Hydrofluorocarbons (HFCs) have become the de facto alternative to chloroflurocarbons (CFCs), since CFC phasing out in 1994, and are used primarily in heating, ventilation and air-conditioning equipment (HVAC). The US and EU now seek to phase-down HFC use due to their own toxicity issues and damaging environmental impact. In addition to these noble reasons, the refrigeration industry currently accounts for 17 % of the world's electricity consumption; any increase in efficiency would therefore be welcomed in both an economic and environmental sense. Finding alternatives to HFCs has created a major technological and scientific challenge. Ideally, any new technology should be made from sustainable sources and offer increased efficiencies and environmental credentials over current practices. Recently, there has been a strong focus on developing solid state materials which demonstrate caloric effects, where refrigeration is caused by an external field which induces a large isothermal entropy change and large adiabatic (isolated system) temperature changes. The external field can take the form of a magnetic field (magnetocaloric), electric field (electrocaloric) or hydrostatic pressure (barocaloric). While, magneto- and electrocaloric effects require large magnetic or electric fields, which are reliant on rare-earth elements for their generation, the same does not apply to the generation of pressure. Thus, in principle, applications based on the barocaloric (BC) effect will have less limitations for commercial realisation.
The potential energy savings through the adoption of BCs over current refrigeration systems has been calculated to be 1260 terawatt-hours. The BC effect in materials is unlocked via the application of external pressure to the material. This causes a structural transformation which is coupled with an increase in temperature, much like a when you stretch an elastic rubber band causing it to heat up. This process of a solid-solid phase transition can be cycled like the established vapour-compression technology to work as a refrigerant. To date few materials have been found to have the BC effect, and those that do vary wildly by type, ranging from metal alloys, to polymers and plastic crystals. This means that although there are few published BC materials, they must be more widespread than first thought.
The scope of this fellowship is to use a combined computational and experimental approach to search, understand and control the BC response of polymorphic materials. I have experience of combining both computational and experimental methods in materials chemistry and have found that this complementarity is essential in order to fully understand structural changes as well as the energetics of those changes. The project will extend our library of solid-state materials built from our new understanding of how to maximise BC effects. Specifically, I will design materials to be able to tune their working temperatures, as industry requires a wide range of temperature-controlled environments. The ultimate goal is to compile a portfolio of materials which have BC responses at different temperatures which can be explored for commercial application as refrigerants and coolants at fixed temperatures. These materials will be non-toxic, easy to dispose of and more efficient than the status-quo of today's technology. The development of solid-state BC materials as refrigerants will:
(1) Reduce the greenhouse gases emissions associated with the refrigeration industry.
(2) Create solid-state materials which can be disposed/recycled more easily than current technologies based on gases/liquids.
(3) Improve efficiency of the heat transfer, reducing refrigeration energy demands.
(4) Improve the knowledge of design principles for controlling materials properties via phase changes which is applicable to many areas including pharmaceuticals, heat batteries and thermo/piezochromic materials.