Dynamic Testing of Cold Gas Sprayed Bipolar Plates–Porous Transport Layer Coating System in Proton Exchange Membrane Water Electrolysis

A key technology to minimize CO2-emissions is the production of hydrogen from water electrolysis. The proton exchange membrane water electrolysis (PEMWE) consists of a stacked system out of bipolar plates (BPP), porous transport layers (PTL) and a membrane electrode assembly (MEA). Research activities are ongoing to minimize material input, reduce costs and increase the performance. For example, the BPP on the anodic side of the stack is currently manufactured of bulk titanium and its substitution by a Ti-coated steel substrate is economically interesting. The main requirements for the BPP-coating are a high coating density, a low electrical resistance and a long lifetime in a harsh electrochemical environment. Coating application on substrates of s ≤ 0.5 mm thickness is conducted with three thermal spraying technologies: Cold Gas Spraying (CGS), High Velocity Air-Fuel (HVAF) spraying and High Velocity Oxy-Fuel (HVOF). Substrate preparation is examined as well. Coating development is conducted with regards to coating thickness, density and oxidation. The examination of coatings includes roughness analysis, structural and chemical analysis. The results allow an evaluation of the suitability of thermally sprayed Ti-coatings by the structural properties for the PEMWE application. Among the three tested processes, CGS is the most suitable for this type of application. The three chosen thermal spraying processes are examined for coating application on metal sheets in context of PEMWE for the first time.

Hydrogen is one of the most efficient energy carriers and can be produced by different methods. Among all the production methods, the proton exchange membrane water electrolyzer (PEMWE) is considered as the most promising technique to produce highly pure hydrogen from renewable energy sources with pure oxygen as by-products with no carbon emissions. The PEMWE technology has reached the early stages of commercial deployment while the mass production is tied to cost reduction. A PEMWE single cell comprises a membrane electrode assembly which considered as a core component where the electrochemical reactions take places in three phase boundaries. It also includes a titanium based porous transport layer (PTL) in anode side and carbon-based gas diffusion layer (GDL) in cathode side for the transportation of water and gas into and out of the cell. Additionally, bipolar plates (BPPs) with grooves provide mechanical support for the cell and distribute the water inside the cell and remove generated gases to the outlet trough flow field distribution channels. PTLs and BPPs, which are metallic components, are designed to endure the corrosive conditions present in the electrolyzer and they both needs protective coatings to stand at high voltage (<2 V), acidic media, temperature (60–80 °C) and oxygen saturated environment (anode).In this research, a modified electroplating process is used to deposit gold thin film as a protective film on both stainless steel (SS) and titanium based BPPs and PTLs, respectively. The electroplating of gold is a mature technology and easy to implement for large scale coating. This process will be impacted by many factors, such as the ingredient of plating solution, arrangement of electrodes, current distribution, and operating parameters. In addition, pre-treating the surface plays an important role to develop the durable thin films with proper adhesion. The gold striking underlayer on the SS substrate passivated the surface oxides and facilitated a dense electroplated chromium layer. Furthermore, a uniform gold protective layer was electroplated on the chromium coated substrate to achieve a promising anti-corrosive property. To evaluate the impact of pre-treatment and the anti-corrosion properties of the developed coating, different physical and electrochemical characterization techniques are conducted. As a result, The Au/Cr/Au coating on the SS substrate showed corrosion current density of 0.84 µA/cm2 and lower degradation as compared to without gold striking underlayer.The surface morphology and the crystallinity and phase analysis are investigated by scanning electron microscopy and X-ray diffraction (XRD), respectively. X-ray photoelectron spectroscopy (XPS) is used to study the surface properties and the bonds between the elements. The contact resistance also is studied under different pressures. In addition, traditional lab-scale durability analysis, using stagnant liquid electrolyte and three-electrode cell setups, might not provide such a precise information for PEM water electrolyzer. The three-electrode setup does not include crucial parameters relating to real cell-operating conditions or contributions to the PTL by other key cell components such as the membrane, catalyst layer, ionomer, and bipolar plates. Flow electrochemical setup is developed in our lab and is used to run the accelerate stress test to check the durability of the coated samples. Potentiodynamic, chronoamperometry and impedance also used to evaluate the samples. Figure 1. (a) Schematic of gold electroplating on the SS substrate, (b) SEM image and EDX analysis of Au/Cr/Au coating.We would like to acknowledge the support of the Natural Sciences and Engineering Research Council of Canada, Canada Research Chair and Mitacs Accelerate program and Intlvac Thin Film for their constant support. Figure 1

Polymer Electrolyte Membrane (PEM) electrolyzers as a promising technology in addressing climate change challenges and facilitating the development of renewable energy sources at lower costs. They offer clean operation and scalability, making them a valuable tool for harnessing energy without leaving any carbon footprint. However, a key challenge to widespread PEM electrolyzer adoption is the cost of the porous transport layer (PTL). In this study, we address this challenge by utilizing stochastic modeling to develop 3D PTL models numerically. To optimize the structural and transport properties of the PTL, we explored a range of combinations for the radius (2, 3, 4, 5 µm) and volumetric fraction (20%, 40%, 60%, 80%, 100%) of small fibers dispersed within a matrix of large fibers (6 µm) (Figure 1). The structural properties (e.g., mean surface roughness, specific surface area) were analyzed numerically, whereas transport properties (e.g., thermal conductivity, electrical conductivity, and diffusivity) were analyzed via pore network modeling. Before further analysis, our model was validated against both experimental and numerical results from previous research works. In our study, we observed that increasing the volumetric fraction of small fibers, while decreasing their radius, led to reduced surface roughness and higher thermal and electrical conductivity. However, this came at the cost of increased tortuosity, which hindered the diffusion and permeability of the material. Conversely, PTLs with a higher volumetric fraction of large fibers exhibited the opposite trend.By combining these insights, we developed customized multi-layer PTLs. These PTLs have a small fiber radius at the catalyst side and a large fiber radius at the flow-field side. This design leverages the advantages of both small and large fiber radii. Our customized multi-layer PTLs demonstrated improved gas removal, higher electrical conductivity, and better heat dissipation while maintaining good surface contact area and reduced roughness. To utilize the benefits of our modeled multi-layer PTL in an electrolyzer cell, the volumetric fractions of the fiber radius should be adjusted based on operating conditions. By tailoring the fiber characteristics and PTL geometries, we can develop optimized PTL models that can be scaled to real-time PEM electrolyzer setups for renewable energy generation, paving the way for a better future. Figure 1

One of the factors leading to a decrease in the efficiency of polymer electrolyte membrane (PEM) electrolyzers is the blockage of water transport pathways through the porous transport layer (PTL). The oxygen bubbles generated from the electrochemical reaction at the catalyst layer accumulate in the PTL, impeding the transport pathways and reaction sites for the reactant water (1). An improved understanding of oxygen bubble accumulation and water transport behaviour in porous transport layers is essential to reduce mass transport losses in PEM electrolyzers. This study presents a method to stochastically generate a PTL composed of sintered titanium (Ti) powders and investigate the transport properties using pore network modeling. A microscale X-ray computed tomography (µ-CT) was performed for a sintered Ti powder PTL sample to obtain a 2D density map. The density map contains material content information, providing higher intensity at the positions with higher material content. With the density map as an input, a stochastic model of the PTL was generated by placing Ti powder particles at positions decided by the density map and a probability function until the model reached the target volume (2). Two critical parameters are considered in this model: the seeding parameter, α, and a filling radius, β. The seeding parameter controls the number of Ti powder “seeds” that act as nucleation sites. The second parameter, the filling radius, allows the model to mimic the morphology of the sintered regions. The structural properties of the stochastic model are investigated by comparing the pore size distribution, throat size distribution, and the porosity profile to the µ-CT reconstruction. Pore network modeling is an alternative to continuum modeling for simulating transport in porous media. Pore network modeling simplifies the solution of differential equations for mass transport by treating the pore space as a network of pores and narrow throats (3). Using pore network modeling as the analysis tool, the in-plane permeabilities of the µ-CT reconstruction and the stochastic model were compared. The stochastic modeling of PTLs will facilitate the detailed parametric studies of PTL structural property impacts on transport and provide novel insights into mass transport behavior in PEM electrolyzers.References H. Ito, T. Maeda, A. Nakano, Y. Hasegawa, N. Yokoi, C. M. Hwang, M. Ishida, A. Kato, and T. Yoshida, International journal of hydrogen energy 35(18), 9550-9560 (2010). A. Ebrahimi Khabbazi, J. Hinebaugh, A. Bazylak, Science Bulletin, 61(8), 601-611(2016).A. Putz, J. Hinebaugh, M. Aghighi, H. Day, A. Bazylak, and J. T. Gostick, ECS Transactions, 58(1), 79-86 (2013).

Optimizing the structure of the porous transport layer (PTL) is crucial for improving the performance of proton exchange membrane water electrolysis (PEMWE), particularly for cells with low anode catalyst loadings. A growing number of studies reveal that catalysts are normally not entirely utilized in PEMWE, whereas the degree of catalyst utilization strongly depends on the structure of the PTL. As the oxygen evolution reaction (OER) at the anode is the limiting reaction step in PEMWE, inefficient use of the anode catalyst layer (aCL) would result in higher activation losses and, thus, cause a waste of unused catalysts [1–3]. This phenomenon becomes more serious when catalyst loading is reduced to meet the eco-friendly requirement of $2 per kgH2 while conserving noble material resources [4].Schuler et al. [1, 5] combined commercial CCMs with different PTL configurations, and found that with different aCL/PTL interface properties, the activation overpotential could have a maximum deviation of 20 mA at 0.1 A/cm2. Peng et al. [2] manufactured an ultra-low Ir loading CCM with 0.03 mgIr/cm2. Optimizing the aCL/PTL interface showed that the activation overpotential can have a maximum deviation of 40 mV at 0.75 A/cm2. Previous studies concluded that the aCL/PTL interface is crucial for improving the catalyst utilization. Consequently, the triple-phase boundary (TPB) site concept at the aCL/PTL interface is gaining more and more attention: the catalysts can only be entirely activated at reaction sites with sufficient water supply, ionic and electronic conductivities, and oxygen removal pathways [3]. According to TPB, not all reaction sites on the aCL meet these requirements. Figure 1 shows the corresponding physical picture. At the contact point of aCL and PTL (S) offers much greater electronic conductivity compared to the pore area (P), where electron removal is limited by the aCL in-plane conductivity (i.e., 1.85×106 S/m vs. 65.8 S/m) [3]. However, beneath the contact area (S), mass transport of oxygen is limited, indicating the necessity of optimizing the aCL/PTL interface.Figure 1: Illustration of physical picture at aCL/PTL interface.In our contribution, we implement a one-dimensional, one-phase model to investigate the interplay between PTL geometry at the aCL/PTL interface and catalyst utilization. The PTL transports water toward the aCL and electrons and oxygen toward the cathode and anode bipolar plates, respectively [6]. To simplify the physical conditions, we assume sufficient water supply and ion removal for the reaction sites on the aCL. Therefore, mass transport and electron transport limitations are only influenced by the aCL/PTL interface properties. Oxygen is assumed to dissolve in water only so that bubble formation does not disturb the reaction sites. Additionally, an ideal heat management condition is assumed in the model to achieve an isothermal condition. Our simulation results are in good agreement with literature, enabling the prediction of activation overpotentials corresponding to the PTL structure at aCL/PTL interface. Moreover, our results illustrate the local aCL behavior, which can be used to optimize the porous structure at the aCL/PTL interface, maximizing catalyst utilization. With our model, we aim to screen for an optimum PTL structure for a given aCL, allowing us to improve PEMWE cell performance by minimization of activation losses.

The anode porous transport layer (PTL) plays a crucial role in improving the energy density of proton exchange membrane (PEM) electrolyzer. The influence mechanism of PTL structural parameters and types on electrolysis performance has been investigated based on the voltage decomposition method and surface morphology characterization in this study. Among the Ti-Powder PTLs, which have relatively fixed and low porosity of 28%, PTL-1 with pore diameter of 4.5 μm performs the best, whereas PTL-4 with pore diameter of 62 μm shows the highest ohmic and mass transport over-potential. Specifically, the Ti-Fiber PTL exhibits changes in both porosity and pore diameter. PTL-6 with 50% porosity and PTL-8 with 75% porosity demonstrate superior performance. And this article develops an equivalent ohmic resistance model of the catalyst layer (CL) and proposes the concept of “substrate deadband” at the PTL-CL interface from the perspective of reaction interface construction. Based on the comparative evaluation of Ti-Powder PTL and Ti-Fiber PTL, it shows that the latter has a higher potential for performance improvement. Furthermore, the structure of Ti-Fiber PTL has been optimized and the current density has increased by 26.2% @ 2V, indicating a direction for the application and manufacturing of next-generation PTL.

Introduction Recently, proton exchange membrane water electrolysis (PEMWE) has been expected as the hydrogen production technologies to convert the renewable energy with regional and temporal unevenness into hydrogen, which can be stored and transported. PEMWE has a high energy conversion efficiency at the high current density, however it is required to reduce the high material cost due to the utilization of noble metals. Currently, the development of new components and the reduction the amount of noble metals have been conducted. The porous transport layer (PTL) is one of the most important elements to improve the efficiency of PEMWE. PTLs have the roles such as the transporting electrons between the catalyst layer (CL) and the end plate, the discharging the generated gas, and supplying water to CL. Therefore, the accurate separation and determination of the polarization in the electrolyzer are essential technologies. In that case, the potential measurement using reference electrodes can be useful. In this study, we measured the anode and cathode polarizations by the elimination of membrane resistance, and evaluated the polarization of anode PTLs with a small size electrolyzer using double references. Experimental Figure 1 shows the schematic drawing of 1 cm2 electrolyzer with double references. Hydrogen storage Pd reference (PdH) were placed on the membrane by the contact with 0.5 M H2SO4. Anode and cathode electrocatalysts were IrOx (TKK) and Pt/C (TKK), respectively. The 1.0 mgIr/cm2 of anode catalyst was decaled on PEM (Nafion®115, DuPont) with Nafion ionomer, and the 1.0 mgPt/cm2 of cathode catalyst was assembled on the membrane as a catalyst coated electrode supported a carbon paper (39BC, SIGRACET®). Pt plated Ti (MMC) and the carbon paper were used as the anode and cathode PTL, respectively. These electrodes were fixed straight (x = 0 mm) or shift (x = 0.3, 0.5, 0.7, 1.0 mm) stacking as shown in Fig. 1. Operation temperature of the electrolyzer conducted at 80℃. DI water was pumped and induced at flow rates of 10 ml/min and 2 ml/min to the anode and cathode, respectively. The performance was evaluated by the chronoamperometry (CA) and the electrochemical impedance spectroscopy (EIS). Results and discussion Figure 2 shows the relationship between the inner resistance R ac obtained from high frequency resistance of EIS and the direct current resistance R dc between references. The slopes of line, which passed through the origin, became larger as the increase of shift amount. As the slope represented θ, they can be written by equation (1). Next, using the α, the relationship between R dc and R membrane is defined by equation (2). Here, assuming that the contact resistance between PTL and CL is sufficiently small, R ac is equal to membrane resistance R membrane. Hence, R membrane can be calculated as α is equal to θ.Figure 3 shows the Tafel plots of anode and cathode polarization curves using reference electrodes of anode or cathode sides, and the membrane iR removed polarization curves E corrected , assuming the reference potential was equivalent to 8 % (= (100-84)/2) from the electrode/electrolyte interface (x = 1.0 mm). E corrected on cathode side was approximately identical to the extrapolated Tafel slope, and there was no mass transfer effect, which is the difference between the two curves. The reason is that the cathode side was only hydrogen generation by supplying electrons. On the other hand, E corrected on anode side showed the overpotential for the extrapolation of Tafel slope above anode potential of 1.4 V vs. PdH, and especially in the high current density area, it was affected by larger mass transfer resistance than cathode side. This overpotential was considered the water/oxygen transfer resistance or/and the transfer resistance related to the electrons in CL around PTL.Figure 4 shows the comparison of overpotential for anode PTLs. In this current density range, these plots showed the linear relationship between the overpotential and the current density. To compare the anode PTLs, PTL A indicated smaller overpotential than PTL B with smaller pore size and bigger porosity.In conclusion, the double references potential measurement with shift arrangement of electrodes enabled to separate the polarization into anode and cathode, and remove the membrane iR. Based on this method, this measurement method using the developed electrolyzer indicated to be able to evaluate the difference of PTL overpotential for the several type PTLs. Acknowledgment This study was supported by the development of fundamental technology for advancement of water electrolysis hydrogen production in advancement of hydrogen technologies and utilization project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) in Japan. Figure 1

Proton Exchange Membrane Water Electrolysers (PEMWEs) is among the most promising approaches for green hydrogen production due to its rapid response times and high-power density operation, which make this electrolysis technology well-suited to harvest the intermittent power from wind and solar plants. Nevertheless, the commercial breakthrough of PEMWE technology continues to face barriers due to its costs [1]. The porous transport layer (PTL) is one of the PEMWE components that facilitates the transport of incoming water to the catalyst layer and the removal of the product gases, hence it is very important for good electrolyser performance. The state-of-the-art PTLs are manufactured by high temperature sintering of titanium fibers or powders, which can generate oxidized surfaces that will reduce PEMWE performance. Furthermore, titanium is listed by the European Union as a critical raw material since 2020 [2], so it is advisable to reduce the amounts of its use to produce PTLs. Additionally, the (micro)structure of state-of-the-art PTLs is not optimized for efficient liquid and gas transport in electrolysis. The manufacturing process plays a key role in achieving PTLs with optimized liquid and gas transport as well as reducing the usage of titanium.In this work, we used lithography to manufacture PTLs in which the (micro-)structure can be optimized and the usage of titanium metal can be significantly reduced. The lithography manufactured PTLs were used as substrates to produce catalyst-coated electrodes (CCE) with (ultra-)low loadings of iridium and the PEMWE performance was evaluated, respect to CCEs manufactured on commercial PTLs. We demonstrate similar performance of the CCEs manufactured with the engineered PTL, with the advantage of using less titanium and being able to tune the (micro-)structure of the component.

The impacts of sintered titanium powder diameter and porous transport layer (PTL) porosity on reactant transport and PTL-catalyst layer (CL) contact in the polymer electrolyte membrane (PEM) electrolyzer were studied using stochastic generation and a pore network model. Enhanced reactant transport was established with increased powder diameter and porosity, observed through increases in single- and two-phase permeabilities. Compared to increasing the powder diameter, increasing the PTL porosity dominated increases in permeabilities, especially at higher porosities (e > 40%). However, we observed a trade-off whereby increasing the powder diameter led to increased surface roughness at the PTL-CL interface. High roughnesses were observed at porosities > 40%. In conclusion, the powder diameter and porosity must be strategically selected for the desired target operating conditions of the PEM electrolyzer.

Proton exchange membrane (PEM) water electrolysis is a technology designed to produce H2 using only water and electricity as inputs; it has gained increased attention in industry and academia due to its advantages over incumbent H2 generation processes (of which the most widely used are steam reforming and coal gasification) namely, low temperature, carbon-neutral and intermittent operation. PEM electrolysis can be instrumental for creating a hydrogen economy, although still much research needs to be carried out before widespread industrial adoption is achieved. PEM water electrolyzers suffer energy losses associated with the chemical reactions and the transport of charge and mass; of these phenomena, mass transport in PEM electrolyzers is the least understood subject, given the complex nature of the interaction of multiphase flows (mainly consisting of liquid water and evolved gases) through micrometric pores. The subject of multiphase flow in water electrolysis and its relationship with the mass transport phenomena in PEM water electrolysis has been a prevalent subject in the literature. Despite numerous attempts at pinpointing the relationship between mass transport overpotential and the operating parameters, there is no clear consensus about which transport mechanisms dominate, nor about how the component design of PEM electrolyzers affects the mass transport. While the effect of temperature and current density on mass transport losses has been extensively studied and is well understood, there are significantly fewer studies that focus on the effect of water flow and pressure. Both water flow and pressure have a direct effect on mechanisms such as bubble nucleation and two-phase flows that occur in the porous structures within a PEM electrolyzer (electrodes and porous transport layers, PTLs). In this work, I studied the effect of water flow and pressure on the mass transport phenomena in PEM electrolyzers. Chapters 1 and 2 provide an introduction to the topic as well as a description of the materials and experimental setups used. Chapter 3 of this thesis depicts the visualization and modeling of bubble nucleation in an operating PEM electrolyzer. I discovered that bubble detachment radii are largely independent of water flow and I identified two types of bubbles: bubbles that detach after reaching a critical size, and bubbles that fill up the pores of a PTL before detaching. Chapter 3 consists of the measurements I carried out regarding the transport of evolved gas through the water-filled pores of a PTL, where I observed that water flow severely impedes the gas transport through the pores and that such impediment is related to a shear stress exerted by the water flow on the pores. Chapter 5 shows the measuring of mass transport losses using electrochemical impedance spectroscopy (EIS) on an operating PEM electrolyzer; the results indicate that pressure and water flow affect the diffusion of gas in the electrode and that the mass transport overpotential depends on design parameters of the PEM electrolyzer, such as electrode thickness and hydrophobicity. Overall, I derived a theoretical framework based on the assumption that the evolved gas in a PEM electrolyzer permeates through the PTL after diffusing from the active sites to the bubble nucleation sites. Such framework, constructed on the basis of the models regarding gas transport in porous media, can be used to explain the mass transport loses in a PEM electrolyzer that arise from operating with increased water flows and pressures. The model I derived can be used in future work as a guideline to optimize the components of a PEM electrolyzer, in particular regarding the hydrophobicity and pore size distribution of PTLs as well as the composition of the catalyst ink to produce the electrodes. Moreover, this work can also be used to further understand the mass transport losses and optimize the operation of PEM electrolyzers to decrease the energy consumption of H2 generation.

Proton exchange membrane water electrolysis (PEMWE) combined with renewable energy sources such as wind, solar, geothermal provides a sustainable solution for green hydrogen production. In structure of a PEMWE, the porous transport layers (PTL) is a key component of a PEMWE. In order to meet the primary requirement of a PEM water electrolyzer, PTL should be corrosion-stable, have good electrical conductivity, and be mechanically stable for operation at differential pressures. Material porous titanium is the most typically used to construct PTL of PEMWE. However, titanium is also oxidized under the harsh conditions of PEMWE. Forming a passive layer of titanium oxide on the surface of titanium greatly reduces the conductivity of titanium. To limit these disadvantages, in this study, a thin layer of platinum was deposited onto the porous transport layers using DC plating technique. The conditions of DC plating were investigated, experimented and evaluated, from which the current density of 3 mA/cm2 for the platinum coating has the best electrical conductivity and corrosion resistance, which contributes to reducing the precious metal content in PEMWE.

In this work, ≈25 μm thin titanium microporous layers (MPLs) with ≈2 μm small pores and low surface roughness were coated and sintered on top of ≈260 μm thick commercial titanium-powder-sinter sheets with ≈16 μm pores, maintaining a porosity of ≈40% in both layers. Serving as porous transport layers (PTLs) on the anode side in proton exchange membrane water electrolyzers (PEMWEs), these pore-graded, two-layer sheets (“PTL/MPL”) are compared to single-layer PTLs in single-cell PEMWEs. The PTL/MPL samples prepared here give a 3–6 mΩ cm2 lower high-frequency resistance (HFR) compared to the as-received single-layer PTL, which is attributed to a partial reduction of the TiO2 surface passivation layer during the MPL sintering process. For ≈1 μm thin anodes with an iridium loading of ≈0.2 mgIr cm−2, the use of an MPL leads to a ≈24 mV improvement in HFR-free cell voltage at 6 A cm−2. As no such benefit is observed for ≈9 μm thick anodes with ≈2.0 mgIr cm−2, mass transport resistances within the PTL/MPL play a minor role. Possible reasons for the higher catalyst utilization in ultra-thin electrodes when using an MPL are discussed. Furthermore, an MPL provides superior mechanical membrane support, which is particularly relevant for thin membranes.

As the most attractive energy carrier, hydrogen production through electrochemical water splitting (EWS) is promising for resolving the serious environmental problems derived from the rapid consumption of fossil fuels globally. The proton exchange membrane water electrolyzer (PEMWE) is one of the most promising EWS technologies and has achieved great advancements. To offer a timely reference for the progress of the PEMWE system, the latest advancements and developments of PEMWE technology are systematically reviewed. The key components, including the electrocatalysts, PEM, and porous transport layer (PTL) as well as bipolar plate (BPP), are first introduced and discussed, followed by the membrane electrode assembly and cell design. The highlights are put on the design of the electrocatalyst and the relationship of each component on the performance of the PEMWE. Moreover, the current challenges and future perspectives for the development of PEMWE are also discussed. There is a hope that this review can provide a timely reference for future directions in PEMWE challenges and perspectives.

To reach Department of Energy (DOE) target of 1$ cost for 1 kg of H2 production in 1 decade the cost of green hydrogen generation needs to decrease. IrOx is a used as an electrocatalyst in anode electrode of proton exchange membrane water electrolyzers (PEMWE) and its loading must decrease below 2 mg/cm2 to reach the cost targets for electrolysis. One of the hurdles of catalyst layers with low IrOx loading is the inplane electric conductivity, which will be low as IrOx is not supported by carbon or other conductive additive. Therefore, the design of porous transport layers (PTLs) becomes critical to ensure a good interface contact area with the catalyst but at the same time optimal oxygen removal from the catalyst. In our earlier study we showed that PTLs with intermediate porosities of ~60 % achieved this goal [1]. In this work we use operando x-ray computed tomography to visualize oxygen transport inside the PTLs for the cells having various catalyst loadings and various PTLs (sintered and fiber). Using a staining agent of NaI we were able to differentiate between water and oxygen as shown by Figure 1. Oxygen transport pathways and oxygen content within the PTLs was studied using various cell configurations and current densities. This work will identify a path forward for designing PTLs for PEMWE.

Hydrogen plays a significant role in the transition of the global energy system towards achieving net-zero emissions. According to the “Hydrogen for Net-Zero” report by Hydrogen Council and McKinsey & Company, the demand for clean hydrogen could reach 140 metric tons (MT) by 2030, with a further increase to 660 MT by 2050. For future high-volume production of green hydrogen, Proton Exchange Membrane Water Electrolysis (PEMWE) is a crucial technology due to its advantages of high-purity hydrogen, large operational current densities, and great energy conversion efficiency [1]. However, the use of precious metal-based catalysts for the sluggish oxygen evolution reaction (OER) on the anode side hinders the high-volume manufacturability of PEMWE. To ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production, developing strategies to reduce Iridium loading to 0.1 - 0.2 mg Ir/cm2 without compromising overall performance is essential. The challenge of reducing Ir loading also involves improving or maintaining the electrical contact between the catalyst layers and the substrate [2-3].Smoltek Hydrogen has made significant strides in achieving low iridium loading through our innovative Porous Transport Electrode (PTE) concept. This approach involves modifying a Porous Transport Layer (PTL) by growing vertically aligned Carbon Nanofibers (CNFs) using our in-house patented technology, efficiently increasing surface area [4]. Following this modification, a protective layer of corrosion-resistant and conductive material (e.g., Platinum) is applied to the CNFs. Subsequently, an OER catalyst layer is deposited utilizing a three-electrode cathodic electrodeposition method (Fig. 1a and 1b). The electrodeposited Ir catalyst exhibits strong adhesion to the CNF PTEs, resulting in a high electrical conductivity [5].In this work, we successfully reduced Ir loadings to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in the half-cell tests (Fig. 1c). In the PEMWE tests, the polarization curves of electrodes with low Ir loading exhibited superior performance compared to cells with significantly higher Ir loading (Fig. 1d). The next step of our research involves conducting constant current durability tests for over 600 hours on PEMWE operation using low Ir loaded PTEs. The aim is to minimize degradation and overcome mass transport limitations, particularly at higher current densities.These unique PTEs developed by Smoltek Hydrogen, with CNF technology, maximize the electrode surface area and pave a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References https://www.iea.org/reports/hydrogen-2156#dashboardMöckl et al. J. Electrochem. Soc., 2022, 169, 064505.Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.https://www.smoltek.com/applications/electrolyzers/Krivina et al. Adv.Mater., 2022, 34, 2203033.https://publications.jrc.ec.europa.eu/repository/handle/JRC104045 Figure 1