Percolation effects in functionally graded SOFC electrodes

A solid oxide fuel cell (SOFC) composite electrode exhibits a superior performance compared to a single phase electrode since the electrochemically active zone is spread into its volume. A functionally graded composite electrode consisting of monosized spherical electrocatalyst and electrolyte particles is sintered numerically by the discrete element method (DEM). The electrochemical performance is evaluated by a resistance network approach using Kirchhoff's current law. In the network discretization each contact between two particles is substituted by a bond resistance defined by contact size and the type of materials in contact.The graded electrode is optimized by varying its composition at the electrolyte/electrode interface and the degree to which the composition decreases linearly towards the current collector/electrode interface. Regarding its electrochemical activity, the graded electrode does not perform significantly better than an optimized uniformly randomly mixed composite electrode but percolation of the graded electrode is improved. In order to demonstrate the importance of percolation effects, a novel better performing electrode is developed which contains electronically conducting particle chains arranged within a random packing of ionically conducting particles.     

MnO2/MCMB electrocatalyst for all solid-state alkaline zinc-air cells

Nanostructured MnO₂/mesocarbon microbeads (MCMB) composite has been prepared successfully for use in zinc-air cell as electrocatalyst for oxygen reaction. The scanning electron microscope (SEM) images showed that the MnO₂ nanorods were formed and covered on the surface of MCMB in bird’s nest morphology. X-ray diffraction (XRD) pattern indicated that the MnO₂ has the hollandite structure with a composition approximating KMn₈O₁₆. By the cathodic polarization curve tests, the nanostructured material demonstrated excellent electrocatalytic activity as a kind of oxygen electrode electrocatalyst compared with electrolytic MnO₂. An all solid-state zinc-air cell has been fabricated with this material as electrocatalyst for oxygen electrode and potassium salt of cross-linked poly(acrylic acid) as an alkaline polymer gel electrolyte. The cell has good discharge characteristics at room temperature.     

Efficient wide-spectrum dye-sensitized solar cell by plasmonic TiN@Ni-MXene as electrocatalyst

Herein, dispersed Ni species over the surface of plasmonic TiN nanocrystals (TiN@Ni) are manufactured by using wetness impregnation method. This developmental material holds abundant surface sites and local surface plasmon resonance property. To further satisfy the requirement as the electrocatalyst for dye-sensitized solar cell (DSSC), bifunctional TiN@Ni nanocrystals are incorporated with monolayer MXene to construct the continuous conductive matrix. The yielded TiN@Ni-MXene film serves as counter electrode, power conversion efficiency(PCE) of corresponding DSSC under conventional irradiation condition is 8.08%, which surpasses as-reference Pt-based DSSC(7.59%). When further adding the NIR irradiation from counter electrode side of device, DSSC achieves an impressive PCE of 8.45%. The superior performance of TiN@Ni-MXene electrode should be attributed to the created active sites on the surface of TiN support, and the plasmonic effect from TiN@Ni nanoparticles via utilizing NIR light. Ni species provide more adsorption sites for triiodide ions, meanwhile the elevated temperature from plasmon-induced photothermal effect can effectively boost the triiodide reducing reaction rates at the interface of electrode and electrolyte. Thus electrocatalytic performance of TiN@Ni-MXene counter electrode is remarkablely enhanced. The strategy here will be beneficial for the design of highly active and stable electrocatalyst for DSSC, as well as realizing the efficient utilization for wide-spectrum solar energy.     

Modelling the porous cathode of a SOFC: oxygen reduction mechanism effect

A composite electrode comprising a porous mixture of solid electrolyte (typically yttria stabilized zirconia, YSZ) and electronically conducting, electrocatalytic material (typically strontium doped lanthanum manganite, LSM) is generally used to improve the cathodic performance of the solid oxide fuel cell (SOFC). The advantage of the composite electrode is that the reaction zone is spread from the electrode/electrolyte interface into the electrode, effectively resulting in a functionally diffuse interface where the charge transfer reaction occurs. The present study proposes a one-dimensional dc and ac model that takes into account mass and charge conservation, transport of species and reaction kinetics. It considers the porous electrode to be a homogeneous medium characterized by a number of parameters, and in particular ionic conductivity and the diffusion coefficient. The influence of kinetic and transport parameters as well as that of the microstructure on the shape of both polarization curves and impedance diagrams is discussed.     

浸渗法制备固体氧化物燃料电池复合阴极研究进展

中低温化是目前固体氧化燃料电池研究的主要方向,影响其发展的主要问题是电解质及阴极材料的研制.浸渗法制备复合阴极能够显著提高电池在中低温下的电化学性能和效率,是目前研究的热点之一.本文介绍了近年来采用具有催化活性的电极材料、贵金属、氧离子传导材料等作为浸渗剂制备复合阴极的研究现状,并对其发展方向进行了展望.     

Palygorskite Hybridized Carbon Nanocomposite as PtRuIr Support for the Methanol Oxidation Reaction

A palygorskite/carbon heterogeneous nanocomposite, a unique hybrid of palygorskite and carbon, was prepared and designed as an electrocatalyst support material for PtRuIr nanoparticles and evaluated for methanol electrooxidation. X‐ray diffraction and transmission electron microscopy results showed that PtRuIr nanoparticles were well‐dispersed on the composite support with highly dispersed tiny crystal alloy phase on the surface of PtRuIr amorphous alloy. X‐ray photoelectron spectroscopy results indicated that the formation of Ru and Ir oxides on the surface of the PtRuIr nanoparticles. The electrochemical results show that the palygorskite hybridized carbon used as electrocatalysts support can improve the electrocatalytic activity towards methanol oxidation and CO tolerance.     

Polyaniline-carbon composite films as supports of Pt and PtRu particles for methanol electrooxidation

Vulcan XC-72 carbon black particles (average size: ca. 50 nm) was incorporated into polyaniline (PANI) matrix by an electrochemical codeposition technique during the electropolymerization process. The doping by carbon particles leads to a higher polymeric degree and a lower defect density in the PANI structure. Furthermore, the incorporation of carbon particles not only increases the electrochemical accessible surface areas (S_a) and electron conductivity of the PANI film, but also decreases charge transfer resistance at PANI/electrolyte interfaces. Therefore, as expected, a fabricated PANI + C composite film with dispersed Pt and PtRu particles exhibited excellent electrocatalytic activity for methanol oxidation due to better Pt dispersion and utilization. The PANI + C composite film is more promising as a support material in electrocatalysis than a PANI film. Meanwhile, a new application for regular carbon black as a doping material into conducting polymer for electrocatalysis was thus demonstrated.     

Novel spherical TiO2 supported PdNi alloy catalyst for methanol electroxidation

A novel PdNi/TiO₂ electrocatalyst for methanol oxidation is fabricated using spherical TiO₂ nanoparticles as support. The structural and electrochemical properties of the PdNi/TiO₂ catalyst are characterized by XRD, TEM and electrochemical analysis. The cyclic voltammograms of PdNi/TiO₂ catalyst show that there is a large methanol oxidation peak in about 0.882 V that is much bigger than that of the commercial PtRu/C catalyst in 0.7 V. The composite TiO₂ material has high catalytic activity without UV light illumination. The electrocatalytic activity and anti-poisoning capability of the PdNi/TiO₂ catalyst are promising, which may become a potential candidate for direct methanol fuel cell.     

Electroreduction of oxygen on Vulcan carbon supported Pd nanoparticles and Pd–M nanoalloys in acid and alkaline solutions

The kinetics of O₂ reduction on novel electrocatalyst materials deposited on carbon substrates were studied using the rotating disk electrode (RDE) technique. Palladium nanoparticles and Pd–M (PdCo and PdFe) nanoalloys supported on Vulcan XC-72R were prepared using two different synthetic routes. The catalyst samples were examined by transmission electron microscopy (TEM) and the average size of metal nanoparticles was determined. Electrochemical measurements were performed in 0.5 M H₂SO₄ and in 0.1 M NaOH solutions. The influence of different synthetic conditions on the values of specific activity and other kinetic parameters was investigated. These parameters were determined from the Tafel plots taking into account the real electroactive area for each electrode. Pd nanoparticles and Pd–M nanoalloys exhibit significantly high electrocatalytic activity for the four-electron reduction of oxygen to water.     

Electrocatalytic activity of Pt nanoparticles deposited on porous TiO2 supports toward methanol oxidation

Porous TiO₂ thin films were prepared on the Si substrate by hydrothermal method, and used as the Pt electrocatalyst support for methanol oxidation study. Well-dispersed Pt nanoparticles with a particle size of 5–7 nm were pulse-electrodeposited on the porous TiO₂ support, which was mainly composed of the anatase phase after an annealing at 600 °C in vacuum. Cyclic voltammetry (CV) and CO stripping measurements showed that the Pt/TiO₂ electrode had a high electrocatalytic activity toward methanol oxidation and an excellent CO tolerance. The excellent electrocatalytic performance of the electrode is ascribed to the synergistic effect of Pt nanoparticles and the porous TiO₂ support on CO oxidation. The strong electronic interaction between Pt and the TiO₂ support may modify CO chemisorption properties on Pt nanoparticles, thereby facilitating CO oxidation on Pt nanoparticles via the bifunctional mechanism and thus improving the electrocatalytic activity of the Pt catalyst toward methanol oxidation.     

负载硅钨杂多酸纳米银修饰电极的电化学性质研究

以硅钨杂多酸作为光催化还原剂制备了纳米银(SiW12-NS)。用PVP作偶联剂,将SiW12-NS修饰到玻碳电极表面,用循环伏安法(CV)研究其电化学行为。结果表明,修饰电极具有良好的电化学响应和电极稳定性,对BrO3-,NO2-具有良好的电催化还原性能。     

Electroreduction of oxygen on Pt nanoparticle/carbon nanotube nanocomposites in acid and alkaline solutions

The kinetics of O₂ reduction on novel electrocatalyst materials deposited on carbon substrates were studied in 0.5 M H₂SO₄ and in 0.1 M NaOH solutions using the rotating disk electrode (RDE) technique. Pt nanoparticles (PtNP) supported on single-walled (PtNP/SWCNT) and multi-walled carbon nanotubes (PtNP/MWCNT) were prepared using two different synthetic routes. Before use, the CNTs were cleaned to minimize the presence of metal impurities coming from the catalyst used in the synthesis of this material, which can interfere in the electrochemical response of the supported Pt nanoparticles. The composite catalyst samples were characterised by transmission electron microscopy (TEM) showing a good dispersion of the particles at the surface of the carbon support and an average Pt particle size of 2.4 ± 0.7 nm in the case of Pt/CNTs prepared in the presence of citrate and of 3.8 ± 1.1 nm for Pt/CNTs prepared in microemulsion. The values of specific activity (SA) and other kinetic parameters were determined from the Tafel plots taking into account the real electroactive area of each electrode. The electrodes exhibited a relatively high electrocatalytic activity for the four-electron oxygen reduction reaction to water.     

CeO(2)/rGO/Pt sandwich nanostructure: rGO-enhanced electron transmission between metal oxide and metal nanoparticles for anodic methanol oxidation of direct methanol fuel cells

Pt-based nanocomposites have been of great research interest. In this paper, we design an efficient MO/rGO/Pt sandwich nanostructure as an anodic electrocatalyst for DMFCs with combination of the merits of rigid structure of metallic oxides (MOs) and excellent electronic conductivity of reduced oxidized graphene (rGO) as well as overcoming their shortcomings. In this case, the CeO(2)/rGO/Pt sandwich nanostructure is successfully fabricated through a facile hydrothermal approach in the presence of graphene oxide and CeO(2) nanoparticles. This structure has a unique building architecture where rGO wraps up the CeO(2) nanoparticles and Pt nanoparticles are homogeneously dispersed on the surface of rGO. This novel structure endows this material with great electrocatalytic performance in methanol oxidation: it reduces the overpotential of methanol oxidation significantly and its electrocatalytic activity and stability are much enhanced compared with Pt/rGO, CeO(2)/Pt and Pt/C catalysts. This work supplies a unique MO/rGO/Pt sandwich nanostructure as an efficient way to improve the electrocatalytic performance, which will surely shed some light on the exploration of some novel structures of electrocatalyst for DMFCs.     

Enhanced electrocatalytic activity for the oxidation of liquid fuels on PtSn nanoparticles

PtSn nanoparticles with different Pt/Sn ratio have been prepared by a chemical reduction method. XRD data indicate that Sn atom is introduced into the Pt lattice. Their electrocatalytic activity is evaluated using cyclic voltammetry (CV), differential electrochemistry mass spectrometry (DEMS), and rotating disk electrode (RDE) experiments. The Pt₉Sn₁ nanoparticles exhibit higher electrocatalytic activity than commercial Pt nanoparticles (E-TEK) for the oxidation of ethanol. The rate constants for the oxidation of formic acid, formaldehyde, methanol, ethanol, glycol, and glycerol on Pt₉Sn₁ electrocatalyst are much higher than that on Pt. The results indicate that Pt₉Sn₁ is an excellent electrocatalyst for the oxidation of liquid fuels. The activation energy studies show that the higher electrocatalytic activity of PtSn catalyst can be ascribed to the bifunctional mechanism, instead of the dilation of Pt crystal structure.     

Ion conducting polyurethane electrolyte with fixed ferrocene groups as redox active sites

Summary Ion conducting polyurethane electrolyte with redox active ferrocene groups which are fixed to the polymer backbone by covalent bonds was prepared. It has been found that the resulting polyurethane electrolyte has high conductivity even at lower temperature. And the temperature dependence of conductivity follows well the Arrhenius equation. Solid state electrochemical property was measured by cyclic voltammetric method with microdisk electrodes at different temperature. The results indicated that the polyurethane electrolyte has good redox stability, as well as reiteration, and show electrochemical activity in the solid state. Received: 15 June 1998/Revised version: 5 October 1998/Accepted: 28 October 1998     

Synthesis and characterization of palladium nanoparticles immobilized on ZrO<Subscript>2</Subscript> nanotubes as a new highly active electrode for methanol electro-oxidation

Palladium nanoparticles/zirconium oxide nanotubes/zirconium (Pd-NPs/ZrO₂-NTs/Zr) electrodes were prepared by electroless plating method. ZrO₂-NTs consisting of individual nanotubes of about 60–80 nm diameters were fabricated by anodizing Zr foil in electrolyte solution containing dimethylformamide, glycerol, water and ammonium fluoride. The morphology and surface characteristics of ZrO₂-NTs and Pd-NPs/ZrO₂-NTs/Zr electrodes studied using scanning electron microscopy as well as energy dispersive X-ray spectroscopy. The results revealed that Pd-NPs were homogeneously deposited on the surface of ZrO₂-NTs. Moreover, electrocatalytic properties of Pd-NPs/ZrO₂-NTs/Zr and flat Pd electrodes toward methanol oxidation were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The results indicated that Pd-NPs/ZrO₂-NTs/Zr electrode represents an enhanced electrocatalytic activity and better stability for methanol oxidation compared to flat Pd. Thus, the Pd-NPs/ZrO₂-NTs/Zr catalyst is expected to be a promising electrode material for direct methanol fuel cells. Additionally, the effects of scan rate, methanol concentration and temperature dependency of methanol oxidation on Pd-NPs/ZrO₂-NTs/Zr electrode have been explored in this study.     

Synthesis of perovskite-like NiTiO3 nanoparticles as an electrode material by a rapid solid combustion technique induced by microwave irradiation

We report a rapid one-step high-yield spontaneous combustion procedure accelerated by microwave irradiation to synthesize NiTiO₃ nanoparticles with high pseudocapacitive behavior. The reaction was performed in a solid state recipe into a home-made melting pot to capture microwave heating, mutate reaction temperature and supply in situ calcination conditions without any external treatment. Structural and morphological characteristics of the obtained product were evaluated in detail where the synthesis of a pure single phase of NiTiO₃ with a particulate morphology and average particle size of about 30 nm was revealed. The electrochemical properties of the fabricated NiTiO₃ nanoparticles was investigated by cyclic voltammetry tests. As expected, the results indicated an acceptable specific capacitance about 257 F g⁻¹ at scan rate of 10 mVs⁻¹ with a good reversible redox reaction and stable cycle life. The capacity retention of about 92% after 1000 cycles showed highly chance of this metal oxide as an electrode material for electrochemical devices.     

Electrophoretic deposition of network-like carbon nanofibers as a palladium catalyst support for ethanol oxidation in alkaline media

A network-like carbon nanofiber (CNF) film with an open porous structure formed by the open space between entangled CNFs is fabricated by electrophoretic deposition. The performance of the CNF film as an electrocatalyst in the presence of electrodeposited Pd nanoparticles for ethanol oxidation in alkaline media is investigated. Cyclic voltammetric analyses show the electrocatalyst has a good electrocatalytic activity toward ethanol oxidation in KOH solution. This is believed to be due to the high dispersion of Pd on the CNF film with a three-dimensional network structure which can provide a large number of available Pd active sites for ethanol oxidation, and to the structural and electrical properties of the film.