Charge Transfer Step Research Articles

(Invited) Confinement Effects on the Redox Reaction of Aromatic Molecules

Introduction Aromatic compounds have been studied as electrode materials for redox flow batteries and electrochemical flow capacitors. Electrochemical flow capacitors, consisting of carbon-based flowable electrodes, incorporate the advantageous characteristics of flow batteries and supercapacitors. Recently, pseudocapacitive flowable electrodes have been reported to achieve enhanced energy densities. The graphitic walls of the slit-shaped micropores in carbon materials have a unique interaction potential energy. Herein, we demonstrate the anomalous redox behavior of aromatic compounds physisorbed in the slit-shaped micropores of activated carbon (AC).1 In addition, we introduce the insight of the confinement effects.2 Experimental 4,5-Dihydroxy-1,3-benzene disulfonic acid disodium salt monohydrate (BQDS) was used as a redox active molecule. A flowable electrode was prepared by simply dispersing carbon material in 1 mM BQDS + 0.5 M H2SO4. Electrochemical measurements of the flowable electrodes were conducted using a rotating disk electrode connected to an automatic polarization system. A mirror-polished glassy carbon rod (diameter, 6 mm) was used as the working electrode, a Pt mesh as the counter electrode, and a reversible hydrogen electrode (RHE) as the reference electrode. Before the electrochemical measurements, break-in potential cycling between 0 and 1200 mV vs. RHE was conducted using a de-aerated flowable electrode at a scan rate of 200 mV s−1 for 100 cycles while rotating the working electrode (1600 rpm). The redox behavior of the flowable electrode was investigated by potential cycling at scan rates of 500–2 mV s−1. Before cyclic voltammetry, the working electrode dispersion was stirred at 2500 rpm for 2 min, and the measurement was commenced after 1 min to obtain reproducible data. In addition, the effect of the micropore geometry of AC on the adsorption-controlled redox reaction was investigated.2 Results and Discussion The electrochemical behavior of various aromatic compounds was studied to demonstrate the proof-of-concept of a micropore-confined electrode reaction. The peak-potential separation (DE p)of BQDSH2/BQDS redox reaction was 330 mV at 5 mV s-1. The value of DE p decreased to 30 mV when carbon black (CB) with negligible microporosity was dispersed in the electrolyte. Remarkably, DE p = 0 mV was observed when micropore-rich AC is dispersed in the electrolyte. Based on the X-ray scattering analysis and HRMC simulations, we found that the micropore-confined aromatic compounds behave as adsorbed species in an adsorption-based system. The charge/discharge performance of a two-electrode cell was investigated. AQDS/AC and BQDS/AC were employed as negative and positive electrodes, respectively. The features of the charge/discharge curves of the cell changed from battery-type to pseudocapacitor-type when these electrodes were used. This behavior is attributed to the rapid charge-transfer step of micropore-confined molecules compared with that of unconfined molecules.In conclusion, we found that the adsorption-controlled process of the redox reaction for BQDS could be achieved using slit-shaped graphitic micropores with widths less than 1 nm in AC. Acknowledgments This work was partially supported by the Electrotechnology of Chubu, Kondo Memorial Foundation, and Tokyo Ohka Foundation for The Promotion of Science and Technology. References D. Takimoto, K. Suzuki, R. Futamura, T. Iiyama, S. Hideshima, and W. Sugimoto, ACS Appl. Mater. Interfaces, 14, 31131 (2022).D. Takimoto, K. Suzuki, S. Hideshima, and W. Sugimoto, Electrochemistry, 91, 077006 (2023).

Adsorption Structure-Activity Correlation in the Photocatalytic Chemistry of Methanol and Water on TiO2(110).

ConspectusPhotocatalysis, a process involving light absorption (band gap excitation), charge separation, interfacial charge transfer, and surface redox reactions, has attracted intensive attention because of the potential applications in solar to fuel conversion. Despite the great efforts devoted to the design of materials and optimization of charge separation and overall efficiency, the molecular mechanism of photocatalytic reactions, for example, water oxidation, is still unclear, mainly because of the complexity of powder catalysts and the aqueous environment which prevent the direct experimental detection of adsorption sites, surface species, and charge/energy transfer dynamics. Without direct evidence, the charge transfer and elementary reaction steps remain elusive, and misleading conclusions are sometimes drawn. For instance, the positively charged 5-fold coordinated Ti sites (Ti5cs) on TiO2 surfaces are argued to propel holes and therefore cannot be active sites for oxidative reactions, regardless of the demonstration by scanning tunneling microscopy (STM). Direct site-specific measurements are thus highly demanded. Surface science studies, which rely on well-defined single crystals and ultrahigh vacuum based techniques, can identify the active sites and active species at the catalyst surfaces and measure the interfacial electronic structure and energy of desorbing species for charge transfer analysis, providing direct evidence for investigating the photocatalytic reaction mechanism at the molecular level.In this Account, the elementary photocatalytic chemistry of methanol and water on TiO2, which are investigated by surface science techniques such as atom-resolved STM, ensemble-averaged mass spectrometer based temperature-programmed desorption/time-of-flight spectroscopy, and photoelectron spectroscopy in combination with theoretical calculations, will be described. Both methanol and water can be photocatalytically oxidized at Ti5cs, producing adsorbed formaldehyde and gaseous •OH radicals, respectively, under ultraviolet (UV) light irradiation. The photocatalytic activity shows salient adsorption structure including adsorption site (terminal/bridging), adsorption state (molecular/dissociative) and adsorption configuration (monomer/cluster) dependence, which comes from the ability to generate terminal anions which are capable of capturing photogenerated holes and exhibit superior photocatalytic activity over their parent molecules. These studies reveal the origin of the correlation between photocatalytic activity and adsorption structure of CH3OH and H2O on TiO2 surfaces and suggest that the simple criteria widely used to analyze the feasibility of charge transfer, i.e., the relative position of the band edges and the molecular orbitals of adsorbates, should be replaced by the change of Gibbs free energy of the charge trapping reaction from the thermodynamic point of view. These results contribute to the fundamental understanding of photocatalysis. Based on our research, future state-resolved and time-resolved studies can provide deeper insight into the charge and energy transfer and transient intermediate species, which will benefit the depiction of the overall photocatalytic reactions, for example, the photocatalyzed oxygen evolution reaction from water.

Analysis, identification, and application of distribution of relaxation times in CMP slurry

This study delves into the mechanistic roles of oxidants, complexing agents, and inhibitors in slurries through of Distribution of Relaxation Times (DRT) analysis. The influence of varying concentrations of these chemicals on electrochemical processes is discussed. This article divides the spectrum obtained through DRT analysis into four different frequency regions and differentiate naming through electrode reaction process: the double-layer charging step, the charge transfer step, the mass transfer step, and the surface transformation step by adsorption or chemical alterations at the electrode surface. The results reveal that the peak observed in the low-frequency range at 10−2–10° Hz is associated with mass transfer step, while the relaxation peak at 10°–102 Hz corresponds to the charge transfer process, while the relaxation peak occurring at 102–104 Hz is linked to the surface transformation step, and the first peak emerging in the 104–106 Hz range is attributed to double-layer charging step.

Ultrafast Hole Trapping in Te-MoTe2-MoSe2/ZnO S-Scheme Heterojunctions for Photochemical and Photo-/Electrochemical Hydrogen Production.

Te-MoTe2-MoSe2/ZnO S-scheme heterojunctions are engineered to ascertain the advanced redox ability in sustainable HER operations. Photo-physical studies have established the steady state transfer of photo-induced charge carriers whereas an improved transfer dynamics realized by state-of-art ultrafast transient absorption and irradiated-XPS analysis of optimized 5wt% Te-MoTe2-MoSe2/ZnO heterostructure. 2.5, 5, and 7.5wt% Te-MoTe2-MoSe2/ZnO photocatalysts (2.5MTMZ, 5MTMZ and 7.5MTMZ) exhibited 2.8, 3.3, and 3.1-fold higher HER performance than pristine ZnO with marvelous apparent quantum efficiency of 35.09%, 41.42% and 38.79% at HER rate of 4.45, 5.25, and 4.92 mmol/gcat/h, respectively. Electrochemical water splitting experiments manifest subdued 583 and 566 mV overpotential values of 2.5MTMZ and 5MTMZ heterostructures to achieve 10 mAcm-2 current density for HER, and 961 and 793 mV for OER, respectively. For optimized 5MTMZ photocatalyst, lifetime kinetic decay of interfacial charge transfer step is evaluated to be 138.67 ps as compared to 52.92 ps for bare ZnO.

Self-assembled La0.7Sr0.3Fe0.9Ni0.1O3-δ-Ce0.8Sm0.2O2-δ composite cathode with a three-dimensional ordered macroporous structure for protonic ceramic fuel cells

Self-assembled La0.7Sr0.3Fe0.9Ni0.1O3-δ-Ce0.8Sm0.2O1.9-δ (LSFN-SDC) composite cathode with a three-dimensionally ordered macroporous (3DOM) structure is synthesized using poly(methyl methacrylate) as the template for protonic ceramic fuel cells. The LSFN and SDC phases both distribute uniformly in the cathode. The SDC phase reduces the thickness of the walls of the 3DOM structure and thus hinders the bulk conduction of electrons. SDC also decreases the specific surface area and the surface oxygen reactivity of the cathode, leading to the suppression of the adsorption and dissociation of O2. However, the SDC phase provides the conduction pathway for oxygen ions and enlarges three phase boundary consequently, which facilitates the charge transfer steps. The thickness of the walls and the specific surface area of the composite cathode are both increased with the rise of the concentration of the nitrate precursor solution, resulting in the acceleration of the cathode process. Nevertheless, an excessive precursor concentration leads to the destroy of the 3DOM structure. The 3DOM composite cathode exhibits the lowest Rp of 0.039 Ω cm2, and a single cell with that cathode shows maximum power density of 1484 mW cm−2 at 700 °C. The cell exhibits a short-term stability of 120 h at 700 °C without noticeable degradation.

Nonadiabatic Charge Transfer within Photoexcited Nickel Porphyrins.

Metalloporphyrins with open d-shell ions can drive biochemical energy cycles. However, their utilization in photoconversion is hampered by rapid deactivation. Mapping the relaxation pathways is essential for elaborating strategies that can favorably alter the charge dynamics through chemical design and photoexcitation conditions. Here, we combine transient optical absorption spectroscopy and transient X-ray emission spectroscopy with femtosecond resolution to probe directly the coupled electronic and spin dynamics within a photoexcited nickel porphyrin in solution. Measurements and calculations reveal that a state with charge-transfer character mediates the formation of the thermalized excited state, thereby advancing the description of the photocycle for this important representative molecule. More generally, establishing that intramolecular charge-transfer steps play a role in the photoinduced dynamics of metalloporphyrins with open d-shell sets a conceptual ground for their development as building blocks capable of boosting nonadiabatic photoconversion in functional architectures through "hot" charge transfer down to the attosecond time scale.

Cycling performance of Li metal anode in localized high concentration electrolyte and dynamic mechanism analysis

In this work, we investigated the apparent cycling performance of lithium metal at different chemical compositions and series current densities; examined the microscopic morphology and thickness variation of the deposition layer on the surface of lithium metal anode and the concentration-depth distribution of trace elements in the solid electrolyte interphase (SEI) film; and characterized the kinetic behavior and features of the elementary steps (mass transfer, charge transfer, electro-crystallization) at Li-electrolyte interface using microelectrode technology and various electrochemical test methods. The results show that the lithium metal anode has better cycling performance in high concentration and localized high concentration electrolyte. At the same time, the experimental results confirm that the formation of spherical crystal nucleus is favored only under certain chemical conditions and certain reaction rate; under these conditions, the induction period and the self-smoothing process of critical crystal nucleus can be found. It suggests that there are determined causal among the apparent performance of lithium metal anode, the kinetic parameters of the interfacial charge transfer step and the electro-crystallization step, and these correlations can be used as a reference for screening and evaluating electrolyte systems and battery operating conditions, providing a reliable kinetic basis for future work.

(Invited) Solvation Control in Deep Eutectic Solvent Electrolytes for Stable Plating/Stripping of Zn in Battery Applications

Within the field of battery applications, deep eutectic solvents (DESs) have emerged as innovative electrolytes for rechargeable Zinc-ion batteries (ZIBs) . ZIBs traditionally employ neutral or weakly acidic aqueous electrolytes, which are susceptible to the standard anode drawback such as dendrite formation and passivation. DES-based electrolytes can facilitate the reversible plating and stripping of Zn, mitigating also dendrite growth . One notable benefit of DES solvents over their aqueous counterparts is that the concentration of electroactive species controls the shape evolution of electrodes during electroplating. For this reason, the coordination chemistry and metal complex formed between the Lewis acid of the metal and the Lewis base of the DES play a central role. Moreover, water can be added to the eutectic mixtures to increase the diffusion coefficient of the electroactive species and lower the electrolyte viscosity without destroying the eutectic nature if the concentration is kept under 40%.Regarding metal plating/stripping processes, DESs offer a notable advantage due to their high capacity to dissolve metal salts, oxides, and hydroxides, inhibiting the formation of insoluble oxides and hydroxides . Moreover, the unique coordination properties of Zn2+ in DESs lead to an atypical voltammetric behavior, characterized by a cathodic peak in the cathodic branch of the anodic-going scan. The mechanistic studies of Zn electrodeposition onto glassy carbon (GC) from DESs have concluded that the metal is formed by the reduction of an intermediate Zn-containing species. Finally, the reactivity of choline chloride and ethylene glycol can impact coordination in that these species can be dehydrogenated at negative potential forming RO¯, which can replace one or more chloride ligands in [ZnCl4]2− . The correlation between the chemistry of Zn2+ solutions and DESs is elucidated, and the peculiarities of Zn electrochemistry can be rationalized in terms of the DES–electrode interface structure. Although few studies on hydrated DESs have been conducted, the literature remains scant.Shi et al. conducted a study on DES composed of ZnCl2 and acetamide with different concentration of water. The authors employed various spectroscopic techniques, including FT-IR, Raman, and 17O NMR, to investigate the effect of water on the coordination geometry of Zn2+ and its consequent impact on Zn plating. Interestingly, the authors observed that the addition of small amounts of water, below the threshold for direct water-water interaction, resulted in significant alterations of the Zn2+ coordination geometry. In fact, based on the accepted view that Zn electrodeposition is a process that involves desolvation and charge-transfer steps, [ZnCl(acetamide)2(H2O)]+ was shown to undergo successive deamidation and dehydration, yielding [ZnCl(acetamide)]+ from which the metal center is finally reduced. Although [ZnCl(acetamide)3]+ is the most stable species, the energy barrier for dehydration is significantly lower than that for deamidation. Therefore, [ZnCl(acetamide)2(H2O)]+ with lower dissociation energy is the actual electroactive species . The solvation of Zn also affects the nucleation overpotential, as Zn2+ in hydrated DES exhibits faster desolvation kinetics, resulting in a lower nucleation overpotential. In addition, Zhao et al. investigated the properties of a “water-in-DES” electrolyte (~30 mol.% H2O) based on the urea/LiTFSI/Zn(TFSI)2 mixture and discovered that the preferential interaction between water and metal cations promotes interfacial charge transfer. Notwithstanding the important contribution of these papers, the mechanism of Zn electrodeposition in DES has not been conclusively assessed. To address this knowledge gap, our research aims to investigate Zn electrodeposition from two distinct, hydrated DESs: ChU and ChEG with approximately 30% H2O content. To gain control of the impact of the cathode material, we carried out our electrochemical tests by employing GC, Zn, Pt and Au electrodes. Furthermore, to evaluate the performance of these electrolytes under realistic device conditions, electrochemical cycling tests were conducted on symmetric CR2023 coin cells.In this study, we have demonstrated the beneficial effect of water addition on reducing the electrolyte viscosity, which consequently resulted in lower anodic and cathodic overpotentials and improved charge/discharge cyclability. Specifically, the electrolytes ChEG and ChU failed due to passivation and short circuits, respectively. The ChU electrolyte showed regular chronopotentiometric transients until cell failure, and this was supported by multiple cyclic voltammetry (CV) measurements, which showed reversible Zn plating/stripping in this system. Notably, our cell cycling tests were performed at higher current densities and exhibited longer lifetimes compared to previous literature reports. The unusual CV patterns observed with gold and glassy carbon (GC) electrodes, featuring cathodic peaks on both forward and backward scans, were elucidated using complementary electrochemical and in situ Raman spectroscopy measurements. Figure 1

Halide-induced lattice disorder in bismuth nanosheets for industrial-current-density CO2-to-formate conversion under neutral condition

Bi-based electrocatalysts emerged as promising candidates to achieve efficient CO2-to-formate conversion, but they still suffered from the unsatisfied formate activity under the neutral condition. Here, halide-induced lattice disorder sites in bismuth nanosheets were proposed to achieve industrial-current-density CO2-to-formate conversion under neutral condition. In-situ Raman spectra and in-situ X-ray diffraction patterns revealed that Cl− extraction led to the formation of abundant lattice disorder Bi active sites, which resulted in the comprehensive surface strains. In-situ Fourier transform infrared spectroscopy unveiled CO2•− was the key intermediate. Additionally, theoretical calculation indicated that the lattice strain induced by Cl− extraction increased the density of states near the Fermi level, which would benefit CO2 adsorption and accelerate rate-determine charge transfer step to form CO2•− intermediates. As a result, the BiOCl-derived Bi nanosheets with abundant lattice disorder exhibited remarkable formate Faradaic efficiency up to 98% under the industrial current density (>200 mA/cm2), and operated continuously for 120 h at 100 mA/cm2 under the neutral condition (pH=7).

Reaction Environment Impacts Charge Transfer but Not Chemical Reaction Steps in Hydrogen Evolution Catalysis

Heterogeneous electrocatalysis involves elementary chemical and charge transfer reaction steps, with the kinetics of each step contributing to the overpotential requirement at a given reaction rate. Typical experiments report on the aggregate rate-overpotential profile with no information about the relative contributions from charge transfer and chemical steps. For the hydrogen evolution reaction (HER), the applied overpotential can be partitioned into a charge transfer overpotential, the overpotential necessary to drive proton-coupled electron transfer (PCET) to and from the surface, and a chemical overpotential, corresponding to a change in surface H activity. Reaction conditions can affect either or both the charge transfer and chemical components. Herein, we employ a Pd membrane double cell to spatially separate the charge transfer and chemical reactions steps of HER catalysis, enabling quantification of the chemical and charge transfer overpotential. We further analyze how each depend on pH, and the introduction of HER poisons and promoters. We find that for a given rate of H2 release, the chemical overpotential is constant across diverse reaction environments whereas the charge transfer overpotential is strongly sensitive to reaction conditions. These findings suggest that reaction condition dependent-HER efficiencies are driven predominantly by changes to the kinetics of charge transfer rather than the chemical reactivity of surface H.

Kinetics of single-crystal nickel-rich cathodes with 4.5 V upper voltage in the view of electrochemical impedance spectroscopy

For lithium-ion batteries with the high energy density, materials monocrystallization is thought to be a solution on overcoming the poor cycle stability of high‑nickel polycrystalline materials, as well as raising the increased cutoff voltage is regarded as a tactic to achieve deeper delithiation against the capacity loss caused by monocrystallization. However, the priority for materials improvement is to deeply recognize the kinetic behaviors, which provide a judgment as to whether this strategy is appropriate, and certain scientific thought as well as guiding principles definitely for the materials commercialization. In this paper, electrochemical kinetics of the single-crystal LiNi0.8Co0.1Mn0.1O2 (SC-NCM811) cathode have been investigated by electrochemical impedance spectroscopy (EIS) with 4.5 V upper voltage in three-electrode configurations assistance with the distribution of relaxation times (DRT) and trusted equivalent circuit models (ECMs) numerical analysis. Along with decrease in frequency, the EIS spectra exhibits three semicircles corresponding to Li+ migration through the cSEI film, the electronic properties of the material and the charge transfer step respectively, as well as a slightly inclined line is attributed to the solid state diffusion process. Additionally, an ‘insulator-to-metal’ transition is found for conductivity properties of materials. More importantly, increasing the upper cutoff voltage reaches deeper delithiation accompanied by the rapid growth of kinetics resistance, i.e. the increase of polarization and degradation of rate performance. Finally, a diagrammatic model for Li+ extraction/insertion is established to illustrate the physicochemical reaction mechanism in the SC-NCM811 electrode.

Study of Predominant Dynamics on the O3-Type Layered Transition-Metal Oxide Cathode by Electrochemical Impedance Spectroscopy for Sodium-Ion Batteries.

The layered transition metal oxides (NaxTMO2) are the most attractive cathode options for the rechargeable sodium-ion batteries (SIBs) owing to their high specific capacity, outstanding sodium desorption ability, and high average operating voltage. However, the kinetic behaviors corresponding to complex and prominent phase transitions are still perplexing. Here, we investigate the detailed electrochemical kinetic characteristics of the NaNi1/3Fe1/3Mn1/3O2 electrode by electrochemical impedance spectroscopy (EIS) in three-electrode configurations assistance with the distribution of relaxation times (DRT) and trusted equivalent circuit models numerical analysis. The complex and prominent phase transformations evolution of O3-P3-O3' in the charge process and O3'-P3'-O3 during the discharge process are reflected at different degrees of frequencies and potentials, and significant contributions for the charge transfer step are established on this basis. As the charge and discharge proceed, the influence on charge transfer process by phase transform will be weak, however, which still has some expression and can be caught by EIS assistance with DRT. Additionally, a diagrammatic model for Na+ extraction/insertion is established to illustrate the physicochemical reaction mechanism in the NaNi1/3Fe1/3Mn1/3O2 electrode. The results definitely provide certain scientific thoughts and guiding principles for the commercialization of NaxTMO2 in SIBs.

Theoretical Investigation of the Electrochemical Oxidation of H2 and CO Fuels on a Ruddlesden-Popper SrLaFeO4-δ Anode.

The electrochemical oxidation of H2 and CO fuels have been investigated on the Ruddlesden-Popper layered perovskite SrLaFeO4-δ (SLF) under anodic solid oxide fuel cell conditions using periodic density functional theory and microkinetic modeling techniques. Two distinct FeO2-plane-terminated surface models differing in terms of the underlying rock salt layer (SrO or LaO) are used to identify the active site and limiting factors for the electro-oxidation of H2, CO, and syngas fuels. Microkinetic modeling predicted an order of magnitude higher turnover frequency for the electro-oxidation of H2 compared to CO for SLF at short-circuit conditions. The surface model with an underlying SrO layer was found to be more active with respect to H2 oxidation than the LaO-based surface model. At an operating voltage of less than 0.7 V, surface H2O/CO2 formation was found to be the key rate-limiting step, and the surface H2O/CO2 desorption was the key charge transfer step. In contrast, the bulk oxygen migration process was found to affect the overall rate at high cell voltage conditions above 0.9 V. In the presence of syngas fuel, the overall electrochemical activity is derived mainly from H2 electro-oxidation and CO2 is chemically shifted to CO via the reverse water-gas shift reaction. Substitutional doping of a surface Fe atom with Co, Ni, and Mn revealed that the H2 electro-oxidation activity of FeO2-plane terminated anodes with an underlying LaO rock salt layer can be improved with dopant introduction, with Co yielding a three orders of magnitude higher activity relative to the undoped LaO surface model. Constrained ab initio thermodynamic analysis furthermore suggested that the SLF anodes are resistant toward sulfur poisoning both in the presence and absence of dopants. Our findings reflect the role of various elements in controlling the fuel oxidation activity of SLF anodes that could aid the development of new Ruddlesden-Popper phase materials for fuel cell applications.

Electrochemistry in a Two- or Three-Electrode Configuration to Understand Monopolar or Bipolar Configurations of Platinum Bionic Implants

Electrodes are used in vivo for chemical sensing, electrophysiological recording, and stimulation of tissue. The electrode configuration used in vivo is often optimised for a specific anatomy and biological or clinical outcomes, not electrochemical performance. Electrode materials and geometries are constrained by biostability and biocompatibility issues and may be required to function clinically for decades. We performed benchtop electrochemistry, with changes in reference electrode, smaller counter-electrode sizes, and three- or two-electrode configurations. We detail the effects different electrode configurations have on typical electroanalytical techniques used on implanted electrodes. Changes in reference electrode required correction by application of an offset potential. In a two-electrode configuration with similar working and reference/counter-electrode sizes, the electrochemical response was dictated by the rate-limiting charge transfer step at either electrode. This could invalidate calibration curves, standard analytical methods, and equations, and prevent use of commercial simulation software. We provide methods for determining if an electrode configuration is affecting the in vivo electrochemical response. We recommend sufficient details be provided in experimental sections on electronics, electrode configuration, and their calibration to justify results and discussion. In conclusion, the experimental limitations of performing in vivo electrochemistry may dictate what types of measurements and analyses are possible, such as obtaining relative rather than absolute measurements.

Ultrafast Dynamics of Photosynthetic Light Harvesting: Strategies for Acclimation Across Organisms.

Photosynthetic light harvesting exhibits near-unity quantum efficiency. The high efficiency is achieved through a series of energy and charge transfer steps within a network of pigment-containing proteins. Remarkably, high efficiency is conserved across many organisms despite differences in the protein structures and organization that allow each organism to respond to its own biological niche and the stressors within. In this review, we highlight recent progress toward understanding how organisms maintain optimal light-harvesting ability by acclimating to their environment. First, we review the building blocks of photosynthetic light harvesting, energy transfer, and time-resolved spectroscopic techniques. Then, we explore how three classes of photosynthetic organisms-purple bacteria, cyanobacteria, and green plants-optimize their light-harvesting apparatuses to their particular environment. Overall, research has shown that photosynthetic energy transfer is robust to changing environmental conditions, with each organism utilizing its own strategies to optimize photon capture in its particular biological niche. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 74 is April 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Oxygen Vacancy‐Mediated Exciton Effect in Hierarchical BiOBr Enables Dichotomy of Energy Transfer and Electron Transfer in Photocatalysis

AbstractUsing solar energy through green and simple artificial photosynthesis systems are considered as a promising way to solve the energy and environmental crisis. However, one of the important primary steps of photosynthesis, i.e., energy transfer, is long being ignored especially in inorganic semiconducting systems due to the small exciton binding energies. Herein, the simultaneous interrogation of the charge transfer and energy transfer steps in a photoexcitation process is proposed by utilizing few‐layered nanosheet‐assembled hierarchical BiOBr nanotubes with rich oxygen vacancies (OVs) as efficient multifunctional photocatalysts. Benefiting from the integrated 1D/2D structure and abundant OV defects, the excitonic effect strikes a delicate balance in the optimized BiOBr photocatalyst, showing not only improved charge carrier separation and transfer but also enhanced exciton generation. As a result, the hierarchical BiOBr nanotubes exhibit high efficiency toward photocatalytic CO2 reduction with an impressive CO evolution rate of 135.6 µmol g−1 h−1 without cocatalyst or photosensitizer. The dominant reactive oxygen species of singlet oxygen (1O2) are discriminated for the first time, which originated from an energy transfer process, with electrophilic character, whereas the minor effect of superoxide anion radical (•O2−) with a nucleophilic rate‐determining step in the photocatalytic aerobic oxidation of sulfides.

Electrochemical Characterization of the Self-Assembled 4,4’-Bipyridine Layers at the Electrode | Ionic Liquid Interface

Self-assembled monolayers (SAMs) have significant importance in many modern applications1-2. The properties of SAMs depend on many aspects, such as the characteristics of individual molecules, forming the monolayer; by the interactions between these molecules; and SAM interactions with the electrolyte; the crystalline surface of the substrate; etc3. Therefore, the fundamental studies of these systems are crucial in determining the function of SAMs in various applications4-5.The aim of the current work was to study the adsorption characteristics of 4,4’- bipyridine from ionic liquid media at different electrodes6.Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were conducted to characterize the electrochemical behavior of the self-assembled 4,4’-bipyridine (4,4’-BP) layers at the Sb(111) and Cd(0001) | 4,4’-BP+1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) interface. All the experiments were carried out in a three-electrode electrochemical cell in a glove-box, i.e., a nitrogen-controlled atmosphere.CV method was used to examine the electrochemical characteristics of the system under investigation within the potential region −0.9 V < E < 0.0 V for Sb(111) and −2.1 V < E < -0.8 V for Cd(0001) vs. Ag|AgCl. The current values increase rapidly at the more negative end of the studied potential region, indicating that reduction processes started at the Sb(111) and Cd(0001) | 4,4’-BP+EMImBF4 interface. In contrast with the data measured in EMImBF4, where the system shows ideal polarisable behaviour in the whole potential range. Interfacial capacitance (C s) values were calculated using the relation Cs=−(Z′′2\U0001d70bf)−1 . Capacitance values calculated depend on the composition of the electrolyte (i.e., on the concentration of 4,4’-BP), electrode material as well as on applied potential. Cs values are lower in the mixture than those measured in pure EMMImBF4 at a certain potential region in the case of both electrode materials. This effect is caused by the adsorption of 4,4’-BP molecules at the electrode surface. The shape of the phase angle vs. frequency (f) curves shows that mixed kinetic processes occur in the whole f range measured (i.e. diffusion and charge transfer steps in addition to adsorption).Acknowledgments:This work was supported by the Estonian Research Council grant PSG249, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).

Application of direct electrometry in studies of microbial rhodopsins reconstituted in proteoliposomes.

Microbial rhodopsins are the family of retinal-containing proteins that perform primarily the light-driven transmembrane ion transport and sensory functions. They are widely distributed in nature and can be used for optogenetic control of the cellular activities by light. Functioning of microbial rhodopsins results in generation of the transmembrane electric potential in response to a flash that can be measured by direct time-resolved electrometry. This method was developed by L. Drachev and his colleagues at the Belozersky Institute and successfully applied in the functional studies of microbial rhodopsins. First measurements were performed using bacteriorhodopsin from Halobacterium salinarum-the prototype member of the microbial retinal protein family. Later, direct electrometric studies were conducted with proteorhodopsin from Exiguobacterium sibiricum (ESR), the sodium pump from Dokdonia, and other proteins. They allowed detailed characterization of the charge transfer steps during the photocycle of microbial rhodopsins and provided new insights for profound understanding of their mechanism of action.

Interplay of Dynamic Constriction and Interface Morphology between Reversible Metal Anode and Solid Electrolyte in Solid State Batteries.

In an all-solid-state battery, the electrical contact between its individual components is of key relevance in addition to the electrochemical stability of its interfaces. Impedance spectroscopy is particularly suited for the non-destructive investigation of interfaces and of their stability under load. Establishing a valid correlation between microscopic processes and the macroscopic impedance signal, however, is challenging and prone to errors. Here, we use a 3D electric network model to systematically investigate the effect of various electrode/sample interface morphologies on the impedance spectrum. It is demonstrated that the interface impedance generally results from a charge transfer step and a geometric constriction contribution. The weights of both signals depend strongly on the material parameters as well as on the interface morphology. Dynamic constriction results from a non-ideal local contact, e.g., from pores or voids, which reduce the electrochemical active surface area only in a certain frequency range. Constriction effects dominate the interface behavior for systems with small charge transfer resistance like garnet-type solid electrolytes in contact with a lithium metal electrode. An in-depth analysis of the origin and the characteristics of the constriction phenomenon and their dependence on the interface morphology is conducted. The discussion of the constriction effect provides further insight into the processes at the microscopic level, which are, e.g., relevant in the case of reversible metal anodes.

Electrochemical Characterization of the Self-Assembled 4,4’-Bipyridine Layers at the Sb(111) | Ionic Liquid Interface

Self-assembled monolayers (SAMs) have significant importance in many modern applications1-2. The characteristics of SAMs depend on many aspects, like the characteristics of individual molecules, forming the monolayer; by the interactions between these molecules; and by SAM interactions with the electrolyte; the crystalline surface of the substrate; etc3. Therefore, the fundamental studies of these systems are crucial to determine the function of SAMs in various applications4-5.The aim of the current work was to study the adsorption characteristics of 4,4’- bipyridine from ionic liquid media and compare the results with previous data measured in aqueous electrolyte solutions.Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were conducted to characterize the electrochemical behavior of the self-assembled 4,4’-bipyridine (4,4’-BP) layers at the Sb(111) | 4,4’-BP+1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) interface. All the experiments were carried out in a three-electrode electrochemical cell in a glove-box, i.e., nitrogen-controlled atmosphere.CV method was used to determine and to evaluate the electrochemical characteristics of the system under investigation within potential region, −0.9 V < E < 0.0 V vs. Ag|AgCl. The current values increase rapidly at E < −0.8 V, indicating that a reduction process started at the Sb(111) | 4,4’-BP+EMImBF4 interface. Thus, unlikely to the data measured in EMImBF4, where the system shows ideal polarisable behaviour in the whole potential range. Interfacial capacitance (C s) values were calculated using relation C s =−(Z′′2\U0001d70bf) −1 . Capacitance values calculated depend on the composition of the electrolyte (i.e., on the concentration of 4,4’-BP) as well as on the potential applied. C s values are lower in the mixture than those measured in pure EMImBF4 at E > – 0.7 V. This effect is caused by the adsorption and formation of the compact layer of 4,4’-BP molecules at the electrode surface. The C s vs. E dependences of the mixture increase significantly at E < −0.8 V (similarly to CV curves), which is not visible in the case of pure EMImBF4. This is also confirmed by small negative phase angle values at E < −0.8 V, where the shape of the phase angle vs. frequency (f) curves shows that mixed kinetic processes occurring in the whole f range measured (i.e. diffusion and charge transfer steps in addition to adsorption). At E > −0.8 V, phase angle values are close to − 80° for Sb(111)|4,4’-BP + EMImBF4 in a wide range of f. Only at low frequency values the mixed kinetic processes (adsorption, diffusion and partial charge transfer) were observed.The formation of ordered 4,4’-BP arrangements was most pronounced in the potential range −0.7 V < E < 0.0 V due to the reductive desorption of 4,4’BP at E < −0.8 V.Acknowledgments:This work was supported by the Estonian Research Council grant PSG249, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).