Graphene key to more fuel-efficient cars

Thermoelectric material converts heat into electricity

Researchers from the University of Manchester have developed a material they say could lead to more fuel efficient cars by more effectively converting waste heat into electricity.

The composite thermoelectric material, a mix of strontium titanium oxide and graphene, can convert heat into an electric current over a broad temperature range, down to room temperature.

The average car loses around 70% of the energy generated by fuel consumption to exhaust heat and friction. Recovery energy from waste heat could be used to recharge batteries or power air conditioning systems.

Professor Freer, from the University of Manchester's School of Materials, a lead researcher on the project, said: “Current oxide thermoelectric materials are limited by their operating temperatures, which can be around 700 degrees Celsius. This has hampered efforts to improve efficiency by utilising heat energy waste for some time.

“Our findings show that by introducing a small amount of graphene to the base material can reduce the thermal operating window to room temperature which offers a huge range of potential for applications.

"The new material will convert 3-5% of the heat into electricity. That is not much but, given that the average vehicle loses roughly 70% of the energy supplied to it by its fuel to waste heat and friction, recovering even a small percentage of this with thermoelectric technology would be worthwhile.”

As well as the high operating temperatures, thermoelectric materials can be toxic. Another challenge is to use a material that is a good conductor of electricity but also dissipates heat well.

Graphene’s properties and small size slow the transfer of heat through the material to the desired lower operating temperatures. The lower cost composite material could be used in the chassis or bodywork to reduce weight compared to traditional materials used.