Understanding the surface segregation behavior of bimetallic CoCu toward HMF oxidation reaction

The surface segregation of graphene encapsulated CoCu alloy facilitates the formation of sub-nanometer lattice on the bimetallic CoCu surface, which promoted the electrocatalytic oxidation of HMF to FDCA. Surface segregation is ubiquitous in multi-component materials and is of great important for catalysis but little is known on the surface structure under graphene encapsulation. Here, we show that the graphene encapsulated CoCu performs well for the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) with the onset potential before 1.23 V RHE and a nearly 100% selectivity of FDCA under 1.4 V RHE . From the experimental results, the unprecedented catalytic performance was attributed to local structural distortion and sub-nanometer lattice composition of the CoCu surface. We accurately show the dispersed Cu doped Co 3 O 4 nano-islands with a lot of edge sites on the bimetallic Co-Cu surface. While, the gradient components effectively facilitate the establishment of built-in electric field and accelerate the charge transfer. Theoretical and experimental results reveal that the surface Co and neighbouring Cu atoms in sub-nanometer lattice synergistically promote the catalysis of HMF. This work offers new insights into surface segregation in tuning the element spatial distribution for catalysis.