A hierarchical CoFeS2/reduced graphene oxide composite for highly efficient counter electrodes in dye-sensitized solar cells

3D graphene: synthesis, properties, and solar cell applications

Three-dimensional (3D) graphene is one of the most important nanomaterials. This feature article highlights the advancements, with an emphasis on contributions from our group, in the synthesis of 3D graphene-based materials and their utilization in solar cells. Chemistries of graphene oxides, hydrocarbons, and alkali metals are discussed for the synthesis of 3D graphene materials. Their performances in dye-sensitized solar cells and perovskite solar cells (as counter electrodes, photoelectrodes, and electron extracting layers) were correlatively analyzed with their properties/structures (accessible surface area, electrical conductivity, defects, and functional groups). The challenges and prospects for their applications in photovoltaic solar cells are outlined.

Freestanding Binder-Free Electrodes with Nanodisk-Needle-like MnCuCo-LTH and Mn1Fe2S2 Porous Microthorns for High-Performance Quasi-Solid-State Supercapacitors

Transition-metal-based layered triple hydroxides (LTHs) are evolving as potential positrode candidates for high-performance supercapacitors; however, their phase stabilization is still critical. Alongside, the availability of limited negatrodes pushes research toward exploring novel alternatives in order to minimize performance limitation issues in the fabricated supercapacitors. Herein, a facile strategy for stabilizing freestanding MnCuCo-LTH-based positrode possessing intermingled nanodisk-needle-like morphology is reported. Alongside, novel high-surface-area negatrodes based on Mn₁Fe₂S₂ exhibiting porous microthorn-like morphology are also optimized. MnCuCo_LTH and Mn₁Fe₂S₂ exhibit remarkably high specific capacities of ∼494 mAh g^-1 (∼2540 F g^-1) and ∼429 mAh g^-1 (∼1546 F g^-1), respectively, at 1 A g^-1. The fabricated quasi-solid-state supercapacitor equipped with a poly(vinyl alcohol) (PVA)-KOH gel electrolyte displays a high specific capacity of ∼144 mAh g^-1 and a specific capacitance of ∼325 F g^-1 at 1 A g^-1. The ultrahigh energy cum power traits of ∼105 Wh kg^-1 (1 A g^-1) and ∼8370 W kg^-1 (at 10 A g^-1) establish an asymmetric supercapacitor as a high-performance energy storage device. This device shows an appreciably high cycling life with a capacitance retention of ∼93% after 10 000 consecutive cycles, at 10 A g^-1. This approach provides a neoteric foresight for developing high-performance advanced energy storage devices equipped with cheaper and eco-friendly components.

Applications of Ceramic/Graphene Composites and Hybrids

Research activity on ceramic/graphene composites and hybrids has increased dramatically in the last decade. In this review, we provide an overview of recent contributions involving ceramics, graphene, and graphene-related materials (GRM, i.e., graphene oxide, reduced graphene oxide, and graphene nanoplatelets) with a primary focus on applications. We have adopted a broad scope of the term ceramics, therefore including some applications of GRM with certain metal oxides and cement-based matrices in the review. Applications of ceramic/graphene hybrids and composites cover many different areas, in particular, energy production and storage (batteries, supercapacitors, solar and fuel cells), energy harvesting, sensors and biosensors, electromagnetic interference shielding, biomaterials, thermal management (heat dissipation and heat conduction functions), engineering components, catalysts, etc. A section on ceramic/GRM composites processed by additive manufacturing methods is included due to their industrial potential and waste reduction capability. All these applications of ceramic/graphene composites and hybrids are listed and mentioned in the present review, ending with the authors' outlook of those that seem most promising, based on the research efforts carried out in this field.

Biomass-derived carbon boosted catalytic properties of tungsten-based nanohybrids for accelerating the triiodide reduction in dye-sensitized solar cells

Manganese tungstate (MnWO₄), zinc tungstate (ZnWO₄), and copper tungstate (CuWO₄) embedded biomass-derived carbon (MWO-C, ZWO-C, CWO-C) was synthesized by hydrothermal treatment and investigated as counter electrode (CE) catalysts to test electrochemical activity. Biomass-derived carbon was used as the shape controlling agent, which changed the morphology of MWO from spherical to spindle-like. Owing to the synergistic effect between tungsten-based bimetal oxides and biomass-derived carbon, the MWO-C, ZWO-C, and CWO-C catalysts exhibited enhanced electrochemical performance in dye-sensitized solar cells (DSSCs) system. The MWO-C, ZWO-C and CWO-C catalysts in DSSCs showed outstanding power conversion efficiency (PCE) of 7.33%, 7.61%, and 6.52%, respectively, as compared with 7.04% for Pt based devices. Biomass-derived carbon improves the catalytic properties of tungsten-based nanohybrids. The results showed that biomass-derived carbon-enhanced inorganic compound as CE catalysts are promising alternatives to Pt-based CE catalysts for energy conversion devices.

Recent progress on nanostructured carbon-based counter/back electrodes for high-performance dye-sensitized and perovskite solar cells

Dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) favor minimal environmental impact and low processing costs, factors that have prompted intensive research and development. In both cases, rare, expensive, and less stable metals (Pt and Au) are used as counter/back electrodes; this design increases the overall fabrication cost of commercial DSSC and PSC devices. Therefore, significant attempts have been made to identify possible substitutes. Carbon-based materials seem to be a favorable candidate for DSSCs and PSCs due to their excellent catalytic ability, easy scalability, low cost, and long-term stability. However, different carbon materials, including carbon black, graphene, and carbon nanotubes, among others, have distinct properties, which have a significant role in device efficiency. Herein, we summarize the recent advancement of carbon-based materials and review their synthetic approaches, structure-function relationship, surface modification, heteroatoms/metal/metal oxide incorporation, fabrication process of counter/back electrodes, and their effects on photovoltaic efficiency, based on previous studies. Finally, we highlight the advantages, disadvantages, and design criteria of carbon materials and fabrication challenges that inspire researchers to find low cost, efficient and stable counter/back electrodes for DSSCs and PSCs.

Cobalt-based heterogeneous catalysts in an electrolyzer system for sustainable energy storage

Nowadays, the production of hydrogen and oxygen focuses on renewable energy techniques and sustainable energy storage. A substantial challenge is to extend low-cost electrocatalysts consisting of earth-abundant resources, prepared by straightforward approaches that display high intrinsic activity compared to noble metals. The expansion of bifunctional catalysts in alkaline electrolytes for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) has become very crucial in recent times. Herein, the recent progress in cobalt-based HER-OER electrocatalysts has been are brushed up and numerous bifunctional cobalt-based catalysts such as cobalt-oxides, phosphides, sulfides, selenides, nitrides, borides, carbides, perovskites, and MOF-based cobalt analogs have been investigated in detail. Specifically, much more attention has been paid to their structural variation, bifunctional activity, overpotential of the overall system, and stability. Cobalt-based catalysts with lower cell voltage, remarkable durability, and unique electronic structures, offer a new perspective in energy-related fields. In recent years, cobalt-based analogs with diagnostic facilities have been introduced due to their electronic structures, tunable d band structures, and tailorable active sites. This perspective also elucidates the present issues, promising ideas, and future forecasts for cobalt-based catalysts. The critical aspects of cobalt-based catalysts and the numerous opportunities, as discussed at the end, can possibly enrich the sustainable energy field.

Interconnected Vertically Stacked 2D-MoS2 for Ultrastable Cycling of Rechargeable Li-Ion Battery

A two-dimensional (2D) layer-structured material is often a high-capacity ionic storage material with fast ionic transport within the layers. This appears to be the case for nonconversion layer structure, such as graphite. However, this is not the case for conversion-type layered structure such as transition-metal sulfide, in which localized congestion of ionic species adjacent to the surface will induce localized conversion, leading to the blocking of the fast diffusion channels and fast capacity fading, which therefore constitutes one of the critical barriers for the application of transition-metal sulfide layered structure. In this work, we report the tackling of this critical barrier through nanoscale engineering. We discover that interconnected vertically stacked two-dimensional-molybdenum disulfide can dramatically enhance the cycling stability. Atomic-level in situ transmission electron microscopy observation reveals that the molybdenum disulfide (MoS₂) nanocakes assembled with tangling {100}-terminated nanosheets offer abundant open channels for Li⁺ insertion through the {100} surface, featuring an exceptional cyclability performance for over 200 cycles with a capacity retention of 90%. In contrast, (002)-terminated MoS₂ nanoflowers only retain 10% of original capacity after 50 cycles. The present work demonstrates a general principle and opens a new route of crystallographic design to enhance electrochemical performance for assembling 2D materials for energy storage.

Encapsulating CoS2–CoSe2 heterostructured nanocrystals in N-doped carbon nanocubes as highly efficient counter electrodes for dye-sensitized solar cells

The CoS₂–CoSe₂@N-doped carbon nanocubes were synthesized through simultaneous sulfurization and selenization of polydopamine coated Prussian blue analogs.