Kazuyo Kobayashi

Platinum-Doped CeO2 Thin Film Catalysts Prepared by Magnetron Sputtering

The interaction of Pt with CeO(2) layers was investigated by using photoelectron spectroscopy. The 30 nm thick Pt doped CeO(2) layers were deposited simultaneously by rf-magnetron sputtering on a Si(001) substrate, multiwall carbon nanotubes (CNTs) supported by a carbon diffusion layer of a polymer membrane fuel cell and on CNTs grown on the silicon wafer by the CVD technique. The synchrotron radiation X-ray photoelectron spectra showed the formation of cerium oxide with completely ionized Pt(2+,4+) species, and with the Pt(2+)/Pt(4+) ratio strongly dependent on the substrate. The TEM and XRD study showed the Pt(2+)/Pt(4+) ratio is dependent on the film structure.

High-temperature supercapacitor with a proton-conducting metal pyrophosphate electrolyte

Expanding the range of supercapacitor operation to temperatures above 100°C is important because this would enable capacitors to operate under the severe conditions required for next-generation energy storage devices. In this study, we address this challenge by the fabrication of a solid-state supercapacitor with a proton-conducting Sn0.95Al0.05H0.05P2O7 (SAPO)-polytetrafluoroethylene (PTFE) composite electrolyte and a highly condensed H3PO4 electrode ionomer. At a temperature of 200°C, the SAPO-PTFE electrolyte exhibits a high proton conductivity of 0.02 S cm−1 and a wide withstanding voltage range of ±2 V. The H3PO4 ionomer also has good wettability with micropore-rich activated carbon, which realizes a capacitance of 210 F g−1 at 200°C. The resulting supercapacitor exhibits an energy density of 32 Wh kg−1 at 3 A g−1 and stable cyclability after 7000 cycles from room temperature to 150°C.

Proton Conduction in Sn0.95Al0.05P2O7 – PBI – PTFE Composite Membrane

Proton-conducting composite membranes were fabricated by blending S n0.95 Al 0.05 P 2 O 7 having an excess of phosphates with polybenzimidazole (PBI) and polytetrafluoroethylene (PTFE). The addition of PBI to Sn 0.95 Al 0.05 P 2 O 7 -P x O 7 powder stabilized the conductivity of the composite, providing higher conductivities than those of stoichiometric Sn 0.05 Al 0.05 P 2 O 7 The addition of PTFE to Sn 0.95 Al 0.05 P 2 O 7 -P x O y -PBI powder reduced the conductivity but increased the tensile strength. The resulting composite membrane exhibited a conductivity of 0.04 S cm -1 at 200°C and a tensile strength of 2.30 MPa. Moreover, a fuel cell made with this composite membrane yielded high power densities exceeding 200 mW cm -2 above 100°C and good durability under unhumidified conditions.

An all-solid-state rechargeable aluminum–air battery with a hydroxide ion-conducting Sb(V)-doped SnP2O7 electrolyte

An anhydrous hydroxide ion conductor, Sn0.92Sb0.08P2O7, can function as an electrolyte for aluminum–air batteries, where aluminum is oxidized to an aluminate species during discharge, and the aluminate species is reduced to aluminum by charging the cell. This battery generated an open-circuit voltage of ca. 1.6 V with a discharge capacity of ca. 800 mA h g−1electrode.

Rechargeable Metal–Air Proton‐Exchange Membrane Batteries for Renewable Energy Storage

Abstract Rechargeable proton‐exchange membrane batteries that employ organic chemical hydrides as hydrogen‐storage media have the potential to serve as next‐generation power sources; however, significant challenges remain regarding the improvement of the reversible hydrogen‐storage capacity. Here, we address this challenge through the use of metal‐ion redox couples as energy carriers for battery operation. Carbon, with a suitable degree of crystallinity and surface oxygenation, was used as an effective anode material for the metal redox reactions. A Sn0.9In0.1P2O7‐based electrolyte membrane allowed no crossover of vanadium ions through the membrane. The V4+/V3+, V3+/V2+, and Sn4+/Sn2+ redox reactions took place at a more positive potential than that for hydrogen reduction, so that undesired hydrogen production could be avoided. The resulting electrical capacity reached 306 and 258 mAh g−1 for VOSO4 and SnSO4, respectively, and remained at 76 and 91 % of their respective initial values after 50 cycles.

Hydroxide ion conduction in molybdenum(VI)-doped tin pyrophosphate at intermediate temperatures

Research efforts focused on alkaline fuel cells have increased with the goal of commercialization. Anion exchange polymers are widely viewed as promising candidates for electrolyte membranes; however, the operating temperature of these polymers is limited to 80 °C or lower. Operation of a fuel cell at elevated temperatures provides the anode catalyst with a high tolerance towards CO and enhances the electrode reaction kinetics. We present a new type of inorganic hydroxide ion-conducting compound that has the potential to meet the demands for intermediate temperature applications. A series of Sn1−xAxP2O7 (AVI = Mo and W) compounds were synthesized, of which Sn0.85Mo0.15P2O7 exhibited the highest electrical conductivity over a wide temperature range (0.02 S cm−1@50 °C, 0.07 S cm−1@100 °C, 0.10 S cm−1@150 °C, and 0.123 S cm−1@200 and 250 °C). Such a high conductivity was also confirmed under conditions of fuel cell operation. The anion exchange capability of this compound was evaluated using spectroscopic and electrochemical analyses, the results of which indicated that hydroxide ions are incorporated into the compound by charge compensation for high valency cations and hydroxide ion conduction is predominant in the temperature range of 50–250 °C.

An intermediate-temperature alkaline fuel cell using an Sn0.92Sb0.08P2O7-based hydroxide-ion-conducting electrolyte and electrodes

Although various types of anion exchange membrane fuel cells have been developed, few alkaline fuel cells capable of operating at temperatures above 100 °C have been reported, due to low chemical and thermal stability of the polymer electrolytes. Sn0.92Sb0.08P2O7 is a hydroxide ion conductor that exhibits high conductivities ranging from 10−2 to 10−1 S cm−1 at elevated temperatures. This report describes the development of an intermediate-temperature alkaline fuel cell using an Sn0.92Sb0.08P2O7-based electrolyte and electrodes. First, a dense and flexible composite membrane, composed of Sn0.92Sb0.08P2O7 and polytetrafluoroethylene (PTFE), was synthesized and characterized. In the composite membrane, a homogeneous distribution of Sn0.92Sb0.08P2O7 particles was obtained at a thickness of 110 μm, yielding hydroxide ion conductivity of ∼10−2 S cm−1 in the temperature range between 75 and 200 °C. Next, the microstructure of the three-phase boundary in the electrode was established by incorporating Sn0.92Sb0.08P2O7 particles into the electrode. Consequently, polarization resistance was reduced dramatically compared to that of the unmodified electrode. Finally, fuel cell tests were conducted using the optimized electrolyte and electrode. The peak power density was 76 mW cm−2 at 75 °C, 94 mW cm−2 at 100 °C, 114 mW cm−2 at 125 °C, 130 mW cm−2 at 150 °C, 132 mW cm−2 at 175 °C, and 147 mW cm−2 at 200 °C. High durability of the present fuel cell was also confirmed at 200 °C.

Intermediate-temperature alkaline fuel cells with non-platinum electrodes

This report describes experimental results that demonstrate that less expensive Ru and Pd catalysts possess activity comparable to Pt when functioning as anode and cathode catalysts, respectively, at 200 °C, which is achieved by using a hydroxide-ion conductive Sn0.92Sb0.08P2O7 electrolyte membrane. The resultant H2/air fuel cell yielded increasing peak power densities with temperature: 60 mW cm−2 at 100 °C, 101 mW cm−2 at 150 °C, and 152 mW cm−2 at 200 °C. Note that the peak power density obtained for the Pt/C anode and cathode was 147 mW cm−2 at 200 °C. High durability of the present fuel cell was also confirmed at 200 °C.

Kinetically driven switching and memory phenomena at the interface between a proton-conductive electrolyte and a titanium electrode

Numerous studies have examined the switching properties of semi- or ion-conductors and isolators; however, most of these have focused on the ohmic resistance characteristics. Here, we report a new type of polarity-dependent switching phenomenon obtained for electrical devices with the configuration: metal working electrode│Si0.97Al0.03H0.03P2O7-polytetrafluoroethylene composite electrolyte│Pt/C counter electrode. The counter electrode is reversibly active for the water vapor oxidation and evolution reactions. The composite electrolyte exhibits high withstanding voltage capability in the bias voltage range of ±7 V. When titanium was employed as the working electrode, the anodic polarization resistance was approximately two orders of magnitude greater than the cathodic polarization resistance. The ohmic resistance of the device was almost unchanged, regardless of the bias voltage polarity. Moreover, kinetically induced high-resistance/low-resistance states could be cyclically switched through positive/negative bias voltage pulses, and these states were also confirmed to be memorized at open circuit.