Mesoporous 3D nitrogen-doped yolk-shelled carbon spheres for direct methanol fuel cells with polymer fiber membranes

In recent years, the oxygen reduction reaction (ORR) performance of N-doped carbon catalysts has made great progress and is now comparable to that of commercial Pt/C. However, the rich porous features of N-doped carbon catalysts give them a very low bulk density, which leads to problems in oxygen mass transfer due to water flooding when they are used as the cathode in fuel cells. Herein, a controllable mesoporous surface of nitrogen-doped yolk-shelled carbon spheres (N-YS-CS) with an extremely regular particle size was synthesized. The mesopores of the N-YS-CS effectively store the hydrophobic agent and form robust hydrophobic tunnels within the close-packed N-YS-CS units, forming an excellent structure for mass transfer at the cathode. This elaborately constructed hydrophobic cathode structure has a larger triple-phase interface than traditional carbon paper in an electrolyte-penetration-type direct methanol fuel cell (DMFC) with a polymer fiber membrane (PFM), and delivers a high power density (55 and 142 mW cm⁻² at 25 °C and 60 °C, respectively) and discharge stability (a run time of over 210 h).