Redox-active ligands enhance oxygen evolution reaction activity: Regulating the spin state of ferric ions and accelerating electron transfer

Jing Liu; Zebin Yu; Jun Huang; Shuangquan Yao; Ronghua Jiang; Yanping Hou; Wenjun Tang; Pengxin Sun; Hongcheng Huang; Mengqi Wang

doi:10.1016/j.jcis.2023.07.083

Redox-active ligands enhance oxygen evolution reaction activity: Regulating the spin state of ferric ions and accelerating electron transfer

J Colloid Interface Sci. 2023 Nov 15;650(Pt B):1182-1192. doi: 10.1016/j.jcis.2023.07.083. Epub 2023 Jul 17.

Authors

Jing Liu¹, Zebin Yu², Jun Huang³, Shuangquan Yao⁴, Ronghua Jiang⁵, Yanping Hou⁶, Wenjun Tang⁶, Pengxin Sun⁶, Hongcheng Huang⁶, Mengqi Wang⁷

Affiliations

¹ School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China; Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, Nanning 530004, PR China.
² School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China. Electronic address: xxzx7514@hotmail.com.
³ School of Civil Engineering and Architecture, Guangxi Minzu University, Nanning 530004, PR China.
⁴ Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, Nanning 530004, PR China.
⁵ School of Chemical and Environmental Engineering, Shaoguan University, Shaoguan 512005, PR China.
⁶ School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China.
⁷ College of Computer Science and Technology, Shandong University of Technology, Zibo 255090, PR China.

PMID: 37478735
DOI: 10.1016/j.jcis.2023.07.083

Abstract

Metal-organic frameworks (MOFs) are considered as one of the most promising catalysts for oxygen evolution reaction (OER). However, only a few have introduced redox-active ligands into MOFs and explored their role in the OER process. In this work, we synthesized FeNi DHBQ/NF using the redox-active ligand 2,5-dihydroxy-1,4-benzoquinone (DHBQ), which exhibited excellent redox activity and required only 207 and 242 mV overpotentials to achieve current densities of 10 and 100 mA cm^-2. Our research confirms that (i) the doping of Fe leads to the formation of Ni → O → Fe electron transfer channels in the MOFs and stronger electron transfer, attributed to the stronger d-π conjugation between the metal center and the ligand and reduced the d-orbital crystal field splitting energy of Fe³⁺; (ii) the rate determination step (RDS) in the OER process of the catalyst is the formation of O*, while Fe and redox-active ligands effectively regulate the adsorption energy of oxygen-containing intermediates, reducing the energy barrier of the RDS; (iii) the redox-active ligands can act as "electron reservoirs" in the electrochemical process, making Ni more readily oxidized to Ni³⁺ or even Ni⁴⁺ at low potentials, which is beneficial to the subsequent OER process.

Keywords: 2,5-Dihydroxy-1,4-benzoquinone; Electron reservoirs; Electron transfer channels; Metal-organic frameworks; Oxygen evolution reaction; Redox-active ligand; d-π Conjugation.