Lv Haoyuan, Zhang Xue-Peng, Guo Kai, Han Jinxiu, Guo Hongbo, Lei Haitao, Li Xialiang, Zhang Wei, Apfel Ulf-Peter, Cao Rui
Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, 710119, Xi'an, China.
Ruhr-Universität Bochum, Fakultät für Chemie und Biochemie, Anorganische Chemie I, Universitätsstrasse 150, 44801, Bochum, Germany.
Angew Chem Int Ed Engl. 2023 Sep 18;62(38):e202305938. doi: 10.1002/anie.202305938. Epub 2023 Aug 16.
The nucleophilic attack of water or hydroxide on metal-oxo units forms an O-O bond in the oxygen evolution reaction (OER). Coordination tuning to improve this attack is intriguing but has been rarely realized. We herein report on improved OER catalysis by metal porphyrin 1-M (M=Co, Fe) with a coordinatively unsaturated metal ion. We designed and synthesized 1-M by sterically blocking one porphyrin side with a tethered tetraazacyclododecane unit. With this protection, the metal-oxo species generated in OER can maintain an unoccupied trans axial site. Importantly, 1-M displays a higher OER activity in alkaline solutions than analogues lacking such an axial protection by decreasing up to 150-mV overpotential to achieve 10 mA/cm current density. Theoretical studies suggest that with an unoccupied trans axial site, the metal-oxo unit becomes more positively charged and thus is more favoured for the hydroxide nucleophilic attack as compared to metal-oxo units bearing trans axial ligands.
在析氧反应（OER）中，水或氢氧根对金属 - 氧单元的亲核进攻形成了一个O - O键。通过配位调节来改善这种进攻很有意思，但很少能够实现。我们在此报告了具有配位不饱和金属离子的金属卟啉1 - M（M = Co，Fe）对OER催化性能的改善。我们通过用连接的四氮杂环十二烷单元在空间上阻断卟啉的一侧来设计并合成了1 - M。通过这种保护，在OER中生成的金属 - 氧物种可以保持一个未被占据的反位轴向位点。重要的是，与缺乏这种轴向保护的类似物相比，1 - M在碱性溶液中显示出更高的OER活性，在达到10 mA/cm²电流密度时过电位降低高达150 mV。理论研究表明，由于存在未被占据的反位轴向位点，金属 - 氧单元带正电更多，因此与带有反位轴向配体的金属 - 氧单元相比，更有利于氢氧根的亲核进攻。
