bluuebunny/crossref_metadata_2025 huggingface dataset:
Iridium Nanosheet Catalysts Supported on Titanium Oxide for Oxygen Evolution Reaction in Polymer Electrolyte Membrane Water Electrolysis
Authors: Shin Dongwon , Lee SangJae , Bak Junu , Roh JeongHan , Lee KwangHo , Chang HyunWoo , Cho EunAe
Published: September 2023

In order to overcome the disadvantage of intermittent production of renewable energy, Polymer electrolyte membrane water electrolysis(PEMWE), which is one of the technologies of producing hydrogen by electrolyzing water, is attracting attention. For the commercialization of PEMWE, it is important to reduce usage of iridium(Ir) for oxygen evolution reaction(OER) in the anode electrode. Many studies have been reported to reduce the amount of iridium used by developing a catalyst with higher performance than the iridium nanoparticle catalyst used as a commercial catalyst. As one of the strategies, the introduction of support materials that can increase the active area of the catalyst is drawing attention. While carbon-based supports are mainly used in other applications, in OER environments, carbon is easily corroded due to high voltage and strong acid conditions. Therefore, it is necessary to use a metal oxide support with high corrosion resistance. In particular, titanium oxide(TiO2) is one of the suitable support candidates because it is a stable material in an acidic OER environment. However, catalysts loaded on TiO2 with nanoparticles cause an electrical contact problem due to the low electrical conductivity of TiO2, which causes a degradation in activity. Many studies have reported doping methods to increase the conductivity of TiO2, but there are also reports that these methods reduce the durability of support. Thus, a new approach to synthesizing a better structure of catalysts is needed to utilize metal oxide support.

Herein, we present an approach to iridium nanosheet (NS) catalysts supported on TiO2(Ir NS/TiO2). Ir NSs were synthesized by an facile method by directly annealing a mixture of Ir precursor and alkali salt. Ir NSs were supported on TiO2 to be utilized as a reaction site and also acts as an electron path to compensate for the low electrical conductivity of TiO2. Ir NS/TiO2 showed superior OER activity and stability under acidic conditions. These results showed that Ir NS/TiO2 could be utilized to reduce the amount of precious metal catalyst in PEMWE and increase the stability of OER supported catalysts.
Substitution of the Nafion® Ionomer with Hydroxypropyl Methylcellulose for Proton Exchange Membrane Water Electrolyzer
Authors: Cha Jeong In , Baik Chaekyung , Pak Chanho
Published: September 2023

The use of green hydrogen as a clean energy carrier has become an essential method of storing renewable energy instead of fossil fuels because of environmental concerns[1,2]. Proton exchange membrane water electrolysis (PEMWE) is one of several methods of producing green hydrogen. A perfluorosulfonic acid ionomer called Nafion® was typically used as a binder in PEMWE for many years. It has excellent chemical stability and high ionic conductivity, but it is expensive and has negative environmental effects [3]. It is therefore necessary to investigate new binders for the anode of PEMWE.

In this study, we present a new electrode manufacturing method using hydroxypropyl methylcellulose (HPMC) binder and demonstrate that HPMC binder can be used sufficiently instead of traditional Nafion® ionomer through single-cell evaluation under PEMWE conditions. Although it has the disadvantage of low proton conductivity, HPMC is cost-effective and eco-friendly. In the case of the PEMWE anode, because water moves into the cell, water can take over the role of hydrogen ion transport instead of the HPMC binder. By the electrode’s interfacial stability test, it was discovered that the HPMC electrode’s form was preserved for 24 hours without any peeling. Further, it can be seen that there is no significant difference in PEMWE performance even if an HPMC binder with relatively low ionic conductivity is used. Additionally, it was established that each electrode demonstrated a low degradation (less than 0.3 mV h-1) in the subsequent 72 h durability test. The proposed affordable new binder HPMC can aid the development of a new electrode and a cost-effective PEMWE system.

References

[1] Y. Li, Y. Sun, Y. Qin, W. Zhang, L. Wang, M. Luo, H. Yang, and S. Guo, Adv. Energy Mater., 2020, 10, 1-20.

[2] Z. Chen, X. Duan, W. Wei, S. Wang, and B. J. Ni, J. Mater. Chem. A., 2019, 7, 14971-15005.

[3] E. Oakton, D. Lebedev, M. Povia, D.F. Abbott, E. Fabbri, A. Fedorov, M. Nachtegaal, C. Copéret, T.J. Schmidt, ACS Catal., 2017, 7, 2346-2352.

[3] Klose, C., Saatkamp, T., Münchinger, A., Bohn, L., Titvinidze, G., Breitwieser, M., Kreuer, K.D., and Vierrath, S., Adv. Energy Mater. 2020, 10, 1903995.
IrxNb1-XO2 Mixed Metal Oxides As Anode Catalyst for PEM Electrolysis: From Fundamentals to Application
Authors: Kroschel Matthias , Strasser Peter
Published: September 2023

Summary. Here we describe the synthesis of IrxNb1-xO2 (mixed) metal oxides powders with several compositions. The catalysts are characterized with a variety of techniques to achieve a structure – activity relation. Furthermore, the effect of annealing temperature is addressed. Promising catalysts were tested in a full electrolysis cell as well.

Abstract. Electrochemical water splitting will play a crucial role in future industries and will contribute to a more sustainable economy. Hydrogen produced by electrolysis is suitable to replace hydrogen produced by fossil fuels, enables the electrification of multiple sectors and can be used as long- and short-term chemical energy storage system [1].

Here we describe the synthesis of IrxNb1-xO2 (mixed) metal oxides powders. Several compositions regarding the Ir/Nb ration are synthesized and studied. The study is based on previous experimental and theoretical findings using model films of IrxNb1-xO2 [2]. We address fundamental properties like crystal structure and composition and furthermore, test the catalysts in full electrolysis cell measurements. The synthesized materials are analysed using a variety of techniques, like XRF, XRD, RDE, BET, SEM, TEM, TGA and conductivity measurements to determine the activity and stability, crystal structure, morphology and conductivity. Furthermore, the effect of the annealing temperature on the above mentioned properties was studied. The optimal composition was determined based on activity and stability measurements in a three-electrode setup and physical properties like the powder conductivity.

The synthesized catalysts could outperform commercial catalysts in terms of activity and stability and can be used with lower Ir loadings. XRD measurements reveals an IrO2 rutile structure with very broad peaks, indicating an amorphous crystal structure.

The most promising catalysts were evaluated in a full electrolysis cell with different loadings.

[1] Getting Hydrogen to the Gigaton Scale; B. S. Pivovar, M. F. Ruth, A. Nakano, H. Furutani, C. Hebling, T. Smolinka; Electrochem. Soc. Interface. 2021, 30, 85.

[2] Molecular Analysis of the Unusual Stability of an IrNbOx Catalyst for the Electrochemical Water Oxidation to Molecular Oxygen (OER); C. Spöri, L. J. Falling, M. Kroschel, C. Brand, A. Bonakdarpour, S. Kuhl, D. Berger, M. Gliech, T. E. Jones, D. P. Wilkinson, P. Strasser
(Invited) Electrochemical Construction of 3-D Catalyst Layer on Ordered Liquid-Gas Diffusion Electrode for Highly Stable and Cost-Efficient PEM Water Electrolyser
Authors: Yan Changfeng , Ding Chao , Lu Zhuo-xin , Shi Yan
Published: September 2023

Proton exchange membrane (PEM) water electrolyser is an ideal way to produce green hydrogen with intermittent renewable energy. The high cost of noble metal in membrane electrode assembly is one of the key problems to be solved for its commercial applications. Developing 3-D electrode with high utilization of noble metal and prominent performance of mass diffusion is a promising solution.

In this work, titanium foil with ordered openings is applied as liquid-gas diffusion layer (LGDL) for anode by photolithography. And 3-Dimensional structural catalyst layer (CL) is coated by controlled pulse electrodeposition. By adjusting the concentration of electrolyte, current density and pulse parameter, catalyst layer with structure of nanowires, nano-urchin and nano-flower can be obtained. With medium current density of 5 mA/cm2, a structure variation from nanowire to nano-urchin could be observed by prolonging the electrodepositing time. While high current density of 20 mA/cm2 was applied, catalyst layer with nano-flower structure was formed. However, similar morphology could not be observed when a flat titanium foil was used as substrate. The controlling mechanism would be studied with scanning electrochemical microscopy to unveil the key controlling issue, such as distribution of local current and steric effect of released gas.

The single cell performance with nano-urchin CL coated ordered LGDL as anode electrode was studied. Though coverage of anode electrocatalyst on PEM is only 45% as the porosity of order LGDL is 55%, the single cell performs excellent activity and stability due to the high surface area, enhanced mass diffusion and structural stability of 3-D CL. With optimized loading of 0.25 mgIr /cm2, initial performance of 1.795 V@ 1 A/cm2 can be obtained. And a prominent performance on stability with decay rate of 4.17 μV/h is shown after 4000h running under 1A/cm2 at 80 ℃. It is predictable that, by further adjusting the pore diameter and porosity of order LGDL to optimize the area of electrocatalyst/membrane interface and mass diffusion, the performance could be further improved to fulfill long-term operation under high current density (＞2A/cm2).

Figure 1
Structural Transformations in Ni (Oxy)Hydroxide Host Structures Under Operating Conditions for Oxygen Evolution Electrocatalysts
Authors: Dionigi Fabio , Zeng Zhenhua , Zhu Jing , Merzdorf Thomas , Klingenhof Malte , Buchheister Paul Wolfgang , Li Wei-Xue , Greeley Jeffrey , Strasser Peter
Published: September 2023

The incorporation of Fe into the brucite-like Ni(OH)2 host structure increases significantly the catalytic activity for the oxygen evolution reaction (OER).1 The resulting hydrotalcite-like crystalline structure is known as NiFe layered double hydroxide (LDH). However, even the most active NiFe LDH catalyst still shows a considerable overpotential for the OER.2 Understanding the nature of the catalytic active sites and the catalytic mechanism in NiFe LDHs are key challenges to develop better OER electrocatalysts, as well as the fundamental understanding of the role of the Ni-based host structure.

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-phases to activated γ-phases.3 The interlayer and in-plane lattice parameters of the OER-active γ-phase were obtained by performing wide angle X-ray scattering (WAXS) measurements on NiFe LDH nanoplatelets during operating electrochemical conditions and were characterized by a contraction of about 8%. Operando WAXS was then performed for other selected catalysts belonging to the transition metal LDH family of materials. Structural similarities of the catalytically active phases will be highlighted. In addition, the structural transformations of β-Ni(OH)2 will be discussed, as potential host structure for novel multi-element catalysts. Also for Ni(OH)2, the γ-phase is found to be the catalytically active phase. However, the structural transformations are more complex, involving multiple limiting phases. Their structural stability is presented and the discussion supported by density functional theory calculations.

References

L. Trotochaud, S. L. Young, J. K. Ranney and S. W. Boettcher, Journal of the American Chemical Society, 2014, 136: 6744-6753.

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

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, 2020, 11 2522.
Nife LDH: From Molecular Understanding to Highly Active Single Cell Measurements
Authors: Klingenhof Malte , Trzesniowski Hanna , Metzler Lukas , Koch Susanne , Dionigi Fabio , Vierrath Severin , Strasser Peter
Published: September 2023

NiFe layered double hydroxide (LDH) is among the most active oxygen evolution reaction catalysts in an alkaline environment. Still, scaling the synthesis of NiFe LDH to application related multi gram scale is yet not fully investigated. This is accompanied with missing understanding of the nature of the catalytic active sites. Furthermore, fully convincing measurements of NiFe LDH in single cell environment with PEM-like activities are not reported up to date.

In this contribution, the detailed successful scaling of the NiFe LDH synthesis to multi-gram scale will be presented. Furthermore atomic-scale investigations of the catalytic active phase revealed by in-situ X-Ray measurements will be presented, showing that oxygen features visible in the oxygen K-edge are contributor to the excellent OER activity of NiFe LDH. Time-resolved measurements of the Ni L-edge show that the formation of the specific oxygen feature is directly accompanied with Ni oxidation. These oxygen features are also found in IrOx catalysts under applied oxygen evolution reaction relevant conditions.1,2 Finally, NiFe LDH was used to prepare membrane-electrode assemblies (MEA) with a previously reported advanced method.3 The resulting MEAs provided PEM-like activities (approx. 2.3 A cm-2 at 1.8 V, 1 M KOH, 80°C) in a single-cell AEMWE setup. Thus, the herein presented work provides successful insights into catalyst synthesis development, in-situ investigations of catalytic active sites as well as implementation of the investigated catalyst into application related full cell measurements.

References

1 Nong, H. N. et al. Key role of chemistry versus bias in electrocatalytic oxygen evolution. Nature
587, 408-413, doi:10.1038/s41586-020-2908-2 (2020).

2 Nong, H. N. et al. The Role of Surface Hydroxylation, Lattice Vacancies and Bond Covalency in the Electrochemical Oxidation of Water (OER) on Ni-Depleted Iridium Oxide Catalysts. Zeitschrift für Physikalische Chemie
234, 787-812, doi:10.1515/zpch-2019-1460 (2020).

3 Koch, S. et al. Toward Scalable Production: Catalyst‐Coated Membranes (CCMs) for Anion‐Exchange Membrane Water Electrolysis via Direct Bar Coating. Advanced Sustainable Systems, doi:10.1002/adsu.202200332 (2022).
Anodized Stainless Steel 316 and 304 Alloys As Bifunctional Water Splitting Electrocatalytic Materials in Alkaline Media
Authors: Heiba Asmaa R. , Abd El-hamid Shimaa , El Sawy Ehab
Published: September 2023

The world is facing a continued increase in population that is accompanied by a high demand for energy. The dependence on fossil fuels caused demand and environmental crises. Therefore, it is necessary to switch to sustainable, clean, and renewable sources of energy immediately. Using hydrogen as a fuel is considered the most cleanest and promising alternative. Producing hydrogen using water electrolysis is the most environmentally friendly and sustainable method, especially when the electricity is generated from renewable sources. Employing electrolysis for hydrogen production is currently limited due to its high cost and low efficiency. For improving the efficiency of the electrolyzers and significantly decreasing the cost, it is necessary to increase the rate of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by designing more active, stable, easy-to-fabricate electrocatalysts that are bifunctional and could be commonly fabricated for both the HER and OER.

The different stainless steel (SS) alloys are common and inexpensive Fe-Ni-based alloys that recently attracted attention not only as conductive substrates for HER and OER catalysts but as electrocatalysts themselves.1 Untreated SS is poorly active towards HER or OER and needs further modification, such as electrochemical anodization followed by high-temperature annealing in different gases, to reach an acceptable activity.2,3 Anodized SS annealed under O2 is shown to be catalytically active towards OER while annealing under H2 is required for HER activity.2,3

Herein, the effect of anodizing the SS316 and SS304 alloys at different potentials and bath compositions (H2O, NH4F, H2SO4, and H3PO4 contents) on the electrode morphology and surface composition will be discussed. The anodized SS electrodes are annealed in different thermal annealing atmospheres (O2, and H2) and annealing temperatures (400-800 Cº). The physical/chemical structure of as received SS (R-SS), the annealed SS (A-SS), the anodized SS (AN-SS), and the anodized-annealed SS (A-AN-SS) electrodes were evaluated using XRD, FESEM, EDS, and XPS. The electrocatalytic behavior of the SS electrodes towards HER and OER in Alkaline solutions is evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS). The results will be discussed thoroughly to correlate the electrochemical behavior to the electrode morphology and surface composition.

References:

S. Anantharaj et al., ACS Sustainable Chem. Eng., 6, 2498–2509 (2018).

A. K. Gomaa, B. S. Shaheen, G. E. Khedr, A. M. Mokhtar, and N. K. Allam, Energy Fuels, 36, 7025–7034 (2022).

M. Kim, J. Ha, N. Shin, Y.-T. Kim, and J. Choi, Electrochimica Acta, 364, 137315 (2020).
Development and Characterization of Microporous Layers on Porous Transport Layers for Proton Exchange Membrane Water Electrolyzers
Authors: Ouimet Ryan J. , Fortiner Serafina , Kulkarni Devashish , Zenyuk Iryna , Erb Bryan , Smeltz Andrew , Capuano Christopher
Published: September 2023

Porous transport layers (PTLs) serve many important functions for proton exchange membrane water electrolyzers. PTLs facilitate fluid transport towards and away from the anode catalyst layer, act as a mechanical support for the membrane, and provide electrical contact with the anode catalyst layer [1]. As a result, PTLs can greatly impact cell performance. However, while there has been an effort to improve similar gas diffusion layers in PEM fuel cells, there has not been a significant effort to optimize the overall form factor and design of PTLs for PEM water electrolyzers.

One of the primary concerns about the current design of PEM water electrolyzer PTLs is how they interact with the anode catalyst layer. In order to ensure proper fluid transport through the PTL, there is significant porosity throughout the PTL including at the anode interface. The large porosity and particle sizes of the PTL can cause heterogeneous contact of the PTL and catalyst layer thus reducing the catalyst utilization. Therefore, high catalyst loadings are required to obtain acceptable performance and durability. One method to address this concern would be to develop a metal microporous layer (MPL) that can be integrated onto a PTL at the anode interface that can withstand the high potentials at the anode while maintaining sufficient fluid transport. The MPL is fabricated using smaller metal particle sizes compared to the bulk PTL, which results in smaller pores creating a more uniform surface. The uniform surface and small pore sizes of the MPL provide a much higher interfacial contact area at the anode interface compared to a traditional PTL and would allow for a more uniform contact pressure across the anode interface. Higher interfacial contact will improve catalyst utilization and facilitate the reduction in anode catalyst loading, leading to reductions in overall electrolyzer capital cost [2].

In this work, prototype PTLs with metal MPLs are developed and tuned for optimal PEM water electrolyzer cell performance. The prototype PTLs with MPLs are characterized to understand how specific properties (thickness, porosity, tortuosity, etc.) influence cell performance. Electrochemical testing shows that adding an MPL at the anode/PTL interface can allow for acceptable cell performance with 90% lower anode catalyst loading compared to when using a baseline PTL.

References

[1] X.-Z. Yuan, N. Shaigan, C. Song, M. Aujla, V. Neburchilov, J.T.H. Kwan, D. P. Wilkinson, A. Bazylak, K. Fatih. The porous transport layer in proton exchange membrane water electrolysis: perspectives on a complex component. Sustainable Energy & Fuels, 6, (2022), 1824-1853.

[2] T. Schuler, J.M. Ciccone, B. Krentcher, F. Marone, C. Peter, T.J. Schmidt, F.N. Büchi. Hierarchically Structured Porous Transport Layers for Polymer Electrolyte Water Electrolysis. Advanced Energy Materials, 10, (2019), 1903216
Cathode Dry Operation of Anion Exchange Membrane Water Electrolysis
Authors: Ito Hiroshi , Wang Ruixiang , Hirose Riku , Kageyama Akane , Ishida Masayoshi , Ohashi Masato
Published: September 2023

The scale of hydrogen production from renewable energy sources is expected to increase worldwide in the future. Water electrolysis is a practical way to produce hydrogen from renewable energy sources. Water electrolyzers that use an anion exchange membrane (AEM) are expected to be new devices for hydrogen (H2) production that achieve high performance at low capital cost.

In AEM water electrolysis, “cathode dry operation” is sometimes applied. In this operation mode, water (electrolyte solution) is supplied only to the anode, not to the cathode where water is consumed in the reaction, keeping the cathode dry. In this way, relatively dry hydrogen can be extracted directly from the cathode, simplifying the hydrogen drying process. When water electrolyzers are installed in large quantities (over 1000 units), the cost of balance of plants (BOPs) is expected to account for the majority of system costs [1], and simplifying the BOPs are important for reducing system costs. However, it was observed that cathode dry operation would cause concentration overpotentials due to water diffusion through the membrane [2], which may limit the current density and membrane thickness to prevent cathode dry-out.

In this study, the effects of electrolyte composition and concentration on the water behavior in the membrane during cathodic dry operation on the electrolysis performance were quantitatively investigated.

AcknowledgementThis work was supported partly by the New Energy and Industrial Development Organization (NEDO) through the Advancement of Hydrogen Technologies and Utilization Project (P 14021). The authors wish to express their gratitude to Tokuyama Corporation for their support and helpful advice.

References

[1] Mayyas et al. Manufacturing cost analysis for proton exchange membrane water electrolyzers, NREL Technical report, NREL/TP-6A20-72740 (2019).

[2] R. Wang et al, Int. J. Hydrog. Energy, 47, 40835 (2022).
Phase-Controlled Synthesis of Nickel-Cobalt-Iron Sulfides By Electrodeposition for Efficient Oxygen Evolution Reaction
Authors: He Rong , Zhou Larissa , Luo Hongmei , Zhou Xiao-Dong , Zhou Meng
Published: September 2023

Water electrolysis is an appealing and sustainable technology to produce clean hydrogen fuels to resolve the energy and environmental crisis. The development of highly efficient, stable, and cost-effective electrocatalysts for oxygen evolution reaction (OER) is crucial for future sustainable energy systems. In this work, the synthesis of nickel-cobalt-iron sulfides deposited on Ni foam (NiCoFeS@NF) was successfully realized via a facile electrodeposition method. It was found that the deposition potentials could affect the phase and nanostructures of nickel-cobalt-iron sulfides. The electrocatalyst NiCoFeS@NF was obtained by applying a deposition potential of -1.2 V (vs. Ag/AgCl), which exhibits superior OER activity in alkaline media with overpotentials of 309 mV and 370 mV to reach the current densities of 20 mA cm-2 and 50 mA cm-2, respectively. The high OER activity of NiCoFeS@NF is mainly attributed to the collaborative advantages of trimetallic sulfides and the porous conductive Ni foam as substrate. The introduce of iron to nickel-cobalt sulfides could generate more active sites for OER, and Ni foam can provide large area for active sites and facilitate the mass transport during the electrochemical process. This study highlights the importance of the construction of trimetallic sulfides with heterostructures, providing insights into the OER performance.
Cobalt-Based Double Electrodeposited Catalysis for Efficient Oxygen Evolution in Anion Exchange Membrane Water Electrolysis
Authors: Han Sanghwi , Yoon Jeyong , Park Hyun S.
Published: September 2023

To produce green hydrogen using anion exchange membrane water electrolysis (AEMWE), high-performance oxygen evolution catalysts are needed. This study presents a novel strategy for increasing the intrinsic and extrinsic activities of Co-based catalysts through sequential electrodeposition of Fe and Co. In a single AEMWE cell, the double-electrodeposited Fe@Co electrode demonstrated a current density of 1,780 mA cm-2 at 1.8V at 50°C. The enhancement of catalytic activity was clearly observed in the Co-Fe pair, but it was not evident in Co catalyst synthesized with other metals. The discovery and analysis of double electroplating provide an innovative approach to non-noble-metal AEMWE, which is an important step toward cost-effective green hydrogen generation.
(Invited) Catalysts, Inks and Electrodes for PEM Water Electrolysis: Scalable Approach for Highly Performed Catalyst Layer Fabrication
Authors: Serov Alexey , Lyu Xiang , Creel Erin , Yu Haoran , Cullen David A. , Kariuki Nancy N. , Park Jaehyung , Myers Deborah J. , Rice Robin , Padgett Elliot , Mauger Scott A , Bender Guido , Foster Jayson , Pylypenko Svitlana
Published: September 2023

The majority of commercially available anodic electrocatalysts for Low Temperature PEM Water Electrolyzers are based on unsupported iridium-based materials. These electrocatalysts can be amorphous or crystalline metallic, oxidic, and/or hydroxide-derived compounds. The planned worldwide installations of electrolyzers (on the order of tens of Gigawatts per year) will require manufacturing of Membrane Electrode Assemblies (MEAs) via highly scalable methods, one of which is Roll-2-Roll production (R2R) [1, 2]. In contrast to spraying techniques, R2R requires the utilization of inks with a higher content of solids, which in the case of extremely dense Ir-based materials may cause a sedimentation of suspended electrocatalysts resulting in overall ink destabilization.

In the presented work a systematic study of ink stability with commercial IrO2 catalysts over a period of 14 days was performed. During this period of time the minimal redispersion of slurries was done to mimic realistic conditions of inks aging. The inks were comprehensively characterized by rheological measurements, zeta potential, particle size distribution (Dynamic Light Scattering) and inks density. A series of decal electrodes was fabricated using Baker bar coating approach (a model of R2R production) and coatings were characterized by contact angle, X-Ray Photoelectron Spectroscopy and Transmission Electron Microscopy.

Detailed electrochemical performance analysis including the separation of voltage losses [3] via Electrochemical Impedance Spectroscopy was performed to compare MEA performance with aging time.

Acknowledgements and Statements.

The authors acknowledge financial support from M2FCT and H2NEW consortia.

References.

[1] J. Sharma, X. Lyu, T. Reshetenko, G. Polizos, K. Livingston, J. Li, D. L. Wood, A. Serov "Catalyst layer formulations for slot-die coating of PEM fuel cell electrodes" Int. Journal of Hydrogen Energy 47 (2022) 35838-3585.

[2] E. B. Creel, K. Tjiptowidjojo, J. A. Lee, K. M. Livingston, P. R. Schunk, N. S. Bell, A. Serov, D. L. Wood III "Slot-Die-Coating Operability Windows for Polymer Electrolyte Membrane Fuel Cell Cathode Catalyst Layers" J. of Colloid and Interface Science 610 (2022) 474-485.

[3] A. Dizon et. al “Advanced Voltage Break Down Analysis by Statistical Open-Source Tool Case Study Based on Polymer Electrolyte Water Electrolysis”, ECS Abstract 242 (2022)
Al/Nb Co-Doped La2Ti2O7 As an Efficient Photocatalyst for H2 Production from Water
Authors: Irvine John , Zhang Hong
Published: September 2023

Al/Nb co-doped La2Ti2O7 has been prepared by a facile sol-gel method and investigated as the photocatalyst for H2 evolution. Optimal photocatalytic H2 production is achieved at the sample of La2Ti1.6Al0.2Nb0.2O7 with a production rate of ~37 µmolg-1h-1, which is ~ 2.5 fold higher than that of pristine sample. Further analysis the substitution of Al and Nb in B-site inhibits the growth of grain size, which helps increase the number of active sites. In addition, the introduction of Al and Nb decrease the Ti3+ species, which plays a negative role in photocatalysis as they could provide recombination spot for the photogenerated charges and thus shorten the electron lifetime.
(Invited) Solar Flow Batteries: Integrated Photoelectrochemical Solar Energy Conversion and Redox Flow Battery Systems
Authors: Jin Song
Published: September 2023

Due to the intermittent nature of sunlight, practical solar energy utilization systems demand both efficient solar energy conversion and inexpensive large scale energy storage. We have developed hybrid solar-charged storage devices called solar flow batteries (SFBs) that integrate photoelectrochemical solar cells with redox flow batteries (RFBs). In these devices, photoexcited carriers collected at the semiconductor-liquid electrolyte interface convert the redox couples to charge up the RFB without external electric bias; which can be discharged to generate the electricity when needed. By matching various silicon solar cells and tandem III-V solar cells (Chem
2018, 4, 2644) with various organic redox couples and optimizing the SFB device design, we improved their round trip solar-to-output electricity efficiency (SOEE) and eventually achieved a record SOEE of 20% with a 500-hour lifetime using high performance tandem perovskite/silicon solar cells (Nature Mater.
2020, 19, 1326). The design principles and the quantitative analysis model for voltage matching solar cells with RFBs (Acc. Chem. Res.
2020,
53, 2611) light up the pathways for achieving even better performance and stability yet maintaining a low cost, which would make these SFBs practical for standalone solar energy conversion and storage systems in remote off-grid locations.
(Invited) Semiconductor/Metal Photocatalytic Membrane for Hydrogen Generation
Authors: Kipkorir Anthony , Ealey Gavin , Costantino Federica , Kamat Prashant V
Published: September 2023

The membrane based assemblies that support gas diffusion electrodes in particular are at the heart of hydrogen fuel cells. The strategy of employing a membrane assembly with supported electrocatalysts can be extended to design photocatalytic membranes. The ion exchange property of a cation exchange membrane, Nafion, can be used to embed semiconductor nanoparticles (e.g., CdS, AgInS2). Similarly, bipolar membrane (BPM) can be employed to load the semiconductor photocatalyst on one side and metal electrocatalyst on the other side. The photocatalytic semiconductor/metal membrane between the two compartments of an H-cell, serves the dual purpose of generating hydrogen while separating the oxidation and reduction products. The talk will focus on preparing photocatalytic membrane and their effectiveness in solar fuel production.
(Invited) Water Oxidation Catalysis with Atomically Defined Active Sites on Nanostructured Materials for Solar Energy Applications
Authors: Brudvig Gary W.
Published: September 2023

Devising cost effective methods for efficiently capturing and storing solar energy is among the grand challenges of science (1). We are using insights from studies of natural photosynthetic systems (2) to develop bioinspired materials for photo-electrochemical water oxidation and solar fuel production by using molecular catalysts and dyes attached to mesoporous metal oxide photoanodes. Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. We are developing anchoring chemistry to attach molecular water-oxidation catalysts to metal oxide surfaces (3), which not only greatly increases the stability of the molecular catalyst but also improves the catalytic performance of the oxide material. Our progress on the development and characterization of molecular iridium, copper and manganese water-oxidation catalysts (4-5), along with their application for photoelectrochemical water oxidation (6) and solar fuel production, will be discussed.

Directing Matter and Energy: Five Challenges for Science and the Imagination, U.S. Department of Energy, Washington, DC, December 2007.

D.J. Vinyard and G.W. Brudvig, Annu. Rev. Phys. Chem. (2017) 68, 101.

J.L. Troiano, R.H. Crabtree and G.W. Brudvig, ACS Appl. Mater. Interfaces (2022) 14, 6582.

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Y. Zhao et al., Proc. Natl. Acad. Sci. U.S.A. (2018) 115, 2902.
Formation of Oxygen Vacancy Gradient TiO2 Via Photoelectrochemical-Driven “Self-Purification” Process
Authors: Kim Kwang Hee , Park Jong Hyeok
Published: September 2023

Solar water splitting by oxide semiconductors is the most ideal strategy for clean and sustainable hydrogen production. However, the application of oxide semiconductors is limited by their poor charge separation efficiency, which results from the short diffusion length of minority carriers and bulk charge recombination. Oxygen vacancy (Vo) is a unique and crucial tool in the metal oxide semiconductor, which not only is one of the intrinsic defects but plays a significant role to modulate their optical, physical, and catalytic properties. For instance, the introduction of oxygen vacancy can suppress electron-hole recombination for efficient solar water splitting. However, it remains challenging to control oxygen vacancies due to their random formation and moving in the lattice of the nanostructure.

In this work, we present a photoelectrochemical (PEC) driven “self-purification” approach for the formation of oxygen vacancy gradient (ΔVo) by reconstructing the disorder overlayer from the TiO2 nanowire photoanode under long-term PEC operation using “self-purification” mechanism. The presence of Vo in oxygen vacancy gradient TiO2 (ΔVo-TiO2) was clearly confirmed by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectra. Also, high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS) analysis showed that the gradient distribution of Vo forms in ~9.5 nm-thickness range of ΔVo-TiO2.

After the “self-purification” process, the photocurrent density of ΔVo-TiO2 doubles compared to that of pristine TiO2 at the 1.23 V vs RHE. Also, we demonstrated that Vo improved the charge separation in bulk region by charge carrier dynamics with time-correlated single-photon counting (TCSPC) analysis. Furthermore, ΔVo-TiO2 exhibits ~95% charge transport efficiency, which is associated with bulk recombination. These results indicate the ~95% photon within the absorption range can be converted to charge. Lastly, we verified the electronic structure of ΔVo-TiO2 by density functional theory (DFT) calculations. ΔVo-TiO2 forms a cascade of energy gradients along the bulk region, which can polarize the charges to form a built-in electric field that thermodynamically boosts charge carrier migration and suppresses bulk charge recombination.

In conclusion, we suppose that the key role of Vo in the bulk region in a metal oxide photoanode is critical to enhancing charge separation in TiO2. Therefore, our demonstration can fully resolve the conventional efforts to establish the optimized Vo for photocatalyst and offer a feasible approach for gradient doping semiconductors synthesis.
Observation of Support-Dependent Water Oxidation Kinetics on Molecularly-Derived Heterogeneous Ir-Oxide Catalysts
Authors: Zhang Hongna , Liu Tianying , Dulock Nicholas , William Benjamin , Wang Yuanxing , Chen Boqiang , Wikar Haden , Wang David , Brudvig Gary W. , Wang Dunwei , Waegele Matthias M.
Published: September 2023

Heterogeneous water oxidation catalysis is central to the development of renewable energy technologies. Understanding the material properties that determine water oxidation activity is critically important for the design of efficient and durable water oxidation catalysts. The electronic structure and surface chemistry of the catalyst influence the accumulation of oxidative charge (holes) on catalytically active sites. Hole distribution dynamics and molecular structure of the active sites are generally accepted to jointly determine activity. However, these properties are typically inherent to materials; it has been difficult to independently tune them on most heterogeneous catalysts, hindering the development of an understanding of their relative influence. Herein, heterogenized dinuclear Ir catalysts (Ir-DHC) supported on different oxides were employed to overcome this challenge. It was found that at low temperatures (288-298 K), the photocatalytic activities of Ir-DHC on indium tin oxide (ITO) and CeO2 supports are comparable within the studied range of fluences (62-151 mW/cm2). By contrast, at higher temperatures (310-323 K), Ir-DHC on ITO exhibits a ∼100% higher water oxidation activity than on CeO2. The divergent activities under these conditions were attributed to the distinct abilities of the supporting substrates to redistribute surface holes. Specifically, ITO is relatively efficient in distributing photogenerated holes between Ir-DHC active sites, whereas CeO2 exhibits sluggish hole redistribution because of its reducibility, thereby limiting hole accumulation at Ir-DHC active sites. The temperature dependence was explained by a temperature induced switch in the rate-determining step of the reaction. These findings highlight the critical role of the supporting substrate in determining the turnover at active sites of heterogeneous catalysts.
(Invited) Photoelectrochemical CO2 Reduction (CO2R) with Si- and III-V Based Systems
Authors: Jaramillo Thomas F.
Published: September 2023

One means to produce carbon-based fuels and chemicals in a sustainable manner is by means of solar photoelectrochemical (PEC) CO2 reduction (CO2R). Many R&D challenges need to be addressed in order to advance this technological area toward commercial applications. This paper will focus on developing catalytic interfaces onto silicon and III-V semiconductor based systems, and exploring the impacts of various microenvironments and reaction conditions on efficiency, selectivity, and durability. Interfaces based on copper-based catalysts will be a general theme, leading to a range of multi-carbon products by means of PEC CO2R.
(Invited) Metal Organic Frameworks for the Storage, Separation, and Purification of Gaseous Fuels
Authors: Thonhauser Timo
Published: September 2023

We have seen a surge of interest in metal organic frameworks (MOFs) over the past decades with more than 100,000 structures reported today. This interest is based on the modular building-block nature of their structure, which makes them tunable and widely applicable to many applications. Of particular interest is the storage, separation, and purification of gaseous fuels with MOFs as a much-needed alternative to the energy-intense processes currently in use. My talk will focus on results of a variety of MOFs that have been obtained by a close integration of synthesis, in situ vibrational spectroscopy, and ab initio materials modeling. In particular, we report on the development and characterization of four MOFs for the purpose of separating linear, mono, and dibranched alkane isomers through selective molecular sieving, which is of significant value in the petrochemical industry. The separation of such alkane isomers is a challenging and important industrial process for the production of premium gasoline, blending components with high research octane number. I will also show recent results that point towards non-standard kinetics in certain separation processes in MOFs as well as results for ultramicroporous MOFs that have the ability to effectively perform separations in the presence of water.
Mechanisms for Charge Selectivity on Semiconducting Photocatalyst Particles
Authors: Kaufman Aaron James , Shen Meikun , Boettcher Shannon W.
Published: September 2023

Overall-water splitting on photocatalysts provides a direct-unassisted path in the conversion of solar energy to chemical energy. Optoelectronic properties (absorbing incident light with long excited state lifetimes) and carrier selective contacts (transporting and transferring the desired electronic carrier to the targeted redox active species) are two key parameters that govern photocatalyst behavior. However, the advantageous small geometry of the highest achieving photocatalysts makes measurement of their carrier selective contacts difficult. Additionally, several mechanisms that enable high energy-conversion efficiencies and large gradients in free energy manifest only at the nanoscale at individual nanoparticle sites. SrTiO3 has been extensively studied and shown to split water with high quantum yields when decorated with HER and OER catalysts. SrTiO3 is used, in this work, as a model system to study mechanisms for charge selectivity on overall-water splitting photocatalyst particles.

Here, we use three sample geometries to measure local, facet, and catalyst-dependent, electrochemical driving forces and their synergistic enhancement of carrier selectivity, (single crystal planar (b), single crystal co-facet exposed planar (a), facetted nanoparticles (c) loaded with OER and HER catalysts [{Pt/CrO3, Rh/CrO3} and CoOOH respectively]). We use ex-situ conductive atomic force microscopy to individually interrogate the electrical properties of nano-scale catalyst/semiconductor junctions decorated on facet-engineered surfaces of SrTiO3. Supporting experiments of SECM and Operando AP-XPS will be used to measure the charge carrier selectivity when an electrolyte is present and connect the ex-situ characterization observations to operando conditions. In summary, these findings demonstrate the underlying mechanisms and the degree that they play, enabling directed research of photocatalyst systems under the two dominant engineering conditions, high optoelectronic properties and charge selective contacts.

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(Invited) An Artificial Leaf with a Solar-to-H2O2 Conversion Efficiency
Authors: Park Jong Hyeok
Published: September 2023

Millions of families around the world remain vulnerable to water scarcity and have no access to drinking water. Advanced oxidation processes (AOPs) are an effective way towards water purification with qualified reactive oxygen species (ROSs) while are impeded by the high-cost and tedious process in either input of consumable reagent, production of ROS, and the pre-treatment of supporting electrolyte. Herein, we couple solar light-assisted H2O2 production from water and photo-Fenton-like reactions into a self-cyclable system by using an artificial leaf, achieving an unassisted H2O2 production rate of 0.77 μmol/(min·cm2) under 1 Sun AM 1.5 illumination. Furthermore, a large (70 cm2) artificial leaf was used for an unassisted solar-driven bicarbonate-activated hydrogen peroxide (BAP) system with recycled catalysts for real-time wastewater purification with requirements for only water, oxygen and sunlight. This demonstration highlights the feasibility and scalability of photoelectrochemical technology for decentralized environmental governance applications from laboratory benchtops to industry.
Growth and Photoelectrochemical Characterization of Epitaxial ZnTe Photocathodes for Carbon Dioxide Reduction
Authors: Shiau Lily , Atwater Harry A.
Published: September 2023

Harnessing solar energy to drive photocatalytic carbon dioxide reduction reactions (CO2RR) provides an appealing pathway to generate hydrocarbon and oxygenated fuels without an external power source. Zinc telluride (ZnTe) is a II-VI semiconductor which has been identified as a promising photocathode material due to its suitable band gap alignments to CO2 reduction reaction potentials, chemical stability, and strong p-type character. Using molecular beam epitaxy (MBE), single crystal and epitaxial layers are synthesized to gain a deeper understanding of fundamental charge transport and reactivity mechanisms between the single crystal ZnTe thin film and the CO2-saturated electrolyte. These findings are of fundamental interest and are also critical to the design of efficient tandem solar fuels generators for unassisted photoelectrochemical CO2R. Epitaxy allows for highly controlled doping of the thin films over a large range of carrier concentrations. This work focuses largely on the synthesis and characterization of nitrogen doped p-type ZnTe via MBE. Films grown in the temperature range of 340–360ºC on GaAs of (100) orientation with a 200 nm undoped ZnTe buffer layer and a 100 nm doped ZnTe layer have been characterized by RHEED, XRD, AFM, and Hall effect measurements. Doping concentrations between 1020 cm-3 and 1018 cm-3 have been achieved. Dark current-voltage measurements have been used to indicate stability of the electrode in aqueous conditions in less than -0.5 V vs RHE. Future work will include further investigations into carrier dynamics via transient absorption spectroscopy and continual development of a tandem, ZnTe-based photocathode.
Tailoring Microenvironment in Bilayer Electrode with Copper and Silver Nanocatalysts for Bicarbonate Electroreduction to Multicarbon Products
Authors: Lee Jungkuk , Liu Hengzhou , Li Wenzhen
Published: September 2023

As compared with CO2 electrolyzers, bicarbonate electrolyzers can achieve direct conversion of CO2 captured solutions to higher-valued chemicals, that can bypass energy-intensive steps of CO2 regeneration and pressurization processes. However, most previous studies have only reported single carbon chemicals (i.e., CO, formate, CH4) as the major products so far. In this presentation, we will present direct electro-reduction of potassium bicarbonate (KHCO3) to multicarbon (C2+) products (i.e., acetate, ethylene, ethanol, propanol) using rationally designed bilayer of Cu and Ag nanosized catalysts. The in-situ generated CO2 was first reduced to CO on the Ag layer, followed by CO reduction to C2+ products on the Cu layer benefiting from locally high concentration of CO. Through optimizing the configurations, compositions, ionomer types, and local hydrophobicity of the bilayer electrode, we have created the favorable microenvironment (high local pH, low water content, etc.) to increase bicarbonate conversion to C2+ products with a largely suppressed hydrogen evolution reaction, and a remarkable C2+ FE of 41.6% at a current density of 100 mA cm−2 was achieved.