New bio-inspired macro-meso-microporous material offers significant improvement in battery performance
A international team of researchers has emulated biological systems and designed multi-scale macro–meso–microporous materials which offer a unique performance boost for applications benefitting from highly enhanced mass transfer and exchange. Examples include photocatalysis, gas sensing and as Li-ion battery electrodes. An open access paper on their work is published in the journal Nature Communications.
The materials deliver 5-, 25- or 40-fold increases in reaction rates compared to unimodal mesoporous materials, when used as photocatalysts, gas sensors or electrodes for Li-ion batteries, respectively.They obtained superior rate capability (∼870 mAh g−1 at 20 A g−1) and high reversible capacity—25 times higher than that of state-of-the-art Li-ion anodes at a similar rate.
The hierarchical nature of the pores also reduces the stresses in these electrodes during the charge/discharge processes, improving their structural stability and resulting in a longer life time for energy storage devices.
Many classes of biological organisms feature hierarchically porous networks in which the pore sizes regularly decrease (and branch) across multiple scales and finally terminate in size-invariant units; examples are plant stems, leaf veins and vascular and respiratory systems. The entire natural porous network, connected within a finite volume, minimizes transport resistance for all the pores and ensures fluent transfer throughout the network. The relationship of the radii of parent and daughter branches is known as Murray’s law.
Since its discovery as the basis for vascular and blood systems, Murray’s law has attracted very little attention and has thus far been completely overlooked in the areas of physics, chemistry and applied materials. By mimicking nature’s hierarchical networks in synthetic materials with multi-scale pores based on Murray’s law, such synthetic Murray materials can potentially offer important structural superiority and performance enhancement for a wide range of applications such as in photocatalysis, gas sensing and Li-ion batteries, which could help mitigating current energy and environmental issues. It is envisioned that the introduction of Murray’s law into the design of materials could revolutionalize properties of engineered materials and launch a new era in the field of materials. However, the original Murray’s law is only applicable to mass transfer processes involving no mass variations. Significant theoretical advances need to be made to apply Murray’s principle more broadly to the fields of chemistry, applied materials and industrial reactions.
The way forward towards its applications also faces bottlenecks in the construction of multi-scale interconnected pores. … Here we demonstrate a bio-inspired, self-assembled material with space-filling macro–meso–micropores (M–M–M) designed based on revisited Murray’s law. The hierarchically porous networks are formed using a bottom-up, layer-by-layer evaporation-driven self-assembly process employing microporous nanocrystals as the primary building blocks under ambient conditions. Such porous Murray materials, composed of interconnected channels with precise dimensions spanning the macro-, meso- and micro-length scales can be fabricated for a broad range of applications.—Zheng et al.
The team, led by Prof Bao-Lian Su, a life member of Clare Hall, University of Cambridge and who is also based at Wuhan University of Technology in China and at the University of Namur in Belgium, applied the new Murray materials to three processes: photocatalysis, gas sensing and lithium-ion battery electrodes. In each, they found that the multi-scale porous networks of their synthetic material significantly enhanced the performance of these processes.
The team used zinc oxide (ZnO) nanoparticles as the primary building block of their Murray material. These nanoparticles, containing small pores within them, form the lowest level of the porous network. The team arranged the ZnO particles through a layer-by layer evaporation-driven self-assembly process.
This creates a second level of porous networks between the particles. During the evaporation process, the particles also form larger pores due to solvent evaporation, which represents the top level of pores, resulting in a three-level Murray material. The team successfully fabricated these porous structures with the precise diameter ratios required to obey Murray’s law, enabling the efficient transfer of materials across the multilevel pore 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.—Co-author Dr Tawfique Hasan
Our work on designing materials according to Murray’s law paves the way for pursuing optimized properties of hierarchically porous materials for various applications.—Zheng et al.
The research was partially supported by the Royal Academy of Engineering.
Xianfeng Zheng, Guofang Shen, Chao Wang, Yu Li, Darren Dunphy, Tawfique Hasan, C. Jeffrey Brinker & Bao-Lian Su (2017) “Bio-inspired Murray materials for mass transfer and activity” Nature Communications 8, Article number: 14921 doi: 10.1038/ncomms14921