Domain Size Manipulation of Perflouorinated Polymer Electrolytes by Sulfonic Acid-Functionalized MWCNTs To Enhance Fuel Cell Performance

Abstract

The application of sulfonic acid-functionalized multiwalled (s-MWNT) carbon nanotubes to manipulate the hydrophilic domain size of Nafion membranes is explored here as an option for tuning the proton conductivity of polymer electrolyte membranes for hydrogen-oxygen fuel cells. The electrochemical impedance experiments provide preliminary evidence of increased proton conductivity, while small-angle X-ray scattering measurements line out enhanced ionic cluster domain size in these composite membranes as the central reason for higher conductivity (70 A for the optimum composite membrane vs 50 A for Nafion 115) values. Scanning electrochemical microscopy indicates synergistic interaction between the sulfonic acid functional groups present in the Nafion membrane and those on the nanotube surface. More interestingly, the nanotube-tailored Nafion membranes ameliorate the performance of fuel cells as confirmed by measurements at a single-cell level, which reveal a maximum power density of 380 mW cm(-2), higher than those of Nafion 115 (250 mW cm(-2)) and recast Nafion (230 mW cm(-2)) membranes. Thus, in addition to providing an elegant means of controlling the ionic cluster size, the strategic approach of using CNT both as an anchoring backbone for -SO(3)H groups to enrich proton conductivity and as a blending agent to improve the mechanical characteristics of the Nafion phase might be helpful in alleviating many critical problems associated with the use of commercial Nafion membranes.

A polybenzimidazole/ionic-liquid-graphite-oxide composite membrane for high temperature polymer electrolyte membrane fuel cells

“…From the plot of the IR corrected voltage vs. log (current density I), the slopes (Tafel type) of the line of PBI and QPBI are approximately 92 mV and 100 mV per decade at PRU of 3.5 and 2.0, respectively. The values are close to the literature reported values (100 mV dec À1 ) on oxygen reduction reaction (ORR) electrodes for phosphoric-acid loaded PBI fuel cells [22,23].…”

“…Catalyst inks were prepared by blending carbon supported catalysts (50 wt.% Pt/C, Alfa Aesar) and polytetrafluoro-ethylene (PTFE, 60 wt.% Aldrich) in a watereethanol mixture under ultrasonic vibration for 10 min [23,24]. Gas diffusion electrodes (carbon paper) incorporated with wet proofed micro-porous layer (H2315 T10AC1) obtained from Freudenburg (FFCCT, Germany) were used as substrates to deposit the catalyst layer for both the anode and the cathode.…”

Microstructure-Property Relationships in Sulfonated Polyether Ether Ketone/Silsesquioxane Composite Membranes for Direct Methanol Fuel Cells

“…SAXS, a nondestructive structural probe, provides statistically significant morphological information about phase-separated polymers. [44][45][46] More details related to various aspects of SAXS analysis of polymers are covered in these review articles. 47,48 The morphologies of the pristine SPEEK and SPEEK composite membranes are reflected by the combined SAXS data, which are shown in Figure 2.…”

The Separation Power of Nanotubes in Membranes: A Review

“…For proton electrolyte membrane fuel cells (PEMFCs) Kannan et al [187] report on the use of a Nafion-based nanocomposite membrane with inclusion of sulfonic acidfunctionalized multiwalled (s-MWNT) carbon nanotubes into the polymer matrix. They observed an improved proton conductivity, which was related to the presence of sulfonic acid groups, with nanotubes as an anchoring backbone and to improve mechanical properties of the membrane.…”