Abstract
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 O(2) measurements were performed by an optical sensor during different kinds of electrochemical experiments. As the glucose concentration increased, a progressive decrease in the O(2) 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 O(2) production were obtained at different glucose concentrations in order to maximize the electrocatalytic activity without any O(2) production on the electrolyzer. During the operation of the electrolyzer at the selected conditions, instead of O(2), added value chemicals were obtained in the anodic compartment of the cell. These products were determined by (1)H and (13)C 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.