Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

The surface science of titanium dioxide

The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Solid-state electrolytes are attracting increasing interest for electrochemical energy storage technologies. In this Review, we provide a background overview and discuss the state of the art, ion-transport mechanisms and fundamental properties of solid-state electrolyte materials of interest for energy storage applications. We focus on recent advances in various classes of battery chemistries and systems that are enabled by solid electrolytes, including all-solid-state lithium-ion batteries and emerging solid-electrolyte lithium batteries that feature cathodes with liquid or gaseous active materials (for example, lithium–air, lithium–sulfur and lithium–bromine systems). A low-cost, safe, aqueous electrochemical energy storage concept with a ‘mediator-ion’ solid electrolyte is also discussed. Advanced battery systems based on solid electrolytes would revitalize the rechargeable battery field because of their safety, excellent stability, long cycle lives and low cost. However, great effort will be needed to implement solid-electrolyte batteries as viable energy storage systems. In this context, we discuss the main issues that must be addressed, such as achieving acceptable ionic conductivity, electrochemical stability and mechanical properties of the solid electrolytes, as well as a compatible electrolyte/electrode interface. This Review details recent advances in battery chemistries and systems enabled by solid electrolytes, including all-solid-state lithium-ion, lithium–air, lithium–sulfur and lithium–bromine batteries, as well as an aqueous battery concept with a mediator-ion solid electrolyte.

Lithium battery chemistries enabled by solid-state electrolytes

Photoelectrochemical (PEC) cells offer the ability to convert electromagnetic energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Hematite (α-Fe(2)O(3)) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and ample abundance. However, its performance as a water-oxidizing photoanode has been crucially limited by poor optoelectronic properties that lead to both low light harvesting efficiencies and a large requisite overpotential for photoassisted water oxidation. Recently, the application of nanostructuring techniques and advanced interfacial engineering has afforded landmark improvements in the performance of hematite photoanodes. In this review, new insights into the basic material properties, the attractive aspects, and the challenges in using hematite for photoelectrochemical (PEC) water splitting are first examined. Next, recent progress enhancing the photocurrent by precise morphology control and reducing the overpotential with surface treatments are critically detailed and compared. The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are finally presented. These methods help to define the obstacles that remain to be surmounted in order to fully exploit the potential of this promising material for solar energy conversion.

Solar Water Splitting: Progress Using Hematite (α‐Fe2O3) Photoelectrodes

Photoelectrochemical properties of high purity and were investigated. Photocurrent efficiencies were measured in various electrolytes and found to depend on the electrolyte used. Direct measurement of spectrophotometric absorption coefficients showed them to be significantly higher than those deduced from i‐V curves indicating that only a fraction of the light absorbed resulted in electrochemically reactive holes. When the lower absorption coefficients were employed the current‐potential curves could be fit within ±1% to the depletion layer theory of Gartner.

Photooxidation of Water at α ‐ Fe2 O 3 Electrodes

Capacitance and conductivity measurements were made on high purity and in liquid junction cells. Flatband potentials and donor densities were determined from Mott‐Schottky plots and evidence for deep and shallow donors is presented. Potentials of zero photocurrent were determined using chopped light and were in excellent agreement in basic solution with flatband potentials calculated from 1 kHz capacitance measurements.

https://iopscience.iop.org/article/10.1149/1.2131535/pdf

Flatband Potentials and Donor Densities of Polycrystalline α ‐ Fe2 O 3 Determined from Mott‐Schottky Plots

Photoactivity of doped αFe2O3 electrodes

Structural transformation of non-oxide chalcogenide glasses. The short-range order of lithium sulfide (Li2S)-phosphorus pentasulfide (P2S5) glasses studied by quantitative phosphorus-31, lithium-6, and lithium-7 high-resolution solid-state NMR

John H. Kennedy

Papers

Photooxidation of Water at α ‐ Fe2 O 3 Electrodes

Flatband Potentials and Donor Densities of Polycrystalline α ‐ Fe2 O 3 Determined from Mott‐Schottky Plots

Photoactivity of doped αFe2O3 electrodes

Structural transformation of non-oxide chalcogenide glasses. The short-range order of lithium sulfide (Li2S)-phosphorus pentasulfide (P2S5) glasses studied by quantitative phosphorus-31, lithium-6, and lithium-7 high-resolution solid-state NMR

Synthesis and characterization of the B2S3Li2S, the P2S5Li2S and the B2S3P2S5Li2S glass systems