Kinetics of hydrogen evolution reaction on Zr0.5Ti0.5V0.6Cr0.2Ni1.2 alloy in KOH electrolyte

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.