Power generation/energy storage by a fuel cell/battery system: Regeneration of the MnO2 positive electrode with gaseous oxygen

Chemical Charging on a MnO2 Electrode of a Fuel Cell/Battery System in a Highly O2-Dissolved Electrolyte

“…To explain these results, the reaction mechanism for the reaction between MnOOH and the oxygen dissolved in the electrolyte is shown in Fig. 5 [10,[20][21][22]. The supplied oxygen gas is dissolved in the electrolyte and the dissolved oxygen diffuses and adsorbs onto the surface of the active material.…”

“…Eq. (10) indicates that the reaction between dissolved oxygen and the EMD electrode is also influenced by the O 2 partial pressure. In the low O 2 partial pressure region, the oxygen concentration on the surface of the electrode increases almost proportionally with O 2 partial pressure.…”

“…Energy storage systems should thus have high energy density as well as instantaneous high power so that they can be operated within several minutes. Taking this fact into account, novel electrochemical systems with a dual function of power generation and energy storage, referred to as fuel cell/battery (FCB) systems, have been suggested [6][7][8][9][10][11]. In FCB systems, the active materials of the negative and positive electrodes can store hydrogen and oxygen gases, respectively, by chemical reactions and this leads to an electrochemical charging process.…”

“…Thus, FCB systems are expected to be preferred candidates for the applications demanding high-energy and high-power-density energy storage such as power tools and electric vehicles. Metal hydride (MH) and manganese dioxide (MnO 2 ) have been found to be suitable materials for the negative and positive electrodes of FCB systems, respectively [7,10,11]. MH can be quickly charged within 10 min by externally supplied hydrogen gas at 0.5 MPa [7].…”

“…MH can be quickly charged within 10 min by externally supplied hydrogen gas at 0.5 MPa [7]. The oxidation reaction between MnOOH and oxygen gas occurs slowly and 13% of the theoretical capacity can be recharged in an hour at 0.2 MPa [10]. Electrodes with a high surface area have been fabricated by the electrodeposition of materials on carbon fibers to investigate oxygen gas charging performance [11].…”