Titanium carbide/reduced graphene oxide (Ti 3 C 2 T z /rGO) gels were prepared by a one-step hydrothermal process. The gels show a highly porous structure with a surface area of ∼224 m 2 g −1 and average pore diameter of ∼3.6 nm. The content of GO and Ti 3 C 2 T z nanosheets in the reaction precursor was varied to yield different microstructures. The supercapacitor performance of Ti 3 C 2 T z /rGO gels varied significantly with composition. Specific capacitance initially increased with increasing Ti 3 C 2 T z content, but at high Ti 3 C 2 T z content gels cannot be formed. Also, the retention of capacitance decreased with increasing Ti 3 C 2 T z content. Ti 3 C 2 T z /rGO gel electrodes exhibit enhanced supercapacitor properties with high potential window (1.5 V) and large specific capacitance (920 F g −1 ) in comparison to pure rGO and Ti 3 C 2 T z . The synergistic effect of EDLC from rGO and redox capacitance from Ti 3 C 2 T z was the reason for the enhanced supercapacitor performance. A symmetric two-electrode supercapacitor cell was constructed with Ti 3 C 2 T z /rGO, which showed very high areal capacitance (158 mF cm −2 ), large energy density (∼31.5 μW h cm −2 corresponding to a power density of ∼370 μW cm −2 ), and long stability (∼93% retention) after 10 000 cycles.
more »
« less
V 2 O 5 –Conductive polymer nanocables with built-in local electric field derived from interfacial oxygen vacancies for high energy density supercapacitors
Generating oxygen vacancies (Vö) in vanadium pentoxide (V 2 O 5 ) has been demonstrated as an effective approach to tailor its electrochemical properties. The present study investigates three different kinds of conductive polymer (CP = PPy, PEDOT, and PANI) coated V 2 O 5 nanofibers with Vö generated at the interface during the polymerization process. Surface Vö form a local electric field and promote the charge transfer kinetics of the resulting Vö-V 2 O 5 /CP nanocables, and the accompanying V 4+ and V 3+ ions may also catalyze the redox reactions and improve the supercapacitor performance. The differences and similarities of three different CP coatings have been compared and discussed, and are dependent on their polymerization conditions and coating thickness. The distribution of Vö in the surface layer and in the bulk has been elaborated and the corresponding effects on the electrochemical properties and supercapacitor performance have also been investigated. Vö-V 2 O 5 /CP can deliver a high capacity of up to 614 F g −1 at a current rate of 0.5 A g −1 and supercapacitors with Vö-V 2 O 5 /CP demonstrated excellent cycling stability over 15 000 cycles at a rate of 10 A g −1 .
more »
« less
- Award ID(s):
- 1803256
- NSF-PAR ID:
- 10121542
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 7
- Issue:
- 30
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 17966 to 17973
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Advances in solution-phase graphene patterning has provided a facile route for rapid, low-cost and scalable manufacturing of electrochemical devices, even on flexible substrates. While graphene possesses advantageous electrochemical properties of high surface area and fast heterogenous charge transport, these properties are attributed to the edge planes and defect sites, not the basal plane. Herein, we demonstrate enhancement of the electroactive nature of patterned solution-phase graphene by increasing the porosity and edge planes through the construction of a multidimensional architecture via salt impregnated inkjet maskless lithography (SIIML) and CO 2 laser annealing. Various sized macroscale pores (<25 to ∼250 μm) are patterned directly in the graphene surface by incorporating porogens ( i.e. , salt crystals) in the graphene ink which act as hard templates for pore formation and are later dissolved in water. Subsequently, microsized pores (∼100 nm to 2 μm in width) with edge plane defects are etched in the graphene lattice structure by laser annealing with a CO 2 laser, simultaneously improving electrical conductivity by nearly three orders of magnitude (sheet resistance decreases from >10 000 to ∼50 Ω sq −1 ). We demonstrate that this multidimensional porous graphene fabrication method can improve electrochemical device performance through design and manufacture of an electrochemical organophosphate biosensor that uses the enzyme acetylcholinesterase for detection. This pesticide biosensor exhibits enhanced sensitivity to acetylthiocholine compared to graphene without macropores (28.3 μA nM −1 to 13.3 μA nM −1 ) and when inhibited by organophosphate pesticides (paraoxon) has a wide linear range (10 nM to 500 nM), low limit of detection (0.6 nM), and high sensitivity (12.4 nA nM −1 ). Moreover, this fabrication method is capable of patterning complex geometries [ i.e. interdigitated electrodes (IDEs)] even on flexible surfaces as demonstrated by an IDE supercapacitor made of SIIML graphene on a heat sensitive polymer substrate. The supercapacitor demonstrates a high energy density of 0.25 mW h cm −3 at a power density of 0.3 W cm −3 . These electrochemical devices demonstrate the benefit of using SIIML and CO 2 laser annealing for patterning graphene electrodes with a multidimensional porous surface even on flexible substrates and is therefore a platform technology which could be applied to a variety of different biosensors and other electrochemical devices.more » « less
-
more » « less
Abstract Electrochemical capacitors (ECs) that store charge based on the pseudocapacitive mechanism combine high energy densities with high power densities and rate capabilities. 2D transition metal carbides (MXenes) have been recently introduced as high‐rate pseudocapacitive materials with ultrahigh areal and volumetric capacitances. So far, 20 different MXene compositions have been synthesized and many more are theoretically predicted. However, since most MXenes are chemically unstable in their 2D forms, to date only one MXene composition, Ti3C2T
x , has shown stable pseudocapacitive charge storage. Here, a cation‐driven assembly process is demonstrated to fabricate highly stable and flexible multilayered films of V2CTx and Ti2CTx MXenes from their chemically unstable delaminated single‐layer flakes. The electrochemical performance of electrodes fabricated using assembled V2CTx flakes surpasses Ti3C2Tx in various aqueous electrolytes. These electrodes show specific capacitances as high as 1315 F cm−3and retain ≈77% of their initial capacitance after one million charge/discharge cycles, an unprecedented performance for pseudocapacitive materials. This work opens a new venue for future development of high‐performance supercapacitor electrodes using a variety of 2D materials as building blocks. -
Hydrated vanadium pentoxide (VOH) can deliver a gravimetric capacity as high as 400 mA h g −1 owing to the variable valence states of the V cation from 5+ to 3+ in an aqueous zinc ion battery. The incorporation of divalent transition metal cations has been demonstrated to overcome the structural instability, sluggish kinetics, fast capacity degradation, and serious polarization. The current study reveals that the catalytic effects of transition metal cations are probably the key to the significantly improved electrochemical properties and battery performance because of the higher covalent character of 55% in the Cu–O bond in comparison with 32% in the Mg–O bond in the respective samples. Cu( ii ) pre-inserted VOH (CuVOH) possesses a significantly enhanced intercalation storage capacity, an increased discharge voltage, great transport properties, and reduced polarization, while both VOH and Mg( ii ) pre-inserted VOH (MgVOH) demonstrate similar electrochemical properties and performances, indicating that the incorporation of Mg cations has little or no impact. For example, CuVOH has a redox voltage gap of 0.02 V, much smaller than 0.25 V for VOH and 0.27 V for MgVOH. CuVOH shows an enhanced exchange current density of 0.23 A g −1 , compared to 0.20 A g −1 for VOH and 0.19 A g −1 for MgVOH. CuVOH delivers a zinc ion storage capacity of 379 mA h g −1 , higher than 349 mA h g −1 for MgVOH and 337 mA h g −1 for VOH at 0.5 A g −1 . CuVOH shows an energy efficiency of 72%, superior to 53% for VOH and 55% for MgVOH. All of the results suggest that pre-inserted Cu( ii ) cations played a critical role in catalyzing the zinc ion intercalation reaction, while the Mg( ii ) cations did not exert a detectable catalytic effect.more » « less
-
It is urgent to enhance battery energy storage capability to satisfy the increasing energy demand in modern society and reduce the average energy capacity cost. Among the candidates for next-generation high energy storage systems, the lithium-sulfur battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1) and cost savings potential.1 In addition to the high theoretical capacity of sulfur cathode as high as 1,673 mA h g-1, sulfur is further appealing due to its abundance in nature, low cost, and low toxicity. Despite these advantages, the application of sulfur cathodes to date has been hindered by a number of obstacles, including low active material loading, low electronic conductivity, shuttle effects, and sluggish sulfur conversion kinetics.2 The traditional 2D planer thick electrode is considered as a general approach to enhance the mass loading of the lithium-sulfur (Li-S) battery.3 However, the longer diffusion length of lithium ions required in the thick electrode decrease the wettability of the electrolyte (into the entire cathode) and utilization ratio of active materials.4 Encapsulating active sulfur in carbon hosts is another common method to improve the performance of sulfur cathodes by enhancing the electronic conductivity and restricting shuttle effects. Nevertheless, it is also reported that the encapsulation approach causes unfavorable carbon agglomeration with low dimensional carbons and a low energy density of the battery with high dimensional carbons. Although an effort to induce defects in the cathode was made to promote sulfur conversion kinetic conditions, only one type of defect has demonstrated limited performance due to the strong adsorption of the uncatalyzed clusters to the defects (i.e.: catalyst poisoning). 5 To mitigate the issues listed above, herein we propose a novel sulfur electrode design strategy enabled by additive manufacturing and oxidative chemical vapor deposition (oCVD).6,7 Specifically, the electrode is designed to have a hierarchal hollow structure via a stereolithography technique to increase sulfur usage. Microchannels are constructed on the tailored sulfur cathode to further fortify the wettability of the electrolyte. The as-printed cathode is then sintered at 700 °C in a reducing atmosphere (e.g.: H2) in order to generate a carbon skeleton (i.e.: carbonization of resin) with intrinsic carbon defects. A cathode treatment with benzene sulfonic acid further induces additional defects (non-intrinsic) to enhance the sulfur conversion kinetic. Furthermore, intrinsic defects engineering is expected to synergistically create favorable sulfur conversion conditions and mitigate the catalyst poisoning issue. In this study, the oCVD technique is leveraged to produce a conformal coating layer to eliminate shuttle effects, unfavored in the Li-S battery performance. Identified by SEM and TEM characterizations, the oCVD PEDOT is not only covered on the surface of the cathode but also the inner surface of the microchannels. High resolution x-ray photoelectron spectroscopy analyses (C 1s and S 2p orbitals) between pristine and modified sample demonstrate that the high concentration of the defects have been produced on the sulfur matrix after sintering and posttreatment. In-operando XRD diffractograms show that the Li2S is generated in the oCVD PEDOT-coated sample during the charge and discharge process even with a high current density, confirming an eminent sulfur conversion kinetic condition. In addition, ICP-OES results of lithium metal anode at different states of charge (SoC) verify that the shuttle effects are excellently restricted by oCVD PEDOT. Overall, the high mass loading (> 5 mg cm-2) with elevated sulfur utilization ratio, accelerated reaction kinetics, and stabilized electrochemical process have been achieved on the sulfur cathode by implementing this innovative cathode design strategy. The results of this study demonstrate significant promises of employing pure sulfur powder with high electrochemical performance and suggest a pathway to the higher energy and power density battery.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9TA04264D
