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.

由于从光催化还原CO ₂（CO ₂ PR）产生CH _4的多电子转移，特别是在长波长辐射下，实现CH _4的高选择性是一个巨大的挑战。本文中，我们合成了一系列单层Ni ₃ X层双氢氧化物（LDH）（m-Ni ₃ X-LDH，X = Cr，Mn，Fe，Co）。当用于CO ₂ PR时，使用Ru-络合物作为光敏剂，CH ₄的选择性表现出火山样趋势，在m-Ni ₃ Mn-LDH处最高。经过进一步优化后，CH _4的选择性接近99％在λ= 600 nm的辐射下实现。因此，结构表征证明存在金属和羟基缺陷位点，其中Ni和O的表面价态表现出火山样趋势，在m-Ni ₃ Mn-LDH处具有最低点。因此，CH ₄的高选择性可以归因于m-Ni ₃ Mn-LDH中有效的电子空穴迁移和分离。此外，在M-镍的富电子的Ni-O键₃的Mn-LDH可以充当吸附点为CO *，促进CO的进一步氢化，以CH ₄和CH改善的选择性₄。