Review on recent progress of nanostructured anode materials for Li-ion batteries

There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

Engineering heterogeneous semiconductors for solar water splitting

Advanced electrodes with a high energy density at high power are urgently needed for high-performance energy storage devices, including lithium-ion batteries (LIBs) and supercapacitors (SCs), to fulfil the requirements of future electrochemical power sources for applications such as in hybrid electric/plug-in-hybrid (HEV/PHEV) vehicles. Metal sulfides with unique physical and chemical properties, as well as high specific capacity/capacitance, which are typically multiple times higher than that of the carbon/graphite-based materials, are currently studied as promising electrode materials. However, the implementation of these sulfide electrodes in practical applications is hindered by their inferior rate performance and cycling stability. Nanostructures offering the advantages of high surface-to-volume ratios, favourable transport properties, and high freedom for the volume change upon ion insertion/extraction and other reactions, present an opportunity to build next-generation LIBs and SCs. Thus, the development of novel concepts in material research to achieve new nanostructures paves the way for improved electrochemical performance. Herein, we summarize recent advances in nanostructured metal sulfides, such as iron sulfides, copper sulfides, cobalt sulfides, nickel sulfides, manganese sulfides, molybdenum sulfides, tin sulfides, with zero-, one-, two-, and three-dimensional morphologies for LIB and SC applications. In addition, the recently emerged concept of incorporating conductive matrices, especially graphene, with metal sulfide nanomaterials will also be highlighted. Finally, some remarks are made on the challenges and perspectives for the future development of metal sulfide-based LIB and SC devices.

Nanostructured metal sulfides for energy storage

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

Compound Copper Chalcogenide Nanocrystals

Nanostructured transition metal sulfides for lithium ion batteries: Progress and challenges

The polyhedral CoS2 with a narrow size distribution was synthesized by a facile solid-state assembly process in a sealed silica tube. The flux of potassium halide (KX; X = Cl, Br, I) plays a crucial role in the formation of polyhedrons and the size distribution. The S22– groups in CoS2 can be controllably withdrawn during heat treatment in air. The obtained phases and microstructures of CoS2, Co3S4, CoS, Co9S8, and CoO depended on heating temperature and time. These cobalt materials, successfully used as the electrodes of lithium ion batteries, possessed good cycling stability in lithium ion batteries. The discharge capacities of 929.1 and 835.2 mAh g–1 were obtained for CoS2 and CoS respectively, and 76% and 71% of the capacities remained after 10 cycles. High capacities and good cycle performance make them promising candidates for lithium ion batteries. The approach combining solid-state assembly and heat treatment provides a simple and versatile way to prepare various metal chalcogeides for energy stor...

Phase-Controlled Synthesis of Cobalt Sulfides for Lithium Ion Batteries

Nanostrcutured particles and polycrystalline thin films of Sn-doped chalcopyrite are synthesized by newly-developed methods. Surprisingly, Sn doping introduces a narrow partially filled intermediate band (IB) located ~1.7 eV (CuGaS2) and ~0.8 eV (CuInS2) above the valance band maximum in the forbidden band gap. Diffuse reflection spectra and photoluminescence spectra reveal extra absorption and emission spectra induced by the IBs, which are further supported by first-principle calculations. Wide spectrum solar response greatly enhances photocatalysis, photovoltaics, and photo-induced hydrogen production due to the intermediate band.

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Observation of an Intermediate Band in Sn-doped Chalcopyrites with Wide-spectrum Solar Response

An intermediate-band (IB) semiconductor CuGa1−xCrxS2 was investigated by the self-consistent many-body GW approach (scGW) and further confirmed by the experimental results. The Cr dopant introduced a partially occupied IB, and the density-of-states analysis indicates the electron transfer between the impurities and host lattice would suppress the non-radiative recombination. The CuGa1−xCrxS2 was synthesized by a high-temperature solid-state reaction and the X-ray photoelectron spectroscopy (XPS) indicated the presence of Cr3+. Due to the Cr dopant, two additional absorption responses were directly observed in the UV–Vis–NIR absorption spectrum. The further photocatalytic investigations verified the IB absorptions could produce highly mobile electrons and holes to degrade dyes. This material leads to lower-energy photon absorption, which could be a promising candidate for the high-efficiency solar cells.

Cr incorporation in CuGaS2 chalcopyrite: A new intermediate-band photovoltaic material with wide-spectrum solar absorption

The indium thiospinels In2S3 and MgIn2S4 are promising host for the intermediated band (IB) photovoltaic materials due to their ideal band gap value. Here, the optical properties and electronic structure of Fe-doped In2S3 and MgIn2S4 have been investigated. All the Fe-substituted semiconductors exhibit two additional absorption bands at about 0.7 and 1.25 eV, respectively. The results of first-principles calculations revealed that the Fe substituted at the octahedral In site would introduce a partially filled IB into the band gap. Thanks to the formation of IB, the Fe-substituted semiconductors have the ability to absorb the photons with energies below the band gap. With the wide-spectrum absorption of solar energy, these materials possess potential applications in photovoltaic domain.

Fe-substituted indium thiospinels: New intermediate band semiconductors with better absorption of solar energy

A simple, safe, and clean molecular precursor-based solution method was developed to fabricate a Cu(In,Ga)(S,Se)2 absorber layer. Low-cost and versatile thioacetic acid was deployed as an effective solvent and suitable sulfur source to dissolve the starting materials, generating a high power conversion efficiency of 8.6% in the final cell.

Mingsheng Qin

Papers

Phase-Controlled Synthesis of Cobalt Sulfides for Lithium Ion Batteries

Observation of an Intermediate Band in Sn-doped Chalcopyrites with Wide-spectrum Solar Response

Cr incorporation in CuGaS2 chalcopyrite: A new intermediate-band photovoltaic material with wide-spectrum solar absorption

Fe-substituted indium thiospinels: New intermediate band semiconductors with better absorption of solar energy

A facile molecular precursor-based Cu(In,Ga)(S,Se)2 solar cell with 8.6% efficiency