Thermodynamic and Electrochemical PEM Electrolysis Process Optimization by Multi-Scale System Simulation

Mathematical modeling of an integrated photovoltaic-assisted PEM water electrolyzer system for hydrogen production

Photovoltaic-based integrated energy systems act as a possible modern technological solution for clean and affordable green hydrogen production. However, research attempts are required from the scientific community to develop power management, control, optimization algorithms, and new techniques for these integrated energy systems effective and economical operation. The integrated energy system considered in this work consists of a solar photovoltaic, battery, grid and proton exchange membrane (PEM) electrolyzer. PEM electrolyzer with a power rating of 100 kW is modelled as a controlled current sink to interfere with the DC bus directly. This work proposes a power management and control algorithm for the photovoltaic-based integrated energy system considering different parameters like availability of solar photovoltaic power, DC link voltage, battery state of charge (SOC), tariff and availability of grid power. Effective power-sharing among the different power sources increases system reliability and stability. Optimization is performed for optimal sizing and costing to achieve economical operation such that these photovoltaic-based integrated energy systems become affordable and are encouraged for wide use. The photovoltaic system operates at the maximum power point through a neural network-based control strategy; in addition to this, stacking in neural network topologies is also discussed for improving system accuracy in tracking the reference voltage for MPPT operation. The DC link voltage is controlled by interfacing the battery with the DC link via a bidirectional buck-boost power converter. The contribution of the work is to highlight the role of renewable energy sources for continuous green hydrogen production. Green hydrogen will be a critical driving force for the future transportation system, fuel cell-based power generation, and industries utilizing hydrogen in direct or indirect forms-that will help transition towards a carbon-free society. Optimization and time-domain simulation results indicated the economic and technical feasibility of the proposed photovoltaic-based integrated energy system for green hydrogen production with the best optimal configuration producing hydrogen at the cost of $ 4.806/kg and total net present cost of $749904.

Proton exchange membrane (PEM) water electrolysis offers significant potential for sustainable production of green hydrogen due to its high current density, superior hydrogen purity, and excellent conversion efficiency. However, widespread industrial implementation remains challenging because state-of-the-art oxygen evolution reaction (OER) catalysts heavily rely on iridium, a precious metal with limited global supply and high costs.1–4 Therefore, considerable research efforts have been dedicated to developing new catalysts requiring lower iridium loadings. Although PEM electrolysis typically operates at elevated temperatures (50-80°C),1 most studies assessing catalyst activity and stability have been performed at room temperature, and the limited available temperature-dependent studies primarily focus on alkaline environments.5,6 In this work, we have systematically investigated the temperature-dependent activity and stability of two representative Ir-based catalysts: a commercial IrO₂ catalyst and a supported core-shell Ir@IrOₓ catalyst. Using a high-temperature rotating-disk electrode (RDE) setup, electrochemical assessments of the activity and stability of the catalysts were performed across a range of operating temperatures from 20°C up to 80°C. We investigated how the increased operating temperature affects the OER activities of these two catalysts, observing not only enhanced kinetics with the increased working temperatures but also altered reaction mechanisms, as indicated by the Tafel analysis of the OER polarization curves. Furthermore, by employing an accelerated stress test protocol, we evaluated the stability of the two catalysts under varied temperatures. Comprehensive in-situ and post-mortem characterization techniques, including in-situ XRD, XPS (Figure 1), TEM, and ICP, were employed to investigate the structural changes of the catalysts during the stability tests, which revealed the accelerated degradation at higher working temperatures, but also the surprisingly high OER stability of the core-shell Ir@IrOx structure under high working temperatures.Figure 1: Comparison the Ir 4f XPS spectra of the sample before and after the stability test at 60 °C.References Carmo, M., Fritz, D. L., Mergel, J. & Stolten, D. A comprehensive review on PEM water electrolysis. Int J Hydrogen Energy 38, 4901–4934 (2013). Wang, C. & Feng, L. Recent advances and perspectives of Ir-based anode catalysts in PEM water electrolysis. Energy Advances 3, 14–29 (2024). Kibsgaard, J. & Chorkendorff, I. Considerations for the scaling-up of water splitting catalysts. Nature Energy 2019 4:6 4, 430–433 (2019). Reier, T., Oezaslan, M. & Strasser, P. Electrocatalytic oxygen evolution reaction (OER) on Ru, Ir, and pt catalysts: A comparative study of nanoparticles and bulk materials. ACS Catal 2, 1765–1772 (2012). Shi, G. et al. Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni-Co Oxide Catalysts with Amorphous/Crystalline Surfaces. ACS Catal 12, 14209–14219 (2022). Lyu, X., Li, J., Yang, J. & Serov, A. Significance of slight ambient temperature variation on the electrocatalyst performance toward oxygen evolution reaction. J Environ Chem Eng 11, 111492 (2023). Figure 1

Green hydrogen & electricity production via geothermal-driven multi-generation system: Thermodynamic modeling and optimization

Evaluation of carbon-supported Pt and Pd nanoparticles for the hydrogen evolution reaction in PEM water electrolysers

Electrolysis – Proton-exchange membrane electrolyzer | Proton exchange membrane water electrolysis: State-of-the-art technique and systems

This article aims to develop a proton exchange membrane (PEM) electrolyzer emulator. This emulator is realized through an equivalent electrical scheme. It allows taking into consideration the dynamic operation of PEM electrolyzers, which is generally neglected in the literature. PEM electrolyzer dynamics are reproduced by the use of supercapacitors, due to the high value of the equivalent double-layer capacitance value. Steady-state and dynamics operations are investigated in this work. The design criteria are addressed. The PEM electrolyzer emulator is validated by using a 400-W commercial PEM electrolyzer. This emulator is conceived to test new DC-DC converters to supply the PEM ELs and their control as well, avoiding the risk to damage a real electrolyzer for experiment purposes. The proposed approach is valid both for a single cell and for the whole stack emulation.

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

This study presents exergetic assessment of a high-pressure hydrogen production system (HPS). The system considered in this study includes a high-pressure proton exchange membrane (PEM) electrolyzer, two heat exchangers, a motor pump system, a circulation pump, and a hot water tank. In order to perform the main objective of this study, the following important parameters are taken into consideration: (1) the operating pressure (ranging from 1 to 200 bar), (2) the operating temperature (ranging from 70 to 80 °C), (3) dead-state temperature (assumed to be 25 °C), (4) the energy efficiency of the PEM electrolyzer (ranging from 0.5 to 1), (5) the pump efficiency (assumed to be 0.8), (6) mass flow rate of hydrogen from PEM electrolyzer (3 kg per hour), and (7) mass flow rate of pure water supplied to the PEM electrolysis (27 per hour). Considering all these parameters, exergy analysis is performed for the HPS. The results show that exergy efficiency of HPS increases with the rise of the operating pressure and temperature. It thus requires a higher amount of energy input. In this regard, there is a strong need to optimize the process.

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.

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

As the focus on green hydrogen production using renewable energy sources (RES) intensifies, selecting the most suitable RES becomes increasingly important. Solar energy has the advantage of being universally available and minimally dependent on natural topography. However, fluctuations in solar output due to factors such as season and weather lead to repetitive increases and decreases in power, posing a challenge to the components of hydrogen production devices, specifically proton exchange membrane water electrolyzers (PEMWE). Therefore, a precise durability evaluation of PEMWE under fluctuating loads is crucial for assessing the remaining lifespan and determining optimal timing for component replacement. However, existing durability evaluation methods, which often rely on periodic cycling or constant maintenance of current and voltage, fail to accurately capture the complex and intermittent nature of RES power. This presentation introduces a high-resolution “realistic” solar profile as an advanced durability evaluation technique for green hydrogen production. Developed by converting actual solar irradiance data from solar panels into current densities in combination with water electrolysis stack data, this profile facilitates a more nuanced understanding of durability under realistic conditions. Additionally, after applying a long-term durability test using this solar profile, the degradation features of core components (catalyst, membrane, porous transport layer) were systematically analyzed through electrochemical, spectroscopic, and microscopic characterizations, providing valuable insights into degradation and recovery dynamics. Notably, the tests featuring the simulated solar profile showed overpotential recovery during “night” periods, potentially due to the formation of active species and the release of residual gases, underscoring the importance of intermittent zero-load steps. Overall, this durability evaluation technique not only diagnoses the precise condition of solar-powered PEMWE but also offers a rational guideline for the development of core components. Moreover, this technique is expected to be applicable to PEMWEs powered by other RES, such as offshore and tidal power, broadening its utility in the field of green hydrogen production technologies.

Electricity and hydrogen co-production via scramjet multi-expansion open cooling cycle coupled with a PEM electrolyzer

Hydrogen production from proton exchange membrane (PEM) water electrolysis is attractive due to its simple and clean nature. Membrane and electrode assemblies (MEAs) of PEM electrolyzers typically use iridium (Ir) as an anode catalyst and Pt as a cathode catalyst. The durability of MEAs plays an essential role for the electrolyzers’ lifetime and cost. However, unlike the well-established MEA durability protocols of PEM fuel cells, there have been a lack of effective procedures for PEM electrolyzer MEA durability evaluation. The objective of this work is to establish a series of test protocols that can help to rapidly evaluate PEM electrolyzer MEA durability. Three testing approaches have been used in this work, which include high-voltage hold (>1.8 V), voltage cycling (1.4 to 1.8 V or 2.0 V), and constant low-current operations. The electrochemical surface area (ECSA) and polarization curves of the MEAs will be obtained after each test. Two categories of anode catalysts have been evaluated using the above durability test protocols: one is the commercial Ir black and the other is Ir supported on tungsten-doped titanium oxide (Ir/WxTi1-xO2) developed at Giner. The supported Ir/WxTi1-xO2 catalyst proves to possess 8-10 x higher mass activity than the Ir black. The MEAs made of these two anode catalysts have been evaluated at a variety of loading, low (0.1 mg/cm2), medium (0.4 mg/cm2) and high (1.0 mg/cm2). Figure 1 shows the durability of these two catalysts after voltage cycling from 1.4 V to 1.8 V: (a) 2 mg/cm2 Ir from Ir black; (b) 0.4 mg/cm2 Ir from Ir/WxTi1-xO2. It can be seen that at medium to high Ir loadings, these two catalysts demonstrates minimal performance decay after voltage cycling. The morphology and structure of MEAs after durability tests will be characterized to correlate to their performance and to elucidate their degradation mechanisms. Acknowledgement: The financial support is from the Department of Energy under the Contract Grant DE-SC0007471. Figure 1

Magnetron sputtered Ir thin film on TiC-based support sublayer as low-loading anode catalyst for proton exchange membrane water electrolysis