Materials Science and Chemistry

Biography

Biography: Akira Yamaguchi

Abstract

To overcome energy and environmental issues we are facing, fuel production from water and/or CO₂ is highly demanding. Making fuels through both H⁺ and CO₂ requires electrons, and the most abundant electron source in the world is water, like natural photosynthesis achieved by oxygen evolution reaction (OER: 2H₂O → O₂ + 4H⁺ + 4e^-). Inspired by the oxygen evolution reaction (OER) center in natural photosynthesis, which is composed of CaMn₄O₅ cluster, numerous numbers of manganese oxide-based catalysts have been developed. However, their activity largely decreased under neutral pH. This work introduces the design strategy to enhance the OER activity of MnO₂ electrocatalysts under neutral pH in terms of the redox chemistry of active Mn species. The key chemical species is Mn³⁺, which works as the intermediate of OER on MnO₂ but unstable under neutral pH. To stabilize Mn³⁺, induction of concerted proton-electron transfer (CPET) and regulation of facet orientation were attempted. Regarding the CPET induction, introduction of pyridine into the electrolyte, which works as a CPET inducer, altered the reaction path and resulted in the activity enhancement. As to the facet orientation regulation, (101)-oriented MnO₂ was synthesized based on the article which reports that Mn³⁺ is stabilized on (101) facet of rutile MnO₂. The electrochemical OER examination revealed that (101)-oriented sample exhibited higher activity than (110)-oriented ones. The results indicate that those two approaches are efficient strategy to enhance the electrochemical OER activity of MnO₂ under neutral pH. Further studies concerning the corporative effect of CPET and facet orientation have been under investigation.