A material that uses the vein structure found within leaves as inspiration could help to improve the performance of rechargeable batteries and high-performance gas sensors, according to a new study. The porous material could extend the lifespan of rechargeable batteries by improving their performance through optimization of the charge and discharge process, as well as working to relieve those stresses within the electrodes that reduce their lifetime.
An international team, whose work was reported in the journal Nature Communications [Zheng et al. Nat. Commun. (2017) DOI: 10.1038/ncomms14921], demonstrated how the material could be used for energy and environmental applications, leading to energy transfers being more efficient, and in high-performance gas sensing or catalysis to break down organic pollutants in water. The study mimicked 'Murray's Law', which claims that the whole network of pores existing on different scales in some biological systems is interconnected to help the transfer of liquids and reduce resistance throughout the network.
In this way, leaf veins or a tree’s plant stems optimize the flow of nutrients for photosynthesis with both high efficiency and minimum energy consumption by regularly branching out to smaller scales. They contain analogous tissues with hierarchical networks of pores, with pore size ratios having evolved to maximize mass transport and rates of reactions.
“The introduction of the concept of Murray's Law to industrial processes could revolutionize the design of reactors with highly enhanced efficiency, minimum energy, time and raw material consumption for a sustainable future”Bao-Lian Su
The team adapted Murray's Law for the fabrication of the first-ever synthetic 'Murray material' by applying it to three processes: photocatalysis, gas sensing and lithium ion battery electrodes. For each, they demonstrated that the multi-scale porous networks of their synthetic material enhanced substantially their performance. As team leader Bao-Lian Su said, “The introduction of the concept of Murray's Law to industrial processes could revolutionize the design of reactors with highly enhanced efficiency, minimum energy, time and raw material consumption for a sustainable future”.
Zinc oxide nanoparticles were used as the main building blocks, with the particles being organized based on a layered evaporation-driven self-assembly process, providing another level of porous networks between the particles. On evaporation, these particles also form larger pores due to solvent evaporation, producing a three-level Murray material. They manufactured the porous structures with the specific diameter ratios needed to obey Murray's law so that the efficient transfer of materials across the multi-level pore network could be enabled.
The team proved that their Murray material can improve significantly the long-term stability and fast charge/discharge capability for lithium ion storage, offering better capacity compared to the graphite material currently used in electrodes. In addition, the pores’ hierarchical nature lessens the stresses in these electrodes during the charge/discharge processes, helping their structural stability and resulting in a longer lifetime for energy storage devices.