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Kwon O, Lee J, Son H, Park J. Quantitative Understanding of Ionic Channel Network Variation in Nafion with Hydration Using Current Sensing Atomic Force Microscopy. Polymers (Basel) 2024; 16:604. [PMID: 38475288 DOI: 10.3390/polym16050604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 11/18/2023] [Accepted: 11/28/2023] [Indexed: 03/14/2024] Open
Abstract
Proton exchange membranes are an essential component of proton-exchange membrane fuel cells (PEMFC). Their performance is directly related to the development of ionic channel networks through hydration. Current sensing atomic force microscopy (CSAFM) can map the local conductance and morphology of a sample surface with sub-nano resolution simultaneously by applying a bias voltage between the conducting tip and sample holder. In this study, the ionic channel network variation of Nafion by hydration has been quantitatively characterized based on the basic principles of electrodynamics and CSAFM. A nano-sized PEMFC has been created using a Pt-coated tip of CSAFM and one side Pt-coated Nafion, and studied under different relative humidity (RH) conditions. The results have been systematically analyzed. First, the morphology of PEMFC under each RH has been studied using line profile and surface roughness. Second, the CSAFM image has been analyzed statistically through the peak value and full-width half-maximum of the histograms. Third, the number of protons moving through the ionic channel network (NPMI) has been derived and used to understand ionic channel network variation by hydration. This study develops a quantitative method to comprehend variations in the ionic channel network by calculating the movement of protons into the ionic channel network based on CSAFM images. To verify the method, a comparison is made between the NPMI and the changes in proton conductivity under different RH conditions and it reveals a good agreement. This developed method can offer a quantitative approach for characterizing the morphological structure of PEM. Also, it can provide a quantitative tool for interpretating CSAFM images.
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Affiliation(s)
- Osung Kwon
- Faculty of Science, Tabula Rasa College, Keimyung University in Seongseo, Daegu 42601, Republic of Korea
| | - Jihoon Lee
- AET Co., Ltd., Daegu 41967, Republic of Korea
| | - Hyungju Son
- AET Co., Ltd., Daegu 41967, Republic of Korea
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Kwon O, Park J, Lee J. Quantitative Study of Charge Distribution Variations on Silica-Nafion Composite Membranes under Hydration Using an Approximation Model. Polymers (Basel) 2023; 15:polym15102295. [PMID: 37242869 DOI: 10.3390/polym15102295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 05/05/2023] [Accepted: 05/07/2023] [Indexed: 05/28/2023] Open
Abstract
Understanding the ionic structure and charge transport on proton exchange membranes (PEMs) is crucial for their characterization and development. Electrostatic force microscopy (EFM) is one of the best tools for studying the ionic structure and charge transport on PEMs. In using EFM to study PEMs, an analytical approximation model is required for the interoperation of the EFM signal. In this study, we quantitatively analyzed recast Nafion and silica-Nafion composite membranes using the derived mathematical approximation model. The study was conducted in several steps. In the first step, the mathematical approximation model was derived using the principles of electromagnetism and EFM and the chemical structure of PEM. In the second step, the phase map and charge distribution map on the PEM were simultaneously derived using atomic force microscopy. In the final step, the charge distribution maps of the membranes were characterized using the model. There are several remarkable results in this study. First, the model was accurately derived as two independent terms. Each term shows the electrostatic force due to the induced charge of the dielectric surface and the free charge on the surface. Second, the local dielectric property and surface charge are numerically calculated on the membranes, and the calculation results are approximately valid compared with those in other studies.
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Affiliation(s)
- Osung Kwon
- Faculty of Science, Tabula Rasa College, Keimyung University in Seongseo, Daegu 42601, Republic of Korea
| | - Jaehyoung Park
- Corporate Research Center, HI FUELCELL Co., Ltd., Daegu 41967, Republic of Korea
| | - Jihoon Lee
- Corporate Research Center, HI FUELCELL Co., Ltd., Daegu 41967, Republic of Korea
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Son B, Park J, Kwon O. Analysis of Ionic Domains on a Proton Exchange Membrane Using a Numerical Approximation Model Based on Electrostatic Force Microscopy. Polymers (Basel) 2021; 13:polym13081258. [PMID: 33924505 PMCID: PMC8069030 DOI: 10.3390/polym13081258] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 04/09/2021] [Accepted: 04/12/2021] [Indexed: 11/18/2022] Open
Abstract
Understanding the ionic channel network of proton exchange membranes that dictate fuel cell performance is crucial when developing proton exchange membrane fuel cells. However, it is difficult to characterize this network because of the complicated nanostructure and structure changes that depend on water uptake. Electrostatic force microscopy (EFM) can map surface charge distribution with nano-spatial resolution by measuring the electrostatic force between a vibrating conductive tip and a charged surface under an applied voltage. Herein, the ionic channel network of a proton exchange membrane is analyzed using EFM. A mathematical approximation model of the ionic channel network is derived from the principle of EFM. This model focusses on free charge movement on the membrane based on the force gradient variation between the tip and the membrane surface. To verify the numerical approximation model, the phase lag of dry and wet Nafion is measured with stepwise changes to the bias voltage. Based on the model, the variations in the ionic channel network of Nafion with different amounts of water uptake are analyzed numerically. The mean surface charge density of both membranes, which is related to the ionic channel network, is calculated using the model. The difference between the mean surface charge of the dry and wet membranes is consistent with the variation in their proton conductivity.
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Affiliation(s)
- Byungrak Son
- Division of Energy Technology, DGIST, Daegu 42988, Korea;
| | - JaeHyoung Park
- Corporate Research Center, HygenPower Co., Ltd., Daegu 42988, Korea;
| | - Osung Kwon
- Tabula Rasa College, Keimyung University, Daegu 42601, Korea
- Correspondence: ; Tel.: +82-53-580-5657
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Albonetti C, Chiodini S, Annibale P, Stoliar P, Martinez RV, Garcia R, Biscarini F. Quantitative phase-mode electrostatic force microscopy on silicon oxide nanostructures. J Microsc 2020; 280:252-269. [PMID: 32538463 DOI: 10.1111/jmi.12938] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 06/05/2020] [Accepted: 06/12/2020] [Indexed: 02/02/2023]
Abstract
Phase-mode electrostatic force microscopy (EFM-Phase) is a viable technique to image surface electrostatic potential of silicon oxide stripes fabricated by oxidation scanning probe lithography, exhibiting an inhomogeneous distribution of localized charges trapped within the stripes during the electrochemical reaction. We show here that these nanopatterns are useful benchmark samples for assessing the spatial/voltage resolution of EFM-phase. To quantitatively extract the relevant observables, we developed and applied an analytical model of the electrostatic interactions in which the tip and the surface are modelled in a prolate spheroidal coordinates system, fitting accurately experimental data. A lateral resolution of ∼60 nm, which is comparable to the lateral resolution of EFM experiments reported in the literature, and a charge resolution of ∼20 electrons are achieved. This electrostatic analysis evidences the presence of a bimodal population of trapped charges in the nanopatterned stripes.
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Affiliation(s)
- C Albonetti
- Consiglio Nazionale delle Ricerche - Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), Bologna, Italy
| | - S Chiodini
- Consiglio Nazionale delle Ricerche - Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), Bologna, Italy.,Instituto de Nanociencia de Aragon (INA), Universidad de Zaragoza, Zaragoza, Spain
| | - P Annibale
- Consiglio Nazionale delle Ricerche - Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), Bologna, Italy.,Present address: Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - P Stoliar
- Consiglio Nazionale delle Ricerche - Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), Bologna, Italy.,National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
| | - R V Martinez
- Materials Science Factory, Instituto de Ciencia de Materiales de Madrid (ICMM), CSIC, Madrid, Spain.,Present address: School of Industrial Engineering, Purdue University, West Lafayette, Indiana, U.S.A
| | - R Garcia
- Materials Science Factory, Instituto de Ciencia de Materiales de Madrid (ICMM), CSIC, Madrid, Spain
| | - F Biscarini
- Consiglio Nazionale delle Ricerche - Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), Bologna, Italy.,Department of Life Sciences, Università di Modena e Reggio Emilia, Modena, Italy.,Center for Translational Neurophysiology-Istituto Italiano di Tecnologia, Ferrara, Italy
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Barnes AM, Liu B, Buratto SK. Humidity-Dependent Surface Structure and Hydroxide Conductance of a Model Quaternary Ammonium Anion Exchange Membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:14188-14193. [PMID: 31596594 DOI: 10.1021/acs.langmuir.9b02160] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Anion exchange membrane (AEM) fuel cells (AEMFCs) are a promising cost-effective alternative energy conversion technology because of the potential implementation of earth-abundant catalysts, obviating the need for precious metals. AEMs, however, have low conductivity and suffer from poor stability. The conductivity of the AEM is inherently tied to the complex phase-separated morphology, as its dependence on the hydration level is not well understood. In this report, we employ phase-contrast tapping mode and conductive-probe atomic force microscopy (cp-AFM) to study the nanoscale surface morphology and hydroxide conductance of a commercially available quaternary ammonium (QA) AEM by FuMA-Tech GmbH (Fumapem FAA-3). The chemical structure of FAA-3 consists of a poly(phenylene oxide) backbone with QA functionality. The morphology of FAA-3 was observed in the bromide (FAA-3-Br-) and hydroxide form (FAA-3-OH-) in dehydrated and hydrated conditions. Under dehydrated conditions, both membranes showed no phase contrast, indicating the absence of phase-separated hydrophilic domains at the surface. At hydrated conditions, FAA-3-Br- shows randomly dispersed isolated clusters, while FAA-3-OH- shows elongated fibrillar structures extending microns in length. cp-AFM of hydrated FAA-3-OH- showed that these elongated regions were insulating. These results provide morphological evidence for the conduction of hydroxide at the surface and its dependence on the hydration level.
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Affiliation(s)
- Austin M Barnes
- Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106-9510 , United States
| | - Brendan Liu
- Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106-9510 , United States
| | - Steven K Buratto
- Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106-9510 , United States
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Überrück T, Neudert O, Kreuer KD, Blümich B, Granwehr J, Stapf S, Han S. Effect of nitroxide spin probes on the transport properties of Nafion membranes. Phys Chem Chem Phys 2018; 20:26660-26674. [PMID: 30320331 DOI: 10.1039/c8cp04607g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Nafion is the most common material used as a proton exchange membrane in fuel cells. Yet, details of the transport pathways for protons and water in the inner membrane are still under debate. Overhauser Dynamic Nuclear Polarization (ODNP) has proven to be a useful tool for probing hydration dynamics and interactions within 5-8 Å of protein and soft material surfaces. Recently it was suggested that ODNP can also be applied to analyze surface water dynamics along Nafion's inner membrane. Here we interrogate the viability of this method for Nafion by carrying out a series of measurements relying on 1H nuclear magnetic resonance (NMR) relaxometry and diffusometry experiments with and without ODNP hyperpolarization, accompanied by other complementary characterization methods including small angle X-ray scattering (SAXS), thermal gravimetric analysis (TGA) of hydration, and proton conductivity by AC impedance spectroscopy. Our comprehensive study shows that commonly used paramagnetic spin probes-here, stable nitroxide radicals-for ODNP, as well as their diamagnetic analogues, reduce the inner membrane surface hydrophilicity, depending on the location and concentration of the spin probe. This heavily reduces the hydration of Nafion, hence increases the tortuosity of the inner membrane morphology and/or increases the activiation barrier for water transport, and consequently impedes water diffusion, transport, and proton conductivity.
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Affiliation(s)
- Till Überrück
- RWTH Aachen University, Institut für Technische und Makromolekulare Chemie, Worringerweg 2, 52074 Aachen, Germany.
| | - Oliver Neudert
- Dept. Technical Physics II/Polymer Physics, University of Technology Ilmenau, 98684 Ilmenau, Germany and GMBU e.V., Erich-Neuß-Weg 5, 06120 Halle (Saale), Germany
| | - Klaus-Dieter Kreuer
- Max-Planck-Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
| | - Bernhard Blümich
- RWTH Aachen University, Institut für Technische und Makromolekulare Chemie, Worringerweg 2, 52074 Aachen, Germany.
| | - Josef Granwehr
- RWTH Aachen University, Institut für Technische und Makromolekulare Chemie, Worringerweg 2, 52074 Aachen, Germany. and Forschungszentrum Jülich, Institut für Energie- und Klimaforschung - Grundlagen der Elektrochemie (IEK-9), 52425 Jülich, Germany
| | - Siegfried Stapf
- Dept. Technical Physics II/Polymer Physics, University of Technology Ilmenau, 98684 Ilmenau, Germany
| | - Songi Han
- University of California Santa Barbara, Department of Chemistry and Biochemistry, Santa Barbara, CA 93106, USA
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