Enhanced Cell Performance Research Articles

Eosin yellowish dye sensitized solid state solar cells with titanium dioxide electrodes composed of nanoparticles/nanowires

The effective usage of TiO2 nanoparticles (NPs) and nanowires (NWs) as dye sensitized solar cell (DSSC) photoanode films prepared by a doctor blade technique using the nanopowders synthesized by the chemical hydrolysis and hydrothermal method, respectively is emphasized here. Material characterization by XRD confirms the formation of anatase phased TiO2 NPs and NWs. The photoluminescence spectral result shows the effective quenching of UV emission in TiO2 NWs than NPs, consequence of reduction in recombination rate, which directly favors for better solar conversion efficiency. PEO/TiO2/LiI/I2 and PEO/PEG/LiI/I2 are used as charge transport media (electrolytes) in the assembled Eosin yellowish (EY) dye sensitized DSSC. The short circuit current density (JSC) of NW based DSSC (TiO2 NWs/EY/PEO/PEG/LiI/I2) is enhanced by 3–4-fold times (1021.8μA/cm2) compared to NPs, which is due to the improved direct electron transport pathway to the collection of electrode. Similarly, the fabricated DSSC gives appreciable improvement in open circuit voltage (VOC) (410.6mV) corresponding to EY dye and both factors lead to remarkable enhancement in solar cell performance as 0.32%. Even though two different electrolytes are employed, TiO2 NW based DSSC performs well compared to NPs, which implies the improved charge transport taking place in NW DSSC.

Systematic study on the functions and mechanisms of micro porous layer on water transport in proton exchange membrane fuel cells

Though it is well known that adding micro porous layers (MPL) in proton exchange membrane fuel cells (PEMFC) can improve fuel cell performance, durability and stability, their functions and mechanisms on water transport are still not fully understood. To determine the functions and the mechanisms of MPL on water transport, systematic experiments have been conducted on fuel cells with and without MPL under wide range of operating conditions. Besides overall cell performance, current density distribution along gas channel and electrochemical impedance spectroscopy are used in the analyses. The experimental results show that the functions and mechanisms of MPL depend on the humidity level and operating temperature. At low and medium temperature, MPL can significantly enhance cell performance under both high and low humidity conditions. Under high humidity conditions, adding an MPL can effectively reduce flooding of the catalyst layer by preventing the formation of liquid water in its much smaller pores than in the GDL. Under low humidity conditions, MPL reduces the loss of water to the gas channels as well as enhances back diffusion, thus reduces membrane dehydration. MPL also reduces Joule heating and further reduce membrane dehydration. At high temperature, the effectiveness of MPL is much reduced under both high and low humidity conditions due to the different mechanism of water transfer.

Passivation of PbS Quantum Dot Surface with l-Glutathione in Solid-State Quantum-Dot-Sensitized Solar Cells.

Surface oxidation of quantum dots (QDs) is one of the biggest challenges in quantum dot-sensitized solar cells (QDSCs), because it introduces surface states that enhance electron-hole recombination and degrade device performance. Protection of QDs from surface oxidation by passivating the surface with organic or inorganic layers can be one way to overcome this issue. In this study, solid-state QDSCs with a PbS QD absorber layer were prepared from thin mesoporous TiO2 layers by the successive ionic layer adsorption/reaction (SILAR) method. Spiro-OMeTAD was used as the organic p-type hole transporting material (HTM). The effects on the solar cell performance of passivating the surface of the PbS QDs with the tripeptide l-glutathione (GSH) were investigated. Current-voltage characteristics and external quantum efficiency measurements of the solar cell devices showed that GSH-treatment of the QD-sensitized TiO2 electrodes more than doubled the short circuit current and conversion efficiency. Impedance spectroscopy, intensity-modulated photovoltage and photocurrent spectroscopy analysis of the devices revealed that the enhancement in solar cell performance of the GSH-treated cells originates from improved charge injection from PbS QDs into the conduction band of TiO2. Time-resolved photoluminescence decay measurements show that passivation of the surface of QDs with GSH ligands increases the exciton lifetime in the QDs.

A highly efficient and stable oxygen reduction reaction on Pt/CeOx/C electrocatalyst obtained via a sacrificial precursor based on a metal-organic framework

Advanced Pt/CeOx/C nanocomposite, where C=porous carbon and multi-walled carbon nanotube (MWCNT), was synthesized using a precursor based on Ce-containing metal organic framework (MOF), via carbonyl chemical route, followed by heat-treatment at 900°C under argon atmosphere. Based on the analyses of powder X-ray diffraction (pXRD) data, and via the Williamson-Hall method, the lattice parameter, stacking fault and micro-strain values on Pt/CeOx/C was found to decrease, whereas the crystallite size increased with respect to the as-prepared sample. Combined with the results of transmission electron microscopy (TEM), these changes were related to the in-situ formation of intimately contacted Pt/CeOx nanoparticles (NPs), well-dispersed onto MWCNT support. However, both the pXRD and TEM results showed that the Pt NPs were agglomerated upon heating and finally detached from the support in the MOF-free samples. Thus, MOF could protect Pt nanoparticles (NPs) from agglomeration at high temperature. The X-ray photoelectron spectroscopy (XPS) showed that the Pt surface was less oxidized in Pt/CeOx/C nanocomposite in comparison to as-prepared and MOF-free samples. Moreover, only the Ce3+ was detected in the nanocomposite. These facts together with Raman spectroscopy and surface electrochemistry experiments assessed the stabilization of the electronic state of Pt° and Ce3+ via the interaction between Pt and CeOx. In addition, enhanced catalytic activity towards the oxygen reduction reaction (ORR) was observed in acid medium. The specific and mass activity at 0.9V/RHE on Pt/CeOx/C were ca. 1279μAcm−2Pt and 870mAmg−1Pt, respectively, ca. 10–11 fold higher than commercial Pt/C (Johnson Matthey, JM) in half-cell. Accelerating durability tests (ADT), after 16,000 potential cycles, demonstrated higher stability of Pt/CeOx/C in contrast to oxide-free and Pt/C (JM) catalyst. Compared with other homemade or commercial Pt/C (JM) cathodes, the innovative cathode catalyst showed enhanced cell performance in a H2/O2 micro-laminar flow fuel cell system.

Synergistic effect of boron/nitrogen co-doping into graphene and intercalation of carbon black for Pt-BCN-Gr/CB hybrid catalyst on cell performance of polymer electrolyte membrane fuel cell

Boron and nitrogen were successfully co-doped into graphene (Gr) nanosheets to which Pt nanoparticles with ∼3.7 nm are uniformly deposited on BCN-Gr. Pt content on BCN-Gr is estimated to be 50 wt.% by TG/DTA analysis. Pt-BCN-Gr is intercalated by different amount of CB (carbon black), and it is designated as Pt-BCN-Gr/CBx (x = 0.0, 0.3, 0.4, 0.5 and 0.6). The membrane electrode assembly is fabricated with commercial Pt-C and Pt-BCN-Gr/CBx as anode and cathode catalysts, respectively. The cell performance is highly consistent with electrochemical active surface area and the best cell performance of 0.54 W/cm2 in power density is achieved for Pt-BCN-Gr/CB0.5. The results show that positive effect of B and N co-doping on cell performance becomes more significant for lower intercalated CB content. Direct comparison between Pt-BCN-Gr/CB and Pt-Gr/CB clearly exhibits that Pt-BCN-Gr/CB shows better cell performance for Pt-BCN-Gr/CB than Pt-Gr/CB at lower CB content. About 28%–157% in cell performance at 0.6 V has been enhanced by B and N co-doping compared with that of Pt-Gr/CB. The enhancement in cell performance and durability is probably attributed to the synergistic effect by B and N co-doping and intercalation by CB.

Enhanced efficiency of Cu(In,Ga)Se2 solar cells with antireflection coating layers of MgF2 and ZnO nanorods

Double antireflection layers consisting of MgF2 and ZnO nanorods layers were grown on a gallium doped MgZnO transparent conducting oxide layer to enhance the efficiency of the Cu(In,Ga)Se2 (CIGS) solar cells. When ZnO nanorods were coated with the MgF2 layer, the weighted global reflectance was decreased to 5.5% and the enhanced solar power conversion of CIGS solar cells was 17%. The enhancement of the solar cell performance was attributed to the reduction in Fresnel reflection by the gradually changed refractive index of the double antireflection coating layers.

Improve the efficiency of CdTe/ZnxCd1−xS all thin films solar cell by annealing

The resistivity of CdS window layer in CdS/CdTe solar cells can be improved with the addition of small amounts of ZnS which may result in the enhancement of solar cell performance. The post growth heat treatment is another vital step for increasing device efficiency. In this work Zn0.3Cd0.7S was deposited by vacuum evaporation technique. To improve the quality of back contact, ZnTe thin film was deposited onto the CdTe surface and heat treated in air at 200°C for 1–3h. A range of devices were fabricated which showed efficiency from 2.7% to 3.48%. A correlation between heat treatment and device efficiency was observed.

Preparation of Nickel Oxide-Samarium-Doped Ceria Carbonate Composite Anode Powders by Using High-Energy Ball Milling for Low-Temperature Solid Oxide Fuel Cells

The characteristics of the starting powder in powder preparation method are important for enhancement of cell performance. In this study, the composite anode powders of NiO–samarium-doped ceria carbonates (SDCC) were prepared by using different NiO loadings (50–70 wt.%) via high-energy ball milling. The composite anode powders were ball-milled in ethanol at a milling speed of 550 rpm. The obtained NiO–SDCC composite anode powders were characterized by XRD, FTIR, FESEM, and EDS. Results indicate that the composite anode powders demonstrated good chemical compatibility between NiO and SDCC, given that no new phases were detected in the XRD analysis. FTIR spectra confirmed that the composite anode powders contain carbonates in amorphous state after high-energy ball milling. FESEM investigation revealed well-distributed fine particles and significant reduction of particle size at nanoscale compared with the powder prepared using NiO particles as the starting material. EDS mapping verified the homogeneity of the composite powder with good elemental distribution. Thus, high-energy ball milling is an effective method to prepare NiO–SDCC composite anode powders within a relatively short processing time.

Density functional theory study of oxygen migration in molten carbonate

The process of oxygen migration in alkali molten carbonate salts has been examined using density functional theory method. All geometries were optimized at the B3LYP/6-31G(d) level, while single point energy corrections were performed using MP4 and CCSD(T). At TS, a O–O–O linkage is formed and O–O bond forming and breaking is concerted. A cooperative “cogwheel” mechanism as described in the equation of CO42−+CO32−→CO32−⋯O⋯CO32−→CO32−+CO42− is involved. The energy barrier is calculated to be 103.0, 136.3 and 127.9 kJ/mol through an intra-carbonate pathway in lithium, sodium and potassium carbonate, respectively. The reliability and accuracy of B3LYP/6-31G(d) were confirmed by CCSD(T). The calculated low values of activation energy indicate that the oxygen transfer in molten carbonate salts is fairly easy. In addition, it is found that lithium carbonate is not only a favorable molten carbonate salt for better cathode kinetics, but also it is widely used for reducing the melting point of Li/Na and Li/K eutectic MC mixtures. The current results imply that the process of oxygen reduction in MC modified cathodes is facilitated by the presence of MC, resulting in an enhancement of cell performance at low operating temperatures.

Enhancement of ZnO Dye-Sensitized Solar Cell Performance by Modifying Photoelectrode Using Two-Steps Coating-Etching Process

ZnO photoelectrodes modified by two-steps coating-etching process with chemical wet etchants for dye-sensitized solar cell were investigated. The ZnO films were coated on a fluorine-doped tin oxide glass substrate and etched by mixed acid solution of HCl:HNO3:distilled water, washed, and thermally treated for the first step. The second step, films coating process was repeated and etched by base solution of diluted NH4OH in distilled water. Surface morphologies of unmodified and modified ZnO films look similar DSSCs with modified photoelectrodes showed efficiency enhancement with maximum power conversion efficiency of 2.29%. From EIS analysis, it was suggested that the fill factor plays an important role on enhancement of power conversion efficiency. The fill factor increased due to the formation of pores structure in the photoelectrodes during etching process.

Mechanical cytoprotection: A review of cytoskeleton-protection approaches for cells

We review a class of cutting-edge approaches for cytoprotection of cells exposed to assaults such as sustained deformations, chemotherapy, radiotherapy, or ischemia. These approaches will enhance cell survival by mechanically protecting the structure and dynamics of the actin cytoskeleton (CSK). Cortical actin provides structural support to the plasma membrane (PM), protecting its integrity. Consequently, assaults can fragment the actin cortex leading to local, mechanical failure of the PM and poration of the cell. This disrupts normal trafficking of biomolecules across the PM, leading to loss of homeostasis and eventually, to cell death and tissue necrosis. Two different approaches to cytoskeletal protection are covered in this review paper. The first is to supply energy-related molecules to maintain and enhance the energy-consuming dynamics of the actin CSK. The second is to stabilize newly formed actin CSK directly¸ for example through cross-linking or reinforcement at PM anchoring sites. Research in this area is clearly still in its infancy. Very few studies have gone beyond characterizing the effects of induced damage to the actin CSK (and subsequent PM collapse). Recent work, focusing instead on sustaining the actin under non-physiological or pathophysiological conditions, has shown great promise. Such cytoskeletal-protection may find medical applications in preventing or minimizing tissue damage when tissues are unhealthy or at risk, or in enhancing cell performance under stress. Here, we condense the relevant cell biology and biomechanics background, assess candidate cytoskeletal protective agents, and review published works that have shown potential for medical benefit in experimental model systems.

Numerical and Experimental Analyses on Deviated Concentration Loss with Alkaline Anion-Exchange Membrane Fuel Cells

The polarization curves of low-temperature fuel cells, such as polymer electrolyte membrane fuel cells, typically have three distinct regimes dictated by certain limiting factors. These kinetic, ohmic, and concentration-loss regimes have overpotentials that are dictated by electrochemical activation, ohmic loss, and reactant concentration, respectively. However, a peculiar polarization curve with a deviated concentration loss regime was recently presented for alkaline anion-exchange membrane fuel cells (AEMFCs), and the cause of this deviation remains unknown to date. In this work, a 2D, steady-state H2/O2 model was developed to simulate transport and reactions in an AEMFC in order to explore the origin and mechanism of deviations in the polarization curve. According to the model, the charge transfer and hydroxyl ion transport resistances in the cathode catalyst layer were rate-limiting factors and contributed to the deviated concentration loss above ∼450 mA cm–2, which was observed in baseline simulations. Improving water management in the cathode catalyst layer was found to be an effective strategy for mitigating the deviated concentration loss and enhancing cell performance, potentially enabling high-performance AEMFCs in the future.

An Improvement of Photoanode Performance for Enhanced Efficiency in Dye-Sensitized Solar Cell

This works focus on an enhancement of dye-sensitized solar cell performance by improving photoanode which directly relates to shunt resistance and series resistance of the cell. Polyethylene glycol solution was prepared by dissolved polyethylene glycol in weight ratio of 10 and 30% in distilled water. ZnO past was prepared by mixing ZnO into polyethylene glycol solution, screened by doctor blade technique on fluorine doped tin oxide glass substrate and annealed at 450 °C for 1 h. The power conversion efficiency and fill factor were achieved as 0.81% and 0.44, respectively, because internal resistances were improved. The internal resistances were found that shunt resistance increased up to 4.35% and series resistance decreased down to 8.00% for 30% weight ratio of polyethylene glycol. These indicated that electron transfer in the cell was achieved in pathway direction.

Effect of hybridization of Pt supported mesoporous-CMK-3 into Pt-CB as cathode catalyst on cell performance and durability in proton exchange membrane fuel cell

Mesoporous carbon molecular sieve, CMK-3 is successfully prepared through the carbonization of hexagonally arrayed mesoporous SBA-15 as a template and Pt nanoparticles are then deposited onto CMK-3. Mesoporous Pt-CB(1 − x)/Pt-CMK-3x hybrid catalysts (x = 0.0, 0.4, 0.5, 0.7 and 1.0) are adopted as a cathode catalyst in polymer electrolyte membrane fuel cell for the purpose of enhancing mass transfer and durability. Transmission electron micrograph and X-ray diffraction micrograph analyses show the uniform dispersion of Pt nanoparticles without any distinct agglomeration through the mesopores of CMK-3 with particle size of ∼2.3 nm. X-ray photoelectron spectroscopy analysis confirms the oxidation state of Pt species deposited onto CMK-3. The electrochemical active surface areas (ECSA) obtained by cyclic voltammetry analysis for various Pt-CB(1 − x)/Pt-CMK-3x are estimated to be 27.4 m2 g−1, 38.9 m2 g−1, 44.7 m2 g−1, 36.9 m2 g−1 and 30.8 m2 g−1 for x = 0.0, 0.4, 0.5, 0.7 and 1.0, respectively. The single cell test shows that the cell performance is highly consistent with ECSA: that is, the cell performance of Pt-CB(0.5)/Pt-CMK-3(0.5) is drastically enhanced by 62% and 322% compared with those of Pt-CMK-3 and Pt-CB alone, respectively. The drastic enhancement in cell performance is attributed to synergistic effect of enhanced mass transfer and fairly good Pt utilization. Accelerated durability test shows a drastic enhancement in durability of Pt-CMK-3 and various Pt-CB/Pt-CMK-3 hybrid catalysts compared to that of Pt-CB. The start-up/shut-down cycling test shows that mesoporous CMK-3 could be an excellent candidate for alternative supporting materials to commercial Pt-CB.

Direct Carbon Fuel Cell Operation on Brown Coal with a Ni-GDC-YSZ Anode

Char products derived from brown coal from Morwell in the Latrobe Valley, Australia, were tested in a solid electrolyte based Direct Carbon Fuel Cell (DCFC) at 850°C. Electrolyte supported button cells were used with a Ni-GDC (gadolinia doped ceria) anode with 15wt% YSZ (yttria stabilised zirconia) for thermal stability and better adhesion with the YSZ electrolyte. The cell performed well under N2 when using demineralised Morwell char as the fuel, generating reproducible V-j and P-j curves and sustaining chronopotentiometric loading of 20mAcm−2 for 2hours with no appreciable signs of voltage decay. Operation with raw Morwell char initially achieved comparable peak power densities to that of the demineralised char, however, subsequent runs with raw Morwell char exhibited decreasing power densities and signs of diffusion-limitations at higher current densities. Ash deposition at the anode is proposed as a possible differentiator of extended cell operability between the two fuels. In addition to fuel-based performance of the DCFC, the response of the anode and system as a whole was closely monitored using Electrochemical Impedance Spectroscopy. Introduction of CO2 into the anode chamber instead of N2 enhanced cell performance and longevity of cell operation under sustained loading. An increase in the ohmic resistance component with increasing current density was observed for Ni-GDC-YSZ anode in N2 atmosphere, but not in H2 atmosphere and it has been attributed to the oxidation of Ni near the electrode/electrolyte interface during current passage and lack of sufficient reducing species to keep Ni in its reduced state.

Enhanced cell performance by controlling the surface morphology of ZnO buffer layers in organic photovoltaic cells

Thin layer of ZnO with mixture of spherical and rod-shaped nanoparticles (NM) was prepared as the buffer layer in inverted organic photovoltaic cells (OPVs). The spherical and rod-shaped ZnO nanoparticles were synthesized through sol–gel method to investigate the effect on surface area of ZnO buffer layer. The prepared samples were made up of a 50/50wt.% mixture of spherical ZnO and rod-shaped ZnO nanoparticles. The surface area of ZnO thin layer prepared with mixture of spherical and rod-shaped nanoparticles has the higher specific surface area than that of ZnO film prepared with spherical or rod-shaped nanoparticles, respectively. The high surface area in buffer layer induced the fast electron transfer in OPVs. Also, the sample NM has the rough surface structure due to the morphology of mixed ZnO nanoparticles. The rough structure increased the contact area at the interface (ZnO buffer layer/active layer). Due to these two reasons, the series resistance (Rs) of the device was decreased. By reduction of the Rs, the current density (Jsc) and fill factor (FF) of device were improved. The highest power conversion efficiency (PCE) with NM is achieved for 2.75% under 100mW/cm2 at AM 1.5G simulated solar emission.

DFT Study of Oxygen Dissociation in Molten Carbonate

Using density functional theory method, we have studied the oxygen dissociation in alkali molten carbonate at the B3LYP/6-31G(d) level. The calculated energies were then verified by MP4 and CCSD(T). A four-formula cluster (M2CO3)4, M = Li, Na, and K was used to describe the molten carbonate. It was found that the adsorption of oxygen to molten carbonate is of a chemical type and leads to the formation of CO5(2-) in MC, which was confirmed for the first time by DFT calculations. The energy barrier for its dissociation is calculated to be 197.9, 116.7, and 170.3 kJ/mol in the (M2CO3)4 cluster, M = Li, Na, and K, respectively. If the reaction of O2 + 2CO3(2-) → 2CO4(2-) is approximated as a one-step reaction, the activation energy is estimated to be 96.2, 15.1, and 68.6 kJ/mol, respectively. The reaction rate is first order to the pressure of oxygen. Surprisingly, the reaction of oxygen dissociation has the lowest energy barrier in sodium carbonate, which is consistent with the recent experimental findings. It is very clear that the molten carbonate salt has directly participated in the ORR process and plays an important role as a catalyst in the cathode of SOFCs. The oxygen reduction has been facilitated by MC and enhanced cell performance has been observed.

Boosting the Performance of ZnO/CdS Core‐Shell Nanorod Array‐based Solar Cells by ZnS Surface Treatment

AbstractWith a view to enhancing the efficiency of ZnO/CdS core‐shell nanorod array‐based semiconductor sensitized solar cells (SSSCs), ZnS surface treatment is envisioned. It is achieved through a thin layer of ZnS being deposited onto ZnO/CdS film by a successive ionic layer adsorption and reaction (SILAR) technique. To ascertain the optimum thickness of ZnS and to enhance the solar cell performance, we have varied the number of SILAR cycles of ZnS deposition. The optimized film is then considered for structural, morphological, and electrochemical studies. The analysis reveals the benefits of ZnS surface treatment on ZnO/CdS core‐shell photoelectrodes in terms of an enhancement of solar cell performance of up to 1.54 % from 1.23 %.

Conical nano-structure arrays of Platinum cathode catalyst for enhanced cell performance in PEMFC (proton exchange membrane fuel cell)

Conical nanostructure arrays of Pt (Platinum) as cathode catalyst are developed using a novel integrated plasma sputtering technique. The integration method involves successive deposition of Pt catalyst arrays one upon another maintaining a uniform time gap. Deposition by integrated approach results in the formation of dense arrays of Pt nanostructure as compared to continuous deposition. These high number density integrated arrays with low Pt loading of 0.10 mg cm−2 at the cathode provide enhanced performance compared to non-integrated cathode catalyst prepared by continuous deposition and standard commercial electrodes with Pt loadings of 1 mg cm−2. The performance is compared on the basis of polarization curve measurements and the calculated power density values. PEM fuel cell with dual integrated cathode showed an improved power density of 0.90 W cm−2, which is higher than continuously deposited cathode catalyst with maximum power density of 0.67 W cm−2 for the same Pt loading of 0.10 mg cm−2.

Impact of Space-Charge Layers on Sudden Death in Li/O2 Batteries.

The performance of Li/O2 batteries is thought to be limited by charge transport through the solid Li2O2 discharge product. Prior studies suggest that electron tunneling is the main transport mechanism through thin, compact Li2O2 deposits. The present study employs a new continuum transport model to explore an alternative scenario, in which charge transport is mediated by polaron hopping. Unlike earlier models, which assume a uniform carrier concentration or local electroneutrality, the possibility of nonuniform space charge is accounted for at the Li2O2/electrolyte and Li2O2/electrode interfaces, providing a more realistic picture of transport in Li2O2 films. The temperature and current-density dependences of the discharge curves predicted by the model are in good agreement with flat-electrode experiments over a wide range of rates, supporting the hypothesis that polaron hopping contributes significantly to charge transport. Exercising the model suggests that this mechanism could explain the observed enhancement in cell performance at elevated temperature and that performance could be further improved by tuning the interfacial orientation of Li2O2 crystallites.