Porous Counter Electrode Research Articles

Novel Symmetric Cell Design for Analyzing All-Solid-State Battery Electrode

All-solid-state lithium batteries (ASSBs) with sulfide-based solid electrolytes (SSEs) have drawn much attention recently for the next-generation batteries. But there are some obstacles to overcome for their practical use. The SSE|cathode interface with poor contact and (electro)chemical instability is the subject of special interest, since it critically aggravates the core performance of battery, including cycling stability and rate capability. In addition to the interfacial property, it has been widely known that Li+ transport characteristics inside the cathode is another key factor in terms of fast and efficient operation of all the lithium battery systems, including the ASSBs. Thus, it goes without saying that the accurate characterization of the interfacial and bulk properties of the cathode is essential to develop the ASSBs.There are limited numbers of test cells to analyze the interface and bulk properties of the battery. First, a conventional half-cell includes Li metal as a counter electrode (CE), which is assumed to have a negligible resistance compared to that of the working electrode (i.e., cathode). It has been reported, however, that the effect of Li CE on total electrochemical signal cannot be disregarded. Moreover, the relative contribution of Li CE to total signal is increasing with the use of the state-of-the-art cathode, whose resistance is getting dramatically lower with technological progress. That is, it is getting difficult to obtain a reliable cathode response by using the two-electrode half-cell configuration. Second, a three-electrode test cell provides the signal of each electrode separately and has been extensively used for the electrochemical analysis. When one uses it for the ASSBs, however, the signals can be erroneous due to the structural distortion caused by the reference electrode (RE) insertion and its own chemical instability, which is especially severe in ASSBs with SSEs. Finally, an alternative cell design to avoid the above problems is a symmetric cell including two identical electrodes facing each other. A general symmetric cell is fabricated by charging/discharging two unit-cell, disassembling them, and re-assembling the identical electrodes to face each other. Unfortunately, a series of such procedure, esp. disassembling/re-assembling, is not applicable to the ASSB systems.In this study, a novel non-destructive potential-controllable symmetric cell (PCSC) is proposed for ASSBs. It features a porous temporary CE (TCE) in parallel between two symmetric electrodes. TCE works as an acceptor or provider of Li to charge or discharge, thereby controls the electrode potential. Symmetric electrodes are then evaluated electrochemically after disconnecting the TCE. As a case study, we investigated and comparatively analyze the electrochemical characteristics of an ASSB cathode, LiNbO3-coated LiNi0.8Co0.1Mn0.1O2, obtained from the conventional test cells and PCSC. Figure presents the impedance spectra of test cells. The two-electrode half-cell impedance is noticeably affected by Li CE over a wide frequency range and the three-electrode cell impedance suffers from severe noise probably caused by RE in the low frequency region. This indicates that both test cells are not suitable for interpreting reliably the interfacial and bulk properties of the cathode. In contrast, the impedance spectra from the PCSC have similar trend to that of three-electrode cell, but provides much more stable impedance spectra, allowing more accurate estimation of interface and bulk characters. In this presentation, the results obtained from DC techniques, such as galvanostatic method, are also comparatively analyzed with conventional test cells and our PCSC. Moreover, the reliability of the estimated values from the PCSC will be discussed by the comparison with those of the previous works. Figure 1

Porous Counter Electrode for Dye-Sensitized Solar Cell by Simple Hydrothermal Method

The porous poly(3,4-ethylenedioxythiophene) (PPEDOT) was synthesized with monomer 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) and zeolitic imidazolate framework-8 (ZIF-8) by simple hydrothermal method. The resultant PPEDOT was employed as counter electrode (CE) in dye-sensitized solar cell (DSSC). The effect of changing DBEDOT/ZIF-8 ratio was studied and results showed that PPEDOT as CE with DBEDOT/ZIF-8 (1 : 1/3) at 80°C demonstrates comparable performance with traditional Pt (CE) in DSSC. Platinum (Pt) and PPEDOT (1 : 1/3) as CEs showed 5.72 and 5.42% efficiency, respectively. The electrochemical and photo-electrochemical as well as impedance spectra measurements revealed that ZIF-8 as template by simple hydrothermal method is a effective way for preparing PPEDOT (CE) in DSSC, which may open up an alternative choice for the future industrial application. In DSSC, PPEDOT (1 : 1/3) is one of the most promising material used for nano-porous thin film when, it serves as counter electrode due to its appropriate low cost, and easy preparation.

Fabrication and Performances of Flexible Monolithic Dye-sensitized Solar Cell Using Metal Reinforced Porous Counter Electrodes

We report here the world’s first large size plastic monolithic dye-sensitized solar cells (DSCs) with size of 1cmx10cm. A novel printable metal-carbon/graphite composite was used as the counter electrode. By transferring this counter electrode on top of working electrode through a cold isostatic pressing technology, flexible monolithic DSC was successfully fabricated. Our results show that charge transfer resistance of carbon/graphite counter electrode was reduced to about 0.2 Ω.cm2 after being reinforced with magnetron sputtering coated Pt nano particles, which is comparable with sandwich structure plastic DSC with commercial Pt/ITO-PET substrates. Keywords: Cold isostatic pressing, flexible monolithic dye-sensitized solar cell, magnetron sputter coating, metal reinforced carbon/graphite composites.

Efficient All-Printable Solid-State Dye-Sensitized Solar Cell Based on a Low-Resistivity Carbon Composite Counter Electrode and Highly Doped Hole Transport Material

Monolithic device architectures provide a route to large-area mesoporous solar cell manufacture through scalable solution-processed fabrication. A limiting factor in device scale-up is availability of low-resistivity printable counter electrode materials and reliable doped charge transport materials. We report an efficient all-printable monolithic solid-state dye-sensitized solar cell (ss-DSC) based on a high-conductivity porous carbon counter electrode and a highly doped 2,2′,7,7′-tetrakis(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) hole transport material (HTM). A review of current state-of-the-art printable porous counter electrodes in DSC literature was conducted and identified blends of graphite/carbon black as promising composites for high-conductivity electrodes. Direct ex situ oxidation of spiro-OMeTAD produced a stable HTM dopant, and its incorporation with one of the lowest-resistivity graphite/carbon black composite materials reported to date drastically decreases device se...

Hierarchical porous carbons as a metal-free electrocatalyst of triiodide reduction for dye-sensitized solar cells

Hierarchical porous carbons (HPCs) are prepared by a one-step hydrothermal route using soluble resols as a carbon source, polystyrene spheres and Pluronic F127 as macroporous and mesoporous templates, respectively. The resulting HPCs comprise continuous macro–meso–micropore networks on the carbon blocks, simultaneously exhibiting large surface areas (501–709 m2 g−1), which are particularly evaluated as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Electrochemical impedance spectra (EIS), Tafel polarization curves, and cyclic voltammograms (CVs) demonstrate that the hierarchical pore system plays a crucial role in promoting the catalytic activities of the HPC CEs. In comparison with other porous carbon CEs, the HPC CEs with various macropores and appropriate micro/mesopores present better catalytic behaviors due to the easier accessibility for electrolyte ions and better utilization of the catalytically active sites, resulting in the higher photovoltaic conversion efficiencies of DSSCs. The optimum photovoltaic conversion efficiency of DSSCs based on HPC CEs is 7.22%, which can even match up to that of the cell with Pt CE (7.25%).

ITO Porous Film-Supported Metal Sulfide Counter Electrodes for High-Performance Quantum-Dot-Sensitized Solar Cells

In this paper, ITO porous films were prepared by the doctor-blade technique to support metal sulfide (CuS, CoS, NiS, and PbS) counter electrodes (CEs) in quantum-dot-sensitized solar cells (QDSCs). The successive ionic layer adsorption and reaction (SILAR) method was used to deposit metal sulfides on the ITO porous films. Since the ITO porous films have high mechanical properties and could offer a large surface area for the large deposition of metal sulfides, the ITO porous film-supported metal sulfide CEs exhibited much higher catalytic activity for polysulfide electrolyte than ITO glass-supported metal sulfide CEs. As a result, the photoeletrochemical performance of QDSCs was greatly improved. In addition, ITO porous film-supported CuS CEs at 12 SILAR cycles exhibited the highest catalytic activity and performance among different CEs, and ITO porous film-supported CoS CEs achieved the second highest catalytic activity and performance, still far higher than the Pt CE, while both ITO porous film-supported NiS and PbS CEs showed similar catalytic activity and performance, significantly lower than that of Pt CE. It is also suggested that many more CE materials can be easily explored and investigated by employing ITO porous films as substrates.

Direct synthesis of platelet graphitic-nanofibres as a highly porous counter-electrode in dye-sensitized solar cells

We synthesized platelet graphitic-nanofibres (GNFs) directly onto FTO glass and applied this forest of platelet GNFs as a highly porous structural counter-electrode in dye-sensitized solar cells (DSSCs). We investigated the electrochemical properties of counter-electrodes made from the highly porous structural GNFs and the photoconversion performance of the cells made with these electrodes.

Polyaniline porous counter-electrodes for high performance dye-sensitized solar cells

Porous polyaniline–camphorsulfonic acid (PANI–CSA) counter-electrodes (CEs) for dye-sensitized solar cells (DSSCs) were fabricated by secondary doping-based polymerization with different porogen decomposition. The average pore diameter was ca. 50 and 150 nm for BPO and AIBN, respectively. The increased Brunauer–Emmett–Teller (BET) surface area of porous PANI–CSA CEs facilitated facile electron exchange between the CEs and the redox electrolyte, resulting in higher electro-catalytic performance than that of Pt-coated indium-doped tin oxide (ITO) CE. The porous PANI–CSA nanostructures with increased BET surface area exhibited an equivalent incident photon-to-electron conversion efficiency (IPCE) of 68.86% and a power-conversion efficiency (PCE, η) of 6.23% compared to DSSCs containing Pt-coated ITO CE (IPCE of 68.70% and η = 6.17%). It is noteworthy that the performance of DSSCs with porous PANI–CSA CEs represented a 101.0% relative efficiency compared to Pt-coated CEs.

Investigation of porous counter electrode for the CO 2 sensing properties of NASICON based gas sensor

In general, solid electrolyte based potentiometric CO 2 sensors respond well to changes in CO 2 concentration, following Nernst equation when dry CO 2 is used. Unfortunately, the sensing capability will be fatally disturbed when these sensors are exposed to humid conditions. To overcome this problem, a sensor using a porous BaCO 3 film as counter electrode (p-Sensor) was fabricated. For the purpose of comparison, sensor without this porous structure (o-Sensor, i.e. an opened counter electrode) and sensor with a dense BaCO 3 film (d-Sensor) also have been fabricated. The electromotive force (EMF) of all sensors exhibited excellence Nernstian behavior with the logarithm of CO 2 concentration in the range 300–755 ppm at 400 °C under dry condition. However, the EMF values of each sensor tended to shift upward with increase of relative humidity. It was found that the relative humidity dependence of EMF originates from both of auxiliary and counter electrodes. Under the same humid conditions, the order of the EMF deviation of three types of sensors was shown as the following: d-sensor > p-sensor > o-sensor. Nevertheless, only p-sensor still remained the Nernstain behavior even under humid conditions. The electron transfer numbers are in good agreement with theoretical value of n = 2. Moreover, the transients were sufficiently sharp, taking less than 1 min for 90% response or recovery. The most important thing is EMF can rapidly recover the original value without any deterioration. The reason for the satisfactory performance of p-sensor under humid condition was suggested to be due to the amount of H 2O molecular adsorbed on the porous counter electrode is very close to that of auxiliary electrode.

Effect of Porous Counter Electrode with Highly Conductive Layer on Dye-Sensitized Solar Cells

Effect of Porous Counter Electrode with Highly Conductive Layer on Dye-Sensitized Solar Cells

Effect of Porous Counter Electrode with Highly Conductive Layer on Dye-Sensitized Solar Cells

A Pt/porous titanium (Ti)/dense Ti/aluminum (Al)/glass composite counter electrode for a dye-sensitized solar cell (DSC) was fabricated and characterized. The introduction of a highly conductive Al film drastically reduced the sheet resistance of the counter electrode to improve the short circuit current and fill factor of the DSC. Porous and dense Ti layers were deposited by the DC magnetron sputtering process. The dense Ti layer protected the Al film from dissolution in the electrolyte solution to stabilize the composite counter electrode. The porous Ti layer with a larger electrochemical active area at the electrolyte/counter electrode interface mainly improved the short circuit current of the DSC. The results indicate the importance of the introduction of porous materials with highly conductive films into the counter electrode of a DSC and the suitability of composite materials of Al and Ti for the counter electrode.

Influence of the interfacial charge-transfer resistance at the counter electrode in dye-sensitized solar cells employing cobalt redox shuttles

We highlight the effect of the interfacial charge-transfer resistance at the counter electrode in dye-sensitized solar cells based on two cobalt redox shuttles, namely cobalt(III/II) tris(2,2′-bipyridine) and cobalt(III/II) tris(1,10-phenanthroline). Highly porous counter electrodes based on poly(3,4-ethylenedioxythiophene) (PEDOT) prepared by electro-oxidative polymerization are compared to the typically employed platinized FTO glass, with the former showing much lower charge transfer resistances for both cobalt complexes, leading to improved fill factors and to linear response of the short circuit photo-current density to light intensity up to one sun. Based on these findings, an excellent power conversion efficiency of 10.3% was achieved with a recently reported organic sensitizer and PEDOT as counter electrode.

Ultratrace Determination of Inorganic Selenium without Signal Calibration

To more readily evaluate the complex biogeochemistry of selenium, a flow-through electrochemical method was developed that can accurately determine Se(IV) concentrations in aqueous samples to part-per-trillion levels without signal calibration. Stripping methods were used in conjunction with a high-efficiency, flow-through cell. The cell was designed with a novel gold working electrode that was separated from a porous counter electrode by a Nafion membrane. Because this design permitted exhaustive deposition of selenium from the sample stream as well as efficient coulometric stripping, determinations obeyed Faraday's law over a reasonably wide range of operating conditions. The method had a minimum quantitation limit of approximately 8 ng and a maximum limit of 800 ng for Se(IV). It was reliable for sample volumes as small as 0.5 mL and as high as 20 mL, thereby allowing determinations from part-per-million to just below part-per-billion levels. Interferences from Cu(II) and arsenate were evident, but only when these species were present at concentrations exceeding 10 mg.L-1. Overall, the method had a performance comparable to hydride-generation atomic absorption spectrometry but with less cumbersome equipment and freedom from calibration.

Mediator Transport in Multilayer Nanocrystalline Photoelectrochemical Cell Configurations

The dye‐sensitized nanocrystalline solar cell utilizing the iodide/triiodide redox mediator served as the system of reference for a theoretical characterization and computational simulation used to scrutinize its performance when viewed as an integral system incorporating a porous counter electrode and a porous spacer layer in between. The concentration profiles of the redox mediator of the thin‐layer solar cell, as well as the concentration (mass‐transfer) overpotential established on the counter electrode and the limiting current of the cell, are affected by the addition of a separation layer between the electrodes and by the geometric and structural properties of the counter electrode itself. Numerical solutions could be obtained from the mathematical model simulating the system that can explain the behavior observed in experimental cells. The feasibility of the porous counter electrode as an alternative is discussed through the model predictions and the experimental kinetic performance data of candidate materials. © 1999 The Electrochemical Society. All rights reserved.