Researchers from Brazil’s Federal University of Paraíba – UFPB and Portugals’ University of Aveiro and LASI (Intelligent Systems Associate Laboratory) have presented a simple and cost-effective approach for the one-step synthesis of MnCo2O4-reduced graphene oxide (MCO-rGO) for use as an anode material in the oxygen evolution reaction (OER).
Both MCO and rGO were formed on a porous Ni foam through a wet chemical process, via oxidation of the spinel phase and the simultaneous thermal reduction of graphene oxide (GO) in an air atmosphere at 300 °C. The (electro)catalytic properties of the MCO-based electrodes were studied in an alkaline medium (1 M KOH) to evaluate the impact of rGO on various OER activity parameters, in controlled amounts of 10 wt% and 20 wt% GO.
The composite with 20 wt% GO exhibited the lowest overpotential, 291 mV at 50 mA cm−2 (η50), which is 37 mV lower than the η50 value for the pure MCO. The Tafel slopes suggested that the MCO-based electrodes are governed by a competitive mechanism between the first electron transfer step and the chemical step following the first electron transfer, with the latter, involving chemical intermediates, being dominant.
In agreement, electrochemical impedance spectroscopy (EIS) results recorded during the OER conditions showed a decrease in the resistance associated with surface intermediates upon the addition of rGO.
This improvement is attributed to the higher electrical conductivity of rGO and a potential increase in electrochemically active surface area. Furthermore, excellent electrochemical stability was achieved at a current density of 50 mA cm−2 for 20 h.
The team reported a low-cost and facile green synthesis route for the preparation of MnCo2O4-reduced graphene oxide (MCO-rGO) composite electrodes directly on porous nickel foam. The successful reduction of GO during the synthesis of MCO nanoparticles was confirmed, demonstrating that this approach provides a simple and effective route for the fabrication of high-performance (electro)catalysts. The excellent OER performance reported in this work is the result of the combined effect of adding rGO and synthesizing directly on the substrate at a low temperature (300 °C), avoiding the use of binders.