In-situ strategies for melamine-functionalized graphene oxide nanosheets-based nanocomposite proton exchange membranes in wide-temperature range applications

The traditional preparation of nanocomposite proton exchange membranes (PEM) is hindered by poor organic-inorganic interface compatibility, insufficient proton-conducting sites, easy aggregation of nanoparticles, and difficulty in leveraging nanoscale advantages. In this study, a novel method involving electrochemical anodic oxidation exfoliation was employed to prepare melamine-coated graphene oxide (Me@GO), which was subsequently subjected to in-situ polymerization with poly(2,5-benzimidazole) (ABPBI) to prepare a Me@GO/ABPBI composite proton exchange membrane. Benefiting from the strong hydrogen bonding and large π stacking interactions, melamine (Me) tightly bound to graphene oxide (GO), effectively preventing the secondary aggregation of GO after exfoliation. Moreover, the abundant alkaline functional groups of melamine enhanced the enhancement of phosphoric acid (PA) retention in the Me@GO/ABPBI membranes, thereby increasing the number of proton-conducting sites. The experimental results indicated that the introduction of Me@GO enhanced membrane properties. For Me@GO at a concentration of 1 wt%, the tensile strength of the 1Me@GO/ABPBI composite membrane reached 207 MPa, nearly 2.52 times that of the pure membrane. The proton conductivity of the 1Me@GO/ABPBI composite membrane reached 0.01 S cm-1 across a wide temperature range (40-180 °C), peaking at 0.087 S cm-1 at 180 °C. Additionally, a single-cell incorporating the 1Me@GO/ABPBI composite membrane achieved a peak power density of 0.304 W cm-2 at 160 °C, nearly 1.46 times that of the pure membrane. Benefiting from the well-dispersed and PA-enriched proton channels provided by Me@GO, the Me@GO/ABPBI composite membrane exhibits excellent prospects for wide-temperature range (40-180 °C) applications.

PAF-6 Doped with Phosphoric Acid through Alkaline Nitrogen Atoms Boosting High-Temperature Proton-Exchange Membranes for High Performance of Fuel Cells

High-temperature proton-exchange-membrane fuel cells (HT-PEMFCs) can offer improved energy efficiency and tolerance to fuel/air impurities. The high expense of the high-temperature proton-exchange membranes (HT-PEMs) and their low durability at high temperature still impede their further practical applications. In this work, a phosphoric acid (PA)-doped porous aromatic framework (PAF-6-PA) is incorporated into poly[2,2'-(p-oxydiphenylene)-5,5'-benzimidazole] (OPBI) to fabricate novel PAF-6-PA/OPBI composite HT-PEMs through solution-casting. The alkaline nitrogen structure in PAF-6 can be protonated with PA to provide proton hopping sites, and its porous structure can enhance the PA retention in the membranes, thus creating fast pathways for proton transfer. The hydrogen bond interaction between the rigid PAF-6 and OPBI can also enhance the mechanical properties and chemical stability of the composite membranes. Consequently, PAF-6-PA/OPBI exhibits an optimal proton conductivity of 0.089 S cm-1 at 200 °C, and peak power density of 437.7 mW cm-2 (Pt: 0.3 mg cm-2 ), which is significantly higher than that of the OPBI.   The PAF-6-PA/OPBI provides a novel strategy for the practical application of PBI-based HT-PEMs.

Construction of Highly Conductive Cross-Linked Polybenzimidazole-Based Networks for High-Temperature Proton Exchange Membrane Fuel Cells

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are of great interest to researchers in industry and academia because of their wide range of applications. This review lists some creative cross-linked polybenzimidazole-based membranes that have been prepared in recent years. Based on the investigation into their chemical structure, the properties of cross-linked polybenzimidazole-based membranes and the prospect of their future applications are discussed. The focus is on the construction of cross-linked structure of various types of polybenzimidazole-based membranes and their effect on proton conductivity. This review expresses the outlook and good expectation of the future direction of cross-linked polybenzimidazole membranes.

A Novel High Temperature Fuel Cell Proton Exchange Membrane with Nanoscale Phase Separation Structure Based on Crosslinked Polybenzimidazole with Poly(vinylbenzyl chloride)

A semi-aromatic polybenzimidazole (DPBI) is synthesized via polycondensation of decanedioic acid (DCDA) and 3,3-diaminobenzidine (DAB) in a mixed phosphorus pentoxide/methanesulfonic acid (PPMA) solvent. Ascribing to in-situ macromolecular crosslinker of ploly((vinylbenzyl chloride) (PVBC), a robust crosslinked DPBI membrane (DPBI-xPVBC, x refers to the weight percentage of PVBC in the membrane) can be obtained. Comprehensive properties of the DPBI and DPBI-xPVBC membranes are investigated, including chemical structure, antioxidant stability, mechanical strength, PA uptake and electrochemical performances. Compared with pristine DPBI membrane, the PA doped DPBI-xPVBC membranes exhibit excellent antioxidative stability, high proton conductivity and enhanced mechanical strength. The PA doped DPBI-10PVBC membrane shows a proton conductivity of 49 mS cm^-1 at 160 °C without humidification. Particularly, it reveals an enhanced H₂/O₂ single cell performance with the maximum peak power density of 405 mW cm^-2, which is 29% higher than that of pristine DPBI membrane (314 mW cm^-2). In addition, the cell is very stable in 50 h, indicating the in-situ crosslinked DPBI with a macromolecular crosslinker of PVBC is an efficient way to improve the overall performance of HT-PEMs for high performance HT-PEMFCs.

Real-Time Monitoring of the Temperature, Flow, and Pressure Inside High-Temperature Proton Exchange Membrane Fuel Cells

The proton exchange membrane fuel cell (PEMFC) system is a highly efficient and environmentally friendly energy conversion technology. However, the local temperature, flow, and pressure inhomogeneity within the fuel cell during the electrochemical reaction process may lead to depletion of PEMFC material and uneven fuel distribution, thus affecting the performance and service life of high-temperature PEMFCs. In this study, micromachining technology is used to develop a three-in-one flexible micro-sensor that is resistant to a high-temperature electrochemical environment (120~200 °C). Appropriate materials and process parameters are used to protect the micro-sensor from failure or damage under long-term testing, and to conduct a real-time micro-monitor of the local temperature, flow, and pressure distribution inside high-temperature PEMFCs.

Enhanced proton conductivity of Nafion membrane induced by incorporation of MOF-anchored 3D microspheres: a superior and promising membrane for fuel cell applications

A novel 3D core-shell material composed of polyacrylate carboxyl microspheres (PCMs) and ZIF-8 nanoparticles was used to promote proton conduction in the Nafion matrix. The Nafion/ZIF-8@PCM membranes displayed excellent proton conductivity (0.24 S cm^-1) and physicochemical properties due to special structural characteristics. More importantly, this new concept has a strong practical guiding significance for the fabrication of novel PEMs.

Real-Time Monitoring of HT-PEMFC

During the electrochemical reaction of a high temperature proton exchange membrane fuel cell (HT-PEMFC), (in this paper HT-PEMFC means operating in the range of 120 to 200 °C) the inhomogeneity of temperature, flow rate, and pressure in the interior is likely to cause the reduction of ion conductivity or thermal stability weight loss of proton exchange membrane materials, and it is additionally likely to cause uneven fuel distribution, thereby affecting the working performance and service life of the HT-PEMFC. This study used micro-electro-mechanical systems (MEMS) technology to develop a flexible three-in-one microsensor which is resistant to high temperature electrochemical environments; we selected appropriate materials and process parameters to protect the microsensor from failure or damage under long-term tests. The proposed method can monitor the local temperature, flow rate, and pressure distribution in HT-PEMFC in real time.

Construction of Stable Wide-Temperature-Range Proton Exchange Membranes by Incorporating a Carbonized Metal-Organic Frame into Polybenzimidazoles and Polyacrylamide Hydrogels

Proton exchange membrane fuel cells (PEMFCs) are promising devices for clean power generation in fuel cell electric vehicles applications. The further request of high-efficiency and cost competitive technology make high-temperature proton exchange membranes utilizing phosphoric acid-doped polybenzimidazole be favored because they can work well up to 180 °C without extra humidifier. However, they face quick loss of phosphoric acid below 120 °C and resulting in the limits of commercialization. Herein UiO-66 derived carbon (porous carbon-ZrO₂ ), comprising branched poly(4,4'-diphenylether-5,5'-bibenzimidazole) and polyacrylamide hydrogels self-assembly (BHC1-4) membranes for wide-temperature-range operation (80-160 °C) is presented. These two-phase membranes contained the hygroscopicity of polyacrylamide hydrogels improve the low-temperature proton conductivity, relatively enable the membrane to function at 80 °C. An excellent cell performance of BHC2 membrane with high peak power density of 265 and 656 mW cm^-2 at both 80 and 160 °C can be achieved. Furthermore, this membrane exhibits high stability of frequency cold start-ups (from room temperature to 80 °C) and long-term cell test at 160 °C. The improvement of cell performance and stability of BHC2 membrane indicate a progress of breaking operated temperature limit in existing PEMFCs systems.

A novel green lignosulfonic acid/Nafion composite membrane with reduced cost and enhanced thermal stability

A green biopolymer, lignosulfonate acid (LSA), was first used as an additive in the Nafion membrane for fuel cell applications. The Nafion/LSA composite membrane displayed enhanced thermal stability and other satisfactory properties due to the stable aromatic groups and multiple active sites of LSA. More importantly, the cost-effectiveness and simple fabrication of such novel composite PEMs make their use in PEMFCs very attractive and economical.

A Review of Recent Developments and Advanced Applications of High-Temperature Polymer Electrolyte Membranes for PEM Fuel Cells

This review summarizes the current status, operating principles, and recent advances in high-temperature polymer electrolyte membranes (HT-PEMs), with a particular focus on the recent developments, technical challenges, and commercial prospects of the HT-PEM fuel cells. A detailed review of the most recent research activities has been covered by this work, with a major focus on the state-of-the-art concepts describing the proton conductivity and degradation mechanisms of HT-PEMs. In addition, the fuel cell performance and the lifetime of HT-PEM fuel cells as a function of operating conditions have been discussed. In addition, the review highlights the important outcomes found in the recent literature about the HT-PEM fuel cell. The main objectives of this review paper are as follows: (1) the latest development of the HT-PEMs, primarily based on polybenzimidazole membranes and (2) the latest development of the fuel cell performance and the lifetime of the HT-PEMs.

Advancements in proton exchange membranes for high-performance high-temperature proton exchange membrane fuel cells (HT-PEMFC)

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) offers several advantages, such as high proton conductivity, high CO tolerance, good chemical/thermal stability, good mechanical properties, and low cost. The proton exchange membrane (PEM) is the critical component of HT-PEMFC. This work discusses the methods of current PEMs development for HT-PEMFC including modifications of Nafion® membranes and the advancement in composite PEMs based on non-fluorinated polymers. The modified Nafion®-based membranes can be used at temperatures up to 140 °C. Nevertheless, the application of Nafion®-based membranes is limited by their humidification with water molecules acting as proton carriers and, thus, by the operation conditions of membranes under a relative humidity below 20%. To obtain PEMs applied at higher temperatures under non-humidified conditions, phosphoric acid (PA) or ionic liquids (ILs) are used as proton carriers in PEMs based on non-fluorinated polymers. The research discussed in this work provides the approaches to improving the physicochemical properties and performance fuel cell of PEMs. The effects of polymer blending, crosslinking, and the incorporation of inorganic particles on the membrane properties and fuel cell performance have been scrutinized. The incorporation of inorganic particles modified with ILs might be an effective approach to designing high-performance PEMs for HT-PEMFC.