Xingmei Guo

Butterflies: inspiration for solar cells and sunlight water-splitting catalysts

Solar cells and photocatalysts to yield hydrogen are two significant strategies for taking advantage of clean and sustainable solar energy, and their light manipulation and harvesting ability will play a dominant role in their conversion efficiencies. Butterflies demonstrate their brilliant colors due to their wonderful skills of light manipulation, originating intrinsically from their elaborate architectures. We review the inspiration of butterflies for solar cells and sunlight water-splitting catalysts, focusing on the nipple arrays in butterfly compound eyes, as well as ridge and hole arrays, and the photonic crystal structures in butterfly wing scales. After giving a brief introduction to the typical architectures, we reveal the physical principles lying behind antireflection of compound eyes and black scales and iridescence of wing scales, respective prototypes are extracted and highlighted for the design and fabrication of solar cells and sunlight water-splitting catalysts. We conclude by reviewing the prospects for the integration of these prototypes and the appropriate materials for solar energy, which is the product of an intimate conversation between humanity and nature, as well as close cooperation between scientists from diverse fields.

Art of blackness in butterfly wings as natural solar collector

We report the investigation of a nano-scale antireflection structure in the black scales of the Troides aeacus butterfly wing, which can be viewed as a natural solar collector. The intelligence of light capturing hides itself in the intricate architectures aside from melanin effect. Reflection and transmission spectra of scales were obtained experimentally as well as with 3D FDTD (three dimensional finite difference time domain) method. Poynting vector maps which show the energy distribution of reflection and transmission in the micro geometric structure were portrayed as well. We demonstrated that the structure related antireflection behaviour is derived from the coupling effect of two main subunits of the hierarchical architecture, which are periodically aligned inverse-V type ridges and sub-wavelength nano-hole arrays.

Controlled pyrolysis of MIL-88A to Fe2O3@C nanocomposites with varied morphologies and phases for advanced lithium storage

Carbon-coated α-Fe2O3 hollow nanospindles and varied-phase Fe2O3@C (γ-Fe2O3@C, αγ-Fe2O3@C, and α-Fe2O3@C) nanobipyramids were prepared by controlling pyrolysis of MIL-88A nanobipyramids at different temperatures and time in air or in nitrogen. The corresponding pyrolysis stage in air, followed by a self-oxidation/reduction-like mechanism in nitrogen was proposed for the first time. When used as anodes for lithium-ion batteries (LIBs), the α-Fe2O3 hollow nanospindles with carbon-coated shells can not only facilitate the contact between the electrode and electrolyte and accommodate mechanical stress and volume change over multiple cycles but also enhance the electronic conductivity of the electrode materials. Benefiting from the unique carbon-coated hollow structure, the α-Fe2O3 nanospindle electrode delivered an over-theoretical capacity of about 1207 mA h g−1 after 200 cycles at 0.2C and reversible lithium storage capacity as high as 961.5 mA h g−1 after 500 cycles at 1C. Moreover, αγ-Fe2O3@C nanobipyramid electrode exhibits a superior specific capacity of 631.6 mA h g−1 at 1C after 150 cycles due to its derived unique nanoflake structure.

Enhanced methanol oxidation performance on platinum with butterfly-scale architectures: toward structural design of efficient electrocatalysts

Enhanced methanol oxidation performance was achieved by combining elaborate butterfly-scale architectures into platinum electrocatalysts using an electroless deposition-detemplating method. The electrochemically active surface area and the forward peak current density for methanol oxidation were dramatically increased by 5 and 5.2 times, respectively, for lamellar-ridge architectured Pt compared to its unarchitectured counterpart. Excellent mass transport properties and efficient catalytic surface accessibility were further demonstrated by finite element simulation.

Butterfly-scale architecture directed electrodeposition of Ag microband arrays for electrochemical detection

Butterfly scales with various elaborate architectures provide a large pool for structural design of microelectrode array arrangements. Here, the ridge array architecture of Troides aeacus butterfly scales was used as guidance to gather an electric field compactly around the ridge tips when a cathode potential was exerted. This tip effect directed the electrodeposition of Ag into microband arrays, on which effective electrochemical detection of hydrogen peroxide was achieved.

Cyclic voltammogram on ridge/pore array architectured electrode inspired by butterfly-wings

Abstract Porous architectured electrodes are intensely investigated for promoting electrochemical performance. Besides the high surface area, mass transport plays an irreplaceable role in the architecture assisting effect, which is, however, far beyond expression due to the complexity and irregularity of various electrode materials. Here, we took advantage of elaborate architectures from butterfly wings and obtained carbon electrode with ridge/pore array hierarchical architecture (ridge/pore-C) using a carbonizing-graphite coating method. A basic one-electron transfer process using the redox couple ferri/ferrocyanide as a benchmark under cyclic voltammetric conditions was conducted. The peak potential separation for ridge/pore-C was decreased by 117 mV compared to its non-architectured counterpart, with obvious enhancement of peak current density, indicating prominent beneficial impact on electrochemical responses. Further finite element simulation demonstrated the additional lateral diffusion within the ridge domain and partial thin layer diffusion within the pore array domain of ridge/pore-C, and simultaneously verified the experimental results. By constructing and investigating the well-organized porous architecture for affecting cyclic voltammogram, this work provides a prototype and cost-effective method for structural design of efficient electrodes by drawing inspiration from nature.