The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

Abstract

The performance and stability of a direct methanol fuel cell (DMFC) with membrane electrode assemblies (MEA) using different Nafion ® contents (30, 50 and 70 wt % or MEA30, MEA50 and MEA70, respectively) and graphitized carbon nanofiber (GNF) supported PtRu catalyst at the anode was investigated by a constant current measurement of 9 days (230 h) in a DMFC and characterization with various techniques before and after this measurement. Of the pristine MEAs, MEA50 reached the highest power and current densities. During the 9-day measurement at a constant current, the performance of MEA30 decreased the most (-124 µV h -1 ), while the MEA50 was almost stable (-11 µV h -1 ) and performance of MEA70 improved (+115 µV h -1 ). After the measurement, the MEA50 remained the best MEA in terms of performance. The optimum anode Nafion content for commercial Vulcan carbon black supported PtRu catalysts is between 20 and 40 wt %, so the GNF-supported catalyst requires more Nafion to reach its peak power. This difference is explained by the tubular geometry of the catalyst support, which requires more Nafion to form a penetrating proton conductive network than the spherical Vulcan.Mass transfer limitations are mitigated by the porous 3D structure of the GNF catalyst layer and possible changes in the compact Nafion filled catalyst layers during constant current production.2

Highly efficient cathode catalyst layer based on nitrogen-doped carbon nanotubes for the alkaline direct methanol fuel cell

“…It is evident that the FAA3 content has little effect on the stability of the fuel cell even though the absolute current values vary between the catalysts. This is unlike what was seen with Nafion and carbon nanofiber supported PtRu as DMFC anode, where the stability of the fuel cell increased until 70 wt% ionomer content [83]. The current decrease is slightly larger for MEA20 (49 µA cm -2 h -1 ) than for the other MEAs (43±2 µA cm -2 h -1 ), which could indicate that 20 wt% of FAA3 is not enough to bind the catalyst layer properly together resulting in quicker erosion and delamination during fuel cell use.…”

“…Previous studies have shown that catalysts supported by high aspect ratio carbon materials require high amounts of ionomer in the catalyst layer (>50 wt%) for optimal performance [81][82][83] and that for a H 2 -fueled, FAA3-based fuel cell with a commercial carbon-supported catalyst the optimum ionomer content is around 25 wt% [80].…”

The correlation of electrochemical and fuel cell results for alcohol oxidation in acidic and alkaline media

“…would be more beneficial [39,40]. Nevertheless, the MEA preparation in Publication IV revealed that with nanostructured carbon support the ionomer-carbon ratios are more difficult to control.…”

“…The MEA preparation was more challenging than expected due to the different polarities of the nanocarbon supports resulting as high variation in electrode inks densities. Nevertheless, the aim of Publication IV was to compare different nanocarbon supports with similar loadings and optimization of the PtRu/GNF catalyst electrodes is outlined elsewhere [40]. In Publication IV, the polarization and chronoamperometric measurements for different…”

Enhanced performance of a silicon microfabricated direct methanol fuel cell with PtRu catalysts supported on few-walled carbon nanotubes

“…The sharp peaks at 25.1°, 44.3°, 64.6° and 77.7° correspond to Nafion membrane as we previously measured [36]. Hexagonal carbon peak C(002) at around 26.3° is dominant but other characteristic peaks, C(100) at around 42 ° and C (101) at 45°, overlap with PtRu diffraction pattern and consequently are not well resolved.…”