Carbon supported polyindole-5-carboxylic acid covalently bonded with pyridine-2,4-diamine copper complex as a non-precious oxygen reduction catalyst

Indole-5-carboxylic acid monomer was electropolymerized on carbon modified glass carbon (GC) electrode, followed by the covalent bonding with pyridine-2,4-diamine by using 1-ethyl-(3-(dimethyl-amino-propyl)carbodiimide (EDAC), N-hydroxysulfosuccinimide sodium salt (NHS) catalyst, and then was complexed with copper ions to obtain the composite (CuINPD/C). The morphology and the chemical composition of the CuINPD/C catalyst were analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Electrochemical measurements such as cyclic voltammetry, rotating disk electrode, rotating ring-disk electrode and electrochemical impedance spectroscopy were applied to obtain the mechanisms of the oxygen reduction reaction (ORR). All electrochemical measurements demonstrate that CuINPD/C is a good catalyst with excellent stability due to copper ions doping and carbon modification, which play a key role in increasing the current density and enhancing the charge transfer kinetics. Moreover, the average electron transfer number is about 3.1, indicating the ORR of CuINPD/C may takes a coexisting pathway involving both the two-electron and four-electron transfers.