SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A standardized procedure for rotating disk electrode (RDE) experiments for the ex-situ characterization of oxygen evolution reaction (OER) catalysts for PEM water electrolyzers. This protocol should allow for the analysis of onset potential, overpotential at a fixed current, catalytic activity, and electrochemical surface area of these catalysts.
Explore the source record for details and available documents.
Renewable hydrogen is becoming globally recognized as a key component required for de-carbonization of our energy system, both as a medium for capture of excess renewable energy sources, vehicle refueling, and as an intermediate for multiple industrial processes. Hydrogen production, via low-temperature electrolysis, is a flexible grid-friendly, clean energy carrying intermediate that enables fast ramp and de-ramp rates as naturally varying solar, wind, and storage systems become a larger percentage of the electricity mix. Analysis shows that by 2050, employing renewable hydrogen at scale can decrease total U.S. CO 2 emissions by about half relative to business as usual, critical to achieving >80% greenhouse gas reduction targets. Energy storage systems help commercial customers reduce their electric bills by storing energy from the grid or from renewable electricity sources when energy is inexpensive, then using that stored energy when demand and prices are high. Proton exchange membrane (PEM) electrolysis is one of the few technologies that can produce hydrogen with zero carbon emissions at relevant scale (hundreds of MWs) in the near term. NREL's research has shown that electrolyzers are fast and flexible enough to participate in energy and ancillary service markets that can help stabilize the grid. In 2015, Proton OnSite (now NEL Hydrogen) introduced the M-series electrolyzer platform, the world's first megawatt PEM electrolyzer for the global energy storage market, offering a carbon-free source of hydrogen fuel or process gas. In addition, the ability to sell the hydrogen into a high value application like vehicle (e.g., light- and heavy-duty and material handling) fueling allows for a layering of revenue streams that creates better business cases for hydrogen energy storage systems (HES). The ability to provide multiple value streams from the fast-responding controllable electrolyzer will have a direct impact on the net cost of hydrogen.
The development and installation of a flexible low-temperature electrolyzer research capability at the multi-MW scale with integrated renewables will help lower the cost barrier to entry for electrolyzer manufactures needing at scale system and stack evaluation and enable more electrolyzer manufactures to accelerate to commercialization with building block scale demonstration and validation. This NREL capability represents a DOE HFTO investment to support the $1B DOE Clean Hydrogen Electrolysis Program working to achieve the Hydrogen Shot goal of $1 for 1 kg hydrogen in 1 decade, lower greenhouse gas emissions and criteria pollutants, build clean energy infrastructure, and provide pathways to private sector uptake.
Driven by environmental and health concerns related to per- and polyfluoroalkyl substances (PFAS), there has been growing interest in developing fluorine-free proton (H + ) exchange membrane (PEM) materials for fuel cells and water electrolyzers. In this study, we present a side-by-side comparison of the key transport properties of submicron thick, PFAS-free amorphous silicon dioxide (SiO 2 ) membranes to Nafion, a fluorinated polymer electrolyte membrane that represents the industry standard for PEM fuel cells and electrolyzers. Here, measurements of proton (H + ) conductivity (σ H + ), hydrogen (H 2 ) permeability (P H 2 ), and electrical resistivity (ρ e – ) were conducted using model thin films comprised of SiO 2 membranes deposited by atomic layer deposition (ALD). Although the H + conductivity of the SiO 2 membranes is 2–3 orders of magnitude lower than Nafion, the addition of phosphorus dopants (PO x ) improves H + conductivity such that the area specific membrane resistance of thin (<50 nm) PO x -doped SiO 2 membranes is more than an order of magnitude lower than Nafion-117. Importantly, the safe operation of such nanoscale membranes within a PEM electrolyzer is feasible thanks to the low H 2 permeability of dense SiO 2 -based membranes, which are predicted to limit H 2 crossover rates to acceptable levels for pressures up to ≈ 100 bar. As a proof-of-principle demonstration, a chip-scale water electrolyzer based on 100 nm thick PO x -SiO 2 membrane is shown to achieve a current density of 2 A cm –2 at a potential of 2.5 V. If this technology can be successfully scaled up, H + conducting oxide membranes offer an attractive PFAS-free alternative to Nafion for efficient and durable water electrolysis and fuel cell technologies.
A critical challenge for the implementation of proton exchange membrane (PEM)-based water electrolyzers for the H2@Scale vision is the capital cost, which is largely driven by related factors of overdesign and highly manual legacy manufacturing methods. Typical electrolyzer cells have an order of magnitude higher membrane thickness and catalyst loading vs. fuel cells, in part because the manufacturing methods being used are not capable of producing uniform and reliable electrodes on thin membranes with low loading. Advanced electrode manufacturing is therefore the key enabler to reduce the cost of the electrolyzer stack, particularly roll-to-roll (R2R) manufacturing of catalyst coated layers (CCLs) and catalyst coated membranes (CCMs). The electrolyzer manufacturing process still relies on traditional sheet-to-sheet (S2S) processes, which requires intensive labor to make parts to meet the specification requirements. This project leverages fuel cell expertise (GM) with Proton’s knowledge of electrolyzer components to develop the electrocatalyst ink formulations and coating processes using slot die (ORNL) and gravure (NREL) coatings, with proof of concept at the pilot-scale (Kodak).
This work aims to evaluate alternative proton exchange membranes (PEMs) that are environmentally safe, cost-effective, and structurally sound for use in PEM fuel cells and water electrolyzers.
X-ray photoelectron spectroscopy (XPS) is one of the most common techniques used to analyze the surface composition of catalysts and support materials used in polymer electrolyte membrane (PEM) fuel cells and electrolyzers, providing important insights for further improvement of their properties. Characterization of catalyst layers (CLs) is more challenging, which can be at least partially attributed to the instability of ionomer materials such as Nafion during measurements. This work explores the stability of Nafion during XPS measurements, illuminating and addressing Nafion degradation concerns. The extent of Nafion damage as a function of XPS instrumentation, measurement conditions, and sample properties was evaluated across multiple instruments. Results revealed that significant Nafion damage to the ion-conducting sulfonic acid species (>50% loss in sulfur signal) may occur in a relatively short time frame (tens of minutes) depending on the exact nature of the sample and XPS instrument. This motivated the development and validation of a multipoint XPS data acquisition protocol that minimizes Nafion damage, resulting in reliable data acquisition by avoiding significant artifacts from Nafion instability. The developed protocol was then used to analyze both thin film ionomer samples and Pt/C-based CLs. Comparison of PEM fuel cell CLs to Nafion thin films revealed several changes in Nafion spectral features attributed to charge transfer due to interaction with conductive catalyst and support species. This study provides a method to reliably characterize ionomer-containing samples, facilitating fundamental studies of the catalyst-ionomer interface and more applied investigations of structure-processing-performance correlations in PEM fuel cell and electrolyzer CLs.
Polymer electrolyte membrane (PEM) water electrolysis is a promising technology to efficiently produce green hydrogen. Irregularities in membrane electrode assembly (MEA) component materials caused by manufacturing, processing, handling, or operation can lead to performance loss and failure. One example is the presence of pinholes in the membrane, which can cause increased gas transport (crossover) and lead to electrical shorting. This work investigates the effects of intentionally introduced pinholes with various sizes up to 350μm in diameter. The presence of the pinholes resulted in minimal impacts on the cell voltage (±30 mV at 4Acm -2 ). However, the pinholes significantly increased H 2 crossover, which decreased hydrogen production efficiency and increased the minimum current density for safe operation. The impacts of the pinhole on the H 2 crossover and efficiency are more severe for open pinhole features than tear-like pinhole features. In conclusion, this research demonstrates that even small pinholes cannot be disregarded from a safety, efficiency, and operating strategy perspective.
Hydrogen is the most common element in the universe, comprising nearly 75% of all normal matter, and it has been used by scientists for centuries, but it was not fully recognized as an element until 1766, when it was isolated by Henry Cavendish. Early work focused on the generation of hydrogen through the oxidation of metals in water, which released hydrogen gas. Hydrogen’s lighter-than-air and flammable properties were immediately used in engines, zeppelins, and as feedstock for a wide variety of chemical reactions. Several approaches were developed for the production of hydrogen with the most common being associated with the production and conversion of hydrocarbon-based fuels. Coal gasification, steam methane reforming, and other reformation processes provide the majority of current hydrogen production due to the relatively low cost of hydrogen produced through these processes. More than 95% of hydrogen production is used for industrial processes rather than energy storage. To facilitate affordable decarbonization of these industrial processes and to advance the use of hydrogen as a fuel in transportation, DOE launched the Hydrogen Shot as part of the Energy Earthshots Initiative. The goal of the Hydrogen Shot is to reduce the cost of clean hydrogen by 80% to $1/kg of clean hydrogen production within one decade (known as the “1 1 1” goal). This is distinct from the Long-Duration Storage Shot, which is the primary focus of this report; however, it is intrinsically linked to bidirectional hydrogen storage. Several important chemical synthesis processes are dependent upon hydrogen, and the production and use of hydrogen is generally driven by its connection to one of these markets. For example, ammonia is one of the most highly produced chemicals in the world and it depends chiefly on hydrogen. Ammonia is primarily used for agricultural fertilizer and is considered to be largely responsible for a doubling of agricultural production per unit of land over the last century. Another one of hydrogen’s primary uses is as a catalyst in petroleum refining during the desulfurization process. Beyond chemical production, hydrogen is used as a reductant in the production of steel and has been demonstrated as a substitute for metallurgical coal in the production of raw iron. It is even used in the hydrogenation reaction for food products to create more shelf-stable semi-solid fats. However, while hydrogen is produced on the order of 100 million metric tons/year globally to feed these industries, more than 95% of hydrogen is produced from hydrocarbons that emit CO2 during the process. Conversely, electrolysis is a process by which electricity is used to separate hydrogen and oxygen in water molecules, usually across a membrane. Hydrogen production via electrolysis lowers the carbon intensity of produced hydrogen when coupled with low-carbon electricity. Currently, global electrolysis capacity is on the order of 1 GW, which equates to about 500 metric tons/day of hydrogen production. To support large-scale industrial decarbonization, capacity will likely need to increase by two to three orders of magnitude. Electrolysis technology is broadly separated into groups that are defined by the electrolyte used, with further subdivision based on the operating characteristics. The majority of commercial electrolyzer systems are based around three main technology groups: liquid alkaline, proton exchange membrane, and solid oxide. Liquid Alkaline (LA) electrolysis is the oldest, most mature, least expensive, and most common commercial technology, with 400 plants in operation by 1902. Its hydrogen output is low relative to the size of the system due to a low current density. LA electrolysis utilizes a liquid potassium hydroxide solution as the electrolyte. Proton exchange membrane (PEM) electrolysis (also known as polymer electrolyte membrane electrolysis), described in 1960, relies on an acid-impregnated polymer membrane as the electrolyte and typically offers three to six times higher hydrogen production per unit cell area than LA electrolysis. Solid oxide electrolysis, or high-temperature electrolysis, utilizes a ceramic cell as the electrolyte and operates on steam rather than liquid water, enabling electrical efficiencies of more than 90%, which is up from 60% with PEM. Two pre-commercial electrolyzer technologies to note are alkaline exchange membrane (AEM) and proton-conducting solid oxide electrolysis cell (SOEC). AEM potentially has the advantages of both LA and PEM technologies in that it is able to use low-cost materials like LA but with the ability to operate at higher output pressures with a smaller footprint like PEM. Proton-conducting SOEC is similar to commercial SOEC, which uses an oxide-conducting ceramic; however, it uses a proton-conducting ceramic that has the potential to operate at lower temperatures and has lower capital costs. Each of these technologies is experiencing a rapid improvement in performance and a reduction in installed cost, and each appears to be well suited to specific applications. Besides differences in the type of electrolyzer used, the main difference in the architecture of bidirectional hydrogen systems is how the hydrogen is stored. Currently, the most cost-effective way to store large amounts of hydrogen gas is underground, such as in large salt caverns that have been hollowed out. These salt caverns are geographically concentrated in small portions of the United States and are not generally near large metropolitan areas; however, other subsurface architectures are being investigated to expand this reach. A more widely deployable option is aboveground pressurized tanks. These systems are about 10 times as expensive because of the materials and safety margins required to hold hydrogen at high pressures. A third option is using materials-based storage, such as liquid organic hydrogen carriers. By reversibly attaching the produced hydrogen to other molecules, it can be stored at near atmospheric pressure and room temperature. This has the potential to reduce the material cost of storage but may result in a reduction in the efficiency of the process because there are both hydrogen uptake and release processes. While materials-based storage has not been used extensively for large-scale hydrogen storage in the past, there is currently significant activity regarding developing materials and processes for use in large-scale hydrogen storage applications. Electrolysis-produced hydrogen offers an unusual opportunity for energy storage applications. Unlike more conventional energy storage approaches, such as batteries, which operate entirely within electrical markets, hydrogen is a valuable product beyond the electric market and can be directed to the most lucrative use. Hydrogen also can be directly converted back to electricity using either a fuel cell or turbine, or it can be sold to other markets, such as chemical synthesis, steel production, or even export. In this way, excess electricity can be upgraded to the most valuable product. Finally, its use can be actively managed between multiple off-takers; for example, local hydrogen storage can provide a specific amount of stored electricity and any excess can be exported to ammonia production. This flexibility is amplified by the fact that hydrogen storage has fully decoupled power and energy components, which allows for affordable scaling options. Together, this allows a substantial amount of creativity to enable the economic utilization of variable power resources while supporting decarbonization of the industry.
Reversible Fuel Cell (RFC) systems offer promising characteristics for stationary long duration energy storage applications. Two main configurations of RFC systems exist: discrete RFC systems and unitized RFC systems. While discrete RFC systems combine independent fuel cell and electrolyzer systems for energy storage, unitized RFC systems utilize a single electrochemical stack and might share balance of plant (BOP) components for both charging and discharging processes. While this configuration reduces upfront capital costs, challenges of unitized RFC designs include potential performance trade-offs due to dual-mode stack design and operational complexities across varying loads and operating conditions. Furthermore, these tradeoffs might be different for low-temperature PEM RFCs than for high-temperature reversible solid oxide cell systems. The goal of this project is to assess unitized RFC system potential in the context of long duration grid energy storage and HFTO's technical targets for different discrete fuel cell and electrolyzer technologies. This presentation presents preliminary review of state-of-the-art unitized RFC cells and assesses how they perform relative to HFTO's technical targets. It also presents literature-derived system configurations worth investigating. This review indicates that lab-scale unitized RFCs are making good progress towards meeting HFTO's technical targets.
Proton exchange membrane water electrolyzers rely on relatively expensive Ir-based catalysts for efficient and durable hydrogen production. To reduce system costs, Ir loadings can be reduced if performance and durability are maintained. Sputter deposition is a readily scalable method to synthesize uniform, low-loading catalyst layers with controlled composition. A catalyst applied directly to the porous transport layer can have advantages for performance, manufacturing simplicity, and catalyst recovery. Suitable porous transport layer porosity can minimize activity losses when reducing loadings. Here, methods are presented to deposit metallic Ir as well as amorphous and rutile Ir oxides. The activity and durability of these materials in the porous transport electrode architecture is evaluated. The metallic and amorphous forms have better initial activity, however, operation at 3 A cm −2 with 0.1 mg Ir cm −2 shows that only rutile IrO 2 maintains performance beyond 100 h with a 50 mV improvement after 700 h. A >10x reduced dissolution rate is shown for rutile IrO 2 . With a low-porosity transport layer and 0.4 mg Ir cm −2 , a steady-state voltage decay rate of 6 µV h −1 is achieved. The results demonstrate that sputter-deposited rutile IrO 2 porous transport electrodes with low Ir loading can be operated at high current density to reduce hydrogen production costs.
Driven by concerns over climate change, interest in CO2 conversion technologies has dramatically increased in recent years. By viewing CO2 as a readily available feedstock, many pathways for the production of carbon-neutral fuels and chemicals become available. In converting CO2, low carbon emitting energy sources must be used to ensure a low carbon footprint of the fuel and chemical products. The low-temperature electrochemical conversion of CO2 is a promising technology and allows for direct integration with renewable electricity sources. The development of low-temperature CO2 electrolysis technologies is informed by both PEM fuel cells and water electrolyzers, both of which are at a higher stage of development. However, CO2 electrolysis operates at a much higher cell voltage (-3V) than other low-temperature electrochemical processes, which can have implications for materials compatibility in the electrolyzer device. Carbon corrosion is of particular concern for the anode of CO2 electrolyzers, as a large driving force for corrosion exists due to the high required cell potentials. In this presentation, recent observations will be shared on carbon corrosion of the anode gas diffusion electrode (GDE) in low-temperature alkaline exchange membrane CO2 electrolysis. Results from ex-situ tests designed to isolate the carbon corrosion process for anode GDEs will be shared. These results will provide guidance on materials selection for CO2 utilization MEAs, which need to have a lifetime of several years to ensure industrial viability.
Proton-exchange membrane (PEM) water electrolysis is a promising technology for producing clean hydrogen by electrochemically splitting water when paired with renewable energy sources. A major roadblock to improving electrolyzer durability is the mechanical degradation of the cell components, which requires an understanding of their mechanical response under device-relevant conditions. However, there is a lack of studies on the mechanical characterization of the PEM and other components, as well as and their interactions. This study aims to address this gap by using a custom-designed testing apparatus to investigate the mechanics of electrolyzer components in uniaxial compression at 25 and 80 °C. Findings show stress-strain response of components have a varying degree of nonlinearity owing to their distinct deformation mechanisms and morphologies, from porous structures to polymers. These results are used to develop an expression for compressive stress-strain response of Nafion membranes and then analyze the deformation of components under applied pressure by using a 1-D spring network model of cell assembly. This work provides a new understanding of mechanical responses of the electrolyzer membrane and cell components, which can help assess material design and cell assembly strategies for improved electrolyzer durability.
A procedure for measuring the ion exchange capacity (IEC) of a proton exchange membrane (PEM).
A procedure for measuring the ion exchange capacity (IEC) of a proton exchange membrane (PEM).
The imperative shift towards decarbonization necessitates the production of clean hydrogen through water electrolysis, powered by renewable energy sources. Among electrolyzer technologies, proton-exchange-membrane (PEM) systems emerge as a promising option for large-scale hydrogen generation due to their modular design and rapid response, aligning well with the intermittency of renewable energy. In this study, we employ a tape casting method to fabricate microporous layers (MPLs), both as a single layer and as a bilayer over commercial porous transport layers (PTLs), to further enhance performance of water electrolyzers. We demonstrate that microporous layers require adequate pore sizes to facilitate gas removal, preventing gas flooding and preserving electrolyzer performance. Our single layer microporous layers exhibit lower overpotentials compared to commercial sintered Ti PTLs by 142 mV at 4 A·cm ⁻2 . Moreover, we show that having an effective microporous layer enhances electrolyzer performance irrespective of the substrate used, offering avenues for cost reduction. We also investigate novel PTL structures with reduced tortuosity and integrated MPL fabricated via phase inversion tape casting, resulting in a performance enhancement of 92 mV. Our findings unravel the critical role of microporous layer structures and their impact on electrolyzer performance.
Proton-exchange membrane water electrolyzers (PEMWEs) are a promising technology for green hydrogen production; however, interfacial transport behaviors are poorly understood, hindering device performance and longevity. Here, we first utilized finite-gap electrolyzer to demonstrate the possibility of proton transfer through water in PEMWEs. The measured high-frequency resistances (HFRs) exhibit a linear trend with increasing gap distance, where extrapolation shows a lower value compared with HFRs in regular zero-gap electrolyzers, indicating that ohmic resistance could be further reduced. We introduce nanochannels to facilitate mass transport, as evidenced by both liquid-fed and vapor-fed electrolysis. Nanochannel electrodes achieve a voltage reduction of 190 mV at 9 A·cm –2 compared with the Ir-PTEs without nanochannels. Furthermore, nanochannel electrodes show negligible degradation through 100,000 accelerated-stress tests and over 2,000 h of operation at 1.8 A·cm –2 with a decay rate of 11.66 μV·h –1 . These results provide new insights into localized transport dynamics for PEMWEs and highlight the significance of interfacial engineering for electrochemical devices.