Apr 7 2017
An international research team has discovered that the performance of applications ranging from rechargeable batteries to high-performance gas sensors can be enhanced by using the natural structure found in leaves. The research team has designed a porous material resembling the veins of a leaf that has the ability to render energy transfers more efficiently. The material can enhance the performance of rechargeable batteries by optimizing the discharge and charge process and by eliminating stresses in the battery electrodes which limit the working life of the batteries. The innovative material can also be applied in the case of high-performance gas sensing or during catalysis to disintegrate organic pollutants dissolved in water.
Credit: University of Cambridge
The international team, which includes researchers from China, the United Kingdom, the United States and Belgium, have designed the bio-inspired material by imitating the rule called ‘Murray’s Law’ that aids natural organisms to remain alive and grow. As per the Law, a complete network of pores occurring on disparate scales in these biological systems is interconnected such that liquid transfer and reduction in resistance is facilitated all over the network. For instance, the stem of a plant or the veins in a leaf optimize the transfer of nutrients essential for photosynthesis in a highly efficient manner with lesser energy consumption by branching out to smaller scales on a regular basis. Similarly, in the case of insects, their tracheal pores have a constant surface area throughout the length of the diffusion pathway in order to enhance the delivery of gaseous oxygen and carbon dioxide.
The research team was headed by Prof Bao-Lian Su, a life member of Clare Hall, University of Cambridge, and who also works at Wuhan University of Technology in China as well as at the University of Namur in Belgium. The team adapted and applied Murray’s Law for producing the first ever synthetic ‘Murray material’ and used it for three processes, namely, gas sensing, photocatalysis, and lithium ion battery electrodes. The researchers discovered that the innovative synthetic material’s multi-scale porous networks remarkably improved the performance of the processes.
This study demonstrates that by adapting Murray’s Law from biology and applying it to chemistry, the performance of materials can be improved significantly. The adaptation could benefit a wide range of porous materials and improve functional ceramics and nano-metals used for energy and environmental applications.
Prof Su
“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.”
The researchers have reported their work in the Nature Communications journal this week, and outlined the method of using zinc oxide (ZnO) nanoparticles as the primary building blocks for their Murray material. Inside the ZnO nanoparticles there are numerous small pores, helping the nanoparticles to form the bottom most level of the porous network. The researchers used a layer-by-layer evaporation-driven self-assembly process to arrange the ZnO particles, thus forming second-level porous networks in-between the particles. While carrying out the evaporation process, larger pores are formed by the particles because of solvent evaporation, illustrating top-level pores, leading to a three-level Murray material. The researchers were victorious in designing the porous structures with accurate diameter ratios needed to conform to Murray’s law, thus allowing efficacious transfer of materials throughout the multilevel porous network.
This very first demonstration of a Murray material fabrication process is incredibly simple and is entirely driven by the nanoparticle self-assembly. Large scale manufacturability of this porous material is possible, making it an exciting, enabling technology, with potential impact across many applications.
Dr Tawfique Hasan, a co-author of the study, who also works at the Cambridge Graphene Centre, part of the University’s Department of Engineering
The researchers used their synthetic Murray material that has accurate diameter ratios across the various pore levels to show that an organic dye can be efficiently broken down in water through photocatalysis. This fact indicates that the dye can easily enter the porous network, resulting in repeated and efficient reaction cycles. The researchers applied the same Murray material—but with a structure identical to that of the breathing networks of insects—for swift and sensitive gas detection at higher repeatability.
The researchers demonstrated that the Murray material developed by them can remarkably enhance the swift charge/discharge capability and long-term stability of lithium ion storage, with an enhancement in capacity of nearly 25 times in comparison with the ultra-modern graphite material that is used at present in lithium ion battery electrodes. The multi-scale composition of the pores even minimizes the stresses in the electrodes throughout the charge/discharge processes, thus enhancing their structural stability and leading to an improved working life of energy storage devices.
The researchers believe that this technology can be efficiently used for materials designs in the case of environmental and energy applications.
The Royal Academy of Engineering partially supported the study.