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, electrocatalysis powered by renewable energy sources has been utilized to remove C-only and N-only pollutants separately, while C,N co-reduction has been under explored. Compared with C-only or N-only reduction reactions, co-electrolysis to generate structurally complicated and functionally diverse C–N bonds are highly desirable yet more challenging. Oximes, which contain C=N bonds, are important precursors in medicine and fine chemical industry. Previous attempts to co-reduce 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 C–N bond via a green electrosynthesis scheme in 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.