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.
Anion exchange membrane water electrolysis (AEMWE) is one of the most promising technologies for producing green hydrogen; however, they still suffer from durability issues. One task is to find suitable electrolyte conditions for anode catalysts that endow them with both high activity and stability. Herein, we benchmark the pH–stability relationship of four typical metal oxides as anode catalysts in the AEMWE. Their electrochemical performance and structural stability were in-depth analyzed through impedance, dissolved composition in the electrolyte, and correlated Pourbaix diagram. NiFe2O4 with the best activity and stability in the strong alkaline (pH = 14) shows terrible stability in pure water, which is then verified due to the severe Fe leaching, and it cannot be alleviated by alkaline pre-activation. Notably, Co3O4 shows comparable activity and stability to IrO2 in pure water and weak alkaline conditions. At pH = 12, it entails only ∼2.18 V to reach 1.0 A cm–2 and stabilizes for 40 h, being superior to others. This work screens out suitable transition metal oxides as a substitute for noble metals and their optimal application scenarios for AEMWE.
危险品化学品经营许可证（带存储）