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Abstract This paper describes the development of mixed B-site pyrochlore Y₂MnRuO₇electrocatalyst for oxygen evolution reaction (OER) in acidic media, a challenge for the development of low-temperature electrolyzer for green hydrogen production. Recently, several theories have been developed to understand the reaction mechanism for OER, though there is an  uncertainty in most of the cases, due to the complex surface structures. Several key factors such as lattice oxygen, defect, electronic structure, oxidation state, hydroxyl group and conductivity were identified and shown to be important to the OER activity. The contribution of each factor to the performance however is often not well understood, limiting their impact in guiding the design of OER electrocatalysts. In this work, we showed mixed B-site pyrochlore Y₂MnRuO₇catalyst exhibits 14 times higher turnover frequency (TOF) than RuO₂while maintaining a low overpotential of ~ 300 mV for the entire testing period of 24 h in acidic electrolyte. X-ray photoelectron spectroscopy (XPS) analysis reveals that this B-site mixed pyrochlore Y₂MnRuO₇has a higher oxidation state of Ru than those of Y₂Ru₂O₇, which could be crucial for improving OER performance as the broadened and lowered Ru 4d band resulted from the B-site substitution by Mn is beneficial to the OER kinetics.