Direct and Indirect Electrooxidation of Glycerol to Value‐Added Products

In this work, different approaches for the direct and indirect electrooxidation of glycerol, a by-product of oleochemistry and biodiesel production, for the synthesis of value-added products and of intermediates for biofuel/electrofuel production, were investigated and compared. For the direct electrooxidation, metallic catalysts were used, whose surfaces were modified by promoters or second catalysts. Bi-modified Pt electrodes (Ptx Biy /C) served as model systems for promoter-supported electrocatalysis, whereas IrO2 -modified RuO2 electrodes were studied as catalyst combinations, which were compared under acidic conditions with the respective monometallic catalysts (Pt/C, RuO2 /Ti, IrO2 /Ti). Furthermore, inorganic halide mediators (chloride, bromide, iodide) and organic nitroxyl mediators (4-oxo-2,2,6,6-tetramethyl-piperidin-1-oxyl and 4-acetamido-2,2,6,6-tetramethyl-piperidin-1-oxyl) were evaluated for indirect electrooxidation. These different approaches were discussed regarding selectivity, conversion, and coulombic efficiency of the electrochemical glycerol oxidation.