bluuebunny/crossref_metadata_2025 huggingface dataset:
OH* Electro-Adsorption Kinetics on Pt (111) in Alkaline: Comparison to the H* Electro-Adsorption
Authors: Lin Chia-Yi , Abruna Hector D. , Suntivich Jin
Published: December 2024

OH* electro-adsorption of platinum plays a critical role in the electrocatalysis of small molecules, including carbon monoxide and methanol. Recently, the OH* electro-adsorption has also been linked to the electrocatalysis of hydrogen evolution reaction and hydrogen oxidation reaction (HER and HOR), widely believed to be the result of the Pt-OH on the Pt-H formation. In addition, OH* is part of the oxygen reduction reaction (ORR) in alkaline fuel cells. In this contribution, we report our investigation on the OH* electro-adsorption of platinum using cyclic voltammetry (CV) as a function of scan rate. Our approach builds on the recently reported rate-dependent CV methodology, which we have developed to measure the kinetics of the Pt-H formation. The adsorption mechanisms are determined by comparing OH* electro-adsorption kinetics as a function of electrolyte chemistry, from pH to the chemistry of cation. Our results show that OH* electro-adsorption rate depends strongly on the ionic strength but weakly on pH. What’s more, the OH* electro-adsorption rate is at least an order of magnitude faster than H* electro-adsorption rate in alkaline. Therefore, we think that the water forming in HOR is limited by H* formation or H2O recombination and the OH* electro-adsorption in ORR is likely not the rate-limiting step.
Oxygen Evolution Reaction Activity and Stability of Copper and/or Manganese Cobalt Spinels
Authors: Liu Christopher Pantayatiwong , Roiron Camille , Atanassov Plamen
Published: December 2024

Gigawatt-scale hydrogen production using proton exchange membrane water electrolyzers may be limited by the availability of iridium (oxide), the current state-of-the-art catalyst for the oxygen evolution reaction (OER) in acid [1]. And yet, iridium-free catalysts have struggled to meet both the activity and stability of iridium oxide, much in part due to the thermodynamic instability of most transition metals in acidic OER conditions. Recently, though, reports of Cu, Co, and/or Mn containing iridium-free spinels have demonstrated promising performance [2–4].

Notwithstanding, the degradation mechanisms of these spinel-type catalysts are not well understood, as well as design strategies to mitigate the degradation. To explore these topics, four iridium-free, spinel-type catalysts were synthesized, characterized, and assessed for activity and stability: CuCo2O4, MnCo2O4, Cu0.5Mn0.5Co2O4, and Co3O4. The synthetic route (sacrificial support method) was built upon a previous study on CuCo2O4 for the alkaline OER by our group [5]. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy were performed to investigate the crystal structure (see Figure 1A), surface oxidation state, and morphology of the catalysts, respectively, both before and after accelerated stress tests (ASTs). Additionally, electrolyte samples were taken before and after ASTs to quantify catalyst dissolution.

From Figure 1B, linear sweep voltammetry measurements revealed that the mixed metal oxides all demonstrated enhanced mass OER activity compared to the monometallic Co3O4. From chronoamperometry measurements at 1.8 V vs. RHE in 0.1 M HClO4 , the mixed metal oxide catalysts lasted over 20 hours before reaching approx. 10% of the initial activity. Stability testing in a membrane electrode assembly (750 mA cm–2 hold, Nafion 212) demonstrated over 500 hours of operation at approx. 2.6 V. Operando X-ray photoelectron spectroscopy (XPS) and near edge X-ray adsorption fine structure (NEXAFS) experiments, along with in-situ inductively coupled plasma mass spectrometry (ICP-MS) measurements, are planned to complement the pre- and post-AST ex-situ catalyst characterization. Although these materials have yet to reach the activity and stability of iridium oxide, they nonetheless provide insights on a promising family of iridium-free catalysts and their development.

Acknowledgements

This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. (DGE-1839285). Any opinion, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Figure 1
Graphene Oxide-Driven Morphological Evolution of MOF: Unleashing High Activity of Derived Co@N-Doped Carbon Electrocatalyst for Water Splitting
Authors: Gayathri Sampath , Arun Kumar Paulraj , Han Jong Hun
Published: December 2024

Developing efficient metal-supported carbon-based electrocatalysts for hydrogen evolution reaction (HER) requires tailored design of metal-organic framework (MOF) precursors. This study explores the unconventional role of graphene oxide (GO) in shaping Co-based leaf-like zeolitic imidazolate framework (ZIF-Co-L) crystals. GO was found to modulate water accessibility in the ZIF reaction medium, directing a transformation in crystal shape from leaf-shape to elongated hexagons. The morphological evolution of MOF was triggered by the presence of hydrophilic GO, which disrupted the hydrogen-bonding interactions among monodentate methylimidazole (mIm) linkers induced by inadequate water. he shape-varied MOF-derived Co-NC@10rGO-(leaf) and Co-NC@40rGO-(hexagon) electrocatalysts exhibit varying HER activity driven by crystal shape and reduced GO (rGO) content. The Co-NC@10rGO-leaf exhibited superior HER activity outperforming Co-NC@40rGO-Hex in alkaline electrolyte with an overpotential of 220 mV at 10 mA cm‒2. The excellent performance of Co-NC@rGO catalysts was attributed to unique shape features, ideal rGO content, abundant active sites, and synergistic effect of metallic Co and N-doped carbon. This shape-varied MOF-derived material approach holds great promise for developing efficient electrocatalysts for hydrogen evolution.

Figure 1
Regulation of the Oxygen Evolution Mechanism in RuO2 By Controlling the Doping Level
Authors: Jun Hyunwoo , Lee Jinwoo
Published: December 2024

Numerous studies focus on replacing IrO2 with RuO2 in the acidic oxygen evolution reaction (OER). Many previous reports conduct doping RuO2 with various heteroatoms to enhance activity and overcome poor stability. However, understanding the impact of doping levels on the OER mechanism remains insufficient. Herein, we observed that increasing manganese doping in RuO2 steadily enhances activity, but excessive doping reduces stability. X-ray absorption spectroscopy confirms electron migration from Mn and Ru atoms to bridging oxygen atoms, thereby increasing Ru-O bond covalency. Theoretical calculations suggest that as Ru-O bond covalency increases, the probability of the lattice oxygen mechanism (LOM) at Ru active sites rises, enhancing activity but diminishing stability. Consequently, doping Mn shifts the OER mechanism from the adsorbate evolution mechanism (AEM) to LOM.
Highly Active Ni Incorporated Co2p Heterostructure As Efficient Hydrogen Evolution Reaction Electrode for Alkaline Water Electrolysis
Authors: Sim Junseok , Kim Wan Sik , Tamboli Asiya M. , IM Sejin , Jung Younghan , OH JunSeok , Kim Chang-Hee
Published: December 2024

The development of efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) is essential for alkaline water electrolysis. Cobalt phosphide (Co2P) is a promising non-noble electrocatalyst material for HER due to its low cost and high stability in alkaline medium. Nevertheless, the HER activity of Co2P needs to be further improved as compared to noble metal based electrocatalysts. In this study, we have incorporated nickel (Ni) into Co2P using a co-sputtering system for enhanced HER performance, considering the junction of Ni/Co2P heterostructure. This junction serves as dual sites for water dissociation at Ni and hydrogen adsorption/desorption at Co2P, which synergistically enhances the HER activity. We also noticed that Ni concentration influences the heterojunction area as highly active site. Too low or high Ni concentration diminishes active sites by few Ni site formation or Ni agglomeration, respectively. Therefore, precise control over the Ni concentration is essential for maximizing the active site. Our optimized Ni incorporated Co2P sample showed outstanding HER performance with low overpotential of ~77 mV at 10 mA/cm2 and Tafel slope of ~47 mV/dec. The findings of this study will provide insight into the relationship between heterojunction formation and HER performance in transition metal-based heterostructure materials.
Cu-Fe Electrocatalysts for Electrochemcial Urea Production from Carbon Dioxide and Nitrate Under Ambient Conditions
Authors: Choi Jinuk , An Tae-Yong , Lim Hyojung , Jo Chanmin , Jeon Minseo , Sim Uk
Published: December 2024

The size of the urea market is more than $131.54 billion in 2023 and continues to grow. However, the production of urea highly relies on traditional Bosch-Meiser process, which utilizes CO2 and NH3 under harsh conditions, contributing to over 1% of the energy consumption of the world. To solve this issue, electrochemical urea production has gained attention for its cost-effective and eco-friendly properties. The electrochemical urea synthesis from nitrate (NO3
-) and CO2 necessitates improvements in both the NO3
- reduction reaction and the CO2 reduction reaction. In this study, CuFe nanoparticles (NPs) are used as catalyst for electrochemical urea production. Cu and Fe, two earth-abundant metals (EAMs), have good activities for the CO2RR and NO3RR, respectively. Also, the work function difference between Cu (4.7 eV) and Fe (4.5 eV) causes the charge transfer from Fe to Cu. This creates a positive charge state in Fe (δ+) and a negative charge state in Cu (δ-), allowing NO3
- and CO2 to easily adsorb onto the Fe surface and the Cu surface, respectively. We present CuFe NPs catalyst for the electrochemical urea production from NO3
- and CO2. Our results show that CuFe NPs exhibit excellent electrochemical urea production (568 µg h-1 cm-2) and faraday efficiency (56 %). It is expected that this research contributes to the efficient urea production under ambient conditions.
Bubble Dynamics at Single-Phase Nickel Nitride and Sulfide for Hydrogen Evolution Reaction
Authors: Tyagi Chinkit , Fabre Bruno , Lagrost Corinne , Tessier Franck , Jullien Marie-Caroline , Bouquet Valérie
Published: December 2024

Hydrogen (H2) is considered a clean and sustainable alternative energy carrier to fossil fuels for meeting future energy demands.1 Electrocatalytic water splitting is a promising approach to producing eco-friendly H2 involving a hydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode.2 However, during these electrochemical gas evolution reactions, gas bubbles evolving at the surface of the electrocatalyst may result in undesired blockage of active sites and can influence the performance of the electrocatalytic process.3

In this study, we optimized the direct growth of single-phase nickel sulfide and nitride (Ni3S2@NF and Ni3N@NF) on metallic nickel foil (NF) and investigated the influence of surface hydrophilicity or hydrophobicity on electrochemical HER through in situ hydrogen bubble dynamics. Contact angle measurements revealed that metallic NF, Ni3S2@NF, and Ni3N@NF electrodes followed a trend of decreasing contact angle in an alkaline solution, indicating that Ni3N@NF exhibited the highest hydrophilicity/aerophobicity.4

In situ bubble visualization demonstrated that hydrophilic/aerophobic Ni3N@NF led to smaller and faster bubble departure, offering more active sites and a lower overpotential. Conversely, decreasing hydrophilicity or aerophobicity resulted in larger bubbles and longer retention times, leading to the unwanted blockage of the active sites and requiring high overpotential for HER. This highlights the significant impact of surface-wetting properties and hydrophilicity on electron and mass transfer during hydrogen generation, particularly at higher current densities.

References

Lewis, N. S.; Nocera, D. G. Natl. Acad. Sci. U. S. A. 2006, 103, 15729.

Turner, J. A. Science 2004, 305, 972.

Angulo, A.; van der Linde, P.; Gardeniers, H.; Modestino, M.; Fernández Rivas, D. Joule 2020, 4, 555.

Tyagi, C.; Fabre, B.; Jullien, M.-C.; Bouquet, V.; Tessier, F. submitted.

Figure 1
Reproducibility in Electrocatalysis
Authors: Hausmann Jan Niklas , Menezes Prashanth W.
Published: December 2024

A bright future for electrochemistry is anticipated due to its crucial role in the decarbonization of our industry and energy economy. In this regard, the number of electrochemists, their publications, the taxpayers' funding, and the number of applied materials has grown substantially in the last decade. This growth in interest has also led to an increase in the complexity of the reported systems, e.g., heterostructures with multiple interfaces.[1] However, studies attempting to reproduce known literature procedures often find different values for activity metrics, such as overpotentials, capacities, or long-term stabilities.[2] Furthermore, in my personal experience, I have not met an electrochemist who would be surprised when a student reports that he could not reproduce the outstanding performance of a recent report. Non-reproducibility is a substantial problem and threatens the foundation of science.[3]

We have performed a study among more than ten different groups across the globe. In this study, three electrode fabrication procedures (electrodeposition, precipitation followed by Nafion-binder-based powder deposition, hydrothermal modification of a metal foam) have been performed three times by all these groups using the same chemicals. A strict and uniform test protocol is applied to obtain activity metrics (overpotential, Tafel slope, charge transfer resistance...) of these electrodes for the electrocatalytic oxygen evolution reaction. Based on this tremendous set of data (>100 electrodes tested under the same conditions), we discuss the following questions:

How reproducible are our current electrochemical methods?

Which factors influence reproducibility?

How can we improve reproducibility?

Literature:

[1] Hausmann, J. N. & Menezes, P. W. A rising mismatch between system complexity, characterization, and theory in electrocatalysis: challenges and solutions. Appl. Catal. B Environ.
2024, 342, 123447.

[2] Peugeot, A. et al. Benchmarking of oxygen evolution catalysts on porous nickel supports. Joule
2021, 5, 1281–1300.

[3] Munafò, M. R. et al. A manifesto for reproducible science. Nat. Hum. Behav.
2017, 1, 0021.
Oxygen Evolution Catalysts with Iridium Oxide Supported on Doped Titanium Oxide: Role of Dopants on Catalysts Reactivity and Stability
Authors: Cazzulani Elena , Atanassov Plamen , Roiron Camille , Cristiani Pierangela , Chiarello Gian Luca , Zargarian Shabnam
Published: December 2024

Titanium dioxide (TiO2) is a semiconductor that has been extensively studied for its thermo and photo catalytic properties due to its high stability, abundant oxygen vacancies and low price. In electrochemistry, titanium dioxide has been used as support for anode catalysts in Proton Exchange Membrane Water Electrolysis (PEMWE). The electrolysis of water into oxygen and hydrogen is kinetically limited by the Oxygen Evolution Reaction (OER) occurring at the positive electrode with a four-electron transfer. The noble metal oxides of Ruthenium and Iridium are currently considered the best electrocatalysts for OER due to their high activity and relatively high IrO2 stability [1]. The high price and scarcity of these precious catalysts prompt a strong interest in minimizing their loading [2]. The use of an electronically conductive support allows to decrease the loading by increasing the surface to volume ratio of precious metal particles. Titania is highly stable at the high potentials used during the OER and can be made conductive using some transition metals as dopants [3].

TiO2 exists in nature in three crystalline forms: rutile, anatase, and brookite but because iridium oxide is used for OER in its rutile phase, and to promote epitaxial growth, this work uses the doped-TiO2 rutile phase as a support for Iridium oxide catalysts.

New synthetic routes based on sol-gel process are used to form (Ru, Nb, Ta)-TiO2 nanoparticles. The size, shape and crystalline structure of the support was controlled by tuning calcination temperature and the Ti precursor. The doped rutile TiO2 particles synthesized consist of an ideal support for iridium oxide nanoparticles deposited by wet impregnation in different loading and phase. The epitaxial growth from rutile TiO2 to rutile IrOx promotes the catalyst support interaction and electrical conductivity.

All the catalysts were characterized by their physico-chemical and electrochemical properties towards the oxygen evolution reaction. The surface morphology and crystallinity of these materials was evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The activity toward oxygen evolution reaction was investigated in liquid electrolyte in a 3-electrode set-up.

[1] Alia, S. M.; Rasimick, B.; Ngo, C.; Neyerlin, K. C.; Kocha, S. S.; Pylypenko, S.; Xu, H.; Pivovar, B. S. Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction. J. Electrochem. Soc 163, 596-603 (2016)

[2] Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D. A comprehensive review on PEM water electrolysis. Int. J. Hydrogen Energy 38, 4901– 4934 (2013)

[3] Bauerfeind, K.C.L.; Laun, J., Frisch, M.; et al. Metal Substitution in Rutile TiO2: Segregation Energy and Conductivity.
J. Electron. Mater. 51, 609–620 (2022)
What's the Status Quo of Performance and Durability for Low-Iridium Loadings with Commercial Catalysts in PEM Water Electrolysis?
Authors: Utsch Nikolai , Scheepers Fabian , Aymé-Perrot David , Dubouis Nicolas , Betremieux Isabelle , Müller Martin Johannes , Peters Ralf
Published: December 2024

Iridium scarcity and the associated challenges for the large-scale deployment of PEM water electrolyzer technology have been addressed in several studies. To meet the targets, several studies have shown that the iridium specific power density needs to be optimized to < 0.10 mgIr W-1.1,2 However, the current state of the art is fuzzy and it's unclear how far we need to go to achieve large-scale deployment of the PEM water electrolyzer. Therefore, we have analyzed four different commercially available catalysts to determine where the current limitations are in realizing large-scale deployment of PEM water electrolysis. Using a common N115 Nafion membrane, we compared the performance for loadings ranging from 0.1 mgIr cm-2 to 0.8 mgIr cm-2 using one catalyst from Alfa Aesar and Umicore together with two catalysts from Heraeus. Sheet resistance was investigated for all loadings and catalysts and correlated with corresponding high frequency resistance and performance. Durability was evaluated using a bottom-up approach, starting with the lowest loading and a total test time of 500 h. With the data presented, we shed light on the current state of the art for low iridium loading in PEM water electrolysis.

Literature

Minke, C., Suermann, M., Bensmann, B. & Hanke-Rauschenbach, R. Is iridium demand a potential bottleneck in the realization of large-scale PEM water electrolysis? Int. J. Hydrog. Energy
46, 23581–23590 (2021).

Clapp, M., Zalitis, C. M. & Ryan, M. Perspectives on current and future iridium demand and iridium oxide catalysts for PEM water electrolysis. Catal. Today
420, 114140 (2023).
Shape-Controlled Iridium Catalysts for OER in PEM Electrolysis
Authors: Xu Heng , Wang Xiaojing , Spendelow Jacob S.
Published: December 2024

Hydrogen is a clean energy carrier that holds the potential to power future transportation.1 One way to generate green hydrogen is proton exchange membrane (PEM) electrolysis with renewable electricity, but this process is limited by the sluggish oxygen evolution reaction (OER).2, 3 Iridium (Ir) catalysts have balanced activity and durability for OER.4, 5 However, due to the scarcity and high cost, the structures of the Ir catalysts must be properly controlled to improve the catalyst performance and reduce Ir loading.6, 7 Currently, most Ir catalysts are nanoparticles without well-defined crystal facets, and it remains largely unknown what Ir surface structure is the most effective for OER.4 Here, we present the facet-selective growth of Ir catalysts by using various shape-controlled seeds. These shape-controlled Ir catalysts exhibit high Ir atom usage efficiency due to the formation of only a few atomic layers of Ir shells. The activity and durability of these shape-controlled Ir catalysts towards OER are evaluated by rotating disk electrode measurements and tested in a PEM electrolyzer. This work demonstrates the possibility to further improve Ir catalyst performance by precise control over the arrangements of catalyst surface atoms.

Acknowledgments

We acknowledge the funding support from the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL) (20240061DR) and the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE).

References

(1) Debe, M. K. Electrocatalyst approaches and challenges for automotive fuel cells. Nature
2012, 486, 43-51.

(2) Wang, Y.; Pang, Y.; Xu, H.; Martinez, A.; Chen, K. S. PEM Fuel cell and electrolysis cell technologies and hydrogen infrastructure development – a review. Energy Environ. Sci.
2022, 15, 2288-2328.

(3) An, L.; Wei, C.; Lu, M.; Liu, H.; Chen, Y.; Scherer, G. G.; Fisher, A. C.; Xi, P.; Xu, Z. J.; Yan, C.-H. Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment. Adv. Mater.
2021, 33, 2006328.

(4) Wang, S.; Shen, T.; Yang, C.; Luo, G.; Wang, D. Engineering Iridium-Based Oxygen Evolution Reaction Electrocatalysts for Proton Exchange Membrane Water Electrolyzers. ACS Catal.
2023, 13, 8670-8691.

(5) Gao, J.; Liu, Y.; Liu, B.; Huang, K.-W. Progress of Heterogeneous Iridium-Based Water Oxidation Catalysts. ACS Nano
2022, 16, 17761-17777.

(6) Alia, S. M.; Pylypenko, S.; Neyerlin, K. C.; Kocha, S. S.; Pivovar, B. S. Activity and durability of iridium nanoparticles in the oxygen evolution reaction. ECS Trans.
2015, 69, 883-892.

(7) Alia, S. M.; Shulda, S.; Ngo, C.; Pylypenko, S.; Pivovar, B. S. Iridium-Based Nanowires as Highly Active, Oxygen Evolution Reaction Electrocatalysts. ACS Catal.
2018, 8, 2111-2120.
Unveiling and Mitigating the Instability of Noble Metal-Free Oxide Electrode for PEM Water Electrolysis
Authors: Wang Jian
Published: December 2024

Developing many sustainable energy technologies (e.g., H2O and CO2 splitting) warrants accelerating the sluggish oxygen evolution reaction (OER) efficiently and economically. However, designing noble-metal-free electrocatalysts (NMFEs) to replace noble-metal-based OER electrocatalysts is tremendously challenging in acidic electrolytes where chemical corrosion is conventionally regarded as a bottleneck factor. So far, few NMFEs reported can be an alternative to Ru-/Ir-based catalysts for acidic OER. Differernt from conventional wisdom, through monitoring the dynamics of the catalytic process during water electrolysis, we unambiguously demonstrated that electrochemical reconstruction instead of chemical corrosion dominantly degraded the OER performance of typical Mn and Co oxides as resentative NMFEs. Based on the uncovered degradation mechanism, we further developed a novel and rational method to overcome the problem of activity-stability trade-off faced by various OER electrocatalysts. Correlative operando characterizations found that our modulation method successfully suppressed the undesired surface reconstructions by mitigating the cationic/anionic redox and catalyst leaching, and meanwhile atomistic calculations revealed that the synergy of dual sites generated more favorable catalytically-active species. The resultant noble-metal-free oxide yielded a record performance among reported NMFEs, and its superior performance was also validated by the PEM water electrolyzer. This work will provide a critical reference for designing NMFEs for PEM water electrolysis.

Reference:

1. Jian WANG*, Controlling dynamic reconstruction chemistry for superior oxygen-evolving catalysts, Chem, 2023, 9 (7), 1645-1657.

2. Jian Wang,* Ying Wang, Junsik Cho, Ting-Shan Chan, Yang Ha, Shu-Chih Haw, Cheng-Wei Kao,Yunze Zhang, Jiayi Tang,Jia Lei,Tong Liu,Siyuan Zhao, Yawen Dai, Aleksandra Baron-Wiechec, Fu-Rong Chen, Wenxiong Wang, Chang Hyuck Choi, Zongping Shao, Meng Ni, Under revision. 2024.
Unraveling the Harmonious Coexistence of Ruthenium States on a Self-Standing Electrode for Enhanced Hydrogen Evolution Reaction
Authors: Ma Joonhee , Kim Soo Young
Published: December 2024

The development of cost-effective, highly efficient, and durable electrocatalysts has been a paramount pursuit for advancing the hydrogen evolution reaction (HER). Herein, a simplified synthesis protocol was designed to achieve a self-standing electrode, composed of activated carbon paper embedded with Ru single-atom catalysts and Ru nanoclusters (ACP/RuSAC+C) via acid activation, immersion, and high-temperature pyrolysis. Ab initio molecular dynamics (AIMD) calculations are employed to gain a more profound understanding of the impact of acid activation on carbon paper. Furthermore, the coexistence states of the Ru atoms are confirmed via aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). Experimental measurements and theoretical calculations reveal that introducing a Ru single atom site adjacent to the Ru nanoclusters induces a synergistic effect, tuning the electronic structure and thereby significantly enhancing their catalytic performance. Notably, the ACP/RuSAC+C exhibits a remarkable turnover frequency (TOF) of 18 s-1 and an exceptional mass activity (MA) of 2.2 A mg-1, surpassing the performance of conventional Pt electrode. The self-standing electrode, featuring harmoniously coexisting Ru states, stands out as a prospective choice for advancing HER catalysts, enhancing energy efficiency, productivity, and selectivity.

Figure 1
Tuning the Hydrophilicity of Polymers for Ion-Solvating Membranes for Alkaline Electrolysis
Authors: Jensen Jens Oluf , Serhiichuk Dmytro , Rajappan Sinu Charamchirail , Xia Yifan , Kraglund Mikkel Rykær , Aili David
Published: December 2024

Ion-solvating membranes constitute an alternative to both porous diaphragms and anion-exchange membranes for alkaline electrolysis. [1,2] The underlying principle is to imbibe a nonporous hydrophilic membrane with concentrated aqueous KOH and thus obtain high ionic conductivity from the sorbed electrolyte. It is well-established that high ionic conductivity can be reached, [3] and the main challenge is to identify or develop polymers with the right affinity for aqueous KOH and with long-term stability in the aggressive environment. Polymers known for their alkaline stability are generally hydrophobic and will not take up KOH. One strategy to promote and control the KOH uptake is to tune the polymer hydrophilicity to the extent that enough KOH is sorbed without dissolving the polymer. [4]

The paper presents recent progress with hydrophilicity adjustment of polymers by hydrophilic functionalities. Hydrophilic tetrazole moieties are particularly stable in the alkaline environment due to deprotonation at high pH and the resulting formation of a negative charge that repels the aggressive hydroxide ions. See Figure 1. It is easy to adhere to the backbone by a click reaction. Chemical stability screening, electrolyte uptake, ion conductivity, and initial electrolyzer tests are presented.

-

References

[1] D. Aili, M. R. Kraglund, S. C. Rajappan, D. Serhiichuk, Y. Xia, V. Deimede, J. Kallitsis, C. Bae, P. Jannasch, D. Henkensmeier and J. O. Jensen. Electrode Separators for the Next-Generation Alkaline Water Electrolyzers. ACS Energy Lett. 8 1900-1910 (2023). DOI: 10.1021/acsenergylett.3c00185

[2] D. Henkensmeier, W. Cho, P. Jannasch, J. Stojadinovic, Q. Li, D. Aili and J. O. Jensen. Separators and membranes for advanced alkaline water electrolysis. In press, Chemical Reviews. DOI: 10.1021/acs.chemrev.3c00694

[3] M. R. Kraglund, M. Carmo, G. Schiller, S. A. Ansar, D. Aili, E. Christensen and J. O. Jensen. Ion-solvating membranes as a new approach towards high rate alkaline electrolyzers. Energy Environ.
Sci. 12, 3313 – 3318 (2019). DOI: 10.1039/c9ee00832b

[4] D. Serhiichuk, S. Rajappan, Y. Krishnan, Y. Xia, M. R. Kraglund, H. A. Hansen, J. O. Jensen and D. Aili. Tetrazole functionalization: A new strategy toward stable ion-solvating polymer electrolytes for alkaline water electrolysis. Submitted. DOI: 10.26434/chemrxiv-2024-29p7m

-

Figure 1. Tetrazole functionalization of poly(styrene-co-acrylonitrile) (SAN) followed by formation of the corresponding potassium tetrazolide. [4]

Figure 1
Investigating Ionomer Interactions on the Catalytic Interface of Model Catalysts (NiO, IrO2)
Authors: Ha Mai-Anh , Leitner Oliver , Isakov Avital , Larsen Ross E , Volk Emily K. , González Héctor , Alia Shaun M
Published: December 2024

Anion exchange membrane electrolysis enables the use of earth abundant metals for the catalyst and other components of the membrane electrode assembly. However, earth abundant metal catalysts may be sensitive to poisoning and degradation due to the extreme pH of the electrolyte or interactions with the ionomer. Plane-wave density functional theory calculations probed the binding strength of different functional groups from popular ionomers (Nafion, Sustainion, tetramethylammonium-based ETFE/Gen 2/Georgia Tech, Versogen) on model catalysts such as Platinum Group Metal IrO2 and earth abundant NiO.1 We evaluated the stability of these various ionomers on these model catalysts, whether they remain intact or degrade, as well as their catalytic effects on the oxygen evolution reaction (OER) e.g. in the presence of OH*. These calculations allowed us to understand the poisoning of active sites: 1) if the functional group bound more strongly than key reaction intermediates, then the ionomer effectively blocked activity by displacing the reaction intermediate; 2) if the functional group introduced competing reactions, then the ionomer was consuming the OxHy* intermediates necessary for OER. Ideally, ionomers remain stable in contact with the catalyst and shuttle hydroxide ions from the cathode to the anode.

1. S. Ghoshal, B. S. Pivovar and S. M. Alia, J. Power Sources, 2021, 488, 229433.

Figure 1
Designing Regio-Chemistry Controlled Ionomers for Enhanced Durability in Anion Exchange Membrane Water Electrolysis with a Focus on High Adhesion and Catalyst Anti-Poisoning
Authors: Park Hyeonjung , Kim Youngkwon , Doo Gisu , Lee CHangsoo , Lee Sechan , Seo Jongsu , Lee Jae Hun , Choi Young-Woo , Kim Sang-Kyung , Cho Hyunseok , Kim MinJoong
Published: December 2024

Anion exchange membrane water electrolysis (AEMWE) holds significant promise for cost-effective and stable hydrogen production when coupled with renewable energy sources. While extensive efforts have been dedicated to enhancing durability and performance in AEMWE systems, relatively few studies have focused on the binders compared to other critical components (such as catalysts, membranes, and cells). In this work, we present a novel approach to address this gap by developing a highly conductive and durable binder specifically tailored for high-performance AEMWE. Our strategy involves a series of regio-chemistry controlled cation polymers denoted as PAP-RR-X, where X represents the degree of regio-irregularity in the polymer backbone (ranging from 0% to 100%). By tuning the ratio of regio-irregular benzyl-type monomers within the entire PAP-RR-X polymer backbone, we achieve remarkable ion-conductivity and strong binding interactions with the catalyst. The steric hindrance introduced by the regio-irregular monomers not only enhances ion-conductivity through a flexible backbone chain but also contributes to exceptional durability by effectively preventing hydroxide ion attack. As a result, the AEMWE system incorporating PAP-RR-X demonstrates both outstanding hydrogen efficiency and long-term durability. Furthermore, we elucidate the intricate interactions between the binder, catalyst, and membrane using X-ray scattering methods, providing valuable guidelines for designing high-performance and robust binders tailored specifically for AEMWE applications.
Poly(2,6-dimethyl-1,4-phenylene oxide)-Based Anion Exchange Membranes Enhanced with 3D-Ionic Triptycene Additive for Water Electrolysis
Authors: Lee Jae Hun , An Seong jin , Chi Won Seok , Kim Ji Eun , Park Hyeonjung , Kim Sang-Kyung
Published: December 2024

In water electrolysis systems, anion exchange membranes (AEMs) play a crucial role in separating the hydrogen and oxygen gases produced, while selectively transporting hydroxide ions between the cathode and anode. Key characteristics of AEMs include high hydroxide ion conductivity and durable stability under challenging alkaline conditions. We introduce a novel approach aimed at overcoming the hurdles related to achieving high ion conductivity and alkaline stability in AEMs. We propose a simple method that incorporates a 3D ionic triptycene additives in a quaternized poly(phenylene oxide) (PPO) polymer matrix to form a blended anion exchange membrane. Triptycene, known for its bulky and rigid molecular structure formed by three interconnected benzene rings, has traditionally posed challenges in polymer chain packing due to its high free volume. Despite its potential, controlling its polymerization degree and enhancing mechanical properties has been difficult due to its complex three-dimensional structure. In this study, we introduced triptycene molecule as ionic additives to polymer matrix without polymerization process. The triptycene was chloromethylated to obtain the triptycene-Cl additive and PT-x blended membranes were quaternized by immersion in TMA solution, which led to a high quaternary ammonium group. The addition of triptycene provided extra quaternary ammonium groups and increased free volume, enhancing hydroxide ion transport efficiency and dimensional stability, despite increased water uptake. Moreover, the inclusion of the 3D ionic triptycene additive contributed to additional free volume within the packing structure of the polymer chains. These properties facilitate efficient transport of hydroxide ions. As the loading of 3D ionic triptycene increased, the QPQT-x blended membranes demonstrated improvements in experimental IEC value, in-plane hydroxide ion conductivity, and water uptake, while suppressing the swelling ratio. The QPQT-20 membrane exhibited satisfactory mechanical stability and high in-plane hydroxide ion conductivity, making it suitable for water electrolyzer cell tests. Compared to a commercial FAA-3-50 membrane, the QPQT-20 membrane exhibited lower and more stable area specific resistance. The BPPO/3D ionic triptycene blended membrane, dual-quaternized and containing 20% 3D ionic triptycene, demonstrates notably superior water electrolyzer cell performance (0.87 A/ cm2 at 2.0 V), in comparison to the commercial FAA-3-50 membrane (0.54 A/cm2 at 2.0 V).
Molecular Engineering of Ion-Conducting Polymer Membranes: Synthesis, Properties, and Applications
Authors: Bae Chulsung
Published: December 2024

Ion-conducting polymers (e.g., proton and hydroxide) are used as polymer electrolyte membranes, and they are a key component of electrochemical energy conversion and storage technologies such as fuel cells, electrolyzers, and flow batteries. For example, hydrogen fuel cell and water electrolyzer industry also heavily relies on Nafion for a proton-conducting membrane for decades, though it is not ideal proton-conducting membrane material for those applications.

Perfluoroalkyl substrates (PFASs), which include Nafion, have recently received significant pressure from government and environmental activist groups due to their environmental and health hazard of PFAS. Thus, the development of alternative ion-conducting polymers based on hydrocarbon polymers (mostly made of C and H) has attracted new attention within polymer society. Compared to perfluorosulfonated Nafion, hydrocarbon ion-conducting polymers can offer advantages of flexible synthetic tunability, lower gas permeability, and importantly lower production cost. However, their systematic polymer chemistry–morphology structure–property relationships are poorly understood until now.

In this presentation, we describe an overview of recent progress in the development of advanced ion-conducting (H+ and OH–) polymers, key membrane properties, and their state-of-the-art performance in in real world applications of hydrogen fuel cells and water electrolyzers.[1,2]

References

[1] S. Adhikari, M. K. Pagels, J. Y. Jeon, C. Bae* “Ionomers for Electrochemical Energy Conversion & Storage Technologies”, Polymer (Perspective Special Issue celebrating the 100 years "From ‘Makromolekel' to POLYMER”), Polymer, 2020, 211, 123080.

[2] S. Noh, J. Y. Jeon, S. Adhikari, Y. S. Kim, C. Bae* “Molecular Engineering of Hydroxide Ion Conducting Anion Exchange Polymers for Electrochemical Energy Conversion Technology” Acc. Chem. Res.
2019, 52, 2745–2755.
Elucidating Hydroxide Transport through Utilization of Asymmetric Feed System: Advancing Towards Pure Water and Vapor Anion-Exchange-Membrane Electrolysis
Authors: Metem Prattakorn , Petrovick John G. , Eriksson Björn , Lindbergh Göran
Published: December 2024

Anion-exchange-membrane water electrolysis (AEMWE) is a nascent green hydrogen production technology. Its main advantage lies in its ability to utilize non-platinum group metals (PGMs) as catalysts and PFSA-free polymer as a membrane, unlike proton-exchange-membrane water electrolysis (PEMWE). It is well-known that, unlike PEMWE, AEMWE suffers greatly from substituting the electrolytic feed solution with a solution of a lower pH (e.g., pure water). Literature has attributed the loss of performance to the lower reaction kinetics of both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and the drastic loss of electrolyte conductivity, which is further exacerbated at higher current density [1]. Notably, it is shown that addition of salt to improve the conductivity of electrolyte does not always equate to a better performance over time, depending on the feed configuration, highlighting the importance of understanding mass transport during cell operation [2]. Therefore, to decouple the causes of the drastic losses of performance in-situ, we have developed a system capable of feeding vapor and liquid into AEMWE asymmetrically. The cell is constructed using a membrane electrode assembly (MEA) fabricated by the catalyst coated membrane (CCM) method, where platinum on carbon (Pt/C) and iridium oxide (IrOx) are coated directly on PiperION® anion exchange membranes. Moreover, we have studied hydroxide crossover both statically using an h-cell test and dynamically in an AEMWE cell. We have shown that, by utilizing various combinations of feeds, including humidified gas, pure water, or KOH, through both cathode and anode, it is possible to study cell performance and hydroxide transport under different conditions. Through which, we have elucidated the performance loss, the importance of hydroxide transport, and a strategy to overcome such losses, thus showing the possibility of advancing toward pure water and low-temperature vapor electrolysis.

[1] Liu, Jiangjin, et al. "Elucidating the role of hydroxide electrolyte on anion-exchange-membrane water electrolyzer performance." Journal of the electrochemical society 168.5 (2021): 054522.

[2] Rossi, Ruggero, Rachel Taylor, and Bruce E. Logan. "Increasing the electrolyte salinity to improve the performance of anion exchange membrane water electrolyzers." ACS Sustainable Chemistry & Engineering 11.23 (2023): 8573-8579.

Figure 1. Schematic of the developed feeding system capable of feeding water vapor and liquid into the electrolyzer.

Figure 1
Divergent Synthesis of Bipolar Membranes Combining Strong Interfacial Adhesion and High-Rate Capability
Authors: Kao Yi-Lin , Chen Lihaokun , Boettcher Shannon , Aili David
Published: December 2024

The use of bipolar membranes has the potential to broaden the scope of active and stable electrode materials in water and CO2 electrolyzers, and to mitigate challenges related crossover. 1,2 However, the high resistance of commercial bipolar membrane materials under reversed bias and their tendency to delaminate currently limit their practical use in these technologies. This contribution presents a new design strategy of bipolar membranes, where the individual anion- and cation exchange layers are derived from the same backbone chemistry to govern interfacial compatibility. This is achieved through divergent functionalization of a styrene-ethylene-butylene copolymer, through installation of sulfonic acid moieties or quaternary ammonium groups. When combined with earth abundant and active water dissociation catalysts, such as TiO2 or SnO2, the bipolar membrane system shows an order of magnitude higher adhesion force (50 N/m) than bipolar membranes derived from Nafion and PiperION. The polarization behavior under reversed bias is investigated in H-cell tests, and further evaluated in water electrolysis experiments. The dependencies on ion exchange capacity and the water dissociation catalyst loading at the interfacial junction are investigated. While benefiting on high adhesion strength fluorine-free chemistry, the optimized membrane supports current densities up to 500 mA/cm2 at 2.5 V in pure water electrolysis mode when combined with a Pt/C cathode and a noble-metal-free Co3O4 anode.

1 Blommaert, M. A.; Aili, D.; Tufa, R. A.; Li, Q.; Smith, W. A.; Vermaas, D. A. Insights and Challenges for Applying Bipolar Membranes in Advanced Electrochemical Energy Systems. ACS Energy Lett
2021, 2539–2548.

2 Tufa, R. A.; Blommaert, M. A.; Chanda, D.; Li, Q.; Vermaas, D. A.; Aili, D. Bipolar Membrane and Interface Materials for Electrochemical Energy Systems. ACS Appl Energy Mater
2021, 4 (8), 7419–7439.

Figure 1
Quasi-Static Force Testing of 4680 Cylindrical Batteries: Implications for Structural Integration in Next-Generation EV Energy Storage Systems
Authors: Ghandily Nima , Klohs Domenic , Kisseler Niklas , Frieges Moritz , Kampker Achim , Heimes Heiner Hans
Published: December 2024

With increasing demands for higher ranges, lower costs, and higher charging performance in electric vehicles (EVs), innovative approaches for the structural integration of batteries are being implemented. This study investigates the response of 4680 cylindrical batteries, featuring nickel manganese cobalt oxide (NMC811) as the cathode active material, to quasi-static force application. The focus is on the implications for structural integration into next-generation EV battery systems. By subjecting the batteries to controlled quasi-static forces, the mechanical robustness and safety characteristics within these integrated systems are assessed. The methodology involves comprehensive testing protocols, including mechanical characterization, capacity analyses before and after deformation, thermal analysis, and the use of design of experiments (DOE) to systematically explore the influence of various mechanical failure scenarios on the cell’s behavior. Additionally, post-mortem analysis was conducted to check the cells for dissolved active material and assess any structural changes to the electrode composition. The findings from this study provide valuable insights for the development of new cell-to-chassis and cell-to-pack approaches to optimize the mechanical integration efficiency and thereby improving the energy density of next-generation EV battery system designs.
Electrochemical Activity of Oxygen in Li-Ion Battery Cathodes from X-Ray Spectroscopic Modeling
Authors: Lomeli Eder , Hsu Sean , Kas Josh Jason , Vinson John , Rehr John , Moritz Brian , Yang Wanli , Devereaux Thomas P.
Published: December 2024

As demand for better performance in energy storage increases, a clear understanding of the charge compensating mechanism in Li-ion battery cathodes is essential for developing next generation battery chemistries and materials. X-ray core level spectroscopies, e.g. x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS), allow for experimental measurement of the electronic structure of battery materials before and after charge, providing the clearest physical picture of electrochemical device operation.

Here, we present numerical modeling of the XAS/RIXS of various battery chemistries compared to experimental measurements in situ. Modeling spectroscopic changes before and after discharge using not only density functional theory (DFT) based techniques but also exact diagonalization atomic multiplet formalisms prove crucial in these materials to accurately model correlation effects seen in their spectra, where reversible changes in the transition metal L3-edge spectroscopy may erroneously point to cationic redox. We address the common concept of transition metal redox, highlight the essential role of oxygen in both reversible and irreversible processes, and the break down in the standard paradigm of cationic/anionic redox.
(Invited) Predictive-Design to Predictive Synthesis of Advanced Sodium Layered Oxide Cathodes By in Situ Synchrotron X-Ray Characterization
Authors: Xu Guiliang
Published: December 2024

The emerging demand for low-cost batteries for electric vehicles and grid-scale energy storage application calls for urgent development of sustainable batteries such as sodium-ion batteries. Layered transition metal oxides are promising cathode materials due to their high specific capacity.However, these cathodes undergo irreversible structural evolution and gradual capacity loss during repeated cycling.Different from the extensive research on the characterization of structural degradation during charge/discharge, understanding on the sophisticated solid-state synthesis of sodium layered oxide cathodes remain elusive. In this talk, we will first introduce an invention of tri-phase intergrowth layered cathode materials that exhibits improved electrochemical and thermal stability through in situ synchrotron X-ray diffraction (SXRD) during solid-state process. We will then present the effect of quenching on the microstrain evolution and structural defect formation, as well as the consequent electrochemical cycling. We will conclude with a recent study on investigating the solid-state synthesis of concentration gradient cathode through combination of in situ SXRD and full-filed Transmission X-ray microscopy (TXM). These results provide valuable guidance on the development of advanced cathode materials from predictive design to predictive synthesis.