Copper selenide - Porous carbon derived from metal-organic frameworks as an efficient electrocatalyst for methanol oxidation

Abstract

In the present study, a metal-organic framework (Cu-MOF) was used as the precursor for synthesis of carbon-encapsulated copper selenides (namely, Cu2-xSe@PCs). After carbonization of Cu-MOF to Cu/Cu2O@PCs, the selenidation process was applied by selenium powder at 500 °C to form Cu2-xSe@PCs. Scanning electron microscopy showed the maintenance of the initial octahedral structure of Cu-MOF after carbonization and selenidation. Nickel foam (NF) was modified with the prepared composite and used as anode in electrochemical cells. Cyclic voltammetric study in alkaline solution (in the absence of methanol) showed highly increased peak currents (∼4 times) on Cu2-xSe@PCs/NF compared to that on Cu/Cu2O@PCs/NF. The electrocatalytic oxidation of methanol in alkaline solution showed lower overpotential and much higher catalytic currents (629.3 mA cm−2 in methanol 0.5 M) on Cu2-xSe@PCs/NF compared to that on Cu/Cu2O@PCs/NF (204.6 mA cm−2). The long-term stability of the proposed electrocatalyst was studied by chronopotentiometry and chronoamperometry. High potential stability was observed when a constant current (22.3 mA cm−2) was drawn from the cell (>4 h). Similar stability was observed for the catalytic current when a constant voltage (1.62 V vs. RHE) was imposed on the electrode in chronoamperometry. In addition, more than 88.5 % of the catalytic current remained after the application of 300 consecutive potential cycles to Cu2-xSe@ PCs/NF in the alkaline solution of methanol. The electrocatalyst was also used in a two-electrode system. Polarization and power density plots showed improved catalytic methanol oxidation by using Cu2-xSe@PCs/NF compared to Cu/Cu2O@PCs/NF. Excellent electrocatalytic properties of the proposed composite towards methanol, long-term stability and the simple synthetic route of the mono-metal electrocatalyst make it a good candidate as the anode of direct methanol fuel cells.