Evaluation and Enhancement of the Oxygen Reduction Reaction Activity on Hafnium Oxide Nanoparticles Assisted by L(+)-lysine

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• 作者：Mitsuharu Chisaka ; ^{chisaka@hirosaki-u.ac.jp" class="auth_mail" title="E-mail the corresponding author} ; Noriaki Itagaki
• 关键词：hafnia ; carbothermal reduction ; catalyst ; cathode ; polymer electrolyte fuel cell
• 刊名：Electrochimica Acta
• 出版年：2016
• 出版时间：20 May 2016
• 年：2016
• 卷：201
• 期：Complete
• 页码：279-285
• 全文大小：1793 K

文摘

Evaluation of the oxygen reduction reaction (ORR) on oxide compounds is difficult owing to the insulating nature of oxides. In this study, various amounts of L(+)-lysine were added to the precursor dispersion for the hydrothermal synthesis of hafnium oxide nanoparticles on reduced graphene oxide sheets (HfO_x–rGO) to coat the HfO_x catalysts with layers of carbon, thereby increasing the conductivity and number of active sites. When the mass ratio of L(+)-lysine to GO, R, was above 26, carbon layers were formed and the amount monotonically increased with increasing R, as noted by cyclic voltammogrametry. X-ray photoelectron spectroscopy and rotating disk electrode analyses revealed that pyrolysis produced ORR-active oxygen defects, whose formation was proposed to involve carbothermal reduction. When 53 ≤ R ≤ 210, HfO_x–rGO contained a similar amount of oxygen defects and ORR activity, as represented by an onset potential of 0.9 V versus the reversible hydrogen electrode in 0.1 mol dm⁻³ H₂SO₄. However, the number of active sites depended on R due to the amount of L(+)-lysine-derived carbon layers that increased both the number of active sites and resistivity towards oxygen diffusion.