Search for: All records

Deriving battery grade materials from natural sources is a key element to establishing sustainable energy storage technologies. In this work, we present the use of avocado peels as a sustainable source for conversion into hard carbon-based anodes for sodium ion batteries. The avocado peels are simply washed and dried then proceeded to a high temperature conversion step. Materials characterization reveals conversion of the avocado peels in high purity, highly porous hard carbon powders. When prepared as anode materials they show to the capability to reversibly store and release sodium ions. The hard carbon-based electrodes exhibit excellent cycling performance, namely, a reversible capacity of 352.55 mAh g⁻¹at 0.05 A g⁻¹, rate capability up to 86 mAh g⁻¹at 3500 mA g⁻¹, capacity retention of >90%, and 99.9% coulombic efficiencies after 500 cycles. Cyclic voltammetry studies indicated that the storage process was diffusion-limited, with diffusion coefficient of 8.62 × 10⁻⁸cm²s⁻¹. This study demonstrates avocado derived hard carbon as a sustainable source that can provide excellent electrochemical and battery performance as anodes in sodium ion batteries.

 

This perspective presents a recently developed approach to organize polymer and polymer composite materials through a new form of light-directed organization of photoreactive polymeric media. Under suitable conditions, such media will interact with light, in a mutual dynamic process, that results in the spontaneous organization of both the input light field and, importantly, the polymer media. New material structures can be created in free-radical-initiated media, polymer blends and polymer–solvent mixtures, as well as possibly more complex, multicomponent formulations. An overview of the underlying principles and chemical phenomena and exemplary material structures are presented. Materials produced using this new processing approach can be used as functional coatings, textured surfaces, and membranes, as well as a host of other applications via selection of polymer composition. Key open questions and areas for further inquiry and advancement are presented. Coupling the dynamics of light pattern formation processes to photoreactive matter is a promising new approach to the organization of materials for a range of critical applications and reveals interesting nonlinear dynamic phenomena in the organization of materials. 

We report observations of photopolymerization driven phase-separation in a mixture of a photo-reactive monomer and inorganic nanoparticles. The mixture is irradiated with visible light possessing a periodic intensity profile that elicits photopolymerization along the depth of the mixture, establishing a competition between photo-crosslinking and thermodynamically favorable phase-separating behavior inherent to the system. In situ Raman spectroscopy was used to monitor the polymerization reaction and morphology evolution, and reveals a key correlation between irradiation intensity and composite morphology extending the entire depth of the mixture, i.e. unhindered phase-separation at low irradiation intensity and arrested phase-separation at high irradiation intensity. 3D Raman volume mapping and energy dispersive X-ray mapping confirm that the intensity-dependent irradiation process dictates the extent of phase separation, enabling single-parameter control over phase evolution and subsequent composite morphology. These observations can potentially enable a single-step route to develop polymer–inorganic composite materials with tunable morphologies. 

Microfiber optic array structures are fabricated and employed as an optical structure overlaying a front-contact silicon solar cell. The arrays are synthesized through light-induced self-writing in a photo-crosslinking acrylate resin, which produces periodically spaced, high-aspect-ratio, and vertically aligned tapered microfibers deposited on a transparent substrate. The structure is then positioned over and sealed onto the solar cell surface. Their fiber optic properties enable collection of non-normal incident light, allowing the structure to mitigate shading loss through the redirection of incident light away from contacts and toward the solar cell. Angle-averaged external quantum efficiency increases nominally by 1.61%, resulting in increases in short-circuit current density up to 1.13 mA/cm2. This work demonstrates a new approach to enhance light collection and conversion using a scalable, straightforward, light-based additive manufacturing process. 

Here presented are the properties and performance of a new metallo‐dielectric waveguide array structure as the encapsulation material for silicon solar cells. The arrays are produced through light‐induced self‐writing combined with in situ photochemical synthesis of silver nanoparticles. Each waveguide comprises a cylindrical core consisting of a high refractive index polymer and silver nanoparticles homogenously dispersed in its medium, all of which are surrounded by a low refractive index common cladding. The waveguide array‐based films are processed directly over a silicon solar cell. Arrays with systematically varied concentration of AgSbF6 as the salt precursor are explored. The structures are tested for their wide‐angle light capture capabilities, specifically toward enhanced conversion efficiency and current production of encapsulated solar cells. Observed are increases in the external quantum efficiency, especially at wide incident angles up to 70°, and nominal increases in the short circuit current density by 1 mA cm−2 (relative to an array without nanoparticles). Enhanced light collection is explained in terms of the beneficial effect of scattering by the nanoparticles along the waveguide cores. This is a promising approach toward solar cell encapsulants that aid to increase solar cell output over both the course of the day and year. 

A new approach is reported to fabricate micropillar arrays on transparent surfaces by employing the light‐induced self‐writing technique. A periodic array of microscale optical beams is transmitted through a thin film of photo‐crosslinking acrylate resin. Each beam undergoes self‐lensing associated to photopolymerization‐induced changes in the refractive index of the medium, which counters the beam's natural tendency to diverge over space. As a result, a microscale pillar grows along each beam's propagation path. Concurrent, parallel self‐writing of micropillars leads to the prototyping of micropillar‐based arrays, with the capability to precisely vary the pillar diameter and inter‐spacing. The arrays are spray coated with a thin layer of polytetrafluoroethylene (PTFE) nanoparticles to create large‐area superhydrophobic surfaces with water contact angles greater than 150° and low contact angle hysteresis. High transparency is achieved over the entire range of micropillar arrays explored. The arrays are also mechanically durable and robust against abrasion. This is a scalable, straightforward approach toward structure‐tunable micropillar arrays for functional surfaces and anti‐wetting applications.