Facile Synthesis of Graphite/PEDOT/MnO₂ Composites on Commercial Supercapacitor Separator Membranes as Flexible and High-Performance Supercapacitor Electrodes

A facile and low-cost method is presented to synthesize graphite/PEDOT/MnO₂ composites with controlled network structures on commercial supercapacitor separator (CSS) membranes for high-performance supercapacitors, in which pencil lead and a cellulose-based commercial supercapacitor separator membrane were applied as the graphite source and the flexible substrate, respectively. The dependence of PEDOT and MnO₂ loading on the structural formation, the electrochemical performance of the hybrid electrode, and the formation mechanism of MnO₂ nanowires are systematically investigated. The optimized electrode possesses a high areal capacitance of 316.4 mF/cm² at a scan rate of 10 mV/s and specific capacitance of 195.7 F/g at 0.5 A/g. The asymmetric supercapacitor device assembled using optimized CSS/Graphite/PEDOT/MnO₂ electrode and activated carbon electrode exhibits a high energy density of 31.4 Wh/kg at a power density of 90 W/kg and maintains 1 Wh/kg at 4500 W/kg. After 2000 cycles, the device retains 81.1% of initial specific capacitance, and can drive a mini DC-motor for ca. 10 s. The enhanced capability of the CSS-based graphite/PEDOT/MnO₂ network electrode has high potential for low-cost, high-performance, and flexible supercapacitors

Constructed Uninterrupted Charge-Transfer Pathways in Three-Dimensional Micro/Nanointerconnected Carbon-Based Electrodes for High Energy-Density Ultralight Flexible Supercapacitors

A type of freestanding three-dimensional (3D) micro/nanointerconnected structure, with a conjunction of microsized 3D graphene networks, nanosized 3D carbon nanofiber (CNF) forests, and consequently loaded MnO₂ nanosheets, has been designed as the electrodes of an ultralight flexible supercapacitor. The resulting 3D graphene/CNFs/MnO₂ composite networks exhibit remarkable flexibility and highly mechanical properties due to good and intimate contacts among them, without current collectors and binders. Simultaneously, this designed 3D micro/nanointerconnected structure can provide an uninterrupted double charges freeway network for both electron and electrolyte ion to minimize electron accumulation and ion-diffusing resistance, leading to an excellent electrochemical performance. The ultrahigh specific capacitance of 946 F/g from cyclic voltammetry (CV) (or 920 F/g from galvanostatic charging/discharging (GCD)) were obtained, which is superior to that of the present electrode materials based on 3D graphene/MnO₂ hybrid structure (482 F/g). Furthermore, we have also investigated the superior electrochemical performances of an asymmetric supercapacitor device (weight of less than 12 mg/cm² and thickness of ∼0.8 mm), showing a total capacitance of 0.33 F/cm² at a window voltage of 1.8 V and a maximum energy density of 53.4 W h/kg for driving a digital clock for 42 min. These inspiring performances would make our designed supercapacitors become one of the most promising candidates for the future flexible and lightweight energy storage systems

Role of Tungsten Doping on the Surface States in BiVO₄ Photoanodes for Water Oxidation: Tuning the Electron Trapping Process

The nanostructured BiVO₄ photoanodes were prepared by electrospinning and were further characterized by XRD, SEM, and XPS, confirming the bulk and surface modification of the electrodes attained by W addition. The role of surface states (SS) during water oxidation for the as-prepared photoanodes was investigated by using electrochemical, photoelectrochemical, and impedance spectroscopy measurements. An optimum 2% doping is observed in voltammetric measurements with the highest photocurrent density at 1.23 V_RHE under back side illumination. It has been found that a high PEC performance requires an optimum ratio of density of surface states (<i>N</i>_SS) with respect to the charge donor density (<i>N</i>_d), to give both good conductivity and enough surface reactive sites. The optimum doping (2%) shows the highest <i>N</i>_d and SS concentration, which leads to the high film conductivity and reactive sites. The reason for SS acting as reaction sites (i-SS) is suggested to be the reversible redox process of V⁵⁺/V⁴⁺ in semiconductor bulk to form water oxidation intermediates through the electron trapping process. Otherwise, the irreversible surface reductive reaction of VO₂⁺ to VO²⁺ though the electron trapping process raises the surface recombination. W doping does have an effect on the surface properties of the BiVO₄ electrode. It can tune the electron trapping process to obtain a high concentration of i-SS and less surface recombination. This work gives a further understanding for the enhancement of PEC performance caused by W doping in the field of charge transfer at the semiconductor/electrolyte interface