bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanocone-Modified Surface Facilitates Gas Bubble Detachment for High-Rate Alkaline Water Splitting
Authors: Ren Qiu , Feng Longsheng , Ye Congwang , Xue Xinzhe , Lin Dun , Eisenberg Sam , Kou Tianyi , Duoss Eric B , Zhu Cheng , Li Yat
Published: August 2024

Alkaline water splitting (AWS) is one of the most attractive technologies for green hydrogen production. In comparison to the acidic proton exchange membrane (PEM), AWS offers greater flexibility in using non-platinum group metal catalysts and could generate higher-purity hydrogen. However, commercial AWS systems are normally operated at a lower current density (~400 mA cm-2) than PEM electrolyzers. To rapidly generate hydrogen at an industrial scale, it is critical to boost the operating current density of AWS to a level of ~1000 mA cm-2. Nevertheless, the significant amount of gas bubbles generated during high-rate AWS could be detrimental to the process. Bubbles can block the catalysts’ active site, hinder electrolyte diffusion, and increase Ohmic resistance, thus deteriorating the reaction rate and restricting the cell voltage efficiency. The detachment of gas bubbles may also damage the catalyst layer. In this study, we demonstrate a general strategy for facilitating bubble detachment by modifying the nickel electrode surface with nickel nanocone nanostructures, which turns the surface into underwater superaerophobic. The simulation and experimental data show that bubbles take a considerably shorter time to detach from the nanocone-modified nickel foil than the unmodified foil. As a result, these bubbles also have a smaller detachment size and less chance for bubble coalescence. The nanocone-modified electrodes, including nickel foil, nickel foam, and 3D-printed nickel lattice, all show substantially reduced overpotentials at 1000 mA cm-2 compared to their pristine counterpart. The electrolyzer assembled with two nanocone-modified nickel lattice electrodes retains >95% of the performance after testing at ~900 mA cm-2 for 100 hours and the surface NC structure is also well preserved, demonstrating its excellent electrochemical and mechanical stability at high current density. Our findings offer an exciting and simple strategy for enhancing the bubble detachment and, thus, the electrode activity for high-rate AWS.
Role of Electrochemical Activation in Evaluating Oxygen Evolution Activity of Ni-Incorporated Bimetallic Tungstate in Alkaline Media
Authors: Karmakar Ayon , Chuang Po-Ya Abel
Published: August 2024

Hydrogen is considered the future fuel and promising alternative towards carbon neutrality. In this context, water electrolysis using renewable electricity is an environmentally benign approach for clean hydrogen production. In water electrolysis, among the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), OER is the rate-limiting due to slow kinetics, high overpotential, and complex pathways. To catalyze the OER, choice of non-precious electrocatalysts is preferred over the precious platinum group metal (PGM)-based catalysts owing to their relatively higher abundance and cost-effectiveness. The feasibility of using non-precious electrocatalysts in alkaline water electrolysis is also favorable for the low-capital cost compared to the acidic one. In lab scale research, the preliminary evaluation of OER electrocatalysts is usually performed using thin-film rotating disk electrodes (TF-RDEs) in a three-electrode system. In this process, the very first step involves multiple cyclic voltammetry (CV) cycles for better wettability of the catalyst layer to the electrolyte, which is considered as electrochemical activation (EA). Incomplete activation of the catalyst layer would lead to inconsistent OER performance of the electrocatalysts. This is much more pronounced in non-precious electrocatalysts compared to the precious ones in alkaline media. Despite that the importance of EA is overlooked most of the time and rarely studied. In this work, the critical role of EA is systematically investigated for Ni-containing bimetallic tungstate in alkaline OER and also compared with that of monometallic counterparts. This study demonstrates more than 1.2-fold performance improvement in OER for bimetallic tungstate. The corresponding insights on the interfacial structure and oxidative surface reconstruction are also noted by using in-situ electrochemical analysis and ex-situ characterizations. The present study is believed to be beneficial for the precise analysis and development of non-precious alkaline OER electrocatalysts.
Elucidating Fundamental Structure-Function Relationships for Iridium Oxide Catalysts in PEM Water Electrolyzers
Authors: Wang Cliffton , Roiron Camille , Cheng Lei , Braaten Jonathan , Atanassov Plamen , Morimoto Yu , Zenyuk Iryna
Published: August 2024

Proton exchange membrane water electrolysis (PEMWE) will contribute substantially towards decarbonization efforts and is expected to make up 40% of the green hydrogen market.1 A primary barrier for PEMWE scale-up is the detrimentally high usage of iridium for the oxygen evolution reaction catalyst. To achieve large-scale PEMWE deployment, loading reductions from 2-3 mgIr cm-2 to 0.10 mgIr cm-2 must occur.2 Such a feat can only be achieved through significant improvements in activity and durability. However, there exists a lack of fundamental understanding in how catalyst properties correlate to performance, thus hindering optimization efforts. The phenomena of catalyst activity/durability are frequently treated with purely empirical approaches, and thus the foundational knowledge needed for improved catalyst design—such as understanding how crystallinity and oxidation states impact performance in a membrane electrode assembly (MEA)—has not been well investigated.3 This work serves to bridge this gap in knowledge by correlating extensive structural characterization data with MEA activity and durability for six commercial IrOx catalysts. Properties such as oxidation states, chemical composition, local atomic/electronic configuration, crystallinity, surface area, and particle size distribution were elucidated for each catalyst in powder and/or MEA form. Following MEA conditioning, catalyst activity was benchmarked via polarization curves and Tafel analysis. Lastly, durability was evaluated by performing a 500h accelerated stress test (adapted from the H2New consortium), with electrochemical characterization conducted every 100h. The presence of amorphous character and the Ir3+ oxidation state was the best determinant of activity. Durability, on the other hand, was associated with greater crystalline character and more redox-stable cyclic voltammogram profiles. Correlations regarding chemical composition, local atomic/electronic configurations, particle size, and surface area will be discussed as well.

Smolinka, T.; Wiebe, N.; Sterchele, P.; Palzer, A.; Lehner, F.; Jansen, M.; Kiemel, S.; Miehe, R.; Wahren, S.; Zimmermann, F. Studie IndWEDe: Industrialisierung Der Wasserelektrolyse in Deutschland: Chancen Und Herausforderungen Für Nachhaltigen Wasserstoff Für Verkehr, Strom Und Wärme.; 2018.

Clapp, M.; Zalitis, C. M.; Ryan, M. Perspectives on Current and Future Iridium Demand and Iridium Oxide Catalysts for PEM Water Electrolysis. Catal Today
2023, 420 (March), 114140. https://doi.org/10.1016/j.cattod.2023.114140.

Lazaridis, T.; Stühmeier, B. M.; Gasteiger, H. A.; El-Sayed, H. A. Capabilities and Limitations of Rotating Disk Electrodes versus Membrane Electrode Assemblies in the Investigation of Electrocatalysts. Nat Catal
2022, 5 (5), 363–373. https://doi.org/10.1038/s41929-022-00776-5.
Overcoming Challenges in Ion-Pair Membrane Technology: Advancements in Fuel Cells and Electrochemical Hydrogen Pumps
Authors: Chhetri Manjeet , Lim Katie , Kim Youngkwang , Maurya Sandip , Park Hyounmyung , De Castro Emory S. , Kim Yu Seung
Published: August 2024

The Membrane Electrode Assembly (MEA) stands as the pivotal element in electrochemical devices such as fuel cells and electrochemical hydrogen pumps (EHP). Notably, ion-pair High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFCs) with reduced phosphoric acid concentrations within the MEA have been innovatively designed, allowing for the integration of diverse ion-conducting binders, known as ionomers, into both the cathode and anode electrodes [1]. This study delineates initial distinctions in MEA configurations among different device types (HT-Fuel cell and EHP), conducting a comprehensive analysis of performance disparities between traditional polybenzimidazole-based systems and various ion-pair proton exchange membranes [2].

Subsequently, a detailed exploration unfolds, focusing on the utilization of ion-pair membranes and different ionomer types for the three aforementioned devices. This comprehensive examination offers a unified comparative analysis encompassing ionomer type, membrane thickness, catalyst:ionomer ratio, and phosphoric acid doping levels, particularly in the context of performance at intermediate temperatures (160℃). Conclusions are drawn based on results derived from both half-cell and single-cell evaluations. Finally, overarching guidelines are presented to inform the formulation of high-performance MEA configurations tailored for ion-pair HT-PEMFCs and EHPs.

References:

[1] Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S. Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells, Nature Energy, 7, 248 (2022).

[2] Lim, K, H; Matanovic, I; Maurya, S; Kim Y; De Castro E. S; Jang, J-H; Park, H; Kim, Y.S. High Temperature Polymer Electrolyte Membrane Fuel Cells with High Phosphoric Acid Retention. ACS Energy Lett., 8, 1, 529–536 (2023).
(Invited) Ionomer-Free Porous-Transport Electrode Design for Proton-Exchange-Membrane Water Electrolysis
Authors: Lee Jason Keonhag , Anderson Grace , Mukundan Rangachary , Weber Adam Z. , Peng Xiong
Published: August 2024

Clean hydrogen, which is set to reduce the carbon footprint for hard-to-decarbonize sectors, relies on large-scale deployment of water-electrolysis technologies, particularly proton-exchange-membrane water electrolyzers (PEMWEs). However, as iridium-based electrocatalysts remain the only option for PEMWEs, its low abundance is likely to become the bottleneck for a sustainable hydrogen economy. Therefore, developing PEMWEs at low iridium loading is an urgent task. Herein, we propose a high-performing and durable ionomer-free porous transport electrode (Ir PTE) that is fabricated using a facile physical vapor deposition method. This fabrication method creates a thin layer of nanosized iridium catalyst that is well attached to the porous transport layer surface. The proposed Ir PTE at ~ 0.1 mgIr/cm2 demonstrates voltage reduction of > 600 mV compared to the traditionally coated PTE at 1.8 A/cm2, and cell voltage degradation of only 29 mV at average rate of 0.58 mV/1000-cycles after 50k cycles of accelerated-stress tests at 4 A/cm2.1 By further designing nano-channel features of the ionomer-free PTE, we demonstrate expedited localized transport features that allow durable operation of PEMWE for over 2000h with degradation rate of 11.7 µV h-1. Moreover, the ionomer-free feature of Ir PTE enables facile recycling of multiple components of PEMWEs, which is critical to enable circular clean hydrogen economy.

Reference:

Lee, J. K. et al. Ionomer-free and recyclable porous-transport electrode for high-performing proton-exchange-membrane water electrolysis. Nat. Commun.
14, 1–11 (2023).
Application of Hipims Coatings to Enhance the Durability and Performance of Structural Components of PEM Electrolyzer Anodes
Authors: Santiago Varela Jose Antonio Antonio , Fernandez Ivan , Diaz Rodriguez Pablo , Wennberg Ambiorn , Panizo Miguel
Published: August 2024

Porous transport layers (PTL) and bipolar plates (BPP) are structural elements that transport water, gases, electrons as well as heat within the electrolysis cells. On the anode side, the state-of-the-art material for BPP and PTL is titanium due its higher corrosion resistance under the operating conditions of electrolysis (high electrochemical potential, acidic and oxidizing environment) compared to other materials [1]. However, titanium components tend to form an oxide layer that rises the interfacial contact resistance (ICR) and leads to a poor performance since metal oxides are semiconductors or insulators. This issue is usually addressed by applying precious metal coatings, such as platinum or gold. In this work, we present the potential of high power sputtering techniques (HiPIMS) to manufacture ultra-low loading Pt coatings (<20 nm) with good homogeneity and high performance at an industrial scale. The influence of HiPIMS parameters on coating-substrate interface, as well as the coating properties have been evaluated. SEM, AFM and HRTEM microscopy have been used to evaluate the coating thickness and morphology. XRD analysis has been carried out to evaluate the influence of the HiPIMS parameters on the growth mode of Pt coatings, tailoring the coating texture from [200] to [111]. HiPIMS technique also provide enhanced density compared with other coating techniques due to the higher ionization achieved in the plasma [2]. The deposition of denser and defect-free coatings by HiPIMS enables the application of stainless steel components. HiPIMS prevents the formation of columnar structures and reduces oxygen diffusion. In this work, Nb- and Ti-based protective coatings have been deposited by HiPIMS on stainless steel 316L. A comparative between coated Ti Gr2 and SS316L has been set, showing the potential to reduce costs in the next generation of PEMWE structural components.

References:

[1] P. Shirvanian and F. van Berkel, Electrochemistry Communications 114 (2020) 106704

[2] K. Sarakinos et al., Surface & Coatings Technology 204 (2010) 1661–1684
Optimization of Transport Components and Electrode Interfaces for Low Iridium Oxide Loading PEM Electrolysis
Authors: Lang Jack Todd , Fortiner Serafina , Ouimet Ryan J. , Kulkarni Devashish , Glenn Jennifer , Capuano Christopher B. , Erb Bryan , Smeltz Andrew , Zenyuk Iryna
Published: August 2024

Moving towards lower iridium oxide (IrOx) catalyst loadings for the anode side of polymer electrolyte membrane water electrolyzers (PEMWE) requires tuning of the catalyst layer-porous transport layer (PTL) interface. To see widespread deployment, PEMWE anodes need to lower the loadings from 1-2 mg/cm2 IrOx down to 0.1 mg/cm2 [1]. The catalyst layer can become less uniform and more disconnected at these lower loadings, so the addition and optimization of a microporous layer (MPL) onto the PTL to improve interfacial contact and in-plane connectivity is essential to move toward the more sustainable lower loadings [2]. First, a set of PTLs with MPLs are made such that morphological properties are varied between them. Then, the PTLs with MPLs are combined with anode catalyst layers with IrOx loadings of 0.7, 0.5, 0.3, and 0.1 mg/cm2 to create cells to record polarization curves, stability tests, and catalyst degradation rates. The morphology of the PTLs and MPLs is quantified using X-ray computed tomography (CT). The important morphological characteristics that can be varied and measured with X-ray CT include porosity, pore size distribution, tortuosity, and thickness for each the MPL and base PTL. Using operando X-ray CT and radiography, oxygen transport through the PTL and channel can be observed to provide further information to the performance of the novel PTLs and MPLs. By using a two-dimensional continuum PEMWE model, insights into the effects on the cell performance and the contact resistance present at the MPL-catalyst layer brought about from PTL and MPL morphology alterations can be extracted to help guide the optimization efforts. Through combining these results, an optimal set of manufacturing/morphological parameters can be found to tune PTL and MPL production for the low-loaded catalyst layers that are needed for the future of PEMWEs.

References:

[1] M. Clapp, C. M. Zalitis, and M. Ryan, “Perspectives on current and future iridium demand and iridium oxide catalysts for PEM water electrolysis,” Catalysis Today, vol. 420, p. 114140, 2023. doi:10.1016/j.cattod.2023.114140

[2] M. Bernt, A. Siebel, and H. A. Gasteiger, “Analysis of voltage losses in PEM water electrolyzers with low platinum group metal loadings,” Journal of The Electrochemical Society, vol. 165, no. 5, 2018. doi:10.1149/2.0641805jes
Oxygen-Deficient Thermal Treatment Boosts Performance of Co-Ni-Fe Oxide Electrocatalyst in Oxygen Evolution Reaction
Authors: Pham Trang Minh , Hnat Jaromir , Surkus Annette-Enrica , Francke Robert
Published: August 2024

The production of green hydrogen through water electrolysis using electricity generated from renewable sources is one of the most promising strategies toward achieving a carbon-neutral economy.[1-3] Water electrolysis is an effective and well-established water splitting process consisting of two half-cell reactions, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at cathode and anode, respectively. Although hydrogen as the value-added product is generated at the cathode, the anodic reaction plays an important role in determining the reaction kinetics of the entire water splitting process due to the multiple-electron transfer.[4] Therefore, developing low-cost and highly active OER electrocatalysts is one of the keys to further improve overall efficiency of water electrolysis. Among various water electrolysis technologies, alkaline water electrolysis (AWE) has been commercialized for many decades and standing for medium-scale hydrogen production and using non-noble metals as electrocatalysts.[5]

Co-, Ni-, and Fe- oxides or (oxy)hydroxides are reported as auspicious OER electrocatalysts for AWE, as well as abundance on earth.[6] In addition, oxygen vacancies in metallic oxides are reported recently as an effective approach to enhance catalyst activity for OER.[7] Herein, we present trimetallic oxides (CoNiFe oxides) annealed in different atmospheres which are oxygen-rich (A; air), an oxygen-poor (M; 1 vol% air in argon), and oxygen-free (H; 5 vol% H2 in argon), respectively, The CoNiFe (2:2:1)/M with a molar ratio of Co : Ni : Fe = 2 : 2 : 1 treated under an oxygen-poor atmosphere (M) exhibits the best performance in 1 M KOH, with an overpotential of 291 mV at 10 mA cm-2
geo, a mass activity at 1.56 V versus the reversible hydrogen electrode (RHE) of ~345 A g-1
catalyst, and a small Tafel slope of 32.0 mV dec-1. Moreover, CoNiFe (2:2:1)/M shows excellent stability in the OER process for at least 50 hours at 100 mA cm-2
geo at lab scale and ~75 h at 400 mA cm-2 in an alkaline electrolyzer. This work presents a simple and effective method to design OER catalysts based on trimetallic oxides with oxygen deficiencies for alkaline water electrolysis.

References:

[1] T. Yusaf, M. Laimon, W. Alrefae, K. Kadirgama, D. Ramasamy, M. Kamal and B. Yousif, Appl. Sci., 2022, 12, 17.

[2] M. Neuwirth, T. Fleiter, P. Manz and R. Hofmann, Energy Convers. Manag., 2022, 252, 115052.

[3] H. L. S. Shiva Kumar, Energy Rep., 2022, 8, 21.

[4] Q. Liang, G. Brocks and A. Bieberle-Hütter, JPhys Energy, 2021, 3, 026001.

[5] Y. D. Zi-You Yu, Xing-Yu Feng, Xingxing Yu, Min-Rui Gao and Shu-Hong Yu, Adv. Mater., 2021, 33.

[6] M. Yu, E. Budiyanto and H. Tüysüz, Angew. Chem. Int. Ed., 2022, 61, e202103824.

[7] K. Zhu, F. Shi, X. Zhu and W. Yang, Nano Energy, 2020, 73, 104761.
Research and Development Needs to Enable Renewable-Powered Liquid Alkaline Electrolyzers
Authors: Lindquist Grace
Published: August 2024

Low temperature electrolysis (LTE) is the most promising method for fully renewable hydrogen production. However, to compete with current hydrogen production methods (which produce CO2), substantial cost reductions and efficiency improvements are necessary. Of the various LTE technologies, liquid alkaline (LA) electrolysis is the most mature. It has proven large scalability and can operate with all earth-abundant materials. However, most conventional LA electrolyzers are limited to lower current density operation than newer LTE technologies.

Most LA electrolyzers operate with uncatalyzed Ni anodes, despite the existence of many highly active catalysts for oxygen evolution in alkaline conditions. This is because catalyzed systems require constant operation, as the catalyst layers degrade and delaminate rapidly upon exposure to the reverse polarization conditions experienced during system shutdown. This limitation prevents the integration of catalyzed electrodes, as even a single unexpected plant shutdown causes significant efficiency and cost losses. Further, this prevents fully catalyzed LA electrolyzers from directly operating with renewable power sources with large power fluctuations. Therefore, the development of reverse-current tolerant catalyst layers is essential to enable high-efficiency renewable energy powered LA electrolyzers.

This talk will detail the mechanisms of electrode degradation during electrolyzer system shutdown. Our findings reveal anode catalyst layers fail through a combined electrochemical and mechanical degradation mechanism. I will discuss key differences in the cathode versus anode operating environments that explain the difference in reverse current tolerance. Considering these results, I will highlight priority research and development directions for developing anode and cathode catalysts for renewable-powered LA electrolyzers.
Limiting Current Density in Water Vapor-Fed Polymer Electrolyte Membrane Electrolyzers
Authors: Ebbert Mary , Litster Shawn
Published: August 2024

Polymer electrolyte membrane water electrolyzers (PEMWE) are a critical technology in development for addressing the need for efficient hydrogen production. In order to make hydrogen a cost-effective fuel or industrial feedstock, the overpotentials across the cell needs to be decreased and platinum-group metal loading reduced. Devising novel electrode structures that enable ultra-high current densities at low oxygen evolution reaction (OER) catalyst (e.g. Iridium oxide) loadings is one approach to achieving efficiency and cost targets. One of the overpotentials that needs to be addressed is due to mass transport limitations within the porous transport layer (PTL) and anode catalyst layer, which could be a limiting factor at ultra-high current densities. When operating at ultra-high current densities, the rate of the OER may reach a point at which oxygen gas bubbles fill the pores of the anode catalyst layer PTL, blocking access of liquid water to the anode catalyst layer. Because of this, there is a possibility that the cell will rely on water vapor diffusion through the evolving oxygen gas to deliver the water reactant to the OER catalyst. To assess the limitation of a PEMWE while relying on water vapor diffusion, a commercially manufactured membrane electrode assembly (MEA) was tested by flowing water vapor into the anode as the reactant. With the aim of identifying a limiting current density (LCD) of the electrolyzer under these conditions, potentiostatic polarization curves were obtained for a range of relative humidities (RH) and back pressures. The RH was varied to assess the impact of reactant concentration on the LCD, while the back pressure was varied to identify the impact of the molecular gas diffusion coefficient on the LCD. In this presentation, we will present our analysis of the significance of the water vapor diffusion transport resistance through the pressure-dependent resistance evaluation. Furthermore, we will discuss application of this approach to evaluating the impact of vapor operation on membrane water transport and OER reaction kinetics.
Electrolyte-Induced Fe-Doping of LaNiO3 Model Surfaces for Water Electrolysis
Authors: Le Phu Tran Phong , Sturm Jacobus Marko , Koster Gertjan , Bieberle-Hütter Anja , Baeumer Christoph
Published: August 2024

Renewable energy needs to be store in different energy forms for the energy transition away from fossil fuels. One of most promising forms is chemicals such as H2 and C-based fuels obtained via electrochemical reactions. The common hinderance in such reactions is the sluggish oxygen evolution reaction (OER), which causes low energy efficiency in conversion devices. Developing highly active, earth-abundant OER electrocatalysts in alkaline media is necessary to boost the performance of such devices. Fe ion content in electrolyte is known to influence the OER-activity of metal oxide electrocatalysts. For example, the Fe incorporation in NiOOH is a well-established and important effect for OER.[1] Here, we present the effect of absorbed Fe on the OER activity of the epitaxial Ni-surface terminated LaNiO3 thin films. The correlation between surface species and OER activity of electrocatalysts was investigated using surface-sensitive low-energy ion scattering and X-ray photoemission spectroscopies. We observe more than an order-of-magnitude boost in OER activity during initial cycling, from 0.15 mAcm-2 to 3.40 mAcm-2 at 1.60 V vs. reversible hydrogen electrode. The activity increase was mainly caused by the incorporation of up to 5 % Fe at the top surface of LaNiO3 film (less than ~1 nm) even though only a very trace amount of Fe ion, 30 ppb, is present in the 0.1 M electrolyte of high purity KOH 99.99 %. Our results demonstrate that the disordered active surface phase, which develops even on single crystalline surfaces, is a complex interplay between the as-prepared (surface) crystalline structure, composition of the solid electrocatalyst and the liquid electrolyte, and has strong impact on the final OER activity, implying that we need to think differently about the crystalline electrocatalysts: crystalline bulk and dynamically changing surface layer.

[1] L. Trotochaud, S.L. Young, J.K. Ranney, S.W. Boettcher, Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation, J. Am. Chem. Soc. 136 (2014) 6744–6753.
Zero-Gap Liquid Alkaline Water Electrolyzers: Challenges in Benchmarking and Directions for Development
Authors: Leonard Daniel , Maurya Sandip , Chavez Luis A , Ybarra Rigobert
Published: August 2024

Green hydrogen is expected to play a central role in the replacement of fossil energy sources, especially in difficult to decarbonize sectors of the economy. Currently, low temperature methods of electrolysis are the only commercially realized sources of green hydrogen. Liquid alkaline water electrolysis (LAWE) is the most widely utilized method of electrolysis, with a 100-year history of use. Given this lengthy history one could be forgiven for assuming that there is little development left. However, standard LAWE materials and cell designs do not achieve the production, efficiencies, and durability necessary to meet the anticipated demand for green hydrogen.

To spur development in this neglected area of hydrogen production, the US Department of Energy, Hydrogen and Fuel Cell Technology Office (DOE-HFTO) added LAWE to its Hydrogen from Next-generation Electrolyzers of Water (H2NEW) Consortium. One of the main tasks for this part of the consortium is to benchmark and validate materials and cell components for LAWE. This includes the development of lab-scale cell hardware and test protocols that can be widely disseminated in the research community. The result of this work will be the development of the methods and materials necessary to achieve robust and reproducible datasets for the improvement of catalysts, separators, cell architecture and operation.

We will present the status of the benchmarking effort. This will include a description and explanation of a lab-scale LAWE test station, electrolyte handling, and hydrogen safety. The requirements for the safe operation of an electolyzer using high concentration alkaline electrolytes differs significantly from more typical proton exchange, or anion exchange membrane systems. We will also discuss common sources of error that can significantly influence cell performance and result in poor reproducibility.

Acknowledgement:

This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office through the Hydrogen from Next-generation Electrolyzers of Water (H2NEW) consortium.
The Experimental Determination of the HOR/HER Activity on Platinum and the pH-, Cation-, and Other Effects (Part 2)
Authors: Brandes Benedikt Axel , Chatzichristodoulou Christodoulos
Published: August 2024

Due to frequent inconsistencies in determining the HOR/HER activity on Pt(pc) we present one of the most extensive datasets on this reaction, ranging over the entire pH scale, various cations and anions, and concentrations, using the common RDE method. Here we explain why the Koutecký-Levich equation must not be used to determine the exchange current density in the micropolarization region, and that pH-buffers may be avoided.

We clarify the anticipated pH dependency on account of the reaction mechanism, how this is influenced by mass transport limitations in most of the pH range, discuss the origin of activity reduction at high pH values, and provide new insights into the H-upd regions.

Figure 1
(Invited) Efficient P-Doping Via Suppressing Bad P−Sn Interaction
Authors: Jang Ji-Hyun
Published: August 2024

The utilization of non-metallic phosphorus (P) doping is recognized for its advantages in enhancing the conductivity of hematite while minimizing recombination. This is attributed to the suppression of electron trapping facilitated by the favorable electron state of P5+. However, our investigation reveals a significant impact on the overall photoelectrochemical (PEC) performance of P-doped Fe2O3 due to tin (Sn) diffusion from the bottom FTO substrate. Upon identifying the unfavorable interaction between the unintentional dopant Sn4+ and intentional dopant P5+, we have developed a straightforward P-doping method. The resulting P:Sn:Ti-Fe2O3 (P:Sn:Ti triple-doped Fe2O3) exhibits a remarkable improvement in photocurrent density, reaching 3.44 mA cm−2 at 1.23 VRHE, surpassing values reported in previous P-doping hematite studies. Following co-catalyst deposition, the NiFeOx/P:Sn:Ti-Fe2O3 photoanode achieves a maximum photocurrent density of 4.30 mA cm−2 at 1.23 VRHE. This study affirms that suppressing the negative interaction between dopants is crucial for significantly enhancing PEC performance.
Mitigating Side Reactions in Electrocatalytic Ammonia Synthesis by Nitrate Reduction
Authors: Zhao Zhenhuan , Wu Nianqiang
Published: August 2024

Electrocatalytic nitrate reduction holds significant promise for generating green ammonia and mitigating pollution, reducing energy input, and exhibiting zero-carbon emissions. However, the intricate multiple electron and proton transfer processes complicate the pathways from nitrate to ammonia, hindering the development of electrocatalysts with high activity and selectivity for practical use. The primary side reactions, such as the conversion of nitrate to gaseous nitrogen species and the hydrogen reduction reaction, limit the Faradaic efficiency of nitrate-to-ammonia conversion. In this work, we have developed a controllable methodology for preparing highly active Cu-based nanocatalysts. These nanocatalysts exhibit remarkable activity and selectivity in the electrochemical nitrate reduction reaction within a flow-cell device, with a high ammonia yield and high Faradaic efficiency.
(Invited) In Situ Study of Catalyst Structural Evolution during CO2 Electroreduction by Development of Electrochemical Liquid Cell TEM
Authors: Zheng Haimei
Published: August 2024

The electrocatalytic CO2 reduction reaction (CO2RR) has attracted significant interest of study in the exploration of sustainable energy and environment. Cu-based materials have demonstrated the capability of converting CO2 to multi-carbon products with high catalytic activity and low cost. Since the performance of heterogenous catalysts is highly susceptible to the catalyst structural changes, unveiling the structure and catalytic active sites during reactions is crucial to the understanding of catalytic mechanisms. Although lots of efforts have been made, it remains a challenge to directly image the atomic structure of a working catalyst in liquid electrolytes due to technical difficulties. Here, I will show our development of in-situ electrochemical liquid cell transmission electron microscopy (TEM) for the study of Cu catalysts during electrocatalytic CO2RR. The novel electrochemical liquid cell allows unprecedented atomic imaging of the catalyst evolution during electrochemical reactions. Our observations reveal that the Cu catalyst-electrolyte interaction under an applied potential (-1.1 v) leads to structural changes of Cu catalyst surfaces. Intermediate structure dynamics have been captured. The propagations and transformations of intermediates result in atomically rough Cu crystal surfaces. The intermediates are further found mediating the mass loss of Cu. Control experiments demonstrate the intermediates can be utilized for enhanced carbon-carbon coupling and the formation of two carbon products. Insights gained from this study are not only valuable to designing novel catalysts, but also useful for understanding of electrified solid-liquid interfaces in general.
(Invited) Photocatalytic H2 Evolution Activity of Anisotropic-Shaped ZnSe-AgInSe2 Solid Solution Quantum Dots with a Near-IR-Responsivity
Authors: Torimoto Tsukasa , Masuoka Ko , Akiyoshi Kazutaka , Uematsu Taro , Kuwabata Susumu , Kameyama Tatsuya
Published: August 2024

Semiconductor nanocrystals, often referred to as quantum dots (QDs), exhibit unique physicochemical properties due to the quantum size effect when their size is less than 10 nm. In our previous works, we successfully synthesized Zn-Ag-In-S (ZAIS) solid solution QDs with a tunable energy gap (Eg) and then reported the photocatalytic activity for H2 evolution depending on their morphology and particle composition [1,2]. However, ZAIS QDs have limited light absorption with wavelengths less than ca. 600 nm, restricting their utilization of near-infrared light in solar light. In this study, we report the preparation of near-IR-responsive QD photocatalysts with use of Zn-Ag-In-Se (ZAISe) solid solution semiconductors. Precise controls over their morphology and particle composition enabled to vary their photocatalytic H2 evolution activity.

ZAISe QDs with different compositions and particle shapes (sphere or rod) were synthesized by thermal decomposition of corresponding metal acetates and selenourea in a mixture solution of oleylamine and dodecane thiol at 250 oC. The chemical composition of QDs was controlled by varying the Zn fraction in metal precursors, ensuring nearly stoichiometric composition.

The obtained QDs with a rod shape had lengths varying from ca. 10 to 100 nm, correlating with an increase in the Zn fraction. The onset wavelengths of absorption spectra of the ZAISe QDs were red-shifted from 500 nm to 900 nm with decreasing Zn fraction, indicating that the Eg of ZAISe QDs was controlled between visible and near-infrared wavelength regions.

The QDs modified with dodecane thiol showed poor dispersibility in water and almost no photocatalytic activity for H2 evolution. In contrast, the surface modification of QDs with 3-mercaptopropionic acid enabled to uniformly disperse in an aqueous solution. The photocatalytic activity of ZAISe QDs was investigated for H2 evolution as a model reaction. The irradiation to ZAISe QDs in an aqueous solution containing Na2S and Na2SO3 as hole scavengers was carried out using Xe lamp light (λ> 350 nm). The H2 evolution rate exhibited a remarkable dependence on both the composition and particle shape of ZAISe QDs. The photocatalytic activity showed a tendency to increase with the enlargement of the Eg of QDs, probably due to the negative shift of conduction band minimum potential. The optimum H2 evolution activity was obtained with rod-shaped QDs having the Eg of 1.65 eV, being twice as large as that of spherical QDs with a similar Eg. This behavior can be attributed to the change of the crystal facets exposed on the QD surface.

References

Kameyama, T. Takahashi, T. Machida, Y. Kamiya, T. Yamamoto, S. Kuwabata, and T. Torimoto, J. Phys. Chem. C, 2015, 119, 24740-24749.

Torimoto, Y. Kamiya, T. Kameyama, H. Nishi, T. Uematsu, S. Kuwabata, and T. Shibayama, ACS Appl. Mater. Interfaces
2016
, 8, 27151-27161.
(Invited) Designing Plasmonic Photocatalysts
Authors: Cortes Emiliano
Published: August 2024

Nanostructured surfaces and colloids with designed optical functionalities - such as plasmonic and photonic nano and metamaterials - allow efficient harvesting of light at the nanoscale. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale [1-4]. One example are plasmonic and photonic catalysts, that can indeed confine solar energy into molecular regions [4-11].

In this talk, I will present our recent efforts in order to understand the intricate realm of losses in plasmonic nanoparticles by studying this issue at the single-particle level. I will present a series of studies trying to correlate plasmonic photocatalytic activity with reactivity, temperature and field at the nanoscale. Our fundamental understanding of light-matter interaction in these systems can hopefully contribute to the rational design of future nanocatalysts; influencing diverse applications such as photocatalysis and temperature management, among others [1-11].

References

[1] E. Cortés, Nature 614, 230-232 (2023)

[2] E. Cortés, et al. Nature Rev. Chem., 6, 259–274 (2022)

[3] E. Cortés, et al. Chem. Rev. 122, 15082–76 (2022)

[4] S. Ezendam, et al. ACS Energy Letters, 7, 778-815 (2022)

[5] M. Herran, et al. Adv. Funct. Mat., 2203418 (2022)

[6] J. Gargiulo, et al. Nature Communications 14, 3813 (2023)

[7] L. Nan, et al. Nano Letters 23 (7), 2883–2889 (2023)

[8] A. Stefancu, et al. ACS Nano 17 (3), 3119–3127 (2023)

[9] L. Hüttenhofer, et al., Adv. Energy Mat., 46, 2102877 (2021)

[10] M. Herran, et al. Nature Catalysis, accepted (2023)

[11] S. Ezendam, et al. ACS Nano, accepted (2023)
(Invited) Photophysics and Photochemistry of Individual Plasmonic Nanostructures
Authors: Link Stephan
Published: August 2024

A surface plasmon in a metal nanoparticle is the coherent oscillation of the conduction band electrons leading to both absorption and scattering as well as strong local electromagnetic fields. These fundamental properties have been exploited in many different ways, including surface enhanced spectroscopy and sensing, photocatalysis, photothermal cancer therapy, and color display generation. Chemical synthesis and assembly of nanostructures are able to tailor plasmonic properties that are, however, typically broadened by ensemble averaging. Single particle spectroscopy together with correlated imaging is capable of removing heterogeneity in size, shape, and assembly geometry and furthermore allows one to separate absorption and scattering contributions. In this talk I will discuss our recent work on distinguishing the different contributions that cause plasmon decay as probed by the homogeneous single-particle linewidth.[1-4] In particular, I will focus on plasmon damping due to energy and charge transfer from the metal to its environment with the goal to mechanistically understand how energy conversion from an incident photon to a plasmon and then a localized excitation can be maximized while circumventing fast metal-intrinsic internal conversion that simply leads to heat generation.
(Invited) Sub-Particle-Resolution Microscopy Reveals Inter-Facet Junction Effects on Particulate Photoelectrodes
Authors: Chen Peng
Published: August 2024

This presentation will describe our recent work in using single-particle/single-molecule imaging approaches to study photoelectrocatalytic properties of particulate semiconductor photocatalysts, important for many solar energy conversion technologies. In anisotropically shaped photocatalyst particles, the different constituent facets differ in their electronic and thus photoelectrocatalytic properties, and between different facets they may form inter-facet junctions at their adjoining edges, analogous to lateral two-dimensional (2D) heterojunctions or pseudo-2D junctions made of few-layer 2D materials. Using subfacet-level multimodal functional imaging, we uncover inter-facet junction effects on anisotropically shaped bismuth vanadate (BiVO4) particles and identify the characteristics of near-edge transition zones on the particle surface, which underpin the whole-particle photoelectrochemistry. The imaging tools, the analytical framework and the inter-facet junction concept pave new avenues towards understanding, predicting and engineering (opto)electronic and photoelectrochemical properties of faceted semiconducting materials, with broad implications in energy science and semiconductor technology.
(Invited) Understanding Carrier-Selective Catalyst/Semiconductor Contacts in Water-Splitting Photoelectrodes and Photocatalyst Particles
Authors: Boettcher Shannon W. , Kaufman Aaron James
Published: August 2024

Heterogeneous electrochemical processes, including photoelectrochemical water splitting to evolve hydrogen and oxygen using electrocatalyst-coated semiconductors, are driven by the accumulation of charge carriers and thus the interfacial electrochemical potential gradients that promote charge transfer. Conventional electrochemical techniques measure/control potentials at the conductive substrate or semiconductor ohmic contact, but are unable to isolate processes and electrochemical potentials at the surface during operation. I will discuss how the nanoelectrode tip of an atomic-force-microscope cantilever can effectively sense the surface electrochemical potential of electrocatalysts coating semiconductor photoelectrodes during operation. This data can be combined with ex-situ electrical measurements, spectroscopy, and materials characterization approaches to provide a comprehensive physical picture of how excited electrons and holes can be effectively separated and catalyst/semiconductor contacts. This new understanding is particularly important for the design of photocatalyst particles where direct electrical measurements of catalyst/semiconductor interface properties is not possible. In these systems we are applying spectroscopic techniques, for example ambient pressure x-ray photoelectron spectroscopy and Stark-effect spectroscopy to understand electric and electrochemical potential distribution and how nanoscale, adaptive, heterogeneous contacts can be controlled to design higher performance photochemical systems.
Small Polaron Dynamics in Transition Metal Oxide Photoelectrodes
Authors: Zhang Jinzhong , Yang Ye
Published: August 2024

The transition metal oxides are widely used in many optoelectronic applications, such as working as charge-transporting layers in solar cells and photoelectrodes in light-driven water-splitting. Considering the ionic bonding nature, the lattice of these oxides can be polarized by the charge carriers due to the strong electron-phonon coupling, giving rise to lattice distortion that fosters a local potential well. This lattice distortion together with the trapped carrier is regarded as a quasi-particle, i.e., a polaron. Here, the photocarrier dynamics in transition metal oxides were investigated using the transient absorption and time-resolved terahertz spectroscopies. We identified the spectral features of small polarons, self-trapped excitons, and free carriers and extracted their dynamics independently. We proposed a molecular model that could successfully explain the non-barrier self-trapping and quantitatively describe the temperature-dependent recombination of self-trapped excitons and the dopant effect on the photocarrier dynamics. Our model also suggested that the recombination of self-trapped excitons at room temperature was dominated by nuclear quantum tunneling. This model also predicted the micro-heterogeneity of the self-trapped species, and thus be able to quantitatively describe the Auger annihilation dynamics of self-trapped excitons.
(Invited) In Situ x-Ray Spectroscopy for Energy Materials
Authors: Dong Chung-Li
Published: August 2024

In response to the worldwide surge in energy demand, the materials scientists devote themselves to the search for clean and sustainable energy. Without the development of cutting-edge renewable energy materials, going green has never been simple. The zero-emission future requires a multifaceted approach. Advanced functional materials for more effective energy conversion, storage, and conservation are the universal focus of energy research. Although the ideas for increasing the efficiency of current energy materials in terms of energy conversion, storage, or conservation are clear and straightforward, they are technically challenging. It is difficult to better engineer materials in an efficient manner for a practical use without knowing the fundamental atomic and electronic structures, particularly how they respond under operating conditions. Synchrotron x-ray spectroscopies, including x-ray absorption and emission spectroscopies are powerful tools to study the local unoccupied and occupied electronic states. In addition, employing the in situ technique permits us to monitor the atomic and electronic structure modulations of the energy material at work. An emerging x-ray spectro-microscopic technique, scanning transmission x-ray microscopy, which provides spatially resolved x-ray spectroscopy. The significance of utilizing x-ray spectroscopy for the atomic and electronic structure characterization of several significant energy material systems, such as advanced nanocatalysts, artificial photosynthesis materials, and smart materials, will be discussed in this presentation. Recent developments of in situ technique, a number of recent studies, and energy science-related Tamkang University (TKU) end-stations at the BL45A and BL27A of TPS will also be presented.
The Synthesis of Highly Durable Pt-Based Hollow Nanocatalysts for Oxygen Reduction Reaction
Authors: Chen Shutang
Published: August 2024

Platinum (Pt) catalysts have been considered as the most active electrocatalyst for the oxygen reduction reaction (ORR) in fuel cells. However, cost and durability of Pt catalysts are the biggest obstacles impeding their practical applications. In this talk, the combination of Pt ion-treatment and acid-treatment methods is developed to prepare Pt-based hollow nanocatalysts. Catalytic results indicated the ORR performance of our Pt-Ni nanocatalysts far exceed that of commercial Pt/C electrocatalysts, in terms of mass-specific activities it is up to a 19-fold increase than that of Pt/C and 6 times than that of Department of Energy requirement (0.44 A/mg Pt). The performance loss of Pt-Ni is negligible even after a prolonged durability test of 300,000 cycles. The in-situ spectroelectrochemical results and theoretical simulation further explain the catalytic mechanism and such excellent durability. We believe our method provides an effective strategy for the rational design of Pt-based alloy nanostructures and will help guide the future development of catalysts for their practical applications in energy conversion technologies.