S. Rodrigues et al., Kinetics of hydrogen evolution reaction on Zr0.5Ti0.5V0.6Cr0.2Ni1.2 alloy in KOH electrolyte, B MATER SCI, 23(5), 2000, pp. 383-391
A hydrogen-storage alloy of the composition Zr0.5Ti0.5V0.6Cr0.2Ni1.2 has be
en investigated for corrosion resistance and hydrogen-evolution reaction (H
ER) in KOH electrolyte of varying concentrations. Activation of the electro
de by absorption of hydrogen takes place after prolonged cathodic polarizat
ion in the potential range of HER. Prior to activation, the open-circuit po
tential is about -0.4 V vs Hg/HgO, OH-, at which the alloy electrode tends
to undergo corrosion with oxygen-reduction reaction (ORR) as the conjugate
reaction, The corrosion-current density measured from Tafel polarization of
ORR is found to be independent of KOH concentration and has an average val
ue of about 30 mu A cm(-2). Subsequent to activation, the open circuit pote
ntial of the electrode is shifted to about -0.93 V vs Hg/HgO, OH-, which is
equal to the reversible potential of HER. The exchange current density val
ues measured from Tafel polarization of HER are marginally higher in relati
on to the values obtained before the electrode is activated. Alternating-cu
rrent impedance spectra in the Nyquist form contain two overlapped semicirc
les. The high-frequency semicircle is attributed to the electrode geometry,
while the low-frequency semicircle is due to the charge-transfer reaction
and double-layer capacitance. The impedance data are analyzed by a non-line
ar least square curve fitting technique and impedance parameters are evalua
ted.