A photoelectrochemical cell utilizing flavonoid anthocyanin dyes extracted from blackberries, along with colloidal TiO2 powder, is shown to convert sunlight to electrical power at an efficiency of 0.56% under full sun. Fluorescence quenching is observed for the excited state of the TiO2-adsorbed anthocyanin dye, cyanin, and the photocurrent spectrum correlates well with the optical absorption of the cyanin-sensitized TiO2 nanocrystalline film. The incident photon-to-current efficiency of 19% at the peak of the visible absorption band of the dye, the open-circuit voltages of 0.5−0.4 V, and short-circuit photocurrents of 1.5−2.2 mA/cm2 are remarkable for such a simple system and suggest efficient charge carrier injection. The ultrafast excited-state dynamics of cyanin in solution are compared with those of surface-adsorbed cyanin on TiO2 and ZrO2 colloids, as well as complexed with Al(III) ions. A transient absorption signal with a risetime of <100 fs for cyanin-sensitized TiO2 nanoparticles is assigned to electrons injected from the dye to TiO2. This signal is fit to a double-exponential decay with time constants of 0.52 and 67 ps. The 0.52 ps component is due to trapping of conduction band electrons or to fast direct recombination with the dye cation, while the 67 ps decay is attributed to trap state mediated indirect recombination. In contrast, stimulated emission with a 2.6 ps decay time is observed for cyanin in solution, cyanin on ZrO2, and cyanin complexed with Al(III) ions. When compared to the photon-to-current efficiency measured for the solar cell, the efficiency estimated from the injection and recombination rate constants suggests that electron recapture by the redox mediator and light screening mechanisms may limit the efficiency of the cell.
A unique solar cell fabrication procedure has been developed using natural anthocyanin dyes extracted from berries. It can be reproduced with a minimum amount of resources in order to provide an interdisciplinary approach for lower-division undergraduate students learning the basic principles of biological extraction, physical chemistry, and spectroscopy as well as environmental science and electron transfer. Electron transfer is the basis of the energetics that drives the processes of life on Earth, occurring in both the mitochondrial membranes of living cells and in the thylakoid membranes of photosynthetic cells of green plants and algae (1). Although we depend on the petroleum and agricultural products of this electron and energy transfer, one of the greatest challenges of the 21st century is that we have yet to create devices that can be used to tap directly into the ultimate source of this energy on an economic scale. An experimental lab procedure was therefore created in order to illustrate the connections between natural and man-made solar conversion within a three-hour lab period.
Metal oxides are reviewed as catalysts to convert H 2 O and CO 2 to fuels using solar energy. For photochemical conversion, TiO 2 has been found to be the most stable and useful oxide material, but it is currently limited by its large bandgap and a mismatch between its conduction band and the redox couples for water splitting and CO 2 reduction. A theoretical framework has been utilized to understand the basic thermodynamics and energetics in photochemical energy conversion systems. This is applied to model systems comprised of Ag 2 O and AgCl to examine why the former reacts thermochemically in air, while the latter reacts photochemically. For thermochemical conversion, zinc-, ceria-, and ferrite-based redox cycles are examined and examples of high-temperature solar reactors driven by concentrated solar radiation are presented. For CO 2 splitting, theoretical solar-to-fuel energy conversion efficiencies can be up to 26.8% for photochemical systems, and can exceed 30% for thermochemical systems, provided that sensible heat is recovered between the redox steps. ■ INTRODUCTIONThe conversion of solar energy into useful forms has reached a critical stage where large-scale industrial applications are allowing it to make significant and promising contributions to our present and future energy needs. In this review, we present some basic concepts and survey a few of the recent developments in the conversion of solar energy into fuel. Several types of systems are possible, some of which are based on thermochemistry, 1 while others are based on photochemistry. 2 Photovoltaic cells and modules 3−7 have also emerged as an important part of the energy mixture of many countries, but they will not be fully examined in this review. The storage of solar energy has recently been reported in this journal. 8 The first section of this review focuses on the photochemical production of fuels and includes a generalized framework that can be used to understand the energetics and mechanism of both photovoltaic (PV) solar cells, as well as solar photochemistry using semiconductor materials. 9−12 This framework will be applied to a consideration of Ag 2 O, which is a model metal oxide system that, in air, seems to react thermochemically but not photochemically. The second half of this review focuses on the solar thermochemical splitting of H 2 O and CO 2 via metal oxide redox cycles. A comparison between metal oxide and solar electrolysis fuel-forming systems will also be presented. ■ DISCUSSIONPhotochemistry and Quantum Solar Converters. Two forms of solar energy conversion are considered. One is thermal conversion, where work can be extracted after sunlight is absorbed as thermal energy, and the other is quantum conversion, where the work output can be taken directly from the light absorber. In a thermal system, solar radiation is absorbed as heat, preferably at some high temperature, which, in turn, is used to drive a heat engine. In a quantum system, a fixed number of photons yield a fixed number of energy quanta, such as excited elect...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.