In this work, electrocatalytic upgrade of n-valeraldehyde to octane with higher activity and selectivity is achieved over Au single-atom catalysts (SACs)–NiMn₂O₄ spinel synergetic composites. Experiments combined with density functional theory calculation collaboratively demonstrate that Au single-atoms occupy surface Ni²⁺ vacancies of NiMn₂O₄, which play a dominant role in n-valeraldehyde selective oxidation. A detailed investigation reveals that the initial n-valeraldehyde molecule preferentially adsorbs on the Mn tetrahedral site of NiMn₂O₄ spinel synergetic structures, and the subsequent n-valeraldehyde molecule easily adsorbs on the Ni site. Specifically, Au single-atom surficial derivation over spinel lowers the adsorption energy (Eads) of the initial n-valeraldehyde molecule, which will facilitate its adsorption on the Mn site of Au SACs–NiMn₂O₄. Furthermore, the single-atom Au surfi-cial derivation not only alters the electronic structure of Au SACs–NiMn₂O₄ but also lower the Eads of subsequent n-valeraldehyde molecule. Hence, the subsequent n-valeraldehyde molecules prefer adsorption on Au sites rather than Ni sites, and the process of two alkyl radicals originating from Mn–C₄H₉ and Au–C₄H₉ dimerization into an octane is accordingly accelerated. This work will provide an avenue for the rational design of SACs and supply a vital mechanism for understanding the electrocatalytic upgrade of n-valeraldehyde to octane.