Abstract
The effect of the synthesis route on the oxygen reduction reaction (ORR) activity of carbon-supported hafnium oxynitride (HfOxNy-C) catalysts in acid media was investigated. Four types of HfOxNy-C catalysts were synthesized by heating carbon-supported hafnium oxide (HfOx-C) prepared via three different impregnation methods and a polymerized complex method at 1023–1223 K for 24–50 h under NH3 gas. Field emission transmission electron microscope images, X-ray diffraction patterns, X-ray photoelectron spectra, cyclic voltammograms, and rotation disk electrode voltammograms were analyzed. Nanosized HfOxNy particles with a cubic Hf2ON2 phase were dispersed onto C powders by any of the four synthesis routes. However, the level and uniformity of the HfOxNy particle size and the crystallinity depended on the synthesis routes rather than the synthesis conditions. The ORR activity of the HfOxNy-C catalysts increased with the increasing crystallinity of the Hf2ON2 phase in the HfOxNy particles. Catalysts prepared via an impregnation method using hydrolysis of hafnium tetrachloride in the dispersion, consisting of nitric acid-refluxed C powders and water, showed (a) the most uniform and smallest HfOxNy particle sizes, in the order of a few nanometers, (b) the highest crystallinity, and (c) the highest ORR current and activity levels.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
