bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Nb-MXenes for Electrocatalysis Applications
Authors: Gandara Meriene , Martins Marta Oliveira , Šljukić Biljana , Gonçalves Emerson Sarmento 
Published: February 2024

MXene is the newest class of 2D materials composed of carbides, nitrides and carbonitrides of transition metals. They are promising materials for electrochemical energy storage and in the field of electrocatalysis1. This work proposes the synthesis of Nb-MXene from MAX phase precursor and its characterization regarding morphology, structure and electrochemical activity.
First, the precursor MAX phase of niobium was produced by mixing Nb, Al and NbC in powder and the reaction process in a tubular furnace, argon atmosphere, at 1640°C, for 3 h. Subsequently, the chemical synthesis was performed at 60 °C, 96 h, by LiF+HCl (1:10 w/w) + 1g of MAX phase, centrifuged and washed with DI water until pH~6 and dried in a vacuum oven.
SEM images (Fig. 1 left) confirmed the morphology2,3 typical of the MAX phase and the effective process of chemical synthesis. The etching process occurred indicating success in the exfoliation, separating the layers forming multilayer MXenes (Fig. 1, right side)2. A mixture of Nb4AlC3 and Nb2AlC was obtained in the MAX phase.
Successful synthesis of MXene is confirmed by shift of the diffraction peaks corresponding to the reflection from (002) plane from 7.36° and 12.75° in case of MAX phase to 5.28°, indicating the removal of Al from the structure2 (Fig. 2).
MXene in a form of a thin film on a conductive substrate was tested for oxygen reduction reaction (ORR) in 3 M KOH electrolyte. Fig. 3 shows a clear increase of current density in O2-saturated solution corresponding to O2 reduction. The peak was visible at 0.7 V with peak current density reaching 0.53 mAcm-2. This supports further exploration of MXene as an electrocatalyst for ORR, including tolerance and stability tests.
References
1- C. Zhan, M. Naguib, M. Lukatskaya, P. R. C. Kent, Y. Gogotsi, D. Jiang. Understanding the MXene Pseudocapacitance, J. Phys. Chem. Lett, 9 (2018) 1223−1228. DOI: 10.1021/acs.jpclett.8b00200
2- Y. Tan, Z. Zhu, X. Zhang, J. Zhang, Y. Zhou, H. Li, H. Qin, Y. Bo, Z. Pan, Nb4C3Tx (MXene) as a new stable catalyst for the hydrogen evolution reaction, International Journal of Hydrogen Energy, 46 (2021) 1955-1966. DOI: 10.1016/j.ijhydene.2020.10.046.
3- M. Shekhirev, C. E. Shuck, A. Sarycheva, Y. Gogotsi, Characterization of MXenes at every step, from their precursors to single flakes and assembled films, Progress in Materials Science, 120 (2021) 100757
https://doi.org/10.1016/j.pmatsci.2020.100757.

Figure 1
An Sub-Micron Double-Layer Capacitance of a Microwell Array for Biomolecular Sensing
Authors: Xie Qiuzhe , Lin Chih-Ting 
Published: February 2024

The interface between a solid and a liquid gives rise to the electric double layer (EDL) through the ion redistribution phenomenon. This effectively neutralizes the surface charges of the solid, and the relationship between the EDL and surface potential is crucial. Although surface potential can be a useful indicator of surface properties, measuring it using existing techniques like kelvin probe microscopy and electroosmotic mobility measurement is challenging as they are complex and difficult to implement as in-situ monitoring techniques.
To address this demand, we used a vertical metal-oxide-metal microwells array to decrease the distance between electrodes and measure EDL capacitance changes induced by surface modifications. The device was fabricated using a layer-by-layer deposition method followed by photolithography and multiple dry etching steps. The diameter of well is around 3 um as SEM image shows. The distance between two electrodes could be scaled down to 100 nm by this method to achieve outstanding characteristics. Cyclic voltammetry was used to accurately estimate surface potential changes. Based on this method, the slope of charging current vs scan rate will be the EDLC.
Next, we demonstrated its potential by detecting Avidin with excellent sensitivity. We applied APTES as the first layer on the sidewall of wells, then NHS-Biotin as the second layer to convert the amine group to an biotin group on the side wall surface. Finally we will immobilize the avidin. The capacitor has significant changed after introducing the avidin onto the sidewall of wells. And the concentration could be low to 100pg/mL for avidin sensing.
Our innovative metrological architecture can be used in diverse biochemical applications to characterize surface-interfaces in real-time.

Figure 1
How to Perform Reliable IR Compensation in Electrocatalysis?
Authors: Zheng Weiran 
Published: February 2024

iR compensation is one of the most used techniques in electrochemical analysis, which is designed to correct the voltage loss between the working electrode and the reference electrode in the electrolyte (Rsolution).[1] It is conducted using two methods frequently, namely the after-the-scan and the on-the-fly methods. A factor is often engaged when performing the iR compensation, which is an empirical value (e.g., 80%~100%) chosen by researchers. After the compensation, the experimental data (mainly electrocatalytic indicators like overpotential and Tafel slope) can be greatly “improved”.[2] However, the abuse of iR compensation, especially in electrocatalysis studies, can generate misleading and exaggerated results.
In this study, we present a detailed analysis of the applicability of the iR compensation technique in current electrocatalysis studies by revisiting the technical assumptions.[3] A few considerations are discussed. Firstly, it is pointed out that the resistance obtained from the electrochemical impedance spectroscopy is not always the resistance that needs to be compensated. The main reason is the involvement of the catalyst material resistance (Rcatalyst) and the contact resistance between the substrate and the catalyst material (Rcontact) (Figure 1). Depending on the types of activity (intrinsic activity, sample activity, electrode activity, and industrial activity) of interest, one should choose different resistance values. For example, only Rsolution should be compensated when studying the electrode activity, but both Rcontact and Rsolution should be compensated for sample activity analysis. Secondly, the resistance may be potential/time-dependent, meaning the value should be measured at the reaction condition, other than the often-used open circuit potential. Thirdly, the distribution of resistance on the catalyst surface sites is uneven, suggesting that one single value cannot be used for sites at different surface traits. Fourthly, most researchers use linear sweep voltammetry (LSV) where the current is always contributed by both the Faradic current and non-Faradic current. However, only the Faradic current should be compensated because non-Faradic current does not flow between the working and reference electrodes.
Regarding these considerations and experimental methods, we further suggested a standard workflow to perform iR compensation in electrocatalysis studies.[3]

Figure 1. Voltage loss across a three-electrode system with a modified working electrode and the corresponding equivalent circuit diagram. (1) surface of the substrate; (2) surface of the catalyst contacting the substrate; (3) surface of the catalyst contacting the electrolyte solution; (4) outer boundary of the diffuse layer; (5) junction of the reference electrode.

Reference:

Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, 2nd ed.; John Wiley & Sons, Inc., 2001

Anantharaj, S.; Noda, S. J. Mater. Chem. A
2022, 10, 17, 9348– 9354

Zheng, W. ACS Energy Lett.
2023, 8, 4, 1952–1958

Figure 1
Surface Modification of Li Metal Anodes Using Ag Nanoparticles and PVDF: An EC-AFM Investigation
Authors: To-a-ran Weerawat , Kim Young-Jun 
Published: February 2024

Lithium metal has captured interest as an attractive anode material for next-generation batteries due to its extremely large theoretical specific capacity (approximately 3800 mAh/g) and low reduction potential. However, challenges related to uncontrolled lithium plating and stripping, unwanted side reactions, and uneven lithium growth on the surface (top growth) contribute to safety concerns and poor cycling performance, hindering the widespread application of lithium metal batteries [1]. In this study, we conducted electrochemical atomic force microscopy (EC-AFM) to investigate the lithium deposition behavior of silver nanoparticles (Ag NPs) on lithium metal substrate surfaces. Kelvin probe force microscopy (KPFM) revealed that Ag NPs possess a lower surface potential than the lithium substrate surface, providing reaction sites for lithium deposition during the plating process. This leads to the formation of a lithium-silver (LiAg) solid solution instead of pure lithium metal, effectively mitigating the issues associated with uncontrolled Li plating. The LiAg alloy phase exhibited improved reversibility compared to bare lithium metal, resulting in improved cycling performance [2]. Additionally, we found that coating the lithium metal surface with a layer of polyvinylidene fluoride (PVDF) promotes bottom-up lithium deposition while physically suppressing dendrite formation. As an ionically conductive but electronically resistant polymer, PVDF allows Li+ transport while suppressing lithium deposition on the top surface [3], reducing safety issues associated with dendrite formation during lithium deposition. Our EC-AFM results reveal the morphological evolution of Ag NPs and PVDF on lithium metal during the plating and stripping process, offering preliminary insights into the underlying mechanisms. Based on our investigations, we propose that the combination of Ag NPs and PVDF could potentially be an effective choice for modifying lithium metal surfaces. This approach aims to enable controlled lithium plating and stripping, as well as bottom-up lithium deposition, with the goal of improving safety and cycling performance for anodes in the next generation of high-energy-density lithium metal batteries, focusing on improving safety and achieving long life cycle.
[1] H. Park et al, Adv. Energy Mater. 2021, 11, 2003039.
[2] S. Jin et al, J. Am. Chem. Soc. 2020, 19, 8818.
[3] J. Yun et al, ACS Energy Lett. 2020, 5, 3108.
Fitting Kinetics of Arbitrarily-Shaped Finite Reactive Features Using Their Scanning Electrochemical Microscopy Images
Authors: Leslie Nathaniel , Mauzeroll Janine 
Published: February 2024

Computer modelling of scanning electrochemical microscopy (SECM) images allows for the kinetics of chemical reactions at surfaces to be fit. Until recently, methods for fitting kinetics from SECM images of reactive features required models with custom geometries that approximated the feature shape.[1,2]

The kinetics of arbitrarily-shaped features can be fit by discretizing the surface into pixels and modelling the surface rate constant of a reaction as a discrete function. The shapes of the underlying reactive feature responsible for hot spots in an SECM image were determined by deconvolution,[3] edge detection,[4] or microscopy and were used to control the surface reaction boundary condition in finite element method simulations. The use of deconvolution or edge detection to obtain an estimate for the shape of the underlying features seen in SECM images was of particular interest since they did not require any characterization of the surface beyond SECM.
Simulated SECM images of reactive features on flat surfaces were controlled using three parameters: the tip to substrate distance of the scanning electrode, the rate constant for the reaction at the surface feature and the erosion and dilation of the initial estimate of the shape of the reactive feature. The parameters of these SECM images were optimized such that the simulated images fit experimental SECM images to obtain shape and kinetic information of reactive sites.
The ability to accurately fit arbitrarily shaped features dramatically broadens the scope of reactive features that can be treated to include features of interest such as grain boundaries, scratches and irregularly shaped inclusions.
[1] Filice, F. P.; Li, M. S. M.; Ding, Z. Simulation Assisted Nanoscale Imaging of Single Live Cells with Scanning Electrochemical Microscopy. Adv. Theory Simul. 2018, 2, 1800124
[2] Leslie, N.; Mena-Morcillo, E.; Morel, A.; Mauzeroll, J. Fitting Kinetics from Scanning Electrochemical Microscopy Images of Finite Circular Features. Anal. Chem. 2022, 94, 44, 15315–15323
[3] Stephens, L. I.; Payne, N. A.; Mauzeroll, J. Super-resolution Scanning Electrochemical Microscopy. Anal. Chem. 2020, 92, 3958– 3963
[4] Stephens, L. I.; Payne, N. A.; Skaanvik, S. A.; Polcari, D.; Geissler, M.; Mauzeroll, J. Evaluating the Use of Edge Detection in Extracting Feature Size from Scanning Electrochemical Microscopy Images. Anal. Chem. 2019, 91, 3944– 3950
Thermodynamic Analysis of Coal Derived Graphite for Battery Anodes Using the Multi-Species, Multi-Reaction Model
Authors: Paul Abigail , Magee Regan , Wilczewski Warren , Wolfe Kody D , Wichert Nathan , Mollah Rafid , Jones Matthew , Trembly Jason , Staser John A. , Garrick Taylor R. 
Published: February 2024

Automotive manufacturers are working to improve individual cell and overall pack design by increasing their performance, durability, and range, while reducing cost. As the time from initial design to manufacture of electric vehicles is decrease, design work that used to rely solely on testing needs to be supplemented or replaced by virtual methods. As electrochemical engineers drive battery and system design using model-based methods, models that have a basis in physics, rather than purely empirical representations, are necessary to allow engineers to drive design through a linkage to manufacturing methods. In this study, we apply the Multi-Species, Multi-Reaction model as popularized by Verbrugge and Baker to an electrochemical system comprised of a counter electrode and a working electrode synthesized from graphite derived from coal.
To do this, the open circuit voltage of the coal derived graphite and a standard commercially available graphite was quantified. Linear sweep voltammetry provided insight into the shift in electrochemical reactions based on the structure and composition of the coal derived graphite. This then allows the MSMR model to capture the thermodynamic performance of the coal derived graphite, and sheds further insight into the performance compared to the standard commercially available system. Commentary on the thermodynamic differences between the systems will be provided and additional analytical techniques may be used to rationalize differences in performance.
Activity and Selectivity Modulation of CO2 Electroreductions at Au-Water Interfaces Via Tuning Localcation Concentrations
Authors: Qin Xueping , Vegge Tejs , Hansen Heine Anton 
Published: February 2024

Electrochemical CO2 reduction reaction (CO2RR) is a promising technique for converting the greenhouse gas CO2 into valuable fuels and chemicals in a clean energy society. To understand the underlying electrocatalytic reaction mechanism from the atomic level, researchers are investigating the role of electrolyte ions, particularly alkali metal cations, in various electrocatalytic reactions including CO2RR. Despite this attention, the impact of alkali metal cations is still a topic of debate, and it remains unclear how cations affect the CO2RR and the competing hydrogen evolution reaction (HER).
In this study, explicit cations and water solvents were added to Au-water interfacial models to simulate the pathways of CO2RR and HER. Two cations (K+, Li+, and/or H+) were used in the model system to create similarly charged Au surfaces, and the local concentration of alkali metal cations (AM+) was adjusted by replacing AM+ (K+ and Li+) with H+. The first electron transfer step was considered critical in electrocatalytic reductions, so CO2 activation and water dissociation were evaluated for CO2RR and HER, respectively. Ab initio molecular dynamics (AIMD) simulations with the slow-growth sampling approach (SG-AIMD) were used to simulate the corresponding reaction mechanisms, and kinetic barriers were obtained through thermodynamic integrations. With these Au-water-cations interfacial models, a systematic study was conducted to investigate the mechanism of CO2 activation at Au-water-2AM+, Au-water-1AM+, and Au-water-0AM+ interfaces. These results show that a high concentration of metal cations with 2AM+ promotes CO2 activation through short-range electrostatic interactions between cations and key intermediates.
Besides CO2 activation, this study also investigated water dissociation during the competing HER. Contrary to the promotion effect observed in CO2RR, local alkali metal cations were found to suppress water dissociation with a high reaction barrier (Figure 1). This can be attributed to the broken connectivity of the hydrogen bond network at Au-water-2AM+ interfaces. The reaction kinetics can be improved by reducing the metal cation concentration. Notably, K+ was found to have a more pronounced promotion effect than Li+ on CO2 activation, while the opposite suppression effect was observed on HER. By tuning the local alkali metal cation concentration, it is anticipated that the overall performance of CO2RR, including both activity and selectivity, can be engineered.

Figure 1
The Chemistry of Interfacial Ions: In Situ XPS and XAS
Authors: Nagra Hassan , Deka Nipon , Favaro Marco , Knop-Gericke Axel , Mom Rik 
Published: February 2024

The choice of electrolyte ions has significant impact on the performance of electrochemical systems, affecting properties such as the electrocatalytic activity and capacitance. To understand how ions influence electrochemical processes, a key step is to determine the chemical behavior of ions at the electrode-electrolyte interface. Here, I will show how X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy (XAS) allow one to obtain such information. Traditionally, these techniques are vacuum-based, only providing a detailed chemical analysis before or after electrochemistry. However, advanced spectro-electrochemical cell design now makes it possible to interface the vacuum needed for XPS and soft XAS with wet electrochemical environments, enabling us to study the electrode-electrolyte interface during electrocatalytic reactions.
Using recent case studies from my group, I will show how operando XPS and soft XAS are able to detect the interfacial ion concentration, the hydration shell structure of the ions, and the electrostatic potential in the double layer. These insights allowed us, for example, to follow the intercalation of Na+ ions into NiFeOx and IrOx in alkaline electrolytes, and to obtain a measure of the double layer layer thickness at a RuOx electrode in 0.1 M H2SO4. Finally, I will give a perspective on how to bring operando XPS from the synchrotron to the laboratory, which will be an important step towards widespread implementation of the technology.

Figure 1
(Invited) In Situ Atomic Force Microscopy and X-Ray Spectroscopy of Electrocatalysts
Authors: Akbashev Andrew 
Published: February 2024

In situ characterization offers an effective way to study and quantify chemical, structural and morphological changes of electrocatalysts as well as to capture the kinetics of transformations and dissolution. For fundamental understanding of electrochemically induced transformations, such in situ experiments require well-defined materials (ideally single crystalline) as they can provide precise potential-dependent quantities that can be used to accurately assess theoretical models and predictions. In this regard, the study of materials under water oxidizing conditions represents a particular challenge due to multiple pathways for the degradation of the surface and bulk and complexity of high-quality material preparation.
In this talk, I will discuss how a combination of in situ microscopy techniques can provide insight into the surface and bulk behavior of electrocatalysts during electrocatalytic water oxidation (OER). Specifically, I will show how operando electrochemical atomic force microscopy (EC-AFM) can be used to record nanoscale changes in the surface morphology during anodic corrosion of a perovskite surface. I will also discuss how operando EC-AFM can be combined with operando transmission X-ray microscopy and scanning electrochemical cell technique to probe the evolution and reactivity of single particles of Co(OH)2. In the end, I will cover key bulk and surface processes that occur in oxides under oxidative conditions as well as possible future development of in situ techniques that can help us probe such transformations.
Operando XAS Investigation of Bimetallic Iron−Molybdenum Sulfide Electrocatalysts for the Hydrogen Evolution Reaction
Authors: Khan Anastassiya , Morozan Adina , Artero Vincent , Zitolo Andrea 
Published: February 2024

Nowadays green hydrogen production has been seen as a key element for the future development and large-scale implementation of fuel cell technology, while electrolyzer technologies represent the most advanced methods for producing pure hydrogen from water. The preparation of efficient, cost-effective, and stable noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) at the cathode of proton exchange membrane electrolyzers (PEMEL) remains one of the main issues that need to be solved to allow the widespread use of hydrogen as an energy carrier.
Molybdenum sulfide (MoSx) is a well-known material showing promising HER catalytic activity, especially in its amorphous state and when doped with other transition metals1. The successful implementation of a bimetallic iron-molybdenum sulfide electrocatalyst for HER into a PEM electrolyzer has been recently reported2. However, the structure of their active sites requires a more elaborate investigation. In this study, we employed operando X-ray absorption spectroscopy to identify potential-induced structural and electronic changes in FeMoSmw bimetallic iron−molybdenum sulfides and MoSmw obtained by a microwave irradiation synthetic approach 2. Extended X-ray absorption fine structure (EXAFS) spectra at Mo and Fe K-edges under operando conditions provided us with accurate structural characterization of the catalytic active sites: while an amorphous MoS3 phase is detected and retained in both MoSmw and FeMoSmw at low potential, a FeS phase is observed at the Fe K-edge, likely explaining the better performance of the bimetallic iron-molybdenum sulfides electrocatalysts compared to iron-free molybdenum sulfides.
References:

Ren, X.; Wang, W.; Ge, R.; Hao, S.; Qu, F.; Du, G.; Asiri, A. M.,Wei, Q.; Chen, L.; Sun, X. An amorphous FeMoS4 nanorod array toward efficient hydrogen evolution electrocatalysis under neutral conditions. Chem. Commun. 2017, 53, 9000−9003.

Morozan, A.; Johnson, H.; Roiron, C.;Genay, G.; Aldakov,D.; Ghedjatti, A.; Nguyen, C.;Tran P.; Kinge, S.; Artero, V. (2020). Nonprecious Bimetallic Iron–Molybdenum Sulfide Electrocatalysts for the Hydrogen Evolution Reaction in Proton Exchange Membrane Electrolyzers. ACS Catalysis. 10. 10.1021/acscatal.0c03692.