Chemically stabilised extruded and recast short side chain Aquivion® proton exchange membranes for high current density operation in water electrolysis

Optimizing Ionomer Distribution in Anode Catalyst Layer for Stable Proton Exchange Membrane Water Electrolysis

The high cost of proton exchange membrane water electrolysis (PEMWE) originates from the usage of precious materials, insufficient efficiency, and lifetime. In this work, an important degradation mechanism of PEMWE caused by dynamics of ionomers over time in anode catalyst layer (ACL), which is a purely mechanical degradation of microstructure, is identified. Contrary to conventional understanding that the microstructure of ACL is static, the micropores are inclined to be occupied by ionomers due to the localized swelling/creep/migration, especially near the ACL/PTL (porous transport layer) interface, where they form transport channels of reactant/product couples. Consequently, the ACL with increased ionomers at PTL/ACL interface exhibit rapid and continuous degradation. In addition, a close correlation between the microstructure of ACL and the catalyst ink is discovered. Specifically, if more ionomers migrate to the top layer of the ink, more ionomers accumulate at the ACL/PEM interface, leaving fewer ionomers at the ACL/PTL interface. Therefore, the ionomer distribution in ACL is successfully optimized, which exhibits reduced ionomers at the ACL/PTL interface and enriches ionomers at the ACL/PEM interface, reducing the decay rate by a factor of three when operated at 2.0 A cm-2 and 80 °C. The findings provide a general way to achieve low-cost hydrogen production.

Life Cycle Assessment and Environmental Life Cycle costing of a unitised regenerative fuel cell stack

Life Cycle Assessment (LCA) and Environmental Life Cycle Costing (eLCC) are useful methods for evaluating the environmental, energy and economic performances of innovative energy storage technologies. By using these methods, the production process of a small Polymer Electrolyte Membrane Unitized Regenerative Fuel Cell (PEM-URFC) stack has been investigated, aiming to assess its environmental, energy and economic impacts at the early design stage and to identify the contributions of its various components on these impacts. Indeed, the PEM-URFC stack includes Critical Raw Materials that affect the product's sustainability. Results show that the highest contributions are associated with the platinum group metals used for the catalyst and, to a lesser degree, the materials and energy used for the bipolar plates and porous transport layers. However, considering that the datasets for representing the impacts of one of the electrocatalysts (Iridium Ruthenium Oxide) are still missing in LCA commercial databases and literature, a sensitivity analysis is performed assuming its impact to be similar to that of other Platinum Group Metals (PGMs) extracted with them (e.g., Platinum, Nickel, Palladium, etc.). The analysis shows a high difference in results due to data and methodological assumptions, making the assimilation of Iridium Ruthenium Oxide to Rhodium the worst scenario, increasing environmental impacts by 37.54 %, energy impacts by 40.48 % and environmental price by 45.08 %. Moreover, the study identified issues for applying life cycle thinking approaches on URFC devices that must be resolved in future studies (e.g., increase the reliability of catalyst inventory data or improve guidelines on energy storage technologies).

Electrochemical Properties and Structure of Membranes from Perfluorinated Copolymers Modified with Nanodiamonds

In this study, we aimed to design and research proton-conducting membranes based on Aquivion®-type material that had been modified with detonation nanodiamonds (particle size 4-5 nm, 0.25-5.0 wt. %). These nanodiamonds carried different functional groups (H, OH, COOH, F) that provided the hydrophilicity of the diamond surface with positive or negative potential, or that strengthened the hydrophobicity of the diamonds. These variations in diamond properties allowed us to find ways to improve the composite structure so as to achieve better ion conductivity. For this purpose, we prepared three series of membrane films by first casting solutions of perfluorinated Aquivion®-type copolymers with short side chains mixed with diamonds dispersed on solid substrates. Then, we removed the solvent and the membranes were structurally stabilized during thermal treatment and transformed into their final form with -SO3H ionic groups. We found that the diamonds with a hydrogen-saturated surface, with a positive charge in aqueous media, contributed to the increase in proton conductivity of membranes to a greater rate. Meanwhile, a more developed conducting diamond-copolymer interface was formed due to electrostatic attraction to the sulfonic acid groups of the copolymer than in the case of diamonds grafted with negatively charged carboxyls, similar to sulfonic groups of the copolymer. The modification of membranes with fluorinated diamonds led to a 5-fold decrease in the conductivity of the composite, even when only a fraction of diamonds of 1 wt. % were used, which was explained by the disruption in the connectivity of ion channels during the interaction of such diamonds mainly with fluorocarbon chains of the copolymer. We discussed the specifics of the mechanism of conductivity in composites with various diamonds in connection with structural data obtained in neutron scattering experiments on dry membranes, as well as ideas about the formation of cylindrical micelles with central ion channels and shells composed of hydrophobic copolymer chains. Finally, the characteristics of the network of ion channels in the composites were found depending on the type and amount of introduced diamonds, and correlations between the structure and conductivity of the membranes were established.

Ce-radical Scavenger-Based Perfluorosulfonic Acid Aquivion® Membrane for Pressurised PEM Electrolysers

A Ce-radical scavenger-based perfluorosulfonic acid (PFSA) Aquivion® membrane (C98 05S-RSP) was developed and assessed for polymer electrolyte membrane (PEM) electrolyser applications. The membrane, produced by Solvay Specialty Polymers, had an equivalent weight (EW) of 980 g/eq and a thickness of 50 μm to reduce ohmic losses at a high current density. The electrochemical properties and gas crossover through the membrane were evaluated upon the formation of a membrane-electrode assembly (MEA) in a range of temperatures between 30 and 90 °C and at various differential pressures (ambient, 10 and 20 bars). Bare extruded (E98 05S) and reinforced (R98 05S) PFSA Aquivion® membranes with similar EWs and thicknesses were assessed for comparison in terms of their performance, stability and hydrogen crossover under the same operating conditions. The method used for the membrane manufacturing significantly influenced the interfacial properties, with the electrodes affecting the polarisation resistance and H2 permeation in the oxygen stream, as well as the degradation rate, as observed in the durability studies.

Approaches to the Modification of Perfluorosulfonic Acid Membranes

Polymer ion-exchange membranes are featured in a variety of modern technologies including separation, concentration and purification of gases and liquids, chemical and electrochemical synthesis, and hydrogen power generation. In addition to transport properties, the strength, elasticity, and chemical stability of such materials are important characteristics for practical applications. Perfluorosulfonic acid (PFSA) membranes are characterized by an optimal combination of these properties. Today, one of the most well-known practical applications of PFSA membranes is the development of fuel cells. Some disadvantages of PFSA membranes, such as low conductivity at low humidity and high temperature limit their application. The approaches to optimization of properties are modification of commercial PFSA membranes and polymers by incorporation of different additive or pretreatment. This review summarizes the approaches to their modification, which will allow the creation of materials with a different set of functional properties, differing in ion transport (first of all proton conductivity) and selectivity, based on commercially available samples. These approaches include the use of different treatment techniques as well as the creation of hybrid materials containing dopant nanoparticles. Modification of the intrapore space of the membrane was shown to be a way of targeting the key functional properties of the membranes.

An Iron-Doped Calcium Titanate Cocatalyst for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is an important challenge in the development and large-scale distribution of energy conversion devices, especially low-temperature proton exchange membrane (PEM) fuel cells. In order to speed up the ORR kinetics and improve fuel cell performance, iron-doped calcium titanate (CTFO) is proposed as a cocatalyst. Fundamental physical and chemical characterizations by means of X-ray diffraction, infrared spectroscopy, and morphological and thermal analyses for the understanding of the functional features of the proposed materials were carried out. Composite catalysts containing different amounts of CTFO additive with respect to platinum (i.e., Pt:CTFO 1:0.5 and 1:1 wt:wt) were studied using a rotating disk electrode (RDE). Fuel cell tests were performed at 80 °C under 30% and 80% relative humidity. The best Pt:CTFO composite catalyst was compared to a bare Pt/C and a Pt/C:CaTiO3−δ 1:1 catalyst, revealing superior performances of the latter at high relative humidity fuel cell operation, as a combined result of an optimized electrolyte-electrode interface and improved ORR kinetics due to the inorganic additive.

Highly active and stable OER electrocatalysts derived from Sr2MIrO6 for proton exchange membrane water electrolyzers

Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr₂CaIrO₆ achieves 10 mA cm^-2 at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO₆ octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr₂CaIrO₆ as anode and low Ir loading (0.4 mg_Ir cm^-2). The cell achieves 2.40 V at 6 A cm^-2 (overload) and no loss in performance at a constant 2 A cm^-2 (nominal load). Thus, reducing Ir use without compromising efficiency and lifetime.

New Generation of Compositional Aquivion®-Type Membranes with Nanodiamonds for Hydrogen Fuel Cells: Design and Performance

Compositional proton-conducting membranes based on perfluorinated Aquivion^®-type copolymers modified by detonation nanodiamonds (DND) with positively charged surfaces were prepared to improve the performance of hydrogen fuel cells. Small-angle neutron scattering (SANS) experiments demonstrated the fine structure in such membranes filled with DND (0-5 wt.%), where the conducting channels typical for Aquivion^® membranes are mostly preserved while DND particles (4-5 nm in size) decorated the polymer domains on a submicron scale, according to scanning electron microscopy (SEM) data. With the increase in DND content (0, 0.5, and 2.6 wt.%) the thermogravimetric analysis, potentiometry, potentiodynamic, and potentiotatic curves showed a stabilizing effect of the DNDs on the operational characteristics of the membranes. Membrane-electrode assemblies (MEA), working in the O₂/H₂ system with the membranes of different compositions, demonstrated improved functional properties of the modified membranes, such as larger operational stability, lower proton resistance, and higher current densities at elevated temperatures in the extended temperature range (22-120 °C) compared to pure membranes without additives.

Green H2 Production by Water Electrolysis Using Cation Exchange Membrane: Insights on Activation and Ohmic Polarization Phenomena

Low-temperature electrolysis by using polymer electrolyte membranes (PEM) can play an important role in hydrogen energy transition. This work presents a study on the performance of a proton exchange membrane in the water electrolysis process at room temperature and atmospheric pressure. In the perspective of applications that need a device with small volume and low weight, a miniaturized electrolysis cell with a 36 cm² active area of PEM over a total surface area of 76 cm² of the device was used. H₂ and O₂ production rates, electrical power, energy efficiency, Faradaic efficiency and polarization curves were determined for all experiments. The effects of different parameters such as clamping pressure and materials of the electrodes on polarization phenomena were studied. The PEM used was a catalyst-coated membrane (Ir-Pt-Nafion™ 117 CCM). The maximum H₂ production was about 0.02 g min⁻¹ with a current density of 1.1 A cm⁻² and a current power about 280 W. Clamping pressure and the type of electrode materials strongly influence the activation and ohmic polarization phenomena. High clamping pressure and electrodes in titanium compared to carbon electrodes improve the cell performance, and this results in lower ohmic and activation resistances.

Different approaches to obtain functionalized alumina as additive in polymer electrolyte membranes

A series of sulfated aluminum oxides (S-Al2O3), investigated as an electrolyte additive in Nafion membranes, was synthesized via three different methods: (i) sol–gel sulfation starting from an aluminum alkoxide precursor, (ii) room temperature sulfation of fumed aluminum oxide, and (iii) hydrothermal sulfation of fumed aluminum oxide. Through the characterization of the synthesized S-Al2O3 by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy, a higher sulfation rate was found to be achieved via a hydrothermal sulfation, and the coordination state of sulfate groups was identified as monodentate. By using this hydrothermally synthesized S-Al2O3 as additive, a composite Nafion-based membrane was realized and compared to plain Nafion, by means of thermal analyses and fuel cell tests. Although higher hydration degree was found for the undoped membrane by differential scanning calorimetry (DSC), improved retention of fuel cell performance upon the increase of operation temperature was observed by using the composite electrolyte, confirming the stabilizing effect of the acidic inorganic additive.

Nafion-Based Proton-Exchange Membranes Built on Cross-Linked Semi-Interpenetrating Polymer Networks between Poly(acrylic acid) and Poly(vinyl alcohol)

We report semi-interpenetrating polymer network (semi-IPN) membranes prepared easily from a cross-linked network using poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) with interpenetrated Nafion for both proton-exchange membrane fuel cell (PEMFC) and proton-exchange membrane water electrolyzer (PEMWE) applications. Thermal esterification between PAA and PVA induced three-dimensional cross-linking to improve mechanical toughness and reduce hydrogen crossover, while the hydrophilic nature of the PAA-PVA-based cross-linked matrix still enhanced the water uptake (WU) and hence conductivity of the Nafion penetrant. The semi-IPN membrane (NPP-95) composed of Nafion, PAA, and PVA with a ratio of 95:2.5:2.5 showed a hexagonal cylindrical morphology and improved thermal, mechanical, and dimensional stability compared to a recast Nafion membrane (re-Nafion). The membrane was also highly effective at managing water due to its low WU and high conductivity. Furthermore, its hydrogen permeability was 49.6% lower than that of re-Nafion under the actual fuel cell operating conditions (at 100% RH and 80 °C). NPP-95 exhibited significantly improved conductivity and PEMFC performance compared to re-Nafion with a current density of 1561 mA/cm² at a potential of 0.6 V and a peak power density of 1179 mW/cm². Furthermore, in the PEMWE performances, NPP-95 displayed about a 1.5-fold higher current density of 4310 mA/cm² at 2.0 V and much lower ohmic resistance than re-Nafion between 60 and 80 °C.

Composite Nafion-CaTiO3-δ Membranes as Electrolyte Component for PEM Fuel Cells

Manufacturing new electrolytes with high ionic conductivity has been a crucial challenge in the development and large-scale distribution of fuel cell devices. In this work, we present two Nafion composite membranes containing a non-stoichiometric calcium titanate perovskite (CaTiO_3−δ) as a filler. These membranes are proposed as a proton exchange electrolyte for Polymer Electrolyte Membrane (PEM) fuel cell devices. More precisely, two different perovskite concentrations of 5 wt% and 10 wt%, with respect to Nafion, are considered. The structural, morphological, and chemical properties of the composite membranes are studied, revealing an inhomogeneous distribution of the filler within the polymer matrix. Direct methanol fuel cell (DMFC) tests, at 110 °C and 2 M methanol concentration, were also performed. It was observed that the membrane containing 5 wt% of the additive allows the highest cell performance in comparison to the other samples, with a maximum power density of about 70 mW cm⁻² at 200 mA cm⁻². Consequently, the ability of the perovskite structure to support proton carriers is here confirmed, suggesting an interesting strategy to obtain successful materials for electrochemical devices.

AQUIVION® perfluorosulfonic acid resin for butyl levulinate production from furfuryl alcohol

Multivariate analysis allowed the optimization of a reaction catalyzed by a robust solid acid Aquivion® P87S.