOFCs are not without their drawbacks. One of the main problems is that they operate at very high temperatures – typically 700 degrees C and above – which causes sealing problems and requires expensive specialist alloys. So Peter and his colleagues are working to find alternative materials that work as efficiently at slightly lower temperatures.
‘There is a push to operate at temperatures of between 500C and 700C, which makes cell sealing simpler and means you can use cheaper materials in the fuel cell system,’ explains Peter.
‘One of the reasons for the necessary higher temperature is the electrolyte material that conducts oxide ions. Conventional materials aren’t sufficiently conductive until 700C and above. So we have been looking at rare earth silicates such as neodymium and lanthanum silicate that have the apatite structure (apatite describes a group of phosphate minerals, the primary one of which includes fluorapatite, chlorapatite and the main component of teeth and bone, hydroxylapatite). These show very good oxide ion conduction in the region that’s needed – 500-700C.
‘Our paper is an investigation into the mechanisms of oxide ion conduction and why these silicates show better conduction than many existing materials. The conventional materials conduct via oxygen vacancies; these systems are different in the sense that they have available, or interstitial, space to accommodate extra oxygen. What they can do is to conduct via this available space.’
The paper – one of more than 150 Peter has written or co-authored – is the result of the longstanding international collaboration with Prof Tim White and his team in Singapore.
‘There is a lot of interest in these apatite electrolytes, and we’ve been working with them for some time now, says Peter, who has more than 20 years’ research experience in the area of solid state/materials chemistry, ranging from SOFCs to high temperature superconductors. ‘We are at the stage where we understand the mechanisms of oxide ion conduction and what we need to do to optimise them. The research is ongoing into electrode materials we would use with them. Once we’re satisfied we have viable electrode materials, the next step is to convince the industry.’