Selective electrosynthesis of aldehydes at industrially relevant current densities via tandem electrochemical–chemical catalysis†

Abstract

Organic electrochemical synthesis, a sustainable alternative to traditional organic synthesis, faces challenges in practical applications, such as limited current density, difficulty in recycling homogeneous electrochemical mediators, and large waste supporting electrolyte generation. In this work, we addressed these challenges by proposing a tandem electrochemical–chemical catalysis strategy, using selective alcohol electrooxidation to valuable aldehydes as a model transformation. Hypochlorite electro-generation and heterogeneous TEMPO-catalyzed alcohol oxidation were decoupled spatially, allowing each step to proceed independently under high rates and selectivity. Consequently, this strategy achieved industrially relevant current densities of 300–600 mA cm⁻² with 64.7–81.8% faradaic efficiencies, resulting in a space–time yield (STY) of up to 516.95 kg (m³ h)⁻¹ for benzaldehyde synthesis that significantly surpassed existing strategies. In addition, this strategy utilized the silica-supported TEMPO catalyst filled in a packed-bed reactor to achieve efficient single-pass conversion of alcohols to the corresponding aldehydes without the need for downstream catalyst separation, substantially reducing energy consumption for downstream separation. Furthermore, we developed a closed-loop tandem electrochemical–chemical catalysis system for gram-scale steroidal aldehyde synthesis, which incorporated an inline liquid–liquid separator for electrolyte recycling, thus significantly reducing the supporting electrolyte waste generation, which aligns with the principles of green chemistry and sustainable development. This work demonstrates a viable approach for the electrosynthesis of value-added organic intermediates under practical current densities with minimal waste electrolyte.