Hybrid MnO2 film with agarose gel for enhancing the structural integrity of thin film supercapacitor electrodes

Agarose Gel-Templating Synthesis of a 3D Wrinkled Graphene Architecture for Enhanced Supercapacitor Performance

The increasing use of rapidly fluctuating renewable energy sources, such as sunlight, has necessitated the use of supercapacitors, which are a type of energy storage system with high power. Chemically exfoliated graphene oxide (GO) is a representative starting material in the fabrication of supercapacitor electrodes based on reduced GO (rGO). However, the restacking of rGO sheets driven by π–π stacking interactions leads to a significant decrease in the electrochemically active surface area, leading to a loss of energy density. Here, to effectively inhibit restacking and construct a three-dimensional wrinkled structure of rGO (3DWG), we propose an agarose gel-templating method that uses agarose gel as a soft and removable template. The 3DWG, prepared via the sequential steps of gelation, freeze-drying, and calcination, exhibits a macroporous 3D structure and 5.5-fold higher specific capacitance than that of rGO restacked without the agarose template. Further, we demonstrate a “gel-stamping” method to fabricate thin-line patterned 3DWG, which involves the gelation of the GO–agarose gel within micrometer-sized channels of a customized polydimethylsiloxane (PDMS) mold. As an easy and low-cost manufacturing process, the proposed agarose gel templating method could provide a promising strategy for the 3D structuring of rGO.

Patterning Islandlike MnO2 Arrays by Breath-Figure Templates for Flexible Transparent Supercapacitors

Although plenty of active materials could be used as supercapacitor electrodes, only limited ones have been engineered to construct transparent supercapacitors. Specially, it is a great challenge to make opaque metal oxides, which often own high energy density, into transparent films. Here, we demonstrate a novel approach to fabricate transparent MnO₂ films for flexible transparent supercapacitors. By utilizing breath-figure polymer films with ordered pores as template, arrays of MnO₂ islands were electrochemically deposited, with high light transmission. The thickness and interspace distance of MnO₂ island arrays could be adjusted by tuning deposition time so that the capacitance and transparency of the electrodes are changed accordingly. Such island array structure can effectively eliminate the internal stress existing in the composite film to avoid cracks during bending operation. The assembled transparent supercapacitor shows a transmittance of 44% at 550 nm and can yield a high capacitance of 4.73 mF/cm² at a current density of 50 μA/cm², demonstrating high flexibility and stability.

A Natural Biopolymer Film as a Robust Protective Layer to Effectively Stabilize Lithium-Metal Anodes

Li metal is considered as an ideal anode for Li-based batteries. Unfortunately, the growth of Li dendrites during cycling leads to an unstable interface, a low coulombic efficiency, and a limited cycling life. Here, a novel approach is proposed to protect the Li-metal anode by using a uniform agarose film. This natural biopolymer film exhibits a high ionic conductivity, high elasticity, and chemical stability. These properties enable a fast Li-ion transfer and feasiblity to accomodate the volume change of Li metal, resulting in a dendrite-free anode and a stable interface. Morphology characterization shows that Li ions migrate through the agarose film and then deposit underneath it. A full cell with the cathode of LiFPO4 and an anode contaning the agarose film exhibits a capacity retention of 87.1% after 500 cycles, much better than that with Li foil anode (70.9%) and Li-deposited Cu anode (5%). This study provides a promising strategy to eliminate dendrites and enhance the cycling ability of lithium-metal batteries through coating a robust artificial film of natural biopolymer on lithium-metal anode.

Natural Triterpenoid-Tailored Phosphate: In Situ Reduction of Heavy Metals Spontaneously to Generate Electrochemical Hybrid Gels

In this work, we reported a biocompatible nature product-based soft material which could convert heavy metals to nanoparticles (NPs) in situ spontaneously in a simple step. We have designed and synthesized a natural triterpenoid-tailored phosphate (methyl glycyrrhetate phosphate (MGP)), and this amphiphilic MGP could form the stable hydrogel and extract gold salt from water, followed by spontaneous in situ AuNP formation without external reductants. Notably, the AuNPs were mainly localized on nanofibers instead of gel cavities, and the resulting MGP-AuNPs hybrid gel exhibited attractive electrocatalytic and conductive properties. In addition, as an efficient leaching extraction agent, MGP hydrogel showed higher affinity toward heavy metals over other common metals on account of the high reduction potential of heavy metals. Our work not only provides a novel yet simple way in generating electrochemical hybrid gels by in situ reduction of heavy metals spontaneously but also expands the application of nature product-based functional materials.

Promising biomass-derived hierarchical porous carbon material for high performance supercapacitor

High surface area, porous carbon materials were obtained from rice husk ash and exhibited good charge storage capacity.

Functional modification mediated value addition of seaweed polysaccharides – a perspective

Value addition of seaweed polysaccharides by their functional modification with various substrates leading to new effects.

Structural and electrochemical analysis of a novel co-electrodeposited Mn2O3–Au nanocomposite thin film

In this work we report the fabrication of both pristine Mn₂O₃ and Mn₂O₃–Au composite thin films on an indium tin oxide (ITO) substrate by a one-step novel co-electrodeposition technique.

Mesoporous CoO nanocubes @ continuous 3D porous carbon skeleton of rose-based electrode for high-performance supercapacitor

Supercapacitors have attracted lots of attentions for energy storage because of their outstanding electrochemical properties, and various kinds of carbon materials have been used to improve the performance. In this work, we innovatively elevate a natural rose-based continuous 3D porous carbon skeleton. The as-prepared carbon skeleton is graphited to some extent and possesses hierarchical interconnected 3D porous structures, providing a high electrical conductive and electrolyte easy-infiltrated substrate for the fabrication of ideal monolithic composite electrodes. Then, we utilized it as scaffold to prepare mesoporous CoO nanocubes @ continuous 3D porous carbon skeleton of rose composite-based electrode for supercapacitor via hydrothermal approach. The obtained material exhibits a noticeable pseudocapacitive performance with a brilliant capacitance of 1672 F/g at 1 A/g and as high as 521 F/g at 40 A/g. It also should be noted that ∼82% of the capacitance was maintained after 3000 cycles at 5 A/g, and only 40% capacitance loss after 1500 cycles at a relatively high current density of 10 A/g.

Solution synthesis of metal oxides for electrochemical energy storage applications

This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices.