Fabrication of nano-network structure anode by zinc oxide nanorods template for passive direct methanol fuel cells

• ZnO nanorods are used as efficient sacrificial template to fabricate nano-network structure (NNS) within anode.
• The DMFC with 50% reduced anode catalyst loading exhibits an enhanced performance.
• The DMFC with NNS exhibits a significant increase in catalyst utilization and mass transfer efficiency.

In this study, zinc oxide (ZnO) nanorods were used as efficient sacrificial template to fabricate nano-network structure (NNS) within anode catalyst layer (CL) and micro-porous layer (MPL) of a membrane electrode assembly (MEA). It resulted in a significant reduction of noble metal catalyst loading and enhancement of performance of a passive direct methanol fuel cell (DMFC). At a Pt–Ru loading of 1.0 mg cm−2, the MEA with NNS in anode CL exhibited a maximal power density of 28.4 mW cm−2 using 2 M methanol solution as fuel at 25 °C. However, for the conventional MEA with a Pt–Ru loading of 2.0 mg cm−2, the maximal power density was 29.0 mW cm−2. With the increase in Pt–Ru loading to 2.0 mg cm−2, the maximal power densities of the MEAs with NNS in anode CL and in both anode CL and MPL reached 38.6 and 40.2 mW cm−2, respectively. The improved performance of the MEAs with NNS was attributed to its property of higher catalyst utilization, higher mass transfer efficiency, and lower charge-transfer resistance compared to the conventional MEAs. However, the construction of NNS within both anode CL and MPL led to a relatively serious problem of cathode flooding, which restrained the further improvement in DMFC's performance. This study provided a perspective to fabricate novel pore structure to obtain high performance of passive DMFCs with low noble metal catalyst loading and low concentration methanol solution.