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Fuel cells are electrochemical devices with high energy efficiency expected to be applied economically and eco-friendly across various energy sectors. Low-temperature polymer electrolyte membrane fuel cells (LT-PEMFCs) using Nafion operates at a relatively low operating temperature (60-80°C) and a full hydration condition. HT-PEMFC is operable at high temperatures (140-180°C), but requires anhydrous conditions to avoid loss of doped phosphoric acid (PA). In this study, polymer membranes designed through with intrinsic microporosity were synthesized through super acid polycondensation. We demonstrated that high proton conductivity (106.33 mS cm-1 at 180℃) is obtained by forming phosphoric acid filled ion-channels within the interconnected microporous structure. Moreover, ion-pair coordinated PIMs are fabricated by methylation of PIMs to improve PA retention even under humidified conditions. It is suggested that the water tolerance of ion-pair coordinated PIMs is improved and can be operated under various conditions regardless of humidification and operating temperature.

A novel inorganic–organic hybrid crosslinker was prepared through synthesis of a fully condensed, high molecular weight ladder-like poly(methacryloxypropyl)silsesquioxane (LPMASQ) in one pot with a facile, base-catalysed system. The fully condensed LPMASQ revealed good thermal (∼380 °C) and electrochemical stability (∼5.0 V) due to the absence of uncondensed silanol groups. LPMASQ also revealed good solubility in various organic solvents and fully gelated 1 M LiPF6 in ethyl carbonate–diethyl carbonate (EC–DEC, 3/7, v/v) electrolyte solution through fast thermal and photocuring even at a very low concentration of 2 wt%. These observations were attributed to the polymeric nature of LPMASQ containing over one hundred methacryl moieties on the rigid double-stranded siloxane backbone. To the best of our knowledge, formation of a gel polymer electrolyte with 2 wt% gelator is the smallest gelation concentration that has ever been reported. This leads to high ionic conductivity (∼6.0 mS cm−1), excellent Coulombic efficiency and battery cell performance, comparable with those of the neat liquid electrolyte. The small crosslinker content, thermal and electrochemical stability, fast thermal and photocuring and facile processing of the LPMASQ based GPEs, as well as excellent Li battery cell performances strongly hold great promise for future industrial battery applications.

Anion exchange membrane fuel cells (AEMFCs) hold the promise of low-cost energy conversion. However, one of the most significant challenges in the development of AEMFCs has been their limited durability, ca. < 1,000 h, when compared to proton exchange membrane fuel cells (PEMFC). The most common explanations for loss in fuel cell performance (AEM degradation, (bi)carbonation, water management, and catalyst aggregation) do not fully explain the irreversible performance degradation that limits the durability of AEMFCs. In our study, we set out to identify the source or causes of that performance loss in AEMFCs. To mitigate known sources of degradation, we applied fully humidified conditions and periodically replenished the cell with a dilute NaOH solution. To resolve the current density dependence of cell degradation we conducted several extended duration experiments at different current densities and observed the lifetimes of those cells. Finally, we conducted a rotating disk electrode (RDE) and 1H NMR spectroscopic experiments to identify the durability-limiting factor. We found that when controlling for the known mechanism of performance loss significant and accelerating performance degradation was present. This pointed to a previously unreported means of performance loss. Lower current densities (higher operating potential) resulted in decreased cell lifetime. These tests led to the electrode rather than membrane degradation as the source for performance loss. Our studies with RDE and 1H NMR experiments identified the generation of phenolic compounds that accumulate at the cathode throughout fuel cell operation. Once produced, the phenolic groups remain tethered to the ionomer, and cannot be removed by replenishment of the cell with a caustic solution. While quick recovery of cell performance occurs after caustic treatment continued to fuel cell operation inevitably leads to more phenol group formation that consumes quaternary ammonium counter ions. Eventually, these compounds reach a critical concentration that results in cell failure. The proposed mechanism is consistent with the degradation behaviors during our long-term test. Finally, we will discuss the mitigation strategy of the observed AEMFC degradation.

Acid retention of phosphoric acid-doped proton exchange membranes (PEMs) is one of the most critical factors that determine the performance and durability of high-temperature PEM fuel cells. However, the mechanism of phosphoric acid loss in the PEMs in the presence of water has not been discussed in terms of the energetics of phosphoric acid. In this study, we investigate the interactions of the phosphoric acid cluster by 31P NMR experiments and density functional theory calculations to propose new phosphoric acid loss mechanism of the phosphoric acid-polybenzimidazole PEM and phosphate-quaternary ammonium ion-pair PEM. The small molecule study suggests that the removal of the phosphoric acid from the phosphoric acid cluster does not occur due to the stronger interaction of phosphoric acid and water. On the contrary, adding water molecules to the PA cluster increases the cluster interaction energy by creating hydrogen bonding. In the phosphoric acid incorporated PEMs, we observed a consistent result that adding water increases the PA cluster volume rather than losing phosphoric acid. However, with excessive water activity, the polymer loses phosphoric acid due to the incapability to hold the water and phosphoric acid beyond a certain level.1 In the phosphoric acid loss process, the equilibrium phosphoric acid composition in the cluster plays a critical role. In the latter part of this presentation, we explain how the acid-base interaction and ion-pair interaction impact the equilibrium phosphoric acid composition the phosphoric acid cluster. We also explain how the equilibrium phosphoric acid composition affects the proton conductivity at different RH level. Finally, we demonstrate the high-temperature membrane fuel cell durability in the presence of water to prove the newly proposed acid loss mechanism. This presentation provides critical insights to design high-temperature proton exchange membranes. Reference 1. A. S. Lee, Y. -K. Choe, I. Matanovic, Y. S. Kim, The energetic of phosphoric acid interactions reveals a new acid loss mechanism, J. Mater. Chem. A. DOI: 10.1039/C9TA01756A (2019).

Anion exchange membrane (AEM) water electrolysis can afford cheaper hydrogen (H2) production compared to the current state-of-the-art of proton exchange membrane (PEM) electrolysis. In AEM electrolysis, i.e., in alkaline environment, platinum group metal (PGM)-free catalysts can be adopted as oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, contrary to the PEM electrolysis in which PGM-catalysts should be used. Furthermore, expensive titanium flow-field that is indispensable in acidic PEM electrolyzer can be replaced by inexpensive stainless flow-field. These advantages of AEM electrolysis make AEM electrolysis attractive technology to produce H2 in low cost. However currently performance of AEM electrolysis is much lower than that of PEM electrolysis. Therefore to make the AEM electrolysis technology viable, significant advancement in AEM electrolysis technology is needed. Many PGM-free OER catalysts measured in aqueous alkaline electrolytes, such as 0.1 M KOH or NaOH, have demonstrated as high activities as that of PGM IrO2 OER catalysts measured in an aqueous acid electrolytes in an electrochemical cell test. This implies that the low AEM electrolysis performance is possibly caused by some detrimental effect of AEM/anion exchange ionomer (AEI) onto catalysts. In this work we exploited different types of catalysts and AEIs to investigate the effect of catalyst-AEI interaction on AEM electrolysis performance. We observed that catalyst-AEI interaction substantially affects the AEM water electrolysis performance. The higher activity and durability of perovskite oxide OER catalyst than IrO2 OER catalyst in AEM water electrolysis can be explained by this catalyst-AEI interaction. In this talk, we will discuss the causes for low AEM electrolysis and possible pathways to improve AEM water electrolysis performance. Acknowledgements The authors gratefully acknowledge research support from the HydroGEN Advanced Water Splitting Materials Consortium, established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office.

Proton exchange membrane fuel cells (PEMFCs) are one of the most promising environmentally friendly energy conversion devices. The high temperature PEMFC system requires simplified heat and water management, which would provide substantial cost benefits and high potential for commercialization. Phosphonated polyaromatic electrolytes are promising candidates as proton conductors at high temperatures due to their ability to conduct protons under the full range of humidity levels and their covalently bound phosphonic acid structure, which eliminates the risk of leaching of the acid group at high humidity conditions. Despite their synthesis of research for more than decades, only few successful examples of phosphonated polymers in the PEMFCs have been reported. Here we present the new synthesis of phosphonic acid-functionalized polyaromatic electrolytes as electrode ionomers of high temperature PEMFCs. The polyaromatic electrolytes were synthesized by acid-catalyzed Friedel-Crafts polycondensation and followed by the SN Ar Michaelis-Arbuzov reaction of aryl pentafluorides. The electrolytes with the ion exchange capacity ranged 1.9-2.2 meq/g have good solubility in polar aprotic solvents, which eases the fabrication of materials as electrode binders. We could obtain the peak power density up to 700 mW/cm2 at current density of 2.1 A/cm2 at 200 °C with the membrane electrode assembly using the phosphonic acid functionalized ionomer. We will compare the fuel cell performance to that of ion-pair coordinated electrode binders1 and discuss the high applicability of the phosphonated polymer electrolytes in high temperature systems. Reference K.-S. Lee, J.S. Spendelow, Y.K. Choe, C. Fujimoto, Y. S. Kim, Nature Energy, 2016, 1, 16120-16124.

Over the past couple of decades, there have been immense research efforts to mitigate the safety concerns of liquid electrolytes in Li batteries, while maintaining practical battery performance.[1] For developing hybrid ionogel electrolytes which possess the requisite thermal, electrochemical, and mechanical properties, while maintaining facile processability with regards to electrochemical device fabrication, we sought out to develop a completely soluble, chemically crosslinkable, ionic-group functionalized hybrid polymer with thermally stable ladder-like structured inorganic backbone. This hybrid ionic polysilsesquioxane crosslinkable polymer with high molecular weight exhibited complete solution processablilty in ionic liquid electrolyte media, while the crosslinkable ionic groups helped to provide high ionic conductivity and enhanced lithium mobility through ionic dissociation of the newly introduced quaternary ammonium group from its counter anion. Polysilsesquioxanes as an inorganic-organic hybrid materials are highly sought out for their exceptional thermal, mechanical, and optical properties.[2] However, the vast majority of hybrid materials are difficult to form free-standing films due to their low molecular weight and brittle nature. Ladder-like polysilsesquioxanes comprise a unique structural class of fully polymeric polysilsesquioxane inorganic-organic hybrids in which a double stranded Si-O-Si inorganic backbone comprises the main chain and organic functional groups are functionalized radially. Moreover, the well-defined, fully condensed inorganic backbone allows for thermoplastic-like behavior and new applications in which thermal curing of uncondensed silanol groups is undesired. A series of ladder-like structured polysilsesquioxanes were synthesized through a controlled hydrolysis-polycondsation reaction. Through fine-tuning of the myriad of reaction conditions for an aqueous base-catalyzed hydrolysis-polycondensation reaction, a facile synthesis of structurally controlled polyphenylsilsesquioxanes as a model compounds were developed. Mechanism and kinetic studies indicated that the condensation reaction proceeded through a T1 structured dimer, which was quantitatively and in-situ formed through hydrolysis of a mild phenyltrimethoxysilane (PTMS) monomer, to give either the cage-structured polyhedral oligomeric silsesquioxanes (POSS) or the corresponding ladder-like silsesquioxanes (LPSQ) with excellent yields. Ladder-like and POSS materials were selectively achieved at higher and lower initial concentrations of PTMS, respectively, and an in-depth spectroscopic analysis of both compounds clearly revealed their structural differences with different molecular weights.[3] Through this newly developed method for obtaining structurally controlled polysilsesquioxanes, we fabrication hybrid gel polymer electrolytes for lithium ion batteries. First of all, the ladder structured polysilsesquioxane copolymers, LPMASQ’s were utilized as crosslinking gelation agent for conventional liquid electrolytes. Through extensive studies, only a mere 2 wt % was required to completely solidify the liquid electrolyte solution. Due to the minscule 2 wt % required to gelate the liquid electrolyte, exceptionally high ionic conductivity (~6 mS/cm) was obtained, which was on par with that with neat liquid electrolyte (~ 7.2 mS/cm), while having high electrochemical stability (~ 5V).[4] Li batteries fabricated with these materials showed that these materials performed exceptionally well at various C-rates for over 100 cycles, retaining 98.5% Coulombic efficiency. These observations were attributed to the polymeric nature of LPMASQ containing over one hundred methacryl moieties on the rigid double-stranded siloxane backbone. For further study, an ionic group functionalized ladder-like polysilsesquioxane was synthesized and used as a crosslinker for an ionic liquid electrolyte, 1 M LiTFSI in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI). Through thermal crosslinking of the polymerizable groups in ionic liquid solution, we were able to fabricate mechanically stable hybrid ionogels with high stability, high ionic conductivity. The lithium ion batteries assembled with hybrid ionogel exhibited excellent cell cycling performance with a high Coulombic efficiency at elevated temperature. A multifunctional crosslinkable and ionic group-functionalized ladder-like polysilsesquioxane was synthesized and utilized as crosslinker for the fabrication of hybrid ionogel electrolytes. Fabricated ionogel electrolytes exhibited exceptional compatibility and solubility with ionic liquid media and through thermal crosslinking enhanced the thermal stability of conventional olefin separators. Moreover, the introduction of ionic functionality gave high ionic conductivity and improved lithium mobility for exceptional lithium ion battery performance. The facile processability as well as exceptional thermal, mechanical, and electrochemical performance, holds great promise for these hybrid ionogel electrolytes for future integration into commercial electrochemical cells. References: Tarascon, J.-M., Armand, M. (2001), Issues and challenges facing rechargeable lithium batteries, Nature, 414, 359-361 A. Walcarius, D. Mandler, J. A. Cox, M. Collinson and O. Lev, J. Mater. Chem., 15, 3663 (2005) S-S. Choi, A.S. Lee, S.S. Hwang and K.-Y. Baek, Macromolecules 48, 6063 (2015). A.S.Lee, J.H. Lee, J.-C. Lee, S.M. Hong, S.S. Hwang and C.M. Koo, J. Mater. Chem. A 2, 1277 (2014).

High temperature-polymer electrolyte fuel cells (HT-PEMFCs) traditionally utilize phosphoric acid-doped polybenzimidazole as proton exchange membrane.1 However, the retention of phosphoric acid within polymer matrix has been pointed out as one of the most critical factors that affect HT-PEMFC durability. Previously, we reported a new HT-PEMFC system in which a quaternary ammonium-functionalized polymer imparted a stronger ionic interaction which we deemed “ion-pair coordination” with phosphoric acid compared with that of polybenzimidazole,2 giving rise to improved water tolerance. In this study, we use a combination of 31P NMR and DFT computations to compare the ionic interactions between representative small molecule organic bases, benzimidazole or tetramethylammonium hydroxide, with phosphoric acid and water. Based of these results, we propose a new phosphoric acid loss mechanism in which the strongly interacting ion pairs can increase the phosphoric acid partition composition towards accommodating more phosphoric acid for better phosphoric acid retention. References Li, J.O. Jensen, R.F. Savinell, N.J. Bjerrum, Prog. Polym. Sci., 2009, 34, 449-477. -S. Lee, J.S. Spendelow, Y.K. Choe, C. Fujimoto, Y. S. Kim, Nature Energy, 2016, 1, 16120-16124.

High temperature proton exchange membrane fuel cells (HT-PEMFCs) offer significant advantages over PEMFCs operating below 100 °C including the lack of need for humidifiers and smaller radiator sizes due to simplified thermal management, potentially providing a solution to vastly reduce the cost of fuel cells and their application to automobiles.1 Polymer electrolytes based on phosphoric acid-doped polybenzimidazole have given decent fuel cell performance, but suffer from stability issues stemming from the leaching of the liquid phosphoric acid carrier electrolyte at either lower temperatures or when exposed to water.2 While our previous development of ion-pair coordinated electrolyte systems improved the versatility of fuel cell operation temperature,3 this study investigates the optimization of HT-PEMFC performance through various electrodes formulation with a phosphonated ionomer based on a pentafluorostyrene,4 mitigating the need for electrode post-doping procedures. In this presentation, we report the benefits of using phosphonated ionomers for ion-pair coordinated membrane fuel cells under anhydrous conditions. References Chandan, M. Hattenburger, A. El-kharouf, S. Du, A. Dhir, V. Self, B.G. Pollet, A. Ingram, W. Buljaski, J. Power Sources, 2013, 231, 264-278. Li, J.O. Jensen, R.F. Savinell, N.J. Bjerrum, Prog. Polym. Sci., 2009, 34, 449-477. -S. Lee, J.S. Spendelow, Y.K. Choe, C. Fujimoto, Y. S. Kim, Nature Energy, 2016, 1, 16120-16124. Atanasov, A. Oleynikov, J. Xia, S. Lyonnard, J. Kerres, J. Power Sources, 2017, 343, 364-372.