Carbon defects enhanced TEMPO redox cycles for high-efficiency urotropine electrosynthesis

Electrocatalysis provides a sustainable alternative route to produce nitrogen-containing molecules. However, poor carbon-nitrogen (C-N) coupling selectivity and limited current density pose challenges to its widespread adoption. Herein, we introduce a carbon-defect enhanced 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) mediated tandem process to tackle both problems. Our hetero-homogeneous system achieves a Faraday efficiency of ~99% with industrial-level current density of ~0.6 A·cm^-2 for urotropine electrosynthesis. In situ near ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron paramagnetic resonance reveal that the boosted activity originated from the oxidation of TEMPOH on the carbon defective sites, which accelerates the redox cycling of the molecular mediator for urotropine formation. This work highlights the catalytic effect of carbon defects on the redox cycling of TEMPO, improves both the selectivity and the rate of the electrocatalytic C-N coupling reaction, and offers insights for designing efficient electrochemical mediated oxidation processes and C-N coupling reactions.