Reactive Spray Research Articles

(Digital Presentation) Large–Scale High-Performance Low Catalyst Loaded Membrane Electrode Assemblies for Advanced Proton Exchange Membrane Water Electrolyzers

Hydrogen is regarded as the next-generation energy carriers for the future hydrogen economy.1 Among the hydrogen production technologies, proton exchange membrane (PEM) water electrolyzers is considered the favored approach for the implementation of the global hydrogen energy transformation due to its several benefits including high power density operation, low ohmic losses and differential pressure operation. However, (i) high cost mainly from the high platinum group metals (PGM) loading in the catalysts layers; (ii) low durability due to instability of the catalysts layers and membrane; and (iii) poor safety because of hydrogen crossover of PEM water electrolyzers have jeopardized their widespread commercialization. Currently, a new Department of Energy Consortium (H2NEW) has targeted hydrogen production from electrolysis, especially PEM water electrolysis, for use as a clean, sustainable fuel, which can achieve $2/kg hydrogen production cost by 2025.2 This requires a balance between the performance, durability and scale-up cost of membrane electrode assemblies (MEAs) for PEM water electrolyzers.In this work, we demonstrate the capability to fabricate large scale MEAs by the unique Reactive Spray Deposition Technology (RSDT), that have one order of magnitude lower PGM loadings in the catalyst layer than the state-of-the-art (SOA) designs, and activity and durability performance comparable to the SOA commercial MEAs. RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition processes into one step and thus substantially reduces the time and cost for their fabrication.3–5 The RSDT fabricated MEA with 680 cm2 geometric area electrodes, and loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode has been tested at current density of 1.8 A cm-2, 50 oC, and 400 psi differential hydrogen pressure. The initial steady-state test for over 250 hours, clearly shows excellent activity and stability. In addition, the RSDT fabricated MEA has integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 %LFL at all current densities from 0.58 to 1.8 A/cm2.Reference1. M. Carmo, D. L. Fritz, J. Mergel, and D. Stolten, Int. J. Hydrogen Energy, 38, 4901–4934 (2013).2. https://www.energy.gov/sites/default/files/2021-09/h2-shot-summit-panel1-lte-status.pdf3. H. Yu et al., Appl. Catal. B Environ., 239, 133–146 (2018) https://doi.org/10.1016/j.apcatb.2018.07.064.4. H. Yu et al., Electrochim. Acta, 247, 1155–1168 (2017) http://dx.doi.org/10.1016/j.electacta.2017.07.093.5. G. Mirshekari et al., Int. J. Hydrogen Energy, 46, 1526–1539 (2021) https://doi.org/10.1016/j.ijhydene.2020.10.112.

Advanced Catalysts for PEM Water Electrolyzers, Fabricated By Reactive Spray Deposition Technology: Study of the Degradation Mechanisms in the Catalysts’ Layers By in-Situ and Ex-Situ Synchrotron X-Ray Absorption Spectroscopy

Development of novel and improved catalysts and membrane electrode assemblies (MEAs) for proton exchange membrane (PEM) based energy conversion devices is of crucial importance for widespread application of the PEM fuel cells (FCs) and water electrolyzers (WEs). These PEM based devices are critical for the Hydrogen Economy (HE) implementation. The HE is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. Currently, the main challenges that the state-of-the-art MEAs for PEMWEs are facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers and time consuming and expensive multi-step fabrication processes; and (ii) poor durability caused by the instability of the catalysts and the materials [1, 2].The reactive spray deposition technology (RSDT), developed at UConn, is a novel methodology for fabrication of advanced MEAs for PEMFCs and PEMWEs [3-5]. The RSDT is a flame assisted method [4, 5] that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large scale (up to 1000 cm2) MEAs [4, 5]. In addition, this technology allows precise control of the composition, morphology, and particle size distribution of wide range of nanoparticles supported and unsupported on carbon, and thus ensures fine tuning of the catalysts’ activity and durability. The RSDT fabricated MEAs have improved activity and durability performance with one order of magnitude lower catalyst loadings in their electrodes in comparison to the state‐of‐the‐art commercial MEAs for PEM water electrolyzers [6]. In this work we report the results from the in‐situ and ex‐situ synchrotron X-ray Absorption Spectroscopy (XAS) studies of the Ir/IrOx (anode) and Pt/C (cathode) catalysts, fabricated by the RSDT. The experiments were performed at beamline 7-BM at NSLS II at Brookhaven National Laboratory. The electronic and atomic structures of the Ir and Pt in the catalyst layers after their fabrication, during operation at different cell voltages, and after long term steady‐state operation were studied by XANES and XAFS, respectively. The results obtained, provide better understanding of the improved activity of the catalysts, as well as of the degradation mechanisms that govern the MEAs’ failure. References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Roller, J., Maric, R., 24(8) December 2015 pp. 1529-1541 (2015).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).

Reactive Spray Drying Approach Towards rGO As Matrix Material for the Cathode of Li-S Batteries

Lithium-sulfur batteries represent a promising alternative to the classical Li-ion technology, particularly due to the high specific energy density combined with the good environmental sustainability of sulfur. Compared to state-of-the-art cathode materials for Li-ion batteries (LiB), which usually contain cobalt and/or manganese, sulfur is less toxic and much more abundant [1]. Additionally, the theoretical capacity of 1.675 mAh g-1 is more than eight times higher than typical cathode materials as Lithium-Nickel-Mangan-Cobalt-Oxide (NMC), Lithium-Cobalt-Oxide (LCO) or Lithium-Iron-Phosphate (LFP) [1,2]. One of the main challenges of sulfur is the so-called “shuttle effect” [1,3]. During lithiation soluble intermediates (polysulfides) migrate to the anode side, further react and precipitate, resulting in a continuous loss of active material and capacity. Next to that, the poor electrical conductivity (5∙10-30 S cm-1) does not allow the utilization of pure sulfur as cathode material [1].To improve the low conductivity, carbon-containing composites have been proposed as cathode material for Li-S batteries for several decades. One possible carbon matrix material is reduced graphene oxide (rGO) [4]. The reduced form of partially oxidized graphite (graphite oxide; GO) is a graphene-like material with high potential for a scale-up to mass production.In our group, we have developed a new synthesis method to rapidly reduce GO using a reactive spray drying technique, where most functional groups can be removed from GO within seconds. The rapid thermal processing leads to a reduced and exfoliated rGO, which still contains small amounts of epoxy groups within the carbon lattice. These remaining oxygen atoms influence the conjugated π-bonds of the graphene-like matrix and thus change the polarity of the surface. A thermal post-treatment for 2 h in Ar/H2 can further reduce the remaining functional groups leading to a highly non-polar surface.It is assumed that oxygen-containing groups (e.g. epoxy and hydroxy) result in a varying adsorption behavior of the polysulfides, affecting the unwanted “shuttle effect” and thus influencing the electrochemical performance [5]. Here, we show the impact of remaining functional groups in rGO on the electrochemical performance of S-rGO composites as cathode material vs. Li/Li+. We compare untreated GO to reactive spray dried and additionally (thermally) post-treated rGO. Furthermore, we analyze the composites in terms of asymmetric and symmetric bonding vibrations as well as crystallinity using FT-IR, RAMAN and XRD.[1] Baikalov, N. et al., Frontiers Energy Research 2020, 8, 207[2] Su, Y.-S. et al., Nature Communications 2013, 4, 2985[3] Ren, W. et al., Energy Storage Materials 2019, 23, 707-732[4] Shastri, M. et al., Ceramics International 2021, 47, 10, B, 14790-14797[5] Ji, L. et al., Journal of the American Chemical Society 2011, 133, 18522-18525

Understanding Proton Exchange Membrane Water Electrolyzer Hydrogen Crossover Mitigation in Reactive Spray Deposition Technology Fabricated Dual Recombination Layers through Distribution of Relaxation Times Analysis

Proton exchange membrane water electrolyzers (PEMWEs) are a promising technology to produce zero-carbon emission, renewable, high-purity hydrogen. [1] There is a need to reduce capital cost while improving performance for the progression of widespread development. The crossover of hydrogen from the cathode into the anode not only restricts cell performance, but also poses a safety hazard, as the crossover reaches the lower explosive limit of hydrogen in oxygen. [2] Previous work has been conducted on the fabrication and testing of Pt recombination layers in PEMWEs. The addition of the Pt recombination layer has proven to be an effective mitigation strategy for hydrogen crossover while improving performance. [3, 4] Further investigation is needed to understand the mechanisms of the Pt recombination layer.In this work, reactive spray deposition technology (RSDT) was used to deposit two Pt recombination layers separated by a membrane. Testing of a single cell 25 cm2 PEMWE was conducted. Polarization analysis, electrochemical impedance spectroscopy, and distribution of relaxation times were used to investigate the cell performance. Results show good cell performance and hydrogen crossover reduction, as well as insight to the mechanisms of the chemical reactions that occur on the dual recombination layer.

(Digital Presentation) Boosting Hydrogen Oxidation Reaction Activity of Nickel Based Catalyst By Reactive Spray Deposition Technology: Effects of Particle Size

Ni-Based materials are one of the most promising candidates for hydrogen oxidation reaction (HOR) in anion exchange membrane fuel cells (AEMFC). However, the performance for pure Ni is limited. In this work, Ni mixed CeO2 nanoparticles supported on carbon black were synthesized for the first time by Reactive Spray Deposition Technology (RSDT) and followed by an oxygen reduction process in a furnace. By controlling the reaction parameters during the RSDT fabrication process, the particle size of Ni/CeO2/C is set at 3 nm. The resultant 3 nm catalyst Ni/CeO2/C catalyst exhibits excellent mass activity (14.92 mA mg-1 Ni) compared to the catalyst without the addition of CeO2 (which is Ni/C 4.39mA mg-1 Ni) as well as the activity of most of the other non-precious metal-based materials for HOR. The excellent electrocatalytic performance indicates that Ni/CeO2/C can be considered as a potential non-precious metal at the anodes for AMEFCs.

Degradation Mechanisms in Advanced MEAs for PEM Water Electrolyzers Fabricated by Reactive Spray Deposition Technology

Proton exchange membrane water electrolyzers (PEMWEs) have demonstrated enormous potential as the next generation hydrogen production technology. The main challenges that the state-of-the-art PEMWEs are currently facing are excessive cost and poor durability. Understanding the failure modes in PEMWEs is a key factor for improving their durability, lowering the precious metal loading, and hence cost reduction. In this work, reactive spray deposition technology (RSDT) has been used to fabricate a membrane electrode assembly (MEA) with one order of magnitude lower Pt and Ir catalyst loadings (0.2–0.3 mgPGM cm−2) in comparison to the precious metal loadings in the stat-of-the-art commercial MEAs (2–3 mgPGM cm−2). As fabricated MEA with an active area of 86 cm2, has been tested for over 5000 h at steady-state conditions that are typical for an industrial hydrogen production system. Herein, we present and discuss the results from a comprehensive post-test analysis of the MEA of interest. The main degradation mechanisms, governing the performance loss in the RSDT fabricated MEA with ultra-low precious metal loadings, have been identified and discussed in detail. All failure modes are critically compared and the main degradation mechanism with the highest impact on the MEA performance loss among the others is identified.

Reactive Spray Drying as a One-Step Synthesis Approach towards Si/rGO Anode Materials for Lithium-Ion Batteries

Lithium-ion batteries with Si anodes are still attracting increasing attention, particularly due to the high specific energy density. The main disadvantage of silicon as anode material is its reduced cell performance in terms of cycling stability. One promising approach to improve this is embedding silicon nanoparticles in a graphene-like matrix via spray drying. All processes described so far need a time- and energy-intensive two-step-synthesis to obtain the graphene-like rGO structure. Here, we present a reactive spray drying process for synthesis of Si/rGO composites. For proper reactor design, the reaction kinetics are investigated by simultaneous thermal analysis in various atmospheres. We can describe thermal decomposition of GO to rGO as a second-order reaction. STA data also show that additional presence of water in the atmosphere due to the one-step synthesis is negligible at temperatures below 600 °C for both the reaction of GO and the additional oxidation of Si. To evaluate the electrochemical performance, the composites are cycled in a half cell setup. Delithiation capacity after cell formation could be raised from 252 mAh g−1 for GO to 327 mAh g−1 for rGO. In addition, we are able to synthesize Si-containing composites suitable for the anode of LiB using our process.

Advanced electrodes for electrochemical energy storage and conversion devices fabricated by reactive spray deposition technology

While different electrochemical devices require electrodes with different microstructures, thicknesses, and catalyst compositions, the reactive spray deposition technology (RSDT) process has been able to demonstrate flexibility to provide what is needed for each application. From developing porous electrodes with platinum group metal catalysts for fuel cell and electrolysis applications, to the fabrication of dense ceramic thin films for solid oxide fuel cell electrolytes, to the fabrication of novel electrodes for rechargeable lithium-ion batteries, the RSDT can be modified to fabricate these layers in a one-step process. Using a combustion flame, the heat generated from the flame is used to provide the energy for sintering ceramic particles into a dense layer and it can be used to decompose a precursor solution into a catalyst particle that contains the desired stoichiometry. The RSDT process has been shown to be an effective method for the development of electrode thin films.

Highly Active and Durable Membrane Electrode Assemblies for Proton Exchange Membrane Water Electrolyzers Fabricated by Reactive Spray Deposition Technology

The reactive spray deposition technology (RSDT) that has been developed at UConn, is one of the most promising new methodologies for direct fabrication of large scale MEAs for proton exchange membrane water electrolyzers (PEMWEs) with ultra-low platinum group metals (PGM) loadings in their catalyst layers [1,2]. The RSDT is an open to air flame assisted method for fabrication of MEAs that combines the catalysts synthesis and direct deposition on the Nafion® membrane in one step [2,3]. Thus, this method eliminates multiple time consuming and expensive steps in the MEA manufacturing process and reduces the fabrication time from days and weeks to hours. As a dry spray methodology with integrated system for in-situ quality control of the catalysts and catalyst layers (CLs),[1] the RSDT allows precise control of the catalysts composition, loading, porosity, thickness, and ionomer content. Furthermore, it has been demonstrated that by controlling the precursor solutions flow rates, and the flame deposition parameters, catalyst layers with gradient distribution in the nanoparticle size, as well as in the PGM loading in the CLs can be achieved, which ensures fine tuning of the activity and durability performance of the MEAs of interest [4].Herein, we will demonstrate the capabilities of the RSDT methodology to fabricate large scale MEAs for PEMWEs, that have one order of magnitude lower PGM loadings in the CLs and activity and durability performance comparable to the state-of-the-art commercial MEAs. RSDT fabricated MEAs with geometric area of the electrodes of 86 cm2 and 680 cm2, and loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode have been tested at conditions typical for industrial electrolyzers. The performed long term steady-state test for over 5000 hours, as well as the measured polarization curves and EIS spectra clearly show excellent activity and durability performance of these MEAs. In addition, the RSDT fabricated MEAs have integrated recombination layers that effectively reduce the hydrogen crossover to below 10 %LFL. Furthermore, comprehensive post-test analysis of the MEAs after 5000 hours of operation has been performed and the degradation mechanisms governing their performance loss were identified and will be discussed in detail.References https://www.hydrogen.energy.gov/pdfs/review20/ta027_maric_2020_o.pdf Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R., 2021.“High-Performance and Cost-Effective Membrane Electrode Assemblies for Advanced Proton Exchange Membrane Electrolyzers: Long-Term Durability Assessment”, International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539.Roller, J., Maric, R., 2015. A Study on Reactive Spray Deposition Technology Processing Parameters in the Context of Pt Nanoparticle Formation, Journal of Thermal Spray Technology, 24(8) December 2015 pp. 1529-1541.Yu, H., Baricci, A., Casalegno, A., Guetaz, L., Bonville, L., Maric, R., 2017. Strategies to mitigate Pt dissolution in low Pt loading proton exchange membrane fuel cell: II. A gradient Pt loading design, Electrochimica Acta, 247(1) 2017, pp. 1169-1179

Novel Synthesis of Si/Rgo Anode Materials for Lithium-Ion Batteries Via Reactive Spray Drying

In recent years, lithium-ion batteries (LiB) with Si anodes attracted increasing attention, particularly due to their high specific energy density. An optimization of this characteristic is extremely important for their extended use as power source not only in portable devices but also in larger applications, such as electric vehicles.The main disadvantage of using silicon as anode material in LIBs is its high volume expansion during lithiation, which leads to various negative effects, such as pulverization, delamination, and an unstable solid electrolyte interface (SEI) [1]. This eventually results in a reduced cell performance, especially in terms of cycling stability. One promising approach to mitigate these issues is to wrap silicon nanoparticles in a graphene-like matrix via spray drying. A suitable starting material for this approach is graphite oxide (GO) [2, 3, 4].In all processes described so far, an additional time- and energy-intensive calcination step is necessary to obtain the graphene-like “reduced graphene oxide” (rGO) structure. Here, we present a new reactive spray drying process for a simplified one-step synthesis of Si/rGO composites using water as solvent. To design the reactor properly, it is necessary to understand the reaction kinetics. Therefore, the reaction is investigated by simultaneous thermal analysis (STA) in various atmospheres. We can describe the thermal decomposition of GO to rGO as a second-order reaction (Arrhenius behaviour). The STA data also show that the additional presence of water in the atmosphere due to the one-step synthesis is negligible at temperatures below 600 °C for both the reaction of GO and the unwanted additional oxidation of Si. We use crystalline silicon nanoparticles (dp ≈ 100 nm) and micrometer-sized graphite oxide prepared via modified hummers method as starting materials. Si and GO are dispersed in water and ultrasonically treated to obtain a stable dispersion. The prepared dispersion is sprayed continuously into a hot reactor (> 500 °C), where the droplets dry in the first reaction zone, forming a Si/GO composite, followed by a thermal decomposition reaction to Si/rGO in the second one. The Si/rGO particles are separated from the hot gas stream via a cyclone. To prevent oxidation, the entire system is operated in an inert atmosphere. To evaluate the electrochemical performance, the as-prepared composites are coated on a copper foil using a water-based binder mixture of styrene-butadiene rubber and caboxymethyl cellulose (SBR:CMC = 1:1). The electrodes are cycled against Li/Li+ in a half cell setup.The specific capacity after cell formation is raised from 275 mAh g-1 for GO to 335 mAh g-1 for rGO due to the reactive spray drying process. A Si/rGO composite with a Si content of 11.5 % shows a capacity of 505 mAh g-1 after the formation. Future studies will focus on further reduction of the oxygen content of rGO and an improved integration of silicon in the carbon matrix.[1] J.W. Choi, D. Aurbach, Nature Reviews Materials 2016, 1 (4), 16013.[2] M. Li et al., Journal of Power Sources 2014, 248, 721-728.[3] J. Lee, J.H. Moon, Korean Journal of Chemical Engineering 2017, 34 (12), 3195-3199.[4] Y. Huang et al., Energy Fuels 2020, 34 (6), 7639-7647. Figure 1

An in situ reactive spray-drying strategy for facile preparation of starch-chitosan based hydrogel microspheres for water treatment application

Hydrogel microspheres (HMs) were prepared from hydroxyethyl starch and carboxymethyl chitosan via in situ reactive spray drying, using epichlorohydrin as the crosslinking agent. SEM characterization showed the HMs were spherical and collapsed structures. The swelling behavior and adsorption performance of the HMs were studied systematically. The experimental results demonstrated that HMs possessed pH and salt sensitiveness and the maximum adsorption capacities of HMs for methylene blue, Eosin Y, Cd2+, Cu2+, and Ni2+ were 106.97 mg/g, 143.55 mg/g, 32.51 mg/g, 47.87 mg/g, and 27.18 mg/g, respectively. Further study indicated that the adsorption isotherms and kinetics were respectively fitted with the Langmuir isotherm model and the pseudo-second-order model. In view of the advantages of in situ reactive spray drying for the preparation of novel pH- and salt- responsive HMs, the strategy presented here has a great application potential in wastewater treatment.

Advanced Catalysts for the Oxygen Evolution Reaction Fabricated By Reactive Spray Deposition Technology: Degradation Mechanisms Governing the Performance Loss during the Long-Term Steady State Operation

Development of novel and improved catalysts and membrane electrode assemblies (MEAs) for proton exchange membrane (PEM) based energy conversion devices is of crucial importance for widespread application of the PEM fuel cells and electrolyzers. These PEM based devices are critical for the Hydrogen Economy (HE) implementation. The HE is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. Currently, the main challenges that the state-of-the-art MEAs are facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers and time consuming and expensive multi-step fabrication processes; and (ii) poor durability caused by the instability of the catalysts and the materials [1, 2].Herein, we demonstrate the capabilities of the unique Reactive Spray Deposition Technology (RSDT) for fabrication of advanced catalysts for the oxygen evolution reaction (OER) and MEAs that could overcome these challenges. The RSDT is a flame assisted method [3, 4] that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large (up to 1000 cm2) MEAs for application in PEM fuel cells and electrolyzers [4]. In addition, this technology allows precise control of the composition, morphology, and particle size distribution of wide range of nanoparticles supported and unsupported on carbon, and thus ensures fine tuning of the catalysts’ activity and durability. Ir/IrOx unsupported catalysts fabricated by RSDT have been studied in half cell configuration by rotating disc electrode (RDE) technique in 0.1 M HClO4 and showed improved activity towards the OER in comparison to the state-of-the-art commercial IrO2 catalyst. Furthermore, MEAs with geometric area of 86 cm2 and one order of magnitude lower Ir loading in the anode catalyst layer in comparison to the state-of-the-art MEAs for PEM water electrolyzers [5], were fabricated by the RSDT and tested for 5000 hours at current density of 1.8 A cm-2, 50 oC, and 400 psi differential hydrogen pressure. Diagnostic tests that include polarization curves, electrochemical impedance spectroscopy, linear sweep voltammetry, and hydrogen crossover measurements were performed periodically in order to evaluate the cell performance change during the long-term durability test. After the test, the MEAs were disassembled and subjected to comprehensive post test analysis. A wide range of techniques including high-resolution TEM, STEM, EDS, SEM, ICP, XCT, XPS, and digital optical microscopy, have been used to study the degradation mechanisms governing the performance loss in the MEAs during the long-term steady state operation, and the results will be presented and discussed in detail in this talk.References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Ayers, K. Current Opinion in Electrochemistry, 18, 9–15 (2019).

Membrane Electrode Assemblies Fabricated By Reactive Spray Deposition Technology for Advanced Proton Exchange Membrane Water Electrolyzers: Study of the Degradation Mechanisms

Proton exchange membrane water electrolyzers (PEMWEs) have demonstrated great potential as the next generation hydrogen production technology1,2. The main challenges that the state-of-the-art PEMWEs are currently facing are: (i) high cost, (ii) low efficiency, and (iii) poor durability performance3. Understanding the failure modes of PEMWEs during the operation is a key factor for improving their durability performance, as well as for lowering the precious metal loading in the catalyst layers and hence for reducing their cost. However, the catalyst degradation mechanisms in PEMWEs during operation, especially for the Ir-based anode catalysts, have not been fully understood.In this work, reactive spray deposition technology (RSDT) has been used to fabricate membrane electrode assemblies (MEAs) with one order of magnitude lower Pt and Ir catalyst loadings in their cathode and anode catalyst layers, respectively, in comparison to the precious metals loading in the state-of-the-art commercial MEAs for PEMWEs 4–6. Two of as- fabricated MEAs with geometric area of 86 cm2, have been tested at steady-state conditions that are typical for commercial hydrogen production system. One of the cells was stopped and disassembled after 50 hours of operation, while the second one was disassembled after it failed after over 500 hours of operation. Herein we present a comprehensive comparative study of both MEAs, aimed at identifying and understanding the degradation mechanisms causing the MEAs failure. The pre- and post-test MEA characterizations are performed by scanning/transmission electron microscopy (S/TEM), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD) and X-ray computed tomography (X-CT). In addition, rotating disk electrode (RDE) technique has been utilized for assessment of the catalytic activities of the RSDT-fabricated anode Ir/IrOx catalysts before and after the failure. The main degradation mechanisms, governing the failure modes in the MEAs of interest, have been identified and discussed. 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).Babic, U. et al. Critical Review — Identifying Critical Gaps for Polymer Electrolyte Water Electrolysis Development Review — Identifying Critical Gaps for Polymer Electrolyte Water. (2017). doi:10.1149/2.1441704jesButtler, A. & Spliethoff, H. Current status of water electrolysis for energy storage, grid balancing and sector coupling via power-to-gas and power-to-liquids: A review. Renew. Sustain. Energy Rev. 82, 2440–2454 (2018).Roller, J. M. & Maric, R. A Study on Reactive Spray Deposition Technology Processing Parameters in the Context of Pt Nanoparticle Formation. J. Therm. Spray Technol. 24, 1529–1541 (2015).Roller, J. M., Kim, S., Kwak, T., Yu, H. & Maric, R. A study on the effect of selected process parameters in a jet diffusion flame for Pt nanoparticle formation. J. Mater. Sci. 52, 9391–9409 (2017).Yu, H. et al. Nano-size IrOx catalyst of high activity and stability in PEM water electrolyzer with ultra-low iridium loading. Appl. Catal. B Environ. 239, 133–146 (2018).

Development of Recombination Layers to Reduce Gas Crossover for Proton Exchange Membrane Water Electrolyzers By Reactive Spray Deposition Technology

Hydrogen is an important material for many different applications including materials processing, oil refining, ammonia production, energy storage, among many others. In commercial development since the 1950s, proton exchange membrane water electrolyzers (PEMWEs) have been identified as a green source of high-purity hydrogen which can be utilized for many applications [1]. While hydrogen produced by PEMWEs has shown significant promise as a clean hydrogen source for fuels or energy storage, there are technical challenges that need to be addressed to allow for its widespread use. One such challenge involves hydrogen crossover. In operation, hydrogen that is formed in the highly pressurized (~400 psi) cathode can diffuse back through the proton exchange membrane and into the anode chamber where oxygen is being formed as a result of the water splitting reaction [2]. This can lead to both safety concerns and performance losses. With the lower flammability limit (LFL) of hydrogen in oxygen around 4 vol%, typical operating conditions of a PEMWE are set such that the hydrogen concentration in the anodic stream does not approach 50% of the LFL. In order to ensure operation of the PEMWE at the desired operating conditions, mitigation strategies have been implemented to reduce the hydrogen crossover. One such mitigation strategy recently published by Klose, Trinke et al. has shown that introducing a platinum recombination layer within the membrane can significantly reduce the hydrogen crossover [3]. This work will examine recombination layers designed to reduce gas crossover of PEMWE technology. The Reactive Spray Deposition Technology (RSDT) process was used to deposit small platinum nanoparticles (~2nm diameter) onto a Nafion® 117 membrane as well as deposit a Nafion® insulating layer to create a PEMWE membrane that is able to effectively recombine hydrogen and oxygen to prevent gas crossover. These recombination layers developed by RSDT are shown to reduce the hydrogen crossover to less than 10% of the lower flammability limit. Additional samples will be developed in order to gain an understanding of how recombination layers work, the mechanism required by these layers to recombine the hydrogen and oxygen, and how to better develop and optimize recombination layers.

An Investigation of the Ammonia-Sensing Mechanism of α-MoO3-Based Chemi-Resistive Sensors

Chemi-resistive ammonia sensors based on alpha-phase molybdenum trioxide (α-MoO3) are a simple and selective technology for measuring the concentration of gaseous ammonia for applications such as human breath sensing and monitoring selective catalytic reduction (SCR) systems [1-7]. The basic operating principle of these sensors is the correlation between the electrical resistance of the sensor and the concentration of ammonia to which the sensor is exposed. Typically, the sensor consists of an interdigitated electrode substrate covered with the α-MoO3 film [1-7]. The electrical resistance of the α-MoO3 film changes as a function of ammonia concentration. This change in resistance of the α-MoO3 film is commonly attributed to the alteration of the charge depletion layer (Λ) of the α-MoO3 particles through the reaction of ammonia with adsorbed oxygen species [5-9]. For α-MoO3, the charge depletion layer model predicts that the resistance of the film should decrease with increasing ammonia concentration. In addition to the charge depletion layer model, other sensing mechanisms have been suggested, such as the partial reduction by ammonia of the surface of the α-MoO3 film [1,2] and the formation of oxygen vacancies in the α-MoO3 lattice [3].The α-MoO3 film can be fabricated by a variety of methods, including sol-gel synthesis, ion beam deposition, hydrothermal synthesis, and flame spray pyrolysis [1-6]. In this work, the α-MoO3 film is fabricated using Reactive Spray Deposition Technology (RSDT) followed by annealing to develop crystallinity. The RSDT is a flame-based process that can be used for the fabrication of α-MoO3 films at a commercial scale. The initial development of ammonia sensors with RSDT-fabricated α-MoO3 films of varying morphology was presented at the 236th ECS Meeting as an oral presentation, “Ammonia-Sensing Properties of α-MoO3 Fabricated by Reactive Spray Deposition Technology (RSDT).” From these initial sensors, the sensor with the strongest response to ammonia was selected for further testing at concentrations between 0.1 ppm and 5 ppm ammonia in dry air at 400°C. These sensing results and the materials characterization of the sensor by SEM and XRD before and after 80 hours of continuous testing are reported in Ebaugh et al. [7] and are shown in Figures 1-3. In Figure 1, the sensing results among the three test cycles comprising the 80 hours of testing are quite repeatable; however, the results consistently depart from the prediction of the charge depletion layer model between 3 ppm and 5 ppm.To better explain this unexpected sensing behavior, additional electrochemical testing and materials characterization is needed. Specifically, normal pulse voltammetry (NPV) can be used to provide data pertaining to the electronic path through the α-MoO3 film and the reaction and transport of chemical species adsorbed on the α-MoO3 film. TEM analysis of the α-MoO3 can show the nanoscale morphology of the sensing material. It is well established that the nanoscale morphology of the metal-oxide film impacts its sensing behavior [8-10]. XPS can also be used to investigate the possible reduction of the surface of the α-MoO3 particles and the formation of oxygen vacancies in the α-MoO3 lattice. Data from the materials characterization of the sensing film (XRD, SEM, TEM, and XPS) will be used in conjunction with sensing results and NPV data to develop an explanation for the sensor behavior observed in [7]. An understanding of the ammonia-sensing mechanism will help to guide the optimization of the RSDT-fabricated α-MoO3 film to improve the performance of the sensor for a wide range of applications.References A. K. Prasad, et al. Thin Solid Films. 436 2003 pp. 46-51.P. Gouma, et al. IEEE Sensors Journal. 10 (1) 2010 pp. 49-53.A. K. Prasad, et al. Sensors and Actuators B: Chemical. 93 2003 pp. 25-30.P Gouma, et al. Journal of Breath Research. 5 2011 p. 037110.A. T. Güntner, et al. Sensors and Actuators B: Chemical. 223 2016 pp. 266-273.D. Kwak, et al. ACS Applied Materials & Interfaces. 11 2019 pp. 10697-10706.T. A. Ebaugh, et al. ACS Applied Materials & Interfaces. Under review.C. S. Rout, et al. Nanotechnology. 18 2007 p. 205504.M. E. Franke, et al. Small. 2 (1) 2006 pp. 36-50.N. Barsan, et al. Fresenius Journal of Analytical Chemistry. 365 1999 pp. 287-304. Figure 1

High-Performance and Durable Membrane Electrode Assemblies Fabricated By Reactive Spray Deposition Technology for Proton Exchange Membrane Electrolyzers

Water electrolysis is a very old and promising technology for hydrogen production that started about two centuries ago. Hydrogen, considered the best source for fuel and energy storage, can be produced by the electrochemical conversion of water into hydrogen and oxygen through the water electrolysis process. Since the 1950s, proton exchange membrane water electrolyzers (PEMWEs) have been commercially developed as a green source of high-purity hydrogen for many chemical applications as well as energy storage. However, high cost, high maintenance, low durability, poor safety, poor reliability, and low efficiency of PEMWEs compared to other available technologies have hampered their widespread commercialization. To address the economic and technical issues of the PEMWEs, research should consider improved electrocatalysts, low cost electrodes, corrosive resistant electrodes, reduction of electrode surface tension, and lower membrane resistance and hydrogen crossover [1, 2].This work presents high-performance, cost-effective and durable membrane electrode assemblies (MEAs; 86 cm2 active area) developed by the unique reactive spray deposition technology (RSDT) [3-6]. The RSDT-fabricated MEAs possess total platinum group metal (PGM) loading of 0.2-0.3 mgPt cm-2 for the Pt/C cathode catalyst layer, and 0.2-0.3 mgIr cm-2 for the Ir/IrOx anode catalyst layer, respectively. This is an order of magnitude reduction of the PGM loadings in the catalyst layers in comparison to the state-of-the-art commercial MEAs, resulting in substantial reduction of the cost of PEMWEs. An ultra-thin Pt recombination layer (Pt RL), positioned between two PEM membranes, was fabricated by RSDT to lower hydrogen cross-over and eliminate the PEMWE’s safety concerns. Furthermore, the RSDT-fabricated MEAs showed stable performance for 3000 hours operation at 1.8 A cm-2, 50°C, 400 psi hydrogen pressure and ambient oxygen pressure without significant loss in the polarization performance.

High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment

Improved activity and durability performance of a two-cell (86 cm2) proton exchange membrane water electrolyzer (PEMWE) stack is reported for the first time. Both membrane electrode assemblies (MEAs) contain one order of magnitude lower platinum group metal (PGM) loadings compared to the state-of-the-art PEMWEs and incorporate novel Pt recombination layers. The high-performance and cost-effective MEAs are fabricated by the unique reactive spray deposition technology (RSDT). This advanced methodology allows for one-step fabrication of MEAs and ensures precise control and distribution of the catalyst composition and loading. The RSDT-fabricated MEAs contain only 0.2 and 0.3 mgPGM cm−2 loading in the cathode and anode electrodes, respectively, and demonstrate excellent activity and durability for over 3000 h of operation at industrially-relevant operating conditions without showing significant loss in performance. This novel work shows that a significant cost reduction for PEMWEs is achieved while maintaining excellent durability, high catalysts activities, and low hydrogen cross-over.

Design and Development of an Innovative Barrier Layer to Mitigate Crossover in Vanadium Redox Flow Batteries

Capacity loss induced by the undesired transport of vanadium ions across the ion-exchange membrane (i.e. crossover) is one of the most critical issues associated with vanadium redox flow batteries. This work reports on the manufacturing and testing of an innovative barrier layer to mitigate crossover. The barrier layer conceptual design is described in detail in the patent application WO 2019/197917. The barrier was deposited directly onto Nafion® 212 using the Reactive Spray Deposition Technology, in which carbon-rich particles (∼4–10 nm in diameter) formed in the flame were deposited simultaneously with a mixture of 1100EW Nafion® and Vulcan® XC-72R (∼40 nm diameter) that was sprayed from air-assisted secondary nozzles. During cycles at fixed capacity, the presence of the barrier layer significantly reduced battery self-discharge; the average variation of battery state of charge compared to a reference cell with Nafion® 115 was reduced from 21% to 7%. Moreover, battery energy efficiency was increased by nearly 5%, indicating that the barrier layer does not significantly hinder proton transport. During cycles at 50 mA cm−2 with fixed cut-off voltages, the barrier layer exhibited stable operation, maintaining a coulombic efficiency around 99.4%. Additionally, the use of the barrier layer projects to a 30% reduction of stack-specific cost.

Nano-sized Pt\u2013NbOx supported on TiN as cost-effective electrocatalyst for oxygen reduction reaction

Proton exchange membrane fuel cells (PEMFC) play a key role for sustainable energy; however, catalyst degradation remains one of the main challenges for competing with traditional energy technologies. The Pt/C commercially available electrocatalysts are susceptible to Pt dissolution and carbon support corrosion. In this context, we design a Pt–NbOx catalyst supported on TiN nanoparticles as an alternative electrocatalyst for the oxygen reduction reaction (ORR). The use of Pt–NbOx reduces materials’ costs by lowering the required platinum loading and improving catalyst performance. The TiN support is selected to improve support stability. The electrocatalyst is successfully synthesized by a one-step flame spray process called reactive spray deposition technology. Electrocatalyst with two different very low Pt loadings (0.032 mg cm−2 and 0.077 mg cm−2) are investigated and their performance as cathode is evaluated by the rotating disk electrode method. The new electrocatalyst based on Pt–NbOx supported on TiN has ORR performance that is comparable to the state-of-the-art Pt/C electrocatalyst. A half-wave potential of 910 mV was observed in the polarization curves, as well as a mass activity of 0.120 A∙mgPt−1 and a specific activity of 283 μA∙cmPt−2 at 0.9 V. These results demonstrate that Pt–NbOx on TiN electrocatalyst has the potential for replacing Pt/C cathode in PEMFC.

Microstructure and Hardness of Titanium Aluminide/Carbide Composite Coatings Prepared by Reactive Spray Method

Microstructure and Hardness of Titanium Aluminide/Carbide Composite Coatings Prepared by Reactive Spray Method