Unraveling the Interfacial Electron Transfer in Various Photocathode Architectures for Advancing a Photobattery

A quintessential element that enables devices to convert solar energy into chemical energy is a photoelectrode. Toward developing such a lithium-ion photobattery for converting and storing the energy captured from light, we herein report the fundamental solid-state electron transfer of an optimized photoelectrode. It combines two materials that are well known to promote photomediated electron transfer in solution: an organic dye, perylene diimide (PDI), and a redox active material, lithium iron phosphate (LFP). The energetic compatibility of the materials to sustain light-mediated electron transfer in the solid state was confirmed by ultraviolet photoemission spectroscopy. Various photoelectrode architectures were fabricated by incorporating PDI into a conventional lithium-ion battery electrode. Illuminating the photoelectrodes revealed that the best configuration of the light harvesting/redox active components was a device fabricated from discrete multiple layers rather than an arbitrary combination of the various materials. Indeed, neither photoscreening nor self-quenching of PDI was found with the optimized architecture. The light-triggered electron transfer process from LFP to excited PDI was confirmed by a decrease in the fluorescence when PDI was deposited on top of an electrode. Encapsulating LFP with a conductive coating was required to enable the charge transfer between the light harvesting components and the redox active components. The role of the conductive material in the light-triggered process was evaluated by Raman spectroscopy. It was found that doped poly(3,4-ethylenedioxythiophene) could replace the commonly used carbon black as the conductive layer. Raman spectroscopy further confirmed the photomediated interfacial electron transfer between the photoelectrode components. The architecture that deactivated the PDI emission most efficiently was an outer coating of PDI on the redox active particles rather than a simple top coating on the electrode. No additional electrochemical features were observed during galvanostatic cycling with PDI, and there was no chemical modification of the materials according to post-cycling analyses. The oxidation of LFP by photoexcited PDI in the photoelectrode was further confirmed by the increase in current during periodic illumination. These findings confirm the suitability of the materials for use in a photoelectrode and pave the way for further device developments

Apple Pectin-Based Hydrogel Electrolyte for Energy Storage Applications

Demand for flexible energy storage devices is rapidly increasing due to the development of new wearable and flexible electronics. These developments require improved integration of energy storage devices to meet the design specifications of these products. Polymer hydrogels are an alternative class of flexible electrolytes that can be used in power source systems. Herein, we present a new sustainable hydrogel electrolyte material made with apple pectin. Using an easy solution casting approach, a bio-based hydrogel was formed via pectin gelation. The resultant hydrogel was made with environmentally benign compounds including water, zinc and/or lithium sulfate salt, and a bio-based polymer. This hydrogel electrolyte exhibits ambient temperature ionic conductivities that are similar to those found in aqueous liquid electrolytes (∼5 × 10–2 S cm–1), depending on electrolyte hydration. Its wide thermal stability window enables the electrolyte to be used at both low temperatures (−20 °C) and intermediate temperatures (50 °C), without significant changes in ionic conductivity (>10–3 S cm–1). By proposing an energy-oriented solution using one of the food industry’s major waste materials, we report a novel approach to processing a bio-based polymer for energy storage purposes