Commercial Proton Exchange Membrane Research Articles

(Invited) Nano-Characterization of the Internal Morphology of Polymer Electrolyte Membranes with Cryogenic Scanning Transmission Electron Microscopy

Polymer membranes play important roles in electrochemical devices such as polymer electrolyte fuel cells. In recent years, there has been a growing interest in alkaline anion exchange membrane (AAEM) fuel cells as the alkaline environment offers a potential low-cost alternative to commercial proton exchange membrane (PEM) fuel cells [1]. Nonetheless, optimization of polymer properties such as ion conductivity and mechanical durability is still necessary to achieve commercially viable AAEM based fuel cells. Often, semicrystalline polymer backbones are selected for AAEM design, aiming to replicate the exceptional performance of Nafion in PEM fuel cells where the crystalline domains are believed to act as cross-linkers, mitigating excessive water uptake and mechanical degradation [2,3].Characterizing the local polymer morphology at the nanoscale is a crucial step in understanding how to optimize the design of AAEMs with enhanced durability and ion conductivity. Imaging polymers using conventional transmission electron microscopy (TEM) techniques is challenging however, due to their inherently-high beam sensitivity and low image contrast. Here, we demonstrate nanometer-resolution mapping of the ordering in polymer electrolyte membranes using cryogenic four-dimensional scanning transmission electron microscopy (cryo-4D-STEM). Conventionally used for mapping inorganic crystalline materials, the 4D-STEM technique has more recently also found applications in mapping semicrystalline, soft materials as well [4,5]. Here, using a model system of semicrystalline hydrogenated polynorbornene (hPN) AAEMs [6], we demonstrate the effects of polymer synthesis including molecular weight and thermal history on crystalline morphology and in turn on the polymer performance. Further, we compare the crystalline architecture of the hPN copolymers to that of Nafion 212 (Figure 1). Our results suggest that polymers with homogeneously distributed, nanometer-size crystalline domains lead to improved water management, a property directly related to the mechanical integrity of the polymer, with possible impacts on ion conductivity. More broadly, the results give new insights into how we can tune AAEM design in order to improve their performance.[1] Dekel, Journal of Power Sources, 375, 158-169. (2018).[2] Yang, et al. Chemical Reviews, 122(6), 6117-6321. (2022).[3] Mauritz & Moore, Chemical reviews, 104(10), 4535-4586. (2004).[4] Panova, et al. Nature materials, 18(8), 860-865. (2019).[5] Bustillo, et al. Accounts of chemical research, 54(11), 2543-2551. (2021).[6] Treichel, et al. Macromolecules, 53(19), 8509-8518. (2020).Figure 1: Cryo-4D-STEM crystallinity maps of hPN-co-iPrMe copolymers with varying syntheses and Nafion 212. We observe improvement in the water management of the copolymer membranes as the crystalline domains are reduced in volume and distributed homogeneously. The chemical structures of the polymers are listed below the crystallinity maps. Figure 1

Supramolecular Modifying Nafion with Fluoroalkyl-Functionalized Polyoxometalate Nanoclusters for High-Selective Proton Conduction.

Fluoroalkyl-grafted polyoxometalate nanoclusters are used as supramolecular additives to precisely modify the ionic domains of Nafion, which can increase the proton conductivity and selectivity simultaneously. The resulting hybrid membranes show significantly enhanced power density in fuel cells and improved energy efficiency in vanadium flow batteries.

Designing a hydrogen generation system through PEM water electrolysis with the capability to adjust fast fluctuations in photovoltaic power

—Hydrogen can be produced through water electrolysis using photovoltaic (PV) power in a way that is both pollution-free and friendly to the environment, rendering hydrogen a clean energy source. Proton Exchange Membrane (PEM) water electrolysis is an efficient hydrogen generation process because of its compact design, fast response, high efficiency and high current density. The fast fluctuations in solar power, however, are difficult for PEM water electrolysers to control effectively. To address the problems caused by intermittent power, a system for producing hydrogen consisting of a solar panel, battery, and commercial PEM electrolyser, alongside an electrical control strategy, is proposed. The Maximum Power Point Tracking (MPPT) Perturb and Observe (P&O) technique is employed for PV systems, while a bidirectional charge controller manages the charging and discharging of the battery. A Proportional-Integral (PI) controller is also utilised for the PEM electrolyser to ensure efficient operation. This setup provides a practical solution for hydrogen production. It enhances efficiency and reduces the risk of damage to the electrolyser, thereby making the process more sustainable and reliable. The proposed approach has been validated by simulation under different conditions. A comparative analysis has also demonstrated that the proposed system can perform well despite having less PV power. When comparing systems with and without batteries for energy storage, the system with the battery for energy storage has a 10% higher energy efficiency under the same operating conditions. This suggests that adding energy storage can increase energy utilization, maintain the DC link voltage constant, and achieve stable hydrogen production.

Supramolecular Modifying Nafion with Fluoroalkyl‐Functionalized Polyoxometalate Nanoclusters for High‐Selective Proton Conduction

Proton exchange membranes with high selectivity are urgently required in energy and electronic technologies. Nafion, a state‐of‐the‐art commercial proton exchange membrane material, faces significant challenges. It suffers from the permeation of undesirable substances, like hydrogen in fuel cells and vanadium ions in redox flow batteries, due to the unmatched sizes between its ionic domains (3~5 nm) and these substances. In this work, we present a supramolecular modification strategy that simultaneously enhances the proton conductivity and selectivity of Nafion. We employ fluoroalkyl‐grafted polyoxometalate (POMs) nanoclusters as supramolecular additives to modify Nafion via co‐assembly. These POMs can precisely and robustly decorate at Nafion ionic domains, with their fluoroalkyl chains anchoring into the perfluorinated matrix while their inorganic clusters stay in the ionic regions. The hybrid membranes, with continuous proton hopping sites and nanoscale steric hindrance offered by POMs, exhibit a 56% increase in proton conductivity and a 100% improvement in proton/vanadium selectivity. This leads to significantly enhanced power density and energy efficiency in fuel cells and vanadium flow batteries, respectively. These results underscore the intriguing potential of molecular cluster additives in improving the functions of ion‐conducting membranes.

Defective Tungsten Oxides with Stacking Faults for Proton Exchange Membrane Green-Hydrogen Generation.

Defects can introduce atomic structural modulation and tailor performance of materials. Herein, it demonstrates that semiconductor WO3 with inert electrocatalytic behavior can be activated through defect-induced tensile strains. Structural characterizations reveal that when simply treated in Ar/H2 atmosphere, oxygen vacancies will generate in WO3 and cause defective structures. Stacking faults are found in defects, thus modulating electronic structure and transforming electrocatalytic-inert WO3 into highly active electrocatalysts. Density functional theory (DFT) calculations are performed to calculate *H adsorption energies on various WOx surfaces, revealing the oxygen vacancy composition and strain predicted to optimize the catalytic activity of hydrogen evolution reaction (HER). Such defective tungsten oxides can be integrated into commercial proton exchange membrane (PEM) electrolyser with comparable performance toward Pt-based PEM. This work demonstrates defective metal oxides as promising non-noble metal catalysts for commercial PEM green-hydrogen generation.

Evaluation of electromethanogenesis in a microbial electrolysis cell using nylon cloth as a separator: Reactor performance and metagenomic analysis

This study aimed to propose a novel approach for simultaneous CO2 abatement and energy storage in microbial electrolysis cells (MECs). The methane (CH4) production from CO2 was achieved in a graphite granule–filled cathodic compartment of an MEC separated by a modified nylon cloth. Using the modified nylon cloth in MEC significantly reduced membrane internal resistance compared with the control where a commercial proton exchange membrane (PEM) was used (PEM: 1746 ± 80 TΩ/cm; nylon cloth: 251 ± 8 TΩ/cm). Consequently, CH4 production realized 72.9 ± 24.4 mL/(L ∙ d) with an average energy efficiency of 121 ± 39% compared with halted electromethanogenesis in PEM-equipped MEC. Metagenomics affirmed the predominance of hydrogenotrophic methanogens Methanocorpusculum and Methanobacterium. Moreover, H2-mediated methanogenesis contributed significantly to electromethanogenesis in nylon-MEC. This study demonstrated that the bioelectrochemical conversion of CO2 into CH4 in a nylon-MEC could be viable for CO2 sequestration combined with energy storage (power to gas).

Experimental Investigation of PEM Water Electrolyser Stack Performance Under Dynamic Operation Conditions

Water electrolysis has been used to produce green hydrogen, for which identifying optimum operation parameters is crucial to improve its energy efficiency and energy consumption. This paper used a commercial proton exchange membrane (PEM) water electrolyser stack (180 W) to demonstrate the correlation between operating current change, temperature, and water flow rate and their impact on the thermal and electrical performance of the stack. It was found that the current control regime and temperature control can offset the voltage ageing in a long-term operating electrolyser with no negative impact on the H2 production rate. For a controlled decreasing current path, in the medium range of operating current, the stack’s energy efficiency was improved by 5%, and 3.7% specific energy consumption can be saved comparing to the standard operation (57.8 kWh·kg−1H2). The results provide insights into the potential optimisation in operation conditions to further increase cell energy efficiency and reduce energy consumption. This new finding sheds light on developing an energy- and cost-saving operating method for long-term green hydrogen production via water electrolysis.

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 meqg-1, above that of the commercial PEM Nafion 112 (0.98 meqg-1), along with a conductivity of 80.4 mScm-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 20mAcm-2. These nanocomposite PEMs demonstrate the potential for valorization of forest biomass waste streams for high value clean energy applications.

Process Parameter Optimization via RSM of a PEM based Water Electrolysis Cell for the Production of Green Hydrogen

In the present work, the operating parameters were optimized using Box Behnken Design (BBD) in response surface methodology (RSM) to maximize the hydrogen production rate (R1) and hydrogen production rate per unit watt consumed (R2) of a proton exchange membrane electrolysis cell (PEMEC), a third response (R3) which was the sum of the scaled values of R1 and R2 were selected to be maximized so that both hydrogen production rate and hydrogen production rate per unit watt consumed could be maximized. The major parameters which were influencing the experiment for enhancing the output responses were oxygen electrode/anode electrocatalyst loading (A), current supplied (B) and water inlet temperature (C). The commercial proton exchange membrane Nafion® was used as the electrolyte. The acetylene black carbon (CAB) supported IrO2 was used as the electrocatalyst for preparing oxygen electrode/anode whereas commercial Pt (40 wt%)/CHSA was used as the H2 electrode/cathode electrocatalyst. The quadratic model was developed to predict the output/responses and their proximity to the experimental output values. The developed model was found to be significant as the P values for both the responses were < 0.0001 and F values were greater than 1. The optimum condition for both the responses were O2 electrode/anode electrocatalyst loading of 1.78 mg/cm2, supplied current of 0.33 A and water inlet temperature of 54°C. The predicted values for hydrogen production rate (R1) and hydrogen production rate per unit watt consumed (R2) were 2.921 mL/min and 2.562 mL/(min·W), respectively obtained from the quadratic model. The error % between the predicted response values and experimental values were 1.47% and 3.08% for R1 and R2, respectively. This model predicted the optimum conditions reasonably in good agreement with the experimental conditions for the enhancement of the output responses of the developed PEM based electrolyser.

Development of metal free biochar based material for water electrolysis hydrogen production using anion exchange membrane: Creating circular economy

In recent days, a steady growth is being noted in hydrogen energy field owing to the global rise in population and increased energy demand. Fast depletion of fossil-based fuels and climate change issues are driving nations towards exploring an alternate energy resource. Hydrogen energy is one such an option owing to availability of simple and cost intensive technology involvement. Alkaline water electrolysis is one of the simplest ways of producing hydrogen utilizing renewable energy and oxygen as the only byproduct thus not contributing to carbon footprint. However, immediate attention is needed to minimize the cost of electrolyzer components, maintenance and energy. Commercial proton exchange membrane water electrolyzers (PEM) in market employ large capital cost due to high-priced Nafion and other PFSA membranes, titanium endplates and noble metal-based electrocatalysts. As a consequence, researchers are looking into the usage of Anionic exchange membrane (AEM) for water/alkali based electrolyzer for producing hydrogen with non-noble metal electrocatalysts and low-cost metal end plates. In this article a waste coconut shell derived biochar is explored as the carbon matrix for base of electrocatalysts to replace other high-cost carbon support for electrocatalyst in water electrolyzer. The structural and electrical properties of the coconut shell biochar are studied and compared with other available carbon supports. To deep drive in the electrolyzer performance this approach is further extended to MEA (Membrane Electrode Assembly) level to study the metal free electrocatalyst behavior in real-time environmental conditions.

Self-Enhancement of Perfluorinated Sulfonic Acid Proton Exchange Membrane with Its Own Nanofibers.

High-performance proton exchange membrane (PEM) is crucial for the proton exchange membrane fuel cell (PEMFC). Herein, a novel "self-enhanced" PEM is fabricated for the first time, which is composed of perfluorinated sulfonic acid (PFSA) resin and its own nanofibers as reinforcement. With this strategy, the interfacial compatibility issue of conventional fiber-reinforced membranes is fully addressed and up to 80 wt% loading of PFSA nanofibers can be incorporated. Furthermore, on account of chain orientation within the PFSA nanofiber, single fiber exhibits super-high conductivity of 1.45 S cm-1, leading to state-of-the-art proton conductivity (1.1 S cm-1) of the as-prepared "self-enhanced" PEM so far, which is an order of magnitude increase compared with the bulk PFSA membrane (0.29 S cm-1). It surpasses any commercial PEM including the popular GORE-SELECT and Nafion HP membranes and is the only PEM with conductivity at 100 S cm-1 level. In addition, the mechanical strength and swelling ratio of membranes are both substantially improved simultaneously. Based on the high-performance "self-enhanced" PEM, high peak power densities of up to 3.6W cm-2 and 1.7W cm-2 are achieved in H2-O2 and H2-Air fuel cells, respectively. This strategy can be applied in any polymeric electrolyte membrane.

Close-packing effect of water clusters within metal-organic framework pores on proton conductivity: a dielectric relaxation phenomenon in loose space and colossal dielectric permittivity.

Proton-conducting metal-organic frameworks (MOFs) have attracted tremendous attention for their promising application in proton-exchange membrane fuel cells. Water clusters play an extremely important role in the proton-conduction process and affect the proton conductivity of host materials. To date, the close-packing effect of water clusters within pores on proton conductivity due to the amorphous structure of commercial proton-exchange membranes is unclear. Herein, we prepared two crystalline MOFs containing different water clusters, namely, [Sm2(fum)3(H2O)4]·3H2O (Sm-fum-7H2O) and [Er2(fum)3(H2O)4]·8H2O (Er-fum-12H2O) (H2fum = fumaric acid), and regulated their proton conductivities by changing the water clusters. As expected, Sm-fum-7H2O showed a high proton conductivity of 6.89 × 10-4 S cm-1 at 333 K and ∼97% RH because of the close packing of the water clusters within the pores triggered by a lanthanide contraction effect, outperforming that of Er-fum-12H2O and some previously reported MOFs. Additionally, Sm-fum-7H2O and Er-fum-12H2O demonstrated high dielectric functions, reaching 2.22 × 103 and 1.42 × 105 at 102.5 Hz, respectively, making Er-fum-12H2O a highly dielectric material. More importantly, broadband dielectric spectroscopy measurements indicated that there was a dielectric relaxation process in Er-fum-12H2O with an activation energy of 0.59 eV. The present findings provide a better understanding of the crucial role of confined water clusters in proton conductivity and the novel phenomenon of the coexistence of proton conduction and dielectric relaxation in crystalline MOF materials.

Manufacturing Challenges, Opportunities, and Successes for PEM Electrolysis at Scale

Hydrogen generation via electrolysis has gained much attention internationally as not only a sustainable source of fuel for the transportation, but as a carrier of energy to capture stranded renewable energy due to the carbon-free chemical cycle and response characteristics of the technology. The barrier to entry preventing this technology from being widely adopted is the overall cost associated with both the upfront capital expense as well as the operating cost incurred over the product life. The majority of this cost is driven by 1) low electrical efficiencies due to the high ohmic resistance of thicker membranes required by electrolysis systems to electrochemically compress generated hydrogen for storage and the overpotential associated with the water splitting oxygen evolution reaction (OER) catalysts typically used, 2) high cost of system and cell stack materials, which need to be durable for up to 100,000hrs at potentials approaching 2V in both reducing and oxidizing environments, and 3) the lack of a robust supply chain for high volume manufacturing to further drive down cost through economies of scale.With 95% of hydrogen currently being produced through the reformation of cheap natural gas, significant cost reductions are necessary for electrolysis to become a viable alternative to the incumbent. Commercial proton exchange membrane (PEM)-based electrolysis has reached scales of several hundred kg/day, providing a relevant pathway for industrial scale hydrogen generation with tremendous opportunity for continuing cost reduction by leveraging system and manufacturing scaling laws and advancements in PEM fuel cell materials, manufacturing, and analysis tools. Order of magnitude improvements in some of the highest cost elements are easily achievable and with more research funding being directed towards hydrogen production, the realization of these reductions is occurring at a faster rate. While many improvements in stack design and materials of construction have been identified and implemented, there are still numerous opportunities to explore that would move electrolysis towards a viable, cost-effective alternative to natural gas reformation. This talk will describe some of the areas of success, where research is still needed, and ultimately how each of these improvements translate into cost and the path to reformation parity.

Reinforced Membranes with PTFE Matrix and Sulfonated Hydrocarbon Electrolyte for PEM Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have emerged as a promising technology for clean energy conversion with various potential applications. Due to its cost-effectiveness, sulfonated hydrocarbon has been researched as an alternative to Nafion, a commercial proton exchange membrane. However, sulfonated hydrocarbon's mechanical and chemical stability remains a critical challenge that needs to be addressed, as the membrane must withstand harsh operating conditions, such as wet-dry mechanisms in high-temperature operations. To compete with perfluorosulfonic acid (PFSA), sulfonated hydrocarbon should be reinforced with a polytetrafluoroethylene (PTFE) substrate. However, there are significant issues with incompatibility between sulfonated hydrocarbon and PTFE substrate.To improve the impregnation, simple and reproducible chemical treatment has been developed to enhance the hydrophilicity of PTFE using a mixture of acids and oxidizing agents. Moreover, surfactant was added to increase compatibility and improve impregnation. After the reinforced membrane was fabricated, the membranes were characterized, including their water uptake and dimensional stability. The reinforced membrane also showed superior mechanical properties, including gas permeability, tensile strength, and dynamic mechanical analysis. To evaluate the degree of impregnation, the transparency of the reinforced membrane was checked for haziness and further analyzed with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) mapping to quantify the impregnation degree. Finally, the performance and durability of the reinforced membrane were measured by single-cell and wet-dry cycling tests.

High Durability of Pemion® Proton Exchange Membranes in Cross-Pressure Accelerated Mechanical Stress Tests

Polymer electrolyte membrane fuel cells (PEMFC) are the dominant technology for hydrogen-powered fuel cell electric vehicles in clean transportation systems. To be suitable for commercialization and applicability in real-world use-cases, light and heavy-duty fuel cell vehicles require lifetimes of over 8,000 and 30,000 hours, respectively [1]. Hence, enhancing the durability of all fuel cell components, particularly the proton exchange membrane (PEM), is of great importance.Recently, fuel cell membranes based on hydrocarbon (HC) chemistries have become increasingly common in the literature [2]. Materials with polyaromatic backbones, tunable electrochemical properties, and low reactant permeability are increasingly seen as potential alternatives to incumbent perfluorosulfonic acid (PFSA) materials [2]. Additionally, as restrictions on the use of fluorinated materials in various industries continue to grow, the importance of HC chemistries will as well. Sulfo-phenylated polyphenylenes (sPPPs) are a particular class of HC materials that show promise [3]. However, the phase separation between hydrophilic and hydrophobic domains within sPPPs may not be as discrete as in PFSAs [3], requiring higher ion exchange capacity (IEC) values than PFSAs to achieve similar protonic conductivity. High IEC typically results in greater material hydrophilicity, which can render membranes dimensionally unstable in a fuel cell [4].State-of-the-art commercial PEMs are now manufactured as thin films (≤ 18 µm), offering small ohmic loss and therefore high fuel cell performance. To improve dimensional stability and eliminate the risks of electrical shorting, PEMs are commonly mechanically reinforced using a porous, inert, and non-ionic substrate, such as expanded polytetrafluoroethylene (ePTFE). In a work by Miyake et al. [5], sulfonated polyphenylene-based ionomer membranes with flexible polyethylene mechanical reinforcement were prepared and the results indicated promising mechanical properties and improved longevity in RH cycling tests. However, there is still a lack of data about the fatigue durability of HC membranes in the literature, and evaluating and comparing the mechanical durability of numerous PEMs with a mechanical reinforcement layer in a traditional wet-dry cycling accelerated stress test would be a time-consuming and thus costly process [6].In our previous work, [7] we combined constant pressure differential across an ePTFE-reinforced perfluorosulfonic acid (PFSA) ionomer membrane with in-situ RH cycles (ΔP-AMST) to simulate the actual mechanical stresses in the fuel cell environment, while accelerating the durability testing for reinforced PEMs. In this study, ΔP-AMST is used to benchmark the fatigue lifetime curves for Pemion® membranes and compare it with a commercial reinforced PFSA-based PEM. The test temperature was set to 90 °C, and dry and wet (90% RH) phases were 60s and 30s, respectively. The hardware and semi-MEA specifications used for the test are shown in Figure 1a-c. A semitransparent polycarbonate spacer plate with 20 mm thickness and a circular aperture (25.4 mm) in the middle was used to allow free expansion of the membrane (Figure 1d). The cathode side was pressurized to create a cross pressure between the two sides and intensify the stress on the membrane during the RH cycling process. The ultimate failure of the membrane is shown in Figure 1e. The radial stress at the center of the deformed membrane is estimated by Hencky’s solution, as reported in our previous work [7]. Figure 1f demonstrates the estimated nominal stress on the membranes as a function of their lifetimes in terms of RH cycles. According to the fatigue S-N curves, reinforced Pemion® membranes afford longer lifetime than incumbent PFSA materials if the membrane edges are well protected. In addition, the impact of IEC on the fatigue durability of Pemion® membranes is investigated and the results are evaluated against stress of dehydration and dynamic mechanical analysis measurements. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Water Dissociation Interfaces in Bipolar Membranes for H2 Electrolysers

In order to meet large scale energy demands in a more sustainable way, water electrolysers could be coupled with the well-developed photovoltaic solar cell technology to provide the energy input for green H2 production. Commercial PEM (proton exchange membranes) electrolysers operate in acidic pH which favours H2 production at the cost of using IrO2 as catalyst for oxygen production at the anode representing a significant drawback for this technology. Contrary, an AEM (anionic exchange membranes) operates in alkaline electrolytes which enables the use of low cost and highly active OER catalyst such as NiCoFeOx,1 however at the expense of including an extra overpotential to drive the H2 production in the electrolyser.2 Using bipolar membranes (BPM), where a cationic exchange membrane CEM is used alongside an anionic exchange membrane, allows the electrolyser to operate at different pHs: at the cathode in an acidic environment to favour H2 production, and alkaline for O2 production at the anode. However, a BPM induces a significant increase in resistance across the electrolyser.2 Recently, it has been demonstrated that by adding metal oxides as water dissociation catalysts, the electrolyser overpotential significantly decreased passing from 8 V to 2.2 V at 500 mA cm-2.3 This milestone in the field was accomplished by using two metal oxides with different point of zero charge (PZC) 3 and 11 for IrO2 and NiO respectively. Interestingly, a similar performance was observed when only TiO2 was used as water dissociation catalyst which PZC sits between IrO2 and NiO.4 Indeed demonstrating the necessity of better understanding of the physicochemical phenomena that governs water dissociation interfaces.Using TiO2 as water dissociation catalyst provides a suitable platform to understand how properties such as conductivity or different doping content affect water dissociation during H2 production in the electrolyser. Therefore, in this work modifications of TiO2 were investigated and its impact on the cell voltage when used between Nafion 212 and Sustainion membranes as CEM and AEM respectively, in a commercial 5 cm2 electrolyser at 60 ⁰C that operates only with DI water. To only benchmark the performance of the BPM, Pt and IrO2 were chosen as H2 and O2 catalysts respectively.

Analysis of PEM Membrane Electrode Assemblies Impact on the Levelized Cost of Hydrogen

Plug is building an end-to-end green hydrogen ecosystem to help its customers meet their business goals and decarbonize the economy. This hydrogen ecosystem is inclusive of production, storage, delivery, and energy generation. As the largest user of liquid hydrogen globally, Plug Power plans to build and operate green hydrogen production plants across North America and Europe. Plug’s hydrogen production plants are based on electrolyzer systems featuring internally developed proton exchange membrane (PEM) based water electrolysis membrane electrode assemblies (MEAs). This paper will review the state of commercial PEM water electrolysis MEAs and provide insight as to what advances in MEA technology are needed to produce hydrogen at a levelized cost of $1/kg.The cell polarization curves for two modeled PEM MEAs are shown in Figure 1. They represent the performance of both commercial and future PEM water electrolyzer technology. As the applied current density to the cell increases, so does the cell voltage, and thus the energy required to produce a kilogram of hydrogen. As the MEA technology in the stack matures, the applied current density, and thus, the hydrogen production rate can increase at a set efficiency. A 155 cell, 1,000 cm2 active area, electrolyzer stack featuring commercial MEAs would produce approximately 220 kg-H2/day at an efficiency of 49 kWh/kg-H2. With the future MEAs, this same stack, operating at the same efficiency, could produce as much as 1,200 kg-H2/day.A hydrogen plant with a production capability of 45 metric tons per day, featuring commercial MEAs, would produce hydrogen at a cost of approximately $6/kg when powered by energy at a price of $35/MWh. The MEA cost represents only a few percent of the total capital expenditure required to build a 45 metric ton hydrogen plant. Thus, MEAs would only contribute a few cents to the estimated $6/kg levelized cost of hydrogen (LCOH). They, however, are responsible for most of the energy consumed at a hydrogen plant. Therefore, the MEAs could account for 50%, or more, of the total cost to produce hydrogen. A savings of $328M to $410M can be realized or every $1/kg reduction in LCOH over the lifetime of a hydrogen plant. Thus, performance improvements in the MEA are paramount to making hydrogen production competitive with other energy carriers.The oxygen evolution catalyst featured in a future MEA would be required to achieve a greater than four-fold increase in activity. The PEM of the future MEA would also be required to support a substantial increase in proton transfer while maintaining its integrity for greater than 100,000 hours. These advances, as well as savings in hydrogen plant capital expenditures, are required to achieve a LCOH of approximately $1/kg at a fixed energy cost of $35/MWh. Even at the lowest projections for capital expenditures, most of the cost of hydrogen will be dominated by power consumption, further highlighting the importance of maturing PEM water electrolysis MEA technology. Figure 1

Hydrogen Production with Seawater-Resilient Bipolar-Membrane Electrolyzers

Commercial proton exchange membrane water electrolyzers (PEMWEs) are highly efficient when operating in ultra-pure de-ionized water. However, introduction of additional ions leads to a reduction in device durability and efficiency. Chloride (Cl-) ions, typically found in high concentrations in seawater, lead to device performance issues driven in part by the chlorine evolution reaction at the anode. At the acidic anode-cation exchange layer interface, corrosive chlorine species (OCl-, HOCl, Cl-) are readily generated due to the facile kinetics of the 2-electron oxidation reaction relative to the desired 4-electron water oxidation reaction. Bipolar membrane water electrolyzers (BPMWEs), however, contain a locally basic anode-anion exchange layer interface, leading to improved thermodynamic favorability for O2 production rather than corrosive chlorine species production. Furthermore, the bipolar membrane can readily block anions and cations from accessing the desired reaction spaces. In this work, we evaluated ion transport, chloride oxidation, and durability of BPMWEs and PEMWEs operating in salt water. BPMWEs exhibit a low Faradaic efficiency of 0.005% for the oxidation of Cl− to corrosive chlorine species at the anode, compared to PEMWEs that can reach a Faradaic efficiency of up to 10% under similar conditions. In addition, BPMWEs demonstrate a device lifetime that is 140 times longer than that of PEMWEs operating in direct seawater electrolysis conditions. Failure modes for each membrane type have been investigated under both ultra-pure and impure water electrolysis conditions and are discussed in this work.

Analysing the Degradation Phenomena of a Commercial Proton Exchange Membrane Water Electrolyzers

Decarbonization of our energy system has become a priority to mitigate climate change. Therefore, the use of renewable energies is mandatory which also requires a long-term storage possibility. Proton exchange membrane water electrolyzers (PEMWE) are ideal for producing green hydrogen for transport, industry and heat. Important advantages are their compactness and high flexibility to operate under dynamical conditions. To be competitive it is necessary on the one hand to reduce the investment costs and on the other hand to ensure a long life of electrolyzers to limit operational expenses. Industry often faces the problem that the operating histories of their stacks are unknown when they are operated by customers. Nevertheless, understanding of the degradation mechanisms is of great importance to develop new components with reduced cost and enhanced durability. Here we analyse the cell components of a commercial PEMWE stack, which has been operated by a customer for long periods of time under unknown conditions, with the help of electrochemical and physical methods. Samples of the operated components were cut at specific locations and characterized in a 4 cm2 single cells. The aged components were successively replaced by new ones or regenerated to isolate and quantify the contribution of individual components on performance losses. This way, we have identified the catalyst coated membrane (CCM) as the component strongest affected by degradation. By using X-ray photoelectron spectroscopy (XPS) we identified different types of contamination like Pb and Fe. Remarkably, they were found on aged and unused components which is an indication for impurities due to the production process. In addition, energy dispersive X-ray spectroscopy (EDS) analysis showed Ca traces which is characteristic of CCM contamination when insufficiently deionized water is used for cleaning cell components, in particular the Ti porous transport layers (PTL). The CCM notably degrades by defects of the catalytic layer, due to contaminations and ionomer rearrangement. Signs of erosion were observed on the cathodic side of the Bipolar Plate (BBP) by means of SEM and atomic force microscopy (AFM), while the electronic conductivity remained unchanged. In contrast a pronounced oxidation concurrent with reduced conductivity is measured for the BPP on the anode side. The combination of electrochemical characterization with stepwise regeneration processes and physical ex situ analysis allows to draw conclusions about the impact of different components on degradation and to analyse the underlying aging mechanism occurring in each component.

Investigating Proton Exchange Membrane Fuel Cell Durability at Intermediate Temperatures (80 – 120 °C)

For several applications the low operating temperature of 60-80 °C of proton exchange membrane fuel cells (PEMFCs) limit their potential use. Increasing this temperature above 100 °C would simplify the water management and increase the temperature of the produced heat which would allow for more effective cooling systems [1,2]. Further, increasing the operating temperature could potentially allow for other benefits, such as the employment of more affordable catalysts, as the reaction kinetics are enhanced at elevated temperatures. However, operating at higher temperatures can cause increased degradation on the utilized components [3].In this work we investigated how commercial proton exchange membrane electrode assemblies (MEA) aged at various temperatures when operating either using a load cycle (based on the New European Drive Cycle) or constant load. The state of health of the MEA was continuously monitored through cyclic voltammetry, electrochemical impedance spectroscopy, linear sweep voltammetry, CO-stripping measurements and polarization curves. The obtained ageing results were evaluated using a physics-based model using COMSOL to better understand what aging mechanisms were pronounced at higher operating temperatures. Finally, the aged MEA were characterized with SEM and TEM analysis.The results show that all samples underwent an ageing process and that the ageing was accelerated at higher temperatures, as can be seen in the figure . Further, the ageing was more pronounced at a higher load. The measurements showed that the main ageing is occurring at the cathode catalyst layer and a drastic reduction in the electrochemical active surface area of the catalyst was observed. The membrane properties were also altered by the ageing, and a minor reduction in the membrane conductivity was observed. Surprisingly, no significant increase in the hydrogen crossover was observed, suggesting that the elevated temperature does not cause significant pinhole formation.The results shed light on the rate and mechanisms for ageing at various temperatures and can be used to determine the cost and benefits of operating at elevated temperatures.