Creating Highly Active Atomic Layer Deposited NiO Electrocatalysts for the Oxygen Evolution Reaction

Atomic layer deposition (ALD) provides a promising route for depositing uniform thin coatings of electrocatalysts useful in many technologies, including the splitting of water. For materials such as NiO (x) that readily form hydrous oxides, however, the smooth, compact films deposited by ALD may result in higher overpotentials due to low catalyst surface area compared to other deposition methods. Here, the use of ALD-NiO thin films as oxygen evolution reaction (OER) electrocatalysts is explored. Thin films of crystalline ALD-NiO are deposited and OER activity is tested using cyclic voltammetry (CV). Fe incorporated from the electrolyte can increase the activity of NiO, and it is shown that the turnover frequency (TOF) increases tenfold by going from an Fe-poor to Fe-rich KOH electrolyte. Applying a potential exfoliates the NiO, increasing the number of electrochemically accessible Ni sites. Interestingly, by X-ray photoelectron spectroscopy (XPS) and CV, it is found that an Fe-rich electrolyte reduces the amount of restructuring and oxidation is found. It is shown that a high surface area, high TOF catalyst may be created by using a two-step process in which the sample is sequentially conditioned in Fe-poor then Fe-rich KOH. This work highlights the importance of pretreatment on catalytic activity for compact NiO films deposited by ALD.