HEXACYANOFERRATE LAYERS AS ELECTRODES FOR SECONDARY CELLS

The zeolite-like hexacyanoferrates, which intercalate cations such as K** plus and NH//4** plus , have been investigated recently with regard to their application to electrochromic displays, electrocatalysts and ion-selective electrodes. Their suitability for use as electrodes in secondary cells, however, has not been described so far. This preliminary report shows that thin layers of hexacyanoferrates of iron and copper are promising electrodes for reversible charging in secondary cells. As with the individual FeHCF and CuHCF electrodes, the shape of the charge-discharge curves of the cell and the current efficiency, which is nearly 100%, do not change during cycling. This points to the highly reversible character of cell operation. On the other hand, the coulombic capacity decreases over 766 cycles by about 70%. Despite this CuHCF corrosion and the low theoretical energy density and charge capacity of hexacyanoferrate layers the high reversibility of such systems is attractive.