A high-performance counter electrode based on poly(3,4-alkylenedioxythiophene) for dye-sensitized solar cells

A poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDOT-Et₂) counter electrode prepared by electrochemical polymerization on a fluorine-doped tin oxide (FTO) glass substrate was incorporated in a platinum-free dye-sensitized solar cell (DSSC). The surface roughness and I⁻/I₃⁻ redox reaction behaviors based on PProDOT-Et₂, poly(3,4-propylenedioxythiophene) (PProDOT), poly(3,4-ethylenedioxythiophene) (PEDOT), and sputtered-Pt electrodes were characterized, and their performances as counter electrodes in DSSCs were compared. Cells fabricated with a PProDOT-Et₂ counter electrode showed a higher conversion efficiency of 7.88% compared to cells fabricated with PEDOT (3.93%), PProDOT (7.08%), and sputtered-Pt (7.77%) electrodes. This enhancement was attributed to increases in the effective surface area and good catalytic properties for I₃⁻ reduction. In terms of the film thickness effect, the fill factor was strongly dependent on the deposition charge capacity of the PProDOT-Et₂ layer, but the aggregation of PProDOT-Et₂ in thicker layers (>80 mC cm⁻²) resulted in decreases in J_SC and the cell conversion efficiency. The charge transfer resistances (R_ct1) of the PProDOT-Et₂ counter electrodes had the lowest value of ∼18 Ω at a deposition charge capacity of 40 mC cm⁻². These results indicate that films with high conductivity, high active surface area, and good catalytic properties for I₃⁻ reduction can potentially be used as the counter electrode in a high-performance DSSC.     

Platinum nanoparticles supported on electrospinning-derived carbon fibrous mats by using formaldehyde vapor as reducer for methanol electrooxidation

The Pt nanoparticles have been well dispersed on electrospinning-derived carbon fibrous mats (CFMs) by using formaldehyde vapor as reducer to react with H₂PtCl₆·6H₂O adsorbed on the CFMs at 160 °C. The prepared electrodes of Pt-CFMs have been characterized by using scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectroscopy, and the performance of the electrodes for methanol oxidation has been investigated by using cyclic voltammetry, chronoamperometry, quasi-steady state polarization and electrochemical impedance spectroscopy techniques. The results demonstrate that Pt-CFMs electrodes exhibit peak current density of 445 mA mg⁻¹ Pt, exchange current of 235.7 μA cm⁻², charge transfer resistance of 16.1 Ω cm² and better stability during the process of methanol oxidation, which are superior to the peak current density of 194 mA mg⁻¹ Pt, exchange current of 174.7 μA cm⁻² and charge transfer resistance of 39.4 Ω cm² obtained for commercial Pt/C supported on CFMs. It indicates that the novel process in which formaldehyde vapor is used as reducer to prepare Pt catalyst with high performance can be developed.     

Low-temperature protonic ceramic membrane fuel cells (PCMFCs) with SrCo0.9Sb0.1O3−δ cubic perovskite cathode

The SrCo_0.9Sb_0.1O_3−δ (SCS) composite oxide with cubic perovskite structure was synthesized by a modified Pechini method and examined as a novel cathode for protonic ceramic membrane fuel cells (PCMFCs). At 700 °C and under open-circuit condition, symmetrical SCS cathode on BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) electrolyte showed low polarization resistances (R_p) of 0.22 Ωcm² in air. A laboratory-sized tri-layer cell of NiO–BZCY7/BZCY7/SCS was operated from 500 to 700 °C with humidified hydrogen (∼3% H₂O) as fuel and the static air as oxidant. A high open-circuit potential of 1.004 V, a maximum power density of 259 mW cm⁻², and a low polarization resistance of the electrodes of 0.14 Ωcm² was achieved at 700 °C.     

Platinum/tin oxide/carbon cathode catalyst for high temperature PEM fuel cell

The performance of high temperature polymer electrolyte fuel cell (HT-PEMFC) using platinum supported over tin oxide and Vulcan carbon (Pt/SnOx/C) as cathode catalyst was evaluated at 160-200 °C and compared with Pt/C. This paper reports first time the Pt/SnOx/C preparation, fuel cell performance, and durability test up to 200 h. Pt/SnOx/C of varying SnO compositions were characterized using XRD, SEM, TEM, EDX and EIS. The face-centered cubic structure of nanosized Pt becomes evident from XRD data. TEM and EDX measurements established that the average size of the Pt nanoparticles were ∼6 nm. Low ionic resistances were derived from EIS, which ranged from 0.5 to 5 Ω-cm² for cathode and 0.05 to 0.1 Ω-cm² for phosphoric acid, doped PBI membrane. The addition of the SnOx to Pt/C significantly promoted the catalytic activity for the oxygen reduction reaction (ORR). The 7 wt.% SnO in Pt/SnO₂/C catalyst showed the highest electro-oxidation activity for ORR. High temperature PEMFC measurements performed at 180 °C under dry gases (H₂ and O₂) showed 0.58 V at a current density of 200 mA cm⁻², while only 0.40 V was obtained in the case of Pt/C catalyst. When the catalyst contained higher concentrations of tin oxide, the performance decreased as a result of mass transport limitations within the electrode. Durability tests showed that Pt/SnOx/C catalysts prepared in this work were stable under fuel cell working conditions, during 200 h at 180 °C demonstrate as potential cathode catalyst for HT-PEMFCs.     

High-performance anode-supported Solid Oxide Fuel Cells based on Ba(Zr0.1Ce0.7Y0.2)O3−δ (BZCY) fabricated by a modified co-pressing process

A modified co-pressing process was developed to fabricate anode-supported dense and uniform Ba(Zr_0.1Ce_0.7Y_0.2)O_3−δ (BZCY) electrolyte films (∼20 μm thick) from BZCY powders with different characteristics; the powders derived from a glycine nitrate process was used for the anode whereas the powders from solid state reaction for the electrolyte. The BZCY electrolyte films sintered at 1350 °C for 6 h reached a conductivity of ∼0.025 S cm⁻¹ at 700 °C, similar to that of BZCY pellet sintered at 1550 °C for 10 h. Further, a test cell based on such an anode-supported BZCY electrolyte demonstrated peak power densities of ∼780 and ∼490 mW cm⁻² at 700 and 600 °C, respectively.     

Performance of a novel type of electrolyte-supported solid oxide fuel cell with honeycomb structure

A novel design, alternative to the conventional electrolyte-supported solid oxide fuel cell (SOFC) is presented. In this new design, a honeycomb-electrolyte is fabricated from hexagonal cells, providing high mechanical strength to the whole structure and supporting the thin layer used as electrolyte of a SOFC. This new design allows a reduction of ∼70% of the electrolyte material and it renders modest performances over 320 mW cm⁻² but high volumetric power densities, i.e. 1.22 W cm⁻³ under pure CH₄ at 900 °C, with a high OCV of 1.13 V, using the standard Ni-YSZ cermet as anode, Pt as cathode material and air as the oxidant gas.     

Electrochromic device with a redox electrolyte

Electrochromic glazing allows the solar energy gain and daylighting in buildings and cars to be controlled. Here we report new results about a special type of electrochromic device. It consists of an electrochromic layer (WO₃) on a transparent electrode, an electrolyte containing Li⁺ cations and a redox system (I⁻/I₃⁻), and a catalyst (Pt) on a second transparent electrode. The electrolyte is based on gelled ionic liquids.The change in the transmittance is extremely high; the visible (solar) transmittance can be switched between 63% (46%) and 1.2% (0.7%). A segmented 30×30 cm² sample with conductor paths reduces the transmittance by a factor of 10 in 8 s.     

Electrochemical properties of cross-linked polymer electrolyte by electron beam irradiation and application to lithium ion batteries

A polymer electrolyte was successfully fabricated for a room temperature operation lithium battery by cross-linking the mixture of oligomeric poly (ethylene glycol) dimethylether (PEGDME) and poly (ethylene glycol) diacrylate (PEGDA) with Li(CF₃SO₂)₂N using electron beam irradiation. The maximum ionic conductivity achieved for the cross-linked solid polymer electrolyte (c-SPE) at room temperature was 2.1 × 10⁻⁴ S cm⁻¹ and the lithium transport number of the electrolyte was around 0.2. The c-SPE showed no reaction heat with lithium metal up to 300 °C. The interface resistance of Li/c-SPE/Li at room temperature was about 45 Ω cm², which is considerable lower than that of 210 Ω cm² for Li/PEO₁₀Li(CF₃SO₂)₂N/Li. The electrochemical window of the polymer electrolyte was above 4 V (versus Li⁺/Li). The initial discharge capacity for the Li/SPE/LiFePO₄-C cell was approximately 90 mAh g⁻¹ for LiFePO₄-C at 1/10 °C rate at room temperature and showed a good cyclability and a high coulombic efficiency of 99.2%.     

Fabrication and evaluation of anode and thin Y2O3-stabilized ZrO2 film by co-tape casting and co-firing technique

Co-tape casting and co-firing of supporting electrode and electrolyte layers could drastically increase productivity and reduce fabrication cost. In this study, Ni-YSZ anode supporting electrode and the YSZ electrolyte with the size of 6.5 cm × 6.5 cm have been successfully fabricated by co-tape casting and co-firing technique. The cell with 1.5 mm anode and 10 μm electrolyte is flat without warping, cracks or delaminations. The power density reaches 661, 856, 1085 mW cm⁻² at 0.7 V and 750, 800 and 850 °C, respectively. The EIS results demonstrate that the cathodic electrochemical resistance is 0.0680 Ω cm², about twice of the anode's which is 0.0359 Ω cm². SEM images show the dense YSZ film had a crack free of surface morphology. The anode and cathode layers are well-adhered to the YSZ electrolyte layer. The La_0.8 Sr_0.2 MnO_3−δ particles do not form a continuous network. Optimization of finer cathodic microstructure and anodic porosity are underway.     

Contribution of Nafion loading to the activity of catalysts and the performance of PEMFC

Different amounts of Nafion loadings (in the range of 0–2.0 mg cm⁻²) were added to a catalyst containing 0.5 mg cm⁻² of Pt; these were prepared by spraying a Nafion solution on an electrode surface. The effect of Nafion loading on the activity of the catalyst and the performance of a proton exchange membrane fuel cell (PEMFC) was investigated by using electrochemical methods such as direct current polarization (using an I–V curve), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and linear scan voltammetry (LSV). The results of the I–V and EIS were compared in order to resolve the ohmic resistance (R_Ω, calculated from the I–V curve) into interfacial and internal resistances (R_if and R_s, simulated from the EIS). The analysis of the electrochemical data revealed that the interfacial resistance (R_if) is closely related to the reactive region of three-phase zones (interfaces among the reactants, electrolyte and catalyst), and it provides a major parameter for diagnosing the activity of the catalysts and the performance of the PEMFC.     

Properties and performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ + Sm0.2Ce0.8O1.9 composite cathode

The properties and performance of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) + Sm_0.2Ce_0.8O_1.9 (SDC) (70:30 in weight ratio) composite cathode for intermediate-temperature solid-oxide fuel cells were investigated. Mechanical mixing of BSCF with SDC resulted in the adhesion of fine SDC particles to the surface of coarse BSCF grains. XRD, SEM-EDX and O₂-TPD results demonstrated that the phase reaction between BSCF and SDC was negligible, constricted only at the BSCF and SDC interface, and throughout the entire cathode with the formation of new (Ba,Sr,Sm,Ce)(Co,Fe)O_3−δ perovskite phase at a firing temperature of 900, 1000, and ≥ 1050 °C, respectively. The BSCF + SDC electrode sintered at 1000 °C showed an area specific resistance of ∼0.064 Ω cm² at 600 °C, which is a slight improvement over the BSCF (0.099 Ω cm²) owing to the enlarged cathode surface area contributed from the fine SDC particles. A peak power density of 1050 and ∼382 mW cm⁻² was reached at 600 and 500 °C, respectively, for a thin-film electrolyte cell with the BSCF + SDC cathode fired from 1000 °C.     

Ba0.5Sr0.5Co0.8Fe0.2O3 − δ + LaCoO3 composite cathode for Sm0.2Ce0.8O1.9-electrolyte based intermediate-temperature solid-oxide fuel cells

A novel Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ + LaCoO₃ (BSCF + LC) composite oxide was investigated for the potential application as a cathode for intermediate-temperature solid-oxide fuel cells based on a Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. The LC oxide was added to BSCF cathode in order to improve its electrical conductivity. X-ray diffraction examination demonstrated that the solid-state reaction between LC and BSCF phases occurred at temperatures above 950 °C and formed the final product with the composition: La_0.316Ba_0.342Sr_0.342Co_0.863Fe_0.137O_3 − δ at 1100 °C. The inter-diffusion between BSCF and LC was identified by the environmental scanning electron microscopy and energy dispersive X-ray examination. The electrical conductivity of the BSCF + LC composite oxide increased with increasing calcination temperature, and reached a maximum value of ∼300 S cm⁻¹ at a calcination temperature of 1050 °C, while the electrical conductivity of the pure BSCF was only ∼40 S cm⁻¹. The improved conductivity resulted in attractive cathode performance. An area-specific resistance as low as 0.21 Ω cm² was achieved at 600 °C for the BSCF (70 vol.%) + LC (30 vol.%) composite cathode calcined at 950 °C for 5 h. Peak power densities as high as ∼700 mW cm⁻² at 650 °C and ∼525 mW cm⁻² at 600 °C were reached for the thin-film fuel cells with the optimized cathode composition and calcination temperatures.     

Evaluation of Ba0.6Sr0.4Co0.9Nb0.1O3−δ mixed conductor as a cathode for intermediate-temperature oxygen-ionic solid-oxide fuel cells

A perovskite-type Ba_0.6Sr_0.4Co_0.9Nb_0.1O_3−δ (BSCN) oxide is investigated as the cathode material of oxygen-ionic solid-oxide fuel cells (SOFCs) with Sm_0.2Ce_0.8O_3−δ (SDC) electrolyte. Powder X-ray diffraction and SEM characterization demonstrate that solid phase reactions between BSCN and SDC are negligible at temperatures up to 1100 °C. The results of thermal-expansion and electrical conductivity measurements indicate the introduction of Ba²⁺ into the A-site of SrCo_0.9N_0.1O_3−δ (SCN) led to a decrease in the thermal-expansion coefficient (TEC) and electrical conductivity of the compound. A TEC of 14.4 × 10⁻⁶ K⁻¹ is observed for BSCN within a temperature range of 200-500 °C. The chemical diffusion coefficient (D_chem) and surface exchange constant (k_ex) of BSCN and SCN are obtained using an electrical conductivity relaxation technique and BSCN prove to have higher D_chem and k_ex than SCN. An area-specific resistance of 0.1 Ω cm⁻² is achieved for BSCN cathodes at 600 °C based on symmetric cells test. Peak power density of ∼1150 mW cm⁻² is reached for a thin-film electrolyte cell with BSCN cathode at 600 °C, which is higher than a similar cell with SCN cathode (∼1008 mW cm⁻²). BSCN is a promising cathode material for oxygen-ionic IT-SOFCs.     

Low-Pt-loading acetylene-black cathode for high-efficient dye-sensitized solar cells

We reported on the synthesis, characterization, and photovoltaic/electrochemical properties of Pt/acetylene-black (AB) cathode as well as their application in dye-sensitized solar cells (DSCs). The Pt/AB electrode was prepared through a thermal decomposition of H₂PtCl₆ on the AB substrate. SEM and TEM observations showed that the Pt nanoparticles were homogeneously dispersed on the AB surface. The Pt-loading content in the Pt/AB electrode was only about 2.0 μg cm⁻², which was much lower than 5–10 μg cm⁻² generally used for the Pt electrode in DSCs. Electrochemical measurements displayed a low charge-transfer resistance of 1.48 Ω cm² for the Pt/AB electrode. Furthermore, when this low-Pt-loading electrode was used as the cathode of DSCs, an overall light-to-electricity energy conversion efficiency of 8.6% was achieved, showing commercially realistic energy conversion efficiency in the application of DSCs.     

BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte-based solid oxide fuel cells with cobalt-free PrBaFe2O5+δ layered perovskite cathode

A new anode-supported SOFC material system Ni-BZCYYb|BZCYYb|PBFO is investigated, in which a cobalt-free layered perovskite oxide, PrBaFe₂O_5+δ (PBFO), is synthesized and employed as a novel cathode while the synthesized BZCYYb is used as an electrolyte. The cell is fabricated by a simple dry-pressing/co-sintering process. The cell is tested and characterized under intermediate temperature range from 600 to 700 °C with humified H₂ (∼3% H₂O) as fuel, ambient air as oxidant. The results show that the open-circuit potential of 1.006 V and maximal power density of 452 mW cm⁻² are achieved at 700 °C. The polarization resistance of the electrodes is 0.18 Ω cm² at 700 °C. Compared to BaZr_0.1Ce_0.7Y_0.1O_3−δ, the conductivity of co-doped barium zirconate-cerate BZCYYb is significantly improved. The ohmic resistance of single cell is 0.37 Ω cm² at 700 °C. The results indicate that the developed Ni-BZCYYb|BZCYYb|PBFO cell is a promising functional material system for SOFCs.     

Laser-printed thick-film electrodes for solid-state rechargeable Li-ion microbatteries

Laser-printed thick-film electrodes (LiCoO₂ cathode and carbon anode) are deposited onto metallic current collectors for fabricating Li-ion microbatteries. These microbatteries demonstrate a significantly higher discharge capacity, power and energy densities than those made by sputter-deposited thin-film techniques. This increased performance is attributed to the porous structure of the laser-printed electrodes, which allows improved ionic and electronic transport through the thick electrodes (∼100 μm) without a significant increase in internal resistance. These laser-printed electrodes are separated by a laser-cut porous membrane impregnated with a gel polymer electrolyte (GPE) in order to build mm-size scale solid-state rechargeable Li-ion microbatteries (LiCoO₂/GPE/carbon). The resulting packaged microbatteries exhibit a power density of ∼38 mW cm⁻² with a discharge capacity of ∼102 μAh cm⁻² at a high discharge rate of 10 mA cm⁻². The laser-printed microbatteries also exhibit discharge capacities in excess of 2500 μAh cm⁻² at a current density of 100 μA cm⁻². This is over an order of magnitude higher than that observed for sputter-deposited thin-film microbatteries (∼160 μAh cm⁻²).     

Intermediate-temperature electrochemical performance of a polycrystalline PrBaCo2O5+δ cathode on samarium-doped ceria electrolyte

A-site cation-ordered PrBaCo₂O_5+δ (PrBC) double perovskite oxide was synthesized and evaluated as the cathode of an intermediate-temperature solid-oxide fuel cell (IT-SOFC) on a samarium-doped ceria (SDC) electrolyte. The phase reaction between PrBC and SDC was weak even at 1100 °C. The oxygen reduction mechanism was investigated by electrochemical impedance spectroscopy characterization. Over the intermediate-temperature range of 450–700 °C, the electrode polarization resistance was mainly contributed from oxygen-ion transfer through the electrode–electrolyte interface and electron charge transfer over the electrode surface. An area-specific resistance as low as ∼0.4 Ω cm² was measured at 600 °C in air, based on symmetric cell test. A thin-film SDC electrolyte fuel cell with PrBC cathode was fabricated which delivered attractive peak power densities of 620 and 165 mW cm⁻² at 600 and 450 °C, respectively.     

Electrode performance and analysis of reversible solid oxide fuel cells with proton conducting electrolyte of BaCe0.5Zr0.3Y0.2O3−δ

Reversible solid oxide fuel cells (R-SOFCs) are regarded as a promising solution to the discontinuity in electric energy, since they can generate electric powder as solid oxide fuel cells (SOFCs) at the time of electricity shortage, and store the electrical power as solid oxide electrolysis cells (SOECs) at the time of electricity over-plus. In this work, R-SOFCs with thin proton conducting electrolyte films of BaCe_0.5Zr_0.3Y_0.2O_3−δ were fabricated and their electro-performance was characterized with various reacting atmospheres. At 700 °C, the charging current (in SOFC mode) is 251 mA cm⁻² at 0.7 V, and the electrolysis current densities (in SOEC mode) reaches −830 mA cm⁻² at 1.5 V with 50% H₂O-air and H₂ as reacting gases, respectively. Their electrode performance was investigated by impedance spectra in discharging mode (SOFC mode), electrolysis mode (SOEC mode) and open circuit mode (OCV mode). The results show that impedance spectra have different shapes in all the three modes, implying different rate-limiting steps. In SOFC mode, the high frequency resistance (R_H) is 0.07 Ωcm² and low frequency resistances (R_L) are 0.37 Ωcm². While in SOEC mode, R_H is 0.15 Ωcm², twice of that in SOFC mode, and R_L is only 0.07 Ωcm², about 19% of that in SOFC mode. Moreover, the spectra under OCV conditions seems like a combination of those in SOEC mode and SOFC mode, since that R_H in OCV mode is about 0.13 Ωcm², close to R_H in SOEC mode, while R_L in OCV mode is 0.39 Ωcm², close to R_L in SOFC mode. The elementary steps for SOEC with proton conducting electrolyte were proposed to account for this phenomenon.     

Preparation and performance of nanostructured porous thin cathode for low-temperature solid oxide fuel cells by spin-coating method

To reduce the cathode–electrolyte interfacial polarization resistance of low-temperature solid oxide fuel cells (SOFCs), a nanostructured porous thin cathode consisting of Sm_0.5Sr_0.5CoO₃ (SSC) and Ce_0.8Sm_0.2O_1.9 (SDC) was fabricated on an anode-supported electrolyte film using spin-coating technique. A suspension with nanosized cathode materials, volatilizable solvents and a soluble pore former was developed. The results indicated that the cell with the nanostructured porous thin cathode sintered at 950 °C showed relatively high maximum power density of 212 mW cm⁻² at 500 °C and 114 mW cm⁻² at 450 °C, and low interfacial polarization resistance of 0.79 Ω cm² at 500 °C and 2.81 Ω cm² at 450 °C. Hence, the nanostructured porous thin cathode is expected to be a promising cathode for low-temperature SOFCs.     

Performance of a new polymer electrolyte incorporated with diphenylamine in nanocrystalline dye-sensitized solar cell

A new solvent-free composite polymer electrolyte consisting of poly(ethylene oxide) (PEO) incorporated into diphenyl amine (DPA) along with KI and I₂ has been developed. The current-voltage characteristics of this nanocrystalline dye-sensitized solar cell measured under simulated sunlight with 1.5 AM at 60 mW/cm² have indicated that this cell generates a photocurrent of 10.2 mA/cm², together with a photovoltage of 810 mV and fill factor of 0.47 yielding an overall energy conversion efficiency of 6.5%. This result suggests that the electron donicity of DPA influences the interaction of nanocrystalline TiO₂ electrode and I⁻/I₃⁻ electrolyte, leading to a high performance of the fabricated solar cell.