Irreversible compositional dynamics on the surface of PtNi alloy under alternating redox environments: Electrochemical and NAP-XPS Study

Athira Lekshmi Mohandas Sandhya

Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Holešovičkách 2, 18000 Prague, Czech Republic

mailmeathira96@gmail.com

Platinum-based bimetallic alloys are known to possess unique activities exceeding those of pure platinum [1,2]. Nevertheless, as a complex multi-component system, it suffers from structural reorganization under operating conditions, strongly affecting its lifetime performance [3,4]. The better understanding on the structural dynamics of a bimetallic catalyst during its interaction with reactive environments is a prerequisite for the catalyst development. Herein we provide an operando electrochemical and spectroscopic study of the surface composition changes in a PtNi catalyst during repetitive oxidation/reduction cycles representing inherent working conditions for numerous redox reactions. Using cyclic voltammetry and near-ambient pressure X-ray photoelectron spectroscopy, a quantitative surface characterization under both realistic environments, i.e. electrified liquid and gaseous at elevated pressure and temperature, is obtained and correlated. We observed that, regardless of the operating environment, the PtNi alloy does not maintain its chemical integrity and undergoes irreversible change in composition profile reflected in surface nickel enrichment and consequent catalyst deactivation.

References:

[1] J. Greeley, I.E.L. Stephens, A.S. Bondarenko, T.P. Johansson, H.A. Hansen, T.F. Jaramillo, J. Rossmeisl, I. Chorkendorff, J.K. Nørskov, Alloys of platinum and early transition metals as oxygen reduction electrocatalysts, Nat. Chem. 1 (2009) 552–556.

[2] V. Stamenkovic, B.S. Mun, K.J.J. Mayrhofer, P.N. Ross, N.M. Markovic, J. Rossmeisl, J. Greeley, J.K. Nørskov, Changing the activity of electrocatalysts for oxygen reduction by tuning the surface electronic structure, Angew. Chemie Int. Ed. 45 (2006) 2897– 2901.

[3] I. Khalakhan, M. Bogar, M. Vorokhta, P. Kúš, Y. Yakovlev, M. Dopita, D.J.S. Sandbeck, S. Cherevko, I. Matolínová, H. Amenitsch, Evolution of the PtNi Bimetallic Alloy Fuel Cell Catalyst under Simulated Operational Conditions, ACS Appl. Mater. Interfaces. 12 (2020) 17602–17610. doi:10.1021/acsami.0c02083.

[4] Y.-T. Pan, H. Yang, Design of bimetallic catalysts and electrocatalysts through the control of reactive environments, Nano Today. 31 (2020) 100832. doi:https://doi.org/10.1016/j.nantod.2019.100832.

Optimization of PEM fuel cell components

Dr. Gábor Pál Szijjártó

Research Centre for Natural Sciences, H-1117 Budapest, Magyar tudósok körútja 2.

szijjarto.gabor@ttk.hu

Importance of fuel cells is needless to be detailed. Sustainable and environmental friendly solutions of this research area are able to be competitive alternatives of fossil based energy sources. Fuel cell development has more directions, because well-chosen material and flow channel geometry of bipolar plates, mechanically stable and good proton conductive polymer electrolyte membranes (PEM), and efficient, low Pt containing (or noble metal free) electrocatalysts all play crucial role in the optimization process. Main profile of our research group is the analysis of electrocatalysts. Last step of this examination process is the fuel cell testing of those samples, which previously turned out to be promising on XRD and CV tests. Electrochemical characterizations, like cyclic voltammetry (CV) or electrochemical impedance spectroscopy (EIS) are able to be carried out not only in the classic 3 electrode system, but on a fuel cell too. Linear relation between H2 desorption peak and Pt loading of cathode was verified by CV. EIS was applied to determine the resistance of catalyst layer. For fuel cell testing, the New European Driving Cycle (NEDC) protocol [1] was used. After optimization of the Pt loading of MEAs, Ti0.8Mo0.2O2-C composite supported anode catalysts were tested [2]. According to NEDC methode, Dynamic Load Cycle (DLC) tests were also carried out. In that case, degradation of MEA could be calculated after a 50 cycle (16.4h) test, by comparison of polarization curves before and after this process. Catalyst testing in dismountable short stack is usually the missing stage between small scale single cell tests and the real stack measurements. Fuel cell for 50 cm2 active area MEAs was designed (including bipolar plates, endplates and current collectors), which is able to work as single cell or it can be improved to a 6-8 MEA short stack. Connection of FC stack with multichannel potentiostat let us to carry out parallel polarization of different MEAs.

References:

[1] https://ec.europa.eu/jrc/en/publication/eur-scientific-and-technical-research-reports/eu-harmonised-test-protocols-pemfc-mea-testing-single-cell-configuration-automotive

[2] Danielle Verde Nolasco, Optimization of membrane electrode assembly for PEM fuel cells”, MSc Thesis, 2021

In situ Small Angle Scattering: Characterization of Energy Materials

Heinz Amenitsch

Graz University of Technology & Austrian SAXS beamline c/o Elettra Sincrotrone Trieste

amenitsch@tugraz.at

Electrochemistry has a considerable technological impact on energy materials, such as fuel cells, supercapacitors and batteries, or on dealloying processes for the generation of nanoporosity. In situ analysis at the nanoscale with SAXS and GISAXS is essential to provide a complete understanding of the fundamental processes responsible for reduced lifetime and performances in energy applications.

Here, the development of an electrochemical cells to be able to conduct such type of investigations (1). The capability of the cell will be demonstrated on the recent results obtained on PtNi catalyst layers of fuel cells during electrochemical cyclic voltammetry (2, 3) as well as on the dealloying of binary systems AgAu and CoPd (4). In both topics, the GISAXS results provide valuable insights in the processes involved, like Ostwald ripening or coalescence.

At the end, an outlook will be given to current projects related to biology and battery research.

References

[1]       M. Bogar, I. Khalakhan, A. Gambitta, Y. Yakovlev, H. Amenitsch, In situ electrochemical grazing incidence small angle X-ray scattering: From the design of an electrochemical cell to an exemplary study of fuel cell catalyst degradation. J. Power Sources. 477 (2020), doi:10.1016/j.jpowsour.2020.229030.

[2]       I. Khalakhan et al., Evolution of the PtNi Bimetallic Alloy Fuel Cell Catalyst under SimulatedOperational Conditions. ACS Appl. Mater. Interfaces. 12, 17602–17610 (2020).

[3]       M. Bogar et al., Interplay among Dealloying, Ostwald Ripening, and Coalescence in PtXNi100-XBimetallic Alloys under Fuel-Cell-Related Conditions. ACS Catal. 11, 11360–11370 (2021).

[4]       M. Gößler et al., In Situ Study of Nanoporosity Evolution during Dealloying AgAu and CoPd by Grazing-Incidence Small-Angle X-ray Scattering. J. Phys. Chem. C. 126, 4037–4047 (2022).

Operando diffraction experiments at MCX @Elettra

Jasper R. Plaisier

Elettra – Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163,5, Basovizza, Trieste Italy

jasper.plaisier@elettra.eu

The beamline MCX (Material Characterisation by X-ray diffraction), officially inaugurated 15 years ago at the Italian synchrotron facility, Elettra – Sincrotrone Trieste, was designed to study nanostructured materials, investigating details of crystalline domain size and shape, lattice defects, and local atomic displacement of static and dynamic nature using Line Profile Analysis (LPA).[1] However,the flexible set-up of the experimental station[2] allows for a wide variety of diffraction experiments in different fields ranging from residual stress analysis in engineering to structure determination of new pharmaceuticals, and from phase identification in cultural heritage to operando battery studies in energy research.
Operando studies have taken an enormous flight within recent years and they now make up about 25% of the experiments on MCX. Most of them are related to batteries, but also new fields are being explored such as the electrochemical reduction of CO2. Here, a short overview will be presented of the experimental set-up of the beamline and the opportunity it offers also for research fuel cells and electrolysers. This will be illustrated by some results of recent experiments performed at MCX. Currently, within the scheme of the upgrade of Elettra, MCX is preparing for a major upgrade of the beamline. This will already start in 2023 with the installation of a brand new 3-circle diffractometer with a Mythen-II detector covering 120° 2Θ. This upgrade will have a major impact on the type of experiments addressed here. Therefore, also the future prospects for operando diffraction studies will be discussed.

References:

[1] L. Rebuffi, J. R. Plaisier, M. Abdellatief, A. Lausi, P. Scardi, Mcx: a synchrotron radiation beamline for x-ray diffrac-tion line profile analysis, Zeitschrift für anorganische und allgemeine Chemie 640 (15) , 3100–3106 (2014).

[2] J. R. Plaisier, L. Nodari, L. Gigli, E. P. R. San Miguel, R. Bertoncello, A. Lausi, The x-ray diffraction beamline MCX at Elettra: a case study of non-destructive analysis on stained glass, Acta Imeko 6 (3), 71–75 (2017).

Hydrogen and Fuel Cell Technologies in the Transportation and Power Sectors

Magdalena Dudek

AGH University of Science and Technology, Faculty of Energy and Fuels

Av. Mickiewicza 30, 30-059 Krakow, Poland

The increasingly negative effects of climate change are leading to a shift towards low-emission energy systems. The advancement of hydrogen and fuel cell technologies is the most important area in renewable energy development, and the current state of hydrogen as a clean, flexible source of energy will be discussed here with a focus on its production and use.

The role of hydrogen in transportation, particularly in turbines, engines and fuel cells, will be analysed. The technologies of hydrogen storage will be discussed along with other forms of fuel storage.

The achievements of AGH UST groups will be highlighted in the area of hydrogen technology and fuel cells application

Solid Oxide Fuel Cells: From UHV to Near Ambient Pressure in Operando Photoemission Spectromicroscopy Analysis

Matteo Amati

Elettra-Sincrotrone Trieste S.C.p.A. di interesse nazionale, Strada Statale 14 – km 163,5 in AREA Science Park 34149 Basovizza, Trieste ITALY

matteo.amati@elettra.eu

Fuel cells are electrochemical devices providing efficient production of electricity directly converting the electrons exchanged in a redox reaction into electric current. One of the issues that impedes their widespread applications is the limited durability of the components and mass transport events that deteriorate the performance. The ESCA Microscopy Beamline team has developed several methodologies based on synchrotron soft X-ray Scanning Photoemission Microscopy (SPEM), allowing a detailed chemical and morphological analysis of the cell components, and providing information about the processes at the interconnections, electrodes and electrode/electrolyte interface in operando conditions. SPEM uses a direct approach to add the spatial resolution to XPS i.e a small focused X-ray photon probe to illuminate the sample. The focusing of the X-ray beam is performed by Zone-Plates and samples surface is mapped by scanning the sample with the focused beam. X-ray beam can be downsized to a diameter of 130 nm, allowing imaging resolution of less than 50 nm with an energy resolution of 200 meV [1]. Only recent electron energy analysers with differentially pumped lens systems allow to perform operando XPS up to near or  ambient pressure. Nevertheless due to the technical complexity and low efficiency it was not possible to export such solution to photoemission spectromicroscopy so far. Solutions developed for photoemission microscopes, based on effusive cells where high- and low-pressure regions are separated by small apertures of a few hundreds micrometers for photons and photoelectrons [2], will be presented and discussed. Recent achievements in the chemical and electronic operando characterization of fuel cell components will be presented, as for example the characterization of a Self-Driven Single Chamber SOFC [3], characterization performed also under operando near-ambient pressure condition [4], providing an overview of the capabilities of this powerful technique.

References:

[1] https://www.elettra.eu/elettra-beamlines/escamicroscopy.html

[2] H. Sezen et al, Surface and Interface Analysis, 2018, 50, 921-926.

[3] B. Bozzini et al. Scientific Report, 2013, 3, 2848.

[4] B. Bozzini et al. Topics in Catalysis, 2018, 61, 1274-1282

Modern trends in improving the performance of PEM water electrolyzers

Peter Kúš

Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Holešovičkách 2, 180 00 Prague 8, Czech Republic

peter.kus@mff.cuni.cz

Our society is progressively leaning towards utilization of renewable sources of energy. Moreover, recent conflict in Ukraine and consequent sanctions against Russia which affect the global gas trade further underline the necessity of a less import-dependent, self-sustainable energy policy. In this regard, the concept of the so-called Hydrogen Economy proves to be very promising. For its successful implementation, the efficiently working proton exchange membrane water electrolyzers (PEM-WEs) are essential. One of the top research priorities in this field is a significant reduction of noble metal reliance, predominantly on anode, through systematic studies of new materials. This talk will cover different approaches on how to improve the performance and durability of PEM-WE not only by employing new catalysts but also by modifying the membrane/catalyst interface. We will be focusing on magnetron sputtering as it is a very dependable, cost-effective and industrially scalable method for depositing thin-film multielement catalysts and is also capable of enlarging the surface of PEM by so-called sputter-etching process. Finally, we will introduce several recent methods for operando analysis of membrane electrode assemblies within PEM-WE single cells which we believe have potential to shed more light on complicated activity-stability relationship of novel catalytic materials.

References:
[1] Hrbek, T; Kúš, P; Kosto, Y; Rodríguez, M. G; Matolínová, I Magnetron-sputtered thin-film catalyst with low-Ir-Ru content for water electrolysis: Long-term stability and degradation analysis manuscript under review in J. Power Sources

[2] Hrbek, T; Kúš, P; Košutová, T; Veltruská, K; Dinhová, TN; Dopita, M; Matolín, V; Matolínová, I Sputtered Ir–Ru based catalysts for oxygen evolution reaction: Study of iridium effect on stability Int. J. Hydrog. Energy, 47 (49): 21033–21043, 2022. doi:10.1016/j.ijhydene.2022.04.224

[3] Hrbek, T; Kúš, P; Yakovlev, Y; Nováková, J; Lobko, Y; Khalakhan, I; Matolín, V; Matolínová, I Sputter-etching treatment of proton-exchange membranes: Completely dry thin-film approach to low-loading catalyst coated membranes for water electrolysis Int. J. Hydrog. Energy, 45 (41): 20776–20786, 2020. doi:10.1016/j.ijhydene.2020.05.245

In operando monitoring templated electrodeposition of mesoporous catalyst films for ORR or HER by Synchrotron GISAXS

Philipp Aldo Wieser

Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9/IV, 8010 Graz, Austria

philipp.wieser@tugraz.at

Liquid crystal (LC) templated electrodeposition is a facile and versatile method to electrodeposit metal films with highly structured mesopores. These mesopores are essential to increase the electrochemically active surface area for Fuel Cell related devices, e.g., for Hydrogen Evolution Reaction^[1] or Oxygen Reduction Reaction^[2]. Previous studies showed that LC templating allowed to tailor pore size^[3], shape^[4], and orientation^[5] of the pores in the deposited film. Generally, these studies suggest that the pores in the film inherit the structure of the LC template.

However, little is known about the interplay between the kinetics of the templated deposition, i.e. the transition from the structure of the LC template to the resulting film. A better understanding of this interplay requires in operando monitoring structural changes during the templated electrodeposition process.

In this work, we characterized the surface structure of Au substrates during templated electrodeposition of Pt and PtNi with in operando Grazing Incidence Small Angle X-Ray Scattering (GISAXS).

We were able to identify a series of structural changes at the film surface: Initially, a nucleation burst of Pt coincides with a loss of preferential alignment of the LC. The morphology of the nucleated Pt corresponds to the substrate. At later stages of deposition, the morphology of the Pt film changes, and vertically aligned pores form. These findings potentially lead to more effective electrodeposition routines and films with higher accessible surface area.

References

[1]       K. Eiler, S. Suriñach, J. Sort, E. Pellicer, Appl. Catal. B Environ. 2020, 265, 118597.

[2]       T. Li, A. J. Senesi, B. Lee, Chem. Rev. 2016, 116, 11128–11180.

[3]       L. Ma, L. Zhou, Y. He, L. Wang, Z. Huang, Y. Jiang, J. Gao, Electroanalysis 2018, 30, 1801–1810.

[4]       Y. Yamauchi, A. Tonegawa, M. Komatsu, H. Wang, L. Wang, Y. Nemoto, N. Suzuki, K. Kuroda, J. Am. Chem. Soc. 2012, 134, 5100–5109.

[5]       K. A. Asghar, J. M. Elliott, A. M. Squires, J. Mater. Chem. 2012, 22, 13311–13317.

Shedding Synchrotron Light on Nanocatalyst Strain Distortion and Dynamics in Electrochemical Environment

Raphaël Chattot (1) *, Isaac Martens (2), Jakub Drnec (2)

(1) CGM, Univ. Montpellier, CNRS, ENSCM, 34095 Montpellier Cedex 5, France
(2) ESRF, The European Synchrotron, 71 Avenue des Martyrs, CS40220, 38043 Grenoble Cedex 9, France
*raphael.chattot@umontpellier.fr

Surface science has driven the development of commercial nanocatalysts for energy conversion and storage applications, by establishing the electronic descriptors that rationalize or even predict the activity of metallic surfaces for numerous reactions in the frame of the Sabatier principle: the ability of the surface to bind adsorbates and the strength of the bonds define the reaction thermodynamics and kinetics. This seminal knowledge has allowed tremendous improvements in electrocatalytic materials according to the ‘catalysts-by-design’ approach, in which lattice strain control is used to tailor catalytic performance. In this presentation, we will see from synchrotron high energy X-ray diffraction experiments that the ‘lattice constant’ in practical noble metal nanocrystals for fuel cell electrocatalysis is everything but ‘constant’. Spacial heterogeneity (distortion) 1 and strong dependence on the conditions (dynamics) 2 of the lattice have fundamental consequences on catalytic activity trends, and can both be used positively as reactivity descriptors for numerous  electrochemical processes.

[caption id="attachment_12970" align="alignnone" width="765"] Figure: Strain dynamics of Pt nanocatalysyst during cyclic voltammetey experiment in 0.1 M HClO4 revealed by operando wide angle x-ray scattering.[/caption]

References:

[1] Chattot, R. et al. Surface Distortion as a Unifying Concept and Descriptor in Oxygen Reduction Reaction Electrocatalysis. Nat. Mater. (2018).

[2] Chattot, R. et al. Electrochemical Strain Dynamics in Noble Metal Nanocatalysts. J. Am. Chem. Soc. 143, 17068–17078 (2021).