Electrocatalytic activities of 3D GB-Pt scaffolds for MOR. (a) Cyclic voltammograms (CVs) tested in 0.5 M H2SO4 electrolyte at 10 mV s-1. (b) CVs tested in 0.5 M H2SO4 and 1 M methanol electrolyte with 20 mV s-1. (c) Comparative Pt mass activity and specific activity of 3D GB-Pt scaffolds, Pt rods, and Pt/C electrocatalysts. (d) Relationship between grain boundary density and MOR mass activity of 3D GB-Pt scaffolds, showing that the electrocatalytic activities are linearly proportional to the densities of grain boundaries. (e) CVs of 3D GB-Pt scaffolds, Pt rods, and Pt/C before and after 5000 CV cycles, showing an excellent durability of the 3D GB-Pt scaffolds. (f) Nyquist plots of 3D GB-Pt scaffolds, Pt rods, and Pt/C electrocatalysts for methanol oxidation at 0.4 V.