A highly crystalline multimetallic nanoframe with a three-dimensional electrocatalytic surface was synthesized by transforming PtNi3 polyhedra into Pt3Ni nanoframes through interior erosion. The resulting nanoframes have a Pt-Skin surface structure that enhances oxygen reduction reaction (ORR) activity. The nanoframes exhibit over 36-fold and 22-fold improvements in mass and specific activities compared to Pt/C catalysts. The nanoframes maintain high crystallinity and have a unique 24-edge structure with a diameter of approximately 2 nm. The Pt-Skin surface structure is formed through controlled thermal treatment and is supported by XPS and EDX analyses. The nanoframes show excellent durability, retaining activity after 10,000 potential cycles. The open architecture of the nanoframes allows for access to both internal and external surfaces, enhancing catalytic performance. The nanoframes also show enhanced HER activity when modified with Ni(OH)2 clusters. The synthesis method can be generalized to other multimetallic nanoframe systems. The study highlights the importance of structural evolution in designing efficient electrocatalysts.A highly crystalline multimetallic nanoframe with a three-dimensional electrocatalytic surface was synthesized by transforming PtNi3 polyhedra into Pt3Ni nanoframes through interior erosion. The resulting nanoframes have a Pt-Skin surface structure that enhances oxygen reduction reaction (ORR) activity. The nanoframes exhibit over 36-fold and 22-fold improvements in mass and specific activities compared to Pt/C catalysts. The nanoframes maintain high crystallinity and have a unique 24-edge structure with a diameter of approximately 2 nm. The Pt-Skin surface structure is formed through controlled thermal treatment and is supported by XPS and EDX analyses. The nanoframes show excellent durability, retaining activity after 10,000 potential cycles. The open architecture of the nanoframes allows for access to both internal and external surfaces, enhancing catalytic performance. The nanoframes also show enhanced HER activity when modified with Ni(OH)2 clusters. The synthesis method can be generalized to other multimetallic nanoframe systems. The study highlights the importance of structural evolution in designing efficient electrocatalysts.