Phase-change materials for green heat transport and storage (CSC)

Global heating is the preeminent challenge currently facing humanity. There is a grave danger of being locked into a “vicious heating cycle”, where an increased need for cooling prompts increased use of the damaging technologies that cause heating. It is thus vital to develop environmentally friendly infrastructure for heating and cooling.

Two specific needs are especially urgent. First, we must find alternatives to current refrigerants, which are both greenhouse gases and ozone depleters. Second, we need thermal batteries to store heat energy between generation and use, since most renewable heat sources (e.g., solar) vary in output over time.

Both of these needs can be met by the same class of “phase-change” materials, since each of these technologies relies on cycling between two phases, taking advantage respectively of a large change in entropy and enthalpy across the phase transition. However, in both cases, the key problem at present is that at least one of these phases is a fluid, which can easily escape into the environment.

The solution is to use materials that have two solid phases: they can thus be incorporated directly into construction materials, with no need for encapsulation, and pose no environmental danger. Our aim is to develop new materials of this kind with properties tuned for commercialisation.

I expect to take on two PhD students in 2022/23 to work in this field: one experimental and one computational.

The experimental project will involve synthesis of new materials that undergo order-disorder phase transitions for these purposes. We will probe their atomic structure using X-ray and neutron diffraction; their dynamic properties by Raman and inelastic neutron scattering; and their thermodynamic behaviour using our high-pressure differential scanning calorimeter (an instrument available at very few universities).

The computational project will involve modelling new materials that undergo order-disorder phase transitions for these purposes. We will perform simulations of varying sophistication, from simple “toy” models to understand the fundamental effects of molecular shape, through empirical potentials for use on large systems, to the most accurate ab initio molecular dynamics models.

The aim is to determine how these materials’ structure gives rise to phase transitions and hence useful functionality, and thus to design the best materials yet known for green cooling and thermal energy storage.