Platinum supported on early transition metal carbides: Efficient electrocatalysts for methanol electro-oxidation reaction in alkaline electrolyte

Abstract

Some classes of electrocatalysts based on Pt supported early transition metal carbides (TMCs) have shown promise for methanol oxidation reaction (MOR). To bridge the material gap, we studied some of the promising and new electrocatalysts for MOR. We synthesized 1%wt Pt/TMCs (TMCs of group IV (Ti and Zr), group V (V, Nb and Ta) and group VI (W)) via wet impregnation method as low loading electrocatalysts for MOR in alkaline media. The synthesized materials were characterized by X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICP-OES), N2 physisorption using Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The activity of the electrocatalysts were elucidated for MOR in alkaline media via combination of experimental and theoretical methods. Among all the investigated electrocatalysts, Pt/NbC was found to have the highest specific activity (3.58 mA cmPt−2) while Pt/ZrC had the least (0.410 mA cmPt−2). Tafel slope measurements for Pt/TMC electrocatalysts with the exception of Pt/TiC varied from region of low potential to region of high potential and were 121.2 ± 11 mV dec−1 and 234 ± 10 mV dec−1 respectively, indicating change in limiting steps from C-H scission to CO poisoning. Density functional theory (DFT) calculations of the binding energies of H and CO on the Pt/TMC surfaces were correlated to their specific activity, and volcano-type relationships were discovered, which indicated that neither too weak nor too strong bond of H and CO on the electrocatalyst surfaces were favorable for high activity during MOR. Finally, a feasible reaction mechanism for Pt/TMC electrocatalysts in MOR was proposed based on the experimental and theoretical results.