Interlayer Expansion Enables Electrochemical Domino C-N Coupling for Formaldoxime Formation in Aqueous Media

Upcycling C- and N-containing pollutants into value-added resources is key to achieving a sustainable society in the near future. In recent years, coelectrolysis powered by renewable energy sources to generate structurally complicated and functionally diverse C-N bonds is highly desirable yet more challenging compared with C-only or N-only reduction reactions. Oximes, which contain C=N bonds, are important precursors in medicine and the fine chemical industry. Previous attempts to coreduce carbon dioxide and nitrate or nitrite yielded formaldoxime (H₂C=NOH) as a byproduct with low selectivity. Herein, we demonstrate a new tandem electrocatalytic pathway to produce H₂C=NOH as the target product using NiFe layered double hydroxides (LDHs) as efficient catalysts. Upon expanding the interlayer spacing of NiFe LDH using dodecyl-sulfonate as an intercalating anion, this catalyst displays a record-high Faradaic efficiency for H₂C=NOH of 31% in aqueous solution at -1.9 V vs reversible hydrogen electrode. Our findings also show that the lengths of alkyl chains can tune the immediate microenvironment surrounding the dual Ni-Fe active sites, thus boosting the C-N coupling yield rate. Kinetic isotopic effect studies and control experiments under H₂ are further carried out to interrogate the electrocatalytic mechanism of this tandem C-N bond formation process. Overall, this study offers a compelling approach to form a C-N bond via a green electrosynthesis scheme in an aqueous medium. Furthermore, this study underscores the importance of precisely regulating the electrochemical microenvironment for enhancing the synergy between dual-metal active sites for efficient domino electrosynthesis.