Glucose and 5-hydroxymethylfurfural adsorption at Pt(111) in alkaline media: a cyclic voltammetry study

The electrochemical oxidation of glucose and 5-hydroxymethylfurfural (5-HMF) at Pt(111) was studied in alkaline media focusing on adsorption and surface poisoning at concentrations from 10⁻⁶ to 10⁻¹ mol L⁻¹. Glucose was able to interact with Pt(111) and be oxidized at both oxide-free and (hydr-)oxide-covered surfaces, the current being dependent on the glucose concentration. The presence of adsorbed hydroxyl ions (Pt(111)-OH) facilitates the glucose oxidation reaction leading to the lowest surface poisoning along the voltammetric cycles. Contrary, the 5-HMF strongly interacts with Pt(111) and although oxidation currents at Pt(111)-OH region increase with 5-HMF concentration, inhibitory effects are observed for concentrations higher than 10⁻⁴ M. The results are explained based on the competition between hydroxyl and 5-HMF adsorption at the surface. According to the literature, the presence of (hydr-)oxides species is essential for furanic compound oxidation after its adsorption. Therefore, the 5-HMF acts as its own poison at high concentrations. In this way, glucose presents a higher activity at Pt(111) than 5-HMF, even in concentrations higher than 10⁻¹ mol L⁻¹.