Enhanced Proton Conductivity in Sulfonated Poly(ether ether ketone) Membranes by Incorporating Sodium Dodecyl Benzene Sulfonate

Abstract

It is of great importance to improve the proton conductivity of proton exchange membranes by easy-handling and cost-efficient approaches. In this work, we incorporated a commercially obtained surfactant, sodium dodecyl benzene sulfonate (SDBS), into sulfonated poly(ether ether ketone) (SPEEK) through solution casting to prepare SPEEK/SDBS membranes. When no more than 10 wt % SDBS was added, the SDBS was well dissolved into the SPEEK matrix, and the activation energy for the proton transfer in the SPEEK/SDBS membranes was greatly reduced, leading to significant enhancement of the membrane proton conductivity. Compared with the SPEEK control membrane, the SPEEK/SDBS membrane with 10 wt % SDBS showed a 78% increase in proton conductivity, up from 0.051 S cm−1 to 0.091 S cm−1, while the water uptake increased from 38% to 62%. Moreover, the SPEEK/SDBS membrane exhibited constant proton conductivity under a long-term water immersion test.

Proton Conductivity through Polybenzimidazole Composite Membranes Containing Silica Nanofiber Mats

“…On the other hand, protons can move via the vehicle mechanism through the hydroxyl, amine or sulfonic groups from the different nanofiber functionalization and imidazole groups present in the PBI, which may interact with water molecules, promoting the proton conductivity. It is also noteworthy that all membranes containing nanofiber mats have lower activation energies than pristine PBI membranes and also lower than hydrated membranes of SPEEK reinforced membranes which values are compress between 9.5 and 48 kJ·mol −1 depending on water content and acid dopant concentration [71,72,73]. On the other hand, activation energies under dry conditions support the proton conduction is mainly due according to a vehicular mechanism, as inferred from the calculated activation energies, with values higher than 55 kJ·mol −1 .…”

Effect of Sulfonation Degree and PVDF Content on the Structure and Transport Properties of SPEEK/PVDF Blend Membranes

“…Sulfonation of PEEK was carried out using concentrated sulfuric acid according to the following procedure: 15 g dried PEEK was entirely dissolved in 300 mL concentrated sulfuric acid (98%) by stirring at 800 rpm at room temperature for a certain period of time before the solution was dumped into the ice/water mixture to precipitate the sulfonate polymer (SPEEK), which were repeatedly washed with deionized (DI) water until the pH reach 7. Then SPEEK was dried in the convection oven at 80 °C for 24 h. By using the titration method according to the literature [13,25], the ion exchange capacities (IECs) and SDs of the prepared SPEEK were determined, and the results are listed in Table 1.…”

“…Studies have shown that PEMs based on sulfonated aromatic hydrocarbon polymers exhibit proton conductivities comparable to Nafion and could become the alternatives to Nafion [9,10,11,12]. Among them, sulfonated poly (ether ether ketone) (SPEEK) has great potential due to its excellent mechanical properties, good chemical resistance, and low cost [13,14]. Unfortunately, large swelling in methanol remains a problem for SPEEK membranes.…”

Performance of Polymer Electrolyte Membrane for Direct Methanol Fuel Cell Application: Perspective on Morphological Structure

“…Essentially, the Grotthuss mechanism offers the diffusivity of protons through a fixed negatively charged ion on the polymer backbone, i.e., Nafion. On the other hand, the vehicle mechanism depends mainly on the free-water molecules as a transportation agent [82][83][84]. From Figure 11, it can be clearly observed that the transport process of a proton occurs simultaneously by bulk and surface transport mechanisms [40].…”