Pulsed laser deposition of nickel oxide films with improved optical properties to functionalize solar light absorbing photoanodes and very low overpotential for water oxidation catalysis

Nickel oxide is a cheap and efficient water oxidation catalyst (WOC). However, its application as anodic cocatalyst in photoelectrochemical cells (PECs) is limited by poor optical properties: it becomes black at positive biasing. Here a pulsed laser deposition (PLD) method is used to produce amorphous nickel oxide thin films with optical and catalytic properties tailored for PECs. The procedure, based on the laser ablation of pure nickel in oxygen at relatively high pressure, allows obtaining a porous or compact layer by simply varying the substrate temperature. The film transmittance is higher than 90% in the visible range for a porous coating. The improved optical properties can solve the issue of parasitic light absorption when Ni oxides are used to functionalize photoanodes. A thin, porous coating of Ni oxides operated as a WOC also shows electrode metrics on-par with the best results in literature, with an overpotential of 355 mV at 1 mA cm−2 and a 62 mV/decade Tafel slope. These results thus open the way for the use of Ni oxides as WOC for photoanodes. An in-depth study of the interplay between the morphological, optical and catalytic features of Ni oxides highlights the versatility of PLD in tuning materials properties.