Switching the O-O Bond Formation Pathways of Ru-pda Water Oxidation Catalyst by Third Coordination Sphere Engineering

Yingzheng Li; Shaoqi Zhan; Lianpeng Tong; Wenlong Li; Yilong Zhao; Ziqi Zhao; Chang Liu; Mårten S G Ahlquist; Fusheng Li; Licheng Sun

doi:10.34133/2021/9851231

Switching the O-O Bond Formation Pathways of Ru-pda Water Oxidation Catalyst by Third Coordination Sphere Engineering

Research (Wash D C). 2021 Apr 13:2021:9851231. doi: 10.34133/2021/9851231. eCollection 2021.

Authors

Yingzheng Li¹, Shaoqi Zhan^{2

3}, Lianpeng Tong⁴, Wenlong Li¹, Yilong Zhao¹, Ziqi Zhao¹, Chang Liu¹, Mårten S G Ahlquist², Fusheng Li¹, Licheng Sun^{1

5

6}

Affiliations

¹ State Key Laboratory of Fine Chemicals, Institute of Artificial Photosynthesis, DUT-KTH Joint Education and Research Centre on Molecular Devices, Dalian University of Technology, Dalian 116024, China.
² Department of Theoretical Chemistry and Biology, School of Engineering Sciences in Chemistry Biotechnology and Health, KTH Royal Institute of Technology, 10691 Stockholm, Sweden.
³ Department of Chemistry, University of California, Riverside, California 92521, USA.
⁴ School of Chemistry and Chemical Engineering/Institute of Clean Energy and Materials, Guangzhou University, No. 230 Wai Huan Xi Road, Higher Education Mega Center, Guangzhou 510006, China.
⁵ Department of Chemistry, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, 10044 Stockholm, Sweden.
⁶ Center of Artificial Photosynthesis for Solar Fuels, School of Science, Westlake University, 310024 Hangzhou, China.

Abstract

Water oxidation is a vital anodic reaction for renewable fuel generation via electrochemical- and photoelectrochemical-driven water splitting or CO₂ reduction. Ruthenium complexes, such as Ru-bda family, have been shown as highly efficient water-oxidation catalysts (WOCs), particularly when they undergo a bimolecular O-O bond formation pathway. In this study, a novel Ru(pda)-type (pda^2- =1,10-phenanthroline-2,9-dicarboxylate) molecular WOC with 4-vinylpyridine axial ligands was immobilized on the glassy carbon electrode surface by electrochemical polymerization. Electrochemical kinetic studies revealed that this homocoupling polymer catalyzes water oxidation through a bimolecular radical coupling pathway, where interaction between two Ru(pda)-oxyl moieties (I2M) forms the O-O bond. The calculated barrier of the I2M pathway by density-functional theory (DFT) is significantly lower than the barrier of a water nucleophilic attack (WNA) pathway. By using this polymerization strategy, the Ru centers are brought closer in the distance, and the O-O bond formation pathway by the Ru (pda) catalyst is switched from WNA in a homogeneous molecular catalytic system to I2M in the polymerized film, providing some deep insights into the importance of third coordination sphere engineering of the water oxidation catalyst.