Role of Cocatalyst on Sn‐Doped Hematite Photoanodes for Photoelectrochemical Glycerol Oxidation: Enhancing the Selectivity Toward C ₃ Molecules in Alkaline pH

The upgrading of glycerol, a low‐value and abundant byproduct of the biodiesel industry, to higher‐value chemicals is an attractive proposition. Photoelectrochemical (PEC) glycerol oxidation is a sustainable and cost‐effective approach for converting glycerol into fuels by harnessing solar energy. In this work, we report on earth‐abundant Sn‐doped α‐Fe 2 O 3 photoanodes cocatalyzed with NiOOH to achieve selectivity toward C 3 molecules in a pH 9.3 buffer solution. Sn‐doped α‐Fe 2 O 3 photoanodes were synthesized through the physical vapor deposition (PVD) technique, followed by high‐temperature annealing. The photoanodes were surface‐passivated with a NiOOH cocatalyst through photoelectrode position. The resulting photoanodes showed a significantly enhanced selectivity toward dihydroxyacetone and glyceraldehyde, reaching values of 52.8% and 20.5%, respectively. In contrast, the selectivity for glycolaldehyde was suppressed by 41.8% compared to that for unmodified Sn‐doped α‐Fe 2 O 3 photoanodes. By combining a PEC study of the glycerol oxidation reaction (GOR) with HPLC analysis, it was found that the Ni 2+ /Ni 3+ redox couple within the cocatalyst selectively oxidizes the primary and secondary hydroxyls of the glycerol and inhibits the reaction pathway toward the generation of C 2 molecules. These insights are critical for understanding the reaction mechanism for oxidizing glycerol into DHA and GLAD on hematite photoanodes in alkaline pH.