bluuebunny/crossref_metadata_2025 huggingface dataset:
Proton-Coupled Electron Transfer Involving Localized Electronic Defects on Solid Surfaces
Authors: Warburton Robert
Published: February 2024

Proton-coupled electron transfer (PCET) is a critical elementary step in many (photo)electrocatalytic transformations. PCET reactions on semiconducting metal oxide surfaces involve proton transfer that is charge compensated by electronic defects, such as electrons or holes. When highly localized as small polarons, these electronic defects are coupled with local bond distortions that accompany the excess or depleted charge. Using anatase TiO2 as a model system, I will describe recent first-principles modeling studies of interfacial PCET on metal oxide surfaces. The PCET reaction free energies involving the cleavage of O–H bonds on TiO2 surfaces varies widely depending on whether the charge-compensating electronic defects are conduction d-band electrons or valence p-band holes. Differences in PCET thermochemistry are accounted for using a Marcus theory framework based on defect energy levels and inner-sphere reorganization energies. The PCET rate constants associated with the cleavage of O–H bonds in the presence of a nitroxyl radical oxidant are calculated using vibronically nonadiabatic PCET theory, where both the transferring electron and proton are treated quantum mechanically. Input parameters to the rate constant expressions are calculated using hybrid periodic density functional theory calculations. These studies highlight the effects of local electronic defects on the PCET reactivity of semiconductor surfaces.
Investigating the Electrochemical Absorption of Hydrogen into Palladium Nanoparticles
Authors: Moumaneix Lilian , Rautakorpi Akseli , Kallio Tanja
Published: February 2024

The apparent simplicity of palladium hydride systems hides complex interactions between hydrogen atoms and the palladium crystalline lattice. Tailoring these interactions is primordial for many industrial and research applications, as the properties of the hydride vary greatly with the concentration of hydrogen. In the field of electrocatalysis, the fine control of the hydrogen concentration may open the way to higher selectivity towards reactions of interest such as carbon dioxide reduction or nitrogen reduction reactions. Recently, our group investigated the electrochemical insertion of hydrogen into Pd nanoparticles (NPs), and more specifically the influence of the insertion potential, insertion duration, temperature and Pd NPs diameter on the hydrogen concentration, reported as H/Pd ratio. Electrochemical hydrogen stripping appeared as a very efficient method to study the Pd hydride composition, and our study is supported by an original model to separate the contributions coming from hydrogen absorption, hydrogen adsorption and hydrogen oxidation, often neglected in the literature. Among the main results, it was found that (i) hydrogen absorption reaches a plateau at about -0.1 VRHE; (ii) an equilibrium between H insertion and desorption is reached after a few seconds for Pd NPs and longer insertion durations do not lead to increase in the insertion rate; (iii) temperatures around 30 – 40 °C are optimal for maximizing the H insertion in Pd NPs, likely due to an optimal balance between the H adsorption rate, and the H diffusion rate into Pd; and (iv) the maximum concentration of H inserted into Pd varies linearly with the Pd NPs diameter in the range of 3.8 – 21.5 nm. Our investigation was carried out in both a three-electrode setup (RDE) with an acidic electrolyte (0.5 M H2SO4) and a proton pump setup (PP) with a proton exchange membrane. The latter, despite being rarely employed in the literature, allows unique investigations in a broad voltage range, i.e. <-0.5 V, and brings insight into the behaviour of catalyst materials in a representative real application device.

Figure 1
Insights into the Structure Sensitivity of Fe-Based Materials for the Oxygen Evolution Reaction
Authors: Martinez Hincapie Ricardo Alonso , Colic Viktor
Published: February 2024

The conversion of renewable energy into storable fuels is fundamental to the meeting of the net-zero CO2 emissions objective by 2050. However, the sluggish kinetics of the oxygen evolution reaction (OER) and the poor stability of electrocatalysts at industrial-level currents remain a problem for electrolyzers 1. Using platinum group metal-free electrocatalysts in anion exchange membrane electrolyzers is an appealing strategy to overcome some of the problems associated with PEM electrolyzers. Fe-based materials offer the possibility for the development of active, stable, and cost-effective electrocatalysts for the OER in alkaline media.

In this work, we explore the influence of structure, composition, or crystalline phase on different Fe-based electrodes for the OER. Different fabrication procedures such as additive manufacturing 2, flame spray synthesis, or pulse laser ablation 3 allow us to have a wide range of Fe-based materials with a well-defined structure/composition/phase. The materials have been extensively characterized by physicochemical methods (XPS, Raman, XRD, ICP) and their electrocatalytic activity evaluates following careful procedures in order to obtain reliable results. The results show that the activity of Fe-rich electrodes is poor. However, if Fe is alloyed with other materials or its surface structure or crystallinity degree is modified, it results in a more active material. This information could guide the synthesis of more active and stable water-splitting materials.

References

S. Cherevko, S. Geiger, O. Kasian, N. Kulyk, J.-P. Grote, A. Savan, B. R. Shrestha, S. Merzlikin, B. Breitbach, A. Ludwig, and K. J. J. Mayrhofer, Catalysis Today,
262 170-180 (2016).

J. Wegner, R. Martínez-Hincapié, V. Čolić, and S. Kleszczynski, Advanced Materials Interfaces,
n/a (n/a), 2202499 (2023).

J. Johny, Y. Li, M. Kamp, O. Prymak, S.-X. Liang, T. Krekeler, M. Ritter, L. Kienle, C. Rehbock, S. Barcikowski, and S. Reichenberger, Nano Research,
15 (6), 4807-4819 (2022).
Decoupling Reaction, Diffusion and Ohmic Processes in Fast-Charging Electrodes: A New Model for CV Data Analysis
Authors: ten Elshof Johan E. , Xia Rui , Zheng Jie , Huijben Mark
Published: February 2024

Fast charging is critical for the efficient storage of energy in devices like electric vehicles and portable electronics. The rate performance of electrodes is limited by the electron transfer rate, the ohmic resistance of the electrode, the size and shape of the primary electrode particles, and the charge carrier diffusion process within the electrodes. However, separating the intrinsic contributions of mass transport and charge transfer from non-equilibrium data obtained under large interfacial polarization is very complex, which limits our understanding of high rate electrodes during charging and discharging. While it is possible to extract the diffusive and capacitive components of an electrode’s capacity from cyclic voltammetry (CV) data using the Dunn method, the Dunn model assumes a constant diffusional overpotential. In reality the ohmic resistance scales with the current, so that the ohmic potential drop across the electrode cannot be neglected a priori for fast charging electrodes in which high current densities are a requirement.

We recently developed a new model based on the Butler-Volmer equation for the kinetics of the electron exchange process, and incorporated the charge carrier diffusion process and the internal ohmic losses, as well as the effect of the shape and dimensions of the primary electrode particles on the effective diffusion rate [1]. The model can provide the relation between current peak voltages and peak currents from a series of sweep rate CV measurements. The ohmic resistance, equilibrium voltage, exchange current (related to the electrochemical reaction rate) and limiting current (related to the charge carrier diffusion coefficient and Nernst diffusion layer thickness) can be extracted as independent variables from the fitted experimental data.

By simulating a range of different high rate Li electrode materials (both cathodes and anodes), we identified influence of the reaction rate on the overpotential as a common significant factor, which explains the nonlinear relation between the potential and the current at peak position in different CV measurements. Our analysis suggests that a higher electrochemical reaction rate seems to be more important for the realization of faster charging batteries than a larger carrier diffusion coefficient.

Finally, our extended model also enables us to predict the overpotential at any applied potential, which is not possible with other current models known till date. This insight helps us to gain more detailed understanding of the relationship between the intrinsic properties of the electrode materials and their rate performance in different reaction stages. This may facilitate further modification of electrode material towards enhanced high rate performance in next-generation batteries.

[1] R. Xia et al., Energy Storage Mater. 53 (2022) 381-390.
Sensor Absorbents for Heavy Metal Ions By Low-Cost Functionalization of Porous Carbons
Authors: Sandberg Mats , Petsagkourakis Ioannis , Beni Valerio
Published: February 2024

Porous carbons are key materials in electrodes for electrochemical energy storage as well as in water purification. Methods to modify porous carbons to enhance their properties as charge storing or water purification materials have been explored during the past decades [1,2]. The main application fields if porous carbon, water purification and energy storage, are highly cost sensitive. For this reason, there is a need to develop low-cost methods to modify porous carbons. Here, the use of benzoxazine chemistry to modify porous carbons is explored. Benzoxazine chemistry can be considered a protection group strategy for phenols, where the phenols from which the benzoxazines are synthesized, are deprotected upon benzoxazine polymerization. Further, benzoxazine polymerization produces Mannich bridges located near phenol groups, motifs that can be used to capture heavy metal ions. More specifically, in the first step, the porous carbons are partially impregnated with benzoxazine monomers, from melt or solutions to afford powders impregnated far below the liquid saturation level of the particles. That is, the particles retain porosity after the impregnation but still have a dry appearance. After impregnation, the particles are heated over the polymerization temperature of the benzoxazine to afford the porous carbon with immobilized functionalities. As phenols can initiate benzoxazine polymerization and be incorporated in the polymer, this method offers a simple route to produce polymerized and immobilized structure at a carbon interface. Here, results on metal ion absorption and the electrochemical response after exposure are presented for carbons modified by impregnation-polymerization of benzoxazines with or without incorporation of phenols. Inks were manufactured from the modified carbons. The electrochemical characterizations were performed on printed arrays of electrochemical cells on a substrate having dimensions of well plates and intended for automatized testing and where the carbon inks were deposited on the working electrodes. This methodology has a potential of simplifying the development of sensor materials and absorbents and can be automatized and potentially be supported with machine learning schemes. The electrochemical responses of exposure of the modified carbon electrodes to metal salt solutions show that impregnation-polymerization of functional benzoxazine can produce absorbents responding electrochemically to metal ion absorption with a scalable process starting from low-cost materials.

References:

[1] Sultana, et al., Clean. Eng. Tech. 6 (2022) 100382

[2] Pognon et al., J. Pow. Sourc. 196 (2011) 4117
Ammonia Recovery from Manure Wastewater and Simultaneous Electrosynthesis and Wastewater Treatment Using Ion Selective Redox Material
Authors: Jin Song
Published: February 2024

The environmental pressure due to greenhouse gas emissions and water contamination generated by livestock manure motivates the development of new approaches to reduce their environmental impacts and improve sustainability. Effective approaches to recover nutrients, especially ammonia, from manure wastewater to produce fertilizer are needed. Here we develop a new electrochemical strategy to achieve simultaneous ammonium (NH4
+) ion recovery and electrochemical synthesis using potassium nickel hexacyanoferrate as the ammonium ion-selective redox material to mediate the process. Our approach is built on our recent advances in designing modular electrochemical synthesis mediated using redox active materials (which we call redox reservoirs). Specifically, NH4
+ (and K+) can be spontaneously uptaken from manure wastewater with a nutrient (NH4
+ and K+) selectivity of ~100% driven by the oxidation of organic matter. Subsequently, NH4
+-rich fertilizers are released electrochemically together with the electrosynthesis of value-added chemicals, such as H2O2 as a disinfectant, without expensive ion-exchange membranes. We will also discuss our preliminary results on simultaneous advanced oxidation processes to improve the treatment of PFAS chemicals in wastewater. These results provide a new conceptual strategy for distributed electrochemical resource recovery and on-demand electrochemical manufacturing that can improve the sustainability of agricultural and wastewater treatment processes
Effect of the Magnetostriction Induced on the Crystalline Structure of Nanoparticulate TiO2 Films Supported on Stainless Steel Mesh Electrodes and Their Relationship with the Photocatalytic Decoloration of Aqueous Orange G Solutions
Authors: Valdez Nava Jesus Israel , Bustos Erika , Martinez Rodriguez Laura Lupita , Espejel-Ayala Fabricio , Sepúlveda-Guzmán Selene , Manriquez Juan
Published: February 2024

The study of ferromagnetism (FM) in non-cubic semiconductor oxides such as defective TiO2 is attractive due to their applications in photocatalysis [1]. FM can be activated in TiO2 nanomaterials by promoting oxygen vacancies (VO) located in paramagnetic defected sites Ti3+VOTi4+. In this context, the VO can induce in Ti3+-doped TiO2 structures remarkable magnetic anisotropy energy (MAE) of 6.51x106 erg/cm3, thus indicating the magnetic saturation should be achieved at magnetic fields (MFs) of ~425 gauss [2,3]. Therefore, magnetostriction can be observed in ferromagnetic TiO2 films as a phenomenon in which their dimensions and shapes are changed when they are magnetized. In this work, stainless steel mesh electrodes (ss) were modified by nanoparticulate TiO2 films (ssTiO2) enriched by Ti3+VOTi4+ sites, to gain an understanding of the effects of magnetostriction on the photocatalytic properties of ferromagnetic TiO2 electrodes. In this way, MFs having intensities (H) of 125, 250, 500, 1000, and 2000 gauss were applied to the ssTiO2 electrodes for 80 min under UV light illumination for increasing the number of Ti3+VOTi4+ sites. Our results revealed that the magnetic lines promoted compression of the TiO2 structure when achieving pressures p>4.67 GPa for H>425 gauss in p=1/2(MAE/4p gauss2)H
2. Consequently, the degree of disorder (0<b<1) of the electron traps at the intra-bandgap state's distribution along the thickness-axis(i.e. the x-axis) of TiO2 films decreased significantly because the fraction of trapped electrons f
trap(x) at the quasi-Fermi level EF(x) was maximized according to f
trap(x)=m[em

(E
F
(x)-E
F
(0))-1], where m=kT/b (k and T are the Boltzmann constant and the absolute temperature) [4,5]. Later, it was observed a significant increase of trapped holes able to carry out the direct photocatalytic oxidation of aqueous orange G (without electron scavenger’s assistance, e.g. gaseous O2). On the other hand, the photogeneration of oxidant •OH radicals decreased dramatically while H increased [6].

[1] Y. Bian et al., RCS Adv.,
11(2021)6284.; [2] D. Kim et al., J. Phys.: Condens. Matter,21(2009)195405.; [3] B. Shao et al., J. Appl. Phys.,115(2014)17A915. [4] N. Kopidakis et al., J. Phys. Chem. B, 107(2003)11307. [5] J. van de Lagemaat et al., J. Phys. Chem. B,104(2000)4292. [6] K.-I Ishibashi et al., J.Photochem.Photobiol.A,134(2000)139-142.

Acknowledgements

The authors thank the National Council for Science and Technology (CONACyT) Mexico for the funding support (grants CB No. 258789 and FOINS No. 3838). JIVN thanks CONACyT for his doctoral fellowship support (grant No. 893260).
Ag Nps@PEDOT Nanocomposite Electrosynthesis at a Polarised Liquid|Liquid Interface
Authors: Cheuquepan William , Quintero Jaime Andrés Felipe , Holzinger Angelika , Scanlon Micheal D.
Published: February 2024

One of Material Science's main challenges is constantly searching for new versatile materials. In this sense, nanocomposites have emerged as an alternative to new substrates due to their unique properties. These hybrid systems are made up of organic polymers with inorganic components. This ideal "tandem" is made up of organic polymers (for example, poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy) and polyaniline (PANI)) with conductive characteristics because of their highly p-conjugated polymeric chains, unique properties, reversible doping/de-doping processes, and controllable chemical/electrochemical properties. Inorganic compounds, such as metallic nanoparticles (NPs), in the organic matrix provide a high surface area and conductivity, acting as protuberances and highly conductive fillers to form a class of material with multidisciplinary applications [1].

There are several methods to generate organic polymers; the electrochemical process is one of the most used due to its versatility and simplicity. This method implies the electrodeposition of the organic polymer on an electrode surface, eliminating the possibility of obtaining a polymeric material separated from the electrode surface and limiting the areas of applicability (polymer firmly attached to the electrode surface). In this sense, the use of a polarised immiscible liquid|liquid (L|L) interfaces is demonstrated as a novel approach for the electrosynthesis of surfactant-free organic thin films, allowing complete control over the thin film morphology [2].

In this work, we present the electrosynthesis of silver nanoparticles@PEDOT nanocomposites based on EDOT polymerization (PEDOT) and the formation of silver nanoparticles by electrochemical polymerisation at a polarised L|L interface. In thermodynamic terms, the oxidant potential of silver ions is insufficient to oxidise 3,4-ethylenedioxythiophene and generate PEDOT. However, under specific conditions (detailed in this presentation), silver ions are reduced while EDOT monomers are oxidised to PEDOT. A deep knowledge of biphasic electropolymerisation coupled with silver nanoparticle formation will help advance the search for new materials for a broad spectrum of applications (antibacterial, electrocatalysis, SERS substrates, biocompatibility substrates, etc.).
Enhancing Material Analysis with Statistical and Computer Vision Techniques: A Comprehensive Approach for Evaluating Electrode Quality
Authors: Vinayakumar Vineetha , Jain Adarsh , Segets Doris
Published: February 2024

The optimization of electrodes for electrocatalysis is critical to the efficient operation of energy conversion applications, i.e., performance and efficiency can be improved by optimizing their fabrication process [1]. In the surface microstructure of anodes has been recognized as a fundamental aspect influencing their functionality [2]. Consequently, it is vital to precisely characterize the microstructure of electrodes. Atomic force microscopy (AFM) has demonstrated to be a potent technique for scrutinizing the nanoscale microstructure of anodes. Nevertheless, AFM has limitations in investigating vast areas, thereby posing a challenge when evaluating the surface microstructure of large-scale electrodes.

In this study, we developed a multi-stage data quantification method to overcome the limitations of AFM to measure large electrode areas. The efficacy of the developed approach that combines statistical analysis and computer vision techniques was validated by scrutinizing anodes made under various spray coating process conditions. The results demonstrated that the proposed method facilitated the in-depth evaluation of the degree of homogeneity, surface smoothness, and the presence of cracks or defects, thereby enabling a comprehensive assessment of electrode quality. It was possible to establish structure-performance relationships and delineate the interdependence between surface morphology and anode performance, activity, and cycling stability by combining surface analysis measurements with electrochemical analysis.

In conclusion, this link between surface and electrochemical analysis will provide critical insights into anode performance and, in turn, drive the development of advanced materials for energy conversion technologies. Therefore, we believe our method has a high potential to expand the material scientist's toolkit and extend its application to analyze the micro/nanostructure of diverse materials in a wide range of applications, providing novel insights for their optimization.

References

Siegmund, D., et al., Crossing the valley of death: from fundamental to applied research in electrolysis. Jacs Au, 2021. 1(5): p. 527-535.

Chatenet, Marian, et al. "Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments." Chemical Society Reviews (2022).
Engineering Gas Diffusion Electrode Microstructures for the Electrochemical Reduction of CO2
Authors: Amireh Senan F. , Jacquemond Remy Richard , Forner-Cuenca Antoni
Published: February 2024

The electrochemical reduction of CO2 has the potential to enable a circular economy where the captured CO2 can be utilized to produce valuable chemicals. However, existing CO2 reduction electrolyzers suffer from limited performance (i.e. low current densities) and short operation times (1-200 hours)1. The gas diffusion electrode (GDE) is a key component which determines system durability and enables higher current density operation. Yet, commercially available GDEs are carbon fiber-based materials, which were developed to fulfill the requirements of polymer electrolyte fuel cells and were repurposed for emerging CO2 electrolyzers. While functional, the commercial GDEs microstructure and surface properties do not meet the requirements of CO2 electrolysis flow cells which leads to their failure within short operation hours. These GDEs fail due to flooding through different mechanisms such as electrowetting2, capillary imbibition3, salt precipitation3, and uneven pressure distribution4. Therefore, there is a need to develop novel GDEs with engineered microstructures and wettability for the unique challenges of CO2 electrolyzers.

In this research, we aim to understand the influence of the GDE microstructure on the durability and performance of CO2 electrolyzers. Instead of leveraging commercially available carbon-fiber based substrates, we conceptualize and deploy a scalable technique to manufacture novel GDEs with tunable microstructure. We hypothesize that tackling the multiphase transport challenges in CO2 electrolyzers requires electrode formats containing a plurality of pore sizes and highly controlled microstructures. Thus, we aim to develop a synthetic methodology affording a high degree of microstructural versatility and low manufacturing costs. We investigate the effect of synthetic parameters on the resulting microstructural (e.g. porosity, pore size distribution) and wetting properties. Furthermore, we aim to correlate the synthetic parameters with the resulting GDE properties (e.g. microstructure, porosity) and the corresponding transport properties (e.g. permeability, capillarity, diffusivity). These properties will be further correlated to the flow cell durability and performance. We hypothesize that tuning the pore size distribution and surface chemistry of the GDEs can enhance mass transport rates and resistance to flooding, which could enable longer operating times and higher current density.

References

D. Wakerley et al., Nat Energy, 7, 130–143 (2022).

K. Yang, R. Kas, W. A. Smith, and T. Burdyny, ACS Energy Lett, 6, 33–40 (2021).

M. E. Leonard, L. E. Clarke, A. Forner‐Cuenca, S. M. Brown, and F. R. Brushett, ChemSusChem, 13, 400–411 (2020).

L. M. Baumgartner, C. I. Koopman, A. Forner-Cuenca, and D. A. Vermaas, ACS Sustain Chem Eng, 10, 4683–4693 (2022).
Electro-Catalytic Nitrogen Reduction by Metal Oxynitride Thin Films: Effect of Metal Oxophilicity, and Role of Lattice Nitrogen
Authors: D'Souza Francis , Ganesan A. , Chukwunenye Precious , Balogun Kabirat , Gharee Mojgan , Cundari Thomas R. , Kelber Jeffry
Published: February 2024

The electrocatalytic reduction of molecular nitrogen to ammonia—the nitrogen reduction reaction (NRR)—is of broad interest as an environmentally- and energy-friendly alternative to the Haber-Bosch process for agricultural and emerging energy applications. Herein, we present our recent findings from collaborative electrochemistry/surface science/theoretical studies that counter several commonly held assumptions regarding transition metal oxynitrides and oxides as NRR catalysts. Specifically, we demonstrate that for the vanadium oxide, vanadium oxynitride, and cobalt oxynitride systems, (a) there is no Mars-van Krevelen mechanism and that the reduction of lattice nitrogen and N2 to NH3 occurs by parallel reaction mechanisms at O-ligated metal sites without incorporation of N into the oxide lattice, and (b) that NRR and the hydrogen evolution reaction (HER) do occur in concert under the conditions studied for Co oxynitride, but not for V oxynitride. Additionally, these results highlight the importance of both O-ligation of the V or Co center for the metal-binding of dinitrogen, and the importance of N in stabilizing the transition metal cation in an intermediate oxidation state for effective N≡N bond activation.1-3

Acknowledgment: This work was supported by the National Science Foundation through grants DMR-2112864 (to JAK, TRC, and FD) and partial support by CHE-1953547 (to TRC). Additional NSF support for the UNT CASCaM HPC cluster via Grant CHE-1531468 is also gratefully acknowledged.

Ganesan, A. Osonkie, P. Chukwunenye, T. Cundari, F. D'Souza, J. Kelber. Electrochemical Reduction of N2 to ammonia by vanadium oxide thin films at neutral pH, J. Electrochem. Soc., 2021, 168, 026504.

Osonkie, A. Ganesan, P. Chukwunenye, F. Anwar, K. Balogun, M. Gharee, I. Rashed, T. R. Cundari, F. D’Souza, and J. A. Kelber, Electro-catalytic reduction of nitrogen to ammonia: The roles of lattice O and N in reduction at vanadium oxynitride surfaces, ACS Adv. Mater & Interface, 2022,
14, 531-542.

Chukwunenye, A. Ganesan, M. Gharaee, K. Balogun, F. Anwar, Q. Adesope, T. R. Cundari, F. D’Souza, and J. A. Kelber, ‘Electrocatalytic Selectivity for Nitrogen Reduction vs. Hydrogen Evolution: A Comparison of Vanadium and Cobalt Oxynitrides at Different pH Values.’ J. Mater. Chem. A, 2022, 10, 21401-21415.
What Controls Activity Trends of Electrocatalytic Water Splitting? - Activation Energy Vs. Frequency Factor
Authors: Zeradjanin Aleksandar R.
Published: February 2024

Electrocatalytic water splitting is a topic of investigation of numerous research groups for decades. Oxygen evolution reaction (OER), as a more complex and more demanding reaction, is more frequently studied, despite of the fact that the simpler hydrogen evolution reaction (HER), is generally not well understood. Nowadays, recurrent approach to electrocatalysis is conquest for more active and more stable electrode materials, very often lacking significant input to better understanding of reaction mechanisms or understanding of what are the drivers of electrocatalytic activity [1].

Importantly, if one asks the key question from the conceptual point of view, and that is: what are the origins of electrocatalytic activity? - the answer will be, in the predominant majority of cases, like 70 years ago. Namely, paradigm of electrocatalysis is Sabatier principle, that suggests optimal (“not too strong, not too weak”) binding of intermediates as main precondition of high reaction rate [2]. Conventional wisdom suggests that confirmation of this should be relatively simple. Namely, Brönsted-Evans-Polanyi (BEP) relations suggest linear relationship between adsorption energy of key intermediates and activation energy. In other words, if we have reliable values of adsorption energies relevant for the electrochemical environment [3], they should form linear dependence with experimentally obtained activation energies.

However, high-temperature hydrodynamic experiments on HER indicate that reducing of activation energy by tuning of adsorption energy of intermediates is not necessarily beneficial for enhancement of HER rate. Namely, HER rate is strongly influenced by preexponential frequency factor. Therefore, we propose discussion that will analyse several key aspects of HER electrocatalysis: 1) interplay of activation energy and preexponential factor as a driver of electrocatalytic activity 2) are BEP relations relevant for electrocatalysis 3) can we assess adsorption energies experimentally 4) what are relevant descriptors that shed light on HER activation process, 5) what else is important beyond Sabatier principle for rate of HER [1-7].

Figure 1. Graphical illustration of four interfacial descriptors relevant for HER. Adapted from Ref. [4] with permission from the PCCP Owner Societies, under the terms and conditions of the Creative Commons Attribution 3.0 Unported License.

References

[1] A.R. Zeradjanin et al, ChemElectroChem
2022,
9, e202101278

[2] A.R. Zeradjanin et al, Electrochimica Acta
2021,
388, 138583

[3] A.R. Zeradjanin et al, Journal of Solid State Electrochemistry
2021,
25, 33

[4] A.R. Zeradjanin et al, PCCP
2020,
22, 8768

[5] A.R. Zeradjanin et al, PCCP
2017,
19, 17019

[6] A.R. Zeradjanin et al, Electroanalysis
2016,
28, 2256

[7] A.R. Zeradjanin et al, ACS Catalysis
2022, 12, 11597

Figure 1
Insight into the Formation and Catalytic Mechanism of “CO Pool” during Electrocatalytic Conversion of CO2
Authors: He Anbang , Du Jun
Published: February 2024

The OC-CO coupling reaction, requiring pairs of *CO or *CHO intermediates absorbed on adjacent Cu sites, is the key elementary reaction during the electrocatalytic conversion of CO2 towards C2 products, where the harsh demand of adjacent *CO cause the transmission and preservation of CO species become the critical step of CO coupling reaction. Among the reported M-Cu (M=Ag, Au, Zn, etc....) tandem catalysts and Cu+-Cu sites, CO goes through the route of “generation-desorption-transmission-deeply reduction” over the catalytic surface. Despite the in-depth studies of the various site’s composition, morphological structures, and catalytic sites arrangement on Cu-based catalysts, the migratory manner on the electrode surface and the concentration and reactivity of CO in the double layer is still obscure, which are essential steps for CO spillover on the surface of Cu-based catalysts and further coupling reactions, as well as the underlying causes of the poor selectivity of CO/C2 products. At the same time, in situtechniques with temporal resolution are still lacking for probing the overflow and inter-diffusion of CO in the double layer.

In this study, based on the rotating disk electrode, we developed an effective means for in situ monitoring of the transport and electrochemical properties of CO in the diffusion layer. Based on theoretical analysis of the electrochemical interface CO species transfer path and time-resolved RRDE techniques, we proved that most of the CO intermediates are favorable to transferred and then reserved in the diffusion layer, leading to an enhanced concentration of CO over equilibrium concentration, and finally benefitted the transmission and reactivity of CO species. By analyzing the reaction chain, combined with in situ ATR-SEIRAS monitor and theoretic calculation, the chemical potential was proved to be enhanced by introducing the “CO pool”, which could be resonated in the reaction chain, raised an increased entropy production and finally led to a resonance-enhanced concentration of by-intermediates, finally strengthening the activity of whole chain-system.

Figure 1
Electrochemical Analysis on Transition Metal Nitride Catalysts for Nitrogen Reduction Reaction
Authors: Flosadóttir Helga Dögg , Hanifpour Ása , Skulason Egill
Published: February 2024

A versatile and sustainable process for ammonia production is needed to ensure a sustainable future for the growing global population, both with regards to fertilizer production as well as energy carrier. Theoretical simulations of transition metal nitride catalysts have demonstrated the possibilityof a nitrogen reduction reaction catalysis cycle on four transition metal nitrides, CrN, VN, ZrN and NbN.[1,2] Reproducible and reliable research and development approaches in the direction of electrochemical reduction of nitrogen towards ammonia are therefore of importance. An operando ammonia quantification methodology for electrochemical catalysis studies has been developed in-house and recently published [3]. Allowing for automatic, quantitative detection of aqueouos ammonia at the ppb level, within minutes from the sample preparation. We have now analyzed all four theoretically proposed TMNs, as well as rutile Niobium oxynitride (NbON) of several stochiometries as thin films on a conductive electrode substrate in ambient environment and aqueouos electrochemical system [3,4].Electrochemical analysis and ammonia quantification suggest NbON of specific stochiometry and ZrN to be promising catalyst candidates, while lacking stability in the environment of choice in these studies.

Literature:

[1] Y. Abghoui, A.L. Garden, J.G. Howalt, T. Vegge and E. Skúlason, Electroreduction of N2 to ammonia at ambient conditions on mononitrides of Zr, Nb, Cr, and V: A DFT guide for experiments. ACS Catalysis, 2016.6(2): p. 635.

[2] Y. Abghoui, A.L. Garden, V.F. Hlynsson, S. Björgvinsdóttir, H. Ólafsdóttir and E.Skúlason, Enabling electrochemical reduction of nitrogen to ammonia at ambient conditions through rational catalyst design. Physical Chemistry Chemical Physics,2015.17(7): p. 4909.

[3] F. Hanifpour, C.P. Canales, E.G. Fridriksson, A. Sveinbjörnsson, T.K. Tryggvason,E. Lewin, . . . H.D. Flosadóttir, Investigation into the mechanism of electrochemical nitrogen reduction reaction to ammonia using niobium oxynitride thin-film catalysts. Electrochimica Acta, 2022.403: p. 139551.

[4] F. Hanifpour, C.P. Canales, E.G. Friðriksson, A. Sveinbjörnsson, T. Tryggvason, Y.Abghoui, . . . E. Skúlason, Operando Quanitification of ammonia produced from computationally derived transition metal nitride electro catalysts. Journal of Catalysis, 2022. 413: p.956
Two-Dimensional Carbon Nitride as a Support of Single Metal Atom for Carbon Dioxide Reduction Reaction
Authors: Posada Perez Sergio , Vidal López Anna , Solà Miquel , Poater Albert
Published: February 2024

Electrochemical conversion of CO2 into added-value chemicals is an important approach to recycle CO2. Heterogeneous catalysis is widely used in industrial applications because of the possibility of facile separation, which reduces the operating costs, although heterogeneous catalysts often have limited selectivity. In contrast, homogeneous catalysts are very selective although they have limited industrial applications due to their cost, the use of precious metals, and the difficulty in separating and recovering the catalysts. Currently, the research community is trying to combine the properties of homogeneous and heterogeneous catalysts. From the heterogeneous catalyst perspective, research has been focused on creating smaller and dispersed catalyst particles. Single-atom catalysts (SACs), which comprise atoms of metal species dispersed on a solid support, are expected to bridge the homogeneous and heterogeneous catalyst properties.

The work described herein explores, by means of density functional simulations, the electrocatalytic CO2 reduction reaction (CO2RR) using several single transition metal atoms anchored in 2D graphitic carbon nitride (g-C3N4),1 focusing on the group XI transition metals since they include Cu, the only transition metal capable of reducing CO2 to hydrocarbons and alcohols with acceptable faradaic efficiencies. Moreover, the Cu1/g-C3N4 system has been experimentally evaluated as CO2RR electrocatalysts. 2D g-C3N4 has been demonstrated to be a competitive candidate for electrocatalytic CO2 reduction since it can act as an active support for single metal-atom catalysts, mainly Cu, Pd, and Pt, and the deposition of Au single atom was experimentally characterized.

The computational hydrogen electrode model has been used to explore the suitability of several transition metals atoms anchored to C3N4, showing that single atoms enhance the catalytic activity of the system as the first proton–electron transfer is thermodynamically favored in comparison to bare carbon nitride support. Our theoretical interpretations are consistent with the experimental results using Cu1/g-C3N4,2 revealing that the competitive H2 generation is favored due to the strong CO binding energies. This fact reinforced the capability of our computational models to predict the behavior of several single metal atom electrocatalysts to reduce CO2, for instance, predicting that Au can promote the methane formation after eight electron-proton transfer processes. Our computational study paves the road to finding suitable metals that catalyze the first proton–electron transfer in the carbon dioxide reduction reaction.

Posada-Pérez, A. Vidal-López, M. Solà, and A. Poater, 2023, Phys. Chem. Chem. Phys, 25, 8574.

Cometto, A. Ugolotti, E. Grazietti, A. Moretto, G. Bottaro, L. Armelao, C. Di Valentin, L. Calvillo and G. A. Granozzi, npj 2D Mater.
Appl., 2021, 5, 63.

Figure 1
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
Activated Vacuum Residue for Efficient Oxygen Reduction Reaction in Alkaline Media
Authors: Jalilov Almaz S.
Published: February 2024

As a potential replacement for Pt-based materials, the heteroatom-doped and metal-free porous carbons have always been a crucial challenge in modern electrocatalysis. On the other hand, petroleum waste, particularly, vacuum residue presents as a carbon-rich precursor for the development of porous carbons for electrocatalysis. Herein, the new catalysts were prepared from vacuum residue gained from the local petroleum industry. The porous carbons (PCs) as the catalysts were prepared via a simple single route activation at 800 °C and 2 hours in the presence of phosphoric acid. PC possesses a high surface area at ~2200 m2/g with mixed micro- and meso porosities as well as high graphitization content. Spectroscopic analyses reveal up to ~6 % of phosphorous doping content. PCs were tested against oxygen reduction reaction (ORR) as an important challenge in electrochemistry. The structural features and the differences in the activating agents for the development of the PCs were compared to decipher the importance of the doped heteroatoms’ environment in ORR. The ORR efficiency of the electrocatalysts was compared against the commercial 5% Pt/C under alkaline conditions to show the potential of the vacuum residue-derived PCs as the sustainable utilization of petroleum waste.