Surface Charge Storage Research Articles

N, P co-doped hierarchical porous carbon from rapeseed cake with enhanced supercapacitance

Biomass shows great potential in synthesizing carbon materials for energy applications because of its renewability and low price. Rationally designing porous carbons with proper morphology and composition are beneficial to promoting its application in energy storage devices. Here, an environmentally friendly approach is proposed to prepare three-dimensional (3D) N, P co-doped hierarchical porous carbon (NP-HPC) for supercapacitors. The 3D cross-linked porous network not only promotes the infiltration of electrolytes, but also boosts the transportation of ion/electron. The high microporosity combined with heterogeneous doping provides more defects and active sites, improving the surface charge storage. Hence, the NP-HPC electrode achieves a high capacitance of 358 F g−1 at 0.05 A g−1 as well as good rate performance of 238 F g−1 at 50 A g−1. Moreover, NP-HPC-based all-solid-state supercapacitor exhibits a long lifespan over 10,000 cycles. The impressive performance of NP-HPC indicates the potential of biomass-derived porous carbons for supercapacitors through simultaneous morphology and doping engineering.

Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na2 Ti3 O7 in Na-Ion Batteries.

Na2Ti3O7 (NTO) is considered a promising anode material for Na‐ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na+/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na2Ti6O13. The enhanced electrochemical performance agrees with the higher Na+ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.

Quantum capacitance of supercapacitor electrodes based on germanene influenced by vacancy and co-doping: A first-principles study

Germanene with high volume/surface ratio similar to graphene is expected to be promising electrodes for supercapacitors. Based on first-principles method, the stability, quantum capacitance, and surface charge storage of vacancy-defected, doped and co-doped germanene were studied. The results suggested that the enhancement of quantum capacitance (CQ) by introducing of transition-metal dopants (Ti, Cr, Mn, and Co) were more effective than that of B/N/Al-dopants. Furthermore, the co-doped germanene exhibited higher quantum capacitance than single-doped, which also owned very high CQ at negative local potential and was potential used as cathode materials for supercapacitors. The presence of vacancy-defect improved the CQ of germanene, whereas the co-doped defected germanene can’t exhibit any advantages than co-doped prefect germanene. In other words, the co-doping is more effective than vacancy-defect to enhance the quantum capacitance of germanene.

Effect of the N/P/S and transition-metal co-doping on the quantum capacitance of supercapacitor electrodes based on mono- and multilayer graphene

The effect of co-dopants (N, P, and S) and transition metals (TMs = Ti, V, Cr, Mn, Co, Ni) presence in mono- and multilayer graphene on the final material geometry, stability, electrical and magnetic properties, and quantum capacitance was systematically investigated using density functional theory (DFT) calculations. The simultaneous presence of dopants and vacancies is more effective than doping alone in enlarging the quantum capacitance of graphene. Incorporation of N, P, and S co-dopants and TMs -dopants significantly improved the quantum capacitance and surface charge storage of graphene. The co-doping of Ti and N/P/S systems are the most outstanding, with the highest quantum capacitance of 239.84 μF/cm2. However, due to the interaction between layers, the quantum capacitance of multilayered co-doped graphene is lower than the capacitance of similarly-doped monolayered graphene. The results demonstrated in this work provide insights on the effective approach of the quantum capacitance enhancement of graphene-based supercapacitor.

Effect of coexistence of defect and dopant on the quantum capacitance of graphene-based supercapacitors electrodes

The influence of doping (B, N, Al, Si, P, S), vacancy, and Stone-Wales defect on stability, electronic structures, quantum capacitance, and surface charge storage of graphene is explored by density functional theory calculations. The results indicate that the quantum capacitance and surface charge storage can be significantly improved by the introducing of defect and doping. Furthermore, the enhancement of doped vacancy-defected graphene is more obvious than that of doped Stone-Wales defected graphene. By analyzing the density of states, it can be obtained that the improvement of quantum capacitance is resulted from the presence of localized states around Fermi level by doping or defect. Moreover, the effect of concentration of doping and defect on the graphene is also explored, and the results suggest that the quantum capacitance increases with the increasing of concentration for most modified graphene-based substrates. The findings can provide effective approach for improving the performance of graphene-based surpercapacitors.

Quantitative Characterization of Pseudocapacitance on Carbon-Based Active Electrode Materials

A pseudocapacitive reaction (PCR) is a surface and/or near surface charge storage behavior accompanying a charge transfer between a guest ion and host active material. The surface induced charge transfer reaction is very fast and stable, because it occurs without solid-state-diffusion of the guest ion and volume changes in the active materials. In addition, a large amount of charge surpassing that gathered from electrochemical double layer (EDL) formation can be stored by PCRs. The more compelling characteristic of the PCR is its collaborative charge storage phenomenon coinciding with EDLs. When the PCR occurs on nanoporous carbon (NPC)-based electrode materials, a drastic improvement in capacity can be achieved with preservation of their intrinsic characteristics that arise from the storage nature of the surface-driven charge. Several reports have demonstrated the superiority of NPCs with PCRs, detailing their significantly high electrochemical performances as active electrode materials for Li and Na ion batteries as well as supercapacitors. Nevertheless, there is little information for the chemisorption-based alkali cation storage behaviors on NPCs. Moreover, there is no method to characterize the level of contribution of the PCR and EDL capacitance, limiting deeper understanding of the PCR in NPCs. Herein, we focused on that the PCRs on NPCs occur through various reaction pathways which have intrinsic activation energy barriers. Therefore, voltage hysteresis of their electrochemical charge/discharge profiles is inevitable in a given voltage window. Owing to the voltage hysteresis, the charge storage capacitance is dependent on the operating voltage window, which could results in variation in the capacitance value according to the characterized voltage range. The voltage-dependent pseudocapacitive behaviors (VD-PCBs) may be used to differentiate the respective contributions of the EDL capacitance and PCR to the overall capacity of NPCs. In this study, heteroatom-enriched NPCs (H-NPCs) were prepared from a nitrogen-containing conjugated polymer precursor by pyrolysis with potassium hydroxide. The voltage-dependent charge storage behaviors of H-NPCs were then characterized by cyclic voltammetry (CV) in different electrolyte systems. From the results, it was confirmed that the pseudocapacitance value can be quantitatively measured through a comparison of CV obtained from different charge carriers. The VD-PCBs on H-NPCs were kinetically fast and highly stable, leading to a high electrochemical performance. In addition, H-NPCs-based lithium ion hybrid capacitors achieved a high specific energy of ~220Wh kg-1 and a specific power of ~5400Wkg-1 with a long-term cycle life of over 500 cycles, demonstrating the usefulness of the VD-PCBs-based H-NPCs.

Deep Insight into Electrochemical Kinetics of Cowpea‐Like Li3VO4@C Nanowires as High‐Rate Anode Materials for Lithium‐Ion Batteries

AbstractOwing to the high theoretical capacity (394 mAh g−1) and appropriate lithiation voltage (0.5–1.0 V vs Li+/Li), Li3VO4 is highly regarded as an attractive anode candidate for high‐safety lithium‐ion batteries. However, its high‐rate performance is seriously restricted by the sluggish electrode kinetics. To address these problems, we synthesize cowpea‐like Li3VO4@C nanowires through a facile electrospinning method. In this well‐designed structure, Li3VO4 nanocrystals are uniformly encapsulated in conductive carbon nanofibers just like peas in their pods. The 1D morphology with high electronic conductivity can afford high Li+ ions diffusion rate and fast surface charge storage mechanism, leading to significantly enhanced electrochemical kinetics. Even after 1000 cycles at 2 A g−1, the reversible capacity of cowpea‐like Li3VO4@C nanowires can be maintained at 318.0 mAh g−1 without obvious capacity decay.

Improved surface charge storage properties of Prosopis juliflora (pods) derived onion–like porous carbon through redox-mediated reactions for electric double layer capacitors

Abstract Turning trash into treasure, the present work divulges the preparation of onion-like porous carbon derived out of the most malignant invasive weed, the Prosopis juliflora. The pods of the Prosopis juliflora are treated hydrothermally and chemically activated using KOH. The effect of activation temperature on the pore formation is investigated to obtain the desired porous carbon. The prepared porous carbon (J–800) has a significant specific surface area of 967 m2 g−1 with unique morphology of onion-like nanostructures and provided a sensible specific capacitance of 274 F g−1 at 1.3 A g−1 in H2SO4 electrolyte. Further, the performance of the device is effectually enhanced by adding KI as redox additive. Interestingly, the increased cell voltage (1.4 V) and improved cell capacitance of 588 F g−1 is obtained. Ultimately, a superior energy density of 35.7 Wh kg−1 at an enhanced power density of 971 W kg−1 is also obtained in the redox additive based aqueous electrolyte. A detailed investigation of the surface storage mechanism is discussed, and the stability of the prepared supercapacitors is also demonstrated. Thus, the most eradicable eco-threat P. juliflora is successfully reformed into an efficient electrode material for the energy storage application.

Molecular Investigation of Oxidized Graphene: Anatomy of the Double-Layer Structure and Ion Dynamics

We investigated the influence of surface oxidization of planar graphene electrodes on charge storage and ion dynamics of supercapacitors. Our approach compared two distinct ionic liquid (IL) electrolytes: tetraethylammonium tetrafluoroborate solvated in acetonitrile (TEA-BF4/ACN) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide solvated in acetonitrile (EMIm-TFSI/ACN). Both experimental electrochemical tests and molecular dynamics (MD) simulations showed positive, electrolyte-specific influences of hydroxyl-free electrode interfaces on capacitance. In the EMIm-TFSI/ACN system, the hydroxylated surface, because of its strong interaction with anions, impeded surface charge storage. On the other hand, in the case of TEA-BF4/ACN, the distribution and orientation of ACN across the system exerted vital influence on the capacitance, especially on the positive hydroxyl-free electrode. Furthermore, MD simulations of ion mobility with respect to the electrode surface in the lateral and perpendicula...

Fabrication of graphene-based electrochemical capacitors through reactive inverse matrix assisted pulsed laser evaporation

Electrodes constituted by nitrogen-doped reduced graphene oxide (NrGO) in combination with NiO nanostructures were fabricated by means of reactive inverse matrix assisted pulsed laser evaporation technique. The structure-composition of the electrode composites was tailored by laser-inducing chemical reactions of graphene oxide (GO) flakes with different precursor molecules (citric acid, ascorbic acid and imidazole) during GO deposition. Structural characterizations reveal the formation of wrinkles and nanoholes in the NrGO sheets, besides their coating with NiO nanostructures. Compositional studies disclose that imidazole precursor promotes the synthesis of NrGO with the largest degree of reduction and nitrogen doping (mainly with graphitic and pyridinic N). Electrochemical analyses of the obtained electrodes reveal that NiO nanostructures increase surface charge storage processes (double layer – pseudocapacitive) over diffusive ones, being the imidazole-based electrodes the ones exhibiting the best performance (up to 114 F cm−3 at 10 mV s−1). Symmetric and asymmetric electrochemical capacitors were also fabricated showing excellent robustness over 10,000 charge-discharge cycles at high specific currents.

Insights into the Crystallinity of Layer-Structured Transition Metal Dichalcogenides on Potassium Ion Battery Performance: A Case Study of Molybdenum Disulfide.

Layer-structured transition metal dichalcogenides (LS-TMDs) are being heavily studied in K-ion batteries (KIBs) owing to their structural uniqueness and interesting electrochemical mechanisms. Synthetic methods are designed primarily focusing on high capacities. The achieved performance is often the collective results of several contributing factors. It is important to decouple the factors and understand their functions individually. This work presents a study focusing on an individual factor, crystallinity, by taking MoS2 as a demonstrator. The performance of low and high-crystallized MoS2 is compared to show the function of crystallinity is dependent on the electrochemical mechanism. Lower crystallinity can alleviate diffusional limitation in 0.5-3.0 V, where intercalation reaction takes charge in storing K-ions. Higher crystallinity can ensure the structural stability of the MoS2 layers and promote surface charge storage in 0.01-3.0 V, where conversion reaction mainly contributes. The low-crystallized MoS2 exhibits an intercalation capacity (118 mAh g-1 ), good cyclability (85% over 100 cycles), and great rate capability (41 mAh g-1 at 2 A g-1 ), and the high-crystallized MoS2 delivers a high capacity of 330 mAh g-1 at 1 A g-1 and retains 161 mAh g-1 at 20 A g-1 , being one of the best among the reported LS-TMDs in KIBs.

HIGH PRECISION SIMULATION ON SURFACE POTENTIAL OF CELLULAR ELECTRETS BY CHARGE SIMULATION METHOD

Surface potential is one of the key properties of charge retain ability and energy storage performance of cellular electrets. Based on charge simulation method (CSM), a high precision simulation algorithm of surface potential of functional dielectrics is proposed in this paper, which can be applied to the simulations of cellular polypropylene after high-voltage corona discharge. In order to validate the modeling, the surface potential of insulating polymer after corona discharge is measured by an electrostatic measurement system and compared with simulation results based on CSM and finite element method (FEM). The result shows that the numerical simulation based on CSM is well consistent with the experimental data, which indicates that the modeling based on CSM can be used in the calculation and analysis of charge storage ability of capacitor and electrostatic generator based on functional electrets. Moreover, as simulation based on CSM has higher precision than FEM, investigation of surface charge storage ability and prediction of electrostatic hazards of insulating dielectrics could be realized by using CSM.

Fabrication of Nanoporous IrO₂/Ir Films for Bioelectrode and Neural Prosthesis Applications.

IrO₂ and Ir are attractive materials for bio-interface applications due to their desirable stability, electrochemical performance, and biocompatibility. Nanostructured IrO₂/Ir possesses several advantageous properties including large surface-to-volume ratio, light weight, super hydrophilic surface, desirable electrochemical capability, and cell adhesion. Herein, we employ a cost-effective process to fabricate uniform nanoporous IrO₂/Ir film by chemical bath deposition, high-vacuum annealing, and electrochemical activation. High-vacuum annealing can remove oxygen from an IrO₂ film to create a nanoporous structure, and we determine the optimized electrochemical activation to transform Ir to IrO₂/Ir. The surface morphology, roughness, hydrophilicity, crystallinity, oxidation state, and charge storage capacity (CSC) of the films were analyzed. The nanoporous IrO₂/Ir film showed a 25% increase of CSC compared to the dense IrO₂ film, and this excellent performance makes it a promising candidate for bio-interface applications. In addition, this fabrication route can be cost-effective process without wasting the expensive noble metal Ir material.

Substituent effect on supercapacitive performances of conducting polymer‐based redox electrodes: Poly(3′,4′‐bis(alkyloxy) 2,2′:5′,2″‐terthiophene) derivatives

ABSTRACTThis work reports the synthesis of novel poly(3′,4′‐bis(alkyloxy)terthiophene) derivatives (PTTOBu, PTTOHex, and PTTOOct) and their supercapacitor applications as redox‐active electrodes. The terthiophene‐based conducting polymers have been derivatized with different alkyl pendant groups (butyl‐, hexyl‐, and octyl‐) to explore the effect of alkyl chain length on the surface morphologies and pseudocapacitive properties. The electrochemical performance tests have revealed that the length of alkyl substituent created a remarkable impact over the surface morphologies and charge storage properties of polymer electrodes. PTTOBu, PTTOHex, and PTTOOct‐based electrodes have reached up to specific capacitances of 94.3, 227.3, and 443 F g−1 at 2.5 mA cm−2 constant current density, respectively, in a three‐electrode configuration. Besides, these redox‐active electrodes have delivered satisfactory energy densities of 13.5, 29.3, and 60.7 W h kg−1 and power densities of 0.98, 1, and 1.1 kW kg−1 with good capacitance retentions after 10,000 charge/discharge cycles in symmetric solid‐state micro‐supercapacitor devices. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 480–495

Iron Oxide Nanosheets As High Performance Cathodes for Lithium-Ion and Sodium-Ion Batteries

Cathodes with high lithium-ion and sodium-ion capacities, the ability to be rapidly charged and discharged, and that are extremely low-cost are needed for numerous applications including electric vehicles, consumer devices, and grid-level energy storage. Iron oxides are of significant interest based on their low cost, low toxicity, and high natural abundance, however iron oxide cathodes typically have low specific capacities and very poor rate capabilities. Our work has shown that synthesizing and stabilizing iron oxide in a nanosheet architecture results in significantly improved lithium-ion charge storage capacities compared to iron oxide nanoparticles at both slow and fast charging/discharging times. The iron oxide nanosheets were determined to have lateral dimensions of ~50 nm, thicknesses of ~1 nm, and be composed of smaller crystallites. From X-ray diffraction, Raman spectroscopy, and high resolution microscopy, the structure of the nanosheets was consistent with maghemite, γ-Fe2O3. The γ-Fe2O3 nanosheets exhibit significantly better electrochemical properties with higher capacities and rate capabilities (110 mAh/g at ~3C) compared with comparable iron oxide nanoparticles. The improved electrochemical performance of γ-Fe2O3 nanosheets has been demonstrated to be related to multiple factors including high surface area, a predominantly surface charge storage process, and higher electronic conductivity. Our recent work has explored using γ-Fe2O3 nanosheets for sodium-ion battery cathodes. The understanding of the unique electrochemical properties, factors that stabilize the nanosheet form, and distinct charge storage mechanism of iron oxide nanosheets furthers the design of improved charge storage materials with improved capacities, rate capabilities, and lower cost.

(Invited) Applying Energy Storage to Tune the Magnetism of Large-Pore Ordered Mesoporous Metal Oxide Thin Films

Polymer-templated mesostructured non-silicate oxide thin films have received much attention in the past on account of their potential for future device applications. However, despite the overall progress made in the synthesis of such materials, “complex” metal oxides are more often than not ill-defined from a structural point of view. The primary reasons are the lack of control over the hydrolysis and condensation reactions of the inorganic precursors used, and the fact that the crystallization of the nanoscale walls is difficult to control. In this talk I will describe the evaporation-induced self-assembly synthesis of cubic mesoporous La1–xCaxMnO3 (LCMO), La1–ySryMnO3 (LSMO) and LiFe5O8 (LFO) thin films using a polyisobutylene-block-poly(ethylene oxide) diblock copolymer as the structure-directing agent. Electron microscopy, GISAXS, XRD, XPS, RBS and SQUID magnetometry all show that these materials are of high quality and thermally stable to over 600 °C. More importantly, they can store charge by topotactic lithium insertion reaction (LFO) and via double-layer capacitance (LCMO/LSMO), which allows for the intriguing possibility of reversibly tuning the magnetization [1, 2]. Collectively, I will show that both approaches provide a method to exert fine control over magnetism in situ, and further might help to better understand (Faradaic) surface charge storage processes. [1] C. Reitz, P. M. Leufke, R. Schneider, H. Hahn, T. Brezesinski, Chem. Mater. 26 (2014) 5745. [2] C. Reitz, C. Suchomski, D. Wang, H. Hahn, T. Brezesinski, J. Mater. Chem. C 4 (2016) 8889.

Nitrogen-doped ordered mesoporous carbon using task-specific ionic liquid as a dopant for high-performance supercapacitors

Abstract

Surface Charge Storage Properties of Selected Graphene Samples in pH-neutral Aqueous Solutions of Alkali Metal Chlorides - Particularities and Universalities

Surface Charge Storage Properties of Selected Graphene Samples in pH-neutral Aqueous Solutions of Alkali Metal Chlorides - Particularities and Universalities

A cost-effective fabrication of iridium oxide films as biocompatible electrostimulation electrodes for neural interface applications

Electrostimulation medical devices for neural diseases require electroactive and biocompatible interface materials to transmit signals from electrodes to targeting tissues. Iridium oxide is an attractive ceramic material for neurostimulation electrodes due to its desirable stability and biocompatibility. In this study, we developed a cost effective and thickness controllable process to fabricate iridium oxide film by chemical bath deposition (CIROF). Surface morphology, crystallinity, roughness, hydrophilicity, and charge storage capacity as well as biocompatibility of the CIROFs with different thicknesses were analyzed. Accordingly, the CIROFs present rough and hydrophilic surfaces for cell attachment and good biocompatibility for cell viability. In addition, the charge storage capacity (CSC) of the as-deposited and the annealed CIROFs were 78.29 mC/cm2 and 71.76 mC/cm2, respectively. Consequently, these results show advantages that make the CIROF a promising neurostimulation electrode material for implantable medical devices in neural systems.

Chemical Bath Deposition of Iridium Oxide Film for Implantable Neurostimulation Electrode Applications

Iridium oxide is an attractive ceramic material for neurostimulation electrodes due to its desirable stability and biocompatibility. Electrostimulation medical devices for neural diseases require electroactive and biocompatible materials to transmit signals from electrodes to targeting tissues. In this study, we developed a cost effective and thickness controllable process to fabricate iridium oxide film by chemical bath deposition. The film thickness can be controlled by modifying solution recipe from 40 nm to 110 nm per batch. Surface morphology, crystallinity, and charge storage capacity of the iridium oxide with different thicknesses were analyzed. Accordingly, the iridium oxide films present rough and hydrophilic surfaces so that the films are expected to suitable for cell attachment and good biocompatibility for cell viability. In addition, the charge storage capacity (CSC) of the iridium oxide films with various thicknesses were significantly higher than platinum which is the conventional stimulation electrode material. Consequently, these results show advantages that make the iridium oxide film a promising neurostimulation electrode material for implantable medical devices in neural systems.