600 nm induced nearly 99% selectivity of CH4 from CO2 photoreduction using defect-rich monolayer structures

Abstract

Owing to multiple-electron transfer of producing CH4 from photocatalytic CO2 reduction (CO2PR), a great challenge is achieving high selectivity of CH4, especially under long-wavelength irradiation. Herein, we synthesize a series of monolayer Ni3X-layered double hydroxide (LDH) (m-Ni3X-LDH, X = Cr, Mn, Fe, Co). When applied for CO2PR, the selectivity of CH4 exhibits a volcano-like trend with the highest point at m-Ni3Mn-LDH using Ru-complex as the photosensitizer. After further optimization, nearly 99% selectivity of CH4 is achieved under irradiation with λ = 600 nm. Accordingly, structural characterizations prove the presence of metal and hydroxyl defect sites, in which the surface valence states of Ni and O exhibit a volcano-like trend with the lowest point at m-Ni3Mn-LDH. Thus, the high selectivity of CH4 could be attributed to the efficient electron-hole migration and separation in m-Ni3Mn-LDH. Moreover, the electron-rich Ni-O bond in m-Ni3Mn-LDH may act as the adsorption site for CO∗, promoting the further hydrogenation of CO to CH4 and improving the selectivity of CH4.