Silk-derived nitrogen-doped porous carbon electrodes with enhanced ionic conductivity for high-performance supercapacitors

Flexible microcolumn array-based silk fibroin for sweat glucose monitoring

Flexible sweat sensors possess the special potential for continuous non-invasive monitoring of human blood glucose. We put forward a flexible microcolumn array sensor, which is designed for health monitoring by means of detecting glucose levels in sweat and capturing physiological signals related to human movement. With the combination of silk fibroin (SF), waterborne polyurethane (PU), and multi-walled carbon nanotubes (MWCNT), this microcolumn film electrode is able to effectively function as a strain sensor benefiting from the superior mechanical performance of PU. The obtained strain sensor exhibits a rapid response time of 0.3s and demonstrates robust stability over 500 cycles, efficiently capturing human pulse and hand movement signals. Prussian Blue (PB) is deposited on the surface of the microcolumn electrode and glucose oxidase (GOx) is sprayed to construct a glucose sensor that can accurately detect glucose in human sweat. The microcolumn array sensor shows and exhibits an excellent sensitivity of 35.28 μA/mM·cm2 within a dynamic range of 0.1-1 mM, and a limit of detection (LOD) of 0.004 mM, which reveals outstanding glucose sensing performance. This microcolumn array sensor demonstrates the potential of silk fibroin in crafting portable, high-performance electrochemical wearable medical devices.

Facile Synthesis of N-Doped Porous Carbon Materials Derived from Bombyx Mori Silk for High-Performance Symmetric Supercapacitors

Heteroatom doping and structural modification can significantly improve the electrochemical properties of carbon materials, but it is difficult to achieve synchronous control of the two. To this end, N-doped porous carbon material (BCNK) was synthesized using bombyx mori silk as carbon source, melamine and KHCO3 as activators. When only melamine is added, the prepared carbon material (BCN) only increases the heteroatom content. When only KHCO3 is added, the prepared carbon material (BCK) only increases the specific surface area and pore volume. The microstructure and heteratom content of carbon materials can be controlled simultaneously by adding two activators at the same time. Electrochemical tests show that the electrochemical performance of BCNK is higher than that of BCN and BCK. It is worth mentioning that the specific surface area of BCNK is much lower than that of BCK, and the heteroatom content is higher than that of BCK, indicating that increasing the heteroatom content is more conducive to achieving excellent electrochemical performance than increasing the specific surface area. This study not only provides a new way for the application of silk in supercapacitors, but also enables researchers to re-understand the relationship between the structure and electrochemical properties of carbon materials.

Efficient Extraction of Phenols from Coal Tar and Preparation of Phenolic Resin-Based Porous Carbon for Advanced Supercapacitor Application

Developing simple and efficient extraction methods for phenolic substances from coal tar, which facilitate their direct transformation into high-performance electrode materials, holds considerable practical significance. In this study, amide-zinc chloride deep eutectic solvents are employed for efficient phenol extraction. The optimal phenol extraction process is subsequently investigated, and it is found that the robust hydrogen bonding interactions between solvents and phenols significantly enhance extraction efficiency. Notably, without the need for back-extraction, formaldehyde and tetraethyl orthosilicate are added to obtain phenolic resin, which can subsequently be directly carbonized to fabricate hydrangea-like porous carbon. The carbonization mechanism of the phenolic resin is studied, and the templating and activating roles of tetraethyl orthosilicate and zinc chloride assist in the formation of this unique structure. Furthermore, the flexible supercapacitor assembled using the prepared porous carbon and gel electrolyte achieves a high energy density of 31.0 Wh kg-1 and demonstrates broad temperature applicability ranging from -25 to 100 °C. This work directly converts the extracted phenolic compounds into phenolic resin and shows potential for fabricating porous carbon materials with diverse structures and enhanced capacitive performance.

Ten-Million-Fold Increase in the Electrical Conductivity of a MOF by Doping of Iodine Into MOF Integrated Mixed Matrix Membrane

The development of electrically conductive membranes is essential for advancing future technologies like electronic devices, supercapacitors, and batteries. Newly synthesized doubly interpenetrated 3D-Cd-MOF (Metal-Organic-Framework) containing angular tetra-carboxylate is found to display very poor electrical conductivity (10-11 S cm-1). However, it exhibits an exceptional ability to adsorb I2 (I2@Cd-MOF) which shows increased electrical conductivity of the order of 10-8 S cm-1. Following these results, the Cd-MOF is integrated into the PVDF-PVP (Polyvinylidene fluoride-Polyvinylpyrrolidone) polymeric mixed matrix membrane (MMM) and explores their I2 adsorption capabilities and electrical conductivities before and after I2 adsorption. Four polymeric MMMs with the loading of Cd-MOF 0, 20, 40, and 50% are tested for their I2 adsorption ability and their respective electrical conductivities. The 50% Cd-MOF-loaded MMM is found to exhibit higher adsorption of I2 (685 mg g-1) and significant enhancement in conductivity from 10-11 to 10-4 S cm-1. The raise in the electrical conductivity by 10 million times is attributed to the synergistic interactions between I2, Cd-MOF, PVDF, and PVP polymers as well as the increase in the concentration of charge carriers (holes) within the frameworks. This work serves as blueprint for controlling charge transfer in MMM to tune their electrical conductivity which opens a large window for advanced device applications.

Development of 3D compound structures and highly wettable carbonate hydroxide electrodes for high-performance supercapacitors

A facile hydrothermal method was employed to fabricate tailored NiCo(CO3)(OH)2 electrodes for high-performance supercapacitors. Ni and Co ions, transition metals with versatile oxidation states, were used, promoting redox reactions. Additionally, a comparative analysis of the characteristics and electrochemical properties between electrodes fabricated with 3D Ni foam substrates and those without substrates was conducted. This comparison emphasizes the critical role of 3D substrate selection in enhancing electrochemical performance during electrode fabrication. Furthermore, carbonate/hydroxide-based transition metal electrodes have been fabricated. Carbonate-based transition metals can substantially increase the wettability of the electrode surface due to their hydrophilicity, which has proven beneficial in aqueous electrolytes. The NiCo(CO3)(OH)2 electrodes with Ni foam substrates and without Ni foam substrates exhibit impressive specific capacitances of 2576.4 and 1460.2 F g-1, respectively, at 3 A g-1. Furthermore, an asymmetric supercapacitor configuration is introduced, utilizing the NiCo(CO3)(OH)2 electrode with a Ni foam substrate and graphene as positive and negative electrodes, respectively. A remarkable energy density of 35.5 W h kg-1 and a power density of 2555.6 W kg-1 at a current density of 2 A g-1 are exhibited by this configuration. Notably, excellent cycling stability is displayed by the asymmetric supercapacitor, with approximately ∼71.3% of its capacity retained after 10 000 cycles. These results highlight the promising potential of the fabricated electrodes and asymmetric supercapacitor configuration for practical energy storage applications.

In-situ synthesized and induced vertical growth of cobalt vanadium layered double hydroxide on few-layered V2CTx MXene for high energy density supercapacitors

Two-dimensional (2D) MXene nanomaterials display great potential for green energy storage. However, as a result of self-stacking of MXene nanosheets and the presence of conventional binders, MXene-based nanomaterials are significantly hindered in their rate capability and cycling stability. We successfully constructed a self-supported stereo-structured composite (TMA-V2CTx/CoV-LDH/NF) by in-situ growing 2D cobalt vanadium layered double hydroxide (CoV-LDH) vertically on 2D few-layered V2CTx MXene nanosheets and interconnecting it with Ni foam (NF) with a self-supported structure to act as a binder-free electrode. In addition to inhibiting CoV-LDH aggregation, the highly conductive V2CTx MXene and CoV-LDH work synergistically to improve charge storage. The specific capacitance of the TMA-V2CTx/CoV-LDH/NF electrode is 2374 F/g (1187 C/g) at 1 A/g. At the same time, the TMA-V2CTx/CoV-LDH/NF exhibits excellent stability, retaining 85.3 % of its specific capacitance at 20 A/g after 10,000 cycles. In addition, the hybrid supercapacitor (HSC) is assembled based on positive electrode (TMA-V2CTx/CoV-LDH/NF) and negative electrode (AC), achieving the maximum energy density of 74.4 Wh kg-1 at 750.3 W kg-1. TMA-V2CTx/CoV-LDH/NF has potential as an electrode material for storing green energy. The research strategy provides a development prospect for the construction of novel V2CTx MXene-based electrode material with self-supported structures.

Biomass-based controllable morphology of carbon microspheres with multi-layer hollow structure for superior performance in supercapacitors

The electrochemical properties of corn starch (CS)-based hydrothermal carbon microsphere (CMS) electrode materials for supercapacitor are closely related to their structures. Herein, cetyltrimethyl ammonium bromide (CTAB) was used as a soft template to form the corn starch (CS)-based carbon microspheres with radial hollow structure in the inner and middle layers by hydrothermal and sol-gel method. Due to the introduction of multi-layer hollow structure of carbon microsphere, more micropores were produced during CO2 activation, which increased the specific surface area and improved the capacitance performance. Compared to commercial activated carbon, the four different morphologies of corn starch CMS had better electrochemical performances. Consequently, the proposed CO2-(CTAB)-CS-CS exhibits a high discharge specific capacitance of 242.5F/g at 1 A/g in three-electrode system with 6 M KOH electrolyte, better than commercial activated carbon with 208.5F/g. Moreover, excellent stability is achieved for CO2-(CTAB)-CS-CS with approximately 97.14 % retention of the initial specific capacitance value after 10,000 cycles at a current density of 2 A/g, while the commercial activated carbon has 86.96 % retention. This implies that the corn starch-based multilayer hollow CMS could be a promising electrode material for high-performance supercapacitors.

MOF-derived NiAl2O4/NiCo2O4 porous materials as supercapacitors with high electrochemical performance

Metal-organic framework compounds are extensively utilized in various fields, such as electrode materials, owing to their distinctive porous structure and significant specific surface area. In this study, NiCoAl-MOF metal-organic framework precursors were synthesized by a solvothermal method, and NiAl2O4/NiCo2O4 electrode materials were prepared by the subsequent calcination of the precursor. These materials were characterized by XRD, XPS, BET tests, and SEM, and the electrochemical properties of the electrode materials were tested by CV and GCD methods. BET tests showed that NiAl2O4/NiCo2O4 has an abundant porous structure and a large specific surface area of up to 105 m2 g-1. The specific capacitance of NiAl2O4/NiCo2O4 measured by the GCD method reaches up to 2870.83 F g-1 at a current density of 1 A g-1. The asymmetric supercapacitor NiAl2O4/NiCo2O4//AC assembled with activated carbon electrodes has a maximum energy density of 166.98 W h kg-1 and a power density of 750.00 W kg-1 within a voltage window of 1.5 V. In addition, NiAl2O4/NiCo2O4 materials have good cycling stability. These advantages make it a good candidate for the application of high-performance supercapacitors.

Laser-induced transient conversion of rhodochrosite/polyimide into multifunctional MnO2/graphene electrodes for energy storage applications

Laser-induced graphene (LIG) has been extensively investigated for electrochemical energy storage due to its easy synthesis and highly conductive nature. However, the limited charge accumulation in LIG usually leads to significantly low energy densities. In this work, we report a novel strategy to directly transform natural rhodochrosite into ultrafine manganese dioxide (MnO2) nanoparticles (NPs) in the polyimide (PI) substrate for high-performance micro-supercapacitors (MSCs) and lithium-ion batteries (LIBs) through a scalable and cost-effective laser processing method. Specifically, laser treatment on rhodochrosite/polyimide precursors induces the thermal explosion, which splits rhodochrosite (10 μm) into MnO2 NPs (12-16 nm) on the carbon matrix of LIG due to the sputtering effect. Benefiting from largely exposed active sites from the ultrafine MnO2 and the synergetic effect from highly conductive LIG, the MnO2/LIG MSCs show a high specific capacitance of 544.0 F g-1 (154.3 mF cm-2; 14.16 F cm-3) at 3 A/g and 82.1% capacitance retention after 10,000 cycles at 5A/g, in contrast to pure LIG (<100 F g-1). Moreover, the MnO2/LIG-based LIBs show the highest reversible discharge capacity of ∼1097 mAh g-1 at 0.2 A/g and ∼ 866.4 mAh g-1 at 1.0 A/g. This study opens a new route for synthesizing novel LIG-based composites from natural minerals.

One stone for four birds: A "chemical blowing" strategy to synthesis wood-derived carbon monoliths for high-mass loading capacitive energy storage in low temperature

Biomass-derived carbon materials are promising electrode materials for capacitive energy storage. Herein, inspired by the hierarchical structure of natural wood, carbon monoliths built up by interconnected porous carbon nanosheets with enriched vertical channels were obtained via zinc nitrate (Zn(NO3)2)-assisted synthesis and served as thick electrodes for capacitive energy storage. Zn(NO3)2 is proved to function as expansion agent, activator, dopant, and precursor of the template. The dense and micron-scale thickness walls of wood were expanded by Zn(NO3)2 into porous and interconnected nanosheets. The pore volume and specific surface area were increased by more than 430 %. The initial specific capacitance and rate performance of the optimized carbon monolith was approximately three times that of the pristine dense carbon framework. The assembled symmetric supercapacitor possessed a high initial specific capacitance of 4564 mF cm-2 (0-1.7 V) at -40 °C. Impressively, the robust device could be cycled more than 100,000 times with little capacitance attenuation. The assembled zinc-ion hybrid capacitor (0.2-2 V) delivered a large specific capacitance of 4500 mF cm-2 at -40 °C, approximately 74 % of its specific capacitance at 25 °C. Our research paves a new avenue to design thick carbon electrodes with high capacitive performance by multifunctional Zn(NO3)2 for low-temperature applications.

In-situ electrodeposited Co0.85Se@Ni3S2 heterojunction with enhanced performance for supercapacitors

Rational design of porous heterostructured electrode materials for high-performance supercapacitors remains a big challenge. Herein, we report the in situ synthesis of Co0.85Se@Ni3S2 hybrid nanosheet arrays supported on carbon cloth (CC) substrate though an efficient two-step electrodeposition method. Compared with pure Co0.85Se and Ni3S2, the well-defined Co0.85Se@Ni3S2 heterojunction possesses enriched active sites, improved electrical conductivity, and reduced ion diffusion resistance. Benefiting from its hierarchically porous nanostructure and the synergistic effect of Co0.85Se and Ni3S2, the as-synthesized Co0.85Se@Ni3S2 electrode delivers a gravimetric capacitance (Cg)/volumetric capacitance (Cv) of 1644.1F g-1/3161.7F cm-3 at 1 A g-1, outstanding rate capability of 60.7% capacitance retention at 20 A g-1, as well as good cycling performance of 87.8% capacitance retention after 5000 cycles. Additionally, a hybrid supercapacitor (HSC) device presents a maximum energy density (E) of 65.7 Wh kg-1 at 696.2 W kg-1 with 93.3% cyclic durability after 15,000 cycles. Thus, this work proposes a simple and effective strategy to fabricate porous heterojunctions as high-performance electrode materials for energy storage devices.

Recent advances in biopolymers-based carbon materials for supercapacitors

Supercapacitors as potential candidates for novel green energy storage devices demonstrate a promising future in promoting sustainable energy supply, but their development is impeded by limited energy density, which can be addressed by developing high-capacitance electrode materials with efforts. Carbon materials derived from biopolymers have received much attention for their abundant reserves and environmentally sustainable nature, rendering them ideal for supercapacitor electrodes. However, the limited capacitance has hindered their widespread application, resulting in the proposal of various strategies to enhance the capacity properties of carbon electrodes. This paper critically reviewed the recent research progress of biopolymers-based carbon electrodes. The advances in biopolymers-based carbon electrodes for supercapacitors are presented, followed by the strategies to improve the capacitance of carbon electrodes which include pore engineering, doping engineering and composite engineering. Furthermore, this review is summarized and the challenges of biopolymer-derived carbon electrodes are discussed. The purpose of this review is to promote the widespread application of biopolymers in the domain of supercapacitors.

Facile Synthesis of Functionalized Porous Carbon by Direct Pyrolysis of Anacardium occidentale Nut-Skin Waste and Its Utilization towards Supercapacitors

Preparing electrode materials plays an essential role in the fabrication of high-performance supercapacitors. In general, heteroatom doping in carbon-based electrode materials enhances the electrochemical properties. Herein, nitrogen, oxygen, and sulfur co-doped porous carbon (PC) materials were prepared by direct pyrolysis of Anacardium occidentale (AO) nut-skin waste for high-performance supercapacitor applications. The as-prepared AO-PC material possessed interconnected micropore/mesopore structures and exhibited a high specific surface area of 615 m² g^-1. The Raman spectrum revealed a moderate degree of graphitization of AO-PC materials. These superior properties of the as-prepared AO-PC material help to deliver high specific capacitance. After fabricating the working electrode, the electrochemical performances including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy measurements were conducted in 1 M H₂SO₄ aqueous solution using a three-electrode configuration for supercapacitor applications. The AO-PC material delivered a high specific capacitance of 193 F g^-1 at a current density of 0.5 A g^-1. The AO-PC material demonstrated <97% capacitance retention even after 10,000 cycles of charge-discharge at the current density of 5 A g^-1. All the above outcomes confirmed that the as-prepared AO-PC from AO nut-skin waste via simple pyrolysis is an ideal electrode material for fabricating high-performance supercapacitors. Moreover, this work provides a cost-effective and environmentally friendly strategy for adding value to biomass waste by a simple pyrolysis route.