Protonation Process Research Articles

Tuning the Acid Hardness Nature of Cu Catalyst for Selective Nitrate‐to‐Ammonia Electroreduction

Electrocatalytic nitrate reduction reaction (NO3RR) in alkaline electrolyte presents a sustainable pathway for energy storage and green ammonia (NH3) synthesis. However, it remains challenging to obtain high activity and selectivity due to the limited protonation and/or desorption processes of key intermediates. Herein, we propose a strategy to regulate the acid hardness nature of Cu catalyst by introducing appropriate modifier. Using density functional theory calculations, we firstly identified that the BaO‐modified Cu showed optimal Gibbs free energies for key NO3RR steps, including the protonation of *NO and the desorption of *NH3. Experimentally, the BaO‐modified Cu catalyst exhibited 97.3% Faradaic efficiency (FE) for NH3 with a yield rate of 356.9 mmol h‐1 gcat‐1. It could also maintain high activity across a wide range of applied potentials and nitrate substrate concentrations. Detailed experimental and theoretical studies revealed that the Ba species could modulate the local electronic states of Cu, enhance the electron transfer rate, and optimize the adsorption/protonation/desorption processes of the N‐containing intermediates, leading to the excellent catalytic performance for NO3‐‐to‐NH3.

Tuning the Acid Hardness Nature of Cu Catalyst for Selective Nitrate-to-Ammonia Electroreduction.

Electrocatalytic nitrate reduction reaction (NO3RR) in alkaline electrolyte presents a sustainable pathway for energy storage and green ammonia (NH3) synthesis. However, it remains challenging to obtain high activity and selectivity due to the limited protonation and/or desorption processes of key intermediates. Herein, we propose a strategy to regulate the acid hardness nature of Cu catalyst by introducing appropriate modifier. Using density functional theory calculations, we firstly identified that the BaO-modified Cu showed optimal Gibbs free energies for key NO3RR steps, including the protonation of *NO and the desorption of *NH3. Experimentally, the BaO-modified Cu catalyst exhibited 97.3% Faradaic efficiency (FE) for NH3 with a yield rate of 356.9 mmol h-1 gcat-1. It could also maintain high activity across a wide range of applied potentials and nitrate substrate concentrations. Detailed experimental and theoretical studies revealed that the Ba species could modulate the local electronic states of Cu, enhance the electron transfer rate, and optimize the adsorption/protonation/desorption processes of the N-containing intermediates, leading to the excellent catalytic performance for NO3--to-NH3.

Bimetallic metal-organic frameworks as electrode modifiers for enhanced electrochemical sensing of chloramphenicol.

Anelectrochemical sensor is presentedfor the detection of the chloramphenicol (CAP) based on a bimetallic MIL-101(Fe/Co) MOF electrocatalyst. The MIL-101(Fe/Co) was prepared by utilizing mixed-valence Fe (III) and Co (II) as metal nodes and terephthalic acid as ligands with a simple hydrothermal method and characterized by SEM, TEM, XRD, FTIR, and XPS. Electrochemical measurements such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) showed that bimetallic MIL-101(Fe/Co) had the faster electron transfer, larger electroactive area, and higher electrocatalytic activity compared with their monometallic counterparts due to the strong synergistic effect between bimetals. Inspired by these results, the MIL-101(Fe/Co)-based sensor was used to detect CAP. Some experiment parameters of pH, Fe and Co molar ratio, MIL-101(Fe/Co) volume, and DPV quiet time were optimized. The direct reduction mechanism of CAP was verified to involve four electrons and four protons process. Finally, the sensitive and selective CAP detection in the concentration range 1 to 200μM with a detection limit of 0.3μM was realized by the proposed sensor. The satisfactory recoveries in tap water and lake water indicated the practicability of the proposed electrochemical sensor. It is expected that this work may open up a paradigm for the preparation of MOF-based electrode modifiers with desired electrocatalytic performance for environmental pollution monitoring.

Photoresponsive Helical Foldamers: Conformational Control Through Double Helix Formation and Light-Induced Protonation.

Helical foldamers constitute particularly relevant targets in the field of host-guest chemistry, be that as hosts or substrates. In this context, the strategies reported so far to control the dimensions and shape of foldamers mainly involve modifications of the skeleton through covalent synthesis. Herein, we prepared an oligopyridine dicarboxamide foldamer substituted by photo-active tetraphenylethylene units (TPE). We demonstrate that it is possible to toggle the length of a helical foldamer by two means. First, the elongation of foldamers can be tuned by adjusting the concentration, as demonstrated by DOSY NMR spectroscopy and X-ray diffraction analyses on both the single and the double helix structures. Secondly, and in a more original manner, a photo-induced protonation process triggered by TPE units promotes a novel pathway to unfold helical foldamers, leading to dramatic conformational and spectroscopic changes.

Promoting Hydrogen Transfer in Electrochemical CO2 Reduction via a Hydrogen on Demand Pathway.

The proceeding of electrochemical CO2 reduction reaction (CO2RR) requires the formation of active hydrogen species for CO2 protonation, while traditional catalysts fail to balance the rate of hydrogen supply and CO2 protonation. Herein, we propose a "hydrogen on demand" mechanism, in which the polarity of the adsorbed CO2 is enhanced to allow the capture of hydrogen from water without forming free hydrogen species, realizing the matching rate of hydrogen supply and CO2 protonation. As a proof of concept, we construct Zn-N sites modified by Se atoms, allowing the proceeding of CO2RR under the "hydrogen on demand" mechanism with superior efficiency. The catalyst achieves an industrial CO current of -539.7 mA cm-2, faradaic efficiencies of CO > 90% over a broad window from -0.5 to -1.1 V vs. reversible hydrogen electrode and a high turnover frequency of 7.6 × 104 h-1 in flow cell. In-situ characterization and theoretical calculations reveal that the introduced Se sites enhance the electron localization around the Zn sites, thus increasing the polarity of adsorbed CO2- with improved ability to acquire hydrogen species from water to facilitate the protonation process.

Time-Resolved Chemical Bonding Structure Evolution by Direct-Dynamics Chemical Simulations.

Direct-dynamics simulations monitor atomic nuclei trajectories during chemical reactions, where chemical bonds are broken and new ones are formed. While they provide valuable information about the ongoing nuclear dynamics, the evolution of the chemical bonds is customarily overlooked, thus, hindering key information about the reaction mechanism. Here we examine the evolution of the chemical bonds for the three main mechanisms of the F- + CH3CH2Cl reaction using quasi-classical trajectories for the nuclei, and global natural orbitals for the electrons. Key findings include (i) bimolecular nucleophilic substitution (SN2) resembles a one-step bond breaking and formation process; (ii) the elimination mechanisms (syn- and anti-E2) feature a sequential two-step process of proton abstraction and Cl- elimination; and (iii) the anti-E2 mechanism is slower, exhibits rebound effects, and gets activated by specific vibrational modes. This study highlights the importance of correctly describing and thoroughly analyzing the dynamical evolution of chemical bonds for chemical reaction mechanistic studies.

Investigating Protonic Surface Exchange Kinetics in Protonic Conducting Electrolysis Cells Using Electrical Conductivity Relaxation

Triple conducting oxides in Protonic Conducting Electrolysis Cells (PCECs) have received considerable attention due to its high activity to steam electrolysis. While extensive research has explored the performance of the air electrode using various methodologies, there are no reports yet on the proton exchange k values of triple-conducting electrode under applied potential by any method to the best of our knowledge. In this study, we propose employing Electrical Conductivity Relaxation (ECR) as a novel approach to investigate protonic surface exchange kinetics under potential. Leveraging state-of-the-art air electrodes as model materials, we conducted protonic hydration processes by transitioning the atmospheric conditions from dry air to humidified air. The evolution of the conductivity relaxation profile was meticulously monitored, and the acquired data was subjected to rigorous analysis through modeling techniques, enabling us to discern the surface exchange rate (k) under varying potentials and steam concentrations. By shedding light on the electrode hydration behavior under semi-working conditions, this work provides valuable insights crucial for the advancement and innovation of next-generation electrodes for PCECs.

Simulation of displacement damage in Si & SiO2 caused by protons

Nowadays Si & SiO2 have been the most widely used materials in semiconductor devices as CPU and other various integrated circuit chips, utilized in aerospace electronic systems, and at the same time protons are important components of cosmic rays that can cause displacement damage in Si & SiO2. Therefore, it is essential to study the displacement damage of Si & SiO2 caused by protons. The software of Geant4 is adopted in this paper, to simulate transportation process of incident protons with different energy in Si & SiO2. The simulation results indicates that primary knock-on atom (PKA) generated by incident proton in Si & SiO2 is predominant in lower energy range, its spatial distribution increases gradually along the direction of incident proton, and the scattering angle of the PKA is about 90°, following a Gaussian distribution approximately. And in lower energy range, 28Si and 16O generated by elastic scattering are a primary source of radiation damage in Si & SiO2. But as the proton energy increases, the contribution of nuclear inelastic scattering becomes more and more important, but the overall level of induced damage diminishes gradually. Meanwhile, the simulation results indicate that with increasing depth of the material, the non-ionizing energy loss (NIEL) increases gradually, and NIEL caused by elastic scattering is higher near the surface layer of the materials, and as for NIEL caused by nuclear inelastic scattering is also higher near the surface layer of the materials. The simulation results in this paper can provide useful data and theoretical guidance for study on Si & SiO2 displacement damage caused by proton irradiation.

Insight into the effect of terminal aromatic group on the mesomorphic, emissive and stimuli-responsive properties of cyanostyrene-based derivatives with multiple applications

Three novel series of cyanostyrene-based derivatives containing pyridine, cyanostyrene and terminal phenyl, naphthyl and anthryl as π-conjugated aromatic unit were synthesized by Suzuki coupling and Knoevenagel reactions. A slight modification in chemical structures induced significant differences in self-assembly property in bulk state, emissive properties in both solution and aggregated states, mechanochromic properties and acidochromism properties. The terminal phenyl cyanostyrene-based derivatives exhibited a mesophase transition from nematic phase to smectic A phase upon elongation of the terminal chain and decreasing temperature, whereas the other terminal naphthyl and anthryl cyanostyrene-based derivatives were non-mesogen, which might be attributed to the increased twisted molecular configuration and geometric anisotropy. All the compounds displayed positive solvatochromic behaviors and the redshift in emission spectra gradually increased from terminal naphthyl compound via phenyl compound to anthryl compound attributing to the enhancement in intramolecular charge transfer. All the compounds displayed emission in both solution and aggregated states due to the twisted molecular configurations or/and distinct intramolecular charge transfer. The terminal phenyl and naphthyl compounds displayed extremely weak mechanochromism, whereas the terminal anthryl compound displayed distinct mechanochromism due to the highly twisted molecular configuration of the anthryl compound. Reversible high-contrast acidochromism was realized for all the compounds due to the reversible protonation and deprotonation process of pyridine. In addition, the good applications in security paper, encrypted ink and bioimaging were also demonstrated. This investigation elucidates that a slight change in chemical structures could induce big differences in characteristics in different states, which afforded effective ways for the construction of multifunctional materials.

Probing the Effect of pH Value and Voltage on the Near‐Surface Proton Concentration at the Electrochemical Interface by In Situ Electrochemical Surface‐Enhanced Raman Spectroscopy (EC‐SERS)

ABSTRACTUnderstanding the variation of proton concentration near the surface of the electrochemical interface is of great significance for understanding the mechanism of electrochemical reactions. In this work, 4‐Mpy molecules that are protonated and deprotonated depending on the surrounding pH value adsorb on the Au nanoparticle film electrode with high SERS activity, and by virtue of the highly interfacial‐sensitive EC‐SERS technique, we systematically studied the effects of electrolyte pH value and external voltage on the protonation and deprotonation of 4‐Mpy at the interface between Au‐NP film electrode and phosphate buffer, to analyze the changes of near‐surface proton concentration at the electrochemical interface. It is found that the pH value of the electrolyte plays a decisive role in the protonation process of 4‐Mpy at the electrode interface at low reduction voltage (< −0.1 V). In acidic and neutral solution, 4‐Mpy exists mainly in protonated form on the electrode surface. However, in alkaline solutions, 4‐Mpy exists mainly on the electrode surface in the form of deprotonation. At high reduction voltage (≥ −0.1 V), the protonation and deprotonation of 4‐Mpy on the electrode surface are mainly determined by the adsorption structure of 4‐Mpy on the electrode surface. At the same time, we conducted a comparative study of 2‐Mpy and 4‐Mpy molecules and found that the adsorption modes were different depending on the position of the N atom. 2‐Mpy is inclined adsorbed on the surface of the Au‐NP film electrode, and 4‐Mpy is vertically adsorbed on the surface of the Au‐NP film electrode.

Modular Synthesis of Polycarbonyl Compounds via Regioselective Hydration of Oxo-Alkynes.

A novel protocol has been developed for the modular synthesis of polycarbonyl compounds by catalytic hydration of 1,3-diketone-tethered alkynes. The hydration process exhibits good regioselectivity and high yields at room temperature, avoiding the use of strong acids and noble metals and the requirement for elevated temperatures. Mechanistic insights suggest that the hydration proceeds through a concerted process of alkyne protonation and remote carbonyl participation. This approach provides direct access to tandem heterocycle dyads and triads.

The Identification of Faults using Magnetic Method in Kulonprogo, Yogyakarta, Indonesia

The aims of this study to identify faults and identify subsurface lithology using magnetic anomaly data in the Kulonprogo. In the acquisition was carried out using a Proton Procession Magnetometer (PPM) Geotron G5 with 62 measurement points and a distance of ±1 km between point. Measurements were made on Kebobutak (Tmok), Aluvium (Qa), Andesit (a), and Sentolo (Tmps) formations. The total magnetic field data processing is done with several correction, namely diurnal correction, IGRF, reduce to equator, upward continuation at an altitude of 2000 m, and reduce to pole, and 2D modelling using the forward modelling method. The result of the analysis obtained magnetic field anomaly values in the range of values -400 to 950 nT. The 2D modelling shows that the research area is composed of 4 dominating rock types, namely andesite rock with a susceptibility value of 94 x 10-3, andesite breccia rock with a susceptibility value of 29 x 10-3, clay rock with a susceptibility value of 0,013 x 10-3, and sandstone with a susceptibility value of 5 x 10-3. The identification result show the existence of faults line on Mount Watuaglik, Mount Kamal, and Mount Bodag.

Integrated “Two‐in‐One” Strategy for High‐Rate Electrocatalytic CO2 Reduction to Formate

AbstractThe electrochemical CO2 reduction reaction (ECR) is a promising pathway to producing valuable chemicals and fuels. Despite extensive studies reported, improving CO2 adsorption for local CO2 enrichment or water dissociation to generate sufficient H* is still not enough to achieve industrial‐relevant current densities. Herein, we report a “two‐in‐one” catalyst, defective Bi nanosheets modified by CrOx (Bi−CrOx), to simultaneously promote CO2 adsorption and water dissociation, thereby enhancing the activity and selectivity of ECR to formate. The Bi−CrOx exhibits an excellent Faradaic efficiency (≈100 %) in a wide potential range from −0.4 to −0.9 V. In addition, it achieves a remarkable formate partial current density of 687 mA cm−2 at a moderate potential of −0.9 V without iR compensation, the highest value at −0.9 V reported so far. Control experiments and theoretical simulations revealed that the defective Bi facilitates CO2 adsorption/activation while the CrOx accounts for enhancing the protonation process via accelerating H2O dissociation. This work presents a pathway to boosting formate production through tuning CO2 and H2O species at the same time.

Sublimation Transformation Synthesis of Dual-Atom Fe Catalysts for Efficient Oxygen Reduction Reaction.

Dual-atom catalysts (DACs) have garnered significant interest due to their remarkable catalytic reactivity. However, achieving atomically precise control in the fabrication of DACs remains a major challenge. Herein, we developed a straightforward and direct sublimation transformation synthesis strategy for dual-atom Fe catalysts (Fe2/NC) by utilizing in situ generated Fe2Cl6(g) dimers from FeCl3(s). The structure of Fe2/NC was investigated by aberration-corrected transmission electron microscopy and X-ray absorption fine structure (XAFS) spectroscopy. As-obtained Fe2/NC, with a Fe-Fe distance of 0.3 nm inherited from Fe2Cl6, displayed superior oxygen reduction performance with a half-wave potential of 0.90 V (vs. RHE), surpassing commercial Pt/C catalysts, Fe single-atom catalyst (Fe1/NC), and its counterpart with a common and shorter Fe-Fe distance of ~0.25 nm (Fe2/NC-S). Density functional theory (DFT) calculations and microkinetic analysis revealed the extended Fe-Fe distance in Fe2/NC is crucial for the O2 adsorption on catalytic sites and facilitating the subsequent protonation process, thereby boosting catalytic performance. This work not only introduces a new approach for fabricating atomically precise DACs, but also offers a deeper understanding of the intermetallic distance effect on dual-site catalysis.

Sublimation Transformation Synthesis of Dual‐Atom Fe Catalysts for Efficient Oxygen Reduction Reaction

AbstractDual‐atom catalysts (DACs) have garnered significant interest due to their remarkable catalytic reactivity. However, achieving atomically precise control in the fabrication of DACs remains a major challenge. Herein, we developed a straightforward and direct sublimation transformation synthesis strategy for dual‐atom Fe catalysts (Fe2/NC) by utilizing in situ generated Fe2Cl6(g) dimers from FeCl3(s). The structure of Fe2/NC was investigated by aberration‐corrected transmission electron microscopy and X‐ray absorption fine structure (XAFS) spectroscopy. As‐obtained Fe2/NC, with a Fe−Fe distance of 0.3 nm inherited from Fe2Cl6, displayed superior oxygen reduction performance with a half‐wave potential of 0.90 V (vs. RHE), surpassing commercial Pt/C catalysts, Fe single‐atom catalyst (Fe1/NC), and its counterpart with a common and shorter Fe−Fe distance of ~0.25 nm (Fe2/NC‐S). Density functional theory (DFT) calculations and microkinetic analysis revealed the extended Fe−Fe distance in Fe2/NC is crucial for the O2 adsorption on catalytic sites and facilitating the subsequent protonation process, thereby boosting catalytic performance. This work not only introduces a new approach for fabricating atomically precise DACs, but also offers a deeper understanding of the intermetallic distance effect on dual‐site catalysis.

Sulfur doping and oxygen vacancy in In2O3 nanotube co-regulate intermediates of CO2 electroreduction for efficient HCOOH production and rechargeable Zn-CO2 battery

By manipulating the distribution of surface electrons, defect engineering enables effective control over the adsorption energy between adsorbates and active sites in the CO2 reduction reaction (CO2RR). Herein, we report a hollow indium oxide nanotube containing both oxygen vacancy and sulfur doping (Vo-Sx-In2O3) for improved CO2-to-HCOOH electroreduction and Zn-CO2 battery. The componential synergy significantly reduces the *OCHO formation barrier to expedite protonation process and creates a favorable electronic micro-environment for *HCOOH desorption. As a result, the CO2RR performance of Vo-Sx-In2O3 outperforms Pure-In2O3 and Vo-In2O3, where Vo-S53-In2O3 exhibits a maximal HCOOH Faradaic efficiency of 92.4% at −1.2 V vs. reversible hydrogen electrode (RHE) in H-cell and above 92% over a wide window potential with high current density (119.1 mA cm−2 at −1.1 V vs. RHE) in flow cell. Furthermore, the rechargeable Zn-CO2 battery utilizing Vo-S53-In2O3 as cathode shows a high power density of 2.29 mW cm−2 and a long-term stability during charge–discharge cycles. This work provides a valuable perspective to elucidate co-defective catalysts in regulating the intermediates for efficient CO2RR.

Photoinduced Hydrosilylation of Fluorinated Alkenes.

A visible-light-induced synthesis protocol for silylmonofluoroalkanes is described. The silylation of alkenyl fluorides using (trimethylsilyl)silanes as organosilicon reagents proceeds well under mild conditions via a sequential photoinduced single-electron transfer and protonation process. The protocol shows a broad substrate scope, transition-metal-free conditions, and high functional group tolerance. A wide variety of silylmonofluoroalkanes were obtained in generally good yields (up to 82%).

Tetrapyrrolic macrocycles self-organization into floating layers and sensory properties of their Langmuir-Schaefer films

The influence of the chemical structure of the 5,10,15,20-tetraphenylporphyrin (I) and 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (II) on their supramolecular organization in floating layers at the air/water interface and sensor properties in Langmuir-Schaefer films has been investigated. It was shown that a minor change in the macrocycle structure (namely, the replacement of a single nitrogen atom from the center to the periphery of macrocycle) has a considerable effect on the surface properties and hysteresis processes of the floating layers. Using the Bruster angle microscopy, it was established that both porphyrins aggregate even before the compression of their floating layers begins. The aggregation is more pronounced in porphyrin I. The analysis of hysteresis loops showed that the formation of a floating layer by the modified porphyrin II requires approximately 100 times more energy than for the unmodified porphyrin I. Using the Langmuir-Schaefer (LS) method, the floating layers were transferred onto solid substrates and the resulting thin films were analyzed by atomic force microscopy, scanning electron microscopy, polarization optical microscopy, and spectrophotometry. The combination of these methods revealed a general tendency of the porphyrins to form 3D structures on the surface of LS-films. The study of the basic properties of the porphyrin's LS-films showed that both porphyrins are diprotonated. The protonation process in porphyrin II occurs at a concentration of HClO4 that is 1000 times lower than that observed in porphyrin I. The greater tendency to protonation of porphyrin II is caused by the availability of both nitrogen atoms (the external nitrogen atom located at the macrocycle periphery and the internal nitrogen atom, which becomes more assesible to interactions due to the distortion of the macrocycle). As for the sensor properties of LS-films for iodide ion in aqueous solutions, it was observed that the diprotonated form of porphyrin I exhibited higher sensitivity due to a more developed film surface because of the presence of a greater number of 3D aggregates. The data obtained can be used in the development of efficient pH-controlled thin-film sensor materials for halide ions.

Dynamic 3D hydrogen-bond network in siloxene-water system enables efficient moisture-enabled electricity generation

Utilizing ubiquitous moisture as an energy source for moisture-enabled electric generator (MEG) has emerged as a significant technological frontier. The migration process of protons at the water/solid interface is crucial for understanding the mechanism of moisture-to-electricity conversion and efficient energy harvesting. However, the lack of clarity on this scientific question has hindered the substantive development of MEG. Here, a novel dynamic three-dimensional (3D) hydrogen-bond network between the interface of siloxene layers was designed through water molecule intercalation. The spatial bridging effect of this dynamic 3D hydrogen-bond network, formed on the siloxene layers, enhances the load transfer capability of the siloxene-water system, thereby randomizing the direction of proton hopping. Experimental and theoretical calculations demonstrate that the dynamic 3D hydrogen-bond network constructed within and between the siloxene layers facilitates rapid proton conduction. Kinetic simulations further confirm that the strength of the hydrogen-bond network accelerates proton transport rate. The current density of siloxene under high humidity increases significantly, reaching 22.37 µA cm−2, which is 122 times that under low humidity, as well as the open-circuit voltage reaches 0.73 V. This work contributes to understanding the microscopic mechanisms behind efficient moisture-enabled electricity and provides a fresh perspective for enhancing MEG performance.

Characterization of 1,1- and 1,2-ethenedithiol, elusive compounds of potential astrochemical interest.

1,1- and 1,2-ethenedithiol are elusive systems that could potentially exist in interstellar space, similar to analogous diols. In this paper, we investigate the structure, stability, and bonding characteristics of these compounds as well as the ions produced by protonation, deprotonation, or simple ionization processes. 1,2-ethenedithiol has two isomers, Z and E, with the most stable conformer being syn-anti for the Z isomer and anti-anti for the E isomer. However, the energy gaps between the different conformers are never larger than 6kJ·mol-1. For 1,1-ethenedithiol, the global minimum is the syn-anti conformer. The vertical and adiabatic ionization processes as well as the intrinsic basicities and acidities of these families of compounds were analyzed and compared with those of the corresponding diols previously reported in the literature. This comparison revealed not only the numerical differences in these thermodynamic properties but also distinct trends between the two families of compounds. State-of-the-art G4 ab initio calculations were employed to calculate the structures and total energies of the systems under investigation. The QTAIM, ELF, and NBO approaches were used to analyze the electron density of all the neutral and charged systems included in our study. Van der Waals contributions, when relevant, were analyzed by locating regions of low reduced density gradient(s) using the NCIPLOT approach.