Nanoporous Covalent Organic Framework and Polybenzimidazole Composites for Proton Exchange Membranes

Abstract

Fabrication and design of proton conduction nanochannels within the solid electrolyte materials is pivotal and challenging in order to develop an efficient proton exchange membrane (PEM) for the use in fuel cells. To address this, we have synthesized a melamine-based Schiff base network type porous covalent organic framework (MCOF) and impregnated phosphoric acid (H3PO4) as the electrolyte into the pores of the MCOF via the vacuum-assisted method. Unfortunately, a stable membrane did not form from H3PO4-loaded MCOF (P@MCOF), and hence, in order to make a strong membrane, mixed matrix membranes (MMMs) were fabricated using P@MCOF as nanofillers and [2,2′-(m-phenylene)-5,5′-benzimidazole] or m-PBI as the membrane forming polymer matrix. Formation of acid base pair occurred in the m-PBI-P@MCOF nanocomposite membrane owing to H-bonding interactions between the filler and polymer. Also, the acidic functionalities in the pores of P@MCOF provides abundant sites for labile proton transport, which enables uninterrupted proton conduction ion channels with low energy barrier in the nanocomposite membranes. Furthermore, all the composite membranes were immersed and loaded with phosphoric acid (PA) to increase electrolyte contents in the resulting MMM-based PEM. Superior proton conductivity, excellent thermal, thermo-mechanical and tensile strength, improved acid (PA) holding efficiency, and improved chemical stability of these PEMs, obtained from MMMs of m-PBI-P@MCOF, were observed in comparison with the PEM of pristine m-PBI. The proton conductivity of m-PBI-P@MCOF-10% membrane at 180 °C is 0.309 S cm–1, a five-fold increment with respect to pristine m-PBI proton conductivity (0.061 S cm–1) under the identical experimental condition. This work clearly illustrates the nature of H-bonded interactions between the nanofillers and polymers which efficiently enhanced proton conduction along with chemical and mechanical durability in the MMM materials.

Mixed Matrix Membranes Fabricated from Nanofillers of a Porous Organic Polymer for Applications as Proton Exchange Membranes

“…This is due to the fact that the OPBI-TBP composites can generate substantial H-bonding interaction with PA through the imidazole ‘–N’ and “N–H” functional groups present in the TBP POPs, along with the imidazole ‘–N’ and “N–H” groups of the OPBI polymer. A similar inference was made earlier by us for synthetically modified MOF and COF-loaded PBI composite membranes. , …”

“…The ion-conducting nanochannels within the MMM network undergo extensive H-bonding, which is responsible for the proton hopping mechanism to imply. 44,60 The composite membrane activation energy plot finds some irregularities from linear shape in a similarity with previous reports, due to the partially operated vehicular mechanism as well. 44,61 Stress−strain Profile of the OPBI-TBP Membranes.…”

“…The appearance of the five newly developed peaks (between 2θ range 8−19°) in the case of MMMs indicates the semicrystalline nature of the composite material and also suggests the presence of interactions in the interfacial region of the MMMs, which is in agreement with earlier reports. 38,39,41,43,44 The * marked semicrystalline peaks also resulted in increased peak intensity in the OPBI-TBP-7% and OPBI-TBP-10% membranes due to the higher TBP loading.…”

“…A similar inference was made earlier by us for synthetically modified MOF and COF-loaded PBI composite membranes. 44,46 To evaluate the efficiency of the OPBI-TBP MMMs toward a severe oxidative environment, all the membranes were kept immersed in Fenton's reagent (which is a composition of 3% H 2 O 2 in 2 ppm FeSO 4 ) for 100 h at 70 °C. From the weight differences of the MMMs before and after treatment with Fenton's reagent, the remaining wt % was calculated, and from this membrane weight loss calculation, the oxidative stability of the MMMs was measured as a function of time and plotted in Figure 4A.…”

Sulfonated Cobalt Metal–Organic Framework Embedded Mixed Matrix Membrane towards Fuel-Cell Applications

“…Fuel cells are widely used due to their high efficiency and rapid startup as well as their desirable power density. Additionally, fuel cells provide complete power operation throughout the shift without any voltage sag and faster refueling, which saves time. , The most broadly used fuel cell type for automotive and portable applications is the polymer electrolyte membrane fuel cell (PEMFC), which consists of an electrolyte, an anode, and a cathode. Protons are transported in the PEMFC from the anode to the cathode using a proton-exchange or polymer electrolyte membrane (PEM), which prevents fuel from passing through the membranes.…”