Dual Cathode Research Articles

Pluronic F127 as auxiliary template for preparing nitrogen and oxygen dual doped mesoporous carbon cathode of lithium-oxygen batteries

Two mesoporous carbon foam (MCF) with nitrogen and oxygen dual doped are fabricated through facile templated hydrothermal process. One using fumed silica as single template is named S-MCF, and another using fumed silica and Pluronic F127 as double templates is named D-MCF. When using Pluronic F127 as an auxiliary template, the D-MCF shows different porous architecture and surface chemical nature from S-MCF, thus they behave differently as cathode materials in Li-O2 batteries. The D-MCF electrode exhibits a slight lower discharge capacity and an increased overpotential than that of S-SCF due to the decreased surface area and oxygen content. However, a better cycle stability was proved for the D-MCF electrode because of its higher nitrogen and lower oxygen content. When further composited with RuO2 nanoparticles, the RuO2/D-MCF cathode can operate 160 cycles with capacity cutoff of 500 mAh g−1, and this prolonged cycle life, compared to the 102 cycles of S-MCF cathode, verifies the superior electrochemical stability of D-MCF further and illuminates the crucial role of carbon substrate in the cathodes of Li-O2 batteries.

Evaluation of Order Mesoporous Carbon as Anode Catalyst for Microbial Fuel Cells Applications

Ordered Mesoporous Carbon (OMC) was evaluated as anode catalyst in a MFC. Bacilus subtilis (B. subtilis) was the microorganism, while the electrolyte was Pharmaceutical Residual Water (PRW). In a dual chamber MFC, the anode and cathode compartments contained N2–saturated PRW and O2–saturated KOH (both electrolytes with pH=9.6), respectively, separated by a Nafion® membrane. The anode catalysts on gas diffusion electrodes in the MFC were: methanol-functionalized OMC, non-functionalized OMC, methanol-functionalized Vulcan XC-72 and commercial Pt/C, all covered by a biofilm of B. Subtilis. Meanwhile, the cathode catalyst was Pt/C. Significantly higher catalytic activity was obtained from functionalized OMC + B. Subtilis in the MFC. The Open Circuit Voltage (OCV) was 0.58 V, with a maximum current density (jcell) of 854 mA m-2. These values were 2.6 and 4.7 times higher than those from Pt/C. The results showed that methanol-functionalized OMC is a metal-free catalyst with high performance for MFCs.

The effect of heating rate on the phase transformation of Ni/Ti multilayer thin films

Ni/Ti multilayer thin films prepared by dual cathode magnetron sputtering were annealed in vacuum at different heating rates. The structural evolution of the multilayer thin films with nanometric modulation periods was studied in-situ by x-ray diffraction using synchrotron radiation. Independently of the multilayer period, a single step rapid reaction occurs at temperatures above 300 °C with the formation of the B2-NiTi austenite phase. The transformation temperature is inversely proportional to the multilayers period (higher temperature for shorter period - 12 nm) and to the heating rate (lower temperature for faster heating rates).

Hybrid Ag2VO2PO4/CFx as a High Capacity and Energy Cathode for Primary Batteries

In this report, we describe the electrochemistry of hybrid dual silver vanadium phosphorus oxide/carbon fluoride (Ag2VO2PO4/CFx) cathodes with various weight ratios. Through modification of the Ag2VO2PO4/CFx ratio, we can control the gravimetric and volumetric capacity, as well as mitigate the voltage drop during high current pulses. The increase in impedance caused by irreversible LiF formation in CFx was reduced by the silver reduction-displacement during electrochemical discharge of the Ag2VO2PO4. Moreover, the addition of graphite was shown to reduce initial voltage delay. When Ag2VO2PO4 dominates the electrode mass (i.e. 75/25 Ag2VO2PO4/CFx) in the hybrid cathode, pulse testing shows less voltage drop and delay, but at the expense of capacity and energy density. As the amount of CFx in the composite increases (i.e. Ag2VO2PO4/CFx ratio of to 50/50 or 25/75), charge capacity and energy density increases, but at the expense of larger voltage drops and delays early in the discharge process. Thus, controlling the Ag2VO2PO4/CFx ratio can be used to tune the electrochemical properties of the dual cathode, allowing for optimization of capacity and power depending on the application.

Combined influence of plasmonic metal nanoparticles and dual cathode buffer layers for highly efficient rrP3HT:PCBM-based bulk heterojunction solar cells

The combined influence of plasmonic metal nanoparticles and dual cathode buffer layers resulted in high-performance rrP3HT:PCBM based BHJ solar cells (PCE ∼5.65%).

High performance polymer solar cells with electron extraction and light-trapping dual functional cathode interfacial layer

For polymer solar cells (PSCs), the interfaces between the back and front contacts with the photoactive layer play a crucial role for charge extraction. Herein, we demonstrate high performance PSCs with dual functional tantalum methoxide (Ta-OMe) cathode interfacial layer, which can reduce the interface energy barrier and form a light trapping structure with reflective metal electrode. The energy level of Ta-OMe is investigated by ultraviolet photoelectron spectroscopy (UPS). The composition of the Ta-OMe film is confirmed by X-ray photoelectron spectroscopy (XPS). The surface morphologies of the photoactive layer with and without Ta-OMe layer are measured by scanning electron microscopy (SEM) and tapping mode atomic force microscopy (AFM). Three polymer donors with different band gaps and two classical fullerene acceptors were selected as photoactive materials for fabrication PSCs. The PSCs with Ta-OMe interfacial layer exhibit superior performance in comparison with devices which Al and Ca/Al based devices. The great enhancement in Jsc is associated with additional absorption (ΔαAbs) and the additional EQE (ΔαEQE). The four parameters of Voc, Jsc, FF, and PCE for device with Ta-OMe reach 0.80V, 18.55mA/cm2, 70%, and 10.18%, respectively, among the best values reported for PTB7-Th:PC70BM based PSCs.

(Invited) Stand-Alone Photoreduction of Carbon Dioxide on Copper Oxide Nanowires Powered By WO3/Dye Dual Absorber

A photoelectrochemical cell, composed of WO3/dye-sensitized solar cell (WO3/DSSC) and copper oxide (CuxO, where x = 1 and 2) nanowires as a dual absorber photoanode and cathode, respectively, is demonstrated as a stand-alone device for CO2 photoreduction to CO, H2 and formate. The single-absorber cell of a WO3 photoanode and CuxO nanowire cathode couple (WO3-CuxO) required the minimum overpotential of ~0.7 V to drive CO2 photoreduction. For the unassisted or stand-alone CO2 photoreduction, a DSSC was coupled to the WO3-CuxO system to construct a dual-absorber cell (WO3/DSSC-CuxO). In the dual-absorber cell, the long-wave band (λ > ca. 500 nm) passed through the semi-transparent WO3 film was absorbed by the dye-sensitized TiO2 electrode of DSSC. The WO3/DSSC-CuxO showed a potential gain of ~0.7 V, which resulted in the CO2 photoreduction successfully without supply of any external potential. In this stand-alone system, the primary CO2 conversion product is CO with solar-to-chemical energy efficiency of ~2.5% while H2 and formate are obtained with the energy efficiencies of 0.7% and 0.25%, respectively, in 5 h.

Effect of Dual Cathode Buffer Layer on the Charge Carrier Dynamics of rrP3HT:PCBM Based Bulk Heterojunction Solar Cell.

In bulk heterojunction (BHJ) solar cells, the buffer layer plays a vital role in enhancing the power conversion efficiency (PCE) by improving the charge carrier dynamics. A comprehensive understanding of the contacts is especially essential in order to optimize the performance of organic solar cells (OSCs). Although there are several fundamental reports on this subject, a proper correlation of the physical processes with experimental evidence at the photoactive layer and contact materials is essential. In this work, we incorporated three different additional buffer layers, namely, tris(8-hydroxyquinolinato) aluminum (Alq3), bathophenanthroline (BPhen) or bathocuproine (BCP) with LiF/Al as conventional cathode contact in both rrP3HT:PC61BM and rrP3HT:PC71BM blend BHJ solar cells and their corresponding photovoltaic performances were systematically correlated with their energy level diagram. The device with dual cathode buffer layer having ITO/PEDOT:PSS/blend polymer/BCP/LiF/Al configuration showed the best device performance with PCE, η = 4.96%, Jsc = 13.53 mA/cm(2), Voc = 0.60 V and FF= 61% for rrP3HT:PC71BM and PCE, η = 4.5% with Jsc = 13.3 mA/cm(2), Voc = 0.59 V and FF = 59% for rrP3HT:PC61BM. This drastic improvement in PCE in both the device configurations are due to the combined effects of better hole-blocking capacity of BCP and low work function provided by LiF/Al with the blend polymer. These results successfully explain the role of dual cathode buffer layers and their contribution to the PCE improvement and overall device performance with rrP3HT:PCBM based BHJ solar cell.

Swift heavy ion irradiation of metal containing tetrahedral amorphous carbon films

Thin carbon films were grown at room temperature on (001) n-Si substrate using dual cathode filtered vacuum arc deposition system. Graphite was used as a source of carbon atoms and separate metallic electrode was simultaneously utilized to introduce Ni or Cu atoms. Films were irradiated by 100MeV Ag7+ ions to fluences in the range 1×1010–3×1011cm−2. Rutherford backscattering spectroscopy, Raman scattering, scanning electron microscopy and atomic force microscopy in conductive mode were used to investigate film properties and structure change under irradiation. Some conductive channels having metallic conductivity type were found in the films. Number of such channels is less than number of impinged ions. Presence of Ni and Cu atoms increases conductivity of those conductive channels. Fluence dependence of all properties studied suggests different mechanisms of swift heavy ion irradiation-induced transformation of carbon matrix due to different chemical effect of nickel and copper atoms.

Self-humidifying membrane electrode assembly with dual cathode catalyst layer structure prepared by introducing polyvinyl alcohol into the inner layer

Short-term constant voltage discharge test of the self-humidifying MEAs with different cathode structure at 60 °C and 30 psi under 20% RH.

Crystal Structure and Optical Properties of Al-Doped ZnO Large-Area Thin Films Using 1500 mm Dual Cylindrical Cathodes.

The large-area Al-doped ZnO thin films are successfully deposited at room temperature on polycarbonate substrate using a 1500 mm dual cylindrical cathodes sputtering system. Those thin films have smooth surfaces (RMS: 9.6 nm) and lower thicknesses deviation (Uniformity: 98.6%) despite of high RF power. The optical transmittance properties of 3.13 wt% Al doped ZnO thin films have above 85% in visible region. A dual cylindrical cathodes sputtering system can fabricate transparent electrode on flexible electronic devices at room temperature for mass production of 6th generation solar cell and display industry.

Continuous mode operation of microbial fuel cell (MFC) stack with dual gas diffusion cathode design for the treatment of dark fermentation effluent

Three microbial fuel cells (MFC) with dual gas diffusion cathode design were operated individually in different operation modes, viz., batch (MFC-BM), semi-continuous (MFC-SCM) and continuous (MFC-CM), using dark fermentation effluent (DFE). MFC-BM depicted lower power density (PD, 1.31 ± 1.75 mW/m2) due to the electron losses and mass transfer limitations, while, MFC-SCM (19.06 ± 2.01 mW/m2) and MFC-CM (15.53 ± 2.51 mW/m2) depicted higher PD. Though MFC-SCM showed higher power output, the energy conversion efficiency (ECE) was higher during MFC-CM (9.85 ± 1.02%) operation over MFC-BM and MFC-SCM operations. Henceforth, the stacking approach was carried out in continuous mode operation using DFE which showed a very good power output along with treatment efficiency. Stack mode operation was carried out at decreasing external loads to increase the overall power output as well as the electron delivering ability of the biocatalyst. Stack MFC depicted its maximum PD (3163 mW/m3; 19.79 mW/m2), across 2 kΩ of external resistance (Rex) along with the treatment efficiency of 80 ± 2%. Further decrement in Rex to 1 kΩ has resulted in lower and unstable PD, due to the inability of the biocatalyst to meet the electron requirement by the circuit. A detailed understanding of the stack MFC was made in terms of electrogenesis, electron discharge, coulombic and energy conversion efficiencies as well as the bioprocess parameters.

(Invited) Simulation Studies of Multilayer Electrode Coatings

The use of extrusion coating for lithium-ion battery electrodes enables the practical possibility of using multilayer coatings to improve battery performance. The use of multilayer coatings of different materials, for example, a LiFePO4 coating next to a LiCoO2 coating, or a NMC coating next to a LiMn2O4 coating, has been experimentally tested in the literature [1-2] and modeling approaches [3-4] to optimize multilayer coatings presented. In this presentation simulation results the effect segregating particles into discrete layers are presented for both high power and high energy cells. References J.F. Whitacre, K. Zaghib, W.C. West, B.V. Ratnakumar “Dual active material composite cathode structures for Li-ion batteries”, J. Power Sources 177 (2008) 528–536.W.B. Chu, D-J. Liu, C.C. Chen. L.-C. Chen, S.-T. Tseng, S.H. Wen, C.R. Yang, U. S. Patent Application US 2014/0162118 A1, Jun. 12, 2014 “Electrode Structure of Lithium Ion Battery”.V. Ramadesigan, R.N. Methekar, F. Latinwo, R.D. Braatz, V.R. Subramanian, “Optimal Porosity Distribution for Minmized Ohmic Drop across a Porous Electrode”, J. Electrochem. Soc. 157 (12) A1328-A1334 (2010).S. Golmon, K. Maute, M. Dunn, “A design optimization methodology for Li+ batteries” J. Power Sources 253 (2014) 239-250

Capacity Enhancement of a Lithium Oxygen Flow Battery

A two-dimensional model is developed for an aprotic lithium oxygen (Li–O2) flow battery, in which the organic electrolyte is recirculated through the cathode to enhance oxygen supply. The conventional Li–O2 battery model is extended to incorporate convection effects. In contrast to the classic flow battery models, the pore structure change caused by the insoluble discharge product of Li–O2 batteries is considered. A parametric study is performed to study the influence of model parameters on cathode specific capacity. Results show that contrary to conventional Li–O2 cells, electrolyte with a lower conductivity would increase the specific capacity of the Li–O2 flow cell. The results also reveal those parameters that are influential to battery capacity. Based on the analysis, two methods, dual layer cathode and alternating electrolyte flow, are proposed to enhance battery capacity. The dual layer cathode has 105% higher capacity than a single layer cathode at the current density of 1.5mAcm−2. Alternating electrolyte flow can increase the cathode capacity by 3.7% at the current density of 0.2mAcm−2.

Effects of dual porosity honeycomb structure in SSC–SDC composite cathode for SOFCs

This study proposed an effective structure for the cathode of SOFC to reduce resistance, the honeycomb structure with dual porosity (micro and macro pores). A Sm0.5Sr0.5CoO3−δ (SSC)–Sm0.2Ce0.8O2−δ (SDC) composite cathode for solid oxide fuel cells, with a noble honeycomb structure comprising of nano and micro-sized pores, was fabricated by electrostatic slurry spray deposition (ESSD). The macro-pores distribute in the whole film with size range of 5–20 μm and micro-pores were formed throughout the skeleton with the size under 1 μm. This dual porosity composite cathode from interface to surface of the electrode was deposited by electrostatic slurry spray deposition (ESSD). Its electrochemical property was evaluated using electrochemical impedance spectroscopy and turned out to be enhanced compared to a conventional porous structure of cathode. The polarization resistances were significantly decreased with increasing measurement temperature.

Enhanced water management in the cathode of an air-breathing PEMFC using a dual catalyst layer and optimizing the gas diffusion and microporous layers

In an air-breathing proton exchange membrane fuel cell (ab-PEMFC), large amounts of water are generated and condensed on the cathode at high current densities due to the low operating temperature. Water management for ab-PEMFCs remains a challenge. In this paper, a cathode with a dual catalyst layer structure is designed, and the gas diffusion layer (GDL) and microporous layer (MPL) are optimized to improve the water management of an ab-PEMFC. A thin hydrophilic layer using perfluorosulfonate (Nafion) as the catalyst binder is coated on the electrolyte membrane to form an inner layer that maintains a good proton transfer rate, while a hydrophobic outer layer is prepared using a mixture of Nafion and polytetrafluoroethylene as the binder, preventing the removal of water under low-humidity conditions and expelling the excess water generated in the high current density area. A membrane electrode assembly (MEA) with this dual catalyst layer cathode exhibits excellent air-breathing performance, as the MEA's water management is greatly improved by the dual layer structure. We also find that the thickness of the MPL and the hydrophobicity of the GDL significantly affect the air-breathing performance of the MEA, and we attempt to optimize these parameters.

Dual gas diffusion cathode design for microbial fuel cell (MFC): optimizing the suitable mode of operation in terms of bioelectrochemical and bioelectro‐kinetic evaluation

AbstractBACKGROUNDUpscaling microbial fuel cells (MFCs) to make them energy‐competitive systems requires a systematic understanding of their operating conditions. This study emphasizes the operation of a new MFC design with two gas diffusion cathodes under three different operational modes (batch mode (MFC‐BM), semi‐continuous mode (MFC‐SCM) and continuous mode (MFC‐CM)), towards increasing the power density, substrate utilization, bioelectrochemical kinetics and energy conversion efficiencies.RESULTSHigher power density was recorded with MFC‐SCM (20.54 mW m−2) followed by MFC‐CM (17.22 mW m−2) and MFC‐BM (0.75 mW m−2). Such power density magnitudes were obtained with high anode projected surface area 220 cm2, which is about 10–100 times larger than frequently used in laboratory‐scale MFCs. On the contrary, susbtrate utilization was higher with MFC‐BM (91–96%) followed by MFC‐SCM (74–84%) and MFC‐CM (53–81%). A higher coulombic efficiency (CE) was obtained with the MFC‐CM (7.5–11.2%), followed by MFC‐SCM (5.4–5.6%) and MFC‐BM (0.5–4%). This is of interest due to its dependence on both current generation as well as substrate utilization. Cyclic voltammograms along with derived bioelectro‐kinetic parameters, i.e. redox Tafel's slopes (βa/βc) and electron transfer co‐efficients (αa/αc), also explained the higher performance of MFC‐CM and MFC‐SCM.CONCLUSIONOutput from this study demonstrates clearly that the new MFC design can be effectively operated under continuous mode operation with high retention time to enhance wastewater treatment along with good amounts of power output. © 2014 Society of Chemical Industry

One-dimensional nanostructured design of Li1+x(Mn1/3Ni1/3Fe1/3)O2 as a dual cathode for lithium-ion and sodium-ion batteries

Potential use of Li1+x(Mn1/3Ni1/3Fe1/3)O2 hierarchical nanofibers as a cathode material in both lithium-ion and sodium-ion batteries.

Monitoring Ion Energy Distribution in Capacitively Coupled Plasmas Using Non-invasive Radio-Frequency Voltage Measurements

A non-invasive method for ion energy distribution measurement at a RF biased surface is proposed for monitoring the property of ion bombardments in capacitively coupled plasma sources. To obtain the ion energy distribution, the measured electrode voltage is analyzed based on the circuit model which is developed with the linearized sheath capacitance on the assumption that the RF driven sheath behaves like a simple diode for a bias power whose frequency is much lower than the ion plasma frequency. The method is verified by comparing the ion energy distribution function obtained from the proposed model with the experimental result taken from the ion energy analyzer in a dual cathode capacitively coupled plasma source driven by a 100 MHz source power and a 400 kHz bias power.

Discharge characteristics of the DUHOCAMIS with a high magnetic bottle-shaped field

For the purpose of producing high intensity, multiply charged metal ion beams, the dual hollow cathode ion source for metal ions (DUHOCAMIS) was derived from the hot cathode Penning ion source combined with the hollow cathode sputtering experiments in 2007. To investigate the behavior of this discharge geometry in a stronger magnetic bottle-shaped field, a new test bench for DUHOCAMIS with a high magnetic bottle-shaped field up to 0.6 T has been set up at the Peking University. The experiments with magnetic fields from 0.13 T to 0.52 T have indicated that the discharge behavior is very sensitive to the magnetic flux densities. The slope of discharge curves in a very wide range can be controlled by changing the magnetic field as well as regulated by adjusting the cathode heating power; the production of metallic ions would be much greater than gas ions with the increased magnetic flux density; and the magnetic field has a much higher influence on the DHCD mode than on the PIG mode.