10.1021/acsami.8b19064.s001 Hyung Jong Choi Hyung Jong Choi Gwon Deok Han Gwon Deok Han Kiho Bae Kiho Bae Joon Hyung Shim Joon Hyung Shim Highly Active Oxygen Evolution on Carbon Fiber Paper Coated with Atomic-Layer-Deposited Cobalt Oxide American Chemical Society 2019 cobalt uniform thickness oxide coating decelerates carbon fiber paper Active Oxygen Evolution optimized ALD-coated carbon fiber paper atomic-layer-deposited CoO x electrochemical water splitting ALD-CoO x film CoO x surface CoO x layers Atomic-Layer-Deposited Cobalt Oxide Carbon Fiber Paper Coated oxygen evolution performance oxygen evolution 2019-02-25 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Highly_Active_Oxygen_Evolution_on_Carbon_Fiber_Paper_Coated_with_Atomic-Layer-Deposited_Cobalt_Oxide/7811531 In this work, we evaluated the oxygen evolution performance of cobalt oxide (CoO<sub><i>x</i></sub>)-coated carbon fiber paper in electrochemical water splitting. For a uniform coating of CoO<sub><i>x</i></sub> layers along the carbon fiber paper, the atomic layer deposition (ALD) technique was applied. We achieved a uniform and conformal coating of atomic-layer-deposited CoO<sub><i>x</i></sub> (ALD-CoO<sub><i>x</i></sub>) on the carbon fiber paper. The overpotential for oxygen evolution measured for the optimized ALD-coated carbon fiber paper was as low as 343 mV at 10 mA cm<sup>–2</sup>, which is competitive with the activity of state-of-the-art CoO<sub><i>x</i></sub> prepared on electrodes with large surface areas. Oxygen evolution is not enhanced after a critical thickness, about 28 nm in our study, is reached. The optimal thickness of the ALD-CoO<sub><i>x</i></sub> film is dependent on two competing effects: the high oxidation state of cobalt ions in thicker CoO<sub><i>x</i></sub> helps the oxygen evolution, whereas the introduction of a thick oxide coating decelerates the rate of charge transfer at the surface.