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Item type:Publication, Access status: with files , A Pd–Pt-based bulk nanoporous alloy with continuous solubility for hydrogenMetal hydrides that enable reversible solute exchange with a reservoir often exhibit a miscibility gap at room temperature. Misfit strain during two-phase coexistence may then lead to degradation on repeated charging/discharging cycles. Furthermore, the miscibility gap impairs continuous and uniform composition tuning for functional applications. We explore electrochemical dealloying as a pathway to macroscopic monolithic samples of nanoporous Pd–Pt with continuous solubility for H at room temperature. The ligament size is tunable in the range of 4–40 nm, and sorption isotherms suggest a miscibility-gap critical point marginally below room temperature. With a maximum hydrogen fraction of 0.5, we demonstrate a reversible actuation strain of 3.3 % and a high cycle stability.Publicationtype: Journal Article28 16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A Mott-Schottky analysis of mesoporous silicon in aqueous electrolyte solution by electrochemical impedance spectroscopyNanoporosity in silicon leads to completely new functionalities of this mainstream semiconductor. In recent years, it has been shown that filling the pores with aqueous electrolytes, in addition opens a particularly wide field for modifying and achieving active control of these functionalities, e.g., for electrochemo-mechanical actuation and tunable photonics, or for the design of on-chip supercapacitors. However, a mechanistic understanding of these new features has been hampered by the lack of a detailed characterization of the electrochemical behavior of mesoporous silicon in aqueous electrolytes. Here, the capacitive, potential-controlled charging of the electrical double layer in a mesoporous silicon electrode (pore diameter 7nm) imbibed with perchloric acid solution is studied by electrochemical impedance spectroscopy. Thorough measurements with detailed explanations of the observed phenomena lead to a comprehensive understanding of the capacitive properties of porous silicon. An analysis based on the Mott-Schottky equation enables the determination of essential parameters such as the flatband potential, the carrier concentration and the width of the space charge region. A comparison with bulk silicon shows that the flatband potential in particular is significantly altered by the introduction of nanopores, as it shifts from 1.4±0.1V to 1.9±0.2V.Publicationtype: Journal Article91 62 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Sulfur-doped Li₁.₃Al₀.₃Ti₁.₇(PO₄)₃ as a solid electrolyte for all-solid-state batteries: First-principles calculations(2023-09-20); ; ; ; Cetinkaya, TuğrulSolid electrolytes are crucial in obtaining high safety standards and high energy densities in all-solid-state batteries (ASSBs). For ASSBs, it is essential to design solid electrolytes with high ionic conductivity. Herein, a density functional theory (DFT) study has been conducted to investigate the impact of substitutional sulfur doping into Li₁.₃Al₀.₃Ti₁.₇(PO₄)₃ (LATP) solid electrolyte which has a sodium superionic conductor (NaSICON) type crystal structure. A comprehensive study of the effect of sulfur doping on structural stability, Li-ion migration path, and electronic properties was carried out. DFT calculations indicate that sulfur doping locally improves the Li-ion migration kinetics which is accompanied by increased polyhedral volumes in the diffusion path. Moreover, experimental and computational studies were carried out on the electronic state of bare and sulfur-doped LATP. Band gap measurements performed by UV–Vis absorption analysis revealed that sulfur doping decreased the band gap from 2.35 eV to 2.10 eV in alignment with the theoretical calculations in which 1.83 eV was obtained in the most stable sulfur-doped configuration. Compared with bare-LATP, it has been validated that S@LATP has better ionic conductivity with reducing activation energy barrier as a solid electrolyte for all-solid-state batteries.Publicationtype: Journal Article130 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effect of the residual silver and adsorbed lead anions towards the electrocatalytic methanol oxidation on nanoporous gold in alkaline mediaNanoporous gold (NPG) obtained by potentiostatic dealloying of an AuAg master alloy was pulverized, filled into a cavity microelectrode and its surface electrochemistry was investigated in NaOH and KOH solutions. This method yielded highly resolved undistorted voltammograms of this polycrystalline material with clear evidences for surface segregation of Ag during storage in air. One cycle in 0.1 M H SO can remove most of the residual Ag from the surface as evidenced by voltammetry after back transfer to alkaline solution and by X-ray photoelectron spectroscopy (XPS). After removal of residual Ag from the surface, the surface undergoes rephasing forming wider 111 and 110 terraces as evidenced by Pb underpotential deposition (UPD). By adjustment of the bulk concentration of Pb species, a selective partial coverage of the high internal surface area of NPG could be intentionally adjusted. Lead species remain attached to the NPG surface at potentials positive of the UPD regions either as plumbates or Pb species as evidenced by XPS. Those tools enable to disentangle effects on the electrocatalysis of the methanol oxidation reaction (MOR) in different potential regions for 1 M methanol in different concentrations of NaOH and KOH. The MOR commences at lower potentials in the presence of residual Ag. At very high potential, the presence of Ag species promotes the oxidation to CO /CO . Tafel analysis after selective blocking of specific facets shows that the 110 terraces promote especially the first step of MOR while the 111 terraces enhance the rate of further steps that are rate-limiting at higher potentials. While high coverages by Pb UPD layers or adsorbed plumbate anions inhibit electrooxidation, the behavior of NPG electrodes with low coverages of Pb species is reminiscent to NPG electrodes with residual Ag. This could be caused by promoting the methoxide and/or OH adsorption at low overpotentials and catalyzing complete oxidation by a surface bound Pb species at higher potentials. The catalytic currents increase with base concentration and are higher for KOH compared to NaOH. Comparable effects of base concentration on the parameters of the Tafel lines suggest that this effect is a result of slightly stronger deprotonation of methanol in bulk KOH solutions. 2 4 2 3 II IV 2- - IVPublicationtype: Journal ArticleScopus© Citations 9 150 406 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , ATR-FTIR in Kretschmann configuration integrated with electrochemical cell as in situ interfacial sensitive tool to study corrosion inhibitors for magnesium substrates(Elsevier, 2020-06-10); ; ; ; Integrated attenuated total reflection – Fourier transform infrared spectroscopy (ATR-FTIR) – Electrochemical impedance spectroscopy (EIS) measurements were used to simultaneously follow chemisorption mechanisms of organic inhibitors as well as their corrosion inhibition efficiency towards magnesium based substrates. Four carboxylic compounds, i.e. 2,5-pyridinedicarboxylic acid (PDC), 3-methylsalicylic acid (MSA), sodium salicylate (SS) and fumaric acid (FA), were selected based on their promising inhibiting capacities and were all shown to chemisorb at the MgO/Mg(OH)2 surface by carboxylate bond formation. Orientation analysis using polarized infrared light showed that carboxylate bonds established using aliphatic carboxylate compound aligned perpendicular to the magnesium surface, whereas carboxylate bonds with aromatic compounds were oriented in plane with the magnesium surface. This different orientation is associated to the involvement of π-interactions in the MgO/Mg(OH)2 – aromatic carboxylate adsorption. Additionally, DFT calculations revealed that the addition of hetero-atoms (i.e. N or OH) in the molecular structure contributes to increased adsorption energies, indicating that next to carboxylate groups also these hetero-atoms are involved in interfacial interactions. Integrating the ATR-FTIR setup with an electrochemical cell allowing for simultaneous EIS measurements lead to two surface phenomena determining the inhibition efficiency. Surface hydroxylation processes on one hand forming a MgO/Mg(OH)2 layer on one hand, and the chemisorption of carboxylate compounds on the other hand. The inhibition efficiency was found to increase in following order: FA < PDC < MSA and was mainly associated to the formation of a MgO/Mg(OH)2 layer. SS was shown to act as a corrosion accelerator rather than a corrosion inhibitor. Despite its high sensitivity for water, both surface processes could be followed in situ by means of ATR-FTIR. Simultaneously, protective properties of the formed films could be quantified by means of EIS. Consequently, integrated ATR-FTIR – EIS methodology has shown to be highly valuable for gaining in-situ insights in the inhibition mechanism, while quantifying the inhibition efficiency. This was even possible for highly active metal substrate as magnesium, although further developments are suggested if one aims to quantify electrochemical constants related to corrosion and other surface processes measured at the low frequencies (i.e. < 1 Hz).Publicationtype: Journal ArticleScopus© Citations 39 180 225 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Stress-charge coupling coefficient for thin-film polypyrrole actuators – Investigation of capacitive ion exchange in the oxidized stateThis work quantifies the actuation behavior of thin electrodeposited polypyrrole films on rigid substrates. During in situ cantilever bending experiments in aqueous perchloric acid, the films remain clamped to their substrate and the film stress is inferred from a small bending of the cantilever. The potential range under study is 0.4–0.8 V versus the standard hydrogen electrode. Within this potential region, the film is in the oxidized state and the actuation arises from capacitive electrode processes. For the volumetric capacitance, c*, we find 0.24±0.01F/mm3. The stress-charge coupling coefficient, ξ, which is defined as the stress variation per volumetric charge density, emerges as −153±11mV. The results are robust, reproducible and independent of the film thickness or the potential scan rate. The experimental value of ξ is supported by an independent estimate, based on a micromechanical model in combination with literature data for the partial molar volume of solvated perchlorate anions and the elastic constants of polypyrrole.Publicationtype: Journal ArticleScopus© Citations 16 353 347 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Synthesis of uniform bulk nanoporous palladium with tunable structureThis work presents systematic investigations on the synthesis of hierarchical nanoporous Pd via electrochemical dealloying of CuPd alloys in sulfuric acid. The impact of electrode potential, dealloying temperature, and additional annealing on microstructure and morphology is explored. Dealloying Cu85Pd15 in 1M sulfuric acid at elevated temperature provides a facile strategy to produce bulk nanoporous Pd samples which are uniform, hierarchically nanoporous, and free of macro-scale cracks. The question “Why will one-step template-free dealloying yield a hierarchical and not unimodal nanoporous structure?” is discussed. The impact of passivation and of a percolating Cu-rich cluster on the pore structure is inspected. A structural instability concept for dealloying of dilute master alloys is preferred as the underlying mechanism. Nanoporous Pd with classical, unimodal pore structure and tunable ligament size ranging from 80 to 270 nm emerges when the as-prepared hierarchical nanoporous Pd is annealed. The material of this study may provide a model system that complements nanoporous Au for studies of bulk nanoscale metal networks as functional and structural materials.Publicationtype: Journal ArticleScopus© Citations 18 383 606