Manipulation of Neighbouring Palladium and Mercury Atoms for Efficient *OH Transformation in Anodic Alcohol-Oxidation and Cathodic Oxygen-Reduction Reactions.

The synergetic effect of neighbouring heterogeneous atoms is capable of enabling unexpected catalytic performance, and the design of a well-ordered atomic structure and elaborating the underlying interactions are crucial for the development of superior electrocatalysts in fuel cells. We demonstrate here that an ordered Pd-Hg intermetallic alloy with dimensions of several nanometers can be subtly manipulated using mild wet - chemical reduction approach. Based on combined results of XPS and HAADF-STEM analysis, the adjacent regions of metallic atoms were found to be evenly occupied by heterogeneous elements from the distribution features of the surface structure. Due to charge transfer from Hg to neighbouring Pd, the down-shift of d-band center in PdHg alloys was theoretically beneficial for desorption of crucial intermediates (*OH), both in anodic ethanol oxidation reaction (EOR) and cathodic oxygen reduction reaction (ORR). In the presence of Hg atoms with lower *OH desorption energy, the rapid dissociation of *OH from Pd facilitated the final H2O formation, with superior ORR efficiency comparable to Pt/C catalysts. Remarkably, the rapid combination of *OH on Hg atoms with CH3CO* on neighbouring Pd atoms unambiguously favored generation of acetate ions (rate-determining) in the catalytic EOR process, resulting in a high mass activity (7.68 A per mgPd). This well-ordered atomic structure also shows excellent long-term stability in ethylene glycol oxidation reaction and ORR.