Characterization of PBI/Graphene Oxide Composite Membranes for the SO2 Depolarized Electrolysis at High Temperature

Abstract

In this work, polybenzimidazole (PBI) membranes with different graphene oxide (GO) contents (0.5, 1.0, 2.0, and 3.0 wt %) as organic filler have been prepared. The X-ray diffraction confirms the incorporation of the filler into the polymeric membrane. The composite GO-based PBI membranes show better proton conductivity at high temperature (110–170 °C) than the pristine one. Moreover, the hydrophobicity of the PBI membranes is also improved, enhancing water management. The chemical stability demonstrates the benefit of the incorporation of GO in the PBI matrix. What is more, the composite PBI-based membranes show better phosphoric acid retention capability. For the first time, the results of the SO2-depolarized electrolysis for hydrogen production at high temperature (130 °C) using phosphoric acid-doped polybenzimidazole (PBI) membranes with the different GO contents are shown. The benefit of the organic filler is demonstrated, as H2SO4 production is 1.5 times higher when the membrane with a content of 1 wt % of GO is used. Moreover, three times more hydrogen is produced with the membrane containing 2 wt % of GO compared with the non-modified membrane. The obtained results are very promising and provide open research for this kind of composite membranes for green hydrogen production by the Westinghouse cycle.

Enhancement of the Green H2 Production by Using TiO2 Composite Polybenzimidazole Membranes

“…Thus, adding a filler created a more compact structure capable of protecting the polymer chains from the attack of the sulfate radicals. These results are in line with the addition of other fillers to the PBI matrix which also increase it chemical stability [ 28 ].…”

“…Even though obtaining high current densities is of importance for the operation of the electrolyzer, as it gives an idea of the reaction rate, the most essential parameter is the production of hydrogen, as its obtention is the purpose of the water molecule splitting processes. However, this production of hydrogen has never been reported for other HyS works, except for our previous work [ 28 ]. Figure 5 shows the actual production of hydrogen as function of temperature and the Faradaic efficiency for each of the employed membranes.…”

“…The higher value in the resistance measured for the membrane with a TiO 2 content of 0.5 wt% can be explained by a low acid retention which, in turn, causes an increase in resistance over the course of the experiment. It can be observed that temperature does not play a relevant role for the ohmic resistance, in fact, the formation of elemental sulfur (Equations (7) and (9)) could minimize the beneficial effect of temperature [ 14 , 28 ]. Regarding the charge transfer resistance, the obtained results help to understand the trend of the linear sweep voltammetries reported in Figure 4 .…”

“…The composite membranes containing TiO 2 were prepared with contents of TiO 2 from 0.5% to 3% (0.5, 1.0, 2.0, and 3.0 wt%) by the solvent casting method as described elsewhere [ 28 ]. Briefly, TiO 2 nanoparticles were dispersed in DMAc for 15 min in an ultrasound bath.…”

“…Furthermore, in a previous work, we employed an organic filler to prepare composite Graphene oxide/PBI membranes which were tested up to 140 °C, showing a superior performance when the GO content was 2.0 wt% in terms of reached current density and hydrogen production [ 28 , 29 ]. In this regard, inorganic fillers have also proven to be a good candidate to be used in proton exchange membranes at high temperature.…”