We report the first successful application of an ordered bicontinuous double-gyroid vanadium pentoxide network in an electrochromic supercapacitor. The freestanding vanadia network was fabricated by electrodeposition into a voided block copolymer template that had self-assembled into the double-gyroid morphology. The highly ordered structure with 11.0 nm wide struts and a high specific surface to bulk volume ratio of 161.4 μm(-1) is ideal for fast and efficient lithium ion intercalation/extraction and faradaic surface reactions, which are essential for high energy and high power density electrochemical energy storage devices. Supercapacitors made from such gyroid-structured vanadia electrodes exhibit a high specific capacitance of 155 F g(-1) and show a strong electrochromic color change from green/gray to yellow, indicating the capacitor's charge condition. The nanostructuring approach and utilizing an electrode material that has intrinsic electrochemical color-change properties are concepts that can be readily extended to other electrochromic intercalation compounds.

The brightest and most vivid colours in nature arise from the interaction of light with surfaces that exhibit periodic structure on the micro-and nanoscale. In the wings of butterflies, for example, a combination of multilayer interference, optical gratings, photonic crystals and other optical structures gives rise to complex colour mixing. Although the physics of structural colours is well understood, it remains a challenge to create artificial replicas of natural photonic structures [1][2][3] . Here we use a combination of layer deposition techniques, including colloidal self-assembly, sputtering and atomic layer deposition, to fabricate photonic structures that mimic the colour mixing effect found on the wings of the Indonesian butterfly Papilio blumei. We also show that a conceptual variation to the natural structure leads to enhanced optical properties. Our approach offers improved efficiency, versatility and scalability compared with previous approaches [4][5][6] .The intricate structures found on the wing scales of butterflies are difficult to copy, and it is particularly challenging to mimic the colour mixing effects displayed by P. blumei and P. palinurus 7,8 . The wing scales of these butterflies consist of regularly deformed multilayer stacks that are made from alternating layers of cuticle and air, and they create intense structural colours (Fig. 1). Although the P. blumei wing scales have previously been used as a template for atomic layer deposition (ALD) 9 , such an approach is not suitable for accurate replication of the internal multilayer structure on large surface areas.The bright green coloured areas on P. blumei and P. palinurus wings result from a juxtaposition of blue and yellow-green light reflected from different microscopic regions on the wing scales. Light microscopy reveals that these regions are the centres (yellow) and edges (blue) of concavities that are 5-10 mm wide, clad with a perforated cuticle multilayer 7 (Fig. 1d,e). For normal light incidence, the cuticle-air multilayer shows a reflectance peak at a wavelength of l max ¼ 525 nm, which shifts to l max ¼ 477 nm for light incident at an angle of 458. Light from the centre of the cavity is directly reflected, whereas retro-reflection of light incident onto the concavity edges occurs by double reflection off the cavity multilayer (Fig. 1g). This double reflection induces a geometrical polarization rotation 10 . If light that is polarized at an angle c to the initial plane of incidence is retro-reflected by the double bounce, it will pick up a polarization rotation of 2c and the intensity distribution through collinear polarisers is therefore given by cos 2 (2c). This leads to an interesting phenomenon: when placing the sample between crossed polarizers, light reflected off the centres of the cavities is suppressed, whereas retro-reflected light from four segments of the cavity edges is detected 10,11 (Fig. 1d, right). In microstructures without this double reflection, both the colour mixing and polarization conversion are absent...

Manufacturing V(2)O(5) in a 3D periodic highly interconnected gyroid structure on the 10 nm length scale is shown to lead to a significant electrochromic performance enhancement. The structured devices surpass previous inorganic electrochromic materials in all relevant parameters: the switching speed, coloration contrast, and composite coloration efficiency. In particular, the 85 ms switching speed lies within a factor of two of video rate. Enhanced ion intercalation into the gyroid morphology can be extended to other transition-metal oxides and is therefore promising for lithium ion batteries, supercapacitors, and sensors.

Gyroid‐structured calcite crystals are grown by templating though self‐assembled copolymer films. The remarkable triply periodic minimal surface is perfectly replicated on the nanometer scale, while single crystallinity is maintained. This is a wholly synthetic route to a crystal morphology found in biological systems, only on a smaller length scale.

Ion intercalation processes into metal oxide porous materials benefit from a high surface-to-volume ratio, while electronic charge transport requires a continuous network morphology. Detailed control over structure formation on the 10 nm length scale is therefore an effective strategy to enhance performance in electrochromic devices, supercapacitors, and batteries. Here we demonstrate the transformation of nickel patterned in a three-dimensional, highly interconnected, periodic nanomorphology into a self-supporting nickel oxide array with hollow struts. The oxidation of nickel gives rise to the nanoscale Kirkendall effect, which substantially increases the surface area of the NiO gyroid framework, without sacrificing its connectivity. Applicable to a vast range of electroplatable metals, this is a versatile route to high surface area metal oxides/chalcogenides which is especially suitable for various thin film applications. Nanostructured NiO electrodes showed substantially enhanced electrochromic performance, combining fast switching speeds with high coloration contrast.