bluuebunny/crossref_metadata_2025 huggingface dataset:
Bridging the Gap between Laboratory and Industrial Scale Electrochemical Characterisation of Raney Ni Electrodes for Alkaline Water Electrolysis
Authors: Prits Alise-Valentine , Maide Martin , Väli Ronald , Tammemägi Mona , Nguyen Huy Quí Vinh , Küngas Rainer , Nerut Jaak
Published: August 2024

The most mature water electrolysis technology is alkaline electrolysis, where an aqueous solution of KOH is used as the electrolyte. While this technology has been used for decades, there is still a lot of potential to improve the performance of these devices. Much research is focused on the optimisation of the electrodes containing novel catalyst materials that lower the activation energy barrier of the electrolysis process. However, one of the issues described by Ehlers et al.1 is that the current academic electrolysis research is done under conditions that are far from practical (e.g. at low current densities, room temperature, and dilute electrolytes).

In this study, we characterise a commercial Raney nickel electrode in various setups using a systematic series of experiments, including a typical laboratory-scale three-electrode setup, two different flow-cell setups and a 10-kW electrolysis stack of 17 cells. In addition to the cell geometry (electrode area ranging from 1 cm2 to 960 cm2), the varied measurement conditions include temperature (ranging from room temperature to 80 degrees Celsius), pressure (from atmospheric pressure to ), electrolyte concentration (from 0.1 M to 30 wt% KOH), and the level of Fe impurities in the electrolyte. The resulting electrochemical data received from different measurement setups and measurement conditions are compared, and insights about the challenges related to correlating laboratory experiments to industrial-scale experiments are provided.

Figure 1. Alkaline electrolysis measurement setups with the typical measurement conditions used to study Raney nickel electrodes within this work – a typical laboratory-scale three-electrode setup (a), two different flow-cell setups (b, c) and a 10-kW electrolysis stack of 17 cells (d).

Acknowledgements

This work was supported by the Applied Research Program of Enterprise Estonia ("Developing and Validating Alkaline Electrolysis Stack Technology with Nanoceramic Electrodes", RE.5.04.22-0109) and by the Estonian Research Council (EAG273 "Highly active electrodes for precious metal free alkaline electrolysers" (1.09.2023−31.08.2024)).

References

J. C. Ehlers, A. A. Feidenhans’l, K. T. Therkildsen, and G. O. Larrazábal, ACS Energy Lett., 8, 1502–1509 (2023).

Figure 1
Intrinsic Activity and Ni-O-Fe Catalytic Active Site in Ni-Based (Oxy)Hydroxides for the Oxygen Evolution Reaction
Authors: Dionigi Fabio , Zeng Zhenhua , Zhu Jing , Merzdorf Thomas , Choi Donggyu , Ligay Darya , Klingenhof Malte , Buchheister Paul Wolfgang , Li Wei-Xue , Greeley Jeffrey , Strasser Peter
Published: August 2024

NiFe layered double hydroxides (LDHs) and (oxy)hydroxides are among the most active electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes.1 However, they still show considerable overpotentials for the OER, i.e. 350 mV at 10 mA cm-2 in pH 13.1, 2 Understanding the nature of the catalytic active sites and the catalytic mechanism in NiFe LDHs are key challenges to develop better OER electrocatalysts.

In this contribution, atomic-scale details of the catalytic active phase will be presented, showing that NiFe LDHs are oxidized under applied anodic potentials from as-prepared α-phase to activated γ-phase.2 The OER active γ-phase was characterized by operando wide angle X-ray scattering (WAXS) in alkaline electrolytes.2 The intrinsic activity was then obtained by an electrochemical impedance method through electrochemical surface area (ECSA) normalization.3 Comparison with other Ni- and Co- based LDHs revealed that NiFe LDH shows the highest intrinsic activity.4 Our density functional theory (DFT) calculations on a γ-phase atomic model showed that O-bridged Ni-Fe reaction centers (Ni-O-Fe) stabilize OER intermediates that are unfavourable on Ni-O-Ni centers and single Fe sites, fundamentally accounting for the high catalytic activity. Furthermore, our DFT calculations predicts that γ-NiFe LDH is close to, but not on, the top of the OER volcano.2,4 Strategies to modify the catalytic active site to approach the top of the volcano will be presented, together with preliminary experimental results. These strategies will involve the design of active sites involving subsurface metal sites and electronic modulation of the Ni-O-Fe sites by introduction of a third transition metal element.

References

F. Dionigi and P. Strasser, Advanced Energy Materials, 6, 1600621 (2016).

F. Dionigi, Z. Zeng, I. Sinev, T. Merzdorf, S. Deshpande, M. B. Lopez, S. Kunze, I. Zegkinoglou, H. Sarodnik, D. Fan, A. Bergmann, J. Drnec, J. Ferreira de Araujo, M. Gliech, D. Teschner, J. Zhu, W.-X. Li, J. Greeley, B. Roldan Cuenya and P. Strasser, Nat. Commun., 11, 2522 (2020).

S.S. Jeon, P.W. Kang, M. Klingenhof, H. Lee, F. Dionigi, P. Strasser, ACS Catal., 13, 1186-1196 (2023).

F. Dionigi, J. Zhu, Z. Zeng, T. Merzdorf, H. Sarodnik, M. Gliech, L. Pan, W.-X. Li, J. Greeley, and P. Strasser, Angew. Chemie IE, 60, 14446 – 14457 (2021)
Accelerated Discovery of Multi-Metallic Nanostructured Catalysts for Anion Exchange Membrane Water Electrolyzers: Oxygen Evolution Reaction
Authors: Farghaly Ahmed A. , Onajah Sammy , Lalley Marja , Kreider Melissa E , Alia Shaun M , Yu Haoran , Myers Deborah J.
Published: August 2024

The current reliance on platinum group metals (PGMs) as electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane (PEM) water electrolyzers, the current industry standard, presents a significant barrier to the widespread adoption of hydrogen as a clean energy carrier. The scarcity and high cost of PGMs necessitate the development of alternative materials and technologies that offer comparable performance at a reduced cost. In this context, anion exchange membrane (AEM) water electrolyzers have emerged as a promising alternative.

This presentation addresses this imperative by focusing on the design and synthesis of nanostructured mesoporous multi-metallic catalysts for AEM water electrolyzers, leveraging earth-abundant materials as alternatives to the rare and expensive PGMs currently employed in PEM water electrolyzers. Transition metal oxides, sulfides, and phosphides are promising candidates to replace PGMs, given their abundance, low cost, and tunable catalytic properties conducive to high OER activity. The OER activity and durability of newly developed multi-metallic transition metal catalysts in an alkaline environment will be discussed in this presentation.

Preliminary results demonstrate that the developed catalysts exhibit high OER activity, achieving a potential of <1.5 V versus RHE at a current density of 10 mA cm⁻² in 1.0 M KOH. Notably, this surpasses the performance of commercial OER catalysts in alkaline environments. Furthermore, the catalyst exhibits superior durability, with < 0.5 mV/h potential loss over 100 h durability test at 10 mA cm⁻² in 1.0 M KOH.

Acknowledgments

This work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the auspices of the Electrocatalysis Consortium (ElectroCat 2.0). Argonne is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under Contract DE-AC-02-06CH11357
.
Solar Thermal Integrated Alkaline Water Electrolyser for Fast Ramping Up
Authors: Bae Dowon , Lecourt Nicolas , Guy Anton , Kim Jungmyung
Published: August 2024

There is significant recent interest in clean hydrogen production from renewable water electrolysis. In general, alkaline water electrolysis (AWE) operates with a voltage of ca. 2 V due to ohmic and overpotential-derived loss (0.7~0.8 V) [1]. In addition, it requires 0.5~1 hours for the ramping-up, which hinders its wider implementation. Our intended solution is to introduce a heat-tolerant electrolyser integrated with a chemically resistant solar thermal collector, providing a heated electrolyte to increase the reactivity [2] and reduce the ramp-up time. In this work, we discuss key dimensional design aspects of the thermal collector for alkaline electrolyser, considering the control feasibility of operating temperature and fluidic parameters. Furthermore, we also demonstrate our proof-of-concept experimental results using our alkaline electrolyser integrated with the solar-thermal collector at an elevated temperature. The time-dependent current output of the solar-thermal integrated AWE over the first 1 h yielded ca. 70% higher compared to the conventional AWE system.

E. Amores, J. Rodríguez, J. Oviedo, A. De Lucas-Consuegra, Open Eng 2017, 7,141–152.

B. Zhang, Q. Daniel, M. Cheng, L. Fan, L. Sun, Faraday Discuss 2017, 198, 169–179

Figure 1
Effect of Catalyst and Electrode Structures on the Operating Current Densities of Liquid Alkaline Water Electrolyzers
Authors: Maurya Sandip , Leonard Daniel , Chhetri Manjeet
Published: August 2024

Liquid Alkaline Water Electrolyzers (LAWEs) stand out as the technology best-suited for cost-effective hydrogen production. They do not require expensive platinum group metal catalysts and have proven durability afforded by nickel-based electrodes and porous separators. While nickel electrodes and porous separators provide chemical stability in highly alkaline conditions, they do suffer from lower catalytic activity for hydrogen and oxygen evolution reactions (HER and OER), and separators possess higher ohmic resistance due to the absence of ion-conducting groups. Consequently, most LAWEs operate at low current densities ranging from 0.2 to 0.6 A/cm2, resulting in a bulky footprint and comparatively lower energy efficiency due to a reduced hydrogen production rate. To address these challenges, considerable efforts have been directed towards developing thin separators and efficient transition metal-based electrocatalysts for HER and OER in alkaline media. However, the majority of studies related to catalysts are limited to half cells, with only a limited number of catalysts evaluated in relevant LAWE configurations.

In this work, we introduce a next-generation Zero-gap LAWE testing capability, benchmarked for performance through H2NEW consortia. Employing this setup, we have evaluated hydrogen and oxygen evolution catalysts under LAWE-relevant conditions on different electrode substrates, each offering a unique electrode structure. Our preliminary findings indicate that Zero-gap LAWEs, when coupled with NiMo cathode and NiFe-type anode catalysts, can operate at current densities exceeding 0.75 A/cm2 at approximately 1.8 V without compromising their short-term durability. In contrast, the benchmark cell exhibited a meager current density of around 0.22 A/cm2. In this presentation, effects of electrode structure, catalyst type, and other relevant parameters related to Zero-gap LAWEs will be discussed in detail.

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.
Understanding the Impact of Conditioning Protocols for Water Electrolyzers on Durability
Authors: Diaz-Abad Sergio , Yu Haoran , Park Jaehyung , Kariuki Nancy N. , Cullen David A. , Myers Deborah J. , Spendelow Jacob S. , Komini Babu Siddharth
Published: August 2024

The global push towards climate neutrality has intensified research efforts on green hydrogen production technologies. Among them, proton exchange water electrolysis (PEMWE) stands out as a highly efficient technology for producing green hydrogen using renewable energies. Nevertheless, a significant reduction in the cost of PEMWE while maintaining its durability over its operational periods is imperative. The DOE’s Hydrogen Earthshot target aims to achieve $1 per 1kg of H2 production within the decade. Reducing the amount of expensive iridium catalysts also reduces the durability of PEMWE. Hence, understanding the degradation mechanisms of low Ir loading PEMWE holds utmost importance. One key step in the evaluation of PEMWE is the break-in or conditioning step. Ensuring optimal conditioning is crucial to guarantee the peak performance of membrane electrode assembly (MEA) before assessing the durability of the catalyst thereby ensuring representative and reproducible results.

This research aims to comprehensively evaluate various conditioning protocols for PEMWE and their impact on durability. Utilizing a combination of electrochemical, electron, and X-ray characterization techniques. Accelerated stress tests (AST) will be conducted after each conditioning protocol to evaluate the degradation rate of the catalyst. Ex-situ characterization of the MEA post-conditioning as well as post-AST offers a comprehensive understanding of how the catalyst’s initial state, such as the iridium oxidation state, following the conditioning step directly influences the durability. The goal is to develop an optimal conditioning protocol for PEMWE, that considers the performance and durability challenges associated with low catalyst loading.

Acknowledgment

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 with support from Dave Peterson and McKenzie Hubert.
Syntheses of Ni-Based Layered-Double Hydroxide Materials Via Liquid Phase Deposition Method for Alkaline Water Electrolysis
Authors: Minamimoto Hiro , Okayama Tatsuya , Mizuhata Minoru
Published: August 2024

For the sustainable society, hydrogen production has received much attention during decades. The alkaline water electrolysis process has been recognized as one of the important processes for hydrogen products. For the achievements of an effective water electrolysis system, the decrease of the overpotential on the oxygen evolution reaction (OER), which is the four-electron and proton transfer process. These complex 4-electron sluggish processes lead to the large energy losses in the whole water electrolysis. Although the noble catalysts such as IrO2 or RuO2 exhibit high OER activity, their large-scale applications are limited due to cost problem. From this point of view, the low-cost transition metal materials, especially Ni-based catalysts, have been extensively studied. And also, it has been reported that the well-defined layered double hydroxide (LDH) structures can promote water oxidation through the interlayer anion effects. Despite this fact, the specific procedures for the preparation of Ni-based LDH structures have not been well established. Therefore, in this study, we have investigated the preparation of Ni-based LDH structures in the aqueous solution at room temperature, the so-called liquid phased deposition (LPD) method.

Through the LPD method, we have synthesized various types of Ni-based LDH structures. As an example, the Ni-Al LDH structures were synthesized on the conductive substrate. It was found that our synthesized Ni-Al LDH exhibited relatively high OER activity and durability against electrochemical potential cycling [1]. In addition, the dependencies of the OER activity on the interlayer anion species were clearly demonstrated. In addition, the other types of Ni alloy LDHs were also prepared and their OER activity was investigated. Through the electrochemical measurements, we have confirmed the advantages of our materials prepared by LPD methods as an anode for alkaline water electrolysis.

References

[1] H. Minamimoto et al., Electrochemistry, 2023, 91(6), 067005.
Unveiling the Impact of Anion-Tuning in Copper-Based Chalcogenides on the Oxygen Evolution Reaction
Authors: Singh Harish , Nath Manashi
Published: August 2024

Transition metal chalcogenides have been found to be particularly effective in promoting electrochemical energy conversion due to their unique electronic structure that facilitates interfacial charge transfer through modulation of electron density around the catalytically active site. Transition metal chalcogenides are relatively inexpensive compared to precious metal based OER catalysts, which makes them attractive for large-scale applications. Moreover, metal chalcogenides exhibit excellent chemical stability, which is important for maintaining the activity of the electrode over time. This study delves into the impact of anion-tuning in metallic chalcogenides on their electrocatalytic efficacy for comprehensive water splitting. Specifically, copper-based chalcogenides (Cu2X, where X = O, S, Se, and Te) undergo systematic examination to investigate the influence of decreasing anion electronegativity and increasing covalency on electrocatalytic performance. Among the copper chalcogenides, Cu2Te has the highest oxygen evolution reaction (OER) activity and can sustain high current density of 10 and 50 mA cm−2 for 12 h. The difference in intrinsic catalytic activity of these chalcogenide surfaces have been also probed through density functional theory calculations, which was used to estimate energy of the catalyst activation step. It was observed that the hydroxyl adsorption on the surface catalytic site is critically important for the onset and progress of OER activity. Consequently, it was also noted that the –OH adsorption energy can be used as a simple but accurate descriptor to explain the catalytic efficiency through volcano-like correlation plot. Such observation will have a significant impact on developing design principle for optimal catalytic surface exhibiting high performance as well as prolonged stability. By understanding the impact of anion electronegativity on catalytic performance, we aim to unravel the underlying principles governing OER and contribute to the rational design of highly efficient catalyst surfaces.
How the Quasi-Eqilibrium Condition Has Obfuscated Electrochemistry in General and the HOR/HER Discussion in Particual (Part 1)
Authors: Chatzichristodoulou Christodoulos , Brandes Benedikt Axel
Published: August 2024

Most reactions in electrocatalysis involve the transfer of multiple electrons. Due to the unlikely transfer of more than one electron at once, such reactions are multistep reactions. However, electrochemical textbooks focus heavily on the one-electron one-step reaction and there seem to be no consensus in the literature on how to treat multistep reactions.

We will elucidate how multistep reactions can be treated in a straightforward manner. In this process we explain that the Tafel slope, despite common practice and a recent IUPAC report, cannot be used to determine the reaction mechanism. This misconception stems from the inappropriate use of the quasi-equilibrium condition in the electrochemical literature.

We continue to show that the concept of the exchange current density cannot be universally defined for multistep reactions and that it is in almost no cases possible to accurately fit a multistep reaction by a simple Butler-Volmer equation.

Finally, we present how the HOR/HER reaction mechanism on Pt can be identified when the Butler-Volmer model is rigorously applied on the two HOR/HER paths dominating the discussion, namely the Tafel-Volmer and Heyrovský-Volmer.

Figure 1
Direct Formation of Nifep Catalytic Films on Anion Exchange Membrane As Efficient HER Catalyst for Water Electrolysis Device
Authors: Wang Tanyanyu , Guo Kaiming , Kunimoto Masahiro , Homma Takayuki
Published: August 2024

Anion exchange membrane water electrolysis (AEMWE) is advantageous in terms of device cost, compared with proton exchange membrane water electrolysis, because non-noble metal-based catalyst in alkaline condition is applicable.1 In AEMWE device, the membrane electrode assemblies (MEAs) plays an important role on the cell performance and stability.2 And the MEAs fabricated by (catalyst-coated-membrane) CCM cathode and (catalyst-coated-substrate) CCS anode is proved to be appropriate configuration.3 In the conventional way, the CCM cathode employs an ionomer/binder to combine the catalyst layer and AEM together, which however suffers the problem of degradation, thus limiting the life time of the device.2 We have reported an electroless deposition process that allows Ni-based metal to be deposited directly on AEM surface, which opens the possibility to fabricate CCM without ionomer/binder.4

In this work, NiFeP films (1 cm × 1 cm in area, ~3 μm in thickness) is electrolessly deposited on Tokuyama A-201 AEM as HER catalyst in room temperature AEMWE device. Electroless deposition method forms NiFeP films on AEM surface without binder, thus avoiding the disadvantage of degradation of the catalyst due to the ionomer/binder. The successfully deposited NiFeP catalyst exhibits outstanding HER performance by delivering -500 mA/cm2 at overpotential of -0.50 V in 1.0 M K2CO3 at room temperature. Furthermore, the NiFeP catalyst shows a good stability by delivering -500 mA/cm2 for at least 20 h without obvious potential loss. The outstanding HER performance of NiFeP should originates from the increased number of active sites caused by porous structure of the interface and the enhanced intrinsic activity caused by the well-tuned electronic structure. A series of characterization would be presented in terms of composition, morphology, phase and electron transfer behavior of the NiFeP films. Our work is hoped to give a new insight of fabrication of MEAs to achieve better performance of AEMWE devices.

References

R. R. Raja Sulaiman, W. Y. Wong, and K. S. Loh, Intl J of Energy Research, 46, 2241–2276 (2022).

Y. Leng et al., J. Am. Chem. Soc., 134, 9054–9057 (2012).

H. Ito et al., J Appl Electrochem, 48, 305–316 (2018).

T. Fujimura, M. Kunimoto, Y. Fukunaka, H. Ito, and T. Homma, Electrochemistry, 89, 192–196 (2021).
Water Splitting and Beyond
Authors: Menezes Prashanth W.
Published: August 2024

Hydrogen (H2) is a clean and environmentally friendly fuel, showcasing significant potential as a viable substitute for traditional fossil energy sources. Electrolysis, particularly the electrolytic splitting of water, emerges as one of the most environmentally benign methods for producing H2.1 Recent advancements have witnessed the emergence of cost-effective and durable catalysts, predominantly leveraging transition metals, demonstrating remarkable efficiency for water splitting Our ongoing research endeavors aim to push the boundaries further by exploring unconventional (non-oxide) catalysts based on non-noble metals. The objective is to identify catalysts that exhibit superior overall catalytic efficiency by a comprehensive investigation into the structural transformations, active sites, surface, and bulk structures under dynamic conditions. Additionally, we are delving into the influence of precatalysts on the properties of the final catalyst, striving for a holistic understanding to optimize the catalytic process.

Water splitting is hindered by the anodic oxygen evolution reaction (OER), a process entailing four-electron transfer and numerous high-energy reaction intermediates.2 Partly, electrochemical organic oxidation reactions (OOR) can effectively supersede the sluggish OER (hybrid-water electrolysis), and accelerate the overall hydrogen production rate.3 This also significantly enhances the techno-economic viability of water-splitting as selective high-valued organic oxidation products are formed at the anode, as opposed to the less valuable oxygen.4 This talk will shed light on the recent developments of selected catalysts for electrocatalytic OER and OOR and will discuss the dynamic state of the catalysts via comprehensive in-situ and ex-situ techniques.5 The ultimate goal is to pave the way toward a concept-guided design system that extends beyond conventional water electrolysis.

References

[1] Chen Z.; Yang H.; Kang Z.; Driess M.; Menezes, P. W., Adv. Mater. 2022, 2108432.

[2] Hausmann J. N.; Menezes P. W., Angew. Chem. 2022, 134, e202207279.

[3] Yang H.; Vijaykumar G.; Chen Z.; Hausmann J. N.; Mondal I.; Ghosh S.; Nicolaus C. J. V.; Laun K.; Zebger I.; Driess M; Menezes P. W., Adv. Funct. Mater. 2023, 2303702.

[4] Kahlstorf T.; Hausmann J. N.; Sontheimer T.; Menezes P. W., Global Challenges 2023, 7, 2200242.

[5] Reith L.; Hausmann J. N.; Mebs S.; Mondal I.; Dau H.; Driess M.; Menezes P. W., Adv. Energy Mater. 2023, 13, 2203886.
Electrocatalysis for Water Splitting Using Layered Zirconium Phosphate Nanomaterials
Authors: Colon Jorge L , Serrano-Rosario Yannelly A. , Muñoz-Torres Sebastián , Gibson Colón Daniella , Liu Biao , García-Machado Gabriela , Defebve Louise M. , Pollock Christopher
Published: August 2024

We are studying new applications of layered zirconium phosphate (ZrP) inorganic nanomaterials [1]. The θ phase of ZrP can be directly ion-exchanged with metal complexes and catalysts, producing intercalated phases useful for artificial photosynthesis schemes for water splitting, amperometric biosensors, and drug delivery applications. Recently, we have demonstrated improved electrocatalytic activity of ZrP nanomaterials loaded with metal ions suitable for the oxygen evolution reaction of water splitting. Electrocatalysts have been incorporated as intercalated species, surface bound, on exfoliated layers, and on nanoparticles of different morphologies (hexagonal platelets, cubes, rods, and spheres). Single and bimetallic electrocatalysts based on earth-abundant materials have been studied. Reduction in overpotentials and increases in mass activity have been achieved. Mixed metal NiFe-intercalated ZrP electrocatalysts at 90% Fe metal content proved to have superior OER electrocatalytic performance (decreased overpotentials, increased mass activities, reduced Tafel slopes) compared to adsorbed counterparts. We have recently prepared CoFe electrocatalysts systems and again the intercalated bimetallic system is more active than the surface-adsorbed one. We are starting to work also with Mn electrocatalysts. We are exploring OER activities of other mixed-metal catalysts on ZrP, bifunctional catalysts, and operando synchrotron X-ray absorption spectroscopy studies to elucidate the nature of the active species. We are also exploring efficient solar H2 production using these supports.

Reference

[1] M. V. Ramos-Garcés; J. González-Villegas; A. López-Cubero; J. L. Colón, Acc.
Mater. Res.
2021, 2, 793-803. DOI: 10.1021/accountsmr.1c00102.
Microstructural Characterization of Porous Transport Layer Coatings
Authors: Arregui-Mena David , Grejtak Tomas , Domingo Marimon Neus , Stelmacovich Genevieve , Pylypenko Svitlana , Liu Chang , Bender Guido , Cullen David A.
Published: August 2024

The porous transport layer (PTL) is a key component in polymer electrolyte membrane (PEM) water electrolyzers and serves the role of controlling the transport of reactants and products to and from the anode. Maintaining a low interfacial contact resistance between the titanium (Ti) fiber or sinter PTL and the iridium (Ir) anode catalyst is critical to maintaining the performance of the electrolyzer cell. This requires costly precious metal coatings, typically Pt, to inhibit the formation of native oxide layers during long-term cell operation. Strategies to reducing the thickness of these costly coatings including surface treatments, such as etching and abrasion, alternative low-cost coating materials, and implementation of microporous layers. It is crucial to understanding the morphologies and degradation mechanisms of these new strategies in order to accelerate the development of cheaper, more robust PTL coatings.

In this work, correlative ex situ characterization methods, including laser confocal microscopy (LCM), focused ion beam (FIB), scanning electron microscopy (SEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM), are utilized to explore the impact surface treatments, such as etching and abrasion, on the Pt coatings uniformity and surface roughness. The thickness, local topography, and continuity of the Pt coating were quantified and correlated with interfacial contact resistance and electrochemical cell performance measurements. Changes to the thickness and composition of the coatings and oxide layers after single-cell tests will also be reported. Overall, these findings aim to guide the development of PTL treatments and coatings, ensuring the creation of highly durable and efficient PEM water electrolyzers that align with the U.S. Department of Energy's Hydrogen Shot goal of reducing the cost of clean hydrogen production to $1 per kilogram by 2031.

Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.
Coupling Cuprous Oxide with Upconversion Materials: A Holistic Approach to Efficient Solar Water Splitting
Authors: Magazov Yerbolat , Kudryashov Vladislav , Amze Magzhan , Nuraje Nurxat
Published: August 2024

Photoelectrochemical (PEC) water splitting is a promising solution for harnessing solar radiation for hydrogen production. This technology combines sunlight capture and water electrolysis processes, resulting in the production of hydrogen and oxygen that can efficiently recombine in fuel cells. However, challenges in materials science still need resolution to establish PEC water splitting as a practical and competitive approach. Copper oxide semiconductors, particularly materials based on cuprous oxide (Cu2O), have attracted attention due to their abundant elemental availability, scalable synthesis methods, and inherent p-type characteristics. To improve the generated photocurrent of the photoelectrode system, photon upconversion (UC) materials can be implemented into water-splitting devices. TTA-based UC is particularly suitable for solar water splitting due to its efficient conversion at low photon intensity. This work highlights the potential application of TTA-based UC in solar-assisted water splitting and highlights the significance of photonic designs and nanointerface engineering to improve the light-harnessing properties of photoactive materials. To the best of our knowledge, our research group was the first to successfully implement the integration of photoactive materials for solar water splitting with an upconversion device based on the TTA mechanism. This strategy allows us to dramatically improve the light-harnessing properties of our photoelectrode by irradiating the photocatalyst from dual perspectives (front and back-side illumination). It has been demonstrated that Cu2O coupled with an upconverter (UC) outperforms bare Cu2O by 56% in terms of produced photocurrent density, namely bare Cu2O produces -0.32 mA·cm-2 at 0V (vs. RHE), whereas Cu2O/UC exhibits a photocurrent of -0.5 mA·cm-2.

Figure 1
(Invited) Unraveling the PEC: Insight and Strategies for Addressing Materials Design By ML Support
Authors: Solarska Renata , Bienkowski Krzysztof , Szejgis Witold
Published: August 2024

Unlimited access to clean, sustainable and renewable source of energy seems to be a dream scenario, however with an assistance of ML (machine learning) support the experimental work which as a matter of fact reveals the right descriptors may gain a powerful tool allowing to omit a time consuming trials path. However, precise definition of descriptors will require an identification of the bottleneck materials parameters, features and processes, thus different architectures and working arrangements will be shown and discussed in this presentation in order to test their usfulness for prediction of novel and better arrangements for hydrogen and other carbon based solar fuels production. When a suitable material is identified, then there are numerous strategies to overcome potential bottlenecks, including doping, nanostructuring, surface modification, vacances optimisation or addition of co-catalysts, thus a game changer is a precise screening of possible predictors in order to identify the most performance determinant factor. Therfore, over 400 tailor-made for PEC reduction process samples based on the semiconductor oxides have been prepared and measured in order to bulid a pre-base for ML tests. In this presentation we will discuss the strengths and weaknesses of different architectures and working arrangements for hydrogen and carbon-based solar fuels production; different materials and working systems, their compositions, geometry, properties will be discussed in view of their impact on the final prediction.
(Invited) Photoelectrode Design for Photoelectrocatalytic Hydrogen Production
Authors: Wang Lianzhou
Published: August 2024

Semiconductor nanomaterials hold the keys for efficient solar energy harvesting and conversion processes like photocatalysis and photoelectrochemical reactions. In this talk, we will give a brief overview of our recent progress in designing semiconductor nanomaterials for photoelectrochemical energy conversion including solar hydrogen generation and low-cost solar cells. In more details, we have been focusing on a few aspects; 1) photocatalysis mechanism, light harvesting, charge separation and transfer and surface reaction engineering of low-cost metal oxide based semiconductors including TiO2, BiVO4 as efficient photoelectrode for photoelectrochemical hydrogen production; 2). The design of ultra-stable composites of perovskite-MOF with improved light emitting and photocatalytic performance.1-5 The resultant material systems exhibited efficient photocatalytic performance and improved power conversion efficiency in solar cells, which underpin sustainable development of solar-energy conversion application.

References
：

1. Adv. Mater., 2018, doi:10.1002/adma.201705666.

2. Angew. Chem, 2019, doi/10.1002/anie.201810583

3. Nature Commun, 2020, (2020) 11:2129

4. Science, 2021, 374, 621.

5. Adv. Mater., 2022, 34 (10), 2106776.
Influence of Oxygen Vacancies in La0.4Sr0.6FeO3-δ
Perovskite Oxide Nanoparticles for the Oxygen Evolution Reaction
Authors: Qing Geletu , Chen Jingyi
Published: August 2024

Iron incorporation is one of the key factors to generate highly active NiFe(OH)x electrocatalysts for the oxygen evolution reaction (OER). However, it remains controversial whether Fe(IV) is present during OER and how the oxygen vacancies in Fe(IV)-containing metal oxides affect their activities. In this work, we develop a facile approach to control oxygen vacancy content, via an ozone treatment under ambient pressure during cooling for the synthesis of La1-x
Sr
x
FeO3-δ
(0 ≤ x ≤ 1, 0 ≤ δ ≤ 0.5x) perovskite oxides - an important class of energy-related materials that contain a rare Fe(IV) oxidation state. We have initially synthesized a series of La1-x
Sr
x
FeO3-δ
compounds using a polymerized complex method. The concentration of oxygen vacancies and Fe(IV) are determined by redox titration, and the crystal structures are derived by analyzing X-ray diffraction patterns using Rietveld refinement. Significant amounts of oxygen vacancies are found in the as-synthesized compounds with x ≥ 0.8: La0.2Sr0.8FeO3-δ
(δ = 0.066) and SrFeO3-δ
(δ = 0.195). A subsequent ambient-pressure ozone treatment approach is able to substantially reduce the amount of oxygen vacancies in these compounds to achieve levels near the ideal oxygen stoichiometry of 3 for La0.2Sr0.8FeO3-δ
(δ = 0.006) and SrFeO3-δ
(δ = 0.021). The oxygenation/deoxygenation kinetics can be tuned by the cooling rate after annealing. As the oxygen vacancy concentration decreases, the structure of SrFeO3-δ
evolves from orthorhombic to cubic, demonstrating that the crystal structures in metal oxides can be highly sensitive to the number of oxygen vacancies. We have further conducted a systematic evaluation of the OER activity and stability of La1-x
Sr
x
FeO3-δ perovskites in 1 M KOH. Their initial OER activity first increases with increasing Sr content (from x = 0 to 0.8), and then decreases when the Sr content is increased to 1. Their stability, as evaluated by monitoring element leaching from the electrodes show that La does not leach at a detectable rate, but Sr and Fe leach substantially. The leaching of Sr occurs at similar rates under open circuit potential (OCP) and OER potential, suggesting a nonelectrochemical dissolution process. The leaching of Fe is, however, strongly dependent on the electrode potential. More Fe leaching is observed at the OER potential than OCP. Additionally, the electrode with higher initial OER activity leaches more Fe. These results indicate that OER facilitates the dissolution of Fe from the electrode. The leaching of Fe, in turn, is considered responsible for the activity loss of La1-

x
Sr
x
FeO3-

δ
during OER. This study brings new insight into the degradation mechanism of La1-

x
Sr
x
FeO3-

δ
and related metal oxides during electro-oxidation processes.
(Invited) Design Rules for (Li-mediated) Photoelectrochemical N2 Reduction to NH3
Authors: Nielander Adam C.
Published: August 2024

The electrochemically-driven N2 reduction reaction (N2RR) offers an alternative route to the traditional Haber-Bosch method for production of NH3. Electrifying NH3 synthesis promises a route to the decarbonization and decentralization of ammonia production, which currently accounts for >1% of annual CO2 emissions. While there have been many studies examining electrochemically-driven production of NH3 in aqueous electrolytes at low-T (≤ 50o C) and low-P (≤20 bar), lithium-mediated N2 reduction (Li-N2R) in nonaqueous electrolytes at low-T and low-P has emerged as a promising method for obtaining reliable electroreduction of N2 to NH3.

With this in mind, our team at SUNCAT and NREL have begun evaluating the opportunity and key design rules necessary for coupling photoelectrochemical methods to the drive the Li-N2R reaction using solar illumination. Nonaqueous, photoelectrochemical Li-N2R promises a route to stable operation that has been a key challenge associated with photoelectrode operation in aqueous electrolytes. Recognizing the energetic constraints associated with the Li-mediated process, we have modeled and mapped the bandgap characteristics necessary for a semiconducting light absorber to drive the Li-N2R reaction and the maximum attainable solar-to-NH3 conversion yields. We have identified III-V based photoelectrodes that meet the modeled requirements and evaluated the surface chemistry at the electrode/electrolyte interface under Li-N2R conditions to understand the how reactive Li-species influence photoelectrochemical performance (e.g., rate, selectivity, stability), how solid-electrolyte interface (SEI) formation and electrolyte selection are mutually influenced by illumination, and how the current density and cycling conditions enforced by solar operation dictate photoelectrochemical N2-to-NH3 performance. We have further extended a neutron-reflectometry technique used for in situ observation of interfacial layer formation to be compatible with light-driven reactions, and with these insights in hand continue our drive toward demonstrating unassisted photoelectrochemical N2-to-NH3 production.
Investigation of Cu-Oxidation and Its Roles in Unassisted CO2 Reduction and Electrochemical Oxygen Evolution
Authors: Basera Pooja , Zoric Marija , Zhao Yang , Boettcher Shannon W. , Codones-Hahn Amy , Bajdich Michal
Published: August 2024

Sunlight-driven photocatalytic CO2 reduction to CO under unassisted (unbiased) conditions was recently demonstrated using heterostructured catalysts that combine p-type GaN with plasmonic Au nanoparticles and Cu nanoparticle co-catalysts (p-GaN/Al2O3/Au/Cu) [1]. However, the exact oxidation state of Cu and the hole transfer directionality between Au and Cu remain under debate. Here, we combine computational and experimental efforts to investigate the different oxidation states of Cu under unassisted photocatalytic operating conditions. Experimentally we found that the Cu nanoparticles are primarily composed of Cu2O and CuO, CuCO3.Cu(OH)2 species, with no detectable metallic Cu present. The calculated bulk thermodynamics confirmed the high stability of CuCO3.Cu(OH)2 which is also validated by its largest contribution in the Pourbaix diagram, consistent with experimental observations. To gain insights into the origin of charge transfer, we simulate material interfaces namely, Au/CuO, Au/Cu2O, and Au/CuCO3.Cu(OH)2. Our theoretical analysis supports experimentally observed light-driven hole transfer from Au to Cu.

More recently significant progress has been made in understanding copper oxide (CuO) behavior at oxidizing electrochemical conditions (> 1.5 V) [2]. In our study, we show CuO transforms into the OER active phase CuOOH, as evident in the bulk Pourbaix diagram presented here. Our calculations show a novel square planar, non-magnetic CuOOH phase. This discovery is supported by calculated Raman spectroscopic analysis, revealing distinct features corresponding to Cu3+ species at 567 and 585 cm-1, closely matching experimental peaks at 587 cm-1. These findings provide insights into the electrochemical properties of copper oxide phases and their relevance towards electrocatalytic OER.

Acknowledgments:

This material is based on work performed by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266.

Reference:

[1] H. A. Atwater et al. ACS Energy Lett, 6, 1849 (2021)

[2] M J. Janik et al. ACS Appl. Mater. Interfaces, 15, 27878 (2023)
(Invited) Solar Fuels Systems: Interfacing Catalysts and Semiconductors for H2 Production, CO2 Reduction, and Related Chemistries
Authors: Jaramillo Thomas F.
Published: August 2024

The production of fuels and chemicals directly from sunlight holds promise as a means to a sustainable, de-centralized means of manufacturing important molecules such as hydrogen, ethylene, and ammonia, among others. There are many technical challenges to overcome with such solar fuels systems. This paper will describe strategies to interface the proper catalysts with semiconductors to achieve improvements in performance, namely activity, selectivity, and durability. This paper will discuss advanced methods to characterize these systems to understand the chemical and physical phenomena at play that govern performance, in order to point towards improved system designs. This includes the study of ‘real-world’ factors such as corrosion and the impacts of diurnal cycling, such that through improved understanding one can accelerate the pathway towards commercialization of solar fuels systems.
(Invited) Designing Photocatalytic Membrane to Direct Electron and Hole Transport
Authors: Kipkorir Anthony , Ealy Gavin , Yu Yiseul , Kamat Prashant V
Published: August 2024

Surface interaction of chromophore or redox active molecule which dictate the efficiency of energy/electron transfer, plays an important role in realizing photocatalytic and optoelectronic applications. Metal halide perovskite nanocrystals are interesting in the sense that they can either transfer energy or selectively transfer electrons or holes to the adsorbed molecules.1,2 The presentation will focus on two specific scenarios of the flow of energy and electron processes in CsPbX3 (X= Br, I) nanocrystal-molecular hybrids. The energy transfer is probed through three moleculr acceptors – rhodamine B (RhB), rhodamine isothiocyanate (RhB-NCS), and rose Bengal (RoseB), which contain an increasing degree of heavy atom pendant groups. Electron and/or hole transfer from excited CsPbX3 nanocrystals to a molecular relay present near the interface offers another avenue to directly convert light energy into chemical energy. Such interfacial electron transfer of semiconductor nanocrystals has been widely explored in photocatalytic processes. A basic understanding of the fundamental differences between the two excited deactivation processes (energy and charge transfer) and ways to modulate them should enable design of more efficient light harvesting assemblies with semiconductor and molecular systems.
(Invited) Electrochemical Modulation of Energy Transfer in Plasmonic-Polymer Hybrid Nanomaterials
Authors: Landes Christy F.
Published: August 2024

The absorption cross-section of plasmonic nanoparticles makes them attractive candidates for light-activated chemistry, but much of the absorbed energy is transformed into heat in the surrounding medium. We propose that one way to overcome this problem is through nonradiative energy transfer to a photo-conductive polymer shell. At the same time, understanding the mechanisms that drive energy-transfer is obscured by the innate heterogeneity of the nanoparticle/polymer interface. I will discuss our recent efforts to apply in-situ single-particle spectroelectrochemistry to quantify the energy transfer efficiency in hybrid nanomaterials comprised of plasmonic cores surrounded by polymer shells.
(Invited) Unraveling Hot Carrier Transfer Processes in Plasmonic Catalysis
Authors: Tagliabue Giulia
Published: August 2024

In the last decade, plasmonic nanoantennas have revolutionized light manipulation and control at the nanoscale. Interestingly, generation of hot carriers in metals upon light absorption have opened new pathways for controlling photo(electro)chemical processes and engineering photocatalysts. Yet, fundamental questions remain about the microscopic details of these complex light-matter interactions.

We have recently developed a well-controlled platform for micro-scale plasmonic photoelectrochemistry studies that leverages the unique properties of monocrystalline microflakes [1] as well as precise nanofabrication methods. Interestingly, the microflakes exhibit well-defined crystal facets and can bridge the properties of bulk metals with those of nanoscale plasmonic antennas, accessing ultra-thin film dimensions (sub 15-nm) that are challenging for polycrystalline films. By performing careful absorption measurements, we explore the photoelectrochemical performance of these hot carrier micro-scale photoelectrodes for inner- and outer-sphere reactions [2], concurrently comparing them to cm-scale devices [3]. This allows us to unravel the interplay of hot carrier generation and transport at metal-liquid and metal-semiconductor interfaces and identify bottlenecks for charge transfer.

[1] Kiani F., Tagliabue G. - High‐Aspect Ratio Au Microflakes via Gap‐Assisted Synthesis – Chemistry of Materials 34 (3), 1278-1288, 2022

[2] Kiani F. et al - Transport and Interfacial Injection of d-band Hot Holes Control Plasmonic Chemistry - ACS Energy Letters, 8 (10), 4242-4250, 2023

[3] Ma J., Oh K., Tagliabue G. - Understanding Wavelength-Dependent Synergies between Morphology and Photonic Design in TiO2-Based Solar Powered Redox Cells – Journal of Physical Chemistry C, 127 (1), 11-21, 2022
(Invited) Boosted Photoelectrochemical Water Splitting Performance by Plasmonic Assisted Ternary Heterostructures
Authors: Xie Fang
Published: August 2024

Traditional semiconducting metal oxide-based photoelectrodes have been extensively explored for energy and environmental applications. However, their performance is hindered by poor light absorption, high charge recombination rates, and low surface kinetics. Some of the recent results will be presented to discuss the rational design of ternary materials systems, which incorporating of metal-organic framework and plasmonic structures into semiconducting metal oxides, as one of the most promising strategies to achieve performances beyond those of bare MOF and/or conventional semiconductors. The application examples of this new generation of composite photoelectrodes in water splitting, CO2 reduction and pollution degradation will be discussed, together with the challenges and prospects.