ELECTROCHEMICAL IMPEDANCE SPECTRA STUDY OF THE HYDROGEN STORAGE ELECTRODE

The hydrogen storage electrode (MH) has been investigated by a.c. impe dance measurements. The electrode impedance has been measured by super imposing an a.c. voltage of 5 mV amplitude ranging between 10(4) and 1 0(-2) Hz. The impedance experiment result indicated that Cole-Cole plo t for the electrode consisted of two obviously comparable semicircles and a slope related to Warburg impedance, and the semicircle in the hi gh frequency region was very different from that in the low frequency region. The very small semicircle in the high frequency region was pro bably a typical double-layer capacitance; the large semicircle in the low frequency region which exhibited marked dependence on the hydrogen content was attributed to the electrochemical Heyrovsky reaction. The two semicircles were both affected by the electrode activation number s and the depth of discharge. The impedance experiment also indicated that the semicircle in the high frequency region was almost independen t of activation number, but that in the low frequency region was not. On increasing the depth of discharge, the two semicircles both reduced at first and increased later.