High Current Density Operation Research Articles

High Performance AEM Water Electrolysis with PGM-Free Electrocatalysts

Water electrolysis technologies for hydrogen production are getting much attention due to drastic cost reduction in renewable energy sources, like solar, wind, tidal etc. Traditional alkaline water electrolysis has limitations of low current density operation, slow system response and low hydrogen discharge pressure. Proton exchange membrane (PEM) water electrolysis offers compact design, high current density operation, fast system response and pressurized discharge hydrogen. However, PEM electrolyzers require the use of Platinum Group Metal (PGM) based electrocatalysts, expensive perfluorinated membranes and specialized component materials due to its acidic environment. These are all hurdles to its widespread commercial adoption. A relatively new technology, the anion exchange membrane (AEM) electrolyzer can potentially combine benefits from PEM and traditional alkaline electrolyzers, offering high current density operation, pressurized discharge gas and low cost – by utilizing PGM-free electrocatalysts and inexpensive component materials due to the less corrosive alkaline operating environment.However, modern AEM electrolyzers have continued to use high loadings of PGM catalysts in both the cathode and anode. Given the magnitude and recent volatility in the market price of many PGM-group metal catalysts (e.g. Ru, Ir, etc.), it is now even more important for AEM electrolyzers to be realized with significantly lower PGM content – and eventually approaching the complete elimination of PGMs.In this study, we evaluate the performance of several low-PGM and PGM-free electrocatalysts for the oxygen evolution (OER) and hydrogen evolution (HER) reactions for high performance and durability. Here, PGM-free Lanthanum Strontium Cobalt (LSC), Nickel Ferrite (NiFeOx) and low PGM Lead Ruthenate (PbRuOx) were used at the anode for the OER. For the HER cathode, PGM-free Nickel Molybdenum (NiMo) and low-PGM PtNi electrocatalysts were evaluated for their in-situ activity and durability. It will be shown that LSC and NiFeOx show comparable performance to IrOx, with a typical steady-state operating voltage at 60oC and 1.0 A/cm2 (with 0.3 M KOH fed to the anode only) below 1.80 V. Cells with PGM-free anode catalysts were operated stably for over 100 hours. At the cathode, NiMo showed relatively higher overpotentials compared to Pt black, PtNi or Pt/C for the HER. Because of this, various strategies were adopted to reduce the PGM loading while achieving high performance and durable AEM electrolyzer operation. The achieved experimental results provide important insights for the development of AEM based water electrolyzer systems and represent an active step towards its commercial viability.

Anode-Fed Anion Exchange Membrane Electrolyzers for Hydrogen Generation Tolerant to Anion Contaminants

Anion exchange membrane water electrolysis has the ability to produce green hydrogen with high voltage efficiencies at low capital cost with zero CO2 emissions. The alkaline environment of these devices allows for the use of economical metal catalysts and anion exchange membranes (AEMs) that conduct hydroxide ions and are less expensive than their proton exchange membrane counterparts. However, research has shown that anion contamination of hydroxide exchange membranes can lead to significant performance losses in anion exchange membrane fuel cells (AEMFCs), particularly when air fed to the oxygen-reducing cathode contains CO2.1 A similar contamination effect occurs in anion exchange membrane electrolyzers (AEMELs), when dissolved CO2 in the electrolyte reacts to form carbonate (CO3 2-) and bicarbonate (HCO3 2-) anions which compete with the hydroxide (OH-) ions that must be conducted through the AEM and ionomer. The presence of these and other anion contaminants can lower the ionic conductivity of the cell. Under high current density operation, an AEMEL undergoes a self-purging process that uses an ionic potential gradient to push hydroxide and anion contaminants through the membrane to the anode. This creates a significant pH gradient between cathode and anode that can lead to concentration polarization which further lowers performance.2 In this work, we use 1-D CO2 transport modeling and experiments to show how altering the electrolyte feed method allows for CO2-tolerant AEMEL operation in several different electrolytes.The unique advantages of AEMELs over AEMFCs and proton exchange membrane electrolyzers (PEMELs) are that (1) this self-purge occurs during normal operation, and (2) they allow for flexibility in the location of the potentially contaminated water feed. In PEMELs, water is intuitively fed to the anode, and cation contaminants are purged through the entire MEA to the cathode. Although water in AEMELs is intuitively fed to the cathode, where it is consumed in the hydrogen evolution reaction, water can diffuse easily through the membrane, allowing for it to be fed as an anolyte to the oxygen-evolving side of the cell. This allows for better contaminant rejection because anions can be concentrated mostly on the anode side of the electrolyzer.The model described in this paper predicts that an anode-fed AEMEL can more easily purge CO2 without contaminating as much of the AEM or inducing as high of a pH gradient due to more rapid self-purging of anions. We find experimentally that AEMELs with DI water anolyte are more tolerant of forced CO2 contamination than those with DI water catholytes, which is likely one of the major reasons for superior anode-feed performance. Furthermore, electrolyzer operation at high current densities can lead to voltage recoveries greater than 200 mV due to self-purging of anions. Although supporting electrolytes such as potassium hydroxide can mitigate catholyte contamination, the anion self-purging shows that electrolyzer operation in DI water and even tap water (containing fluoride, chloride, and nitrates) can improve when employing an anode feed.1. Y. Zheng et al., Energy Environ. Sci., 12, 2806–2819 (2019).2. B. P. Setzler, L. Shi, T. Wang, and Y. Yan, in ECS Meeting s, vol. MA2019-01, p. 1824–1824, IOP Publishing (2019) https://iopscience.iop.org/article/10.1149/MA2019-01/34/1824.

Understanding Performance and Durability with KOH and DI-Water Fed Anion Exchange Membrane Electrolyzers

Anion Exchange Membrane electrolyzers (AEMELs) have increased in popularity in recent years due to their potential to combine the benefits from proton exchange membrane electrolyzers and traditional alkaline electrolyzers – namely, high current density operation, pressurized H2 discharge and lowering cost by utilizing low-cost earth abundant electrocatalysts and inexpensive component materials. In the AEMEL, the oxygen evolution reaction (OER) electrode plays a critical role dictating the overall efficiency of the cell due to sluggish OER activity and species transport. In our previous study, we optimized the OER electrode structure by investigating the effects of catalyst loading, catalyst type, the porous transport substrate and additive carbon [1] – resulting in an excellent performance of 1.55 V operation at 1.0 A/cm2.Though that study led to high performance, all of those gains were made using KOH electrolyte being fed to the cell, not deionized (DI) water. The use of DI water complicates AEMEL operation as the liquid phase can no longer be relied on to carry any of the ionic charge – this possibly can reduce the electrochemically active surface area (ECSA) [2]. It has also been stated that pure water operation may have negative consequences on cell durability. Therefore, to allow for AEMELs to operate efficiently on DI water, it is important to understand how the ion transport and charge transfer resistance change as cells are transitioned from KOH to DI water operation. It is also important to understand what effects even trace amounts of KOH can have on behavior. Lastly, the effect of the ionomer properties on the OER anode performance should be well-understood.In this study, we investigate the role of alkaline feed pH on the performance and durability of AEMELs. When shifting from alkaline feed to DI water, it will be shown that there is an increase in ohmic and charge transfer resistance, resulting in significant voltage loss. Because the alkaline feed enhances electrode conductivity by connecting catalyst active sites to the conductive ionomer and AEM [2-3], new electrode structures are needed that allow for enhanced ECSA and lower resistances with DI water feeds. In this work, that was accomplished by creating a four-layer electrode structure as well as manipulating the cell operating conditions. Lastly, our team enabled the use of a high IEC ionomer in the anode catalyst layer by introducing a cross-linker and introducing smaller, cryo-milled ionomer particles. This was important to overcome adhesion issues that can come from high water uptake and swelling in high-IEC ionomers [4-5]. This paper will focus not only on performance, but also longevity, with several cells being stably operated for more than 500 hours continuously.

Investigating the Influence of Humidity on Liquid Water Transport Mechanisms in Fuel Cell Gas Diffusion Layers Using Operando X-Ray Computed Tomography

The intermittent nature of many renewable energy sources, such as solar and wind, presents the need to acquire on-demand renewable energy either through energy storage or energy production methods. The polymer electrolyte membrane (PEM) fuel cell is quickly becoming an attractive solution as it can produce high power densities under a rapid change in load while producing zero local carbon emissions [1] and is ideal for large-scale applications, such as automotive [2]. However, barriers to their widespread implementation are attributed to the high costs associated with mass transport losses at high current density operation due to inefficiencies in liquid water management in the gas diffusion layer (GDL) [3][4]. Understanding the relationship between liquid water distributions in the cathode GDL and transport properties of PEM fuel cells under varying operating conditions can lead to improved GDL configurations for improved performance. Previously, studies have been conducted to characterize the effect of operating temperature on liquid water pathways in GDLs by using 3D imaging techniques on operando PEM fuel cells [5]. High-speed, high-resolution 3D imaging techniques, such as computed tomography (CT), enable the visualization of dynamic pore-scale effects and are advantageous in elucidating transport mechanisms in the GDL.In this work, the effect of operating relative humidity on the formation of liquid water pathways in the GDL will be explored by imaging an operando PEM fuel cell with synchrotron X-ray CT. To date, a custom PEM fuel cell has been developed in-house which features a novel design with two rotary unions on either side of the cell. The rotary unions enable continuous rotation of the cell during imaging, and thus are central to achieving high temporal resolution for visualizing the development of preferential water pathways. High spatial resolution (pixel resolution of 1.44 microns per pixel [6]) is also obtained with the synchrotron beam, which allows for the visualization of liquid water in individual pores at the microscale in the GDL. Visualizing water in the micropores of the GDL can help us further understand water transport mechanisms within the complex structure of the GDL to ultimately develop methods to expel excess water efficiently. In the next steps of this research, we will use the results from electrochemical testing and the reconstructed images of the fuel cell to draw important conclusions about the relationship between liquid water distributions in the GDL and fuel cell performance. As well, the effect that operating relative humidity has on this relationship will be determined. The aim of this work is to inform optimal design for GDL materials for improved PEM fuel cell performance, which will ultimately accelerate their utilization on a global scale as a reliable and sustainable energy source.[1] P. Shrestha, CH. Lee, K. F. Fahy, M. Balakrishnan, N. Ge, and A. Bazylak, “Formation of Liquid Water Pathways in PEM Fuel Cells: A 3-D Pore-Scale Perspective,” Journal of The Electrochemical Society, vol. 167, no. 5, p. 054516, Jan. 2020, doi: 10.1149/1945-7111/ab7a0b.[2] S. Park, J. W. Lee, and B. N. Popov, “A review of gas diffusion layer in PEM fuel cells: Materials and designs,” International Journal of Hydrogen Energy, vol. 37, no. 7, pp. 5850– 5865, Apr. 2012, doi: 10.1016/J.IJHYDENE.2011.12.148.[3] Y. Nagai et al., “Improving water management in fuel cells through microporous layer modifications: Fast operando tomographic imaging of liquid water,” Journal of Power Sources, vol. 435, p. 226809, Sep. 2019, doi: 10.1016/J.JPOWSOUR.2019.226809.[4] U. U. Ince et al., “3D classification of polymer electrolyte membrane fuel cell materials from in situ X-ray tomographic datasets,” International Journal of Hydrogen Energy, vol. 45, no. 21, pp. 12161–12169, Apr. 2020, doi: 10.1016/J.IJHYDENE.2020.02.136.[5] Hong Xu, Shinya Nagashima, Hai P. Nguyen, Keisuke Kishita, Federica Marone, Felix N. Büchi, Jens Eller, Temperature dependent water transport mechanism in gas diffusion layers revealed by subsecond operando X-ray tomographic microscopy, Journal of Power Sources, Volume 490, 2021, 229492, ISSN 0378-7753, https://doi.org/10.1016/j.jpowsour.2021.229492.[6] Canadian Light Source, “Detectors,” BMIT. [Online]. Available: https://bmit.lightsource.ca/tech-info/detectors/. [Accessed: 05-Apr-2022].

Comparison of Serpentine and Interdigitated Monopolar Plates on the Performance of an Anion Exchange Membrane Fuel Cell By CFD

The continuous energy demand and the growing population have focussed the scientific research on developing alternative energy sources or green fuels.The anion exchange membrane fuel cell (AEMFC) arises as an excellent alternative because of its low-cost electrocatalyst used at the cathode, energy production, and no pollutants emissions to the environment. Nowadays, several studies have been conducted to improve the performance of the AEMFC modifying membrane materials, types of gas diffusion layers (GDL), and catalysts, among other cell components.However, the design of the flow channels by changing plate topologies and materials is still under development. About flow channels topologies, conventional geometries array (pin, straight, parallel, and serpentine) flow fields lead the flow in the direction parallel to the electrode surface, and the reactive gas flow towards the catalyst layer (CL) mainly by molecular diffusion. On the other hand, interdigitated flow fields provide convection velocity normal to the CL and forced convection flow in GDL for better mass transfer. The interdigitated flow fields could prevent water flooding and improve high current density operations performance.These flow fields have been tested in proton exchange membrane fuel cells (PEMFC) with excellent results at low current densities. Nonetheless, there is an essential balance and management of water in an AEMFC. It presents simultaneous production and consumption of water in anode and cathode, respectively, where the production is twice the consumption.Poor water management could provoke anode flooding or membrane drying. These scenarios are undesirable due to mass transport limitations, membrane polymer degradation, and cathodic channels flow can be flooded. Therefore, an appropriate design of flow field that allows the correct water balance on AEMFC is needed for optimal performance. This research deals with the computational fluid dynamic (CFD) comparison of serpentine and interdigitated flow fields on the performance of an AEMFC. For the development of this model, the Navier-Stokes and Brinkmann equations were implemented for momentum transfer. In addition, the average mixture model represents the transport of chemical species, and the Butler-Volmer equation denotes the electrochemical reaction at the CL; water balance is analyzed at low and high current densities to evaluate the scenarios above mention.Preliminary results indicate that a serpentine design is functional at the anode due to the water management is favored. An interdigitated flow field is implemented at the cathode to improve the distribution of the reactants from channels until the CL.

(Invited) Bipolar Membranes with a 3D Junction of Interlocking Electrospun Fibers

Bipolar membranes (BPMs), typically laminated layers of anion-exchange and cation-exchange polymers, have the unique capability of splitting water at a potential near 0.83 V. Such membranes are used in electrodialysis membrane separation processes. They also have applications in water electrolyzers, CO2 electrolysis cells, and self-humidifying fuel cells. We report here on recent developments regarding BPMs with a high interfacial area, 3D nanofiber junction.Membranes were prepared by first creating a bipolar junction layer, by the simultaneous electrospinning of anion-exchange and cation-exchange polymers, with the addition of catalyst nanoparticles to facilitate water splitting. Solvent vapor exposure and hot-pressing closed all interfiber pores, to create a dense film of interpenetrating and interlocking nanofibers of positively and negatively charged polymers. In one fabrication method, dense films of solution cast anion and cation-exchange polymers were hot-pressed onto the opposing surfaces of the junction layer to create a tri-layer BPM. Membranes were also fabricated by electrospinning all three layers of the BPM: first spinning anion-exchange fibers, followed by dual fiber spinning with catalyst spraying, and then spinning only cation-exchange fibers. Solvent exposure and hot-pressing closed all interfiber voids.BPMs were made with a junction layer 12-15 mm thick, where the total membrane thickness was 50-80 mm. Membranes were prepared with both hydrocarbon and fluoropolymer ionomers, e.g., sulfonated poly(ether ether ketone) or perfluorosulfonic acid as the cation-exchange polymer and either quaternized poly(phenylene oxide), AEMIONä (an imidazolium-based polymer sold by Ionomr Innovations, Inc.), or PiperION (a poly(aryl piperidinium) from Versogen) as the anion-exchange polymer. A variety of different junction layer catalysts powders were examined, including Al(OH)3 and graphene oxide. Membranes were evaluated in an H-cell for the collection of steady-state current-voltage data and in a flow cell for long-term constant current water splitting (electrolysis) operation, typically with an aqueous Na2SO4 electrolyte. The 3D junction membranes performed exceptionally well: (i) the water splitting potential was low (near the expected value of 0.83 V), (ii) the transmembrane voltage drop was small at high currents (e.g., a voltage drop of 1.1 V up to 1.1 A/cm2), and (iii) the extended bipolar reaction zone for water splitting with interlocking fibers allowed for high current density operation with no evidence of membrane degradation.In this talk, the effect of membrane composition (the type/amount of anion and cation exchange polymers and choice of catalyst) and structure (the thickness of the layers) on short-term and long-term membrane performance will be discussed. Results will be presented for operating the bipolar membrane in water splitting and water generation modes.

(Digital Presentation) Interfacial Durability of Anion Exchange Membrane Water Electrolyzers (AEMWEs)

There is a growing industrial appeal of anion exchange membrane water electrolyzers (AEMWEs) to produce hydrogen. This is spurred by the recent advancements in high current density operation capability with relatively low overvoltage performance. Cost reduction has been pursued by reducing the reliance on expensive platinum group metal (PGM) catalysts while still achieving long-term, continuous operation conditions most relevant to the industry: high current densities above 2 A/cm2 while retaining overvoltage performance so that overall cell potential is less than 2V.Along with a selection of appropriate PGM-free catalysts, other approaches exist that drive down the associated cost to produce hydrogen from water splitting. Sources of water are extended to brackish and even seawater to further drive down costs due to the removal of costly water purification requirements. The introduction of salt to the water source may improve overvoltage performance in an AEMWE by raising electrolyte conductivity, however, it may also lead to some unknown instability within more severe high current operating conditions. The challenge remains that AEMWE durability testing is not standardized, and more minute interfacial degradation mechanisms between ionomer, catalyst, membrane, and electrolyte are not well characterized for many industrially relevant materials. When approaching AEMWE performance improvements with PGM-free and variable electrolyte content in water solution sources, the long-term performance needs to be demonstrated in a stable and reliable manner.A series of in-situ Raman experiments are presented in coordination with ex-situ spectroscopic and physical analysis of components in PGM-free AEMWEs that are expected to contribute to overall degradation of electrolyzer performance. Interfacial durability improvements are sought by providing insight into the main sources of failure during high current and long-term operations. Electrochemical testing protocols are also developed and presented in order to seek standardization of testing procedures. In-line gas chromatography (GC) analysis is also presented in tandem with other analytical methods to confirm product gas purity and corroborate hypotheses on possible degradation mechanisms.

Temperature Distribution Analysis of PEM Electrolyzer in High Current Density Operation By Numerical Simulation

An advantage of polymer electrolyte membrane water electrolysis (PEMWE) over other water electrolysis technologies is its ability to operate at high current densities. However, resistive heating during . In this study, the internal cell temperature distribution at high current densities up to 12 A cm-2 is evaluated through numerical simulation. The correlation between the temperature gradient in the cell and the flow rate of water supplied is examined. An increase in water supply is effective in minimizing high temperature gradients at higher current densities.

Superhydrophobic fluorinated carbon powders for improved water management in hydrogen fuel cells

Under high current density operation, the efficiency of polymer electrolyte fuel cells (PEFCs) can dramatically decrease. This is due to water accumulation at the cathode side, preventing oxygen diffusion to the electrocatalyst. As such, effective water management is of vital importance by use of a suitable gas diffusion layer (GDL) and/or microporous layer (MPL). MPLs generally consist of carbon black as the porous electron conducting phase, and polytetrafluoroethylene (PTFE) as a hydrophobic binder. Here, we instead use superhydrophobic fluorinated carbon powder in the MPL as a novel material to decrease the required PTFE content. It is confirmed that the water contact angle of the MPL can be increased from 131° to 151° by using fluorinated carbon. Moreover, the fluorinated carbon MPL shows lower oxygen transport resistance at high humidity. Furthermore, in single fuel cell tests at various temperatures and relative humidity values, the I–V performance is significantly and consistently better than for the conventional MPL. These results confirm that fluorinated carbon is a promising new material for water management in the MPLs of PEFCs.

Near‐Infrared Light‐Emitting Diodes from Organic Radicals with Charge Control

AbstractOrganic radicals with fluorescence from doublet‐spin energy manifolds circumvent efficiency limits from singlet–triplet photophysics in organic light‐emitting diodes (OLEDs). The singly occupied molecular orbital (SOMO) in radicals enables the higher potential performance. The SOMO also presents substantially lower energy frontier orbitals compared to conventional fluorescent emitters for device operation, which can cause severe electron trapping that limits the performance of radical OLEDs. To improve optoelectronic performance, electron donor–acceptor‐mixed hosts are used to control charge transport for enhanced radical electroluminescence by charge recombination on SOMO and frontier orbitals. The (2‐chloro‐3‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl‐based radical is designed to test the charge‐controlled device architectures in OLEDs by transient analysis and device characterization studies. Efficient radical OLEDs with 4.7% maximum external quantum efficiency are reported—showing substantial advances in performance for OLEDs with peak emission beyond 800 nm. In addition, substantially improved performance at higher current density operation and more than two orders of higher lifetime stability are achieved with mixed hosts. These results enable pathways to infrared‐emitting devices with applications ranging from communications to bioimaging.

Engineering Electrodes with Bimodal Pore Size Distributions for Next-Generation Electrochemical Devices

In many electrochemical conversion devices such as low temperature fuel cells or water electrolyzers, the transport of reactants to and products from the catalyst layer is facilitated by porous structures referred to as gas diffusion layers or porous transport layers. They bridge the gap between flow fields and catalyst layers and their mass transport capabilities become especially critical at high current density operation. Excessive accumulations of reaction products or a lack of fresh reagents stall out the electrochemical conversion resulting in reduced efficiencies or even damage to the system itself due to fuel starvation1. Thus, to realize cost-competitive electrochemical systems we must overcome the fundamental challenge of multiphase flows in which liquid and gaseous phases flow through porous structures in opposing directions.In recent years, porous electrodes have been adapted to better address these issues and improve performance. For example, the addition of a layer with reduced pore size facing the catalyst layer (i.e., micro porous layer) was shown to increase performance in fuel cells and electrolyzers2–4. Furthermore, chemical5 as well as mechanical6,7 methods of creating dedicated liquid and gas pathways in the structure have been investigated with promising results. These approaches are however intrinsically limited by the microstructure of the material they are applied to.Inspired by the success of these modifications, we propose a novel structure containing both a pore size gradient as well as dedicated water and gas pathways in the form of bimodal pore size distributions (Figure 1). This material is generated by depositing a metal in the presence of gas evolution to form a structure containing microscopic and macroscopic pores. This type of material has in the past been used successfully to improve boiling heat transfer8, another process faced with the counterflow of liquid and gas. They have also been investigated as high surface area material for microbial anodes9 and have been postulated to find application in other electrochemical devices such as batteries or fuel cells10. In this talk, I will discuss the synthetic approach to manufacture self-standing porous electrodes using an electrochemical flow platform and elucidate the correlation between applied electrochemical parameters and resulting material microstructure. Properties such as electrode thickness and pore sizes can be adjusted during the synthetic process to suit the requirements of specific applications exhibiting complex mass transport requirements.Acknowledgements:This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 899987.

The combined impact of trimethyloctadecylammonium chloride and sodium fluoride on cycle life and energy efficiency of soluble lead-acid flow battery

The development and commercialization of SLRFB is obstructed due to its limited cycle life. The cycle life is prevented due to the formation of Pb dendrites, sluggish kinetics of Pb+2/PbO2 redox species, partial reversibility of PbO2, and O2 evolution during charging. SLRFB has common electrolyte reservoir, therefore, it is desirable to add both anode and cathode benefitting additives together in the electrolyte. But, such kind of study is very limited in the literature. By considering this, first time, the present work demonstrates the combined effect of trimethyloctadecylammonium chloride and NaF/LiF as electrolyte additives on the electrochemical performance and cycle life of SLRFB. Compared with the pristine electrolyte, the kinetics and reversibility of Pb2+/PbO2 redox couple are improved in the presence of additives. Both Pb and PbO2 electrodeposits are smooth, compact and uniform in the presence of additives. The lifespan of SLRFB without any additive is limited to 45 charge/discharge cycles due to shorting of the electrodes. The CE has been decreased from 93 % to 74 % in 46th cycles at a charging current density of 20 mA cm2. However, in the presence of additives, the cell has been successfully cycled for over 500 cycles with an average CE, VE and EE of 94 %, 78 % and 74 % respectively. The cell also showed the maximum specific capacity 50 mAh cm−2 over 100 cycles when cycled at 50 mA cm2 current density for 1 h, such high current density operation is very scarce in the literature.

High Performance AEM Water Electrolysis with Aemion® Membranes

By 2030 up to 50% of energy is expected to be carried in the bonds of H2. Global electrolysis capacity must increase from the current 240 MW to an anticipated 300 GW in 2030 and 3500 GW in 2050 to enable this transition. Alkaline and PEM electrolyzers are commercially mature with the currently market share of new installations roughly an equal split between these technologies. However, each of these electrolyzers are associated with challenges – alkaline electrolyzers operate at low current density, and require high concentration electrolytes (30 wt% KOH) to conduct hydroxides through the porous electrode separator (I.e., Zirfon). PEM electrolyzers use a proton conductive membrane to enable high current densities, however, running the reaction in acidic electrolyte requires platinum group catalysts and component coatings that hinder scalability at 2050 targets.AEM water electrolyzers address both of these challenges by pairing anion exchange membrane with alkaline electrolyte to enable high current density operation, at high pressure, without noble metal catalysts. These attributes enable the most cost-effective green hydrogen - bringing the DOE hydrogen shot target of $1/kg within reach.Anion exchange membrane chemistries have previously hindered this type of electrolyzer – AEMs based on quaternary amines, or pendant imidazolium groups chemically degrade in concentrated alkaline electrolyte, and mechanically degrade (from swelling) in low concentration alkaline media. Ionomr’s Aemion+ membranes are based on a sterically-protected polybenzimidazole chemistry and are chemically robust (stable in up to 10 M KOH), and exhibit low swelling to enable operation in low concentration electrolytes. These membranes are an enabling technology for long duration water and CO2 electrolysis.This talk highlights how Ionomr’s Aemion+ membranes enable performance in excess of 1 A/cm2 at 1.8 V with non-PGM catalysts and a variety of configurations, and >4000 hours of durability in continuous operation. Figure 1

(Invited, Digital Presentation) Photo-Electrochemical Water and CO2 Reduction Devices Operating Under Concentrated Radiation

Achieving high current densities while maintaining a high energy conversion efficiency is one of the main challenges for enhancing the economic competitiveness of solar fuel producing photo-electrochemical devices [1]. I will discuss two device implementations utilizing concentrated irradiation to achieve high current density operation. The water-splitting device is utilizing thermal integration to sustain high performance while dealing with high current density and the corresponding overpotentials [2]. I will quantify the theoretical increase in the maximum efficiencies at given current densities of photoelectrochemical devices resulting from thermal synergies. I will then discuss device implementation of such an approach and show how more realistic device models (multi-dimensional, multi-scale, multi-physics) can be used to support the device implementation and its operational understanding [3]. I will then show how the design principles developed for water splitting can be translated to CO2 reduction devices and discuss a corresponding device implementation.[1] M. Dumortier, S. Tembhurne, S. Haussener, Energy Environmental Science, 8: 3614-3628, 2015.[2] S. Tembhurne, F. Nandjou, S. Haussener, Nature Energy, 4: 399-407, 2019.[3] S. Tembhurne, S. Haussener, Journal of The Electrochemical Society, 163: H1008-H1018, 2016.

Low‐Dimensional Electrocatalysts for Acidic Oxygen Evolution: Intrinsic Activity, High Current Density Operation, and Long‐Term Stability

AbstractProduction of green hydrogen (H2) by water electrolysis is important for achieving the global mission of carbon neutrality. For this, acidic water electrolysis with a higher current density operation and energy conversion efficiency compared with alkaline water electrolysis has attracted much attention. The four‐electron‐transfer oxygen evolution reaction (OER) limits the overall efficiency of water electrolysis devices. In recent years, low‐dimensional OER catalysts have been extensively explored to increase the overall efficiency of such devices, but most of them work well only at low current density and show unsatisfied long‐term stability. In this review, recent progress in acidic OER is discussed and three aspects including intrinsic activity, high current density operation, and long‐term stability are focused upon. Strategies to improve these aspects including surface chemistry engineering, constructing porous structure, and protecting the active sites’ are comprehensively reviewed. Finally, prospects for developing high‐performance catalysts with high current density operation and long‐term stability for industrial applications are proposed.

All‐Solid‐State Vertical Three‐Terminal N‐Type Organic Synaptic Devices for Neuromorphic Computing

AbstractArtificial synaptic devices are the basic composition units for neuromorphic computing processors that realize massive parallel computing. However, the n‐type organic transistors have failed to achieve good performance as an artificial synaptic device for neuromorphic computing until now. Here, a vertical three‐terminal n‐type organic artificial synapse (TNOAS) using a lithium ion‐based organic dielectric and the n‐type donor–acceptor (D–A) conjugated polymer‐naphthalene‐1,4,5,8‐tetracarboxylic‐diimide‐thiophene‐vinyl‐thiophene (NDI‐gTVT) as the channel is proposed. The TNOAS achieves nonvolatile conductance modulation with high current density operation (≈10 KA cm−2) at low voltage and mimics the basic functions of biological synapses, such as long‐term synaptic plasticity and paired‐pulse facilitation. The minimum energy consumption of a response event triggered by a single action potential is 6.16 pJ, which can be comparable with p‐type counterparts. Moreover, simulation using handwritten digital datasets exhibit a high recognition accuracy of 94%.

Anti-Demagnetization Analysis of Fractional Slot Concentrated Windings Interior Permanent Magnet Motor Considering Effect of Rotor Design Parameters

This work investigates the effect of design parameters of permanent magnets (PMs) and flux barriers (FBs) in the rotor on the anti-demagnetization ability (ADA) of fractional slot concentrated windings interior PM (IPM) motors for electric scooters. A 2.5 kW IPM motor (12 slots and 8 poles) is designed for a wide speed range, and its ADA associated with different PM and FB arrangements is studied under high temperature and high current density operations. The analysis shows the relationship between the ADA and characteristic current (<inline-formula> <tex-math notation="LaTeX">$I_{\mathrm {ch}}$ </tex-math></inline-formula>, defined as the ratio of PM flux linkage to <inline-formula> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula>-axis inductance). It is also found that proper designs of FBs can significantly improve the ADA of the IPM motor without much affecting <inline-formula> <tex-math notation="LaTeX">$I_{\mathrm {ch}}$ </tex-math></inline-formula>. Thus, the motor ADA and performance can be simultaneously improved. Finite element analysis is used for evaluation, and experiments are conducted to validate the analysis.

Influence of Supporting Electrolyte on Hydroxide Exchange Membrane Water Electrolysis Performance: Catholyte

Alkaline or hydroxide exchange membrane water electrolysis (HEMWE) is a promising technology for green hydrogen production using platinum group metal-free catalysts and stainless steel, an advantage of alkaline water electrolysis (AWE), and a gas-impermeable membrane, a parallel to proton exchange membrane electrolysis (PEMWE). However, the HEMWE requires supporting electrolytes and there is minimal understanding of their role on the respective reactions. Without SELs, HEMWE performance and durability are worse than PEMWE systems. Herein, consistently feeding potassium hydroxide anolyte, we systematically study the effects of catholyte SELs in HEMWEs including dry vs. wet operation, cation effects, anion effects, and cation/OH ratios on cell potential and stability. We report that (i) hydration of the cathode improves high current density operation by preventing dehydration of the hydroxide exchange membrane (HEM), (ii) there was no correlation between cation type and cell potential, (iii) cell potential and high frequency resistance did not correlate with SEL conductivity, (iv) cathodic carbonate SEL had a significant negative effect on cell performance, (v) increased cation/OH ratio also caused increased cell potentials. Overall, this study concludes that feeding water or potassium hydroxide solution is desirable to improve the AEMWE performance.

Anode Catalysts in CO2 Electrolysis: Challenges and Untapped Opportunities.

The field of electrochemical carbon dioxide reduction has developed rapidly during recent years. At the same time, the role of the anodic half-reaction has received considerably less attention. In this Perspective, we scrutinize the reports on the best-performing CO2 electrolyzer cells from the past 5 years, to shed light on the role of the anodic oxygen evolution catalyst. We analyze how different cell architectures provide different local chemical environments at the anode surface, which in turn determines the pool of applicable anode catalysts. We uncover the factors that led to either a strikingly high current density operation or an exceptionally long lifetime. On the basis of our analysis, we provide a set of criteria that have to be fulfilled by an anode catalyst to achieve high performance. Finally, we provide an outlook on using alternative anode reactions (alcohol oxidation is discussed as an example), resulting in high-value products and higher energy efficiency for the overall process.

Improvement of polymer electrolyte fuel cell performance by gas diffusion layer with relatively hydrophilic surface

To improve the performance of polymer electrolyte fuel cells under high current density operation, the flooding problem in gas diffusion layers (GDLs) should be solved. In this study, a novel GDL with a relatively hydrophilic surface, consisting of hydrophilic and hydrophobic pores, which yielded a wettability distribution in the thickness direction, was proposed to achieve smooth water transport. First, we fabricated GDLs with surfaces partially hydrophilized by Nafion, and we demonstrated that the cell performance improved with this treatment. Cell performance tests suggest that a GDL with optimized surface treatment could reduce the water accumulation compared with the hydrophobic GDL used in this study; it could also improve cell performance owing to low mass transport losses. To verify the surface treatment-induced improvement in the oxygen diffusivity of the GDL, the water transport in the GDL was simulated using a lattice Boltzmann method. The results showed that the water accumulation in the GDL with surface treatment was small because the water flow was limited to the thin relatively hydrophilic region. Consequently, the oxygen diffusivity was higher than that of the hydrophobic GDL. Therefore, the flooding problem can be suppressed by the surface treatment, which yields a relatively hydrophilic surface.