Proton-conducting Polymer Research Articles

Molecular Vibration and Physicochemical Performance of Proton-Conducting Solid Polymer Electrolyte Membrane based on CMC/PVA/CH3COONH4

This work studied examined the influence of ammonium acetate (CH3COONH4) on CMC/PVA-based solid polymer electrolyte (SPE) membranes, focusing on molecular vibration, proton conductivity, and physicochemical properties. SPE membranes were prepared via the casting solution method with varying CH3COONH4 concentrations to determine the optimal proton conductivity. Various characterizations, including FTIR, EIS, XRD, and TGA, were performed. The optimal membrane condition was achieved with 10 wt-% CH3COONH4 in the CMC/PVA (80/20) blend, yielding proton conductivity of 3.93×10⁻⁴ S/cm and favorable mechanical, thermal, and crystallinity properties, making it suitable for proton-conducting polymer applications. Keywords: ammonium acetate, carboxymethyl cellulose, ionic conductivity, poly(vinyl alcohol), proton battery, solid electrolyte membrane

Acid Modified Carbon Support with Proton Conductive Properties for Polymer Electrolyte Membrane Fuel Cell Applications

Proton exchange membrane fuel cell (PEMFC) are one of highly efficient electrochemical energy conversion technologies, with a potential to replace conventional fossil-fueled power generators for vehicles and stationary applications. One of the challenges for widespread use of PEMFC is to minimize the amount of platinum (Pt) to lower the cost of PEFCs. Therefore, optimizing electrocatalyst design to improve Pt mass activity is required. In the conventional PEMFC electrocatalyst, the proton conductive polymers such as Nafion are contained to transport protons to the Pt surface. However, the main problem of Nafion in catalyst layer (CL) is the inhomogeneously covered on commercial catalyst of Vulcan/Pt (CB/Pt) surface leads a low proton conductivity or high O2 diffusion resistance. Furthermore, the SO3 − groups of the polymers are strongly adsorbed onto the Pt surface and decreasing Pt active sites to lower the catalytic activity. Hence, it’s necessary to develop a new CL without using ionomer (Nafion).An acid modified carbon support with proton conductive properties was considered for PEMFC applications. In our previous study, we synthesized a high-density -SO3H modified carbon support (named SCB) by covalent bonding and loaded Pt on SCB (SCB/Pt) to conductive proton. Attained a higher O2 diffusivity at high current density range because without Nafion added [1]. However, this method of destroying the sp2 structure of carbon has the problem of reducing the durability and electrical conductivity of carbon. In this work, we changed the acid modify carbon method from chemical modification to physical modification which using proton conductivity polymer adsorb on carbon surface to conductive proton. Polybenzimidazole (PBI) having a side chain of trifluorosulfonimide (PBI-TFSI) was chosen as a proton conductor adsorbed on carbon surface because PBI-TFSI was reported to have high proton conductivity [2].In this study, instead of adding Nafion as a proton conductor after loading Pt on carbon support, Pt is directly loaded on carbon support coated with PBI-TFSI to fabricate novel catalyst, CB/PBI-TFSI/Pt, and CL was fabricated. Absence of ionomer is expected to improve O2 diffusivity in the CL and also avoid specific adsorption of SO3 − groups on the Pt surface. Principal experiment of this study is synthesis composite, characterize the catalyst properties and evaluate of electrochemical cell performance. As the control catalyst, commercial CB/Pt (TKK10V30E) was used.The PBI-TFSI content of CB/PBI-TFSI was estimated by CHN elemental analysis, which revealed that its C: H: N atomic ratio was 0.37: 95.59: 0.61. Considering that all the nitrogen was originating from PBI-TFSI, and side chain of graft ratio is 73.25%, the PBI-TFSI content of CB/PBI-TFSI was determined to be 4.5%. Thermal stability of the catalysts was compared by thermogravimetric analysis (TGA). As the results, CB/PBI-TFSI displayed a one-step weight loss similar to that of CB with a degradation temperature around 650°C, while SCB started to drop at 550°C [1]. This superior thermal stability of CB/PBI-TFSI compared to SCB was because sp3 defect was not introduced by using polymer wrapping method, while chemical modification method used to SCB introduced sp3 defects. Such a good thermal stability is expected to offer the high electrochemical durability in the PEMFC operation. The Pt loading of CB/PBI-TFSI/Pt determined from the TGA weight residue at 900 °C was 30 wt% comparable with CB/Pt. The size of the Pt nanoparticles in both CB/PBI-TFSI/Pt and CB/Pt was analyzed by TEM. The determined sizes of the Pt nanoparticles in CB/PBI-TFSI/Pt and CB/Pt were 2.04 ± 0.3 and 2.10 ± 0.2 nm, respectively. The comparable Pt loading and size of Pt nanoparticles in CB/Pt and CB/PBI-TFSI/Pt mean that these samples can be used in comparative studies.For the electrochemical characterization, the electrochemical active surface area (ECSA) was determined using the hydrogen adsorption/desorption (HAD) method and the polarization curves are operated using H2/air. The results indicated that the cell of CB/PBI-TFSI/Pt exhibits activity over 1.0 A/cm2 current density even without ionomer. However, compare with commercial catalyst of CB/Pt with Nafion, CB/PBI-TFSI/Pt still shows a lower cell performance because the higher resistance between Nafion membrane and CL. Additional improvements to the proton conductivity of the acid-grafted carbon support and the reduction of the interfacial resistance between PEM and CL could potentially further increase the PEMFC performance. O2 diffusivity as well as the fuel cell operation under the low humidity will also discuss.[1] Yoshihara R, Wu D, Phua YK, Nagashima A, Choi E, Jayawickrama SM, et al. Journal of Power Sources. 2022;529:231192.[2] Han H, Miura H, Motoishi Y, Tanaka N, Fujigaya T. Polymer Journal. 2021;53:1403-11. Figure 1

Perpendicularly Stacked Array of PTFE Nanofibers As a Reinforcement for Highly Durable Composite Membrane in Proton Exchange Membrane Fuel Cells

The configuration of reinforced composite membrane (RCM), composed of porous polytetrafluoroethylene (PTFE) as a mechanical reinforcement and perfluorosulfonic acid (PFSA) as a proton conductive polymer has gained a large interest due to its promisingly high performance for polymer electrolyte membrane (PEM) fuel cells. However, the inaccessible polymeric nanocomposites in preparing RCMs are still faced with critical challenges associated with immiscible interactions between hydrophilic sulfonate groups in PFSA and the hydrophobic nanoporous PTFE matrix. Herein, we report a well-refined and facile fabrication strategy for producing a cross-aligned PTFE (CA-PTFE) framework. The electric-field guided electrospinning enables the creation of unique micron-scale, grid-type PTFE matrix, which is synthesized by annealing of electrospun conjugated polymers resulting in the removal of carrier polymer and the formation of continuous fibrious structure via fusion of PTFE particles. The CA-PTFE RCM embodying uniformly impregnated PFSA in a grid-type PTFE matrix, facilitates hydration of the membranes, with minimal swelling and efficient diffusion of protons through concentrated sulfonate groups. The CA-PTFE RCM adopted cell showed outstanding fuel cell currents during both low and high humidity operation, with a current density of 1.38 A cm−2 at 0.6 V and maximum power density of 0.85 W cm−2 under RH 100% condition. Furthermore, the CA-PTFE RCM was able to achieve a long-lasting single-cell operation with a significantly low hydrogen crossover (less than 5 mA cm−2 at 0.4 V) even after 21,000 wet/dry cycles, which surpasses the standard of membrane durability for transportation application. The rational design of fibrous PTFE reinforcements opens up new engineering opportunities for the future development of high-stability PEM fuel cells.

All-Solid-State Rechargeable Air Batteries Using Redox Active Naphthoquinone in the Negative Electrode

Typical air batteries are composed of metallic negative electrode, liquid electrolyte, and gas (oxygen) diffusion positive electrode. The use of metals often causes dendrite growth, which deteriorates the durability of the air batteries similar to the secondary batteries. The liquid electrolyte poses the risk of leakage, limiting application of air batteries to small devices. Recently, air batteries that use organic redox molecules as the negative electrode have been explored. This type of emerging air batteries can be charged/discharged by the redox reactions of the organic molecules associated with protons. We have recently succeeded in developing an all-solid-state rechargeable air batteries (SSAB) combining a redox-active organic molecule as negative electrodes and a proton-conductive polymer membrane as solid electrolyte. We initially focused on 2,5-dihydroxy-1,4-benzoquinone (DHBQ) as the redox-active molecule and commercial Nafion as the solid electrolyte1 (Fig. 1a and b) to fabricate an SSAB. For improving the capacity and cyclability, polymeric DHBQ was also used. In the present study, the principle of SSAB was further verified with other redox-active organic molecules. 1,4-Naphthoquinone (NQ) was used for the negative electrode, which is known to undergo reversible redox reaction via two electrons / two protons transfer process (Fig. 2a). Nafion or a hydrocarbon-based polymer electrolyte membrane (SPP-QP)2 developed at the University of Yamanashi was used as the solid electrolyte (Fig. 2b). Pt/CB (TEC10E50E, Tanaka Kikinzoku) or Pt/GCB catalyst (TEC10EA50E, Tanaka Kikinzoku) was used for the oxygen electrode. NQ, carbon powder (Ketjen black, Tanaka Kikinzoku) and Nafion were used for the inks to be used for the negative electrode. The ink was sprayed onto one side of the electrolyte membrane. The ink for the oxygen electrode composed of Pt/CB or Pt/GCB and Nafion. was similarly sprayed onto the other side of the membrame to obtain catalyst-coated membrane (CCM). SSAB was tested at a cell temperature of 40 °C and 100% RH. Cyclic voltammograms (CV) were obtained at a scan rate of 20 mV s-1 and all charge-discharge cycling tests were performed at 15 C rate. The redox potential of the negative electrode observed in the CV measurements was 0.47 V (vs RHE) for DHBQ and 0.34 V (vs RHE) for NQ, indicating that NQ with a lower redox potential could provide higher electromotive force. Fig. 3 shows the charge-discharge curves of SSABs, in which DHBQ or NQ was used as the negative electrode. The SSAB-DHBQ had an open circuit voltage of 0.80 V, a discharge capacity of 73 mAh g-1, and a Coulomb efficiency of 58%, while the SSAB-NQ had an open circuit voltage of 0.88 V, a discharge capacity of 78 mAh g-1, and a Coulomb efficiency of 85%. Replacing Nafion with the SPP-QP membrane resulted in improved Coulomb efficiency (98%) since SPP-QP was much less permeable than Nafion and thus suppressed oxygen permeation to the negative electrode. Acknowledgement This work was partly supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, through Grants-in-Aid for Scientific Research (KAKENHI 23H02058). References 1) M. Yonenaga, Y. Kaiwa, K. Oka, K. Oyaizu, K. Miyatake, Angew. Chem. Int. Ed., 62, e202304366(2023).2) J. Miyake, R. Taki, T. Mochizuki, R. Shimizu, R. Akiyama, M. Uchida, K. Miyatake, Sci. Adv., 3, eaao0476 (2017). Figure 1

Novel Mesoporous Carbon Supporting PGM As an Effective ORR Catalyst in PEM Fuel Cells

Polymer electrolyte membrane (PEM) fuel cells convert the chemical energy of hydrogen and oxygen into electrical energy through a proton-conducting polymer membrane. These cells are highly valued in compact applications such as electric vehicles and portable power systems for their high power density and low operating temperatures. The catalyst support plays a crucial role, not only anchoring the catalyst nanoparticles but also enhancing Oxygen Reduction Reaction (ORR) activity through heteroatom doping, facilitating mass transfer via microchannels, and improving conductivity.1 Mesoporous carbon, merging electrochemical and high surface area properties, serves as an ideal catalyst support. Its mesoscopic structures enable high dispersion of electrocatalysts, and although mesopores contribute relatively less to surface area compared to micropores, they are more effective for mass transport. 2-3 We employ Metal Organic Frameworks (MOFs)-derived porous carbon, synthesized through pyrolysis, to provide structurally optimized mesoporous support that enhances surface area and electrochemical stability. MIL-101 is a highly porous, crystalline MOF known for its exceptional surface area and potential in gas storage, separation, and catalysis.4 Our research details the production of a series of mesoporous carbon C-X-MIL-101 (X = NH2, CH3, NO2, OMe) through carbonization of X-MIL-101 MOFs at 1100 °C followed by acid etching to remove residual aluminum oxides, resulting in high-surface-area, controlled-mesoporosity carbon materials. Platinum nanoparticles are subsequently embedded using a solvent impregnation method to produce Pt@C-X-MIL-101, optimizing platinum use and preventing surface deposition. The resulting Pt@C-X-MIL-101 catalysts have been tested in fuel cell and comprehensive findings will be presented at the conference. Zaman, S., Wang, M., Liu, H., Sun, F., Yu, Y., Shui, J., ... & Wang, H. (2022). Trends in Chemistry, 4(10), 886-906.Chang, H., Joo, S. H., & Pak, C. (2007). Journal of Materials Chemistry, 17(30), 3078-3088.Xu, J. B., & Zhao, T. S. (2013). RSC Advances, 3(1), 16-24.Zorainy, M. Y., Alalm, M. G., Kaliaguine, S., & Boffito, D. C. (2021). Journal of Materials Chemistry A, 9(39), 22159-22217.

Correlation of proton conductivity and free volume in sulfonated polyether ether ketone electrolytes: A positron annihilation lifetime spectroscopy study

Proton-conducting polymers play a pivotal role in clean energy technologies and various industrial applications, with a significant emphasis on enhancing energy efficiency and minimizing environmental impact. Sulfonated polyether ether ketone (SPEEK), which is renowned for its proton conductivity, has emerged as a key material in electrochemical processes, notably in proton exchange membrane (PEM) fuel cells. This study investigated the proton conductivity and dielectric behavior of SPEEK electrolytes at varying degree of sulfonation (DS) of 65% and 80%, correlating these properties with free volume profiles determined by positron annihilation lifetime spectroscopy (PALS). The SPEEK-65 and SPEEK-80 electrolytes were prepared via a controlled sulfonation process and characterized by FTIR, TGA, and SEM analyses. Proton conductivity and dielectric measurements were conducted at temperatures ranging from 300 to 370 K and frequencies ranging from 20 Hz to 1 MHz. The results revealed that SPEEK-80 exhibited a maximum proton conductivity of 3.4 × 10−2 S/m at 300 K and 1 MHz, which was significantly greater than the 4.38 × 10−3 S/m observed for SPEEK-65 under the same conditions. PALS analysis demonstrated a notable increase in free volume with increasing DS, with SPEEK-80 showing a higher o-Ps lifetime and intensity, indicating larger free volume sizes and fractions. These findings underscore the critical interplay between DS, free volume, and proton conductivity, offering insights into optimizing SPEEK-based electrolytes for advanced electrochemical applications.

Key Control Characteristics of Carbon Black Materials for Fuel Cells and Batteries for a Standardized Characterization of Surface Properties

AbstractCarbon Blacks (CBs) are primarily used in electrocatalysis as support materials for nanoparticulate electrocatalysts. In fuel cells, CBs, catalysts, and proton conductive polymers (ionomers) undergo a dispersion/homogenization process for electrode coating. The interactions between components in dispersion and the surface of CB particles are complex. The surface characteristics of CB particles impact slurry formulation, electrode coating, and the resulting electrode layer, affecting fuel cell and battery performance and durability. This study investigates commercially available CBs such as Vulcan XC72R, Ketjen Black EC‐300J, Ketjen Black EC‐600JD, and Super C65, focusing on application‐relevant key control characteristics (KCCs). The KCCs include physicochemical features like electrical conductivity (electron transport through the catalyst layer, CL), oxygen‐containing surface groups (hydrophilicity/phobicity of the CL, catalyst functionalization), surface basicity/acidity, ionomer adsorption, and particle dispersibility (catalyst ink stability). KCCs are determined by particle bulk electrical conductivity, Boehm titration (BT), isoelectric point (IEP), and Hansen solubility parameters (HSP). HSP, understood as similarity parameters for particles, indicate how nanoparticle surfaces interact with liquids during dispersion. The proposed KCCs serve as a starting point for characterizing CBs and guiding product design to obtain meaningful structure‐property relationships, essential for a successful energy transition.

(Invited) Comparison of Catalyst-Coated Electrodes vs. Catalyst-Coated Membranes in PEM Water Electrolysis Cells

The PEM (Proton-Exchange Membrane or Polymer Electrolyte Membrane) cell concept [1] is used in fuel cells and water electrolysis cells. PEM water electrolysis is a compact, efficient and flexible technology for the production of “green-hydrogen” from renewable (intermittent) energy sources. The unit cell (Figure 1) is made of several adjacent functional layers: (i) the proton-conducting polymer membrane (1); (ii) two catalysts layers (CLs) for hydrogen/oxygen evolution containing platinum group metals or PGMs (2;2’); (iii) a porous transport layer used for mass transport of reactants/products and electricity distribution (3;3’); (iv) water flow fields for water circulation (4;4’); bipolar plates (5;5’). From a practical viewpoint, the CLs can be deposited on either side of the interfaces formed between the polymer membrane and the porous transport layer: (i) on the supporting porous transport layers to form catalyst-coated electrodes which are then hot pressed against the bare membrane to form membrane – electrode assemblies; (ii) directly onto the membrane to form catalyst-coated membranes (CCM).The aim of this paper is to evaluate the efficiency and durability of both concepts, drawing on recent advances in manufacturing techniques to reduce the loading of PGM catalysts.[1] W.T. Grubb Jr., Batteries with Solid Ion-Exchange Electrolytes. Journal of the Electrochemical Society. 106 (1959) 275-279.[2] C. Rozain, P. Millet, Electrochemical characterization of Polymer Electrolyte Membrane Water Electrolysis Cells, Electrochimica Acta, 131 (2014) 160-167. Figure 1. Schematic diagram showing the cross-section of a PEM water electrolysis cell [2]. Figure 1

Synthesis, Characterization, and Fabrication of Nickel Metal-Organic Framework-Incorporated Polymer Electrolyte Membranes for Fuel-Cell Applications.

Proton-conducting sulfonated polymer metal-organic framework (MOF)-based composite membranes were synthesized by anchoring the nickel MOF (Ni-MOF) to the aromatic sulfonated polymer backbone. In this work, we sulfonated two different polymers, poly(1,4-phenylene ether ether sulfone) (PEES) and poly ether ether ketone (PEEK), with a controllable sulfonation degree, and the synthesized Ni-MOF was incorporated into the sulfonated polymers to prepare a polymer electrolyte membrane. The effect of an MOF as a pendant moiety on the polymer backbone had a significant effect on properties such as water uptake, thermal, mechanical, and oxidative stabilities, swelling ratio, ion-exchange capacity (IEC), morphology, proton conductivity, and fuel-cell performance. The presence of an MOF structure enhanced the water retention capacity of the composite membranes. Adding Ni-MOF to the composite membrane improved the fuel-cell performance by increasing the OCV and power density. Among the synthesized electrolytes, the 3 wt % Ni-MOF-incorporated sPEEK membrane displayed a power density of 319 mW/cm2 with a cell voltage of 0.79 V, which was higher than the pure sulfonated polymer. Thus, the developed composite membranes are suitable for fuel-cell applications.

Sulfonated poly(ether ether ketone)-Protic ionic Liquid-Based anhydrous Proton-Conducting composite polymer electrolyte membranes for High-Temperature fuel cell applications

A high-temperature polymer electrolyte membrane fuel cell (PEMFC) has enormous potential to produce clean energy with minimal environmental pollution along with high energy density and conversion efficiency. In the present work, anhydrous proton-conducting polymer electrolyte membranes for prospective high-temperature fuel cell application were successfully prepared using different protic ionic liquids (PILs) and sulfonated poly(ether ether ketone) (SPEEK). The protic ionic liquids (PILs), 2-hydroxyethylammonium formate, diethylmethyl ammonium triflate, 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide, 1,2-dimethyl imidazolium bis(trifluoro methylsulfonyl)imide, and diethylmethylammonium methanesulfonate were selected based on their favorable physicochemical properties. The effect of the incorporation of the PIL on the structural, thermal, and electrical transport properties of the composite SPEEK polymer electrolyte membranes was studied. The prepared polymer electrolyte membranes (PEMs) were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and electrochemical impedance spectroscopy (EIS) techniques. FTIR results indicated an interaction between the PIL and the SPEEK, which resulted in homogeneous and flexible membranes. The DSC results confirmed good miscibility and elucidated plasticizing effect of the incorporated PIL on the SPEEK polymer matrix. All the PEMs showed good thermal stability and high-temperature anhydrous proton conductivity, achieving best proton conductivity, ≈8 × 10–3 S cm−1 at 120 °C and low activation energy ≈0.26 eV, making it suitable for prospective high-temperature PEMFC applications.

Anchoring of Fe-MIL-101-NH2 to the Polymer Membrane Matrix through the Hinsberg Reaction to Promote Conductivity of SPEEK Membranes.

SCPEEK@MOF proton exchange membranes, where SCPEEK is sulfinyl chloride polyether ether ketone and MOF is a metal-organic framework, were prepared by doping Fe-MIL-101-NH2 into polymers. The amino group in the MOF and the -SOCl2 group in thionyl chloride polyether ether ketone cross-link to form a covalent bond through the Hinsberg reaction, and the prepared composite membrane has stronger stability than other electrostatic interactions and simple physical doping composite membranes. The formation of covalent bonds improves the water absorption of the composite membrane, which makes it easy for water molecules to form hydrogen bonds. Moreover, SPEEK as a proton conductive polymer and the synergy of MOFs improve the proton conductivity of composite membranes. The composite membranes were characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The swelling rate, water absorption, mechanical stability, ion exchange capacity, and proton conductivity of the pure sulfonated polyether ether ketone (SPEEK) membrane were compared with those of the mechanically doped SPEEK/MOF membrane and the composite membrane SCPEEK@MOF doped with different ratios of Fe-MIL-101-NH2, and all of the SCPEEK@MOF showed superior performance. When the Fe-MIL-101-NH2 loading rate of the composite membrane is 2%, the proton conductivity of the composite membrane can reach 0.202 S cm-1 at 363 K and a 98% relative humidity, which is much higher than that of the SPEEK/MOF membrane obtained by simple physical doping under the same conditions.

Effect of Plasma pretreatment and Graphene oxide ratios on the transport properties of PVA/PVP membranes for fuel cells

In this study, a novel proton-conducting polymer electrolyte membrane based on a mixture of polyvinyl alcohol (PVA)/polyvinyl pyrrolidone (PVP) (1:1) mixed with different ratios of graphene oxide (GO) and plasma-treated was successfully synthesized. Dielectric barrier dielectric (DBD) plasma was used to treat the prepared samples at various dose rates (2, 4, 6, 7, 8, and 9 min) and at fixed power input (2 kV, 50 kHz). The treated samples (PVA/PVP:GO wt%) were soaked in a solution of styrene and tetrahydrofuran (70:30 wt%) with 5 × 10−3 g of benzoyl peroxide as an initiator in an oven at 60 °C for 12 h and then sulfonated to create protonic membranes (PVA/PVP-g-PSSA:GO). The impacts of graphene oxide (GO) on the physical, chemical, and electrochemical properties of plasma-treated PVA/PVP-g-PSSA:x wt% GO membranes (x = 0, 0.1, 0.2, and 0.3) were investigated using different techniques. SEM results showed a better dispersion of nanocomposite-prepared membranes; whereas the AFM results showed an increase in total roughness with increasing the content of GO. FTIR spectra provide more information about the structural variation arising from the grafting and sulfonation processes to confirm their occurrence. The X-ray diffraction pattern showed that the PVA/PVP-g-PSSA:x wt% GO composite is semi-crystalline. As the level of GO mixing rises, the crystallinity of the mixes decreases. According to the TGA curve, the PVA/PVP-g-PSSA:x wt% GO membranes are chemically stable up to 180 °C which is suitable for proton exchange membrane fuel cells. Water uptake (WU) was also measured and found to decrease from 87.6 to 63.3% at equilibrium with increasing GO content. Ion exchange capacity (IEC) was calculated, and the maximum IEC value was 1.91 meq/g for the PVA/PVP-g-PSSA: 0.3 wt% GO composite membrane. At room temperature, the maximum proton conductivity was 98.9 mS/cm for PVA/PVP-g-PSSA: 0.3 wt% GO membrane. In addition, the same sample recorded a methanol permeability of 1.03 × 10−7 cm2/s, which is much less than that of Nafion NR-212 (1.63 × 10−6 cm2/s). These results imply potential applications for modified polyelectrolytic membranes in fuel cell technology.

Investigation of Manufacturing Process Related Structure and Performance of the Fuel Cell Electrode Thanks to Small Angle Neutron Scattering

With climate change and fossil fuel sustainability concerns faced globally, proton exchange membrane fuel cell (PEMFC) based electric vehicles have been recognized as a promising alternative. However, large-scale commercialization requires progress in performance, cost and durability, for which the electrode (catalyst layer) is the limiting component. The electrode is composed of nanoparticles of platinum (Pt) catalyst on a carbon (C) support, embedded in a proton conductive polymer (ionomer). It is obtained from a slurry (catalyst ink) after evaporating solvent consisting of a water and alcohol mixture. The structural properties of the slurry, including the ionomer and carbon dispersions, catalyst aggregation and ionomer coverage onto the Pt/C composite strongly influence the performance and durability of the final electrode. Nevertheless, currently little is known of these structures, particularly with regards to the dispersion of the ionomer component onto the surface of porous carbon, despite the fact it is now established that it plays a crucial role in the operation of the fuel cell. The lack of information leaves research and development to be heavily reliant on a trial and error basis. Developing a detailed understanding of the dispersion and its correlation to fuel cell performance is key in advancing the PEMFC electrode.However, the heterogeneous nature of these inks, with only short-range order observed on both micro- and nano- scales, makes them difficult to study by conventional laboratory techniques. Small angle neutron scattering (SANS) has been identified as a suitable method for the study of the electrodes as it is not hindered by the ink opacity as in optical techniques (commonly used to study dispersions) and allows to probe the bulk structures in the 1-100 nm scale relevant for each component. In particular, contrast variation (CV) SANS exhibits a major advantage in studying such complex systems, where scattering signal from multiple components can be deconvoluted by matching the scattering length density of the solvent to that of a desired component. Nevertheless, data on the ink itself is missing and it has only been investigated in a handful of studies by SANS.1-3 Shibayama et al.1 proposed a structural model of Pt/C aggregates coated by an ionomer shell in a water-based ink. Yoshimune et al.2 demonstrated that the amount of Pt on the carbon surface alters the thickness and density of said ionomer layer. Harada et al.3 were able to distinguish adsorbed and deposited ionomer on the composite surface as well as quantize their distribution.Yet although ink composition is known to impact the dispersion greatly, no systematic investigation linking its many variables has been conducted. For example, the ionomer will conform differently in a water/alcohol solvent used commercially in contrast to a water-based one. The porosity of the carbon support will impact distribution of Pt on its surface as well as the degree of ionomer penetration into the support. Additionally, although the fundamental understanding of the ink structure is imperative, it has seldom been further linked to the performance of the electrode itself.Therefore, the aim of this project is to utilize CV-SANS to study the impact of each catalyst ink component on the structure of the dispersion, and their relation to each other, through altering only a single variable at a time. The variables include the components as well as their proportions, such as the carbon concentration or the ionomer to carbon ratio. The performance of the electrode manufactured from said ink compositions will then be evaluated using electrochemical studies. Recently we performed CV-SANS studies on the ink, investigating the extent of ionomer adsorption on the Pt/C composite as a function of both carbon type and presence of Pt in the system. Both carbon supports studied, high surface area carbon with surface nano-pores accessible to the ionomer, and graphitized carbon, which has high internal porosity, yet inaccessible to the ionomer, pose an interest in industrial applications. Indeed, from these preliminary results it is evident platinum plays a significant role in the ink structure, particularly in the case of graphitized carbon (figure 1). The ink system will be quantitatively characterized using a singular value decomposition method already employed in literature to give insight into parameters such as the amount of ionomer adsorbed onto the carbon surface or the structure of the layer. References 1 M. Shibayama, T. Matsunaga, T. Kusano, K. Amemiya, N. Kobayashi and T. Yoshida, J Appl Polym Sci, , DOI:10.1002/app.39842.2 W. Yoshimune and M. Harada, https://doi.org/10.1246/cl.190017, 2019, 48, 487–490.3 M. Harada, S. I. Takata, H. Iwase, S. Kajiya, H. Kadoura and T. Kanaya, ACS Omega, 2021, 6, 15257–15263. Figure 1

Controlled Synthesis of Proton-Conductive Porous Organic Polymer Gels via Electrostatically Stabilized Colloidal Formation

Controlled Synthesis of Proton-Conductive Porous Organic Polymer Gels via Electrostatically Stabilized Colloidal Formation

Proton-Conducting Ceramic Membranes for the Production of Hydrogen via Decarbonized Heat: Overview and Prospects

Proton-conducting ceramic membranes show high hydrogen ion conductivity in the temperature range of 300–700 °C. They are attracting significant attention due to their relevant characteristics compared to both higher-temperature oxygen ion-conducting ceramic membranes and lower-temperature proton-conducting polymers. The aim of this review is to integrate the fundamentals of proton-conducting ceramic membranes with two of their relevant applications, i.e., membrane reactors (PCMRs) for methane steam reforming (SMR) and electrolysis (PCEC). Both applications facilitate the production of pure H2 in the logic of process intensification via decarbonized heat. Firstly, an overview of various types of hydrogen production is given. The fundamentals of proton-conducting ceramic membranes and their applications in PCMRs for SMR and reversible PCEC (RePCEC), respectively, are given. In particular, RePCECs are of particular interest when renewable power generation exceeds demand because the excess electrical energy is converted to chemical energy in the electrolysis cell mode, therefore representing an appealing solution for energy conversion and grid-scale storage.

A Review of Solid-State Proton-Polymer Batteries: Materials and Characterizations.

The ever-increasing global population necessitates a secure and ample energy supply, the majority of which is derived from fossil fuels. However, due to the immense energy demand, the exponential depletion of these non-renewable energy sources is both unavoidable and inevitable in the approaching century. Therefore, exploring the use of polymer electrolytes as alternatives in proton-conducting batteries opens an intriguing research field, as demonstrated by the growing number of publications on the subject. Significant progress has been made in the production of new and more complex polymer-electrolyte materials. Specific characterizations are necessary to optimize these novel materials. This paper provides a detailed overview of these characterizations, as well as recent advancements in characterization methods for proton-conducting polymer electrolytes in solid-state batteries. Each characterization is evaluated based on its objectives, experimental design, a summary of significant results, and a few noteworthy case studies. Finally, we discuss future characterizations and advances.

Robust Proton Conduction against Mechanical Stress in Flexible Free-Standing Membrane Composed of Two-Dimensional Coordination Polymer.

Introduction of mechanical flexibility into proton-conducting coordination polymers (CPs) is in high demand for future protonic applications such as fuel cells and hydrogen sensors. Although such mechanical properties have been primarily investigated in one-dimensional (1D) CPs, in this study, we successfully fabricated highly flexible free-standing CP membranes with a high surface-to-volume ratio, which is beneficial for enhanced performance in the aforementioned applications. We fabricated a layered CP, Cu2 (NiTCPP) (H4 (H2 TCPP); 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin), in which a two-dimensional (2D) square grid sheet composed of tetradentate nickel porphyrins and paddlewheel-type copper dimers was connected to each other by weak van der Waals forces. The mechanical flexibility was evaluated by bending and tensile tests. The flexural and Young's moduli of the membrane were significantly higher than those of conventional Nafion membranes. Electrochemical impedance spectroscopy analysis revealed that the in-plane proton conductivity of the membrane was maintained even under applied bending stress. Because the X-ray diffraction analysis indicates that the proton-conducting pathway through the hydrogen bonding network remains intact during the bending operation, our present study provides a promising strategy for the fabrication of new and advanced 2D CPs without using substrates or additional polymers for protonic devices.

Studies on Polybenzimidazole and Methanesulfonate Protic-Ionic-Liquids-Based Composite Polymer Electrolyte Membranes.

In the present work, different methanesulfonate-based protic ionic liquids (PILs) were synthesized and their structural characterization was performed using FTIR, 1H, and 13C NMR spectroscopy. Their thermal behavior and stability were studied using DSC and TGA, respectively, and EIS was used to study the ionic conductivity of these PILs. The PIL, which was diethanolammonium-methanesulfonate-based due to its compatibility with polybenzimidazole (PBI) to form composite membranes, was used to prepare proton-conducting polymer electrolyte membranes (PEMs) for prospective high-temperature fuel cell application. The prepared PEMs were further characterized using FTIR, DSC, TGA, SEM, and EIS. The FTIR results indicated good interaction among the PEM components and the DSC results suggested good miscibility and a plasticizing effect of the incorporated PIL in the PBI polymer matrix. All the PEMs showed good thermal stability and good proton conductivity for prospective high-temperature fuel cell application.

Two Proton Conductive Coordination Polymers Constructed by an Unprecedented Structural Transformation of a Phosphine-Based Tricarboxylate Ligand

The phosphine-based tricarboxylate 2-(3,3′-dioxo-1λ5-1,1′-(3H,3′H)-spirobi[2,1-benzoxaphosphol]-1-yl)benzoic acid (L) has been intensely studied due to its unique configuration and readily oxidizable phosphorus center. However, the coordination of L with metals have been largely ignored in the field of coordination polymers (CPs). Herein, we report two CPs, [Zn3(L1)2(dib)2(H2O)]·9H2O (1) and [Cu3(L2)2(dib)2]·3H2O (2) (H3L1 = tris(2-carboxyphenyl)phosphine oxide, H3L2 = 2,2′-phosphinico-dibenzoic acid, dib = 1,4-di(1H-imidazol-1-yl)butane), synthesized based on L. Strikingly, despite the initial use of L, the structures of 1 and 2 reveal that L undergoes two unprecedented in situ structural changes after coordination with the metal ion. In 1, L is transformed to the phosphine oxide derivative L1, while in 2, it is transformed to the phosphinic acid derivative L2. With the aid of the flexible ligand dib, the one-dimensional (1D) chain structure of 1 and three-dimensional (3D) supramolecular structure of 2 were constructed. For 1 and 2, especially in 1, there are abundant hydrogen bonds between the framework and the lattice water molecules, which are conducive to the formation of excellent hydrophilic channels and the transport of protons. Electrochemical experimental results show that 1 and 2 exhibit high proton conductivities (σ) of more than 10–4 S cm–1 over a wide temperature range of 303–353 K and low activation energies (Ea) at 98% relative humidity. Compared with the σ value of the initial ligand L (3.12 × 10–5 S cm–1), the best σ values of 1 and 2 are improved by 28 times and 6 times, respectively, and Ea is also reduced from 0.39 to 0.13 eV for 1 and 0.12 eV for 2. This is the first report of proton-conducting polymers based on a phosphine-based carboxylate ligand, involving two in situ structural transitions of the ligand.

All-Solid-State Rechargeable Air Batteries Using Dihydroxybenzoquinone and Its Polymer as the Negative Electrode.

A proof-of-concept study was conducted on an all-solid-state rechargeable air battery (SSAB) using redox-active 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and its polymer (PDBM) and a proton-conductive polymer (Nafion). DHBQ functioned well in the redox reaction with the solid Nafion ionomer at 0.47 and 0.57 V vs. RHE, similar to that in acid aqueous solution. The resulting air battery exhibited an open circuit voltage of 0.80 V and a discharge capacity of 29.7 mAh gDHBQ -1 at a constant current density (1 mA cm-2 ). With PDBM, the discharge capacity was much higher, 176.1 mAh gPDBM -1 , because of the improved utilization of the redox-active moieties. In the rate characteristics of the SSAB-PDBM, the coulombic efficiency was 84 % at 4 C, which decreased to 66 % at 101 C. In a charge/discharge cycle test, the capacity remaining after 30 cycles was 44 %, which was able to be significantly improved, to 78 %, by tuning the Nafion composition in the negative electrode.