Synthesis and characterization of core–shell structured M@Pd/SnO2–graphene [M = Co, Ni or Cu] electrocatalysts for ethanol oxidation in alkaline solution

Abstract

Core–shell structured M@Pd/SnO₂–graphene (Gr), [M = Co, Ni or Cu] electrocatalysts were synthesized using ethylene glycol as a reducing agent with the aid of microwave irradiation in a two-step process. XRD, TEM and EDX analysis techniques were employed to physically characterize the prepared electrocatalysts. They revealed the formation of SnO₂–Gr as a support, surrounded by M as a core that was coated with Pd as a shell. The M@Pd/SnO₂–Gr electrocatalysts showed a gradual negative shift of their Pd(111) and Pd(200) diffraction peaks when compared to those in the XRD pattern of Pd/Gr. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were employed to investigate the electrocatalytic activity of the prepared electrocatalysts for ethanol oxidation in NaOH solution. Increased ECSA values were recorded at the M@Pd/SnO₂–Gr electrocatalysts, especially Cu@Pd/SnO₂–Gr [467.49 m² g⁻¹] in relation to that at Pd/Gr. The presence of cobalt, nickel or copper in the M@Pd/SnO₂–Gr electrocatalyst improved the ethanol oxidation mass activity of Pd/Gr by 4.42, 4.78 or 5.84, respectively. A chronoamperometry test demonstrated enhanced electrochemical durability for the fabricated core–shell structured electrocatalysts. Lowered charge transfer resistance values were also measured at these electrocatalysts during the ethanol oxidation reaction. Based on the results in previous reports, core–shell structured Cu@Pd/SnO₂–Gr is a potentially valuable electrocatalyst for fuel cell applications.