TEMPO-assisted electrocatalytic dehydrogenation of piperazine to pyrazine over CuCo2O4/NF

This study addresses key challenges in traditional liquid organic hydrogen carrier (LOHC) dehydrogenation—such as dependence on high temperatures or precious metal catalysts—and electrode passivation in direct electrosynthesis. Using 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and its derivatives as media, we examined the electrocatalytic dehydrogenation of piperazine to pyrazine. Through systematic evaluation of 27 electrolyte systems based on diffusion coefficient ( D ) and electron transfer rate constant ( k ⁰), synergistic effects among components were identified. An optimal system of ACN + TBAPF 6 + TEMPO was selected for low-concentration piperazine reactions; for higher concentrations (e.g., 0.1 M), a mixed solvent of ACN and water was used to improve solubility. CuCo 2 O 4 /NF as dehydrogenation catalyst in this optimized electrolyte was further investigated. The electrocatalyst promotes TEMPO redox cycling and piperazine dehydrogenation, achieving high initial conversion (99.6%) and selectivity (79.9%) at 1.55 V ( vs . RHE), along with sustained stability over 288 h (the conversion of 90.9%, the selectivity of 67.8%). Mechanistic studies reveal that 2,2,6,6-tetramethyl-1-oxo-piperidinium (TEMPO⁺) regeneration on CuCo 2 O 4 /NF proceeds in two steps, enabling a rapid dynamic redox equilibrium that facilitates homogeneous piperazine oxidation. This dehydrogenation system follows a multi-step EE' pathway.