Intermediate temperature proton‐conducting membrane electrolytes for fuel cells

Yamamoto

et al. 2015

J. Electrochem. Soc.

Rechargeable fuel-cell batteries (RFCBs) that employ organic chemical hydrides as hydrogen storage media have potential as nextgeneration power sources; however, the reversible storage and release of hydrogen remains a significant challenge. In particular, the hydrogenation of organic compounds during cell charge is difficult to achieve with 100% conversion. However, this report demonstrates that quinones, especially anthraquinone (AQ), can function as a hydrogen carrier for RFCBs, where AQ is hydrogenated to anthrahydroquinone (AH 2 Q) during charge and AH 2 Q is dehydrogenated to AQ during discharge. This redox reaction occurred at a more positive potential than that for hydrogen reduction, so that undesired hydrogen production can be avoided by adjusting the charge voltage to 1 V. The resulting RFCB maintained 100% electrical capacity at room temperature, 91% at 50 • C, and 63% at 75 • C of the respective initial performance with coulombic efficiencies greater than 90% after 300 cycles. Moreover, the RFCB functioned as a secondary battery with energy densities of 0.8-3.4 Wh kg −1 , power densities of 9.5-258.9 W kg −1 , and as a fuel cell with power densities of 0.001-0.26 W cm −3 . Based on the performance and degradation data, the limitations of this RFCB and directions for future research are discussed. A system or device capable of operating an electrochemical cell alternately in electrolyzer and fuel cell modes is called a rechargeable or regenerative fuel cell (RFC).1,2 Applications for RFCs include large-scale renewable energy storage and middle-scale emergency or auxiliary power sources, 3 where hydrogen is usually stored outside the fuel cell to obtain substantially high energy. In contrast, RFCs can be used as energy storage systems for portable electronic devices by integration of the fuel cell with the hydrogen storage medium; however, such electrochemical cells should be classified as batteries rather than fuel cells, because the fuel is not supplied from an external source, but is an integral part of the device. 4 Thus, we have designated this type of cell as a rechargeable fuel-cell battery (RFCB).Hydrogen storage with high capacity, excellent reversibility, and good cycle stability is a key technology for both RFC and RFCB. Typical hydrogen storage methods (in addition to liquefaction or compression of hydrogen) include the physical and chemical adsorption of hydrogen atoms or molecules into materials such as activated carbon and metal hydrides. Activated carbon often requires low temperatures (>−200• C) and/or high pressures (<10 MPa) to achieve high hydrogen adsorption capacity.5 Metal hydrides typically release hydrogen at high temperatures (>150• C). 6 Thus, it is difficult to use these materials as reversible hydrogen carriers for RFCBs because a series of hydrogen production, storage, supply, and utilization processes cannot be conducted under the RFCB operating conditions (e.g., room temperature to 80• C at ambient pressure). Organic chemical hydrides, such as benzene/cyclohexane, tolue...

Section: Methodsmentioning

confidence: 99%

Rechargeable PEM Fuel-Cell Batteries Using Quinones as Hydrogen Carriers

Nagao

Yamamoto

et al. 2015

J. Electrochem. Soc.

“…16 An alternative approach is to operate direct woody biomass fuel cells in the temperature range of 100250°C; 17 operating fuel cells at such temperatures results in relatively high energy conversion efficiencies to electricity and heat. 18 A fuel cell that consists of a proton-conducting Sn 0.9 In 0.1 P 2 O 7 -based electrolyte and a catalytically active Pt/C anode produced open-circuit voltages (OCVs) around 700 mV and peak power densities of 1432 mW cm…”

Section: Introductionmentioning

confidence: 99%

High Performance Anode for Direct Cellulosic Biomass Fuel Cells Operating at Intermediate Temperatures

Hibino

Bulletin of the Chemical Society of Japan

et al. 2017

Cellulosic biomass resources have considerable potential as a renewable energy source that can be used for the cogeneration of electricity and heat. The utilization of these resources generally requires three major systematic processes: gasification, gas processing, and gas utilization. If a power generator could operate using wood resources directly as fuels, then this system could be significantly simplified, thereby reducing initial equipment cost and enhancing application flexibility. An intermediate-temperature fuel cell could possibly realize such an operation; however, the fuel-cell characteristics, especially the catalytic activity of the Pt/C anode, are not sufficient at present. In this study, we attempted to improve the anode activity by alloying Pt with other metals, followed by optimization of the alloy in terms of its atomic ratio and content. The resulting PtFe/C anode yielded higher power densities (3742 mW cm ¹2 ) and energy densities (125169 Wh kg ¹1) at 250°C for fuels composed of cypress, tissue paper, and cotton, compared to those obtained using the Pt/C anode, despite its smaller Pt loading.

“…[20][21][22] Two electrolyte membranes were prepared according to previously reported procedures. 13,23 One was a composite membrane consisting of 96.2 wt% SIPO and 3.8 wt% polytetrafluoroethylene (PTFE) with a thickness of approximately 250 μm.…”

Section: Methodsmentioning

confidence: 99%

Design of a Rechargeable Fuel-Cell Battery with Enhanced Performance and Cyclability

Hibino

Nagao

et al. 2016

J. Electrochem. Soc.

Electrochemical devices integrating a fuel cell with a hydrogen storage medium are able to function as secondary batteries. Batteries incorporating a partially oxygenated carbon anode with a RuO 2 /C cathode exhibit excellent reversibility, but their performance is not yet sufficient for secondary battery applications. This is due to excessive oxygenation of the anode, degradation of the cathode and the excess weight of the electrolyte membrane. In the present work, we addressed these challenges through various improvements in the design of a rechargeable proton-exchange membrane battery. These included coating the surface of a significantly oxygenated carbon anode (O/C atomic ratio 0.131) with carbon black nanoparticles, nanocrystallization of a carbon-free RuO 2 cathode (avg. crystallite size 1.1 nm) and the synthesis of an inorganic-organic composite electrolyte membrane. As a result of these optimizations, coulombic efficiencies of over 95% were achieved during charge/discharge over the voltage range of 0.0-1.5 V at 75 • C. The resulting device exhibited an initial capacity of 330 mAh g −1 and was stable over 300 cycles, with maximum energy and power densities of Hydrogen is a promising medium for the storage and supply of electricity through water-electrolysis/fuel-cell operation.1,2 The primary application of hydrogen in this context would be to store surplus power when the quantity of electricity produced by natural energy sources exceeds that required by a consumer.3-5 Rechargeable fuel cells capable of operating alternately in electrolyzer and fuel cell modes are recognized as the optimum systems because they are smaller and more compact than conventional systems based on isolated water electrolyzer and fuel cell units.6-8 The key technology necessary for such devices is hydrogen storage, which is currently accomplished via liquefaction and compression of the gas or by the physical or chemical adsorption of hydrogen atoms or molecules in/on materials such as metal or organic chemical hydrides.9,10 However, an energy input is required for these processes that in turn increases the overall cost. Furthermore, the hydrogen tanks and lines employed in such systems negatively impact their volumetric energy density.To mitigate these problems, rechargeable fuel-cell batteries (RFCBs) containing a hydrogen storage medium have been proposed. [11][12][13] During the operation of such batteries, hydrogen production, storage, supply and utilization processes must be conducted at the anode under the standard operational conditions of the cell, such as between room temperature and 80• C and at ambient pressure. In this context, oxygen-functionalized microporous carbons (MPCs) are promising hydrogen storage media, due to their excellent reversibility. 13 The redox pair between carbonyl (C=O) and phenol (C-OH) groups is one of the most important hydrogen carrier sites in such carbon anodes. The origin of this redox reaction is ascribed to the following equilibrium reaction between the two functional groups.This reaction...