Effect Of Cations Research Articles

(General Student Poster Award Winner, 3rd Place) Probing the Trends of Cation Interactions in Cation Exchange Membranes Using Raman Spectroscopy

Cation exchange membranes (CEMs) are an ion exchange polymer which selectively shuttles cations through their structure. CEMs are used for a wide range of electrically driven processes, including electrolysis, fuel cells, and electrodialysis. Historically, fluorinated polymers have been used as CEMs, with the most prevalent being Chemours’ Nafion polymer. These materials and their synthesis can produce harmful, long-lived environmental toxins that may provide challenges to scaling to meet material demand. Therefore, significant research is being directed towards finding non-fluorinated CEMs with similar functionality. One promising candidate has been sulfonated poly-ether-ether-ketone (SPEEK), which has similar ion exchange capabilities as Nafion, while being low cost and non-fluorinated.In electrochemical reactors, the effect of different cations in electrolyte solutions has shown high importance for overall conductivity and can affect reaction selectivity, activity, and durability. The cations which move through the CEM (mobile ions) can interact with the fixed sulfonate functional groups on the polymer backbone. While there is significant research on mobile ion effects on the performance of Nafion1, far less work has been done in this area with SPEEK2. Additionally, there are no direct comparisons between Nafion and any non-fluorinated polymer on how the polymer backbone affects these mobile ion interactions.One method to study CEM-ion interactions is with Raman Spectroscopy, which uses a monochromatic light to initiate and observe Raman scattering from matter. While Raman spectra have been obtained for Nafion, we have not found Raman spectra of SPEEK in the presence of different electrolyte compositions. Here, we use Raman spectroscopy paired with water uptake and conductivity measurements to compare the differences of how a variety of mobile cations (H+, NH4+, Li+, Na+, K+, Rs+, Cs+, Mg2+, Ca2+, Sr2+) interact with the fixed sulfonate functional groups found in Nafion and SPEEK. We report that the two polymers show differences in the strength of the interactions between the mobile ions and fixed groups, which leads to changes in physical properties, including water uptake and conductivity. With these findings, more informed decisions of the applications of fluorinated vs non-fluorinated polymers for various electrochemical purposes can be made.Key

Limiting Current Investigations for PEM Water Electrolysis in the Presence of Metal Cations

Pretreatment and purification of water is necessary to use it as a feed for the oxygen evolution reaction (OER) at the anode of PEM water electrolysis (PEMWE). Fresh water typically contains several multivalent cations such as Ca2+ and K+. In addition, iron cations may accumulate in PEMWE over a long period of time due to corrosion of system components and fittings of the PEMWE. The presence of these multivalent cations in the feed water causes higher ohmic resistance of the cell and higher iR-free voltages, resulting in a performance loss.[1] Furthermore, the cations can be transported by the water crossover stream from anode to cathode and by diffusion transport.[2] In other words, even traces of metal cations drastically influence the efficiency and durability of PEMWE stacks. Despite this knowledge, contamination with multivalent cations is one to the main reason for the breakdown of PEMWE stacks.[3]Very interestingly, simulations of cationic contamination for PEM fuel cells (PEMFCs)[4] have shown that the distribution of metal cations in the through-plane direction depends on the proton current through the membrane. The cation concentration profile indicates an accumulation of metal cations close to the cathode side and leads to an increase of the proton transport resistance. In addition, the simulations indicate that in case of a complete substitution of protons by metal cations, the proton transport resistance approaches infinity. Finally, the proton current cannot increase further and a limiting current is reached.[4] The transfer/adoption of these simulations from PEMFC to PEMWE allows to clarify the behavior of the limiting current in dependence of the nature of metal cations such as Ca2+ and K+ and their concentrations, which is still poorly understood to date.In this work, we investigated if the concept of limiting protonic current from simulations for the PEMFC can be (partially) transferred to PEMWE on a laboratory scale. For this purpose, we evaluated the effect of trace metal cations in the anode feed water on the performance of a PEMWE single cell and quantified the cation concentration in the membrane using spectroscopic techniques such as micro X-ray fluorescence (µ-XRF) and energy-dispersive X-ray (EDX). Electrochemical measurements were carried out in an in-house PEMWE test bench equipped with a single cell of 5 cm2 geometric electrode area and potentiostat with booster. Commercially available catalyst coated membranes with a loading of 0.3 mg cm-2 geo of Pt/C and 1 mg cm-2 geo of IrOx were used. The measurements were carried out at atmospheric pressure and a cell temperature of 80°C. First, a conditioning procedure was performed using highly purified feed water (>20 MΩ cm at room temperature) until a stable cell performance had been achieved. Cation contamination experiments were conducted by introducing various concentrations of metal sulfates (1-100 µmol L-1 cation concentration) into the anode feed water. Performance evaluation was carried out by measuring the polarization curves and electrochemical impedance spectroscopy (EIS) to determine the Tafel slope, overvoltage, and high frequency resistance (HFR). µ-XRF and EDX spectroscopy techniques were used to detect the cation concentration profile along the membrane.We observed a significant rise of the cell voltage by adding cations to the anode water feed within few hours. More precisely, a limiting current density of 1 A cm-2 geo after 16 hours of exposure to 100 µmol L-1 K+-ions in the anode feed water was determined using the Koutecký-Levich equation. This result is in line with our first simulations. The switch back to purified feed water allows us to monitor the dynamics of the performance recovery process obtained from EIS data. Additional measurements of the polarization curves and HFR were used to distinguish between reversible and irreversible degradation processes due to the cation contamination. Very interestingly, a partial reversibility was observed after the K+-contamination, as the limiting current increased from 1 to 2 A cm-2 geo after 16 hours recovery with purified water feed.Altogether, this study evaluated the transferability of limiting protonic current concept from simulations in PEMFC to PEMWE to uncover the impact of trace metal cations in the anode feed water on the performance of PEMWE.[1] C. Immerz, M. Singer, F. Hasché, B. Bensmann, M. Suermann, R. Hanke-Rauschenbach, M. Oezaslan, Meet. Abstr. 2020, MA2020-02, 2456.[2] M. Friedrichs-Schucht, F. Hasché, M. Oezaslan, ECS Trans. 2023, 111, 3.[3] N. Danilovic, K. E. Ayers, C. Capuano, J. N. Renner, L. Wiles, M. Pertoso, ECS Trans. 2016, 75, 395.[4] B. L. Kienitz, H. Baskaran, T. A. Zawodzinski, Electrochim. Acta 2009, 54, 1671.

Electrolyte Effects on Reactive Carbon Capture in Ionic Liquids

Reactive carbon capture (RCC), or integrated CO2 capture and electrochemical conversion, is a promising strategy to improve the energy efficiency and technoeconomics of the electrochemical reduction of CO2 from dilute sources. Ionic liquids are a class of functional solvents for RCC that can have high CO2 solubility and complex with CO2 to make an adduct species that lowers the activation energy and associated onset potential for CO2 reduction. Work is ongoing at the Center for Closing the Carbon Cycle, a DOE Energy Frontier Research Center, to understand which aspects of direct aqueous electrochemical CO2 reduction are translatable knowledge for RCC using ionic liquids. RCC behavior in imidazolium ionic liquids has been studied on exemplar catalysts including Ag and Sn as a function of variable electrolyte properties including ionic liquid concentration, solvent, supporting electrolyte cation, and pH. In particular, the effect of alkali cations was notably different from the behavior reported for aqueous-only CO2 reduction, with alkali species inhibiting CO2 reduction product selectivity in the presence of ionic liquid. In addition, the reduction of imidazolium carboxylate compounds has been investigated for further insight into the reduction of ionic liquid imidazolium cation-CO2 adducts.

Direct Observation of Intermediates for Carbon Dioxide Reduction Reaction in Concentrated Electrolytes

There is a growing need to utilize CO2 and realize a carbon-neutral society from the perspective of environmental problems caused by CO2 from fossil fuel-based processes. In this trend, electrochemical carbon dioxide reduction reaction (CO2RR), which converts CO2 to valuable fuels and chemicals with renewable energy, is attracting attention[1]. However, CO2RR has many challenges, including its low product selectivity. In particular, the hydrogen evolution reaction (HER), which occurs at the potential close to the standard electrode potential of CO2RR, reduces the selectivity of CO2RR, especially in aqueous electrolytes such as KHCO3 [2] [3]. Therefore, we focus on a concentrated electrolyte, which is used as a means of HER suppression in water-based Li-ion batteries[4], to improve the selectivity of CO2RR. A concentrated electrolyte is an electrolyte with a high salt concentration, which can improve the electrochemical stability of water by creating a specific water environment[5]. Furthermore, due to its high salt concentration, the effect of anions and/or cations may become significant[6][7]. However, there has been no detailed understanding of how the electrolyte concentration affects the complex reaction pathway of CO2RR.Here, we report the effect of concentrated electrolytes on the reaction process of CO2RR by directly observing reaction intermediates in situ while applying the potential. The product selectivity of CO2RR in 22.2, 42.0, and 61.7 mol kg– 1 of concentrated electrolyte was evaluated. Gas chromatography (GC) analysis confirms the suppression of HER in the series of concentrated electrolytes compared to 0.1 M KHCO3, a common aqueous electrolyte. In addition, an increase in the Faradaic efficiency of C2H4 was observed in ~ 42.0 mol kg– 1, implying a concentration-dependent change in the CO2RR reaction pathway (Fig.1). To elucidate the cause of the high C2H4 selectivity, in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), which allows direct observation of the reaction intermediates, was performed. The results showed that as the electrolyte concentration was increased, the peaks at 1400 to 1500 cm– 1 region became more pronounced at low potential. We also observed the difference in the potential dependency for the intensity of CO adsorbates peak at 2100 cm–1 by electrolyte concentration. We will then discuss the effect of electrolyte concentration on the intermediates, unraveling the concentration-dependent change of the C2H4 selectivity. The work highlights the use of concentrated electrolytes to open up additional knobs for tuning the product selectivity of CO2RR, simply by designing an electrolyte component.[1] De Luna, P. et al, Science. 2019 364, 350.[2] Pan, F.; Yang, Y. Energy Environ. Sci. 2020, 13, 2275–2309.[3] Hori, Y. et al, Electrochim. Acta. 1994 39, 1833–1839.[4] Han, J. et al, Energy Environ. Sci. 2023 16, 1480.[5] Ko, S. et al, Electrochem. Commun. 2020 116, 106764.[6] Shin, S. J. et al, Nat. Commun. 2022 13, 5482.[7] Varela, A. S. et al, ACS Catal. 2016 6, 2136-2144. Figure 1

Deconvoluting Alkali Metal Cation and Hydroxide Anion Effects on the Alkaline Hydrogen Evolution and Oxidation Reactions on Platinum

The platinum (Pt) catalyzed hydrogen evolution and oxidation reactions (HER/HOR) usually show considerable slower kinetics in alkaline electrolytes than that in acidic environment. The fundamental origin of such distinct kinetics has been a topic of considerable interest. In general, the electrode-electrolyte (Pt-water) interface in alkaline electrolytes is far more complex than the acidic environment due to the presence of alkali metal cations (AM+) and hydroxide anions (OH-) as potential competitive surface adsorbates and interfacial species that may fundamentally change the local chemical environment. Despite considerable efforts in probing the HER kinetics in alkaline electrolytes, the effects of different species are often highly convoluted, and the exact role of each specie is difficult to resolve.Herein, we conduct a systematic study to deconvolute the effects of AM+ and OH- by designing twenty-eight electrolytes from 0.001M NaOH to 1M NaOH. Our study reveals a nontrivial dependence of HER/HOR activities on the AM+ or OH- concentrations. The electrochemical measurements and electrochemical impedance spectroscopy (EIS) analyses demonstrate an apparent correlation between the kinetic exchange current density, charge transfer resistance and the electrical double layer capacitance. It is found that the increasing OH - concentration reduces the electrical double layer thickness, increases the surface electric field and the OHad coverage to lower the kinetic barrier for water dissociation (for HER) or Had and OH - recombination (for HOR). The Na+ shows a positive effect at low concentration by decreasing the double layer thickness and increasing surface electric field to polarize the interfacial water; but a negative effect at high concentration by forming ion pairs that reduces interfacial water polarization and rigidify the interfacial water layer to slow the transport of the reactants and products to and away from the electrode surface. These combined effects result in a complex cation and pH dependent HER/HOR activities. This study for the first time deconvolute the effect of AM+ and OH- concentrations and establishes a comprehensive view of their roles in the Pt-catalyzed alkaline HER/HOR, offering valuable insights for further electrocatalyst design.

Li+ Conduction Properties and Local Structures of Sodium Iodide Doped with Li+ and BH4 -

Background The most of the solid electrolytes for all-solid-state Li and Na batteries have been developed based on the single alkali compounds in which other alkali ions do not coexist in the same lattice. The mixing of two alkali cations in the same phase results in the deterioration of the ion conductivity (mixed cation effect) [1]. Hence, the mixing of two alkali cations has been avoided for the preparation of solid electrolytes. On the other hand, our group has focused on the conduction of the “doped” Li+ in Na compounds, particularly for NaI. NaI-NaBH4-LiI is the NaI-based solid solution where the host Na+ and I- are replaced by Li+ and BH4 -, respectively [2, 3]. Although the concentration of Li+ is less than 10 mol%, the dominant conduction ions in NaI-NaBH4-LiI has been proven to be the doped Li+ [4]. The Li+ conduction mechanism was also discussed from the atomic point of view; “off-centered” Li+ was considered as one of the origins for the dominant Li+ conduction in NaI-LiI [5]. In this study, the local structure of Li+ in NaI-NaBH4-LiI is investigated from the perspective of Li+ conduction. Reverse Monte Carlo (RMC) simulation was performed based on the neutron total scattering data. During the simulation, swapping among I- and BH4 - was considered to represent the random distribution of BH4 -. The local environment of Li+ in NaI-NaBH4-LiI will be extracted by partial pair distribution function of the modeling structure. Experimental The sample fabrication and storage were conducted in Ar-filled glove box. NaI, NaBH4 and LiI were mixed in a given molar ratio and mixed by hand. The mixed powder was sealed in the chrome steel vessel with 10 pieces of balls (10 mm in diameter) and ball-milled for 5 hours. In this study, the concentration of Li+ and BH4 - were 10 and 5 mol %, respectively. The sample was post-annealed at 250°C in the glove box. For the conductivity measurement, the ball-milled NaI-NaBH4-LiI was pelletized by uniaxial pressing at approximately 270MPa. The pellet (10 mm and 1mm in diameter and thickness, respectively) was set in the PEEK cylinder with the inner diameter of 10 mm. Stainless steel (S.S.) disks were used for the blocking electrodes. The PEEK cylinder with the solid electrolyte pellet sandwiched by two S.S. disks was set in the hermetic cell. The conductivity was measured by AC impedance method (1 MHz ~ 1 Hz) with the temperature range of 250°C and 30°C. Neutron total scattering measurements of NaI-NaBH4-LiI were performed at NOVA, beamline BL21 with a 90 deg. (Q (= 2π/d = 4πsinθ/λ) = 1 ~ 82 Å-1) detector bank at Japan Proton Accelerator Research Complex (J-PARC). To avoid the absorption of neutrons, 7LiI and Na11BD4 were used for the raw materials. The atomic configuration of NaI-Na11BD4-7LiI was modeled by an RMC simulation using RMCProfile [6]. During the simulation, the swapping among I- and 11BD4 - tetrahedron was considered to represent the random distribution of 11BD4 -. Results and Discussions The results of RMC simulation are summarized in the Figure. The Bragg profile, the structure factor, (S(Q)) and the reduced pair distribution function (G(r)) are well fitted. Hence, not only the long-range periodic structure but the local structures which are often hidden in the background of the diffraction data were reproduced. The partial pair distribution functions (gij (r)) of Na-11B and 7Li-11B are calculated based on the modeling structure (Figure (d) and (e)). The Na-11B correlation was observed over a long-range, indicating that the position of Na and BD4 - is randomly deviated from the ideal crystallographic sites. On the other hand, the nearest neighbor distance between 7Li and 11B was not uniform and the long-range correlation was not confirmed. These results indicate that the doped Li+ was trapped by BH4 -. The conduction properties of NaI-NaBH4-LiI will be discussed based on its local structure.

Exploring the Impact of Excess Cations in Acidic CO2 Reduction Reaction

To anticipate high performance in the electrocatalytic reactions, a comprehensive understanding of the electric double layer (EDL) is essential. Experimental, spectroscopic, and computational studies of the EDL have been reported for understanding the performance in electrocatalytic reactions such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR). Notably, in the CO2RR, previous studies have revealed the accumulation of cations near the outer Helmholtz plane (OHP) significantly has an impact on the reaction performance, product selectivity, and partial current density. The presence of these cations induces various effects, such as creating a strong electric field, altering local pH levels, stabilizing the intermediates, and specific adsorption. However, unraveling the sole cation effect remains challenging due to the system's complexity and hierarchical characteristics. Moreover, experiments predominantly conducted under favorable conditions for understanding the electric field and stabilization effects have left the specific adsorption effect relatively unexplored. Specific adsorption involves direct coordination with the electrode at the inner Helmholtz plane (IHP), with the degree determined by catalyst type and electrolyte conditions. Previous studies have highlighted the significant impact of specific adsorption on current density and intermediate stabilization, with potassium (K+) and cesium (Cs+) cation exhibiting the most pronounced effect owing to their minimal hydration degree compared to the lithium (Li+) and sodium (Na+).Acidic CO2RR has recently garnered attention for its high carbon efficiency (CE) and energy efficiency (EE). However, the abundance of hydronium ions can lead to a favorable occurrence of HER over CO2RR due to its facile protonation. To mitigate this challenge, excess cations have been employed to suppress the hydronium ion migration and enhance the performance of the CO2RR, which means accumulated cation layer at the OHP can suppress the HER and stabilize the intermediates of the CO2RR simultaneously. Meanwhile, in the excess cation condition, adsorbed cations can be dominant on the electrode originated from the excess cations, which is not investigated intensively. For the better performance of the electrocatalytic reactions in the acidic condition, we need to elucidate the EDL formed in the presence of the excess cations.In here, we investigated the electrode-electrolyte interface in the different cation species during the acidic CO2RR through the attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS), which can give the local information such as the adsorbed species on the metal and free species near the electrode. We confirmed the different product distribution and interface depending on the cation species, especially in the excess cations (1 M M+, M = Li, K, Cs). Specific adsorption in the presence of the excess cations can alter the product distribution, and it differs from the low cation concentration (0.1 M M+, M = Li, K, Cs). In final, to clarify the effect originated from the excess cations, we confirmed the interface on the copper and silver, which major products are C2+ and C1, respectively.

Slowing the crystallization speed to prepare high-efficiency flexible tin-based perovskite solar cells

In this study, five hydrochlorides are used as additives to slow the crystallization rate between SnI2 and AI (A+=MA+, FA+, Cs+) to prepare high-quality perovskite films. This study on film morphology, crystallization and non-radiative recombination demonstrates the effects of organic amine cations with different chain lengths on the quality of thin films. A flexible solar cell device with a lead-free perovskite film doped with PACl is also obtained achieving an efficiency of 5.52 %.

Effect of the A-Site Cation on the Lattice Thermal Conductivity of Nitride Perovskites

Effect of the A-Site Cation on the Lattice Thermal Conductivity of Nitride Perovskites

Specific Adsorption of Alkaline Cations Enhances CO-CO Coupling in CO2 Electroreduction.

Electrolyte alkaline cations can significantly modulate the reaction selectivity of electrochemical CO2 reduction (eCO2R), enhancing the yield of the valuable multicarbon (C2+) chemical feedstocks. However, the mechanism underlying this cation effect on the C-C coupling remains unclear. Herein, by performing constant-potential AIMD simulations, we studied the dynamic behavior of interfacial K+ ions over Cu surfaces during C-C coupling and the origin of the cation effect. We showed that the specific adsorption of K+ readily occurs at the surface sites adjacent to the *CO intermediates on the Cu surfaces. Furthermore, this specific adsorption of K+ during *CO-*CO coupling is more important than quasi-specific adsorption for enhancing coupling kinetics, reducing the coupling barriers by approximately 0.20 eV. Electronic structure analysis revealed that charge redistribution occurs between the specifically adsorbed K+, *CO, and Cu sites, and this can account for the reduced barriers. In addition, we identified excellent *CO-*CO coupling selectivity on Cu(100) with K+ ions. Experimental results show that suppressing surface K+-specific adsorption using the surfactant cetyltrimethylammonium bromide (CTAB) significantly decreases the Faradaic efficiency for C2 products from 41.1% to 4.3%, consistent with our computational findings. This study provides crucial insights for improving the selectivity toward C2+ products by rationally tuning interfacial cation adsorption during eCO2R. Specifically, C-C coupling can be enhanced by promoting K+-specific adsorption, for example, by confining K+ within a coated layer or using pulsed negative potentials.

Effect of Cation and Anion Vacancies in Ruthenium Oxide on the Activity and Stability of Acidic Oxygen Evolution

Effect of Cation and Anion Vacancies in Ruthenium Oxide on the Activity and Stability of Acidic Oxygen Evolution

Synergistic Regulation of DNA Morphology by Metal Cations and Low pH.

As a flexible biomolecule, the spatial structure of DNA is variable. The effects of concentration, metal cations, and low pH on DNA morphology were studied. For the high concentration of DNA, the cross-linked branch-like or network structures were formed. For the low concentration of DNA, isolated, random and freely loose linear DNA chains were presented. These phenomena were related to the intermolecular interactions. Branch-like DNA structures were reformed with the addition of metal cations to the low concentration of DNA at pH 7-4, suggesting the negative charges of DNA were neutralized, thus transforming the spatial structure of DNA into a low charge density morphology and presenting the hypochromic effect. Compared to the monovalent alkaline metal cations, more negative charges of DNA were screened by the alkaline-earth metal cations. Distinct DNA morphologies were observed for pH 3. The linear and condensed DNA structures were simultaneously observed, which was met regardless of the solution with or without the addition of metal cations. This was further confirmed by the absorbance of DNA. Compared to the pure DNA, bulky and aggregated DNA collapsed structures were formed when the sodium and magnesium cations were added to the reaction solution. In addition, it was verified that the condensed DNA structures failed to revert back to the chain structure by neutralizing acidic solutions with alkali, but the compacted DNA spheres became loose. The conductivities of various DNA morphologies were measured. They were morphology-dependent. This study provides guidance forthe behavior of DNA in the acidic solutions and further promotes the application of DNA in DNA-based nano-optoelectronic devices.

Cation Effect of Bio‐Ionic Liquid‐Based Electrolytes on the Performance of Zn‐Ion Capacitors

AbstractZn‐ion capacitors (ZICs) are emerging as promising energy storage devices due to their low cost. Currently, aqueous‐based electrolytes are primarily used in ZIC which have shown issues related to low Zn deposition/stripping efficiencies, and Zn dendrites formation, resulting in device failure. To overcome these issues and to develop environmentally benign energy storage devices, here we have studied bio‐ionic liquid electrolytes (bio‐ILs) in both symmetric and asymmetric capacitors. Choline acetate (ChOAc) and betaine acetate (BetOAc) in water were investigated as electrolytes for capacitors in the presence and absence of Zn salts. Spectroscopic analysis showed that Zn solvation in the electrolytes changes significantly with the change in cation which affects the electrochemical reactions and capacitor performance. Raman analysis showed the Zn complex formed in the case of ChOAc is [Zn(OAc)4]2− whereas for BetOAc is [Zn(OAc)5]3− thereby the Zn deposition/stripping in ChOAc‐based electrolyte is quite stable whereas in case of BetOAc, Zn deposition/stripping is unstable. In the ChOAc electrolyte, the Zn/activated carbon asymmetric cell showed a capacity of >90 F g−1 at 0.1 A g−1 and a capacitance close to 40 F g−1 at 0.5 A g−1 with ∼82 % capacity retention after 3000 cycles, whereas BetOAc could only be used in symmetric cell capacitor. This study shows that bio‐ILs can be used as sustainable electrolytes in energy storage devices wherein the cation plays a significant role in the capacitor performance.

Effects of DOM and cations on the diffusion migration of PPCPs through ion exchange membranes

The transportation of pharmaceuticals and personal care products (PPCPs) in ion-exchange membranes was worrying, especially in complex substrates. Dissolved organic matter (DOM), the complexation of PPCPs and the membrane pollution formed by DOM were often confused in the existing studies. This paper investigated the diffusive migration patterns of three kinds of (PPCPs) through ion exchange membranes (IEMs) in complex substrates. Triclosan (TCS) exhibited the most probability of migration. Without considering the interference of environmental factors, more than 90 % of TCS was adsorbed by IEMs. The migration of sulfadiazine sodium (SD) and carbamazepine (CBZ) was less than 5 %. The DOM and cations altered the interaction of PPCPs and IEMs. DOM fouling on IEMs converted the direct strong binding of TCS to IEMs to indirect weak binding, and increased the transmembrane migration of TCS consequently. The presence of cations (Ca2+ and Mg2+) increased the inorganic binding of TCS to IEMs, and also promoted the transmembrane migration of TCS. However, coexisting of Mg2+ and humic acid (HA) decreased TCS migration through anion exchange membrane (AM), but increased TCS migration through cation exchange membrane (CM) due to the increasing of solution potential. The research provided a theoretical basis for exploring the safety of product solutions in IEMs systems.

Structural Variety of Extended Arrays of Pancake-Bonded TCNQ Radicals: Steric Effect of the Bulky Cations

Structural Variety of Extended Arrays of Pancake-Bonded TCNQ Radicals: Steric Effect of the Bulky Cations

Study on the Effect of Cations on Morphology in the Preparation of Vaterite Calcium Carbonate from Dolomite

AbstractIn this paper, the effect of trace components in dolomite on the morphology of vaterite calcium carbonate is studied in the CaCl2‐NH3‐CO2 system, with a focus on the effect of cations (Mg2+, Fe3+, Si4+, and Al3+) in the solution. Ca2+, NH4+, Mg2+, Fe3+, Si4+, and Al3+ in the digestion solution are proportionally prepared into a solution by analyzing the calcium rich digestion solution which is obtained by digesting dolomite with ammonium chloride solution. Under the optimal conditions, NH3 is introduced at a rate of 0.5 L min−1 for 1 h, CO2 is introduced at a rate of 0.5 L min−1 for 1 h and rotation speed of 500 r min−1 to prepare the vaterite calcium carbonate. The results show that the addition of Mg2+, Fe3+, Si4+, and Al3+ can promote the growth of vaterite calcium carbonate. Among them, adding Mg2+ and Si4+ can promote the dispersion of vaterite, Fe3+ and Al3+ can cause agglomeration of vaterite. Material Studio software is used to predict the crystal morphology of vaterite calcium carbonate under ideal conditions, and the calculation results are basically consistent with the experimental results.

Electrocatalytic CO2 reduction over Ag/CuSn Electrodes: Modulation of C1, C2, and C3+ products

Combining different metals has proven to be an effective methodology for fabricating electrodes that can manipulate reduction products in electrochemical (EC) CO2 reduction. In this study, CuSn and EC treated CuSn were surface-modified with Ag via sputter deposition. EC CO2 reduction was performed at various applied potentials in KHCO3, K2CO3, and KOH electrolytes. The effects of cations and anions were tested to examine the variation in reduction products. The major reduction products were H2 and C1 compounds (CO, CH4, formate), as well as C2 compounds (C2H4, ethanol, and acetate). Minor products included C1 compounds (methanol), C2 compounds (acetaldehyde and glycolaldehyde), and C3+ compounds (propanol and isopropanol), along with C2H6 and C3+ hydrocarbon products. The variation of C2+ hydrocarbons was explained by Fischer-Tropsch (F-T) chemistry. The oxidation states of Cu and Sn, as well as the Cu/Sn ratios, were examined before and after EC CO2 reduction using depth-profiled X-ray photoelectron spectroscopy. The experimental factors—catalyst composition, applied potential, and electrolyte composition—interacted to create a complex reaction environment. This combined approach provides valuable insights into identifying optimal conditions for achieving desired product selectivity.

Effect of cation in sodium/potassium-based geopolymer coatings for the fire protection of steel structures

Common geopolymers (GPs) are activated by alkaline solutions of potassium (K) or sodium (Na). Although both properties have been extensively investigated, comparative studies on their fire resistance are still lacking. In this research, Na/K-based GPs were applied as fire-protective steel coatings. Their fire protection was evaluated by a fire test named “burn-through”. When the Aluminum/Silicon (Al/Si) molar ratio equaled 0, both GPs showed intumescence (expansion upon heating) during the fire test. The final maximum temperatures of the protected steel plate (TS) were as low as 309/335°C for Na/K-GP. However, with Al/Si=0.54, K-based GP (TS=410°C) exhibited intumescence and better fire protection than Na-based GP (TS=587°C) which even cracked. Physico-chemical properties of the GP samples were characterized before and after the fire test, including electron probe micro-analysis, dynamic mechanical analysis, and 29Si solid-state MAS (CP) NMR. Material softening was proved to come from the consumption of Si (Q2) and caused the following intumescence. Such structure was formed in K-based GP regardless of Al/Si ratio while Si (Q2) atoms were only present in Na-based GP at low Al/Si ratio. It is therefore proven that K-based GP is more appropriate to protect steel than Na-based GP, due to its intumescent property, especially when the Al/Si ratio is high.

Cation effects on the alkaline oxygen reduction reaction

Cation effects on the alkaline oxygen reduction reaction

Electrolyte Effects in Electrocatalytic Kinetics†

Comprehensive SummaryTuning electrolyte properties is a widely recognized strategy to enhance activity and selectivity in electrocatalysis, drawing increasing attention in this domain. Despite extensive experimental and theoretical studies, debates persist about how various electrolyte components influence electrocatalytic reactions. We offer a concise review focusing on current discussions, especially the contentious roles of cations. This article further examines how different factors affect the interfacial solvent structure, particularly the hydrogen‐bonding network, and delves into the microscopic kinetics of electron and proton‐coupled electron transfer. We also discuss the overarching influence of solvents from a kinetic modeling perspective, aiming to develop a robust correlation between electrolyte structure and reactivity. Lastly, we summarize ongoing research challenges and suggest potential directions for future studies on electrolyte effects in electrocatalysis. Key ScientistsIn 1956, Marcus theory was developed to describe the mechanism of outer‐sphere electron transfer (OS‐ET). In 1992, Nocera et al. directly measured proton‐coupled electron transfer (PCET) kinetics for the first time, and their subsequent research in 1995 investigated the effects of proton motion on electron transfer (ET) kinetics. In 1999 and 2000, Hammes‐schiffer et al. developed the multistate continuum theory for multiple charge reactions and deduced the rate expressions for nonadiabatic PCET reactions in solution, laying the theoretical foundation for the analysis of PCET kinetics in electrochemical processes. In 2006, Saveant et al. verified the concerted proton and electron transfer (CPET) mechanism in the oxidation of phenols coupled with intramolecular amine‐driven proton transfer (PT). Their subsequent work in 2008 reported the pH‐dependent pathways of electrochemical oxidation of phenols.Electrolyte effects in electrocatalysis have gained emphasis in recent years. In 2009, Markovic's pioneering work proposed non‐covalent interactions between hydrated alkaline cations and adsorbed OH species in oxygen reduction reaction (ORR)/hydrogen oxidation reaction (HOR). In 2011, Markovic et al. significantly enhanced hydrogen evolution reaction (HER) activity in alkaline solution by improving water dissociation, which was assumed to dominate the sluggish HER kinetics in such media. In comparation, Yan et al. applied hydrogen binding energy (HBE) theory in 2015 to explain the pH‐dependent HER/HOR activity. Cations play a significant role in regulating the selectivity and activity of carbon dioxide reduction (CO2RR). In 2016 and 2017, Karen Chan et al. introduced the electric field generated by solvated cations to explain the cation effects on electrochemical CO2RR. Conversely, in 2021, Koper et al. suggested that short‐range electrostatic interactions between partially desolvated metal cations and CO2 stabilized CO2 and promoted CO2RR.Recent researches have combined the exploration of the electrical double layer (EDL) structure with theoretical analysis of PCET kinetics. In 2019, Huang et al. developed a microscopic Hamiltonian model to quantitatively understand the sluggish hydrogen electrocatalysis in alkaline media. In 2021, two meticulous studies from Shao‐Horn's group analyzed the effects of cations on reorganization energy and the impacts of hydrogen bonds between proton donors and acceptors on proton tunneling kinetics, respectively. Electrolyte effects on proton transport process were researched in recent years. In 2022, Hu et al. and Chen et al. proposed that the cation‐induced electric field distribution and pH‐dependent hydrogen bonding network connectivity played essential roles in proton transport, separately.