Tag Archives: Kersti Hermansson

Regulation of CO oxidation with Pd additives on Nb2CO2 MXene

Authors: Xilin Zhang, Chang Xu, Yiying Zhang, Cheng Cheng, Zongxian Yang, Kersti Hermansson,

Catalytic properties of the 2D material Nb2CO2 (MXene) with a surface oxygen vacancy and a supported single Pd atom in it (Pd/OV-Nb2CO2) is explored using DFT calculations. It is found that the single Pd atom can be stably anchored in the oxygen vacancy and out of three mechanisms for carbon monoxide oxidation were studied for our model catalyst and one of them shows promising features, namely CO oxidation via a tri-molecular Eley–Rideal (TER) mechanism which has a small activation barrier of 0.42 eV. This result may provide some guidance for the selection of anode materials with high CO-tolerance and high efficiency in removing CO from H2 for PEMFCs.

International Journal of Hydrogen Energy, Volume 46, Issue 12, 2021,

https://doi.org/10.1016/j.ijhydene.2020.11.278

Multiparametric analysis by paper-assisted potentiometric sensors for diagnostic and monitoring of reinforced concrete structures

Authors: Noemi Colozza, Sara Tazzioli, Alessandro Sassolini, Lorenzo Agosta, Maria Giuseppina di Monted, Kersti Hermansson, Fabiana Arduini

Reinforced concrete has been employed worldwide as a leading building material for public and private structures as well as in modern sculptural art. Although the unrivalled mechanical strength and modelling versatility of this material, several interrelated processes are responsible for its progressive degradation (e.g., carbonation, penetration of aging-promoting agents), decreasing its long-last durability and representing a risk for the public security or the cultural heritage. With the aim to tackle this issue, the present work reports a novel configuration of a screen-printed sensor, obtained by the combination of flexible and robust polyester support and wax-printed filter paper device for the direct application on the concrete surface. Our sensor consists of a polyester-printed three-electrochemical cell that allows dual measurements on reinforced concrete, namely (i) the evaluation of corrosion probability of the metallic reinforcements (which outperforms the half-cell potential standard method) and (ii) the employment of a pH-sensitive iridium oxide film for the measurement of the pH of concrete. The paper was used as a porous material capable of ensuring the electrochemical connection between the Ag/AgCl printed electrode and the concrete solid matrix, acting also as a protective envelope for the electrode. After the laboratory tests, which revealed the noteworthy performances of the sensors in distinguishing among different levels of corrosion as well as measuring the pH of concrete, the developed sensor was applied for on-site measurement at the Giacomo Manzù Museum (Ardea, Italy), demonstrating its suitability for the real application to cultural heritage conservation. Overall, this easy-to-handle and non-invasive diagnostic device provides an innovative analytical approach for the on-site and prompt multiparametric monitoring of the physico-chemical phenomena that endanger the long-lasting preservation of reinforced concrete structures.

Sensors and Actuators B: Chemical
Volume 345, 15 October 2021, 130352

https://doi.org/10.1016/j.snb.2021.130352

Space-Resolved OH Vibrational Spectra of the Hydration Shell around CO2

Authors: Pavlin D. Mitev, W. J. Briels, and Kersti Hermansson

The CO2 molecule is weakly bound in water. Here we analyze the influence of a dissolved CO2 molecule on the structure and OH vibrational spectra of the surrounding water. From the analysis of ab initio molecular dynamics simulations (BLYP-D3) we present static (structure, coordination, H-bonding, tetrahedrality) and dynamical (OH vibrational spectra) properties of the water molecules as a function of distance from the solute. We find a weakly oscillatory variation (“ABBA”) in the ‘solution minus bulk water’ spectrum. The origin of these features can largely be traced back to solvent–solute hard-core interactions which lead to variations in density and tetrahedrality when moving from the solute’s vicinity out to the bulk region. The high-frequency peak in the solute-affected spectra is specifically analyzed and found to originate from both water OH groups that fulfill the geometric H-bond criteria, and from those that do not (dangling ones). Effectively, neither is hydrogen-bonded.

J. Phys. Chem. B 2021, 125, 51, 13886–13895

https://doi.org/10.1021/acs.jpcb.1c06123

Vertical-Flow Paper Sensor for On-Site and Prompt Evaluation of Chloride Contamination in Concrete Structures

Authors: Noemi Colozza, Sara TazzioliSara Tazzioli, Alessandro Sassolini, Lorenzo Agosta, Maria Giuseppina di Monte, Kersti Hermansson, and Fabiana Arduini

Corrosion occurring in reinforced concrete has turned into a primary concern of the current century, concrete being the most ubiquitous and predominant material used in the construction industry. Among the many interrelated processes that trigger corrosion of metallic reinforcements, the penetration of chloride ions into the concrete matrix is the most insidious threat. Herein, we developed the first electrochemical device entirely made of paper that allows for the direct, prompt, and noninvasive evaluation of free chloride ion contamination in concrete-based constructions. Our device is based on a three-layer wax-modified filter paper, consisting of two Ag/AgCl screen-printed electrodes that are interfaced by a junction pad in a sandwich-like configuration. Filter paper allows for generating a vertical-flow potentiometric device capable of measuring the electrochemical potential between two solutions containing different concentrations of chloride ions, which are separately drop-cast on the top and bottom layers. After demonstrating the analytical performance of the device, the same principle was applied to the evaluation of the chloride contents in different concrete samples, exploiting paper as a suitable interfacing material for potentiometric measurements on the cement solid surface. Laboratory-prepared concrete samples with known chloride contents were first assessed, and then, the paper-based vertical-flow device was applied to real concrete structures at the Giacomo Manzù Museum (Ardea, Italy) for the evaluation of chloride contamination caused by the proximity to the seaside. The capability of our device to provide timely warning of the risk conditions of concrete-based artifacts was demonstrated.

Anal. Chem. 2021, 93, 43, 14369–14374

https://doi.org/10.1021/acs.analchem.1c03363

Modelling Bulk Electrolytes and Electrolyte Interfaces with Atomistic Machine Learning

Authors: Yunqi Shao, Lisanne Knijff, Florian M. Dietrich, Kersti Hermansson,  Chao Zhang

imageBatteries and supercapacitors are electrochemical energy storage systems which involve multiple time-scales and length-scales. In terms of the electrolyte which serves as the ionic conductor, a molecular-level understanding of the corresponding transport phenomena, electrochemical (thermal) stability and interfacial properties is crucial for optimizing the device performance and achieving safety requirements. To this end, atomistic machine learning is a promising technology for bridging microscopic models and macroscopic phenomena. Here, we provide a timely snapshot of recent advances in this area. This includes technical considerations that are particularly relevant for modelling electrolytes as well as specific examples of both bulk electrolytes and associated interfaces. A perspective on methodological challenges and new applications is also discussed.

Batteries & Supercaps 2021, 4, 585.

https://doi.org/10.1002/batt.202000262

Thermodynamics of dissociated water motifs at oxide-bulk water interfaces: The TiO2 anatase (0 0 1) case

Authors: Giuseppe Zollo, Kersti Hermansson, and Lorenzo Agosta

Water on metal oxides interfaces generate a variety of ordered motifs that depend on the structural properties of the exposed solid surfaces. Here we emphasize the importance of considering the thermodynamic state of the surrounding liquid to find the interface structures in real systems. In particular, using ab initio molecular dynamics, we have studied the thermodynamic behavior of the water induced reconstructed (WIR) anatase (0 0 1) surface under full hydration. The long standing issue of the reconstruction symmetry in this facet of the anatase, that is the TiO2 stable phase at the nanoscale, is addressed showing that the stable state for a WIR surface in vacuum and in bulk water are different, the latter depending on the thermodynamic state of the system. Thermally activated surface phase transitions between (2×4) and (2×3) symmetries are lead by the surface relaxation caused by the molecular adsorption and release phenomena at the interface. Our approach enables the validation to aqueous environment of surface-confined water structures derived in vacuum, emphasizing the role of the thermodynamics conditions for characterizing solid-liquid interfaces especially for nano sized systems.

Applied Surface Science, 550, 2021, 149354

https://doi.org/10.1016/j.apsusc.2021.149354

Supercooled liquid-like dynamics in water near a fully hydrated titania surface: Decoupling of rotational and translational diffusion

Authors: Lorenzo Agosta, Mikhail Dzugutov, and Kersti Hermansson

We report an ab initio molecular dynamics (MD) simulation investigating the effect of a fully hydrated surface of TiO2 on the water dynamics. It is found that the universal relation between the rotational and translational diffusion characteristics of bulk water is broken in the water layers near the surface with the rotational diffusion demonstrating progressive retardation relative to the translational diffusion when approaching the surface. This kind of rotation–translation decoupling has so far only been observed in the supercooled liquids approaching glass transition, and its observation in water at a normal liquid temperature is of conceptual interest. This finding is also of interest for the application-significant studies of the water interaction with fully hydrated nanoparticles. We note that this is the first observation of rotation–translation decoupling in an ab initio MD simulation of water.

J. Chem. Phys. 154, 094708 (2021)

https://doi.org/10.1063/5.0039693

Lignin Intermediates on Palladium: Insights into Keto‐Enol Tautomerization from Theoretical Modelling

Authors: Ageo Meier de Andrade, Pemikar Srifa, Peter Broqvist, and Kersti Hermansson

It has been suggested in the literature that keto‐to‐enol tautomerization plays a vital role for lignin fragmentation under mild conditions. On the other hand, previous modelling has shown that the adsorbed keto form is more stable than enol on the Pd(111) catalyst. The current density functional theory study of lignin model molecules shows that, in the gas‐phase, keto is more stable than enol, but on the Pd surface, we find enol conformers that are at least as stable as keto. This supports the experimental result that the favourable reaction pathway for lignin depolymerization involves keto‐enol tautomerization. An energy decomposition analysis gives insights concerning the origin of the fine energy balance between the keto and enol forms, where the molecule–surface interaction (−7 eV) and the molecular strain energy (+3 eV) are the main contributors to the adsorption energy.

ChemSusChem, 2020, 13, 6574-6581

https://doi.org/10.1002/cssc.202001560

The water/ceria(111) interface: Computational overview and new structures

Authors: Andreas Röckert, Jolla Kullgren, Peter Broqvist, Seif Alwan, and Kersti Hermansson
 
Thin film structures of water on the CeO2(111) surface for coverages between 0.5 and 2.0 water monolayers have been optimized and analyzed using density functional theory (optPBE-vdW functional). We present a new 1.0 ML structure that is both the lowest in energy published and features a hydrogen-bond network extending the surface in one-dimension, contrary to what has been found in the literature, and contrary to what has been expected due to the large bulk ceria cell dimension. The adsorption energies for the monolayer and multilayered water structures agree well with experimental temperature programmed desorption results from the literature, and we discuss the stability window of CeO2(111) surfaces covered with 0.5–2.0 ML of water.
 

Identification of High‐Performance Single‐Atom MXenes Catalysts for Low‐Temperature CO Oxidation

Authors: Cheng Cheng, Xilin Zhang, Zongxian Yang and Kersti Hermansson

On the basis of first‐principles calculations, Fe, Co, Ni, Cu, Zn, Ru, Rh, Ag, Ir, Pt, and Au decorated Mo2CO2δ monolayers are investigated as potential single‐atom catalyst (SAC) candidates for low‐temperature CO oxidation reaction. From a first screening based on intuitive criteria concerning metal sintering, CO poisoning, and O2 adsorption strength, the Zn/Mo2CO2δ system is selected for further scrutiny by means of reactivity calculations for different CO concentrations. A lower barrier is found for Eley–Rideal reaction mechanism than for the Langmuir–Hinshelwood mechanism. The low Eley–Rideal barrier (0.15 eV) is attributed to the fact that the Zn atom weakens the O‐O bond considerably and the electrophilic attack of CO weakens it further. The main conclusion is that this system is a promising low‐temperature SAC candidate with a lower energy barrier for CO oxidation than noble metal and other 2D SAC systems investigated.

Adv. Theory Simul., 2019, 2: 1900006.

https://doi.org/10.1002/adts.201900006