Natural law of branching holds key to improving batteries and reactors

A biological law which governs the structure of branching systems in nature is the basis for research at Cambridge University which, it is claimed, could improve performance of a range of devices from rechargeable batteries to high-performance gas sensors.

The research, led by Prof Bao-Lian Su of Clare Hall, Cambridge University, and working with teams from Su’s other institutions - Wuhan University of Technology in China and the University of Namur in Belgium - is making and studying materials whose structures obey Murray's Law.

This a rule is seen in branching structures such as circulatory and respiratory systems in animals and in leaf pores, where networks of pores of different scales are interconnected in such a way as to assist the transport of materials through the system and reduce the energy needed to push them through the system.

The team has synthesised its materials from particles of zinc oxide, a mineral that is porous at the nanometre scale. Using a layer-by-layer evaporation-driven self-assembly process, the researchers made a material that incorporates pores between each ZnO particle. As the solvent evaporates, this creates further pores, larger than both those in the particles themselves and those introduced in the self-assembly process. This structure is known as a "three-level Murray material". Manipulation of the process ensures that the diameter of the pores followed the ratio seen in the natural Murray’s law.