Breaking the selectivity barrier in glycerol electrooxidation to glyceraldehyde via redox mediation

Aldehydes are valuable intermediates with widespread industrial applications, and their traditional synthesis relies on chemical oxidation that is often hazardous and environmentally unfriendly. Electrochemical oxidation offers a more sustainable and milder alternative; however, it faces challenges such as aldehyde overoxidation and susceptibility to base-catalyzed Cannizzaro disproportionation. Electrochemical glycerol oxidation to glyceraldehyde is a representative example, which typically requires precious metal-based electrocatalysts but still suffers from low selectivity and activity. Here, we report a metal-free oxidation strategy mediated by 2,2,6,6-tetramethylpiperidine-1-oxyl. By systematically investigating the redox thermodynamics and kinetics of TEMPO across a broad pH range, we construct a Pourbaix diagram and elucidate the relative kinetics of each reaction step. These insights allow us to explain the anomalously high apparent Faradaic efficiency (~200%) observed under acidic conditions, and identify neutral media as the optimal environment for selective glyceraldehyde production. Under optimized conditions, our system achieves a glyceraldehyde Faradaic efficiency exceeding 93% and a partial current density of 23.3 mA cm –2 at 0.57 V — more than doubling the performance of the best reported precious metal-based systems. Furthermore, the versatility of this strategy extends to the selective oxidation of other primary alcohols to their corresponding aldehydes with near-unity selectivity.