The Effects of Coordinated Molecules of Two Gly-Schiff Base Copper Complexes on Their Oxygen Reduction Reaction Performance

Zhe Ma,Xianqiang Huang,Ya Chu,Jinsheng Zhao,Chonggang Fu,Hongmei Du

doi:10.3390/catal8040156

Abstract

In this study, two simple Schiff base copper complexes [Cu(H2O)2(HL)]·2H2O (Complex 1) (H3L = 2-OH-4-(OH)-C6H2CH=NCH2CO2H) and [Cu(py)2(HL)] (Complex 2) (Py = pyridine) were initially achieved and authenticated by single-crystal X-ray structure analyses (SXRD), powder X-ray diffraction analyses (PXRD), FT-IR spectroscopy, and elemental analyses. The SXRD reveals that the Cu2+ center in Complex 1 exhibited a distorted square pyramidal geometry, which is constructed based on phenolate oxygen, water molecules, carboxylate oxygen, and imine nitrogen from a deprotonated H3L ligand in an NO4 fashion. The Cu2+ atom in Complex 2 had distorted square pyramidal geometry, and was coordinated with two pyridine molecules and one Gly-Schiff base ligand, exhibiting an N3O2 binding set. Additionally, the free water molecules in Complex 1 linked independent copper complexes by intermolecular hydrogen bond to form a 2D framework. However, the one-dimensional chain supramolecular structure of Complex 2 was formed by the intermolecular O–H…O hydrogen bonds. The oxygen reduction performance of the two complexes was analyzed by cyclic voltammetry (CV) and the rotating disk electrode (RDE) method. Both complexes could catalyze the conversion of oxygen to water through a predominant four-electron pathway, and the Cu–NxOy moieties might be the functional moieties for the catalytic activity. The catalytic pathways and underlying mechanisms are also discussed in detail, from which the structure–activity relationship of the complexes was obtained.

Highlights

Studies on coordination compounds have been well developed, and the developed organometallic complexes have been widely used in many fields, such as the catalysts used in the chemical and petrochemical industries [1], the molecular recognition reagents used in analytical measurements [2], and the oxygen reduction catalysts used in fuel cells [3]
The simple copper complexes reported in this study show satisfactory ORR activities in neutral aqueous solutions and might be used as competitive cathodic catalysts in microbial fuel cells due to their low preparation costs
The two complexes had simple and similar structures, but the difference is that the water molecules used as ligands in Complex 1 are replaced by pyridine molecules in Complex 2

Summary

Introduction

Studies on coordination compounds have been well developed, and the developed organometallic complexes have been widely used in many fields, such as the catalysts used in the chemical and petrochemical industries [1], the molecular recognition reagents used in analytical measurements [2], and the oxygen reduction catalysts used in fuel cells [3]. Many new fields have been developed, such as macrocyclic coordination compounds [4], supramolecular complexes [5], metal-organic frameworks [3], and functional complexes [5]. Gross Zeev summarized a variety of metallocorroles as ORR catalysts in a review and presented the effects of the metal center and the side substituent of the macrocycles on the performance of the electrocatalysts [10]

Methods

Findings

Discussion

Conclusion