bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance and Durability of Poly(norbornene) Anion-Conducting Membranes and Ionomers
Authors: Kohl Paul , Park Habin , Shah Parin 
Published: February 2024

Low-temperature, polymer-based water electrolyzers using anion conductive polymers have several potential advantages over acid-based polymer electrolyzers. However, the long-term durability of the anion conducting polymer membrane and ionomer remains to be demonstrated.
In this study, a family of norbornene-based copolymers and terpolymers have been used in fuel cells and electrolyzers to provide high conductivity (>200 mS/cm at 80oC) and superior mechanical properties. The factors affecting the voltage and durability of alkaline electrolyzers will be reported.
Low Loading and High Utilization Ratio of Iridium Catalyst Coated Smoltek Carbon Nanofibers Used as Anode Material for PEM Water Electrolyzers
Authors: Wen Xin , Penninckx Bastien , Sanchez Jaime Sanchez , Ehrnberg Ellinor , Li Qi , Wenger Fabian 
Published: February 2024

Proton exchange membrane water electrolyzers (PEMWE) are a core technology for the future green hydrogen production market. The installed power for PEMWE is estimated to be 40 GW by 2030 [1]. The oxygen evolution reaction (OER) catalyst on the anode side is dominated by Iridium (Ir)-based materials, one of the rarest noble metals in the crust of Earth. It is critical to lower the loading of Ir-based catalyst to ≈ 0.1 mg Ir/cm2 without compromising the overall performance to enable the mass manufacturing targets. It is a big challenge due to the poor electrical contact between the resulting catalyst layers and the anode substrate [2-3]. To reach this goal, Smoltek invented an advanced porous transport electrode (PTE) concept using its proprietary carbon nanofiber (CNF) technology [4] and unique Ir coating technology. An anode porous transport layer (PTL) is first modified by vertically aligned CNFs to increase surface area, followed by coating a corrosion-resistant and conductive layer (e.g. Platinum) and a subsequent OER catalyst layer (Fig. 1a). Cathodic electrodeposition in a three-electrode static cell was performed for Ir-based catalyst deposition. We demonstrate that with this method, the morphology and deposition process of Ir are controllable at very low loading amounts (≥ 0.1 mg Ir/cm2). An Ir coating layer can be formed on the highly structured CNF-based surface. The electrodeposited Ir has strong adhesion with the CNF PTEs, resulting in a high electrical conductivity [5].
This unique Ir-electrodeposited CNF PTEs structure maximizes the anode surface area and paves a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market.

References

Stiber et al. Adv. Energy Mater., 2021, 11, 2100630.

Möckl et al. J. Electrochem. Soc., 2022, 169, 064505.

Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.

https://www.smoltek.com/applications/electrolyzers/

Krivina et al. Adv.Mater., 2022, 34, 2203033.

Figure 1
Investigating the Stability of Electrodeposited NiMo Alloy for Hydrogen Evolution Reaction in Alkaline Media
Authors: Majeed Abdul , Etzold Bastian J.M. 
Published: February 2024

A lot of efforts have been devoted to develop highly active noble-metal-free catalysts for hydrogen production by water electrolysis.1,2 Nevertheless, the stability of such catalysts, yet equally important, is rarely touched. NiMo alloy is an emerging catalyst for hydrogen evolution reaction (HER) in alkaline media.3 In the present work, we studied the stability of NiMo alloy for HER under alkaline (1M KOH, Fe-free) conditions as a model catalyst. Using electrodeposition at room temperature, we deposited NiMo alloy onto nickel foam substrates. A long-term (20h) stability test at a fixed current density of -100 mA cm-2 was carried out using chronopotentiometry. Electrochemical active surface area (ECSA) and HER polarization curves were determined prior and after this stability test. Here, obvious activity loss is observed. The ECSA of NiMo catalyst after chronopotentiometry test increases by 10%. Thus, an obvious increase in the overpotential is observed upon normalizing the catalytic current with ECSA (Figure 1a). As further stability test 100 CV cycles at a scan rate of 100 mV s-1 from 0 to –350 mV vs. RHE were carried out, the catalysts then hold for 30 min at open circuit potential and again 100 CV cycles carried out. A clear drop in activity during the second 100 cycles is also observed here and especially at the higher current density of 60 mA cm-2 (Figure 1b). In summary, we found that NiMo, though active initially, loses its activity with time under HER conditions in alkaline media.
References

Vesborg, P. C. K.; Seger, B.; Chorkendorff, I. Phys. Chem. Lett.
2015, 6, 951– 957.

Zou, X. X.; Zhang, Y. Soc. Rev.
2015, 44, 5148– 5180.

Kuznetsov, V. V.; Gamburg, Y. D.; Zhulikov, V. V.; Krutskikh, V. M.; Filatova, E. A.; Trigub, A. L.; Belyakova, O. A. Electrochim. Acta
2020, 354, 136610.

Figure 1
Visualization of Bubble Behaviors in Flow Fields of PEM Water Electrolyzer
Authors: WU Lizhen , Pan Zhefei , LIU Yun 
Published: February 2024

Proton exchange membrane water electrolyzer (PEMWE) has been considered to be a promising technology for green hydrogen production, primarily because of its significant advantages in terms of high efficiency, high purity and fast dynamic response [1]. During its operation, hydrogen/oxygen evolves from the catalyst layer (CL), transports through the diffusion layer (DL) and then releases to the flow channel, forming various two-phase flow regimes, including bubbly, slug, annular, etc [2]. The presence of bubbles not only covers the electrode surface, but also blocks the water delivery, creating a large mass transfer resistance and even terminating the cell operation [3]. Another issue associated with bubble management is that the conventional parallel and serpentine flow-field configurations showed a poor self-pumping effect, exhibiting a mismatch between bubble evolution and removal rates [4]. To address this issue, therefore, some novel flow field designs have also been proposed in recent years, but the underlying mechanism how two-phase flow regime in flow-filed channels affects the electrolyzer performance is still not clear.
In this work, we investigate the effect of two-phase behavior on the electrolyzer performance via a visualization approach, as illustrated in Figure 1. Our preliminary results have shown that an increase of water supply flow rate has insignificant effect on the electrolyzer performance even at high current densities. It is observed that with increasing the water supply rate, many bubbles are still covering the electrode surface, meaning that water cannot be effectively supplied to the CL. To address this issue, a degassing layer, with a thinner rib and a wider channel, is introduced to the flow field design, which is able to promote the self-pumping effect of gas bubbles. This novel design can facilitate the rapid detachment of bubbles from the electrode surface, providing more paths for the water penetration into the CL.

Acknowledgement

This work was fully supported by a grant from the National Natural Science Foundation of China (Project No. 52022003).

References

Razmjooei, T. Morawietz, E. Taghizadeh, et al, Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer, Joule, 5(7) (2021) 1776-1799.

Rakousky, U. Reimer, K. Wippermann, et al, An analysis of degradation phenomena in polymer electrolyte membrane water electrolysis, J. Power Sources, 326 (2016) 120-128.

Villagra, P. Millet, An analysis of PEM water electrolysis cells operating at elevated current densities, Int. J. Hydrog. Energy, 44(20) (2019) 9708-9717.

O. Majasan, J.I.S. Cho, I. Dedigama, et al, Two-phase flow behaviour and performance of polymer electrolyte membrane electrolysers: Electrochemical and optical characterization, Int. J. Hydrog. Energy, 43(33) (2018) 15659-15672.

Figure 1
Elucidating the Role of Flow Fields in Bubble Removal from Porous Transport Layers
Authors: Zhu Lijun , Tugirumubano Alexandre , Bazylak Aimy 
Published: February 2024

Accelerating bubble removal from the porous transport layer (PTL) will be the key to reaching high current densities and cell efficiencies for polymer electrolyte membrane (PEM) water electrolyzers by improving catalyst utilization through reduced bubble accumulation for enhanced water transport to reach reaction sites 1,2. Previous studies have reported non-uniform bubble distributions within the PTL, where bubble saturation under the flow field lands was higher than that under the channel 3–5. This bubble distribution heterogeneity was attributed to the PTL/flow field interface and PTL/catalyst layer interface, which caused non-uniform outlet and non-uniform inlet conditions for bubble transport within the PTL, respectively. As such, determining the impact of the interfacial conditions on bubble removal from the PTL is critical for optimizing designs for next generation PTLs that need to exhibit low reactant mass transport resistances for PEM water electrolyzers.
In this study, we elucidated the effects of the PTL/flow field interface on bubble transport in the PTL and specified the role of flow fields in bubble removal from the PTL. First, X-ray computed tomography (CT) was employed to reconstruct the microstructure of a titanium fibre-based PTL. Pore network modelling was then implemented to simulate and analyze the multiphase flow behaviour within the PTL under two kinds of outlet boundary conditions, i.e., with and without a flow field. We showed a dramatic non-uniform bubble distribution within the PTL when using an outlet condition with a flow field, while a uniform bubble distribution occurred in the PTL when using an outlet condition without a flow field. We attributed this to the existence of flow fields that lead to longer gas transport pathways through the PTL regions under the flow field lands. This study demonstrates the effects of flow fields on hindering bubble transport within the PTL and informs the need of tailored designs of the PTL/flow field interface for accelerating bubble transport in the PTL.

References

J. K. Lee and A. Bazylak, Joule, 5, 19–21 (2021).

S. Yuan et al., Prog. Energy Combust. Sci., 96, 101075 (2023).

J. K. Lee et al., Cell Reports Phys. Sci., 1, 100147 (2020).

C. H. Lee et al., J. Power Sources, 446, 227312 (2020).

S. De Angelis et al., J. Mater.
Chem. A, 9, 22102–22113 (2021).
Operando Identification of Temperature-Dependent Pore-Scale Gas Saturations in PEM Water Electrolyzers
Authors: Ham Chaeyoung Tina , Shrestha Pranay , Lytle Spencer , Bazylak Aimy 
Published: February 2024

Polymer electrolyte membrane (PEM) water electrolysis is a promising solution for the chemical storage of intermittent renewable energy in the form of clean hydrogen (1). For the widespread adoption of this technology, the efficiency of PEM electrolyzers must be improved through informed material design and tailored operating conditions to compete with incumbent carbon-emitting technologies (2). A main source of inefficiency is related to mass transport losses, where oxygen gas, a by-product of the anode reaction, accumulates in the anode porous transport layer (PTL) and hinders reactant liquid water delivery to reaction sites (3). Although extensive studies have explored this two-phase flow phenomenon, the consideration of operating temperature on gas accumulation in the PTL adds further complexity. A duality in temperature effects has been reported in the literature where increasing the operating temperature may encourage gas coverage which obstructs liquid water transport, but it may also enhance liquid water delivery due to favorable fluid property changes in viscosity and surface tension (4). Efforts have been made previously to reconcile these competing observations using 2D visualization methods (5), however a closer investigation using 3D visualization techniques will provide valuable pore-scale insights in the comprehensive understanding of the impact of operating temperature on gas transport in the PTL, and subsequently mass transport losses in the PEM electrolyzer.
In this work, we employed operando X-ray computed tomography (CT) to visualize three-dimensional (3D) pore-scale gas saturations in the PTL at various industrially relevant operating conditions. Specifically, a custom in-house electrolyzer was imaged with synchrotron CT at five different temperatures (40°C, 50°C, 60°C, 70°C, 80°C) and current densities ranging from 0.5 A/cm² to 4.0 A/cm² with 0.5 A/cm² incremental steps. Electrochemical impedance spectroscopy and Tafel measurements were also acquired to characterize the relationship between gas distributions and corresponding mass transport overpotentials. Considering X-ray transparency, a model PTL made of carbon fibers was used to achieve sufficient contrast to quantify water and gas in the obtained images. Using precise volume registration and subtraction methods, pore-scale gas distributions in the PTL were quantified to reveal changes in bubble accumulation and coverage area at different operating temperatures and over operation time. The novel insights from this work will aid in our understanding of the complex relationship between operating temperature and multiphase flow phenomena in the PTL, which is vital for tailoring operating conditions of PEM electrolyzers to curtail the costs of green hydrogen production.
Utilization of 3-D Volume of Fluid Simulations to Understand Oxygen Evolution through Multilayer Porous Transport Layers for PEMWE Improvement
Authors: Sepe Mitchell , Cho Hyunseok , Shimpalee Sirivatch 
Published: February 2024

In this work, direct numerical modeling techniques were applied to 3-D generated porous transport layers (PTL), with the addition of a microporous layer (MPL), to understand the effect pore structure has on oxygen evolution. Proton Exchange Membrane Water Electrolyzers rely on PTLs to remove oxygen from the catalyst layer. Traditionally, an MPL is added to the PTL surface in contact with the catalyst layer. This creates a bilayer PTL, which is believed to improve oxygen removal, while maintaining liquid saturation. Two questions arise when creating a PTL sample for PEMWE application. First, how thick should the MPL be to achieve adequate oxygen removal? Second, is a bilayer PTL sufficient, or does a multilayer PTL result in improved oxygen removal?
The objectives of this work are to observe the influence that the MPL has on oxygen transport, the effect of the MPL on oxygen removal when compared to a single layer PTL, determine an ideal MPL to PTL ratio, and identify if multilayer PTLs aid in oxygen removal. Each sample is created through an improved image processing technique that eliminates the need for interface communication when meshing. This process allows for multilayer PTL structures to be created as one geometry. Due to the improved imaging technique, meshing of these complex structures is possible. The Finite Volume Method combined with a volume of fluid model was used to simulate two phase flow, liquid water and gaseous oxygen, through all PTL samples. Each PTL/MPL combination has three different MPL thickness, which corresponds to a PTL/MPL ratio of 90:10, 80:20, and 70:30. Bilayer, trilayer, and quadlayer PTL samples were also studied. Oxygen bubble evolution, growth, and surface interaction through all sample microstructures was observed. In-plane and through-plane permeability, liquid saturation, and liquid/gas interfacial area were calculated from simulation results. Findings from this work will provide insight into ideal MPL thickness and number of MPL layers for improved oxygen removal inside PEMWEs.
Novel Strategies for Efficient Water Electrolysis
Authors: Wågberg Thomas , Gracia-Espino Eduardo , Hu Guangzhi 
Published: February 2024

A growing global population in parallel with an increased prosperity seen from a global perspective have raised the need for energy and raw material resources exponentially. These increased needs have led to a number of negative consequences such as pollution, raw material shortages, increasing carbon dioxide levels in the atmosphere, and not least a threatening global warming. Renewable energy will be essential to break the dependence of fossil fuels, but due to the intermittency of renewables a storable non-fossil alternative is needed. Hydrogen represents one of very few sustainable options to store renewable energy on large scale and for seasonal variations. Here, we present novel strategies on water electrolysis driven by photovoltaics, with a focus on the development of state-of the art electrocatalysts based on earth-abundant transition metals, doped with sulphur and phosphor [1]. We show that by tuning parameters such as adsorption energy, morphology and conductance of the electrocatalysts we can achieve solar-to hydrogen efficiency approaching 20 % [2]. We discuss on strategies, mechanisms and challenges in the field of PV-driven electrolysis.
[1] Ekspong, J; Larsen, C; Stenberg, J;, Kwong, WL; Wang, J; Zhang, J; Johansson, EM; Messinger, J; Edman, L; Wagberg T, Solar-Driven Water Splitting at 13.8% Solar-to-Hydrogen Efficiency by an Earth-Abundant Electrolyzer, ACS Sustainable Chemistry & Engineering, sc-2021-03565f (acssuschemeng.1c03565). (2021)
[2] H Zhang, A Aierke, Y Zhou, Z Ni, L Feng, A Chen, T Wågberg, G Hu, A high‐performance transition‐metal phosphide electrocatalyst for converting solar energy into hydrogen at 19.6% STH efficiency, Carbon Energy, 5 (1), e217 (2022)
(ECS Carl Wagner Memorial Award) Free Electrons to Molecular Bonds and Back - The Dark Side of Solar Fuels and Chemicals
Authors: Strasser Peter 
Published: February 2024

The rising share of renewable electricity in power generation is testament to the increasing importance of solar/wind-electric routes to harvest sun light in form of free electrons. While some electricity will always be used directly or stored short-term in batteries, an increasing portion of it calls for direct conversion into valuable molecular solar e-fuels and e-chemicals, possibly followed by a later re-conversion into power. These “dark” e-conversion processes are made possible by electrocatalysis at electrified solid-liquid interfaces, coupled to mass and charge transport in the electrolyte bulk. New catalyst and ion conducting materials along with an understanding of the origin of reaction kinetic and transport barriers are needed for the design of ever more efficient, electrochemical interfaces in galvanic and electrolytic devices for the production and use of fuels and chemicals.
This presentation reports on a few examples of advances in our design and understanding of electrocatalytic materials, interfaces and mechanisms relevant to the conversion of electricity into energy or value-added molecular compounds. Experimental approaches covered range from in-situ/operando spectroscopic, microscopic, scattering and spectrometric techniques at the microscale to new diagnostic tools and analyses of mass transport at the macroscopic device level. Examples include generation and use of green hydrogen and the conversion of CO2.

Figure 1
Evaluation of Degradation Processes in Alkaline and PEM Water Electrolyzers
Authors: Sánchez Batalla Beatriz , Mariappan Sakthivel , Bogolowski Nicky , Weidlich Claudia , Drillet Jean-Francois 
Published: February 2024

In the struggle against climate change, hydrogen has been considered as a key player, since it can be used as a fuel in electrochemical devices, but also as feed in the chemical and metallurgical industry. However, only if this hydrogen is produced by CO2-free process, the net zero-emission goals will be achieved. Green hydrogen can be obtained by water electrolysis using renewable electricity as power source. While alkali (AEL) and acid (PEMEL) electrolyzers are the most advanced technologies, further improvements especially in terms of catalyst stability are still needed to increase their lifetime and economical profitability for megawatt and gigawatt scaling-up.
In this work, we report on electrochemical degradation tests of commercially available AEL and PEMEL single cells with 5 cm2 active, geometrical surface. The AEL anode and cathode consist of Raney-Ni electrodes with PTFE binder supported on a Ni grid, separated by a Zirfon diaphragm. 30% KOH at 80°C was used as electrolyte in both chambers. The commercial catalyst coated membrane (CCM) for PEMEL consists of 2 mgIr/cm2 anode and 1 mgPt/cm2 cathode coated on Nafion N117. Titanium felt and carbon paper were used as porous transport layers in the anode and cathode side, respectively. Ultrapure water at 60 °C was used as electrolyte in both sides. For long-term electrochemical tests, current density of 0.5 A/cm2 and 2 A/cm2 was applied to the AEL and PEMEL cells, respectively, for 1000 h. Since at nominal current density, low degradation rate was expected, accelerated degradation tests (ADT) were performed at two identical cells by using triangular polarization profile aiming to reflect dynamic electrolyzer operation in case of e.g., direct coupling with wind turbine. Thereby, the current density was varied between 0.05 - 1 A/cm2 for AEL and 0.05-3 A/cm2 for PEMEL for at least 1000 h. After each 100 h period during both constant and triangular polarization experiments, the cell was electrochemically characterized by impedance spectroscopy and current/voltage (UI) profiles and anolyte and catholyte were collected for ICP-OES measurements in order to evaluate dissolved species. After test, the cells were disassembled and the cell components were analyzed by SEM/EDX, XRD and XPS technique. By correlating the physicochemical with the electrochemical changes in the components of the cell, main degradation mechanisms will be exposed.