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.     

Photocurrent and photoelectrochemical hydrogen production with tin porphyrin and platinum nanowires immobilized with nafion on glassy carbon electrode

Platinum nanowires mixed with Tin meso-tetra (4-pyridyl) porphine dichloride and nafion solution was used to modify the surface of glassy carbon electrode for photocurrent generation and photo-electrochemical hydrogen production. Different concentrations of porphyrin (50 μM, 100 μM, 300 μM and 500 μM) and platinum loading (200 μg/cm², 400 μg/cm², 600 μg/cm² and 800 μg/cm²) were tested at −150 mV Vs Ag/AgCl in reaction cell containing the modified glassy carbon electrode as working electrode, platinum wire as counter electrode and Ag/AgCl as reference electrode, under illumination to determine the optimum, based on photocurrent production in 50 mM potassium hydrogen phthalate buffer (pH 3) containing 0.1Na₂SO₄ as supporting electrolyte. Optimum photocurrent was obtained at 100 μM tin porphyrin and 600 μg/cm² platinum loading. Detectable amount of hydrogen was produced at −350 mV Vs Ag/AgCl under irradiation with visible light.     

Enhanced electrochemical hydrogen storage capacity of activated mesoporous carbon materials containing nickel inclusions

Electrochemical properties of activated ordered mesoporous carbon (OMC) containing nickel inclusions are investigated using cyclic voltammetry and galvanostatic charge/discharge techniques. The hard-template-route prepared OMC is of structurally well-ordered two-dimensional hexagonal structure with a high specific surface area of 1896.95 cm² g⁻¹, a pore volume of 1.781 cm³ g⁻¹ and a pore size of 5.1 nm, respectively. It is shown that OMC/0.3Ni electrode displays the highest specific capacitance of 186.1 Fg⁻¹, almost 1.4 times higher than that of pure OMC electrode. The hydrogen storage capacity of pure OMC electrode is 87 mAh g⁻¹ and there exists no discharge platform. With the amount of nickel addition increasing, there appears a relatively stable discharge platform, and the discharge capacity reaches a maximum of 170 mAh g⁻¹ as the molar ratio of Ni:OMC is 0.3, almost two times higher than that of pure OMC electrode. The electrochemical properties of OMC can be greatly improved with incorporation of nickel powders. The Ni activated OMC electrodes display a high capacity retainability with strong resistance against oxidation and corrosion.     

Platinum-sputtered electrode based on blend of carbon nanotubes and carbon black for polymer electrolyte fuel cell

A novel Pt-sputtered electrode based on a blend layer of carbon black (CB) and carbon nanotubes (CNTs) is developed for polymer electrolyte fuel cells. The Pt is sputtered on the surface of the blend to form a catalyst layer. The CNTs generate a pore in the blend layer, and the CB provides a high surface roughness for the blend layer. At a CNT content of 50 wt.%, the maximum value (20.6 m² g⁻¹) for the electrochemical area of the Pt is obtained, which indicates that the surface area of the blend layer exposed for Pt deposition is the largest. The power density of a membrane-electrode assembly (MEA) employing the Pt-sputtered electrodes shows a linear increase with electrochemical area. The mass activity of the optimized Pt-sputtered electrode with a Pt loading of 0.05 mg cm⁻² is 8.1 times that of an electrode with a Pt loading of 0.5 mg cm⁻² prepared using a conventional screen-printing technique. Excellent mass transfer is obtained with the Pt-sputtered electrode.     

Supported PtRu on mesoporous carbons for direct methanol fuel cells

We prepared and characterized several cryogel mesoporous carbons of different pore size distribution and report the catalytic activity of PtRu supported on mesoporous carbons of pore size >15 nm in passive and in active direct methanol fuel cells (DMFCs). At room temperature (RT), the specific maximum power of the passive DMFCs with mesoporous carbon/PtRu systems as anode was in the range 3–5 W g⁻¹. Passive DMFC assembly and RT tests limit the performance of the electrocatalytic systems and the anodes were thus tested in active DMFCs at 30, 60 and 80 °C. Their responses were also compared to those of commercial Vulcan carbon/PtRu. At 80 °C, the specific maximum power of the active DMFC with C656/PtRu was 37 W g⁻¹ and the required amount of Pt per kW estimated at 0.4 V cell voltage was 31 g kW⁻¹, a value less than half that of Vulcan carbon/PtRu.     

Synthesis conditions, light intensity and temperature effect on the performance of ZnO nanorods-based dye sensitized solar cells

We present in this work a careful study of the different parameters affecting vertically-aligned ZnO-nanorods (NRs) based dye sensitized solar cells (DSCs). We analyze the effect of synthesis conditions, light intensity, UV light and working temperature, and correlated them to the final photovoltaic properties of the DSC. Although similar studies can be found in the literature for DSCs based on TiO₂, this work is, to our knowledge, the first detailed study carried out for DSC based on vertically-aligned ZnO nanorods. The ZnO NRs were grown between 1.6 and 5.2 μm long. Electrodes made with 1.6 ± 0.2 μm thickness were used to analyze parameters such as synthesis conditions, light intensity (800-1500 W m⁻²), UV light irradiation and temperature (25-75 °C). We have also carried out initial analysis of the solar cell lifetime under continuous light irradiation at 45 °C, and analyzed the ZnO electrode before and after testing. The best photovoltaic response was characterized by a power conversion efficiency of 1.02%, with J_sc of 3.72 mA cm⁻², V_oc of 0.603 V and 45% FF (at 72 °C), for a ZnO NR electrode of 5.2 μm thickness. Comparison of our power conversion efficiency values with published data is also presented, as well as a brief discussion on the possible reasons behind the low power conversion efficiency observed for these type of solar cells.     

Mesoporous carbon-encapsulated NiO nanocomposite negative electrode materials for high-rate Li-ion battery

In this study, a novel mesoporous carbon-encapsulated NiO nanocomposite is proposed and demonstrated for Li-ion battery negative electrode. The nanostructure of the electrode composes of an ordered mesoporous CMK-3 as a 3D nanostructured current collector with micorporous channels for Li⁺ transportation. In addition, exclusive formation of NiO nanoparticles in the confined space of the ordered mesoporous carbon is achieved using the hydrophobic encapsulation route. The half-cell assembled with the synthesized NiO/CMK-3 nanocomposite is able to deliver a high charge capacity of 812 mAh g⁻¹ at the first cycle at a C-rate of 1000 mA g⁻¹ and retained throughout the test with only 0.236% decay per cycle. Even the C-rate as high as 3200 mA g⁻¹, a charge capacity of 808 mAh g⁻¹ contributed by the NiO nanoparticles in CMK-Ni is obtained, which shows excellent rate capability for NiO with utilization close to 100%. The result suggests fast kinetics of conversion reaction for NiO with Li⁺. It also indicates the blockage of the pore channels by NiO nanoparticles does not take place in the synthesized NiO/CMK-3.     

Ru oxide supercapacitors with high loadings and high power and energy densities

Supercapacitors with very high energy and power densities have been constructed with hydrous ruthenium oxide powder prepared by a sol–gel method and annealed at 110 °C. Novel features of the capacitors, which improve their performances, are the use of a carbon fibre paper support, a Nafion separator, and Nafion as a binder. 1 M sulfuric acid was employed as the electrolyte. The performances of the supercapacitors were characterized by cyclic voltammetry, impedance spectroscopy and constant current discharging. The interfacial capacitance increased linearly with increasing ruthenium oxide loading to at least 50 mg cm⁻² on each electrode. The gravimetric capacitance of the Ru oxide measure by impedance reached 742 F g⁻¹ (9.66 F cm⁻²) at a loading of 13.0 mg cm⁻², and an interfacial capacitance of 34.9 F cm⁻² (682 F g⁻¹) was obtained at 51.2 mg cm⁻². The average effective series resistance was 0.55 Ω, the electronic resistance of the electrodes was negligible, and their ionic resistances were <0.42 Ω. The average power density for full discharge at 1 A cm⁻² for supercapacitors with 10 mg cm⁻² Ru oxide increased by 39% when 5% Nafion binder was added. The maximum average power density for full discharge was 31.5 W g⁻¹ while the maximum energy density was 31.2 Wh kg⁻¹. At a 1 mA discharge rate a specific capacitance of 977 F g⁻¹ of Ru oxide was obtained.     

Preparation of mesoporous carbons from amphiphilic carbonaceous material for high-performance electric double-layer capacitors

Amphiphilic carbonaceous material (ACM), with nanoscale dispersion in alkaline aqueous solutions, is synthesized from green needle coke. As a special precursor with small particle size, plenty of functional groups and widened d₀₀₂ simultaneously, ACM guarantees subsequent ACM-based activated carbons (AACs) with high specific surface area over 3000 m² g⁻¹ as well as well-developed mesoporous structure after KOH activation. Such pore properties enable AACs’ high performances as electrode materials for electric double-layer capacitors (EDLCs). In particular, surface area up to 3347 m² g⁻¹ together with notable mesopore proportion (26.9%) gives sample AAC814 outstanding EDLC behaviors during a series of electrochemical tests including galvanostatic charge/discharge, CV and electrochemical impedance spectroscopy. The electrode gets satisfactory gravimetric and volumetric specific capacitance at the current density of 50 mA g⁻¹, up to 348 F g⁻¹ and 162 F cm⁻³, respectively. Furthermore, for the mesoporosity, there is only a slight capacitance reduction for AAC814 as the current density reaches 1000 mA g⁻¹, indicating its good rate performance. It is all the ACM's unique characteristics that make AACs a sort of competitive EDLC electrode materials, both in terms of specific capacitance and rate capability.     

Fabrication of platinum coated nanoporous gold film electrode: A nanostructured ultra low-platinum loading electrocatalyst for hydrogen evolution reaction

The electrolytic hydrogen evolution reaction (HER) on platinum coated nanoporous gold film (PtNPGF) electrode is demonstrated. The deposition of platinum occurred as a spontaneous redox process in which a copper layer, obtained by underpotential deposition, was oxidized by platinum ions, which were reduced and simultaneously deposited. The present method could provide a very low Pt-loading electrode and the results demonstrated that ultra thin Pt coating effected efficiently and behaved as the nanostructured Pt for electrocatalytic hydrogen evolution reaction. The loading of Pt was calculated as 4.2 × 10⁻³ μg cm⁻² for PtNPGF electrode. The current density at −0.4 V and −0.8 V vs. Ag/AgCl was as high as 0.66 A μg⁻¹ Pt and 3 A μg⁻¹ Pt, respectively and the j₀ was evaluated as 0.03 mA cm⁻² or 8 mA μg⁻¹ Pt. The results indicated that increasing electrode area had no catalytic effect, but the nanostructure nature of as-fabricated electrode and submonolayer deposition of copper resulted in electrocatalytic activity for PtNPGF electrode.     

Electrodeposited porous-microspheres Li-Si films as negative electrodes in lithium-ion batteries

A porous-microspheres Li-Si film (PMLSF) is prepared by multi-step constant current (MSCC) electrodeposition on Cu foil. Its structure and morphology are characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). As negative electrodes of lithium-ion batteries, the PMLSF electrode delivers the first gravimetric and geometric charge capacities of 2805.7 mA h g⁻¹ and 621.9 μA h cm⁻² at the current density of 25.5 μA cm⁻², and its initial coulombic efficiency is as high as 98.2%. When the PMLSF electrode is cycled in VC-containing electrolyte, the superior cycling performance can be obtained. After 50 cycles, 96.0% of its initial capacity is retained at the current density of 50.0 μA cm⁻². Electrochemical impedance spectra (EIS) research confirms the positive effect of VC additive on the behavior of the PMLSF electrode.     

Mesoporous nano-Co3O4: A potential negative electrode material for alkaline secondary battery

A potential negative electrode material (mesoporous nano-Co₃O₄) is synthesized via a simple thermal decomposition of precursor Co(OH)₂ hexagonal nanosheets in the air. The structure and morphology of the samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the nano-Co₃O₄ is present in mesoporous hexagonal nanoparticles. The average size of holes is about 5-15 nm. The electrochemical performances of mesoporous nano-Co₃O₄ as the active starting negative electrode material for alkaline secondary battery are investigated by galvanostatic charge-discharge and cyclic voltammetry (CV) technique. The results demonstrate that the prepared mesoporous nano-Co₃O₄ electrode displays excellent electrochemical performance. The discharge capacity of the mesoporous nano-Co₃O₄ electrode can reach 436.5 mAh g⁻¹ and retain about 351.5 mAh g⁻¹ after 100 cycles at discharge current of 100 mA g⁻¹. A properly electrochemical reaction mechanism of mesoporous nano-Co₃O₄ electrode is also constructed in detail.     

Effect of Ti sublayer on the ORR catalytic efficiency of dc magnetron sputtered thin Pt films

A series of thin Pt films were deposited by dc magnetron sputtering directly on a commercial hydrophobic carbon paper substrate having a thin microporous Vulcan-XC72 layer or upon a thin Ti sublayer sputtered on the top of the microporous carbon film. The electrocatalytic properties of the sputtered Pt films toward the oxygen reduction reaction were investigated in 0.5 M H₂SO₄ solution and in a hydrogen PEM fuel cell. The catalyst with ultralow Pt loading of 22 μg cm⁻² deposited on a 33 Å thick Ti sublayer is robust, mechanically stable, possesses highly developed surface area and improved catalytic efficiency. Its performance as a MEA cathode in a single hydrogen PEM fuel cell (577 mA cm⁻² at 0.4 V cell voltages and a maximum power of 0.954 W) proved to be much superior compared to that of MEA with the same cathode Pt loading but without Ti sublayer (173 mA cm⁻² at 0.4 V, 0.231 W, respectively).     

Pseudo-capacitance of composite electrode of ruthenium oxide with porous carbon in non-aqueous electrolyte containing imidazolium salt

Pseudo-capacitance of composite materials where ruthenium oxide particles are loaded on activated carbon has been evaluated in the electrolyte of 1-ethyl-3-methyl imidazolium tetrafluoroborate dissolved in acetonitrile. The composite materials prepared by conventional a sol-gel method have dispersed structure of ruthenium oxide particle of tens nanometer diameter on the surface of activated carbon. The extent of the pseudo-capacitance of the composite electrodes in the imidazolium salt electrolyte, estimated by the comparison of the capacitance per surface area of electrode in different non-aqueous electrolyte, is ca. 3-5 μF cm⁻² in addition to the double-layer capacitance of ca. 6 μF cm⁻², depending on the loading status of ruthenium oxide. The symmetric cell consisting of the composite electrode containing 18 wt% of ruthenium oxide and the imidazolium salt electrolyte provides cell capacitance based on the pseudo-capacitance by a constant-current test.     

Enhanced electrocatalytic activity of platinum supported on nitrogen modified ordered mesoporous carbon

Nitrogen-modified ordered mesoporous carbon is synthesized via the 900 °C carbonization of polyaniline-coated mesoporous carbon. The electronic states of nitrogen atoms are investigated by XPS technique. Pyridinic nitrogen and quaternary nitrogen generate disorders and curvatures on the surface of graphitic carbon layers with nitrogen atoms replacing carbon atoms at the edges and the interior of carbon stacking, and thus offering beneficial anchoring sites for PtCl₆²⁻ ions. Pyridinic nitrogen and pyrrolic nitrogen offer p electrons to the sp² hybridized graphitic carbon layers, decreasing the inner electrical resistance of the catalytic carbon layer, enhancing the rate of proton diffusion, and transporting more free electrons to oxidative platinum. Due to the advantageous modification of the electronic structure of carbon atoms, platinum nanoparticles with a narrow size distribution are homogenously dispersed onto the surface of nitrogen-modified ordered mesoporous carbon, as evidenced by TEM images. Electrochemical tests show that the samples loaded platinum calcined at the 900 °C exhibit the optimum loading performance among as-made catalysts and a gradually decreased decay in electro-catalytic activity with time, with the current density stabilized at 3.64 mA cm⁻², which is far higher than that of mesoporous carbon (0.15 mA cm⁻²).     

Preparation of a porous carbon from ferrocene-loaded polyaniline and its use in hydrogen adsorption

A porous carbon made of polyaniline with different ferrocene loadings was prepared through carbonization and thermal chemistry activation with KOH. The ferrocene served as a pore-forming agent and a resource of iron nanoparticles. N₂ adsorption/desorption measurements showed that the specific surface area and pore volume ranged from 2681 to 3246 m² g⁻¹ and from 1.56 to 2.06 cm³ g⁻¹, respectively, with increasing ferrocene loadings. Similarly, hydrogen adsorption also increased from 5.3 to 6.2 wt% at 77 K/5 MPa and 0.6 wt% to 0.85 wt% at 293 K/8 MPa. Scanning electron microscopy, X-ray diffraction and energy dispersive X-ray analysis showed that iron nanoparticles were embedded in the carbon matrix or dispersed on the surface. The large specific surface area and big pore volume improved the original hydrogen adsorption heat up to 7.2 kJ mol⁻¹ for the best sample.     

Proton transport, water uptake and hydrogen permeability of nanoporous hematite ceramic membranes

For the first time, mesoporous acid-free hematite ceramic membranes have been studied as proton conductors. The xerogels after calcination at 300 °C for 1 h were mesoporous, as is mentioned above, with a BET surface area of 130 ± 2 m² g⁻¹, an average pore diameter of 3.8 nm and a pore volume of 0.149 ± 0.001 cc g⁻¹. A sigmoidal dependence of the conductivity and the water uptake with the RH at a constant temperature was observed. The conductivity of the ceramic membranes increased linearly with temperature for all relative humidities studied. The highest value of proton conductivity was found to be 2.76 × 10⁻³ S cm⁻¹ at 90 °C and 81% RH. According to the activation energy values, proton migration in this kind of materials could be dominated by the Grotthuss mechanism in the whole range of RH. The low cost and high hydrophilicity of these ceramic membranes make them potential substitutes for perfluorosulfonic polymeric membranes in proton exchange membrane (PEMFCs). In addition, since hydrogen permeability values are in the range of 10⁻⁹ to 10⁻¹⁰ mol cm⁻¹ s Pa, in order to fabricate oxide-based PEMs that are capable of keeping streams of H₂ and O₂ from mixing, a separation layer with pore sizes <2 nm whose pores are filled with water will be needed.     

Study of Pt electrode dissolution in H2O2-containing H2SO4 solution using an electrochemical quartz crystal microbalance

Pt electrode dissolution has been investigated using an electrochemical quartz crystal microbalance (EQCM) in H₂O₂-containing 0.5 mol dm⁻³ H₂SO₄. The Pt electrode weight-loss of ca. 0.4 μg cm⁻² is observed during nine potential sweeps between 0.01 and 1.36 V vs. RHE. In contrast, the Pt electrode weight-loss is negligible without H₂O₂ (<0.05 μg cm⁻²). To support the EQCM results, the weight-decrease amounts of a Pt disk electrode and amounts of Pt dissolved in the solutions were measured after similar successive potential cycles. As a result, these results agreed well with the EQCM results. Furthermore, the H₂O₂ concentration dependence of the Pt weight-decrease rate was assessed by successive potential steps. These EQCM data indicated that the increase in H₂O₂ accelerates the Pt dissolution. Based on these results, H₂O₂ is known to be a major factor contributing to the Pt dissolution.     

Synthesis of mesoporous polythiophene/MnO2 nanocomposite and its enhanced pseudocapacitive properties

Mesoporous nanocomposite of polythiophene and MnO₂ has been synthesized by a modified interfacial method, aiming to develop electrode materials for supercapactitors with an enhanced cycle performance and high-rate capability. The N₂ adsorption/desorption isotherm test of the prepared hybrid indicates a high surface area and a typical mesoporous feature. A uniform hierarchical microstructure with submicron-spheres assembled from ultrathin nanosheet with diameters less than 10 nm has been confirmed by field-emission scanning electron microscopy and transmission electron microscopy. The employed interfacial synthesis is found to be advantageous to retard the overgrowth of nuclei. The retention of 97.3% of its initial capacitance after 1000 cycles at a charge/discharge rate of 2 A g⁻¹ indicates excellent cycle performance of the nanocomposite electrode. At a high-rate charge/discharge process of 10 A g⁻¹, the nanocomposite electrode retained 76.6% of its capacitance at 1 A g⁻¹, suggesting good high-power capability. The important roles of polythiophene in the as-prepared nanocomposite are highlighted in terms of their functions on enhancing the electrical conductivity and constraining the dissolution of manganese oxides during charge-discharge cycles.     

A novel synthesis of mesoporous carbon microspheres for supercapacitor electrodes

Mesoporous carbon microspheres (MCMs) with the diameters of 0.5-2.0 μm, main mesopore sizes of 2.6-4.0 nm and specific surface areas of 449-1212 m² g⁻¹ are synthesized by a novel hydrothermal emulsion-activated method. The typical MCMs as electrode materials have a specific capacitance of 157 F g⁻¹ at a high current density of 10.0 A g⁻¹ in 6 M KOH aqueous solution. The resultant MCMs electrode materials with high current charge and discharge capability in 6 M KOH aqueous solution provide important prospect for electrode materials in supercapacitors which could offer high power density for electric vehicles.