Artificial opal photonic crystals and inverse opal structures - fundamentals and applications from optics to energy storage

Photonic crystals (PhCs) influence the propagation of light by their periodic variation in dielectric contrast or refractive index. This review outlines the attractive optical qualities inherent to most PhCs namely the presence of full or partial photonic band gaps and the possibilities they present towards the inhibition of spontaneous emission and the localization of light. Colloidal self-assembly of polymer or silica spheres is one of the most favoured and low cost methods for the formation of PhCs as artificial opals. The state of the art in growth methods currently used for colloidal self-assembly are discussed and the use of these structures for the formation of inverse opal architectures is then presented. Inverse opal structures with their porous and interconnected architecture span several technological arenas - optics and optoelectronics, energy storage, communications, sensor and biological applications. This review presents several of these applications and an accessible overview of the physics of photonic crystal optics that may be useful for opal and inverse opal researchers in general, with a particular emphasis on the recent use of these three-dimensional porous structures in electrochemical energy storage technology. Progress towards all-optical integrated circuits may lie with the concepts of the photonic crystal, but the unique optical and structural properties of these materials and the convergence of PhC and energy storage disciplines may facilitate further developments and non-destructive optical analysis capabilities for (electro)chemical processes that occur within a wide variety of materials in energy storage research

3D vanadium oxide inverse opal growth by electrodeposition

Three-dimensional vanadium pentoxide (V2O5) material architectures in the form of inverse opals (IOs) were fabricated using a simple electrodeposition process into artificial opal templates on stainless steel foil using an aqueous solution of VOSO4.χH2O with added ethanol. The direct deposition of V2O5 IOs was compared with V2O5 planar electrodeposition and confirms a similar progressive nucleation and growth mechanism. An in-depth examination of the chemical and morphological nature of the IO material was performed using X-ray crystallography, X-ray photoelectron spectroscopy, Raman scattering and scanning/transmission electron microscopy. Electrodeposition is demonstrated to be a function of the interstitial void fraction of the artificial opal and ionic diffusivity that leads to high quality, phase pure V2O5 inverse opals is not adversely affected by diffusion pathway tortuosity. Methods to alleviate electrodeposited overlayer formation on the artificial opal templates for the fabrication of the porous 3D structures are also demonstrated. Such a 3D material is ideally suited as a cathode for lithium ion batteries, electrochromic devices, sensors and for applications requiring high surface area electrochemically active metal oxides

2D and 3D photonic crystal materials for photocatalysis and electrochemical energy storage and conversion

This perspective reviews recent advances in inverse opal structures, how they have been developed, studied and applied as catalysts, catalyst support materials, as electrode materials for batteries, water splitting applications, solar-to-fuel conversion and electrochromics, and finally as photonic photocatalysts and photoelectrocatalysts. Throughout, we detail some of the salient optical characteristics that underpin recent results and form the basis for light-matter interactions that span electrochemical energy conversion systems as well as photocatalytic systems. Strategies for using 2D as well as 3D structures, ordered macroporous materials such as inverse opals are summarized and recent work on plasmonic–photonic coupling in metal nanoparticle-infiltrated wide band gap inverse opals for enhanced photoelectrochemistry are provided

In Pursuit of an Easy to Use Brain Computer Interface for Domestic Use in a Population with Brain Injury

This paper presents original research investigating a sensor based, ambient assisted smart home platform, within the framework of a brain computer interface (BackHome). This multimodal system integrates home-based sensors, mobile monitoring, with communication tools, web browsing, smart home control and cognitive rehabilitation. The target population are people living at home with acquired brain injury. This research engaged with the target population and those without brain injury, who provided a control for system testing. Aligned with our ethical governance a strong user centric ethos was foundational to participant engagement. Participant experience included three individual sessions to complete a pre-set protocol with supervision. Evaluation methodology included observations, time logging, completion of protocol and usability questionnaires. Results confirmed the average accuracy score for the people without brain injury was 82.6% (±4.7), performing best with the cognitive rehabilitation. Target end users recorded an average accuracy score of 76% (±11.5) with the speller logging the highest accuracy score. Additional outcomes included the need to refine the aesthetic appearance, as well as improving the reliability and responsiveness of the BCI. The findings outline the importance of engaging with end users to design and develop marketable BCI products for use in a domestic environment. DOI: 10.17762/ijritcc2321-8169.150610

P300 Brain Computer Interface Control after an Acquired Brain Injury

Brain-Computer Interfaces (BCI) are systems that can be controlled by the user through harnessing their brain signals. Extensive research has been undertaken within a laboratory setting with healthy users to illustrate the usability of such systems. To bring these systems to users with severe disabilities it is necessary to develop simple, easy to use systems that can be operated by non-experts outside of the lab and are evaluated by real end users preferably through a user centered design approach. This paper presents a user centered evaluation of a P300 BCI operated by non-expert users in a rehabilitation center with a control group of five healthy participants without acquired brain injury (ABI) and five end users with ABI. Each participant aimed to complete the 30-step protocol three separate times and rate his or her satisfaction from 0 to 10 on the Visual Analogue Scale after each session. Participants then rated their satisfaction with the BCI on the extended QUEST 2.0 and a customized usability questionnaire. The results indicated that end-users were able to achieve an average accuracy of 55% compared to the control group that reported an average of 78%. The findings indicated that participants were satisfied with the BCI but felt frustrated when it did not respond to their commands. This work was phase one of three to move the BCI system into end users homes. Key recommendations for advancing the P300 BCI towards an easy to use, home-based system were identified, including reducing the complexity of the setup, ensuring the system becomes more responsive and increasing the overall functionality. DOI: 10.17762/ijritcc2321-8169.15016

New routes towards the formation of tin oxide inverted opals for charge storage applications

New routes to formation of tin oxide inverted opals with unique morphologies are presented. Inverted opals with walls formed from assemblies of tin oxide nanocrystals are formed from tin acetate precursor, while mesoporous walls are formed when tin alkoxide precursors are used. The inverted opals are investigated by a variety of techniques in order to determine their structure and the dependence of electrochemical properties on the type of precursor used. We found that the initial discharge capacity of the inverted opal based batteries reaches 1200 mAhg-1 but quickly fades afterwards, as it is typical for tin oxide based anodes. Careful investigation of processes occurring in the tin oxide inverted opal anodes may lead to improvement of their performance improvement, and further development of self-supported tin oxide based anodes

High performance inverse opal Li-ion battery with paired intercalation and conversion mode electrodes

Structured porous materials have provided several breakthroughs that have facilitated high rate capability, better capacity retention and material stability in Li-ion batteries. However, most advances have been limited to half cells or lithium batteries, and with a single mode of charge storage (intercalation, conversion, or alloying etc.). The use of dual-mode charge storage with non-traditional material pairings, while maintaining the numerous benefits of nanoscale materials, could significantly improve the capacity, energy density, stability and overall battery safety considerably. Here, we demonstrate an efficient, high capacity full inverse opal Li-ion battery with excellent cycle life, where both the cathode and anode binder-free electrodes are composed of 3D nanocrystal assemblies as inverse opal (IO) structures of intercalation-mode V2O5 IO cathodes and conversion-mode Co3O4 IO anodes. Electrochemically charged Co3O4 IOs function as Li-ion anodes and the full V2O5/Co3O4 cell exhibits superior performance compared to lithium batteries or half cells of either IO material, with voltage window compatibility for high capacity and energy density. Through asymmetric charge-discharge tests, the V2O5 IO/Co3O4 IO full Li-ion cell can be quickly charged, and discharged both quickly and slowly without any capacity decay. We demonstrate that issues due to the decomposition of the electrolyte with increased cycling can be overcome by complete electrolyte infiltration to remove capacity fading from long term cycling at high capacity and rate. Lastly, we show that the V2O5 IO/Co3O4 IO full Li-ion cells cycled in 2 and 3-electrode flooded cells maintain 150 mA h g-1 and remarkably, show no capacity fade at any stage during cycling for at least 175 cycles. The realization of an all-3D structured anode and cathode geometry with new mutually co-operative dual-mode charge storage mechanisms and efficient electrolyte penetration to the nanocrystalline network of material provides a testbed for advancing high rate, high capacity, stable Li-ion batteries using a wide range of materials pairings