Immiscible Metal-Regulated Surface Segregation Enables Core-Shell Bi-PtMn Catalysts With Benchmark Performance in Direct Methanol Fuel Cells.

Although the Bi-Pt ensemble effect endows Bi-Pt-based catalysts with remarkable CO tolerance in the methanol oxidation reaction (MOR), the lack of precise atomic-level control over Bi-Pt surface structures leads to an intrinsic activity-selectivity trade-off. Herein, we propose a facile immiscible-metal-induced surface-segregation strategy to construct a core-shell Bi-PtMn catalyst that simultaneously achieves outstanding MOR performance and high selectivity toward the CO-free pathway. Exploiting the immiscibility between Mn and Bi enables precise regulation of surface-segregated Bi, leading to a well-defined core-shell structure with an ordered L10-PtMn core and a PtBi shell. The catalyst delivers benchmark mass activity of 61.81 A mgPt -1, 4.0 and 16.2 times that of Bi-Pt and Pt/C, respectively. Furthermore, as a practical anodic electrocatalyst for direct methanol fuel cells, the catalyst achieves a peak power density of 294.21 mW cm-2 at an ultralow Pt loading of 0.5 mgPt cm-2. Mn lowers the barrier of the rate-determining step by facilitating C─H bond cleavage, as corroborated by theoretical calculations and kinetic isotope effect (KIE) measurements. This work provides a design principle based on immiscible metal thermodynamics for atomic-level surface engineering of electrocatalysts.