Shape-controlled porous heterogeneous PtRu/C/Nafion microspheres enabling high performance direct methanol fuel cells
An anode catalytic layer for direct methanol fuel cells (DMFCs) with decreased PtRu loading as low as 1.0 mg cm−2 has been prepared by an electrospray method. The morphology of the electrosprayed composite of PtRu/C/Nafion/polyethylene oxide (PEO) is altered from irregular particles to porous microspheres and to nanofibers by adjusting the PEO content. A hybrid structure is assembled using the porous microspheres as the anode catalytic layer for DMFCs, leading to a remarkable enhancement in the maximum power density of 35.4 mW cm−2, which is ∼50% higher than that of the conventional one at the same PtRu loading of 1.0 mg cm−2 and is even comparable to that (31.5 mW cm−2) of the conventional one at a higher PtRu loading of 2.0 mg cm−2. Further investigation reveals that the improved performance is mainly attributed to its hierarchical factual structure. In the primary structure, a single microsphere is with well-distributed PtRu/C and is fully rich in nano-pores and nano-channels, resulting in an increase in the electrochemical active surface area and higher catalyst utilization. In the secondary structure, micro-sized pathways are formed by the stereoscopic microspheres, resulting in enhanced mass transport, higher current density and power density.