Hydrogen Gas-Rechargeable Metal Hydride Electrode for Ni-MH Battery (II)

Abstract

The present study is a follow-up of a previous work on hydrogen gas-rechargeable metal hydride ͑MH͒ electrode for Ni-MH battery. The hydrogen pressure drop in a NiOOH/H 2 battery during hydrogen absorption and electrochemical discharge was monitored. It was seen that hydrogen was simultaneously absorbed by the MH pellet electrode during discharge at higher pressures, and that the pellet released some hydrogen from the bulk when discharged at lower pressures. Electrochemical impedance spectroscopic analysis showed that the charge transfer step at the MH anode was influenced by the magnitude of hydrogen pressure. The higher hydrogen pressure resulted in a smaller semicircle and therefore a smaller charge transfer impedance.

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

“…(17)) and that the O 2 reduction reaction occurs on MnO 2 because of its electrocatalytic function as a fuel cell cathode (from Eqs. (16) and (17)). In addition, the electrode also discharged for approximately 20 min (i.e.…”

“…(17)), and the recharged MnO 2 can function as a fuel cell cathode (from Eqs. (16) and (17)). Furthermore, the recharged MnO 2 can electrochemically discharge without oxygen being supplied even after the fuel cell reactions.…”

“…To construct this type of novel bi-functional FCB system, the electrode materials are required to possess the following characteristics: (i) the negative electrode materials should be reduced by hydrogen gas (gaseous charging) and be oxidized during electrochemical reactions and (ii) the positive electrode materials should be oxidized by oxygen gas (gaseous charging) and be able to be reduced electrochemically [8]. Metal hydrides (MHs) are well suited for the negative electrode of the FCB system because they adsorb gaseous hydrogen [7,[10][11][12][13][14][15][16] and have been used as active materials in NiMH secondary batteries [15][16][17][18][19][20][21] as well as in air-metal batteries [11,[22][23]. It has been reported that MH can be rapidly charged to more than 70% of its theoretical capacity within 10 min by pressurized (0.3 and 0.5 MPa) gaseous hydrogen and that the charged MH can be electrochemically discharged by the reactions shown below [7]:…”