Intermetallic Pt₃In concave tetrahedra for oxygen reduction electrocatalysis in proton exchange membrane fuel cells

Scaling proton exchange membrane fuel cells (PEMFCs) demands efficient and durable electrocatalysts for the cathodic oxygen reduction reaction (ORR). Concave surfaces and intermetallic phases have been proven to promote the activity and stability of Pt-based catalysts, yet integrating these two structural features in one catalyst remains challenging. Herein, we achieve this in a class of intermetallic, concave tetrahedral Pt₃In (i-ct-Pt₃In), through a sequential Pt(111)-selective wet-chemical etching and indium-enabled morphology-preservable annealing. The i-ct-Pt₃In/C catalyst delivers a mass activity of 2.49 A mg_Pt^-1 in acidic media, preserving 97.8% of its activity after 30,000 cycles. In phosphate-containing electrolytes, it achieves a mass activity of 0.3 A mg_Pt^-1, representing a 7.5-fold improvement over commercial Pt/C and translating to a peak power density of 1.0 W cm^-2 in a high-temperature PEMFC at 160 °C. Theoretical calculations verify weakened adsorption of oxygenates and phosphate anions on concave Pt₃In(111) relative to flat Pt(111), accounting for enhanced ORR kinetics and phosphate tolerance. This work highlights the potential of ordering morphological nanocrystals for energy electrocatalysis.