Design of Earth-abundant and Robust Water Splitting Electrocatalysts with Autocatalytic Feedback Mechanisms

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K15388
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 36020:Energy-related chemistry
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: Li ailong 国立研究開発法人理化学研究所, 環境資源科学研究センター, 特別研究員 (30854682)
• Project Period (FY): 2020-04-01 – 2022-03-31
• Keywords: Electrocatalysts / Redox / Hydrogen

Outline of Final Research Achievements

I discovered how the bottom-up assembly of Mn-redox reactions can realize catalytic systems which are resistant to environmental fluctuations. Mn has a wide range of oxidation states ranging from 2+ to 7+, including incrementally change the oxidation state, as well as charge comproportionation and disproportionation reactions, which connect discrete redox states of Mn species. The main catalytic cycle of water oxidation on Mn oxides is the sequential redox cycle of 2+, 3+, and 4+, which proceeds when a positive potential is applied. However, when the potential is too positive, dissolution of Mn oxide in the form of Mn7+ occurs. The Guyard reaction is a charge comproportionation reaction promoted by phosphoric acid, which recombines Mn2+ and Mn7+ to form Mn3+. The newly formed Mn species with valence states below 7+ might be re-engaged in the OER redox cycles, and thus contribute to the stability of the catalyst.

Free Research Field

Chemistry

Academic Significance and Societal Importance of the Research Achievements

開発したシステムは、太陽電池や風力発電による再生可能な電力を水素、アモルファス、炭化水素などの化学エネルギーに変換するための水電解槽に不可欠な水の酸化を行うことができます。水酸化の酸化環境は最先端のレアメタル触媒をも腐食させ、太陽光や風力エネルギーの断続性により変動する運転電圧のわずかな変化が腐食の動態を著しく悪化させるため、水酸化の酸化還元力を高めることが重要です。しかし、たった1つの酸化還元反応の導入で触媒の寿命が大きく変化することから、触媒研究におけるネットワーク設計の重要性が明らかになりました。