Tuning the electrocatalytic 2- and 4-electron reduction of oxygen by electrodeposited hybrid graphene-Co/Mn porphyrin coatings

Abstract

Coatings, obtained by one step electrodeposition of self-assembled positively charged Co, Mn tetra(N-methyl-4-pyridyl) porphyrin (CoP and MnP, respectively) or both metalloporphyrins with negatively charged carboxyl-rich graphene oxide, were characterized using microscopic (SEM, TEM, AFM), spectroscopic (UV–vis, Raman, XPS), and electrochemical (cyclic voltammetry, chronoamperometry, RRDE) methods. We show that coatings based on Co or Mn porphyrin on glassy carbon electrodes efficiently catalyze oxygen reduction in basic solutions by a main 2e-reduction to produce the H2O2 useful chemical. However, it is possible to convert the process into a 4e-reduction process by cobalt porphyrin-based coatings comprised also of controllable amounts of Mn porphyrin which acts as a H2O2 dismutation agent. Electrodes containing both metalloporphyrins (MnP/CoP =1.2) showed longer term stability during oxygen reduction at a potential of −0.35 V vs. Ag/AgCl in comparison to ones containing only cobalt porphyrin: turnover frequencies of 0.30 and 0.17 s−1, respectively. The concept of integrating various multi-tasking non noble-based catalysts in electrodeposited graphene derivatives can be exploited for further development of practical devices able to produce chemicals or energy.