Rechargeable PEM Fuel-Cell Batteries Using Porous Carbon Modified with Carbonyl Groups as Anode Materials

Abstract

Rechargeable fuel-cell batteries (RFCBs) operate by hydrogen storage and release at the anode, while oxygen evolution and reduction reactions occur at the cathode. High-surface-area porous carbon was treated with HNO 3 to produce an anode material with carbonyl and phenol groups on the surface, thereby providing redox sites for hydrogen storage and release. The HNO 3 -activated carbon anodes were characterized with respect to use in a RFCB operated from room temperature to 75 • C with a voltage range of 0-2.0 V. The quantity of carbonyl groups and the corresponding reduced phenol groups increased with the O/C atomic ratio of the oxygenated carbon, by which the electrical capacity was increased to reach a maximum of 125 mAh g −1 at an O/C atomic ratio of 0.114. The optimal temperature and charge voltage for performance and cyclability were determined to be 50 • C and 1.25 V, respectively. The charge and discharge times remained at ca. 93% of the respective initial values after 300 cycles. The RFCB with the modified porous carbon anode provided energy densities of 2.5-13.8 Wh kg −1 and power densities of 46.4-296.3 W kg −1 (normalized according to the mass of the entire cell). Problems with energy supply and use are related not only to global warming, but also to environmental issues, and this has accelerated the development of highly efficient and environmentally-friendly power sources.1-3 In recent years, metal-air batteries have been the focus of significant interest in the field of advanced energy storage systems because they employ a lighter cathode that operates on abundant oxygen in the air.4,5 While these batteries offer the promise of very high energy densities, they only deliver current densities in the order of 1 mA cm −2 , 6 which are one or two orders of magnitude lower than the required level. Safety and cyclability concerns must also be addressed for practical applications. In contrast, hydrogen-air fuel cells draw far higher current densities than those for metal-air batteries, while achieving energy densities comparable to those for metal-air batteries. 7,8 Nevertheless, fuel must be continuously supplied from an external source; therefore, hydrogen production, storage, and distribution are required. To avoid the obstacles associated with these systems, rechargeable fuel cell systems, which operate with alternate electrolyzer and fuel cell modes, are considered an attractive and potentially viable power source.9-11 The key technology necessary for this application is hydrogen storage with high capacity and good cyclability. Currently, the standard hydrogen storage methods are cryo-adsorption on activated carbon, compressed gas tanks, and metal hydrides.12,13 However, hydrogen tanks require high pressures, while metal hydride systems release hydrogen at high temperatures, which would mean the fuel cell and the hydrogen storage systems would have to be separate.As an alternative approach, a new concept of a unitized rechargeable fuel cell has been proposed by integration of a fuel cell with a hydrog...

Microwave Synthesis of High Activity FeSe2/C Catalyst toward Oxygen Reduction Reaction

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

“…13 The resulting electrolyte had a density as high as 90 mg cm −2 . In the present study, a lighter electrolyte was obtained by employing a composite membrane composed of SIPO and sSEBS.…”

“…[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. The other was a composite membrane composed of 80 wt% SIPO and 20 wt% sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene (sSEBS) with various thicknesses between 37 and 133 μm.…”

“…[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…”

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

“…room temperature to 80 °C at ambient pressure). Quinones and partially oxygenated carbons are regarded as promising hydrogen‐storage media, owing to their excellent reversibility and good cyclability. The origin of hydrogen storage and release is attributed to the following equilibrium reaction between the two functional groups [Rection ]: …”