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

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

doi:10.34133/2021/9851231

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 (pda2– =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.

Highlights

In a typical solar fuel generation device of either electrochemical or photoelectrochemical driven, it often consists of a fuelforming cathodic half-reaction, such as hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2-RR), or nitrogen reduction reaction (NRR), and acquires protons 4e−), and electrons
Our experimental results clearly revealed that the water nucleophilic attack (WNA) O-O bond formation pathway of single-site Molecular water oxidation catalysts (MWOCs) can switch to the I2M mechanism by changing the local environment, such as shortening the intermolecular distance of catalyst active center, via a homopolymerization method in this case
Electrochemical properties of complex 1 in solution and complex 2 that is immobilized on glass carbon (GC) electrode via electropolymerization were investigated by cyclic voltammograms (CVs) and differential pulse voltammograms

Summary

Introduction

In a typical solar fuel generation device of either electrochemical or photoelectrochemical driven, it often consists of a fuelforming cathodic half-reaction, such as hydrogen evolution reaction (HER), carbon dioxide reduction reaction While the orientation of hydrophobic/hydrophilic substituent groups of MWOCs is a key factor contributing to the different reaction mechanisms [18], modifying the third coordination sphere of the catalyst is another approach to adjust their local environment and facilitate the I2M O-O bond formation pathway. These findings encouraged us to manipulate the catalytic water oxidation pathway of Ru(pda) complexes using combined strategies of direct ligand modification and local catalytic environment design. Our experimental results clearly revealed that the WNA O-O bond formation pathway of single-site MWOCs can switch to the I2M mechanism by changing the local environment, such as shortening the intermolecular distance of catalyst active center, via a homopolymerization method in this case

Results and Discussion

Discussion

Materials and Methods

Conflicts of Interest