A simple in situ deposition of metal alloys on graphite surface based on Sb, Bi, Cu, and Sn as an electrocatalyst for V 3 + / V 2 + redox reaction

The electrocatalytic effect of Sb3+, Bi3+, Cu2+, and Sn2+ ions is investigated for V3+/V2+ redox reaction on graphite electrode, and their binary, ternary, and quaternary ions are also studied for the first time. Herein, metal ions are reduced, and the electrodeposition of metals is carried out in situ during the V3+/V2+ redox reaction by a rapid one-step process. Scanning electron microscope-energy dispersive X-ray mapping analyses show that target metals are homogeneously distributed on the electrode surface and deposited in nano-sized particles with the size of 50 to 100 nm. The deposited metals and metal alloys are also verified by X-ray photoelectron spectroscopy. A series of cyclic voltammogram studies for the V3+/V2+ couple in the presence of different metal ion compositions are performed to examine Ipa/Ipc and ∆E values. Sb3+ has the Ipa/Ipc (0.81) value closest to 1 and the smallest ∆E (118 mV) values among the single ions. Electrochemical impedance spectroscopy experiments reveal a significant decrease in the charge transfer resistance value for the V3+/V2+ redox couple in all-metal combinations. The best electrochemical activities are achieved in the presence of metal combinations containing Sb and Bi, and the lowest Rct value (0.11 Ω) is reached in the Cu-Sb-Bi alloy. The present study suggests that the in situ modification of the graphite electrode with nano-particles of metals and metal alloys by one-step electrochemical deposition exhibits potential use for vanadium redox flow batteries.