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      Vacancies in functional materials for clean energy storage and harvesting: the perfect imperfection

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          Abstract

          Manipulating vacancies in functional materials offers scientists a powerful tool to design advanced materials for clean energy applications.

          Abstract

          Vacancies exist throughout nature and determine the physical properties of materials. By manipulating the density and distribution of vacancies, it is possible to influence their physical properties such as band-gap, conductivity, magnetism, etc.This can generate exciting applications in the fields of water treatment, energy storage, and physical devices such as resistance-change memories. In this review, we focus on recent progress in vacancy engineering for the design of materials for energy harvesting applications. A brief discription of the concept of vacancies, the way to create and control them, as well as their fundamental properties, is first provided. Then, emphasis is placed on the strategies used to tailor vacancies for metal–insulator transitions, electronic structures, and introducing magnetism in non-magnetic materials. Finally, we present representative applications of different structures with vacancies as active electrode materials of lithium or sodium ion batteries, catalysts for water splitting, and hydrogen evolution.

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          Most cited references47

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          Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells.

          Organolead trihalide perovskite materials have been successfully used as light absorbers in efficient photovoltaic cells. Two different cell structures, based on mesoscopic metal oxides and planar heterojunctions have already demonstrated very impressive advances in performance. Here, we report a bilayer architecture comprising the key features of mesoscopic and planar structures obtained by a fully solution-based process. We used CH3NH3 Pb(I(1-x)Br(x))3 (x = 0.1-0.15) as the absorbing layer and poly(triarylamine) as a hole-transporting material. The use of a mixed solvent of γ-butyrolactone and dimethylsulphoxide (DMSO) followed by toluene drop-casting leads to extremely uniform and dense perovskite layers via a CH3NH3I-PbI2-DMSO intermediate phase, and enables the fabrication of remarkably improved solar cells with a certified power-conversion efficiency of 16.2% and no hysteresis. These results provide important progress towards the understanding of the role of solution-processing in the realization of low-cost and highly efficient perovskite solar cells.
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            Activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies.

            As a promising non-precious catalyst for the hydrogen evolution reaction (HER; refs ,,,,), molybdenum disulphide (MoS2) is known to contain active edge sites and an inert basal plane. Activating the MoS2 basal plane could further enhance its HER activity but is not often a strategy for doing so. Herein, we report the first activation and optimization of the basal plane of monolayer 2H-MoS2 for HER by introducing sulphur (S) vacancies and strain. Our theoretical and experimental results show that the S-vacancies are new catalytic sites in the basal plane, where gap states around the Fermi level allow hydrogen to bind directly to exposed Mo atoms. The hydrogen adsorption free energy (ΔGH) can be further manipulated by straining the surface with S-vacancies, which fine-tunes the catalytic activity. Proper combinations of S-vacancy and strain yield the optimal ΔGH = 0 eV, which allows us to achieve the highest intrinsic HER activity among molybdenum-sulphide-based catalysts.
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              Is Open Access

              Ionic transport in hybrid lead iodide perovskite solar cells

              Solar cells based on organic–inorganic halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behaviour such as current–voltage hysteresis and a low-frequency giant dielectric response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chemical origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extracted from the current–voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and experimental study suggest that hybrid halide perovskites are mixed ionic–electronic conductors, a finding that has major implications for solar cell device architectures.
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                Author and article information

                Contributors
                (View ORCID Profile)
                Journal
                CSRVBR
                Chemical Society Reviews
                Chem. Soc. Rev.
                Royal Society of Chemistry (RSC)
                0306-0012
                1460-4744
                2017
                2017
                : 46
                : 6
                : 1693-1706
                Affiliations
                [1 ]Zernike Institute for Advanced Materials
                [2 ]University of Groningen
                [3 ]9747 AG Groningen
                [4 ]The Netherlands
                Article
                10.1039/C6CS00571C
                28098299
                524fc331-aa4f-450a-9bfd-160653261f06
                © 2017
                History

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