Titanium Dioxide Grafted on Graphene Oxide: Hybrid Nanofiller for Effective and Low-Cost Proton Exchange Membranes

Abstract

A nanostructured hybrid material consisting of TiO2 nanoparticles grown and stabilized on graphene oxide (GO) platelets, was synthesized and tested as nanofiller in a polymeric matrix of sulfonated polysulfone (sPSU) for the preparation of new and low-cost nanocomposite electrolytes for proton exchange membrane fuel cell (PEMFC) applications. GO-TiO2 hybrid material combines the nanoscale structure, large interfacial area, and mechanical features of a 2D, layered material, and the hygroscopicity properties of ceramic oxides, able to maintain a suitable hydration of the membrane under harsh fuel cell operative conditions. GO-TiO2 was synthetized through a new, simple, one-pot hydrothermal procedure, while nanocomposite membranes were prepared by casting using different filler loadings. Both material and membranes were investigated by a combination of XRD, Raman, FTIR, thermo-mechanical analysis (TGA and Dynamic Mechanical Analysis) and SEM microscopy, while extensive studies on the proton transport properties were carried out by Electrochemical Impedance Spectroscopy (EIS) measurements and pulse field gradient (PFG) NMR spectroscopy. The addition of GO-TiO2 to the sPSU produced a highly stable network, with an increasing of the storage modulus three-fold higher than the filler-free sPSU membrane. Moreover, the composite membrane with 3 wt.% of filler content demonstrated very high water-retention capacity at high temperatures as well as a remarkable proton mobility, especially in very low relative humidity conditions, marking a step ahead of the state of the art in PEMs. This suggests that an architecture between polymer and filler was created with interconnected routes for an efficient proton transport.

Applications of Ceramic/Graphene Composites and Hybrids

“…It also improved mass transfer, compared to a layer by layer rGO electrode, augmenting Pt dispersion and increasing oxidation resistance as well. Regarding the electrolyte membrane, Simari et al [ 85 ] synthesized a composite of TiO 2 @GO with sulfonated polysulfone as an alternative to the most common Nafion membrane, which may dehydrate easily reducing proton conductivity. The composite showed 22% higher water uptake and 5% higher ion exchange capacity, with the TiO 2 @GO hybrid limiting the degradation of sulfonic acid groups.…”

Nanocomposite Membranes for PEM-FCs: Effect of LDH Introduction on the Physic-Chemical Performance of Various Polymer Matrices

“…X-ray diffraction (XRD) measurements were performed using the Cu-Kα radiation of a Bruker Axis Diffractometer/Reflectometer (D8) equipped with a Dynamic Scintillation Detector, NaI, and with a Göbel mirror [ 61 ]. Spectra were collected at room temperature in the 2θ range from 5° to 40°, in steps of 0.03°, and the counting time was 1 s/step [ 47 ].…”

“…For this study, LDH based on Mg 2+ /Al 3+ (2:1 metals ratio) with NO 3 − interlayer anion was chosen and membranes at 3 wt.% of filler loading with respect to the polymer were prepared by simple solution intercalation. According to the literature, 3 wt.% of loading has been demonstrated to be the optimal one in most of the nanocomposite systems and for various types of inorganic materials [ 45 , 46 , 47 , 48 , 49 ]. Additionally, during our previous works, we have demonstrated that the introduction of 3 wt.% of LDH material can ensure the maximum improvement in terms of transport properties, conductivity values, and mechanical properties either in the case of Nafion-based [ 50 ], sPEEK-based [ 51 ], and sPSU-based [ 46 ] composite membranes.…”

Sulfonated Polyether Ether Ketone and Organosilica Layered Nanofiller for Sustainable Proton Exchange Membranes Fuel Cells (PEMFCs)

“…For each membrane, the dumping factor plot exhibits a single peak, which can be assigned to the α transition (T g ) of the ionic clusters of the polymer. While Nafion [36] exhibits a T g of ca. 120 • C, the α-transition for SPEEK is shifted at remarkably higher temperatures, i.e., above 200 • C. This indicates this polyaromatic polymer can definitively withstand higher operating temperatures with respect to the Nafion benchmark.…”