Studying the Competition between Glucose Oxidation and Oxygen Evolution Reaction: Toward a Membrane-Free Electrolyzer for the Production of H₂ and Added Value Products

This study aims to systematically evaluate the competition between the oxygen evolution reaction (OER) and glucose oxidation reaction (GOR) in order to find the working conditions of a membrane-less glucose electrolyzer. For this purpose, a H electrochemical cell (H-cell) has been used to isolate the cathodic and anodic compartments. In the latter, in situ O₂ measurements were performed by an optical sensor during different kinds of electrochemical experiments. As the glucose concentration increased, a progressive decrease in the O₂ production rate was observed during the chronoamperometry step at 1.7 V vs RHE. At a glucose concentration of 40 mM, the OER can be entirely replaced by glucose oxidation on the Ni-based anodic catalyst. On the other hand, onset potentials for real O₂ production were obtained at different glucose concentrations in order to maximize the electrocatalytic activity without any O₂ production on the electrolyzer. During the operation of the electrolyzer at the selected conditions, instead of O₂, added value chemicals were obtained in the anodic compartment of the cell. These products were determined by ¹H and ¹³C NMR, and the results showed that formic acid was the main product after 46 h of the electrolysis experiment (1.5 V vs RHE). Other products such as lactic acid and gluconic acid were also identified. The innovative experimental approach used in this study can be extended to other conditions, organic molecules, and catalysts. Furthermore, it serves as a starting point to establish a roadmap to a membrane-less electrolyzer to produce hydrogen and added value products.