The oxygen evolution reaction (OER, 2H₂O→O₂ + 4H⁺ + 4e^-) is one of the important key of the energy devices, especially for the water electrolysis cells for hydrogen production. Since the OER proceeds via a multistep process and, thus the reaction has a large overpotential, the precious metal oxides such as IrO₂ were used for OER electrocatalysts. However, the such precious metal oxides are not appropriate for large-scale applications considering their high cost and low reserves. Alkaline water electrolysis is one of the easiest methods for hydrogen production and it has a simple configuration using low-cost materials. LiNiO₂ have exhibited highly potential toward OER due to its high conductivity among 3d transition metal oxides, and stability in alkaline condition.

LiNiO₂ is a layered structure consisting of NiO₂ slabs made of edge-sharing NiO₆ octahedrons and lithium ions inserted in the slabs at the octahedral sites. In this layered LiNiO₂ material, Ni³⁺ ions are in the low-spin configuration, and they are thought to be correlated with high OER activity. Although the layered structure of LiNiO₂ can stabilize significant amounts of Ni³⁺ species, the OER activity of LiNiO₂ is still lower than expected. Although many papers have reported the performance of LiNiO₂-corted anode, the morphology and surface area as well as synthesis method could affect the OER and the intrinsic activity of LiNiO₂ is not well investigated. In this study, we prepared Li_1-xNi_1+xO₂ thin films by pulsed laser deposition and investigated the electrochemical performance for OER activity of Li_1-xNi_1+xO₂.

LiNiO₂ thin film was successfully prepared by pulsed laser deposition (PLD). A Nd:YAG laser operating at a wavelength of 532 nm was focused on a sintered LiNiO₂ target. We used a chamber which can be evacuated to a base pressure of 5.0 x 10^-4 Pa by means of a turbo-molecular pump. When depositing LiNiO₂ thin film, the total pressure of O₂ was fixed to 10 Pa. A Ni-corted Si(100) substrate was used for film deposition. The substrate temperature was fixed to 200 ^oC. The target (f10) was produced by sintering Li₂O and NiO₂ powder at 1000 ^oC for 8.5 h in air. Structural analysis of LiNiO₂ was carried out by XRD. The electrochemical measurements were conducted in an aqueous 7M KOH solution using a potentiostat (Hokuto Denko HSV-110) connected to as a working electrode an RHE reference electrode, and Ni wire as a counter electrode. The solution was purged with N₂ gas for 30 min before the measurement. Cyclic voltammetry (CV) were obtained between 0.2 V and 1.6 V vs. RHE at 50 mV/s. The surface morphology was analyzed by AFM. The doping level of Li⁺ and OER activity as well as the state of Ni were mainly discussed in this paper.