Ni Inverse Opals for Water Electrolysis in an Alkaline Electrolyte

A vertical electrophoretic deposition technique was employed to prepare polystyrene (PS) colloidal crystals with negligible crystallographic defects. The colloidal crystals were plated with Ni, followed by selective removal of PS microspheres to fabricate inverse opals. With adjustments in relevant processing parameters, we were able to obtain inverse opals in multiple layers with excellent surface uniformities. The inverse opals were used as the electrode material for water electrolysis. Results from current-potential polarizations in 1 M KOH aqueous solution indicated that the catalytic abilities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) increased with the layers of inverse opals. Estimation of the effective current densities determined that the entire area of the inverse opals was available for electrochemical reactions. In galvanostatic measurements for both OER and HER, the inverse opals demonstrated stable voltage profiles without notable degradations for 120 h. Compared with a planar Ni plate, the inverse opals exhibited a significantly reduced overpotential for the water electrolysis.