Oxygen Evolution Reaction Performance Changes with Varying Crystallinity and Thickness of Atomic Layer Deposited RuO2 Film

Abstract

As the world's population grows and the energy consumption has increased, the use of fossil fuels is gradually increasing. The carbon dioxide emitted from burning fossil fuels is a major cause of greenhouse effect. Therefore, hydrogen is widely recommended as an energy source to alternate fossil fuels due to its high energy per mass, no production of pollutant. Among several ways to obtain hydrogen, electrolysis of water is considered the most promising method. However, the slow-rate determining step of the oxygen evolution reaction (OER) compared to hydrogen evolution reaction (HER) is a main reason for interrupting wide use of electrolysis of water in the industry. So, there have been various research for enhancing the effectiveness of water electrolysis.The development of OER electrocatalysts is needed for promote the efficiency of OER process, noble metals-based materials has been researched due to its superior activity. Among noble metals, RuO2 has been researched as promising catalyst for oxygen evolution, and the efficiency of the catalyst varies on the preparation technique (e.g., sputtering, hydrothermal methods and sol-gel). Therefore, there have been diverse studies to enhance the RuO2 electrocatalytic effectiveness of oxygen evolution via crystallinity control, increase of electrochemically active surface area by adjusting synthesizing method of RuO2 film.Atomic Layer Deposition (ALD) has strengths of large-area uniformity, excellent conformality, and being able to control the thickness of the film at the atomic scale. ALD is suitable technique to deposit catalysts materials conformably on 3D nano-structured complex materials, so the catalytic activity in the OER can be improved by increasing the surface-to-volume ratio. Therefore, ALD is assumed as a suitable synthesizing method for electrocatalyst. Besides, ALD allows low mass loading of catalyst material which is most needed factor in the industrial area. However, there have no enough research of ALD RuO2 for OER analyzing condition (crystallinity, thickness) for obtaining enhanced OER performance.In this report, RuO2 film was prepared based on ALD on Carbon Fiber Paper (CFP) at different deposition temperature and it showed different crystallinity, one was amorphous, the other one was crystalline. The crystalline one showed better OER performance due to its enlarged active sites of OER. We analyzed their growth characteristics and material properties by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), XRD spectrometer (XRD). And dependence of film thickness of ALD RuO2 films was also studied. Electrocatalytic properties of ALD RuO2 on CFP was measured in three-electrode. It showed low overpotential and Tafel slope, which shows electrocatalytic performances. Figure 1