Atomic Layer Deposition and Annealing of Co3O4 for Electrocatalytic Oxygen Evolution

Abstract

In the fight against climate change, renewable energy must be employed to reduce fossil fuel dependence. However, intermittent renewable energy sources like wind and solar require grid energy storage to be feasible at a large scale. Hydrogen shows promise as an energy storage medium, and is also an important chemical feedstock. However, current production of hydrogen is carbon-intensive, and green hydrogen produced by water electrolysis is expensive due to a lack of highly effective, non-precious metal oxygen evolution (OER) electrocatalysts. Co3O4 is one of the most effective metal oxide OER electrocatalysts, but thin films of Co3O4 produced via atomic layer deposition (ALD) have never been explored for OER. Uniform thin films of Co3O4 were successfully produced via ALD using CoCp2 and O3 precursors, and the crystallinity and stoichiometry of these thin films were studied before and after annealing using X-ray photoelectron spectroscopy and X-ray diffraction. The catalytic decomposition of O3 by Co3O4 during ALD was mitigated by using a 200 °C deposition temperature and a 10 s long O3 pulse at 10 torr. 7 nm and 27 nm thick films showed no difference in surface stoichiometry after being deposited by ALD. Annealing under H2 reduced Co3O4 films to CoO, as did annealing under N2 at a high temperature. 27 nm Co3O4 films were found to be much more crystalline than 7 nm Co3O4 films before annealing, and 27 nm films showed improvements in crystallinity after annealing while 7 nm films did not.