Suitable Morphology Makes CoSn(OH)6 Nanostructure a Superior Electrochemical Pseudocapacitor

Perovskite CoSn(OH)6 nanocubes with tuned d-band states towards enhanced oxygen evolution reactions

The CoSn(OH)6 perovskite hydroxide is a structure stable and inexpensive electrocatalyst for the oxygen evolution reaction (OER). However, the OER activity of CoSn(OH)6 is still unfavorable due to its limited active sites. In this work, an Fe3+ doping strategy is used to optimize the d-band state of the CoSn(OH)6 perovskite hydroxide. The CoSn(OH)6 catalyst with slightly Fe3+ doped nanocubes is synthesized by a facile hydrothermal method. Structure characterization shows that Fe3+ ions are incorporated into the crystal structure of CoSn(OH)6. Owing to the regulation of the electronic structure, CoSn(OH)6-Fe1.8% exhibits an OER overpotential of 289 mV at a current density of 10 mA cm-2 in OER electrochemical tests. In situ Raman spectroscopy shows that no obvious re-construction occurred during the OER for both CoSn(OH)6 and CoSn(OH)6-Fe1.8%. DFT calculations show that the introduction of Fe3+ into CoSn(OH)6 can shift the d-band center to a relatively high position, thus promoting the OER intermediates' adsorption ability. Further DFT calculations suggest that incorporation of an appropriate amount of Fe3+ into CoSn(OH)6 significantly reduces the rate-determining Gibbs free energy during the OER. This work offers valuable insights into tuning the d-band center of perovskite hydroxide materials for efficient OER applications.

Stable CO2reduction under natural air on Ni-Sn hydroxide photocatalyst with dynamic renewable oxygen vacancies

Advanced photocatalysts are highly desired to activate the photocatalytic CO2reduction reaction (CO2RR) with low concentration. Herein, the NiSn(OH)6with rich surface lattice hydroxyls was synthesized to boost the activity directly under the natural air. Results showed that terminal Ni-OH could serve as donors to feed protons and generate oxygen vacancies (VO), thus beneficial to convert the activated CO2(HCO3-) mainly into CO (5.60μmol g-1) in the atmosphere. It was flexible and widely applicable for a stable CO2RR from high pure to air level free of additionally adding H2O reactant, and higher than the traditional gas-liquid-solid (1.58μmol g-1) and gas-solid (4.07μmol g-1) reaction system both using high pure CO2and plenty of H2O. The strong hydrophilia by the rich surface hydroxyls allowed robust H2O molecule adsorption and dissociation at VOsites to achieve the Ni-OH regeneration, leading to a stable CO yield (11.61μmol g-1) with the enriched renewable VOregardless of the poor CO2and H2O in air. This work opens up new possibilities for the practical application of natural photosynthesis.

Tailoring the Hollow Structure within CoSn(OH)6 Nanocubes for Advanced Supercapacitors

The enhanced application performance of hollow-structured materials is attributed to their large surface area with more active sites. In this work, the hollow CoSn(OH)₆ nanocubes with increased surface area and mesopores were derived from dense CoSn(OH)₆ nanocube precursors by alkaline etching. As a result, the hollow CoSn(OH)₆ nanocubes-based cathode electrode exhibited a higher area-specific capacitance of 85.56 µF cm^-2 at 0.5 mA cm^-2 and a mass-specific capacitance of 5.35 mF g^-1 at 0.5 mA cm^-2, which was more extensive than that of the dense precursor. Meanwhile, the current density was increased 4-fold with good rate capability for hollow CoSn(OH)₆ nanocubes.

Durable and eco-friendly peroxymonosulfate activation over cobalt/tin oxides-based heterostructures for antibiotics removal: Insight to mechanism, degradation pathway

Potential leaching of Co ions could decrease the catalytic activity and cause secondary pollution of water, thereby threatening ecological safety and human health. In response, the in-situ generation of well-dispersed Co₂SnO₄ and SnO₂ with fine interfacial feature was constructed for PMS activation toward efficient tetracycline degradation and lower cobalt ion leaching feature. The synergistic effect of Co₂SnO₄ and SnO₂ endowed Co₂SnO₄-SnO₂ an outstanding catalytic performance for tetracycline degradation in alkaline condition. Meanwhile, the catalysts can effectively degrade the quinolones, dyes and mixture pollutant solution. The excellent performance can attributed to the in-situ introduction of SnO₂, which stabilizes the microstructure and provides an effective electronic pathway to enhance the activity of Co₂SnO₄ in the Co₂SnO₄-SnO₂. In optimized condition, the tetracycline degradation efficiency was enhanced to 94.9% within 20 min and maintained the stability at least four cycles. The degradation rate constant of Co₂SnO₄-SnO₂ was 0.149 min^-1, which was about 1.93, 2.98, 11.5 times higher than of Co₂SnO₄, Co₃O₄ and SnO₂, respectively. Notably, the leaching performance of Co₂SnO₄-SnO₂ was greatly suppressed to be 7.45 ug/L, which was lower than that of Co₂SnO₄ (6.41 mg/L) and Co₃O₄ (1.12 mg/L). Radical quenching and EPR experiments showed that singlet oxygen (¹O₂), rather than hydroxyl active species and sulfate radicals, played a predominating role for PMS activation in the Co₂SnO₄-SnO₂/PMS system. The intermediates and degradation routes for tetracycline degradation were characterized by liquid chromatograph-tandem mass spectrometry. This study expected to provide a novel strategy to construct heterostructural catalysts with lower cobalt ion leaching for the activation of PMS.

Synthesis of a Co-Sn Alloy-Deposited PTFE Film for Enhanced Solar-Driven Water Evaporation via a Super-Absorbent Polymer-Based "Water Pump" Design

Solar-driven water evaporation is a promising solution to water pollution, the energy crisis, and water shortages. However, the approach in which the photothermal film is in direct contact with bulk water for water evaporation may lead to a large amount of heat loss, thereby reducing the light-to-heat conversion efficiency (η) of the photothermal film. Here, a highly efficient solar-driven water evaporation system was developed using a Co-Sn alloy-deposited Teflon (PTFE) film (Co-Sn alloy@PTFE) and super-absorbent polymers (SAPs) supported with a floating foam substrate. The Co-Sn alloy with full-spectrum (200-2500 nm) absorption characteristics is devoted to high light-to-heat conversion, while the porous PTFE with high mechanical performance can support the Co-Sn alloy. We used density functional theory to prove that the Co-Sn alloy had a strong adhesive force with PTFE without surfactants due to the high adsorption energy between the (101) crystal plane of the Co-Sn alloy and the hydroxyl group on the PTFE film. Importantly, via the SAP-based "water pump" design, we improved the η of the Co-Sn alloy@PTFE film to 89%, mainly because the SAP not only effectively performed water transportation but also markedly reduced the heat loss of the Co-Sn alloy@PTFE film. Our work highlights the strong potential of Co-Sn alloy@PTFE-based light-to-heat conversion systems for realizing highly effective solar energy-driven water evaporation.

Simple synthesis of CoSn(OH)6 nanocubes for the rapid electrochemical determination of rutin in the presence of quercetin and acetaminophen

Schematic presentation of the synthesis of CoSn(OH)₆ nanocubes modified with SPCE towards the electrochemical detection of rutin.

Rapid colorimetric determination of dopamine based on the inhibition of the peroxidase mimicking activity of platinum loaded CoSn(OH)6 nanocubes

Platinum nanoparticles were loaded on CoSn(OH)6 nanocubes via a co-precipitation method. The material (NCs) is shown to be a viable peroxidase mimic that catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by hydrogen peroxide (H₂O₂) to generate oxidized TMB (oxTMB) with absorption at 652 nm. The formation of the blue color can be observed in <30 s. Thus, a visual and colorimetric assay was worked out for H₂O₂. It has a detection limit as low as 4.4 μM and works in the 5 to 200 μM concentration range. The method was also used to detect dopamine (DA) which is found to inhibit the enzyme mimicking activity of the NCs. Hence, less blue color is formed in its presence. The respective DA assay has a linear response in the 5.0 to 60 μM concentration range and a 0.76 μM detection limit. Graphical abstractSchematic diagram of a visual colorimetric method for determination of H₂O₂ and dopamine (DA) with the aid of color change of 3,3',5,5'-tetramethylbenzidine (oxTMB), based on the peroxidase-like activity of Pt/CoSn(OH)₆ nanocubes.

Nonsiliceous Mesoporous Materials: Design and Applications in Energy Conversion and Storage

In this work, the progress in the design of nonsiliceous mesoporous materials (nonSiMPMs) over the last five years from the perspectives of the chemical composition, morphology, loading, and surface modification is summarized. Carbon, metal, and metal oxide are in focus, which are the most promising compositions. Then, representative applications of nonSiMPMs are demonstrated in energy conversion and storage, including recent technical advances in dye-sensitized solar cells, perovskite solar cells, photocatalysts, electrocatalysts, fuel cells, storage batteries, supercapacitors, and hydrogen storage systems. Finally, the requirements and challenges of the design and application of nonSiMPMs are outlined.

A cabbage leaf like nanostructure of a NiS@ZnS composite on Ni foam with excellent electrochemical performance for supercapacitors

In the present study, a NiS@ZnS composite nanostructure was synthesized on a nickel foam substrate by a facile chemical bath deposition (CBD) method.

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using in situ activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V vs Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ -0.8 V vs Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities.

Superior charge storage performance of WS2 quantum dots in a flexible solid state supercapacitor

Defect induced enhanced charge storage performance of WS₂ quantum dots in a flexible solid state supercapacitor.

Advance Aqueous Asymmetric Supercapacitor Based on Large 2D NiCo2O4 Nanostructures and the rGO@Fe3O4 Composite

NiCo₂O₄ nanostructure is a widely studied pseudocapacitor material because of its high specific capacitance value. Most of the time, the thickness of the nanostructure inhibits the electrode material from whole-body participation and causes sluggish charge transportation. These phenomena directly interfere with the electrochemical performance of the electrode, such as specific capacitance value, stability, energy density, and so forth. Here, two different thin two-dimensional morphologies (nanosheet and nanoplate) of the NiCo₂O₄ nanocomposite with a large lateral size are reported using ammonia as a hydrolyzing agent. The large size and flat surface of the as-synthesized materials offer enormous active sites during the electrochemical reaction, and the thin wall makes the ion penetration and transportation very effective and facile. Therefore, the NiCo₂O₄ nanosheet and nanoplate structures exhibited high specific capacitance values of 1540 and 1333 F/g, respectively, with excellent rate and good cycling stability. Here also, two different advance aqueous asymmetric supercapacitors have been reported utilizing two NiCo₂O₄ nanostructure materials as positive electrodes and the rGO@Fe₃O₄ composite as a negative electrode, which exhibited excellent rate and high specific energy without sacrificing the specific power. We also studied the electrochemical activity of the rGO@Fe₃O₄ composite at different compositions.

Electrical and Electrochemical Properties of Conducting Polymers

Conducting polymers (CPs) have received much attention in both fundamental and practical studies because they have electrical and electrochemical properties similar to those of both traditional semiconductors and metals. CPs possess excellent characteristics such as mild synthesis and processing conditions, chemical and structural diversity, tunable conductivity, and structural flexibility. Advances in nanotechnology have allowed the fabrication of versatile CP nanomaterials with improved performance for various applications including electronics, optoelectronics, sensors, and energy devices. The aim of this review is to explore the conductivity mechanisms and electrical and electrochemical properties of CPs and to discuss the factors that significantly affect these properties. The size and morphology of the materials are also discussed as key parameters that affect their major properties. Finally, the latest trends in research on electrochemical capacitors and sensors are introduced through an in-depth discussion of the most remarkable studies reported since 2003.

Facile Synthesis of Unique Hexagonal Nanoplates of Zn/Co Hydroxy Sulfate for Efficient Electrocatalytic Oxygen Evolution Reaction

Cost-effective, highly active water oxidation catalysts are increasingly being demanded in the field of energy conversion and storage. Herein, a simple modified hydrothermally (MHT) synthesized zinc and cobalt based hydroxyl double salt, that is, Zn_4-xCo_xSO₄(OH)₆·0.5H₂O (ZCS), has been exfoliated for the first time as an efficient electrocatalyst for oxygen evolution reaction (OER) in alkaline medium. Morphology investigation suggests the evolution of unique hexagonal nanoplates of ZCS material. As OER catalyst, it requires only 370 and 450 mV overpotential to achieve 10 and 100 mA cm^-2 current density, respectively. More importantly, performance at the overpotential over 400 mV and durability of the designed material have been found to be superior to those of commercial RuO₂ catalyst. In the designed ZCS material trace amounts of cobalt species lead to higher mass activity of 146 A g^-1, compared to that of the RuO₂ catalyst (83 A g^-1) at the same overpotential of 370 mV. The outstanding activity and stability of the cost-effective material emerges from the promotional effect of Zn ions, which are present as the principal constituent in the electrocatalyst, and they also protect the cobalt ions in the matrix during its long-term electrochemical test. It is important to note that an appropriate ratio of zinc and cobalt ions synergistically helps to create an economically viable and environmentally suitable electrocatalyst in comparison to other related transition metal based materials.

One step synthesis of Ni/Ni(OH)2 nano sheets (NSs) and their application in asymmetric supercapacitors

Ni/Ni(OH)₂ NSs were prepared by a facile hydrothermal method using EtOH as reducing agent. Asymmetric device is fabricated using AC and Ni/Ni(OH)₂ NSs as electrodes, with optimized specific capacitance of 62 F g⁻¹ and a maximum energy density of 23.45 W h kg⁻¹.

Photo-Fenton process in a Co(ii)-adsorbed micellar soft-template on an alumina support for rapid methylene blue degradation

Co(ii)-mediated photo-Fenton degradation of methylene blue was achieved for the first time on the admicellar layer supported on an alumina surface.

2D materials for renewable energy storage devices: Outlook and challenges

We review cost-effective, clean and durable alternative energy devices based on 2D materials.