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14. Structure-transport relationships of poly(aryl piperidinium) anion-exchange membranes: Eeffect of anions and hydration

Author

Luo, Xiaoyan, Rojas-Carbonell, Santiago, Yan, Yushan, and Kusoglu, Ahmet

Subjects
Engineering, Macromolecular and Materials Chemistry, Materials Engineering, Chemical Sciences, Chemical Engineering, Chemical sciences
Abstract

Hydroxide-exchange membrane (HEM) fuel cells are emerging energy conversion technologies. A significant effort has been expended to develop new HEMs with enhanced transport functionality, which has driven the need for understanding how transport of hydroxide and other anions in these membranes is related to hydration and nano-morphology. In this work, we report the results of a systematic study on poly(aryl piperidinium)-based on terphenyl (PAP-TP-85), a HEM that previously showed promising fuel cell performance and durability. Membrane water uptake and anion conductivity in liquid and vapor water, as well as the impact of counter-anion forms on these properties, are investigated and compared with a commercial anion exchange membrane (AEM), Fumasep FAA3, and proton-exchange membranes (PEMs), Nafion and sPEEK. Different water uptake in liquid vs. saturated vapor is observed for both AEMs (i.e., PAP and FAA3), indicating Schroeder's paradox, regardless of anion form. Morphology of AEMs examined via small-angle X-ray scattering (SAXS) shows weak phase-separation, regardless of hydration level and anion type, which is attributed to the reduced chemical dissimilarity between the backbone and ionic moieties. Despite both AEMs' amorphous nanostructure, PAP-AEM has a higher ion conductivity than FAA3. Water content plays a more significant role than does temperature in controlling the anion conductivity in water vapor. In liquid water, normalized conductivity shows a universal dependence on hydration, regardless of the anion form. Moreover, in water vapor, conductivity is influenced more by ion mobility than ion concentration, and depends mainly on hydration. Thus, ion transport in disordered AEMs is governed primarily by hydration, in contrast to phase-separated ionomers, where ion transport is governed by nanostructure-hydration interplay. This study demonstrates the importance of hydration level and ion mobility for anion transport in amorphous AEMs and provides an understanding of parameters governing their transport properties.

Published
2020

28. Regulating the Third Metal to Design and Engineer Multilayered NiFeM (M: Co, Mn, and Cu) Nanofoam Anode Catalysts for Anion‐Exchange Membrane Water Electrolyzers.

Author

Yang, Xiaoxuan, Liang, Jiashun, Shi, Qiurong, Zachman, Michael J., Kabir, Sadia, Liang, Junwu, Zhu, Jing, Slenker, Benjamin, Pupucevski, Max, Macauley, Natalia, Kropf, A. Jeremy, Zeng, Hao, Strasser, Derek, Myers, Deborah J., Xu, Hui, Zeng, Zhenhua, Yan, Yushan, and Wu, Gang

Subjects
COPPER, ION-permeable membranes, PLATINUM group, ELECTROLYTIC cells, GREEN fuels, OXYGEN evolution reactions, CATALYSTS, IRON-nickel alloys, TRACE metals
Abstract

Alkaline anion‐exchange membrane water electrolyzers (AEMWEs) for green hydrogen production have received intensive attention due to their feasibility of using earth‐abundant platinum group metal (PGM)‐free catalysts. Herein, the third metal is incorporated into NiFe‐based catalysts to regulate their electronic structures and morphologies, aiming to achieve sufficient oxygen evolution reaction (OER) activity and performance in AEMWEs. The ternary NiFeM (M: Cu, Co, or Mn) catalysts are featured with multiple layered structures and nanofoam network morphologies, consisting of highly OER‐active amorphous Ni‐rich oxide shells and electrically conductive metallic alloy cores. The physical and electronic perturbations to the NiFe induced by a third element lead to a fine‐tuning of the redox ability of the metal sites at the reaction centers, which breaks the scaling relationship between OH* and O* intermediates at the reaction centers. Thus, the unique structural configuration and electronic regulation simultaneously benefit catalytic activity and performance improvements. These NiFeM nanofoam catalysts demonstrated promising anode performance in actual AEMWEs, comparable to the IrO2 reference, especially at high current densities. Notably, using various electrolytes (e.g., KOH solution or pure water) for AEMWEs exhibited a different performance trend among studied NiFeM catalysts, likely due to dynamic changes of catalysts under various OER environments. [ABSTRACT FROM AUTHOR]

Published
2024
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31. Partial oxidation of Step-Bound Water Leads to Anomalous pH Effects on Metal Electrode Step-Edges

Author

Schwarz, Kathleen, Xu, Bingjun, Yan, Yushan, and Sundararaman, Ravishankar

Subjects
Physics - Chemical Physics, Condensed Matter - Materials Science
Abstract

The design of better heterogeneous catalysts for applications such as fuel cells and electrolyzers requires a mechanistic understanding of electrocatalytic reactions and the dependence of their activity on operating conditions such as pH. A satisfactory explanation for the unexpected pH dependence of electrochemical properties of platinum surfaces has so far remained elusive, with previous explanations resorting to complex co-adsorption of multiple species and resulting in limited predictive power. This knowledge gap suggests that the fundamental properties of these catalysts are not yet understood, limiting systematic improvement. Here, we analyze the change in charge and free energies upon adsorption using density-functional theory (DFT) to establish that water adsorbs on platinum step edges across a wide voltage range, including the double-layer region, with a loss of approximately 0.2 electrons upon adsorption. We show how this as-yet unreported change in net surface charge due to this water explains the anomalous pH variations of the hydrogen underpotential deposition (Hupd) and the potentials of zero total charge (PZTC) observed in published experimental data. This partial oxidation of water is not limited to platinum metal step edges, and we report the charge of the water on metal step edges of commonly used catalytic metals, including copper, silver, iridium, and palladium, illustrating that this partial oxidation of water broadly influences the reactivity of metal electrodes., Comment: 9 pages, 8 figures and 3 tables

Published
2016
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32. Atomically dispersed Iridium on Mo2C as an efficient and stable alkaline hydrogen oxidation reaction catalyst.

Author

Fang, Jinjie, Wang, Haiyong, Dang, Qian, Wang, Hao, Wang, Xingdong, Pei, Jiajing, Xu, Zhiyuan, Chen, Chengjin, Zhu, Wei, Li, Hui, Yan, Yushan, and Zhuang, Zhongbin

Subjects
HYDROGEN oxidation, IRIDIUM, PRECIOUS metals, HYDROGEN evolution reactions, ATOMIC hydrogen, FUEL cells, PLATINUM group
Abstract

Hydroxide exchange membrane fuel cells (HEMFCs) have the advantages of using cost-effective materials, but hindered by the sluggish anodic hydrogen oxidation reaction (HOR) kinetics. Here, we report an atomically dispersed Ir on Mo2C nanoparticles supported on carbon (IrSA-Mo2C/C) as highly active and stable HOR catalysts. The specific exchange current density of IrSA-Mo2C/C is 4.1 mA cm−2ECSA, which is 10 times that of Ir/C. Negligible decay is observed after 30,000-cycle accelerated stability test. Theoretical calculations suggest the high HOR activity is attributed to the unique Mo2C substrate, which makes the Ir sites with optimized H binding and also provides enhanced OH binding sites. By using a low loading (0.05 mgIr cm−2) of IrSA-Mo2C/C as anode, the fabricated HEMFC can deliver a high peak power density of 1.64 W cm−2. This work illustrates that atomically dispersed precious metal on carbides may be a promising strategy for high performance HEMFCs. High-performance hydroxide exchange membrane fuel cells rely on the anode loading of platinum-group metals. Here, the authors report a highly active hydrogen oxidation electrocatalyst which contains atomically dispersed Ir on Mo2C nanoparticles supported on a carbon substrate. [ABSTRACT FROM AUTHOR]

Published
2024
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49. Promoting Hydrogen Evolution and Oxidation by Reconstructing Hydrogen-Bonding Network of Interfacial Water

Author

Sun, Qiang, primary, Oliveira, Nicholas J, additional, Yan, Yushan, additional, Kwon, Soonho, additional, Goddard, William, additional, Li, Jingkun, additional, Tyukhtenko, Sergiy, additional, Guo, Jason, additional, Myrthil, Nathalie, additional, Lopez, Steven, additional, Kendrick, Ian, additional, Mukerjee, Sanjeev, additional, Ma, Lu, additional, Ehrlich, Steven, additional, and Jia, Qingying, additional

Published
2023
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