Increase In Cell Voltage Research Articles

Controllable Lenses for Photovoltaic Energy Generation Enhancement

Fixed-focal point solar concentrators have been used in high-power density applications. However, the inability to control the focal point often saturates the energy generation of the cells and exposes them to excessive heat. In this condition, the efficiency of solar cells drops rapidly and results in low energy production. This paper introduces a controllable focal point lens to maximize the energy generation of thin-film and thick-film solar cell. An electrowetting phenomenon is used to control the curvature and the focal point of the lens. The voltage that is applied across the lens directly controls the light intensity on solar cell areas. Therefore, it can control the energy generation and operating temperature of the cells. Experimental results prove the effectiveness of the focal point lens in energy generation enhancement in thick and thin films. Thick-film solar cells generate more power at high electrowetting voltage, whereas thin films that maximize the power at low electrowetting voltage. The P-V curves of thick films demonstrated a decrease in solar cell voltage of the maximum power point. Thin-films demonstrated an increase in cell voltage of the maximum power point at higher electrowetting voltage of low sunbeam intensities. The controllable lens increased the energy production by 78%.

The dynamic-state effects of sodium ion contamination on the solid polymer electrolyte water electrolysis

Na+ is a likely intrinsic impurity in water and is a potential cation impurity in the solid polymer electrolyte water electrolysis. In this paper, the dynamic-state effect of low concentration of Na+ is studied by adding Na+ into the deionized water fed in the SPE water electrolyser. The dynamic variation of cell voltage results show that the cell performance degraded more severely in the presence of Na+ impurity by anode poisoning than by cathode poisoning. The severity and poisoning rate of the cell depend on the Na+ concentration, water flow rate and cell temperature. However, the current density does not impact the extent of the cell voltage increase. In the meantime, an external reference electrode is used to measure the anode and cathode potentials. The performance degradation is mainly ascribed to the increase in cathode overpotential by anode poisoning. EIS measurements show that the performance difference primarily comes from the kinetics loss rather than the ohmic loss. The decrease of available protons in the three phase boundaries may lead to the increase in charge transfer resistance. The electron probe microanalysis tests show that Na+ remains in CCM even recovered with deionized water, which results in only partially recovered cell performance.

Degradation of methyl orange waste water by electrochemical oxidation method

Degradation of methyl orange (MO) waste water was conducted by electrochemical oxidation method with PbO2/Ti electrode as anode. PbO2/Ti electrode was fabricated by electrochemical deposition of PbO2 on Ti foil. The micrograph and crystal structure of PbO2 show that uniform coating of PbO2 on titanium foil was obtained and the dominant crystal structure was β-PbO2. Degradation experiments of MO solution indicate that the degradation rate increased with cell voltage and solution conductivity. In addition, air aeration also improved the degradation of MO solution; but an increase in cell voltage or input energy decreased the energy efficiency of MO removal. The energy efficiency reached over 0.1mg kJ−1 under a cell voltage lower than 15V, and the removal rate could reach 90%.

Flexible All-Solid-State Asymmetric Supercapacitors Based on Free-Standing Carbon Nanotube/Graphene and Mn3O4Nanoparticle/Graphene Paper Electrodes

We report the design of all-solid-state asymmetric supercapacitors based on free-standing carbon nanotube/graphene (CNTG) and Mn(3)O(4) nanoparticles/graphene (MG) paper electrodes with a polymer gel electrolyte of potassium polyacrylate/KCl. The composite paper electrodes with carbon nanotubes or Mn(3)O(4) nanoparticles uniformly intercalated between the graphene nanosheets exhibited excellent mechanical stability, greatly improved active surface areas, and enhanced ion transportation, in comparison with the pristine graphene paper. The combination of the two paper electrodes with the polymer gel electrolyte endowed our asymmetric supercapacitor of CNTG//MG an increased cell voltage of 1.8 V, a stable cycling performance (capacitance retention of 86.0% after 10,000 continuous charge/discharge cycles), more than 2-fold increase of energy density (32.7 Wh/kg) compared with the symmetric supercapacitors, and importantly a distinguished mechanical flexibility.

Carbon nanoporous layer for reaction location management and performance enhancement in all-vanadium redox flow batteries

In this study, the performance and reaction location in a VRFB was investigated with a carbon paper electrode that was modified to include a thin layer of multi-walled carbon nanotubes. The nanotube layer was introduced into the electrode at locations on the negative and positive electrode nearest the membrane and nearest the flow field. Results with the nanotube layer on the positive electrode yielded small changes in the performance, despite the location. However, when the nanotube layer was introduced on the negative electrode, the performance was greatly improved when it was closest to the current collector. In this configuration, an 8% increase in power density and a 65mV increase in cell voltage were observed, compared to a cell with raw carbon paper. This is attributed to the increase in active area of the nanoporous structure in a location where the reaction is favored to occur.

Nitrate reduction with biotic and abiotic cathodes at various cell voltages in bioelectrochemical denitrification system

Electrochemical treatment of nitrate ions was attempted using different catalysts on the cathode in bioelectrochemical denitrification systems. The carbon cathode coated by biofilm (biocathode) could remove 91 % of nitrate ions at 1.0 V, which was almost same as the Pt-coated electrode (90 %). The exchange current density of biocathode was 0.0083 A/m(2), which was almost 22 times higher than with an abiotic plain carbon cathode. The formation of intermediate products in nitrate reduction varied depending on the cell voltage. At 0.5 V, a large portion of nitrate was converted to ammonia, but at more increased cell voltage (0.7 and 1 V) a high amount of nitrite ions was found with little ammonia formation in cathodic solution. The maximum nitrate removal rate was 0.204 mg NO(3)-N/cm(2)d by biocathode, while plain carbon paper showed only 0.176 mg NO(3)-N/cm(2)d. Electrochemical analysis of chronoamperometry showed a higher stable current generation for biocathode (3.1 mA) and Pt-coated cathode (2.8 mA) as compared to plain carbon (0.6 mA) at 0.7 V of poised voltage.

Novel high-performance solid oxide fuel cells with bulk ionic conductance dominated thin-film electrolytes

The overall performance of ionic conducting electrolyte layers is a key factor for determining the power density of solid oxide fuel cells (SOFCs). The aim of this work is to investigate high performance SOFC electrolyte layers developed in our lab via a low cost wet-chemical processing method. In this paper, SOFCs with bulk ionic conductivity dominated thin-film electrolyte demonstrate superior electrochemical performances. Conventional materials for SOFCs are applied in this work: Ni–YSZ cermet as the anode, yttria-stabilized zirconia (YSZ) as the electrolyte, gadolinia-doped ceria (CGO) as the Sr-diffusion barrier layer, and LSCF or LSC as the cathode. At 0.7 V and 600 °C, single cells with an active LSCF and LSC cathode area of 4 × 4 cm2 obtain a power density of 0.7 and 1.4 W cm−2, respectively. According to electrochemical impedance spectroscopy (EIS), the ohmic resistance of the single cells is almost one order of magnitude lower than the conventionally fabricated SOFCs. Due to the improved performance of the electrolyte, SOFCs are able to deliver high power output at reduced operating temperature and increased cell voltage.

A comparison of cathodes for zero gap alkaline water electrolysers for hydrogen production

Selected coatings on nickel or stainless steel micromeshes have been examined as electrocatalysts for hydrogen evolution in conditions mimicking those found in zero gap alkaline water electrolysers. Voltammetry in 4M NaOH at a temperature of 333K, shows that Pt, NiMo and RuO2 are the coatings of choice giving a superior performance particularly at higher current densities. NiMo and RuO2 coatings also give stable performance during a 10 day electrolysis in a laboratory, zero gap, alkaline water electrolysis cell with a hydroxide conducting membrane; when combined with a NiFe(OH)2 coated anode, a current density of 1Acm−2 is achieved with a cell voltage of ∼2.1V. Pt catalyses H2 evolution efficiently at short times of electrolysis but cells with a Pt cathode show an increase in cell voltage from 2.05V to 2.23V during the first two days of operation.

Electro-oxidative process for the mineralization of solvent and recovery of plutonium from organic wastes

Mediated electrochemical oxidation is a promising technique for the destruction of organic compounds. Destruction of tributyl phosphate (TBP) in normal paraffin hydrocarbon (NPH) in nitric acid medium containing electro-generated Ag(II) was studied. Initially, the effect of uranium, presence of DBP along with uranium in the organic phase and direct electrochemical oxidation without catalyst (Ag) on the destruction of 30% TBP/NPH system was evaluated. For a comparison, the rate of destruction of NPH alone was studied. Further, radioactive laboratory waste solution was tested for the destruction of organic waste under similar experimental conditions. The electrolyte used in the system was 0.5 M AgNO3 in 8 M HNO3 at 333 K. The uniqueness in all these experiments is the use of a double end open porcelain diaphragm for the isolation of electrodes. Though there would be a slight reduction in the efficiency, two major hurdles viz., reduction in the concentration of nitric acid and reduction in the volume of catholyte resulting in an increase in cell voltage were avoided. The problem of the migration of Ag+/Ag2+ and accumulating at the cathode site was overcome by using double end open diaphragm and thorough mixing. The results revealed that the rate of destruction of organics is favoured in the presence of uranium in organic phase and with increase in temperature.

In Situ Electrochemical Characterization of Proton Exchange Membrane Fuel Cells Fabricated with Pd–Pt–Ni Cathode Catalysts

The performance of a proton exchange membrane fuel cell (PEMFC) with Pd–Pt–Ni as an oxygen reduction reaction catalyst has been evaluated and analyzed with operation time using current–voltage polarization, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The cell performance increases continuously in the whole current density range with the cell operation time, but the rate of increase slows down gradually and the performance becomes constant on the seventh day. The invariable membrane resistance and the continually decreasing charge transfer resistance as indicated by the EIS data illustrate that the enhanced interfacial kinetics at the cathode contributes to the cell voltage increase. CV data reveal that the electrochemical active surface area decreases, while the catalyst surface changes from Pd-enrichment to Pt-enrichment and the peak potential for surface oxide stripping shifts positively due to metal dissolution, with operation time. The latter serves as the origin for the enhancement in catalytic activity and the overall cell performance. With the Pt-mass activity and specific activity improvement, respectively, by factors of 1.8 and 1.9 compared to commercial Pt, the Pd–Pt–Ni alloys are promising cathode catalysts for PEMFC.

Increased Electrical Output when a Bacterial ABTS Oxidizer is Used in a Microbial Fuel Cell

Microbial fuel cells (MFCs) are a technology that provides electrical energy from the microbial oxidation of organic compounds. Most MFCs use oxygen as the oxidant in the cathode chamber. This study examined the formation in culture of an unidentified bacterial oxidant and investigated the performance of this oxidant in a two-chambered MFC with a proton exchange membrane and an uncoated carbon cathode. DNA, FAME profile and characterization studies identified the microorganism that produced the oxidant as Burkholderia cenocepacia. The oxidant was produced by log phase cells, oxidized the dye 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), had a mass below 1 kD, was heat stable (121°C) and was soluble in ethanol. In a MFC with a 1000 Ω load and ABTS as a mediator, the oxidizer increased cell voltage 11 times higher than atmospheric oxygen and 2.9 times higher than that observed with ferricyanide in the cathode chamber. No increase in cell voltage was observed when no mediator was present. Organisms that produce and release oxidizers into the media may prove useful as bio-cathodes by improving the electrical output of MFCs.

Anodic electron shuttle mechanism based on 1-hydroxy-4-aminoanthraquinone in microbial fuel cells

In microbial fuel cells (MFCs), the electron transfer from microorganisms to the cell anode is a decisive factor on the power output. Though quinone derivatives can function as electron shuttles, the electron shuttle pathways have so far not been demonstrated. In this paper, the mechanism of electron shuttle via an exogenous mediator was studied in MFCs using Geobacter metallireducens ( G. metallireducens). 1-hydroxy-4-aminoanthraquinone was labeled by fluorescamine and the product (HAQ-F) showed strong and stable fluorescence. The addition of HAQ-F into MFCs increased cell voltage from 170 mV to 290 mV, suggesting that the redox mediator could facilitate electron transfer from bacteria to anode. Further, confocal laser scanning microscopy imaging indicated that HAQ-F was present in microbial cells, demonstrating that the redox mediator shuttled across the membranes to get reduced within cells.

In Situ XPS for Evaluating Ceria Oxidation States in SOFC Anodes

Ceria is being considered as an electrocatalyst component for fuel-flexible SOFC anodes. With Ce3+ and Ce4+ oxidation states, ceria can function as a mixed ionic-electronic conductor, transporting both O2- ions and electrons. It remains unclear what role these oxidation states play during SOFC operation. This study addresses these issues using ambient-pressure XPS in a single-chamber cell to characterize thin-film CeO2-x electrodes on a YSZ electrolyte during electrochemical oxidation of H2 and reduction of H2O at 620 {degree sign}C. Voltage-current curves for the ceria film electrodes reveal sharp changes in resistance as a function of applied voltage from positive to negative bias. XPS measurements during electrochemical characterization show the extent of near-surface Ce4+ reduction to Ce3+ with increasing cell voltage. Increased oxidation to Ce4+ at large negative voltages correlates with a resistance drop due to H2 oxidation activity. These findings provide insight into how CeO2-x influences electrochemical fuel oxidation or H2O reduction.

Aqueous HCl electrolysis utilizing an oxygen reducing cathode

The effects of various process parameters on the cell voltage and chlorine current efficiency (CCE) in a Half-MEA (Nafion ® 115 membrane-Loading: 0.4 mg Pt/cm 2) oxygen reducing membrane electrolysis cell employing a dimensionally stable anode (DSA ®) were studied. Process parameters under investigation included anolyte concentration, anolyte flow rate, anolyte temperature, oxygen flow rate and applied current density. The effect of the latter parameters on the cell voltage and CCE was determined quantitatively. Taguchi and ANOVA techniques were employed for experimental design and data analysis, respectively. It was observed that increasing either of anolyte flow rate, anolyte concentration, oxygen flow rate and anolyte temperature caused a decrease in cell voltage and an increase in CCE. At the same time, increasing current density linearly increased cell voltage. Current density and the anolyte flow rate had the highest contributions, of 49.7% and 30.62%, to the cell voltage, respectively. On the other hand, the oxygen flow rate and the anolyte flow rate had the highest contributions, of 57.19% and 23.66%, on the CCE, respectively.

Photosynthetic microbial fuel cells with positive light response

The current study introduces an aerobic single-chamber photosynthetic microbial fuel cell (PMFC). Evaluation of PMFC performance using naturally growing fresh-water photosynthetic biofilm revealed a weak positive light response, that is, an increase in cell voltage upon illumination. When the PMFC anodes were coated with electrically conductive polymers, the rate of voltage increased and the amplitude of the light response improved significantly. The rapid immediate positive response to light was consistent with a mechanism postulating that the photosynthetic electron-transfer chain is the source of the electrons harvested on the anode surface. This mechanism is fundamentally different from the one exploited in previously designed anaerobic microbial fuel cells (MFCs), sediment MFCs, or anaerobic PMFCs, where the electrons are derived from the respiratory electron-transfer chain. The power densities produced in PMFCs were substantially lower than those that are currently reported for conventional MFC (0.95 mW/m(2) for polyaniline-coated and 1.3 mW/m(2) for polypyrrole-coated anodes). However, the PMFC did not depend on an organic substrate as an energy source and was powered only by light energy. Its operation was CO(2)-neutral and did not require buffers or exogenous electron transfer shuttles.

Improving phosphate buffer-free cathode performance of microbial fuel cell based on biological nitrification

To reduce the amount of phosphate buffer currently used in Microbial Fuel Cell's (MFC's), we investigated the role of biological nitrification at the cathode in the absence of phosphate buffer. The addition of a nitrifying mixed consortia (NMC) to the cathode compartment and increasing ammonium concentration in the catholyte resulted in an increase of cell voltage from 0.3 V to 0.567 V (external resistance of 100 Ω) and a decrease of catholyte pH from 8.8 to 7.05. A large fraction of ammonium was oxidized to nitrite, as indicated by an increase of nitrate-nitrogen (NO 3 −–N). An MFC inoculated with an NMC and supplied with 94.2 mgN/l ammonium to the catholyte could generate a maximum power of 2.1 ± 0.14 mW (10.94 ± 0.73 W/m 3). This compared favorably to an MFC supplied with either buffered or non-buffered solution. The buffer-free NMC inoculated cathodic chamber showed the smallest polarization resistance, suggesting that nitrification resulted in improved cathode performance. The improved performances of the phosphate buffer-free cathode and cell are positively related to biological nitrification, in which we suggest additional protons produced from ammonium oxidation facilitated electrochemical reduction of oxygen at cathode.

Comparison of Direct and Mediated Electron Transfer for Cellobiose Dehydrogenase from Phanerochaete sordida

Direct and mediated electron transfer (DET and MET) between the enzyme and electrodes were compared for cellobiose dehydrogenase (CDH) from the basidiomycete Phanerochaete sordida (PsCDH). For DET, PsCDH was adsorbed at pyrolytic graphite (PG) electrodes while for MET the enzyme was covalently linked to a low potential Os redox polymer. Both types of electrodes were prepared in the presence of single walled carbon nanotubes (SWCNTs). DET requires the oxidation of the heme domain, while MET occurs partially via the heme and the flavin domain at pH 3.5. At pH 6 MET occurs solely via the flavin domain. Most probably, the interaction of the domains decreases from pH 3.5 to 6.0 due to electrostatic repulsion of deprotonated amino acid residues, covering the surfaces of both domains. MET starts at a lower potential than DET. The midpoint potentials at pH 3.5 for the flavin (40 mV) and the heme domain (170 mV) were determined with spectroelectrochemistry. The electrochemical and spectroelectrochemical measurements presented in this work are in conformity. The pH dependency of DET and MET was investigated for PsCDH. The optimum was observed between pH 4 and 4.5 pH for DET and in the range of pH 5-6 for MET. The current densities obtained by MET are 1 order of magnitude higher than by DET. During multicycle cyclic voltammetry experiments carried out at different pHs, the PsCDH modified electrode working by MET turned out to be very stable. In order to characterize a PsCDH modified anode working by MET with respect to biofuel cell applications, this electrode was combined with a Pt-black cathode as model for a membraneless biofuel cell. In comparison to DET, a 10 times higher maximum current and maximum power density in a biofuel cell application could be achieved by MET. While CDH modified electrodes working by DET are highly qualified for applications in amperometric biosensors, a much better performance as biofuel cell anodes can be obtained by MET. The use of CDH modified electrodes working by MET for biofuel cell applications results in a less positive onset of the electrocatalytic current (which may lead to an increased cell voltage), higher current and power density, and much better long-term stability over a broad range of pH.

Effects of Organic Impurities on Chloralkali Membrane Electrolyzer Performance

Laboratory chloralkali membrane electrolyzer tests showed a dramatic voltage increase and mild catholyte foaming when low levels of chloromethyl triethylammonium chloride (CTACl), a quaternary ammonium salt, were present in the feed brine. Current efficiency was not measurably affected by CTACl. In contrast, laboratory membrane electrolyzers showed no voltage sensitivity to sodium gluconate, bisphenol A, or triethylamine, contaminants that are often present in interfacial polycarbonate plant byproduct brine. The voltage increase and onset of catholyte foaming were rapid when the feed was switched from ultrapure brine to CTACl-containing brine, requiring about 3 h to achieve a steady state. Both effects were completely reversible, but the system required about 20 h to return to baseline voltage after the feed was switched back to ultrapure brine. The cell voltage was remarkably sensitive to CTACl: 8 ppm CTACl yielded a 200 mV voltage increase vs ultrapure brine. Cyclic voltammetric measurements with CTACl-spiked brine showed no effect of CTACl on anode or cathode overpotentials. At steady state, 87% of the feed chloromethyl triethylammonium ion (CTA+) is recovered either in the electrolyzer catholyte as the hydroxide, CTAOH (56%), or in the depleted brine as CTACl (31%), which demonstrates that CTA+ is rather stable toward chloralkali conditions. It is concluded that the increased cell voltage is caused by chloromethyl triethylammonium ions adsorbing onto membrane ion exchange sites, which reduces the population of sites for sodium ion transport, and that catholyte foaming is caused by the presence of CTAOH in the catholyte. An adsorbent screening study showed that various carbons, including Ambersorb 572, are effective for CTACl removal from brine. A laboratory electrolyzer fed with Ambersorb 572 treated plant brine showed normal voltage and no catholyte foaming.

Direct electrolytic preparation of cerium/nickel hydrogen storage alloy powder in molten salt

The preparation of CeNi5 by direct electrochemical reduction of mixed powders of cerium oxide (CeO2) and nickel oxide (NiO) (atomic Ce/Ni ratio, 1:5) in a molten mixture of CaCl2 and NaCl (mass CaCl2/NaCl ratio, 7:3) at 820 °C has been studied. The influence of process parameters, such as sintering temperature, cell voltage, and temperature of the molten salt, on the electrolysis process are reported. The current–time plots are shown at constant voltage electrolysis under different conditions. The composition and morphology of the products were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results show that pure CeNi5 can be prepared by direct electrochemical reduction of mixed CeO2/NiO pellets sintered at 850–1250 °C in CaCl2/NaCl melt at a voltage of 2.5 V or higher for 11 h. The product from the electrolysis was in the form of porous pellets and could be readily ground into CeNi5 alloy powder. At a voltage of 2.5 V or higher, the reduction of the mixed oxide starts from NiO to Ni, followed by that of CeO2 on the surface of the newly formed Ni to form CeNi5 alloy. The reduction rate increases with increasing cell voltage and temperature of molten salt.

Feasibility study of using carbon aerogel as particle electrodes for decoloration of RBRX dye solution in a three-dimensional electrode reactor

The decoloration of RBRX from simulated dye wastewater in three-dimensional electrode reactor using granular carbon aerogels (CAs) as particle electrodes was experimentally investigated. Decolorization ratio can keep as high as 95% in the 100th run of treatment. Particular attention was paid to probe the function of the CAs through comparing the decolorization ratio of three-dimensional electrode reactor with single adsorption and two-dimensional electrode reactor. Conditional experiments were conducted to evaluate the effect of various parameters such as cell voltage, air flowrate, particle electrode dose, initial dye concentration and pH of the dye solution. The results showed that the decolorization rate increased with increasing cell voltage and particle electrode dose, but decreased with increasing the initial dye concentration. The decolorization rate increased firstly and then kept almost unchanged with the increase of airflow. In addition, the decolorization rate can be also controlled by the pH of the dye solution. The decolorization of RBRX was based on the break of the azo double bonds and the destruction of the other unsaturated bonds.