IMPEDANCE STUDIES OF POROUS LANTHANUM-PHOSPHATE-BONDED NICKEL ELECTRODES IN CONCENTRATED SODIUM-HYDROXIDE SOLUTION

The hydrogen evolution reaction (HER) was investigated on a lanthanum- phosphate-bonded nickel (LPBN) powder electrode in 30 wt.% NaOH at 70- degrees-C using ac impedance and steady-state polarization techniques. Circuits containing one or two constant-phase elements (CPEs) in para llel with a resistance and corresponding to fractal and porous electro de models were tested in order to interpret the ac impedance data. The experimental impedance spectra were well described by the porous elec trode model and the circuit containing two CPEs. The results obtained from the ac impedance and steady-state measurements allowed the mechan ism and kinetics of the HER to be evaluated. Comparison of these param eters with those obtained on the polycrystalline nickel electrode in 1 M alkaline solution at 25-degrees-C indicates that an increase in act ivity is principally due to an increase in the real surface area.