bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aqueous Polysulfide-Based Redox Flow Battery with Soluble Molecular Catalysts
Authors: Lei Jiafeng , Lu Yi-Chun 
Published: August 2024

Aqueous polysulfide-based redox flow batteries (RFBs) are promising for large-scale energy storage applications due to their low cost and high safety1. However, polysulfide negolyte suffers from poor kinetics, resulting in low operating current density and low energy efficiency2-5. Herein, we proposed a molecular catalyst strategy to transfer the sluggish electrochemical polysulfide reduction reaction to a fast chemical reaction via homogeneous catalysis. Inspired by the electron transport chain in the respiratory process, we selected riboflavin sodium phosphate (FMN-Na) as the molecular catalyst to transfer electrons from electrode to polysulfide with the disulfide bond cleavage6. The reaction rate (or turnover frequency) kobs is determined to be 33 s–1 at 1 M K2S4 solution, and this spontaneous chemical electron transfer process is verified by ultraviolet-visible light spectroscopy. In the polysulfide-ferrocyanide (S-Fe) RFB, the overpotential is dramatically decreased from over 800 mV to 241 mV at 30 mA cm–2 with the assistance of FMN-Na as the molecular catalysts. The catalyzed S-Fe RFB and polysulfide-iodide RFB showed stable operation for over 1,000 cycles at 40 mA cm–2. This work offers a simple but effective method to resolve the bottleneck for aqueous polysulfide-based RFBs, and such a homogeneous catalysis strategy may shed light on other flow battery systems with poor kinetics. We will combine operando spectroscopic techniques and theoretical calculation to discuss the possible reaction mechanism and intermediate.
Acknowledgment
This work is supported by two grants from the Research Grants Council (RGC) T23-713/22-R and RFS2223-4S03.
Reference

Y. Yao, J. Lei, Y. Shi, F. Ai and Y.-C. Lu, Nat. Energy, 2021, 6, 582-588.

Z. Li and Y.-C. Lu, Nat. Energy, 2021, 6, 517-528.

X. Wei, G.-G. Xia, B. Kirby, E. Thomsen, B. Li, Z. Nie, G. G. Graff, J. Liu, V. Sprenkle and W. Wang, J. Electrochem. Soc., 2015, 163, A5150.

Z. Li, M. S. Pan, L. Su, P.-C. Tsai, A. F. Badel, J. M. Valle, S. L. Eiler, K. Xiang, F. R. Brushett and Y.-M. Chiang, Joule, 2017, 1, 306-327.

J. Lei, Y. Yao, Y. Huang and Y.-C. Lu, ACS Energy Lett., 2023, 8, 429-435.

J. Lei, Y. Zhang, Y. Yao, Y. Shi, K. L. Leung, J. Fan and Y.-C. Lu, Nat. Energy, 2023, DOI: 10.1038/s41560-023-01370-0.
Sodium Polysulfides As Catholytes for Redox Flow Batteries
Authors: Zuleta Suarez Ernesto Camilo , Lehmann Michelle , Yang Guang , Self Ethan 
Published: August 2024

Redox flow batteries based on sodium polysulfide (Na2Sx) show promise due to sodium's high solubility in organic solvents (e.g., diglyme. However, when x is lower than 5, sodium polysulfide exhibits low solubility (less than 0.1 molal), limiting the nominal capacity of this redox-active material. Sodium phosphorothioate complexes, Na2P2Sx, have been reported as an alternative to Na2Sx. Incorporating phosphorus into the polysulfide structure improves their solubility in organic solvents, specifically in diglyme.
This presentation will describe the synthesis and characterization of sodium phosphorothioate complexes (Na2P2Sx, where x = 6, 7, 8, and 9) for nonaqueous redox flow batteries. The structure of these materials is explored using 31P NMR and 23Na NMR spectroscopy, Raman spectroscopy, and X-ray diffraction analysis. Overall, 31P NMR results indicate that P5+ is tetrahedrally coordinated in all structures and that Na-P-S compounds have a common PS3- moiety. Ongoing efforts are aimed at providing more precise assignments to the 31P bands and correlating these findings with complementary structural information obtained from 23Na NMR and Raman spectroscopy.
Electrochemical properties of sodium polysulfide and sodium thiophosphate catholytes, specifically Na2S8 and Na2P2S8, were also compared using CV. The voltammogram of Na2S8 revealed two clear redox reactions in the 1.5-3 V range vs. Na/Na+ due to a multi-step electron transfer process involving the S2-/S0 redox center. In contrast, Na2P2S8 exhibited a larger peak separation (~2 V) and lower peak currents at a given scan rate, potentially indicating a significant activation barrier associated with the rearrangement of the thiophosphate’s polyanionic structure during reduction/oxidation. Despite the substantial voltage hysteresis, Na2P2S8 displayed stable cycling performance, with a slight increase in peak current after 100 cycles. This behavior is consistent with measurements on RFBs containing a Na2P2Sx catholyte, where an electrode activation process increased the cell’s reversible capacity, likely due to subtle changes in the electrode’s surface chemistry during repeated oxidation/reduction. Finally, preliminary flow cell measurements on Na2P2S7 catholyte show reversible voltage profiles after the formation step with deep discharge. Overall, this presentation demonstrates that Na-P-S catholytes represent a promising material for high energy, low-cost redox flow batteries.
Acknowledgements
This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the U.S. Department of Energy through the Energy Storage Program in the Office of Electricity.
Functionalisation of Carbon Catalyst Support By Plasma Treatment for PEMFC Cathode
Authors: Blanchard Pierre-Yves , Parnière Alice , Donzel Nicolas , Cavaliere Sara , Rozière Jacques , Jones Deborah J. 
Published: August 2024

Proton exchange membrane fuel cell (PEMFC) is one promising electric device to replace the combustion engine using fossil fuel especially for heavy-duty transport. One of the main issue for the widespread of this technology on the European roads is the cost and degradation of their components over time. The sluggish reduction of dioxygen at the cathode require high amount of noble metal (i.e. platinum). Under PEMFC operating conditions, carbon as catalyst support is unstable.
This study presents a new approach to improve the stability of the cathode components (catalyst, carbon support and ionomer) thanks to the enhancement of the interaction between the three entities and to reduce carbon corrosion. Plasma treatment were performed on different carbon black sources (different surface area and porosity) to functionalize their surface by nitrogen function using different gas. The modified carbons were characterized by TEM, XPS, Raman spectroscopy, calorimetry, elemental analysis. The plasma treatments were reproducible and allow controlling the degree of functionalisation. The nitrogen doped carbons were catalysed by platinum nanoparticles. A better dispersion of the nanoparticles was observed by TEM showing the interest of the plasma treatment. Cyclic voltammetry were performed and a better catalytic activity toward the electrochemical reduction of O2 was observed.[1] Isothermal titration calorimetry experiments were carried out and show an improved interaction between the nitrogen functionalized carbon and the ionomer.
[1] A. Parnière, P.-Y. Blanchard, S. Cavaliere, N. Donzel, B. Prelot, J. Rozière, D.J. Jones, Nitrogen Plasma Modified Carbons for PEMFC with Increased Interaction with Catalyst and Ionomer, J. Electrochem. Soc.
169 (2022) 044502.

Figure 1
Tuning the Bifunctional Properties of Cell Reversal-Tolerant Ir-Pt Electrocatalysts for HOR and Oer
Authors: Seidel Philipp , Ioselli Giulia , Blaseio Sonja , Yoon Sooyoung , Hasché Frédéric , Oezaslan Mehtap 
Published: August 2024

Hydrogen starvation is still a big problem in PEM fuel cells [1]. In order to provide protons and electrons to the cathode during H2 starvation, the carbon oxidation reaction (COR) takes place at the anode [2]. To solve this issue, there are three main strategies: (i) utilization of corrosion resistant support materials, (ii) integration of extensive and complex system mitigation strategies and finally (iii) the addition of co-catalyst to promote the oxygen evolution reaction(OER) instead of COR. [3, 4]
In this work, platinum-iridium (PtIr) nanoparticles (NPs) have been designed as a novel bifunctional electrocatalysts to accelerate either the hydrogen oxidation reaction (HOR) or the OER depending on the reaction conditions. Our catalyst concept is the combination of both functionality (HOR and OER) in single Pt-Ir alloy nanoparticles (NPs) deposited on the same support material. The Pt-Ir NPs with Pt:Ir ratios of 1:1 and 3:1 were prepared by two different (colloidal and wet-impregnation) routes. Very interestingly, the oxidation states of platinum and iridium as well as the particle size strongly vary depending on the synthesis route. More precisely, the wet-impregnation enables preparing Pt-Ir NPs of 3 – 4 nm size and mainly in the metallic state, while strongly oxidized NPs with ~2 nm size are produced by colloidal route. Despite the different oxidation states and particle sizes, the Pt-Ir NPs show considerable activity for HOR and OER compared to pure commercial Pt/C and IrOx catalysts. Very interestingly, the bifunctionality of these Pt-Ir is highly reversible and is robust during accelerated stress tests. Operando Quick-X-ray Absorption Near Edge Structure (XANES) spectroscopy were performed to provide fundamental insights into the reversibility and catalytically active states of these bifunctional catalysts under the working conditions by jumping with the potential between HER and OER within few seconds. The combination of operando XANES, RDE and MEA data show that the bifunctional approach is a promising way to improve the cell reversal-tolerant properties of anode catalyst materials compared to the state-of-the-art Pt-IrOx catalyst materials.
References:
[1] P. Mandal et al, J. Power Sources 2018, 397, 397-404.
[2] C.Qin et al, Catalysts 2016, 6, 197.
[3] M. Tovini et al, J. The Electrochem. Soc. 2021, 168, 06452.
[4] R. Marić et al., J. The Electrochem. Soc. 2020, 124520.
Breaking through the State-of-the-Art Frontier in Oxygen Electrocatalysis: Geometry Adaptive Catalysts (GACs)
Authors: Cepitis Ritums , Ivanistsev Vladislav , Kongi Nadezda 
Published: August 2024

The grand challenge in oxygen electrocatalysis lies in overcoming scaling relations. The theoretical activity volcano positions the ideal catalyst at the apex. However, the OH–OOH scaling relation determines a linear path on the volcano surface that limits the activity. The current state-of-the-art (SOTA) in modeling confirms this scaling relation, at the same time it hinders the experimental development of novel oxygen reduction reaction (ORR) catalysts, impeding progress in sustainable energy solutions. To address this challenge, we propose to use the geometry effect and introduce the concept of Geometry Adaptive Catalysts (GACs).[1]
The geometry effect, based on preliminary research, involves changing catalytic activity by adjusting the adsorption energy of intermediates through the control of catalyst geometry. Our goal is to break through the SOTA frontier for ORR by synthesizing GACs and supporting our efforts with theoretical and computational modeling of the geometric effect. In this work we aimed to utilize the geometry effect by synthesizing GACs with various controlled structures, including specific intersite distances, and variable curvature. This enables precise control of catalyst geometry, allowing manipulation of catalytic activity and overcoming scaling relations. Key geometric parameters, namely inter-site distance, curvature, and specific stabilizations of ORR intermediates, are explored to test our hypothesis: Controlling catalyst geometry adjusts the ORR mechanism and adsorption energies of intermediates, enabling the switching, pushing, and even bypassing of scaling relations.
This approach holds promise for substantial improvements in environmental sustainability and human life quality, with broad applicability to various electrocatalytic reactions beyond ORR.

References

[1] R. Cepitis, V. Ivaništšev, J. Rossmeisl, N. Kongi, Geometry-adaptive catalysts for elevating towards the ideal oxygen electrocatalysis, (2023) preprint. DOI: 10.26434/chemrxiv-2023-g63m2-v2
[2] R. Cepitis, N. Kongi, J. Rossmeisl, V. Ivanistsev, Surface curvature effect on Dual-Atom site oxygen electrocatalysis. (2023) ACS Energy Letters, 8, 1330-1335. DOI: 10.1021/acsenergylett.3c00068
(Invited) Efficient Ternary Nicuw Hydrogen Oxidation Catalysts for Anion Exchange Membrane Fuel Cells
Authors: Liu Guimei , Shao Minhua 
Published: August 2024

Anion exchange membrane fuel cells (AEMFCs) offer prospective approaches to replace proton exchange membrane fuel cells via cost-effective catalysts and membranes. While significant progress has been made in efficient nonnoble electrocatalysts for oxygen reduction reaction in alkaline media, the hydrogen oxidation reaction (HOR) in the alkaline condition still relies on high platinum loadings to compensate for its sluggish kinetics. Therefore, developing efficient non-noble metal electrocatalysts with Pt-like HOR performances in alkaline electrolytes is highly desired but a great challenge.
The hydrogen binding energy (HBE) has been identified as the primary descriptor for the HOR. Additionally, an unfavorable hydroxide binding energy (OHBE) is considered the rate-determining step in the Volmer reaction to generate water. Therefore, an ideal catalyst for HOR should achieve a balance between HBE and OHBE. However, despite being a promising non-noble metal, nickel exhibits excessively high HBE and lacks active sites for hydroxide adsorption, which hinders its further application in the real fuel cell.
In this work, NiW was successfully deposited onto Cu to form a ternary Ni-Cu-W alloy catalyst by a chemical reduction method. Through XPS spectra, we found the charge transfer from Ni to W to give Ni a higher valence state, contributing to a weakened hydrogen binding energy. Electrochemical measurements observed Ni-Cu-W exhibit an kinetic activity with 117.9 mA/mgNi at η= 50 mV, which is the highest among the reported platinum group metal-free catalysts. Ni-Cu-W alloy showcased robust stability, with no activity degradation during an accelerated long-term durability test between a low overpotential (-0.1 ~ 0.1 V, vs RHE) with 10,000 cyclic voltammetry scans and only a 5.7% activity loss at η= 50 mV when applying more larger overpotential (-0.1 ~ 0.2 V) with the same cycles. When assembled with this catalyst as anode and Pt/C as cathode, it delivered a peak power density of 289 mW/cm2. Both experimental and theoretical studies were conducted to gain insights into the catalyst's enhanced performance. Our findings revealed that the incorporation of Cu into the catalyst significantly weakened the adsorption of hydrogen species, while simultaneously lowering the energy barrier required for the absorption of hydroxide ions. These key observations might shed light on the underlying mechanisms responsible for the catalyst's improved activity and stability.
Machine Learning Accelerated Identification of Bifunctional Active Sites in Metal-Organic Framework Derived Metal Oxide Heterostructures for High-Performance Zinc-Air Batteries
Authors: CHOI Jong Hui , Kim Dong Won , Chun Hoje , Kang Jeung Ku 
Published: August 2024

The demand for electrochemical energy storage (ESS) systems and their market size has drastically increased in many applications ranging from portable devices through electric vehicles to large-scale grid systems over the past decades. Yet, a more advanced ESS is required due to the safety issues and limited energy density of currently commercialized lithium-ion batteries (LIBs) for wide and matured applications. As a solution to this challenge, zinc-air batteries (ZABs) have gained tremendous attention due to their high energy density, low cost, environmental friendliness, and much lower fire risk characteristics. ZABs utilize oxygen from the atmosphere at their cathode during discharge, where the atmospheric oxygen is reduced to hydroxide via an oxygen reduction reaction (ORR). On the other hand, hydroxide is released as oxygen via oxygen evolution reaction (OER) during charge. The fact that oxygen is drawn directly from the air enables high gravimetric and volumetric energy densities of ZABs compared to those of commercial LIBs. However, the sluggish kinetics of the four-electron transfer steps in ORR and the mass transport of oxygen in OER remain major challenges for the practical application of ZABs. Meanwhile, precious metal-based catalysts such as Pt/C and RuO2 are known to have good catalytic activity towards ORR and OER. However, the integration of different catalysts into the same cathode is very difficult. Additionally, the high cost and natural scarcity of novel metals limit their usage for practical applications.
We synthesized a bifunctional CoO/Mn3O4 heterostructure (CMH) OER/ORR electrocatalyst which was derived from metal-organic framework (MOF) for excellent activities in ZABs. The CMH cathode exhibited high ORR and OER performances, as demonstrated by the higher ORR current density than that of the Pt/C catalyst as well as the low OER overpotential exceeding those of the RuO2 catalyst. Remarkably, atomic structures of the CMH were elucidated using global optimization of genetic algorithm integrated with the machine learning force field. By adopting first-principles electronic structure calculations, we further revealed the charge transfer and active sites for both reactions in the identified heterojunction. Furthermore, assembling CMH cathode and Zn metal anode into a ZAB full-cell configuration achieves a ~5.5-fold higher energy density of 879 Wh kg-1 exceeding those of commercial lithium-ion batteries (LIBs), a high-discharge outstanding power density that is 1.39 times higher than novel metal catalysts, and robust cycle stability with negligible voltage decay which is far superior to that of benchmark Pt/C+RuO2 electrocatalysts.
Functionalization of Organic Redox Mediators to Mitigate Crossover in Chemically Regenerative Redox Fuel Cells
Authors: Bacabe Rémi , Jones Deborah J. , Rozière Jacques , Donzel Nicolas , Dupont Marc , Lecoeur Frederic , Cavaliere Sara , Niebel Claude , Blanchard Pierre-Yves 
Published: August 2024

Chemically regenerative redox fuel cells are promising alternatives to conventional PEMFCs as stationary energy conversion devices since they avoid platinum-based catalyst at the cathode for the oxygen reduction reaction thanks to the chemical oxidation of the mediators in an external tank[1]. The requirements for the mediator are a high standard redox potential (0.6 V vs. SHE), high diffusion coefficient and fast electron transfer kinetic to reach high power density. Furthermore, the mediator must be stable in acidic medium (pH<1) and at the operating temperature of the system (40 to 80°C). The durability of the system will depend on the physico-chemical properties as well as on the chemical reactivity with oxygen in order to regenerate the reduced redox mediator. Loss of performance over time can be attributed to the crossover of the solubilized species from the cathode to the anode side and to the chemical instability over redox reaction. Crossover phenomena are commonly observed in aqueous organic redox flow battery using (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) as reactive species[2].
In this study, several mediators based on TEMPO with different PEG chain length are synthesized and characterized. The goal of the functionalization is to mitigate the crossover rate of the mediator through the membrane. Fuel cell tests were performed giving access to performance and power decrease over time. For a deeper understanding of the origin of performance losses, an ex situ electrochemical setup was developed to assess the impact of functionalization toward crossover.
[1] Singh R, Shah AA, Potter A, Clarkson B, Creeth A, Downs C, et al. Performance and analysis of a novel polymer electrolyte membrane fuel cell using a solution based redox mediator. J Power Sources 2012;201:159–63. https://doi.org/10.1016/j.jpowsour.2011.10.078.
[2] Small LJ, Pratt HD, Anderson TM. Crossover in Membranes for Aqueous Soluble Organic Redox Flow Batteries. J Electrochem Soc 2019;166:A2536–42. https://doi.org/10.1149/2.0681912jes.

Figure 1
Investigating the Impact of Air Pollutants on Fuel Cell Performance and Durability: Experimental and Modeling Approaches
Authors: Abd El Kader Ahmad , Marchand Marielle , Affonso Nóbrega Pedro Henrique , Beauger Christian 
Published: August 2024

Fuel cells hold immense promise as efficient and sustainable power sources for transportation and stationary applications. However, their operation can be severely impacted by air pollutants, particularly sulfur dioxide (SO2) and nitrogen oxides (NOx). These pollutants can adsorb onto the platinum catalyst, leading to a decrease in fuel cell performance and durability.
In this study, we investigate the impact of SO2 and NO2 on PEM fuel cell performance and durability. The contamination tests were carried out at a constant current density of 0.5 A.cm−2, and they consisted of four steps: a pre-poisoning step to evaluate initial performance (15-16 h), poisoning step (50 h), self-recovery in a pure air stream (20-21 h) and a driven CV-induced recovery. Electrochemical characterizations were carried out at the end of each step (Polarization curve, Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and H2 Crossover). Our initial investigation involved contaminating a single fuel cell with a low concentration of 0.1 ppm of sulfur dioxide (SO2). Remarkably, this resulted in a 1.1% decrease in cell voltage. Building on this foundation, our ongoing research aims to delve deeper into the impact of individual pollutant concentrations (SO2 and NO2) and their combined effects, considering varying temperatures and current densities to simulate real-world conditions.
Simultaneously, a comprehensive model is being developed using Simscape in Matlab. The model accounts for the pollutants either as single-component gases or as a mixture. For single-component gas adsorption, the Langmuir Isotherm model is employed. To capture the competitive adsorption of SO2 and NO2 on platinum in gas mixtures, we are testing the Modified Competitive Langmuir Isotherm Model. The model will further be calibrated and validated using the experimental results.
This combined experimental and modeling approach will provide a comprehensive understanding of the impact of air pollutants on fuel cell performance and durability. The insights gained from this study can inform the development of mitigation strategies and enhance the robustness of fuel cells in real-world applications as well as the sizing of a filter.

Figure 1