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Highlights: [•] Multiple interim CVs during start-up/shutdown cycling lead to severe degradation. [•] The degradation results from additional Pt dissolution and carbon corrosion. [•] The CV causes depassivation of Pt oxides formed on Pt particles during cycling tests. [•] The surface oxidation-reduction process of Pt particles leads to high Pt dissolution. [•] The reduced Pt again catalyzes carbon corrosion effectively during cycling tests. [Copyright &y& Elsevier]

Abstract: We found high activity and durability for oxide-supported Pt catalysts for the oxygen reduction reaction (ORR). These catalysts were supported on Sn0.96Nb0.04O2–δ (Pt/Sn0.96Nb0.04O2–δ ; BET area of support, 37m2 g−1; Pt loading, 10.0wt%) and Sn0.96Sb0.04O2–δ (Pt/Sn0.96Sb0.04O2–δ ; BET area of support, 33m2 g−1; Pt loading, 12.3wt%), by use of the rotating disk electrode (RDE) technique, and measured the I–E performance of single H2-air polymer electrolyte fuel cells (PEFCs) using these catalysts as the cathode. The nanoparticulate supports Sn0.96Nb0.04O2–δ and Sn0.96Sb0.04O2–δ had an aggregated structure similar to that of carbon black (CB). The electrochemically active surface area of Pt, estimated by cyclic voltammetry measurements with the RDE, reached 79.7m2 g−1 (Pt/Sn0.96Nb0.04O2–δ ) and 68.6 m2 g−1 (Pt/Sn0.96Sb0.04O2–δ ). The ORR activity of Pt/Sn0.96Nb0.04O2–δ exceeded that of a commercialized Pt catalyst supported carbon black (Pt/CB). Higher durability was confirmed for Pt/Sn0.96Nb0.04O2–δ and Pt/Sn0.96Sb0.04O2–δ compared to that of Pt/CB with a test protocol for start/stop cycling recommended by the Fuel Cell Commercialization Conference of Japan (FCCJ) [1]. Single cells using these catalysts showed I–E performance superior to that for the Pt/CB at operating potentials above 0.4V. For operating potentials below 0.4V, a slight amount of Sn dissolution from the Sn0.96Sb0.04O2–δ support occurred, resulting in degradation of the cell performance due to Pt poisoning by Sn re-deposition, but no noticeable degradation at Sn0.96Nb0.04O2–δ was found, due to the suppressed Sn dissolution. [Copyright &y& Elsevier]

Abstract: The corrosion of carbon black (CB) support materials for polymer electrolyte fuel cells was investigated by use of two standard accelerated testing protocols, square wave cycling (E =0.9–1.3V vs. RHE, holding 30s at each E) and triangular wave cycling (E =1.0–1.5V vs. RHE, at a scan rate of 0.5Vs−1) protocols, which were operated with H2 (anode) and N2 (cathode) atmospheres at 80°C and 100% RH. Severe decreases of the electrochemically active surface area (ECSA), mass activity (MA@0.85 V) and cell performance resulting from the simulated start-up/shutdown cycling are ascribed to the detachment of Pt particles from the CB support due to carbon corrosion and structural collapse, as well as Ostwald ripening. First, the simulated start-up/shutdown cycling brings about the surface corrosion of the CB particles, and thereafter it transforms the crystalline carbon into amorphous carbon, which subsequently undergoes corrosion. This continual corrosion process of the CB support leads to a significant thickness reduction of the Pt/CB cathode catalyst layer and the severe detachment of Pt particles from the CB. On the CB particles, the slower square wave cycling brings about their overall corrosion, including the surface defects and anchoring centers where Pt particles are well attached and dispersed, whereas the faster triangular wave cycling brings about corrosion locally at more unstable surface defects on the CB particles. This is why the estimated cycle half-life N 1/2 (at which ECSA is estimated to decrease to ca. 1/2 of the initial value) for the Pt/CB cathode catalyst was 10 times shorter with the square wave cycling compared to that with the triangular wave cycling. The effect of overall cycling time vs. cycle number is also discussed. [Copyright &y& Elsevier]

Abstract: We synthesized Pt catalysts supported on titanium nitride nanoparticles (Pt/TiN, Pt loading, 8.9wt%) by a colloidal method. The Pt nanoparticles were found to exhibit a characteristic hexahedral shape with clear faceting, with a lattice structure that was highly oriented to that of the TiN support, indicating a strong interaction between the Pt nanoparticles and the TiN support. We evaluated the electrochemical activity of the Pt/TiN both without and with mixing with electronically conducting acetylene black (AB), the latter denoted as Pt/TiN+AB. The electrochemically active surface area (ECSA) of Pt in Pt/TiN+AB was noticeably larger than that of Pt/TiN, reaching 108m2g(Pt) −1 as a maximum, which was close to the geometrically estimated Pt surface area (127m2 g(Pt) −1), based on transmission electron microscopy. By means of a potential step cycling test (0.9–1.3V vs. RHE) simulating start/stop cycles in polymer electrolyte fuel cells (PEFCs), it was found that both of the TiN-based catalysts exhibited superior durability compared to commercial Pt catalysts supported on carbon black (Pt/CB) or graphitized carbon (Pt/GCB), based on the ECSA values. The mass activities at 0.85V of both of the TiN-based catalysts for the oxygen reduction reaction (ORR) were also higher than those for commercial Pt/CB or Pt/GCB during the potential step cycling test. The superiority of the TiN catalysts must have arisen as a result of the stabilization of the Pt nanoparticles due to their strong interaction and well matched crystallographic structures, as well as the complete elimination of nanopores from the support surfaces. [Copyright &y& Elsevier]

Abstract: We synthesized a Pt catalyst supported on Sn0.96Sb0.04O2−δ with a random network structure for the cathode of the polymer electrolyte fuel cell (PEFC). The Sn0.96Sb0.04O2−δ support, synthesized by the flame combustion method, was in the form of nanometer-sized particles with a partially agglomerated structure similar to that of carbon black (CB) and with a high surface area, 125m2 g−1. The structure was considered to be beneficial in reducing the contact resistance between the Sn0.96Sb0.04O2−δ support particles and in dispersing the nanometer-size Pt particles. We applied the nanocapsule method to synthesize the Sn0.96Sb0.04O2−δ -supported Pt catalyst (Pt/Sn0.96Sb0.04O2−δ ). The electrochemically active surface area (ECA) of Pt reached a maximum of 60.2m2 g(Pt) −1, and the high values were maintained during the potential step cycling test (0.9–1.3V) simulating the start/stop cycling of PEFCs. The oxygen reduction reaction activity of the Pt/Sn0.96Sb0.04O2−δ catalyst exceeded that of Pt supported on carbon black (Pt/CB). We conclude that the random network structured Sn0.96Sb0.04O2−δ might be a good candidate support material for the cathode of PEFCs. [Copyright &y& Elsevier]

Abstract: The electrical resistivity of the Zn1−x−y Ga x In y O system was investigated as a function of the dopant content and mean dopant ion radius. The electrical resistivity of all members of the system exhibited metallic behavior as a function of temperature. The lowest electrical resistivity at 873K fell to 2.81×10−3 (Ωcm) in Zn0.99Ga0.0073In0.0027O. In cases with the same dopant content, the resistivity strongly depended on the mean dopant ion radius, but the Seebeck coefficient was unrelated to those radii. Regardless of dopant content, the minimum resistivity of this system appeared around a mean dopant ion radius of 0.54Å. Evidently, the carrier mobility is strongly dependent on the magnitude of the mean dopant ion radius and any structural distortion. [Copyright &y& Elsevier]

Abstract: We have measured the electrical power density of a single cell of a solid oxide fuel cell (SOFC) with (Ba0.3Sr0.2La0.5)InO2.75 as an electrolyte at an operating temperature of 800 °C. A moistened mixture of 10% hydrogen in argon, constituted the fuel gas; air was the oxidant gas. We selected (La0.6Sr0.4)(Mn1−x M x )O3−δ (M =Co, Ni) (x =0–0.3) and Ni as cathode and anode materials. The power density was dependent on the amount of the transition metal doped into the cathode; the use of (La0.6Sr0.4)(Mn0.9Co0.1)O3−δ as a cathode material enabled us to reach a maximum power density of 0.61 W/cm2. We also investigated the diffusion of the constituent elements around the interface between the cathode and the electrolyte by X-ray diffraction and X-ray energy dispersive analysis (EDX). We found that the constituent elements Mn, Co, Ni and In diffused to the opposite phase. We suggest that this cation diffusion would change the electrical conductivity of the cathode and electrolyte around the interface and would affect the cathodic reaction. The interface resistance between the (Ba0.3Sr0.2La0.5)InO2.75 electrolyte and the (La0.6Sr0.4)(Mn1−x M x )O3−δ (M =Co and Ni) (x =0–0.3) cathode was characterized by the direct current two-probe method. It showed minimum values at x =0.1(Co) and x =0.2(Ni), suggesting that the interface properties might strongly affect the power generation of the SOFC. [Copyright &y& Elsevier]

Abstract: We have synthesized the perovskite oxides of the (Ba0.3Sr0.2La0.5)(In1−x Fe x )O3−δ system and measured the total electrical conductivity as a function of temperature and oxygen partial pressure. It was found that the single-phase composition region extended from x =0.0 to x =1.0, and that the Fe valence increased from 3.06 to 3.50 in that region. The electrical conductivity was semiconducting from x =0.0 to x =0.40 and metallic from x =0.50 to x =1.0. The total electrical conductivity at 800 °C also increased with the Fe content and achieved a maximum value of 140 (S/cm) at x =1.0. From the dependence of the electrical conductivity on the oxygen partial pressure, we conclude that above x =0.50, the majority carriers are holes. The estimated hole conductivity increased exponentially with the amount of Fe4+ cation present. The oxide ion conductivity was dependent on the oxygen vacancy content. [Copyright &y& Elsevier]

Abstract: We have conducted an electrical power generation experiment using a single cell of solid oxide fuel cell (SOFC) with (Ba0.3Sr0.2La0.5)InO2.75 as an electrolyte at an operating temperature of 800 °C. A moistened 10% hydrogen/argon mixture constituted the fuel gas, and air was the oxidant gas. As cathode and anode materials, we selected (La0.6Sr0.4)(Mn1−x Fe x )O3−δ (x =0–0.6) and Ni, respectively. The power density proved to be dependent on the Fe content of the cathode; use of (La0.6Sr0.4)(Mn0.6Fe0.4)O3−δ as a cathode material enabled us to reach a maximum power density of 0.58 W/cm2. An analysis of X-ray Absorption Near-Edge Structure (XANES) taken to detect mixed valence of Mn and Fe showed that each valence was over 3.0. We also investigated, by X-ray diffraction and energy dispersive X-ray analysis (EDX), the diffusion of the constituent elements around the interface between the cathode and the electrolyte. Our results showed that the Mn, Fe and In diffused to the opposite phase. The interface resistance between electrolyte and electrode, which was measured by the direct current two-probe method, reached a minimum value at x =0.4, suggesting that the electronic conductivity of the interface would strongly affect the power generation. [Copyright &y& Elsevier]

Abstract: A solid oxide fuel cell (SOFC) in which (Ba0.3Sr0.2La0.5)InO2.75 was used as an electrolyte was fabricated in order to characterize its electrical power generation. Moistened 1% hydrogen gas balanced with argon gas was used as the fuel gas to prevent reduction of the electrolyte. The chemical reaction between the electrolyte and some electrode materials has been investigated by X-ray diffraction. The appropriate electrodes are Pt and Ni for the cathode and anode, respectively. The maximum power density was 0.51 (W/cm2) at 800 °C. [Copyright &y& Elsevier]

Total electrical conductivity of (Ba0.5+xLa0.5-x)2(In1-xMx)2O5.5 (M=Zr and Ce) and (Ba0.5-xLa0.5+x)2(In1-xMx′)2O5.5 (M′=Mg, Ca and Sr) solid-solution systems was measured as functions of temperature and oxygen partial pressure. The oxide-ion conductivity of all the solid-solution systems increased at first with an increase in the unit cell free volume. However, it showed a maximum value at a unit cell free volume and then decreased. All the solid-solution systems showed a similar dependence of the oxide-ion conductivity on the unit cell free volume, even if they have different average ionic valences in the A- and B-sites. From the results of the Raman spectra measurement, the decrease of conductivity in the larger unit cell free volume range is presumed to arise from the local distortion of oxygen octahedra. [Copyright &y& Elsevier]

In order to establish clear criteria for designing highly active and highly durable oxygen electrode for reversible solid oxide fuel cells, we have focused on the effect of samaria-doped ceria (SDC) interlayers prepared on YSZ solid electrolyte surface on the performances of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF)-SDC composite oxygen electrode. Symmetrical cells with the configuration, LSCF-SDC|SDC interlayer|YSZ|SDC interlayer|LSCF-SDC, were constructed. We prepared two kinds of SDC interlayers, one from a mixed solution of cerium 2-ethylhexanoate (denoted as octoate) and samarium octoates (o-interlayer) and another from a mixed solution of cerium and samarium nitrates (n-interlayer). The LSCF-SDC electrodes with o-interlayer and n-interlayer exhibited very similar performances in both the anodic and cathodic reactions at 900 °C. When temperature was decreased to 800 °C, an increase in overpotentials was observed. However, the LSCF-SDC electrode with o-interlayer exhibited superior performance to that with n-interlayer. It was found that the entire surface of the YSZ electrolyte disk was well covered with a dense o-interlayer of uniform thickness. Such an interlayer enables uniform transport of oxide ions to and from the LSCF-SDC electrode, resulting in an enlarged effective reaction zone (ERZ). The I-E performance of the LSCF-SDC|o-interlayer|YSZ cell was found to be comparable to that of the identical electrode prepared on a dense SDC sintered electrolyte disk (as a reference). This observation supports our views regarding the essential role of a dense interlayer with uniform thickness in enhancing the performance of reversible solid oxide cells. [ABSTRACT FROM AUTHOR]

Abstract: Ln2Zr2O7 (Ln=Yb, Y, Gd, Eu, Sm, Nd, La) system changed from fluorite (F)-type to pyrochlore (P)-type phases when the ionic radius ratios, r(Ln3+)/r(Zr4+), were larger than 1.26. The oxide-ion conductivity showed sharp maximum at the vicinity of the phase boundary between the F- and P-type phases. The frequency dependence of dielectric constant () and dielectric loss factor () were successfully explained by the superimposition of Debye-type polarization due to dopant-vacancy associate and electrode–electrolyte interfacial polarization by the numerical calculation. The peak of dielectric loss tangent (tan δ) was ascribed to the dopant-vacancy associate. The εr (0) and dielectric constant of the associate (εr 0) showed also the maximum values at the vicinity of the phase boundary between the F- and P-type phases. [Copyright &y& Elsevier]

Abstract: Dielectric relaxations were investigated for the solid solution system Ce1−x Nd x O2−δ (0.0≦ x ≦0.5) having a fluorite-type structure, which is a typical oxide-ion conductor. The dielectric constants showed anomalously large values at low frequencies and high temperatures. Numerical analysis of frequency dependence of dielectric constant (ε r′) clarified that the anomalously large ε r′ originated from the superimposition of both Debye-type polarization and interfacial polarization between electrolyte and electrode. Two kinds of Debye-type relaxations observed were ascribed to defect associates, (NdCe′− V O¨)· and (NdCe′− V O¨−NdCe′) x . The Debye-type polarizations were also confirmed by analyzing the dielectric loss factor (ε r″). When the oxide-ion conductivity decreased in the heavy Nd-doped samples, both the Debye-type and the interfacial polarizations also decreased, suggesting that ordering of oxygen vacancy suppressed the electric field response of Debye-type polarization, resulting in the decrease of oxide-ion conductivity. [Copyright &y& Elsevier]

Abstract: The relationship between oxide-ion conductivity and ordering of oxide ion in the (Y1−x La x )2(Ce1−x Zr x )2O7 system having a pyrochlore-type composition was investigated. The crystal phase of the system with a variable cation radius ratio, but with a constant lattice parameter, changed from a rare-earth-C (C)-type phase to a pyrochlore (P)-type phase through a fluorite (F)-type phase with increase in the composition (x), depending on the cation radius ratio r(A3+)/r(B4+), which is a measure of ordering degree of oxygen vacancies. The oxide-ion conductivity increased once up to x =0.15, and then decreased with increasing x. This change of the electrical conductivity was understood on the basis of the ordering degree of oxide ion. The Rietveld analyses of X-ray and neutron diffraction patterns, and Raman spectroscopy supported the ordering effect of oxide ion on the conductivity. [Copyright &y& Elsevier]

The electrical conductivity of the LaY1−xInxO3 (x=0.0–0.7) system has been studied from the viewpoint of crystal chemistry. The high temperature form of LaYO3 (x=0.0) was ascertained to be the Sm2O3-type (B-type rare earth) structure, not perovskite-type one. The X-ray diffraction (XRD) experiments revealed that the samples with x=0.05 and 0.10 were the mixed phase of Sm2O3-type and perovskite-type structure, and changed to perovskite phase in the range of x≧0.20. From oxygen partial pressure dependence of the electrical conductivity, it was found that both the Sm2O3-type and the perovskite-type single phases showed hole conduction, but the mixed phase did oxide-ion one. The electrical conductivity of the LaY1−xInxO3 (x=0.0–0.7) system increased with increasing x, and showed the maximum value in the range of x=0.05–0.10, and then decreased with increasing x. The occurrence of oxide-ion conduction was discussed from the viewpoint of lattice distortion in the mixed phase. [Copyright &y& Elsevier]

Growth of finely dispersed nanocatalysts by exsolution of metal nanoparticles from perovskite oxides under reducing conditions at elevated temperature is a promising approach of producing highly active catalytic materials. An alternative method of exsolution using an applied potential has been recently shown to potentially accelerate the exsolution process of nanoparticles that can be achieved in minutes rather than the hours required in chemical reduction. In the present study, we investigate exsolution of nanoparticles from perovskite oxides of La 0.43 Ca 0.37 Ni 0.06 Ti 0.94 O 3-γ (LCTNi) and La 0.43 Ca 0.37 Ni 0.03 Fe 0.03 Ti 0.94 O 3-γ (LCTNi-Fe) under applied potentials in carbon dioxide atmosphere. The impedance spectra of single cells measured before and after electrochemical poling at varying voltages showed that the onset of exsolution process occurred at 2 V of potential reduction. An average particle size of the exsolved nanoparticles observed after testing using a scanning electron microscopy was about 30–100 nm. The cells with the reduced electrodes exhibited desirable electrochemical performances not only in pure carbon dioxide (current density of 0.37 A cm−2 for LCTNi and 0.48 A cm−2 for LCTNi-Fe at 1.5 V) but also in dry hydrogen (0.36 W cm−2 for LCTNi and 0.43 W cm−2 for LCTNi-Fe). [ABSTRACT FROM AUTHOR]

• The PtCoSn/Ta-SnO 2 catalyst exhibits remarkably improved ORR kinetics and specific ORR activity. • The incorporation of Sn favors O 2 adsorption and dissociation. • The PtCoSn/Ta-SnO 2 catalyst shows exceptional load cycle durability. For polymer electrolyte fuel cells (PEFCs), platinum-based catalysts for the air cathode supported on metal oxides such as SnO 2 exhibit highly promising durability. Yet, the activity for the oxygen reduction reaction (ORR) has still not been sufficiently high toward widespread application. Here, we report a new type of catalyst with significantly boosted ORR activity, based on PtCoSn alloy nanostructures formed on Ta-doped SnO 2 support (PtCoSn/Ta-SnO 2). The ORR activity of the PtCoSn/Ta-SnO 2 catalyst is evaluated in acidic media (0.1 M HClO 4) from 20 to 80 °C. The apparent rate constants (k app) for the ORR on PtCoSn/Ta-SnO 2 are found to be about 4.5 and 1.5 times greater than those of commercial Pt and Pt 3 Co alloy catalysts supported on carbon black (c-Pt/C and c-Pt 3 Co/C), respectively, and increase with temperature, in accordance with an Arrhenius-type relation from 20 to 60 °C. The enhanced ORR rates of the PtCoSn/Ta-SnO 2 catalyst can be correlated with an increase in the preexponential factor of the Arrhenius equation, together with a lowered activation energy. Experimental and density functional theory results reveal that the incorporation of Sn facilitates O 2 adsorption and dissociation, which is beneficial to overcome the kinetic limitation of ORR. Moreover, the durability of PtCoSn/Ta-SnO 2 examined by potential-step cycling between 0.6 and 1.0 V at 80 °C has been found to be much higher as compared with c-Pt/C and c-Pt 3 Co/C. [Display omitted] [ABSTRACT FROM AUTHOR]