Electrode Cell Configuration Research Articles

New Insights and Strategies for the Efficient Use of Conjugated Porous Polymers in Photoelectrochemical Solar Fuel Production

Solar energy conversion into fuels such as hydrogen through photoelectrochemical (PEC) cells is an attractive way to solve the problems present in the actual energetic system. (1) Despite the advances that have been made in this line, it is still necessary to develop new materials and cell configurations to take this technology to a higher scientific level. The application of organic polymers in PEC is a hot topic that continues to grow due to the promising optoelectronic properties of this class of semiconductors. Conjugated polymers exhibit advanced properties because of it particular conjugation that confers it a huge conductivity through the whole structure. (2) In particular, Conjugate Porous Polymers (CPP) offers a higher photostability and robustness that is fundamental for long term application, but their synthesis often leads to a large-particle powder, unsuitable for preparing thin films, key to preparing high-quality thin films, limiting its applicability in PEC.(3)In this work, we present two innovative strategies that allow the efficient use of these materials in photoelectrochemical cells. The first consists of a synthetic route through mini or ultra-mini emulsion synthesis that provides particles from 500 nm to 20 nm, adequate for thin film preparation. The second consists in the design of suitable monomers to be electropolymerised, obtaining high quality thin films and highly controlled thickness. These strategies allow the complete characterization of the optoelectronic properties of the CPPs, since the thin films obtained are of high quality and stable over time. In this way, several polymers have been prepared and the electronic structure was determined by a combination different techniques such as XPS, electrochemistry and UV-VIS spectroscopy, revealing the suitability to be used as photoelectrodes.The photoelectrochemical properties were analyses by means of linear sweep voltammetry, chronoamperometry, and Photopotential measurements suggesting its potentiality for solar energy conversion. In addition, attending o the conductivity type and electronic properties, both photoelectrodes and tandem cells have been designed by combining them with different materials such as TiO2. The formed hybrid photoelectrodes have been characterized by X-ray diffraction, SEM, EDX and AFM. A series of photoelectrochemical measurements have been performed in a three electrode cell configuration, using the hybrid materials as working electrodes. (4)Hybrid photoelectrodes present improved photovoltages and photocurrents compared to TiO2 and CPP alone, confirming adequate light absorption and charge transfer between them. Besides, Electrochemical Impedance Spectroscopy (EIS) was performed to confirm the improved charge transfer observed when illuminating the hybrid photoelectrodes. Furthermore, the designed tandem cells were connected to a gas chromatograph and the hydrogen evolution was confirmed and quantified. Keywords: Photoelectrochemistry, Solar fuels, Organic materials, Conjugate Porous Polymers, References M. Grätzel, Photoelectrochemical cells. Nature. 414, 338–344 (2001).M. Liras, M. Barawi, V. A. de la P. O’Shea. Chem. Soc. Rev. 48, 5454–5487 (2019).M. Barawi, L. Collado, M. Gomez-Mendoza, F. E. Oropeza, M. Liras, V. A. de la P. O’Shea, C. Adv. Energy Mater. 18, 2101530 (2021).M. Barawi, E. Alfonso-González, C.G. López-Calixto, A. García, A. García-Sánchez, I. J. Villar-García, M. Liras, V.A. de la Peña O'Shea. Small, 18, 37. 2201351 (2022). Acknowledgements This work was supported by the Spanish national project NovaCO2 (PID2020-118593RB-C22) and ERC POC (NanoCPP). M.B thanks the Juan de la Cierva Incorporación grant (IJC2019 – 042430 –I).

Enhance of Anticorrosive Properties of Green-PU-Silica Coatings by Incorporation of Lignin

The tailored combination of organic polymers and inorganic ceramics can produce organic-inorganic hybrid (OIH) coatings to act as corrosion protection barriers.1 ,2 In this work, we proposed the use of glycerol and lignin as polyol sources to prepare green polyurethane to be used in the sol-gel synthesis of PU-silica hybrid coating for steel corrosion protection. The PU pre-polymer was synthesized from MDI (4,4’-methylenebis (phenyl isocyanate)), glycerol and lignin, and then it was functionalized with APTES ((3-aminopropyl) triethoxysilane) to ensure the covalent conjugation with polysilanol network formed from TEOS (Tetraethyl orthsilicate) sol-gel reactions leading to a class II hybrid. Three samples were synthesized varying the proportion between the polyols, one sample containing only glycerol (ZL_PU-S) and the others with a molar ratio of GlyOH:LigOH of 7.5 and 16.1 (FL_PU-S and HL_PU-S, respectively).The effects of lignin content on the structure and properties were evaluated. FTIR and 13C NMR showed the formation of the PU-silica hybrid and the total incorporation of lignin to the PU chain. TGA showed that the presence of lignin into the OIH matrix improved the thermal stability allowing to continuous increase of the initial temperature of mass loss: T5% = 173, 186 and 190 °C for ZL_PU-S, HL_PU-S and FL_PU-S, respectively. The steel substrate coated with the OIH show a water contact angle of 90° for the samples HL_PU-S and FL_PU-S and 80° for ZL_PU-S. The electrochemical impedance spectroscopy analysis performed in a three electrode cell configuration with a NaCl 3.5% solution, showed that the coating with the higher lignin concentration, FL_PU-S, have a |Z| of over 1010 Ω.cm2 for the lowest frequency point and a phase angle of approximately -90° during the 28 days of analysis. The FL_PU-S had better performance than the coating without lignin, ZL_PU-S, that presented |Z|=107 Ω.cm2 on the initial period of immersion with a decrease of two decades in value through out the subsequent period of analysis. In summary, the addition of lignin to the PU polymeric matrix enables the production of a green OIH coating with high efficiency for corrosion protection of steel substrates.Acknowledgments: This work was supported by the Brazilian funding agencies CNPq, FAPESP, CAPES and by PROPe UNESP.Keywords: Renewable feedstock, green coating, PU-silica, lignin, corrosion protection, sol-gel process, hydrophobic coating.1-BRAZ, Á. G.; PULCINELLI, S. H.; SANTILLI, C. V. Glycerol-based polyurethane-silica organic-inorganic hybrid as an anticorrosive coating. Progress in Organic Coatings, v. 169, p. 1069392-HARB, S. V. et al. Siloxane–PMMA hybrid anti-corrosion coatings reinforced by lignin. Surface and Coatings Technology, v. 275, p. 9-16.

Direct growth of MoS2-Ni3S2 core-shell nanowire array on nickel foam as a bifunctional electrode for supercapacitor and electro-oxidation of methanol

Herein, molybdenum sulfide-nickel sulfide (MoS2-Ni3S2) core shell nanowires were directly grown on nickel foam by one step hydrothermal process. The MoS2-Ni3S2 was employed as electrode for supercapacitor electrode and methanol oxidation. The MoS2- Ni3S2 electrode exhibited the specific capacitance of 792 F g-1 at a current density of 1 A g1 in a three electrode cell configuration in 1 M KOH electrolyte and maintained the current density up to 168.7 A g -1 in 1 M KOH electrolyte mixes with 0.5 M methanol. This work confirmed the suitability of the transition metal sulfides for energy storage and electrooxidation of methanol.

N,P‐Codoped, Low‐Density, Amorphous Carbon Foam for High‐Performance Supercapacitors: Polymer‐Based Scalable Production at Low Cost

Herein, a large‐scale production of low‐dense (1.7–2.0 mg cc−1) amorphous carbon foam (char) is demonstrated by simple combustion of an epoxy‐based intumescent composite followed by annealing in argon at 600–900 ºC. It is observed that a balance among physical, chemical, and structural characteristics results in highest electrochemical energy storage performance. For example, the char annealed at 700 ºC (ATA 700) has a specific surface area of 970.55 m2 g−1, a highest pore width diversity (1.87–212.26 nm), moderate sp2‐C and N,P heteroatom contents, highest graphitic‐N, and moderate C–P binding networks. These characteristics promote 1109.7 and 310.4 F g−1 specific capacitances in ATA 700 char with 1 m H2SO4 for three and two electrode cell configurations, respectively, at 0.1 A g−1 specific current. Importantly, the cell demonstrates 97.25% coulombic efficiency and 86.3% capacitance retention after 20 000 charge–discharge cycles (8 A g−1). A highest energy density of 43.1 Wh kg−1 and 20 kW kg−1 peak power density are attained. Such performances are attributed to the hierarchically distributed mesopores and micropores for efficient charge and mass transports along with suitable heteroatoms contents. Therefore, this study brings enormous promise for low‐cost and scalable production of efficient electrodes for electrochemical energy storage.

Electrode response of NaFeTiO4 in aqueous supercapacitor cells

We report electrochemical performance of a calcium ferrite type NaFeTiO4 electrode for capacitor cell applications. High-resolution transmission electron microscopy results confirmed single-phase polycrystalline surface property comprising non-uniform grain distribution. X-ray photoelectron spectrum (XPS) analysis results confirmed presence of Fe3+ and Ti4+ oxidation states. The electrochemical performance of NaFeTiO4 in a three-electrode capacitor cell using different aqueous electrolytes: 1 M H2SO4, 1 M Na2SO4, and 1 M Li2SO4 confirmed superior performance only for capacitor cell with 1 M H2SO4 exhibiting typical pseudo-capacitive response in cyclic voltammetry. In contrast, the cell response of NaFeTiO4 with 1 M Na2SO4 and 1 M Li2SO4 electrolytes was electric double-layer charge (EDLC) accumulation induced capacitive effect predominantly. The electrolyte-driven distinct charge storage mechanism has been attributed to surface adsorption-induced redox action in the former whereas the EDLC response in the latter is attributed to larger size of the hydrated Na+ and Li+ ions causing charge accumulation at the interface. An excellent cyclic stability up to 10000 cycle with capacity retention up to 91% and coulombic efficiency ~ 100% has been noted @ 1 Ag−1 in 1 M H2SO4. Two electrode symmetric cell results exhibit similar pseudo-capacitive response as in three electrode cell configuration. The material delivered maximum power density ~ 18 kW/kg @ 10 Ag−1 and energy density ~ 2.55 Wh/kg @ 0.1 Ag−1 in a three-electrode-cell configuration whereas for a two-electrode cell, corresponding values are ~ 3.13 kW/kg @ 0.43Ag−1 and ~ 2.26 Wh/kg @ 0.04 Ag−1.

A New Cell Configuration for a More Precise Electrochemical Evaluation of an Artificial Solid‐Electrolyte Interphase

AbstractThe study of an artificial solid‐electrolyte interphase (SEI) can lead to a misinterpretation of the electrochemical results obtained with the classical cell configuration due to so‐called edge effect. A technical solution is presented here that minimizes the edge effect by using a new cell configuration with a polypropylene disc. A new cell configuration allows a simple electrochemical evaluation of an artificial SEI with a more precisely defined effective area and homogeneously distributed current density. The application of such a technical solution manifests itself through better defined deposition and stripping curves in relation to surface electrochemistry and can differ significantly from the results obtained with the classical cell configuration. Finally, a model system ‐ a lithium electrode protected with trimethylolpropane ethoxylate triacrylate polymer‐was used to evaluate and compare the new cell configuration with the classical two electrode cell configuration.

Optimization of cobalt-manganese binary sulfide for high performance supercapattery devices

Hybrid supercapacitors have attained incredible attention for their versatile worth in energy storage applications, still desire to enhance the specific energy and power limit by employing an electrode material with flashing electrochemical performance. Transition metal sulfides for their high electrochemical activities and better conductivity are promising electrode materials. Here we report the performance optimization of binary metal sulfide synthesized by the sonochemical approach. Initially, cobalt and manganese sulfides were prepared, then the composition of cobalt and manganese was varied in binary metal sulfides. The phase structure, elemental analysis, and morphological aspects were studied via X-ray, diffraction (XRD), energy dispersive X-Ray spectroscopy (EDX), and scanning electron microscopy (SEM). The electrochemical test in three electrode cell configuration reveals that Co0.5Mn0.5S exhibited prime electrochemical performance compared to all other compositions. A specific capacity of 713.13 C/g at 3 mV/s and 536.0 C/g (specific capacitance of 893.3 F/g) at 1.0 A/g was obtained from Co0.5Mn0.5S. This electrode material was further utilized in an asymmetric (supercapattery) device along with activated carbon. The electrochemical analysis of the supercapattery device was carried out in two electrode assembly. The fabricated device has achieved exceptional specific energy of 61.34 Wh/kg at a specific power of 850 W/kg and retains specific energy of 9.92 Wh/kg while providing remarkable specific power of 8500 W/kg. In addition, the device also demonstrated outstanding capacity retention of 90.19% after 2000 consecutive GCD cycles at 10 A/g. Moreover, the device performance was further scrutinized by a simulation approach in terms of capacitive and diffusive contributions. These impressive results demonstrate that the Co0.5Mn0.5S is a favorable electrode material for high performance supercapattery applications.

Morphological engineering of novel nanocrystalline Cu2Sn(S,Se)3 thin film through annealing temperature variation: Assessment of photoelectrochemical cell performance

Robust nanocrystalline Cu2Sn(S,Se)3 (CTSSe) thin films have been synthesized for the first time by arrested precipitation technique (APT) through arrest and release of ions from complexed solution and used as potential photocathode for photoelectrochemical cell application. The assessment of annealing temperature variation on the optostructural and optoelectronic performance of CTSSe thin films was studied. It was noticed that the annealing temperature, effectively modifies the absorption and crystalline properties of CTSSe thin films. Optical absorption interpretations elucidated the direct allowed nature of transitions with alteration of band gap energy from 1.68-1.50 eV as the annealing temperature increases. Structural studies from the XRD demonstrates the shifting of diffraction peak to the lower 2θ values with the average crystallite size in the range 19 to 28 nm. A comparative study of XRD and Raman spectra revealed the formation of cubic CTSSe crystal structures. Surface morphological alterations from a small bunch of nanograins to nanorocks to nanocubes were manifested with effective variation in annealing temperature. The compositional studies demonstrates the presence of Cu1+, Sn4+, S2− and Se2− oxidation states in Cu2Sn(S,Se)3 thin film synthesized by APT. Single phase cubic crystal formation from HRTEM and SAED results, verify good crystallinity of synthesized CTSSe thin film. Furthermore, the J-V curves shows the highest photoelectrochemical cell efficiency of 0.42 % for bare CTSSe photocathode with two electrode cell configuration of glass/FTO/Cu2Sn(S,Se)3/(I−/I3−)/graphite. A reduced charge transfer resistance (Rct) from the EIS plots supports for the improved PEC efficiency.

Surfactant decorated polypyrrole-carbon materials composites electrodes for supercapacitor

The current effort discuss the fabrication of improve electrode materials for supercapacitor comprise of surfactant doped polypyrrole‑carbon materials composites integrated with graphene, amine functionalized multiwalled carbon nanotubes and hybrid carbon assembly. The spectroscopic characterizations demonstrate the establishment of a well-built state of charge swap complex among surfactant doped polypyrrole and carbon materials that disclose the occurrence of polymer‑carbon phases and promote well-built polarization. The electrodes are assembled in the three electrode cell configuration with graphite sheet current collector. The composite SDBSDPPy-HC holds a specific capacitance of 1086 F g−1 at scan rate 5 mV s−1 in 6 M KOH electrolyte solution. SDBSDPPy-HC exhibit only 10% losses in specific capacitance over 2500 cycles i.e. 90% preservation of specific capacitance at a current density 1 A g−1.

Nano-architectured porous Mn2O3 spheres/cubes vs rGO for asymmetric supercapacitors applications in novel solid-state electrolyte

In this study, we have proposed a facile cost-effective hydrothermal route to synthesis homogeneously dispersed porous cubic structure Mn2O3 nanospheres (230 nm) and nanocubes (250 nm) nano-architectures to fabricate an efficient energy storage device. Mesoporous Mn2O3 spheres and cubes are exhibiting higher specific surface area (36.27 cm3 g−1 and 17.87 cm3g-1) and pore size (4.88 nm and 3.64 nm) respectively and in three electrode cell configuration they are showing an excellent specific capacitance of 345 F g−1 and 321 F g−1 at 0.2 A g−1, respectively. Notably, the fabricated asymmetric solid-state supercapacitor (Mn2O3 nanospheres/nanocubes (positive electrode) and rGO electrodes (negative electrode)) are presenting an outstanding electrochemical performances with novel PVA-LiNO3 gel solid-state electrolyte; ultrahigh energy density of 46 W h kg−1 at a power density of 247 W kg−1 and excellent capacitance retention of 95% after 5000 cycles are observed. Moreover, practical and operation ability of the device are successfully demonstrated by lighting up the 21 LEDs lights in series like ALU letters. Thus, the reported porous cubic Mn2O3 nano-architectured electrode material synthesis strategy is more beneficial to the low cost, mass production for superior energy storage and viable alternative material for the existing commercially available materials.

Sweet‐Lime‐Peels‐Derived Activated‐Carbon‐Based Electrode for Highly Efficient Supercapacitor and Flow‐Through Water Desalination

AbstractIn the present work, highly porous activated carbon with an excellent surface area has been successfully synthesized from the agricultural waste product; sweet lime peels (Citrus limetta) using a facile chemical approach. The structural and morphological properties of sweet lime peels derived activated carbon (SLP‐AC) were studied using X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). Brunauer‐Emmett‐Teller (BET) surface area and pore structure were studied using nitrogen adsorption‐desorption isotherms. Electrochemical characterizations were performed in two and three electrode cell configurations using techniques like cyclic voltammetry (CV), Galvanostatic charge‐discharge (GCD) and electrochemical impedance spectroscopy (EIS) in aqueous (1 M H2SO4 and 1 M NaCl) and ionic liquid electrolytes (EMIMBF4). SLP‐AC based electrodes showed high electrochemical charge storage capacity of 421.67 F/g (at 1 A/g) along with outstanding cyclic stability up to 10000 GCD cycles. Fabricated supercapacitor device demonstrated high energy density of 45.53 Wh/kg in the ionic liquid electrolyte. SLP‐AC was also used to prepare the porous sponge electrodes to study their applicability in flow‐through electrode capacitive deionization (CDI), where it achieved the maximum electrosorption capacity of 22.8 mg/g. The electrosorption results fitted well with the Langmuir isotherm and the kinetics study indicates a pseudo‐first‐order kinetic model for the electrosorption of salt ions onto the electrodes surface. This confirms the outstanding performance of SLP‐AC as a highly stable and low‐cost electrode material for supercapacitors and water desalination applications.

New Hybrid Photoelectrodes Composed of TiO2 and Nanostructured Conjugated Porous Polymers for Enhanced Photocurrents in Solar Energy Conversion Cells

Photoelectrochemical water splitting is one of the most interesting alternatives to produce hydrogen in a clean way by solar energy conversion.(1) Despite the huge potential and great advances, new materials need to be developed in order to take this technology to a commercial level. At present, different materials as oxides, oxisulfides and metal chalcogenides are being investigated as photoelectrodes in photoelectrochemical cells. However, achieving high STH (Solar To Hydrogen) using a single material as a photoelectrode is a very tricky objective. Therefore, hybrid materials are getting a lot of attention lately. (2) In this work, we present a hybrid material formed by the heterojunction of a novel synthesized organic conductive polymer and TiO2 nanocrystals. The nanostructured conjugated porous polymer is based on dithiothiophene moiety (Nano-CMPDTT) and was synthesized by Sonogashira cross coupling reaction from precursors in mini-emulsion conditions. In order to elucidate the electronic structure and the ability of this material to be used as a photocatalyst, HOMO and LUMO positions were determined by cyclic voltammetry. The energy diagram shows an ideal position of the energy bands in order to use the synthesized polymer as an electron injector to TiO2 in photocatalytic reactions. In order to test the photoelectrochemical behavior of this hybrid material, TiO2 NCs suspensions and organic polymer has been deposited by spin coating in ITO glasses. The formed films have been characterized by X-ray diffraction, SEM, EDX and AFM. Photoelectrochemical measurements have been performed in a three electrode cell configuration, using the hybrid material as the working electrode. The hybrid material presents an enhancement in photovoltages and photocurrents values. Electrochemical Impedance Spectroscopy (EIS) was performed to confirm the improved charge transfer observed when illuminating the hybrid material in comparison to the TiO2 nanocrystals alone. By simulating the electron charge transfer by using an equivalent circuit, a decrease in the resistance associated with this phenomenon was found. This confirms that the presence of the polymer in the hybrid material improves the absorption of light, charge transfer and reduces electron-hole recombination, making this hybrid a good candidate to be used as a photoelectrode for the hydrogen evolution reaction.

Synthetic Method Dependent Physicochemical Properties and Electrochemical Performance of Ni-Doped ZnO

Nickel doped zinc oxide (Ni/ZnO) nanostructures have the potential to improve the performance of electrochemical capacitors. This study investigates the preparation of Ni/ZnO nanomaterials by facile co-precipitation (CPM) and hydrothermal (HTM) methods. The effect of the synthesis methods on the optical, structural, chemical and morphological properties of ZnO products is investigated using ultra violet (UV)-visible spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrometry (EDX), room temperature photoluminescence (PL), fourier transform infrared (FTIR) and Raman spectroscopy. Finally, the electrochemical performance of the synthesized nanorods was examined by the fabrication of a supercapacitor using standard three electrode cell configurations and tested with a cyclic voltammogram (CV) and galvanostatic charge-discharge (GCD) measurements. The results showed that the samples synthesized by HTM exhibited improved electrochemical capacitance performance with higher current density. The discharge curves are linear in the total range of potential with constant slopes, showing perfect capacitance. In conclusion, Ni/ZnO nanoparticles synthesized by this method with further optimization have the potential to lead to high-efficiency supercapacitors.

Importance of microstructure and interface in designing metal oxide nanocomposites for supercapacitor electrodes

In this work, we demonstrate that designing metal oxide nanocomposite with an optimized nanocarbon to metal oxide ratio is required to realize the best electrochemical performance. Using carbon nano-onion (CNO) and TiO2 composite as a model system, it is evidenced that the formation of interfacial structure and the existence of electrical percolation networks are essential to enhance electrical performance of the composite. When the aforementioned conditions are satisfied, CNO/TiO2 hybrid nanocomposites (CTHNs) with only 11wt% TiO2 loading exhibits excellent electrochemical performance. The maximum specific capacitance obtained for this composite electrode is 386Fg−1 at a scan rate of 5mVs−1, which is the highest reported value till date in a TiO2 composite electrode measured in a two electrode cell configuration. At this composition, excellent electrochemical stability is obtained with only 5% capacitance degradation over 2000cycles. As the TiO2 loading increases the electrochemical performance decreases.

Microelectrodes As Effective Tools to Evaluate Biodiesel Corrosiveness By Electrochemical Techniques

Corrosion is one of the main concerns for using biodiesel as an alternative fuel. Nowadays, the vast majority of studies are done by immersion tests and the monitoring of its physicochemical properties during degradation reactions. The low conductivity of biodiesel and the development of high ohmic drops has restricted the use of electrochemical techniques for understanding the mechanisms involved in the corrosion processes. The addition of supporting electrolytes is often used to increase the conductivity and reduce the ohmic drop. In organic media as biodiesel, unfortunately, it is suspected that supporting electrolytes are not inert and can give misleading results. Microelectrodes are sensors with at least one dimension in the range of few micrometers (~50) and its geometry mostly depend on its application. Due to the small currents registered in microelectrodes, the effects of the ohmic drop become insignificant, even in very resistive electrolytes as biodiesel. In this work, we propose the use of microelectrodes as a methodology to evaluate the corrosion rate of metals, particularly copper, by EIS without any addition of supporting electrolytes (water or other contaminants). Two different types of microelectrodes (i.e. single classic and array) with disk geometry were constructed and characterized by different techniques (optical microscopy, SEM and cyclic voltammetry). Single classic microelectrodes were constructed manually by introducing a metallic wire (working electrode) into a capillary glass. The arrays with sixteen and twenty-five microelectrodes were constructed by photolithography technique. The impedance measurements were done in a Gamry ref. 600 potentiostat/galvanostat using a two electrode cell configuration were a Pt foil was used simultaneously as counter and reference electrode (i.e. short-circuited to the corresponding inlets of the potentiostat) and the microelectrode was the working electrode. The frequency range was from 100 kHz to 5 mHz, with an amplitude of potential perturbation of 30 mV rms (with lower perturbation of potential no response is obtained). For both types of microelectrodes, two time constants were observed, one at high frequencies and the other at low frequencies. The former corresponds to the electrolyte and the latter to interfacial phenomena between the electrolyte and the metal surface. Both hypothesis were corroborated using three different types of experiments. In the first case, another quality of biodiesel was used. Degraded biodiesel was obtained by introducing a copper foil, increasing the temperature and bubbling air during 5 days. With degraded biodiesel a reduction in the impedance at high frequencies was observed in both types of microelectrodes, as a result of the higher conductivity of the electrolyte. In the second case, an inert metal (Pt) was used as a microelectrode (single classic) and it was observed an increase in the impedance with respect to copper, due to the low activity that Pt has in biodiesel. Additionally, an array of copper with 25 microelectrodes was left in contact with degraded biodiesel during 60 h. Every 12 h the impedance was monitored and recorded. The results showed an increase in this parameter as a consequence of the growth in the corrosion layer formed on the surface of the metal in contact with the biofuel. As the corrosion layer growths the rate of the electron transfer reactions at the interface is reduced. In all cases, the second semicircle observed in Nyquist diagrams started at 0.3 – 0.1 Hz. A decrease in the phase angle at medium frequencies (1-0.1 Hz) was observed when the number of microelectrodes increased as a result of a higher kinetic for the change transfer process, due to the higher area and the interfacial character of the signal. Figure 1

Controlling hydrogen evolution on iron electrodes

Aiming to develop a cost effective means to store large amounts of electric energy, NiFe batteries were produced and tested under galvanostatic conditions at room temperature. Multiple regression analysis was conducted to develop predictive equations that establish a link between hydrogen evolution and electrode manufacturing conditions, over a wide range of electrode/electrolyte systems. Basically, the intent was to investigate the incidence of lithium hydroxide and potassium sulphide as electrolyte additives on cell performance. With this in mind, in-house built Fe/FeS based electrodes were cycled against commercially available nickel electrodes on a three electrode cell configuration. A 3 × 4 full factorial experimental design was proposed to investigate the combined effect of the aforementioned electrolyte additives on cell performance. As a consequence, data from 144 cells were finally used in conducting the analysis and finding the form of the predictive equations. Our findings suggest that at the level of confidence alpha = 0.05, the presence of relatively large amounts of the soluble bisulphide would enhance the performance of the battery by reducing electrolyte decomposition.

Two and Three Electrode Electrochemical Cells for Ambient and High Temperature Battery Materials Research

Introduction Coin cells and Swagelok cells are typically used for two and three electrode electrochemical testing of metal ion battery materials. Commercial three electrode laboratory cells are also available, but are typically expensive and often use elastomeric seals, which react with electrolyte and are not compatible with high temperatures. The use of traditional 2325 coin cell hardware at high temperature applications is limited by the 60°C softening temperature of the cell gasket. At 60°C, the pressure generated by highly volatile solvents can cause the cell to rupture. This is especially troublesome for Mg battery research where volatile solvents are generally used and high temperatures are needed for better intercalation kinetics. Two and three electrode Swagelok cells are more difficult to prepare than standard coin cells. They typically use PTFE ferrules, and care must be taken as PTFE is reactive with electrolyte at low potentials. Here we describe cell hardware based on Conflat vacuum fittings. Typically Conflat vacuum fittings use copper or Viton gaskets. These can either cause a short circuit between two Conflat fittings or react with electrolyte. We have found gasket materials made from stable polymers form effective insulating, electrolyte resistant and high temperature seals in laboratory test cells. Experimental Conflat cells were constructed using standard 2.125" Conflat blank and bored flanges. HDPE or PTFE gaskets were punched from 0.125" sheets using a circular die press. Two electrode cells used the same inner cell stack as a two electrode coin cell (spring, spacer, electrodes, separator). Three electrode cells included a Li or Mg ring reference electrode. 2325 coin cell hardware was used for comparative testing. Results and Discussion Figure 1 shows the cycling performance of a LiFePO4 (LFP) vs Li two electrode Conflat cell using 1M LiTFSI in PC at 30oC. It shows no capacity fade and identical performance as coin cells.Figure 2 shows the cycling of a two electrode Li4Ti5O12 (LTO)/Li Conflat cell tested at high temperatures. No capacity fade was detected below 110oC. As the temperature is increased, reactions with the electrolyte caused the capacity to fade due to increased impedance from electrolyte decomposition reactions.Figure 3 shows the cycling performance of a Mo6S8/Mg/Mg three electrode Conflat cell containing a highly volatile tetrahydrofuran (THF) based electrolyte at 60°C. We have found that three electrode cells using such volatile electrolytes at this temperature are extremely unreliable and difficult to make using coin cell hardware. The conflat cell, on the other hand cycled reversibly, during which time the voltages of the Mg counter and Mo6S8working electrode were accurately measured without electrolyte polarization using the third electrode.Conflat cells are excellent low cost cell hardware that use readily available parts. They are simple to assemble can be made into two and three electrode cell configurations and particularly useful for high temperature studies. We consider Conflat cells an excellent alternative to coin and Swagelok cell hardware especially in Mg battery research where the electrolyte is volatile and moderately high temperatures are used. Three electrode measurements at high temperature of Li and Mg battery materials and further details regarding Conflat cell design will be discussed.

Biopolymer-Assisted Synthesis of λ-MnO2Nanoparticles As an Electrode Material for Aqueous Symmetric Supercapacitor Devices

λ-MnO2 nanoparticles have been successfully synthesized using macromolecules like starch and dextrose. The X–ray diffraction pattern shows the cubic structure of the λ-MnO2. Morphological studies show the synthesized particles to be of nanospherical structure. The FTIR spectrum confirms the presence of Mn–O bonds. From the charge–discharge analysis λ-MnO2 was found to exhibit the highest specific capacitance of 384 F g–1 at a specific current discharge of 1 A g–1. The symmetric aqueous supercapacitor device exhibits the 44 F g–1 at a specific current discharge of 1 A g–1. We have obtained higher specific capacitance for λ-MnO2 in three electrode cell configuration and two electrode supercapacitor cells. This is higher than previous reports of λ-MnO2 three electrode cell and two electrode systems. All the three electrochemical measurements (cyclic voltammetry, galvanostatic charge–discharge, and impedance) proved that the λ-MnO2 was a good electrode material for a supercapacitor.

Transference number and structural analysis of proton conducting polymer electrolyte based on poly(ϵ-caprolactone)

Poly(ϵ-caprolactone) (PCL) is used as the polymer host to dissociate ammonium thiocyanate (NH4SCN). Free standing solid polymer electrolytes of varied weight ratios are prepared by solution casting technique with tetrahydrofuran as solvents. Impedance measurement shows the highest ionic conductivity achieved at room temperature is 1·01×10−4 S cm−1 for PCL incorporated with 26 wt-% NH4SCN. In transference number analysis, the total ionic transference number is calculated to be 0·966 using blocking electrode cell configuration. The value of t+ is evaluated to be 0·21 using reversible electrode cell configuration. The ohmic portion of steady state current indicates the existence of mobile ion pairs or higher aggregates. In X-ray diffraction analysis, crystalline peaks were deconvoluted from the continuous halo with high goodness of fit. The degree of crystallinity as a function of salt concentration is estimated and is in exact agreement with ionic conductivity variation, concluding that accommodation of salt into the polymer matrix depresses the crystalline phase of PCL.

Application of Electrochemical Impedance Spectroscopy for Fuel Cell Characterization: PEFC and Oxygen Reduction Reaction in Alkaline Solution

AbstractThe most common method used to characterise the electrochemical performance of fuel cells is the recording of current/voltage U(i) curves. Separation of electrochemical and ohmic contributions to the U(i) characteristics requires additional experimental techniques like electrochemical impedance spectroscopy (EIS). The application of EIS is an approach to determine parameters which have proved to be indispensable for the characterisation and development of all types of fuel cell electrodes and electrolyte electrode assemblies [1]. In addition to EIS semi‐empirical approaches based on simplified mathematical models can be used to fit experimental U(i) curves [2].By varying the operating conditions of the fuel cell and by the simulation of the measured EIS with an appropriate equivalent circuit, it is possible to split the cell impedance into electrode impedances and electrolyte resistance. Integration in the current density domain of the individual impedance elements enables the calculation of the individual overpotentials in the fuel cell (PEFC) and the assignment of voltage loss to the different processes. In case of using a three electrode cell configuration with a reference electrode, one can directly determine the corresponding overvoltage. For the evaluation of the measured impedance spectra the porous electrode model of Göhr [3] was used. This porous electrode model includes different impedance contributions like impedance of the interface porous layer/pore, interface porous layer/electrolyte, interface porous layer/bulk, impedance of the porous layer and impedance of the pores filled by electrolyte.