Electrochemical performance evaluation of tin oxide nanorod‐embedded woven carbon fiber composite supercapacitor

Tin oxide (SnO₂) nanorod (NR)‐fabricated composite capacitors have been developed by vacuum‐assisted resin transfer molding process. The NRs were synthesized on carbon fiber by following hydrothermal synthesis method. Such SnO₂ grown woven carbon fiber (WCF) capacitor that contains structural and energy storage functions saves system weight and volume; hence, it could offer benefits to electric vehicle, aerospace, and portable electric device industries. The SnO₂‐WCF was considered as electrode and exhibited enhanced surface area relative to bare WCF. Energy storage performances of SnO₂‐WCF capacitors were characterized by cyclic voltammetry, galvanostatic charge‐discharge, and electrochemical impedance spectroscopy measurements, and improved specific capacitance (0.148 F/g), energy density (15.06 mWh/kg), and power density (1.16 W/kg) were achieved at 30 mM of SnO₂ concentration. Hence, this study shows that the growth of SnO₂ NRs on WCF surfaces offers accessible surface area for electric charge and presented potential application of SnO₂‐WCF composites to energy storage industries.     

Compact energy storage: Opportunities and challenges of graphene for supercapacitors

碳纳米储能材料发展迅速,质量容量性能不断刷新。但通常碳纳米材料的密度较低,导致其体积比容量有限,在很多时候很难将材料水平上的优异性能反映到最终的器件上。发展高体积能量密度储能材料,在器件水平上实现致密储能,对推动储能材料和器件的实用化至关重要。作为其它sp2碳质材料的基本结构单元和一种柔性二维材料,石墨烯通过组装可以实现纳米结构致密化,在致密储能方面具有先天优势。本文以石墨烯在超级电容器中的应用为主,分别从材料、电极、器件3个层次讨论了实用化储能器件的设计原则,梳理了高体积能量密度碳基储能材料的研究进展,重点介绍了高体积容量碳电极材料的致密化设计理念,强调了从器件角度考虑储能材料设计的重要性,并对致密储能面临的机遇和挑战作了分析。     

Pinecone biomass-derived activated carbon: the potential electrode material for the development of symmetric and asymmetric supercapacitors

Activated carbon, from biomass (pinecone), was synthesized by conventional pyrolysis/chemical activation process and utilized for the fabrication of supercapacitor electrodes. The pinecone-activated carbon synthesized with 1:4 ratio of KOH (PAC4) showed an increase in surface area and pore density with a considerable amount of oxygen functionalities on the surface. Moreover, PAC4, as supercapacitor electrode, exhibited excellent electrochemical performances with specific capacitance value ∼185 Fg⁻¹ in 1 M H₂SO₄, which is higher than that of nonactivated pinecone carbon and 1:2 ratio KOH-based activated carbon (PAC2) (∼144 Fg⁻¹). The systematic studies were performed to design various forms of devices (symmetric and asymmetric) to investigate the effect of device architecture and operating voltage on the performance and stability of the supercapacitors. The symmetric supercapacitor, designed utilizing PAC4 in H₂SO₄ electrolyte, exhibited a maximum device-specific capacitance of 43 Fg⁻¹ with comparable specific energy/power and excellent stability (∼96% after 10 000 cycles). Moreover, a symmetric supercapacitor was specially designed using PAC4, as a positive electrode, and PAC2, as a negative electrode, under their electrolytic ion affinity, and which operates in aqueous Na₂SO₄ electrolyte for a wide cell voltage (1.8 V) and showed excellent supercapacitance performances. Also, a device was assembled with poly(3,4-ethylene dioxythiophene) (PEDOT) nanostructure, as positive electrode, and PAC4, as a negative electrode, to evaluate the feasibility of designing a hybrid supercapacitor, using polymeric nanostructure, as an electrode material along with biomass-activated carbon electrode.     

Rapid synthesis of chitin-based porous carbons with high yield,high nitrogen retention,and low cost for high-rate supercapacitors

It is a great challenge to simultaneously achieve high yield, high nitrogen retention, and low cost for chitin-based porous carbons (PCs) while obtaining highly porous structure. Herein, copper (II) chloride dihydrate (CuCl₂ 2H₂O) is innovatively used as the microwave absorber and also porogen for direct synthesis of PCs from chitin via microwave heating. A very short duration of 10 minutes is achieved for this synthesis, because microwave irradiation renders a rapid heating rate of 126°C min⁻¹ during the initial 5 minutes. In addition, the melted CuCl₂ wraps the chitin to preserve its overall structure during synthesis, thus obtaining a yield as high as 36% and a nitrogen retention up to 5.2%. Furthermore, a low temperature of about 600°C that triggers the redox reactions of CuCl₂ into Cu to achieve well-developed porous structure (specific surface area up to 1535 m² g⁻¹) is observed, suggesting a merit of low cost for this synthesis. The PC-based electrode exhibits not only a high specific capacitance of 227 F g⁻¹ at 0.5 A g⁻¹ in 6 mol L⁻¹ KOH electrolyte but also a good rate capability with a high capacitance retention of 67.7% even at an ultra-high current density of 50 A g⁻¹. Owing to these promising capacitive performances of PCs, the fabricated supercapacitor can remain 70.1% of the energy density when the power density was dramatically increased by 20 times.     

Preparation and photo-induced charge transfer of the composites based on 3D structural CdS nanocrystals and MEH-PPV

We report the synthesis of 3D structural CdS nanocrystals by a simple biomolecule-assisted hydrothermal process. The CdS nanocrystals are composed of many branched nanorods with the diameter of about 50 nm, and the length of about 250 nm. The phase and crystallographic properties are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffractometry (XRD). The composites based on CdS nanocrystals and poly[2-methoxy-5-(2-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) have been prepared by spin-coating of the mixture in the common solvent. The optical properties of the composites are investigated using ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectroscopies. A significant fluorescence quenching of MEH-PPV in the composites is observed at high CdS nanocrystals/MEH-PPV ratios, indicating that the photo-induced charge transfer occurred due to the energy level offset between the donor MEH-PPV and the acceptor CdS nanocrystals. The obvious photovoltaic behavior of the solar cell made from this composite further demonstrates the mentioned photo-induced charge transfer process.     

Effect of porosity and crack on the thermoelectric properties of expanded graphite/carbon fiber reinforced cement-based composites

Cement-based composites is a promising type of structural material, which has prospective applications in relieving the urban heat island effect in summer and melted snow with low energy consumption. However, the major drawbacks of cement-based composites are heterogeneity, porosity, and brittleness. Porosity and microcrack have considerable influence on the thermoelectric of cement-based composites applied in large-scale concrete structures in future. This paper studied in detail the effect of porosity and crack on thermoelectric properties of the cement-based composite. The proper pores and cracks in the cement matrix are advantageous to enhance the Seebeck effect, but meanwhile it also reduces the electrical conductivity. So combined with Seebeck effect, electrical conductivity and other factors, it can obtain a comparatively low electrical conductivity (0.063S cm⁻¹) of expanded graphite/carbon fiber reinforced cement-based composites (EG-CFRC), but EG-CFRC manifests the maximum thermoelectric figure of merit (ZT) has reached 2.22 × 10⁻⁷ when the porosity is 3.90%. With different porosity, the Seebeck effect of prepared EG-CFRC was strengthened when the crack existed. The effect is most pronounced by a factor of 2 when the porosity is 28.90%. Therefore, based on stabilizing the conductivity, the crack is fittingly made to have a good effect on the Seebeck coefficient.     

Recent progress in structural development and band engineering of perovskites materials for photocatalytic solar hydrogen production: A review

Photocatalytic water splitting for hydrogen production is a promising technology for the conversion of solar light to clean energy. In this perspective, several semiconductors have been under investigation, but they show less efficiency, selectivity and stability for hydrogen production. Recently, perovskites are most demanding due to their exceptional characteristics such as controlled structure and morphology, adjustable band structure, controlled valence state, adjustable oxidation state and visible light response. This review highlights structural classification of perovskites and band engineering for solar energy assisted photocatalytic hydrogen production. In the main stream, overview and fundamentals of perovskite materials for selective solar to hydrogen conversion are presented. The structural modification and band alteration to stimulate quantum efficiency and stability are specifically demonstrated. Photoactivity enhancement through metals, noble metals, non-metals doping, oxygen vacancies and fermi level adjustments are also deliberated. The role of perovskites with binary semiconductors towards hydrogen production has also been discussed. Up conversion effect of doping luminescent agents (Er, Ho, Eu, Nd) for improved photocatalytic activity by band gap narrowing is also deliberated. Various conventional and non-conventional synthesis methods for perovskites including solid-state, hydrothermal, sol-gel, co-precipitation, spray-freeze drying, microwave assisted, spray pyrolysis, low temperature combustion, pulse laser deposition and wet chemical method for enhanced photocatalytic activity are also demonstrated in this work. Finally, the key challenges and future directions for sustainable energy systems are also included.     

Recent advances in the US Department of Energy’s energy storage technology research and development programs for hybrid electric and electric vehicles

This paper provides an overview of recent advances in battery technology resulting from the Department of Energy’s (DOE’s) energy storage research and development (R&D) programs for hybrid electric vehicles (HEVs) and electrical vehicles (EVs). The DOE’s Office of Advanced Automotive Technologies (OAAT) is working with industry, national laboratories, universities, and other government agencies to develop technologies that will lead to a reduction in the petroleum used and the emissions generated by the transportation sector. The programs reviewed in this paper are focused on accelerating the development of energy storage technologies that are critical for the commercialization of HEVs and EV. These include the research conducted at DOE’s national laboratories to develop the high-power batteries needed for hybrid electric vehicles (HEVs) and the collaborative research with the US Advanced Battery Consortium (USABC) to develop the high-energy batteries needed for EVs.