Studies on nano composites of SPEEK/ethylene glycol/cellulose nanocrystals as promising proton exchange membranes

Alternative proton exchange membrane based on a bicomponent anionic nanocellulose system

As integral parts of fuel cells, polymer electrolyte membranes (PEM) facilitate the conversion of hydrogen's chemical energy into electricity and water. Unfortunately, commercial PEMs are associated with high costs, limited durability, variable electrochemical performance and are based on perfluorinated polymers that persist in the environment. Nanocellulose-based PEMs have emerged as alternative options given their renewability, thermal and mechanical stability, low-cost, and hydrophilicity. These PEMs take advantage of the anionic nature of most nanocelluloses, as well as their facile modification with conductive functional groups, for instance, to endow ionic and electron conductivity. Herein, we incorporated for the first time two nanocellulose types, TEMPO-oxidized and sulfonated, to produce a fully bio-based PEM and studied their contribution separately and when mixed in a PEM matrix. Sulfonated nanocellulose-based PEMs are shown to perform similarly to commercial and bio-based membranes, demonstrating good thermal-oxidative stability (up to 190 °C), mechanical robustness (Young's modulus as high as 1.15 GPa and storage moduli >13 GPa), and high moisture-uptake capacity (ca. 6330 % after 48 h). The introduced nanocellulose membranes are shown as promising materials for proton-exchange material applications, as required in fuel cells.

Proton Exchange Membranes from Sulfonated Lignin Nanocomposites for Redox Flow Battery Applications

Redox flow batteries (RFBs) are increasingly being considered for a wide range of energy storage applications, and such devices rely on proton exchange membranes (PEMs) to function. PEMs are high-cost, petroleum-derived polymers that often possess limited durability, variable electrochemical performance, and are linked to discharge of perfluorinated compounds. Alternative PEMs that utilize biobased materials, including lignin and sulfonated lignin (SL), low-cost byproducts of the wood pulping process, have struggled to balance electrochemical performance with dimensional stability. Herein, SL nanoparticles are demonstrated for use as a nature-derived, ion-conducting PEM material. SL nanoparticles (NanoSLs) can be synthesized for increased surface area, uniformity, and miscibility compared with macrosized lignin, improving proton conductivity. After addition of polyvinyl alcohol (PVOH) as a structural backbone, membranes with the highest NanoSL concentration demonstrated an ion exchange capacity of 1.26 meq g-1, above that of the commercial PEM Nafion 112 (0.98 meq g-1), along with a conductivity of 80.4 mS cm-1 in situ, above that of many biocomposite PEMs, and a coulombic efficiency (CE), energy efficiency (EE) and voltage efficiency (VE) of 91%, 68% and 78%, respectively at 20 mA cm-2. These nanocomposite PEMs demonstrate the potential for valorization of forest biomass waste streams for high value clean energy applications.

Advances in the use of cellulose-based proton exchange membranes in fuel cell technology: A review

Fuel cells are electrochemical, ecologically friendly appliances that transform chemical energy into electricity in a clean, simple, and effective manner. With the advancement of technology in the field of computer science, electronic downsizing, and the ongoing need for mobility, the demand for portable energy sources such as fuel cells has considerably increased. The proton exchange membrane, which is designed to be a good conductor for protons while isolating electrons to move from the anode to the cathode, imprinting them an external circuit, and thus creating electricity, is at the heart of such an energy source. Perfluorosulfonic acid-based (NAFION) membranes, first introduced over 50 years ago, are still the state of the art in the field of fuel cell proton exchange membranes today. However, because of the numerous drawbacks connected with the usage of NAFION membranes, the scientific community has shifted its focus to producing new generation membranes based on natural materials, such as cellulose. Therefore, we believe that a review of the most recent studies on the use of cellulose as a material for proton exchange membranes in fuel cells may be very much appreciated by the scientific community.

Recent Developments on Bioinspired Cellulose Containing Polymer Nanocomposite Cation and Anion Exchange Membranes for Fuel Cells (PEMFC and AFC)

Hydrogen fuel cell (FC) technologies are being worked on as a possible replacement for fossil fuels because they produce a lot of energy and do not pollute the air. In FC, ion-exchange membranes (IEMs) are the vital components for ion transport between two porous electrodes. However, the high production cost of commercialized membranes limits their benefits. Various research has focused on cellulose-based membranes such as IEM with high proton conductivity, and mechanical, chemical, and thermal stabilities to replace the high cost of synthetic polymer materials. In this review, we focus on and explain the recent progress (from 2018 to 2022) of cellulose-containing hybrid membranes as cation exchange membranes (CEM) and anion exchange membranes (AEM) for proton exchange membrane fuel cells (PEMFC) and alkaline fuel cells (AFC). In this account, we focused primarily on the effect of cellulose materials in various membranes on the functional properties of various polymer membranes. The development of hybrid membranes with cellulose for PEMFC and AFC has been classified based on the combination of other polymers and materials. For PEMFC, the sections are associated with cellulose with Nafion, polyaryletherketone, various polymeric materials, ionic liquid, inorganic fillers, and natural materials. Moreover, the cellulose-containing AEM for AFC has been summarized in detail. Furthermore, this review explains the significance of cellulose and cellulose derivative-modified membranes during fuel cell performance. Notably, this review shows the vital information needed to improve the ion exchange membrane in PEMFC and AFC technologies.

Current status and future perspectives of proton exchange membranes for hydrogen fuel cells

The world is on the lookout for sustainable and environmentally benign energy generating systems. Fuel cells (FCs) are regarded as environmentally friendly technology since they address a variety of environmental issues, such as hazardous levels of local pollutants, while also delivering economic advantages owing to their high efficiency. A fuel cell is a device that changes chemical energy contained in fuels (such as hydrogen and methanol) into electrical energy. A wide variety of FCs are commercially available; however, proton exchange membranes for hydrogen fuel cells (PEMFCs) have received overwhelming attention owing to their potential to significantly reduce our energy consumption, pollution emissions, and reliance on fossil fuels. The proton exchange membrane (PEM) is a critical element; it is made of semipermeable polymer and serves as a barrier between the cathode and anode during fuel cell construction. Additionally, membranes function as an insulator between the cathode and anode, facilitating proton exchange and inhibiting electron exchange between the electrodes. Due to the excellent features such as durability and proton conductivity, Nafion membranes are commercially viable and have been in use for a long time. However, Nafion membranes are costly, and their proton exchange capacities degrade over time at higher temperatures and low relative humidity. Other types of membranes have been considered in addition to Nafion membranes. This article discusses the problems connected with several types of PEMs, as well as the strategies adopted to improve their characteristics and performance.

MXene potassium titanate nanowire/sulfonated polyether ether ketone (SPEEK) hybrid composite proton exchange membrane for photocatalytic water splitting

A cross-linked sulfonated polyether ether ketone (C-SPEEK) was incorporated with MXene/potassium titanate nanowire (MKT-NW) as a filler and applied as a proton exchange membrane for photocatalytic water splitting. The prepared hybrid composite PEM had proton conductivity of 0.0097 S cm⁻¹ at room temperature with an ion exchange capacity of 1.88 meq g⁻¹. The hybrid composite proton exchange membrane is a reactive membrane which was able to generate hydrogen gas under UV light irradiation. The efficiency of hydrogen gas production was 0.185066 μmol within 5 h for 12% wt of MKT-NW loading. The results indicated that the MKT-NW/C-SPEEK membrane is a promising candidate for ion exchange with hydrogen gas evolution in photocatalytic water splitting and could be applied as a renewable source of energy to use in various fields of applications.

A cross-linked sulfonated polyether ether ketone (C-SPEEK) was incorporated with MXene/potassium titanate nanowire (MKT-NW) as a filler and applied as a proton exchange membrane for photocatalytic water splitting.

Acid–base core–shell microspheres are incorporated into proton exchange membranes to effectively alleviate the rapid decline in proton conductivity at low humidity

The development of a proton exchange membrane (PEM) that can avoid rapid decay of proton conductivity under low humidity is of great significance for the practical application of PEMFC. In this study, acid–base core–shell microspheres (PCSMs-MA@TAC) with a carboxylic acid core and a triazine shell were synthesized by distillation-precipitation polymerization using cross-linked carboxylic acid microspheres (PMAA) as seeds. These PCSMs were then incorporated into a sulfonated poly(ether ether ketone) matrix to make hybrid membranes. Incorporation of PCSMs microspheres can not only strengthen the vehicle mechanism by increasing the water uptake of the membrane, but also the acid–base pairs formed at the SPEEK/PCSMs interface provide a new low-energy barrier pathway for proton hopping, thereby enhancing the proton conduction of the Grotthuss mechanism. The results show that when the content is 10 wt%, the proton conductivity of the SPEEK/PCSMs-MA@TAC composite membrane can reach 0.161 S cm−1 at 80°C and 100% RH, which is 19.3% higher than the SPEEK control membrane (0.135 S cm−1). In particular, even at 60% RH, the proton conductivity of the SPEEK/PCSMs-MA@TAC-10 composite membrane is still 67 mS cm−1, which is 3.16 times higher than that of the SPEEK membrane. Therefore, the SPEEK/PCSMs-MA@TAC composite membrane can maintain superior performance even under high temperature and low humidity conditions.

Constructing anhydrous proton exchange membranes based on cadmium telluride nanocrystal-doped sulfonated poly(ether ether ketone)/polyurethane composites

Cadmium telluride (CdTe) nanocrystals with thiol stabilizers have been applied widely in the fields of energy storage and transformation. The aim of this work is to develop anhydrous proton exchange membranes (PEMs) by introducing CdTe nanocrystals bearing thioglycolic acid (tga) or mercaptopropionic acid (mpa) stabilizers into sulfonated poly(ether ether ketone) (SPEEK) and polyurethane (PU) systems. In the prepared SPEEK/PU/CdTe membranes, CdTe nanocrystals could provide desirable properties such as improving mechanical strength and enhancing proton conductivity by combining with phosphoric acid (PA) molecules. Successful preparation of SPEEK/PU/CdTe/PA membranes was demonstrated by the identification of high and stable proton conductivity and satisfactory thermal/chemical stability and mechanical properties. The fine appearance of membranes revealed uniform dispersion of components. Measurements of properties showed that the SPEEK(74%)/PU/CdTe-mpa(20/60/20)/100%PA membrane as a candidate anhydrous PEM is promising for use in high-temperature proton exchange membrane fuel cells. Specifically, the recommended membrane showed a proton conductivity of 1.18 × 10^-1 S cm^-1 at 160 °C and 3.96 × 10^-2 S cm^-1 at 100 °C, lasting for 600 h, and a tensile stress of 14.6 MPa at room temperature. Mixing inorganic CdTe nanocrystals with polymers to form inorganic/organic composite membranes is effective for producing anhydrous PEMs with cheaper polymers without functional groups to conduct protons.

R, M. K, Y. WW, J. P. Recent Progress in the Development of Aromatic Polymer-Based Proton Exchange Membranes for Fuel Cell Applications

Proton exchange membranes (PEMs) play a pivotal role in fuel cells; conducting protons from the anode to the cathode within the cell's membrane electrode assembles (MEA) separates the reactant fuels and prevents electrons from passing through. High proton conductivity is the most important characteristic of the PEM, as this contributes to the performance and efficiency of the fuel cell. However, it is also important to take into account the membrane's durability to ensure that it canmaintain itsperformance under the actual fuel cell's operating conditions and serve a long lifetime. The current state-of-the-art Nafion membranes are limited due to their high cost, loss of conductivity at elevated temperatures due to dehydration, and fuel crossover. Alternatives to Nafion have become a well-researched topic in recent years. Aromatic-based membranes where the polymer chains are linked together by aromatic rings, alongside varying numbers of ether, ketone, or sulfone functionalities, imide, or benzimidazoles in their structures, are one of the alternatives that show great potential as PEMs due totheir electrochemical, mechanical, and thermal strengths. Membranes based on these polymers, such as poly(aryl ether ketones) (PAEKs) and polyimides (PIs), however, lack a sufficient level of proton conductivity and durability to be practical for use in fuel cells. Therefore, membrane modifications are necessary to overcome their drawbacks. This paper reviews the challenges associated with different types of aromatic-based PEMs, plus the recent approaches that have been adopted to enhance their properties and performance.

Nanocellulose applications in sustainable electrochemical and piezoelectric systems: A review

Recent studies advocate the use of cellulose nanomaterials (CNs) as a sustainable carbohydrate polymer in numerous innovative electronics for their quintessential features such as flexibility, low thermal expansion and self-/directed assembly within multiphase matrices. Herein, we review the contemporary advances in CN-built electrochemical systems and highlight the constructive effects of these nanoscopic entities once engineered in conductive composites, proton exchange membranes (PEMs), electrochromics, energy storage devices and piezoelectric sensors. The adopted strategies and designs are discussed in view of CN roles as copolymer, electrolyte reservoir, binder and separator. Finally, physiochemical attributes and durability of resulting architectures are compared to conventional materials and the possible challenges/solutions are delineated to realize the promising capabilities. The volume of the up-to-present literature in the field indeed implies to nanocellulose overriding importance and the presented angles perhaps shed more lights on prospect of the biosphere's most dominant biomaterial in the energy-related arena that deserve attention.