Hydrogen Bubble Templating of Fractal Ni Catalysts for Water Oxidation in Alkaline Media

Dynamic hydrogen bubble templating of Ni (NiDHBT) electrodes was used to prepare highly porous films with enhanced properties toward the oxygen evolution reaction (OER). Upon varying the electrodeposition conditions, Ni films with a macroporous primary structure and highly porous cauliflowerlike secondary structure were formed. These films are able to develop an extended electrochemically active surface area, up to 270-fold increase compared to a Ni plate. They exhibit stable overpotential (η250 = 540 mV) at j = 250 mA cmgeometric–2 in 1 M KOH electrolyte, which is 300 mV less positive than at the Ni plate. Fe incorporation onto these NiDHBT structures can further lower OER overpotentials to η250 = 310 mV. NiDHBT films are remarkably stable over prolonged polarization and are characterized by a low Tafel slope (29 mV/decade) that extends up to j = 100 mA cmgeometric–2, attributed to both superaerophobic characteristics with a contact angle of ca. 160° between the surface and an air bubble and superhydrophilic characteristics with less than 25° between the surface and a water droplet.