Abstract This study reports the superior performance of graphene nanosheet (GNS) materials over Vulcan XC incorporated as a cathode catalyst in Li–O2 battery. The GNSs employed were synthesized from a novel, eco-friendly, and cost-effective technique involving chamber detonation of oxygen (O2) and acetylene (C2H2) precursors. Two GNS catalysts i.e., GNS-1 and GNS-2 fabricated with 0.3 and 0.5 O2/C2H2 precursor molar ratios, respectively, were utilized in this study. Specific surface area (SSA) analysis revealed significantly higher SSA and total pore volume for GNS-1 (180 m2 g−1, 0.505 cm3 g−1) as compared with GNS-2 (19 m2 g−1, 0.041 cm3 g−1). GNS-1 exhibited the highest discharge capacity (4.37 Ah g-1) and superior cycling stability compared with GNS-2 and Vulcan XC. Moreover, GNS-1 demonstrated promising performance at higher current densities (0.2 and 0.3 mA cm−2) and with various organic electrolytes. The superior performance of GNS-1 can be ascribed to its higher mesopore volume, SSA, and optimum wettability compared to its counterparts.
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Experimental Studies of Carbon Electrodes With Various Surface Area for Li–O2 Batteries
Li−O2 batteries with carbon electrodes made from three commercial carbons and carbon made from waste tea leaves are investigated in this study. The waste tea leaves are recycled from household tea leaves and activated using KOH. The carbon materials have various specific surface areas, and porous structures are characterized by the N2 adsorption/desorption. Vulcan XC 72 carbon shows a higher specific surface area (264.1 m2/g) than the acetylene black (76.5 m2/g) and Super P (60.9 m2/g). The activated tea leaves have an extremely high specific surface area of 2868.4 m2/g. First, we find that the commercial carbons achieve similar discharge capacities of ∼2.50 Ah/g at 0.5 mA/cm2. The micropores in carbon materials result in a high specific surface area but cannot help to achieve higher discharge capacity because it cannot accommodate the solid discharge product (Li2O2). Mixing the acetylene black and the Vulcan XC 72 improves the discharge capacity due to the optimized porous structure. The discharge capacity increases by 42% (from 2.73 ± 0.46 to 3.88 ± 0.22 Ah/g) at 0.5 mA/cm2 when the mass fraction of Vulcan XC 72 changes from 0 to 0.3. Second, the electrode made from activated tea leaves is demonstrated for the first time in Li−O2 batteries. Mixtures of activated tea leaves and acetylene black confirm that mixtures of carbon material with different specific surface areas can increase the discharge capacity. Moreover, carbon made from recycled tea leaves can reduce the cost of the electrode, making electrodes more economically achievable. This study practically enhances the discharge capacity of Li−O2 batteries using mixed carbons and provides a method for fabricating carbon electrodes with lower cost and better environmental friendliness.
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- Award ID(s):
- 1833048
- NSF-PAR ID:
- 10101019
- Date Published:
- Journal Name:
- Journal of Electrochemical Energy Conversion and Storage
- Volume:
- 16
- Issue:
- 4
- ISSN:
- 2381-6872
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract High surface area graphitic mesoporous carbons (M‐mGMC; M=Ni, Fe, Co or Ni‐Fe) were synthesized
via catalytic graphitization using a hard template based synthesis method. In house prepared SBA‐15 silica material was impregnated with metal precursors to obtain M/SBA‐15, template for M‐mGMC synthesis. These materials were studied using different material characterization techniques, such as nitrogen adsorption desorption (BET), X‐ray diffraction (XRD) analysis, Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Specific surface area ranging from 1,227.9 m2g−1to 1,320.7 m2g−1was observed for four M‐mGMCs. Raman spectroscopy, XPS and wide angle XRD suggested presence of graphitic structure in these materials along with disorders. Electrocatalytic performance of these materials along with conventional carbon black (Vulcan XC‐72) were evaluated in a single‐stack proton exchange membrane fuel cell (PEMFC). Pt/NiFe‐mGMC exhibited enhanced electrocatalytic activity compared to Pt/Ni‐mGMC, Pt/Fe‐mGMC and Pt/Co‐mGMC electrocatalysts. However, Pt/NiFe‐mGMC lacked adequate proton transport in membrane electrode assembly (MEA) compared to Pt/Vulcan XC‐72. This exploratory study showed that NiFe‐mGMC may find application as electrocatalyst support material in PEMFC. -
null (Ed.)Rice hull ash (RHA, an agricultural waste) produced during combustion of rice hulls to generate electricity consists (following dilute acid leaching) of high surface area SiO2 (80–90 wt%) and 10–20 wt% carbon (80 m2 g−1 total). RHA SiO2 is easily extracted by distillation (spirosiloxane) producing SDRHA, which offers an opportunity to develop “green” hybrid lithium-ion capacitors (LICs) electrodes. SDRHA consists of 50–65 wt% SiO2 with the remainder carbon with a specific surface area of ≈220 m2 g−1. SDRHA microstructure presents a highly irregular and disordered nanocomposite composed of nanosilica closely connected via graphene layers enhancing Li-ion mobility during charge/discharge process. SDRHA electrochemicalproperties were assessed by assembling Li/SDRHA half-cells and LiNi0.6Co0.2Mn0.2O2 (NMC622)-SDRHA full-cells. The half-cell delivered a high specific capacity of 250 mA h g−1 at 0.5C and retained a capacity of 200 mA h g−1 at 2C for 400 h. In contrast to the poor cycle performance of NMC based batteries at high C-rates, the hybrid full-cell demonstrated a high specific capacitance of 200 F g−1 at 4C. In addition, both the half and full hybrid cells demonstrate excellent coulombic efficiencies (∼100%). These results suggest that low cost and environmentally friendly SDRHA, may serve as a potentialalternative electrode material for LICs.more » « less
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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
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Hydrogen (H2) is largely regarded as a potential cost-efficient clean fuel primarily due to its beneficial properties, such as its high energy content and sustainability. With the rising demand for H2 in the past decades and its favorable characteristics as an energy carrier, the escalating USA consumption of pure H2 can be projected to reach 63 million tons by 2050. Despite the tremendous potential of H2 generation and its widespread application, transportation and storage of H2 have remained the major challenges of a sustainable H2 economy. Various efforts have been undertaken by storing H2 in activated carbons, metal organic frameworks (MOFs), covalent organic frameworks (COFs), etc. Recently, the literature has been stressing the need to develop biomass-based activated carbons as an effective H2 storage material, as these are inexpensive adsorbents with tunable chemical, mechanical, and morphological properties. This article reviews the current research trends and perspectives on the role of various properties of biomass-based activated carbons on its H2 uptake capacity. The critical aspects of the governing factors of H2 storage, namely, the surface morphology (specific surface area, pore volume, and pore size distribution), surface functionality (heteroatom and functional groups), physical condition of H2 storage (temperature and pressure), and thermodynamic properties (heat of adsorption and desorption), are discussed. A comprehensive survey of the literature showed that an “ideal” biomass-based activated carbon sorbent with a micropore size typically below 10 Å, micropore volume greater than 1.5 cm3/g, and high surface area of 4000 m2/g or more may help in substantial gravimetric H2 uptake of >10 wt% at cryogenic conditions (−196 °C), as smaller pores benefit by stronger physisorption due to the high heat of adsorption.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1115/1.4043229
