Stability of Ni and Ti in Hydrogen Evolution in the Presence of 1-Butyl-3-methylimidazolium Tetrafluoroborate

Abstract

Ni and Ti electrodes were tested for hydrogen evolution reaction in water electrolysis using electrolytes containing 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM center dot BF4) ionic liquid. Reductive currents of Ni and Ti at low potentials in BMIM center dot BF4 (12 wt%) and KOH (6 wt%) aqueous electrolytes originate from hydrogen evolution with considering the electrolyte composition and the electrochemical window of the ionic liquid, which was confirmed by Pt electrode. While the Ti electrode shows a similar hydrogen evolution activity to the Ni electrode in the BMIM center dot BF4 aqueous electrolyte, its activity is inferior to the Ni electrode in the KOH aqueous electrolyte without the ionic liquid. The existence of the ionic liquid in aqueous electrolyte appears to change the hydrogen evolution kinetics at both Ni and Ti electrodes as seen in Tafel analysis. This is partly because BMIM center dot BF4 is susceptible to hydrolytic decomposition of BMIM+ owing to the hydrogen at C2 position and of BF4- incurring HF formation. A measurement of electrode weight loss after a potentiostatic experiment and an accompanying SEM analysis indicate the surface roughening of the electrodes and the pore formation on the surface of Ti in the presence of BMIM center dot BF4. This change in surface morphology can be attributed to HF that could be formed from the hydrolytic instability of BMIM center dot BF4.