Bidirectional generation of structure and properties through a single molecular foundation model.

Recent successes of foundation models in artificial intelligence have prompted the emergence of large-scale chemical pre-trained models. Despite the growing interest in large molecular pre-trained models that provide informative representations for downstream tasks, attempts for multimodal pre-training approaches on the molecule domain were limited. To address this, here we present a multimodal molecular pre-trained model that incorporates the modalities of structure and biochemical properties, drawing inspiration from recent advances in multimodal learning techniques. Our proposed model pipeline of data handling and training objectives aligns the structure/property features in a common embedding space, which enables the model to regard bidirectional information between the molecules' structure and properties. These contributions emerge synergistic knowledge, allowing us to tackle both multimodal and unimodal downstream tasks through a single model. Through extensive experiments, we demonstrate that our model has the capabilities to solve various meaningful chemical challenges, including conditional molecule generation, property prediction, molecule classification, and reaction prediction.

Probing Local pH Change during Electrode Oxidation of TEMPO Derivative: Implication of Redox-Induced Acidity Alternation by Imidazolium-Linker Functional Groups.

The chemical degradation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-based aqueous energy storage and catalytic systems is pH sensitive. Herein, we voltammetrically monitor the local pH (pHlocal) at a Pt ultramicroelectrode (UME) upon electro-oxidation of imidazolium-linker functionalized TEMPO and show that its decrease is associated with the greater acidity of the cationic (oxidized) rather than radical (reduced) form of TEMPO. The protons that drive the decrease in pH arise from hydrolysis of the conjugated imidazolium-linker functional group of 4-[2-(N-methylimidazolium)acetoxy]-2,2,6,6-tetramethylpiperidine-1-oxyl chloride (MIMAcO-T), which was studied in comparison with 4-hydroxyl-TEMPO (4-OH-T). Voltammetric hysteresis is observed during the electrode oxidation of 4-OH-T and MIMAcO-T at a Pt UME in an unbuffered aqueous solution. The hysteresis arises from the pH-dependent formation and dissolution of Pt oxides, which interact with pHlocal in the vicinity of the UME. We find that electrogenerated MIMAcO-T+ significantly influences pHlocal, whereas 4-OH-T+ does not. Finite element analysis reveals that the thermodynamic and kinetic acid-base properties of MIMAcO-T+ are much more favorable than those of its reduced counterpart. Imidazolium-linker functionalized TEMPO molecules comprising different linking groups were also investigated. Reduced TEMPO molecules with carbonyl linkers behave as weak acids, whereas those with alkyl ether linkers do not. However, oxidized TEMPO+ molecules with alkyl ether linkers exhibit more facile acid-base kinetics than those with carbonyl ones. Density functional theory calculations confirm that OH- adduct formation on the imidazolium-linker functional group of TEMPO is responsible for the difference in the acid-base properties of the reduced and oxidized forms.

Cl-/Cl3- Redox Voltammetry to Recognize the Interfacial Layer on Positively Electrified Carbon in "Water-in-Salt" Electrolytes.

A "Water-in-Salt" electrolyte solution (WiSE) is a promising aqueous medium for lithium-ion batteries containing highly concentrated electrolytes. For the increased kinetic overpotential of water oxidation in WiSE, the formation of an interfacial layer (IFL) on a positively electrified electrode is crucial. Nonetheless, most related studies have been restricted to theoretical approaches. In this Article, we voltammetrically study the Cl-/Cl3-/Cl2 redox reaction on Pt and glassy carbon (GC) electrodes in WiSE containing LiTFSI (WiSELiTFSI) and demonstrate that careful monitoring of Cl-/Cl3- redox voltammetry can allow recognition of an IFL formed on a positively electrified electrode. The voltammetric wave attributed to the electro-oxidation of Cl- on a GC electrode was negatively more shifted as the molal concentration of LiTFSI was increased from 0.5 to 6 m, while there was no shift on Pt. Also, there was voltammetric resolution into two peaks associated with Cl-/Cl3- and Cl3-/Cl2 on the GC electrode in WiSELiTFSI, while only unresolved, one redox-paired voltammograms were observed on Pt, regardless of the molal concentration of LiTFSI. These two main voltammetric features indicate the LiTFSI-induced IFL coupled with Cl- and Cl3- on a GC electrode induced by an applied potential of ∼2 V versus the point of zero charge (PZC). We found other halide/halogen redox reactions did not show differentiated voltammetric behaviors in WiSELiTFSI, which demonstrates the uniqueness of the Cl-/Cl3- redox reaction for recognizing the IFL formed on a positively charged electrode surface. Lastly, a strong interaction between the IFL and Cl species was also confirmed by XPS measurements.

Redox-Transition from Irreversible to Reversible Vitamin C by Pore Confinement in Microporous Carbon Network.

Enhancement of redox-reversibility in electroactive species has been studied because of fundamental interest and their importance for energy storage systems. Various electroactive molecules suffer from redox-irreversible behavior, and this is a critical reason for their exclusion as redox electrolytes in energy storage systems. In this article, we fully demonstrated that ascorbic acid (ASC), which is an abundant but redox-irreversible molecule, can become redox-reversible when it is confined in microporous carbon regimes. From a theoretical perspective, redox-reversibility in an electrochemical reaction coupled with an irreversible chemical process can be greatly enhanced due to kinetic acceleration toward the inverse direction of the chemical reaction by accumulation of products in the nanoconfined regime. However, the kinetic acceleration in a nanoconfined domain shows limitations for enhancing the redox-reversibility, which indicates that stabilization of the species undergoing an irreversible chemical process is another important factor for redox-reversibility enhancement. The origin of nanoporous confinement of ASC and its enhanced redox-reversibility was rationalized by molecular dynamics simulations. We found that ASC-clusters of a fully protonated ASC and its conjugated base formed inside carbon pores, which would be a main driving force for its confinement in microporous carbon networks. Lastly, we demonstrated a prototype energy storage device using redox-reversible ASC in microporous carbon as the half electrode, which shows the feasibility of ASC as a possible redox electrolyte in an aqueous energy storage system.

Comparison of Netarsudil/Latanoprost Therapy with Latanoprost Monotherapy for Lowering Intraocular Pressure: A Systematic Review and Meta-analysis.

PURPOSE: Netarsudil is a Rho kinase inhibitor and the first new class of clinically useful ocular hypotensive agents. In this study, we conducted a systematic literature review and meta-analysis to summarize and synthesize the available evidence on the efficacy and safety of fixed-dose combination (FDC) therapy with netarsudil/latanoprost in patients with glaucoma. METHODS: We identified relevant studies in PubMed, Ovid Medline, Embase, and Cochrane Central until April 2021. The quality of the studies and the level of evidence were assessed using the Risk of Bias tool. Efficacy was measured as the mean difference in reducing intraocular pressure (IOP), and safety was assessed by the risk of conjunctival hyperemia (CH) due to FDC therapy, netarsudil monotherapy, or latanoprost monotherapy. RESULTS: Four studies met the predefined eligibility criteria and were included in the meta-analysis. The mean difference in the reduction in IOP after 2 weeks and 4 to 6 weeks of drug administration was -2.41 mmHg (95% confidence interval [CI], -2.95 to -1.87) and -1.77 mmHg (95% CI, -2.31 to -1.87), respectively, in patients receiving FDC therapy versus those receiving latanoprost monotherapy. On the other hand, latanoprost monotherapy had a greater effect in reducing IOP than netarsudil monotherapy after 4 to 6 weeks of administration (mean difference, 0.95 mmHg; 95% CI, 0.43 to 1.47). The risk of CH was significantly higher with both FDC therapy and netarsudil monotherapy compared to latanoprost monotherapy in week 12, where the relative ratio was 3.01 (95% CI, 1.95 to 4.66) and 2.33 (95% CI, 1.54 to 3.54), each. CONCLUSIONS: Netarsudil/latanoprost FDC therapy has a significantly greater effect on reducing IOP than latanoprost alone. The symptoms of CH were mostly mild, and only a few glaucoma patients discontinued the medication owing to CH in earlier clinical trials. Therefore, it would be beneficial to consider the administration of netarsudil/latanoprost FDC therapy in patients with glaucoma.

Triiodide-in-Iodine Networks Stabilized by Quaternary Ammonium Cations as Accelerants for Electrode Kinetics of Iodide Oxidation in Aqueous Media.

The Zn-polyiodide redox flow battery is considered to be a promising aqueous energy storage system. However, in its charging process, the electrode kinetics of I- oxidation often suffer from an intrinsically generated iodine film (I2-F) on the cathode of the battery. Therefore, it is critical to both understand and enhance the observed slow electrode kinetics of I- oxidation by an electrochemically generated I2-F. In this article, we introduced an electrogenerated N-methyl-N-ethyl pyrrolidinium iodide (MEPI)-iodine (I2) solution, designated as MEPIS, and demonstrated that the electrode kinetics of I- oxidation were dramatically enhanced compared to an I2-F under conventional electrolyte conditions, such as NaI. We showed that this result mainly contributed to the fast electro-oxidation of triiodide (I3-), which exists in the shape of a I3--in-I2 network, [I3-·(I2)n]. Raman spectroscopic and electrochemical analyses showed that the composition of electrogenerated MEPIS changed from I3- to [I3-·(I2)n] via I5- as the anodic overpotential increased. We also confirmed that I- was electrochemically oxidized on a MEPIS-modified Pt electrode with fast electrode kinetics, which is clearly contrary to the nature of an I2-F derived from a NaI solution as a kinetic barrier of I- oxidation. Through stochastic MEPIS-particle impact electrochemistry and electrochemical impedance spectroscopy, we revealed that the enhanced electrode kinetics of I- oxidation in MEPIS can be attributed to the facilitated charge transfer of I3- oxidation in [I3-·(I2)n]. In addition, we found that the degree of freedom of I3- in a quaternary ammonium-based I2-F can also be critical to determine the kinetics of the electro-oxidation of I-, which is that MEPIS showed more enhanced charge-transfer kinetics of I- oxidation compared to tetrabutylammonium I3- due to the higher degree of freedom of I3-.

Mechanically Rotating Intravascular Ultrasound (IVUS) Transducer: A Review.

Intravascular ultrasound (IVUS) is a valuable imaging modality for the diagnosis of atherosclerosis. It provides useful clinical information, such as lumen size, vessel wall thickness, and plaque composition, by providing a cross-sectional vascular image. For several decades, IVUS has made remarkable progress in improving the accuracy of diagnosing cardiovascular disease that remains the leading cause of death globally. As the quality of IVUS images mainly depends on the performance of the IVUS transducer, various IVUS transducers have been developed. Therefore, in this review, recently developed mechanically rotating IVUS transducers, especially ones exploiting piezoelectric ceramics or single crystals, are discussed. In addition, this review addresses the history and technical challenges in the development of IVUS transducers and the prospects of next-generation IVUS transducers.

Temporally Resolved Electrochemical Interrogation for Stochastic Collision Dynamics of Electrogenerated Single Polybromide Droplets.

In this article, we present electrochemical interrogation for collision dynamics of electrogenerated individual polybromide ionic liquid (PBIL) droplets through chronoamperometry combined with fast scan cyclic voltammetry (CA-FSCV). In the CA mode of CA-FSCV, a Pt ultramicroelectrode (UME) acts as the electrochemical generator for PBIL droplets by holding the oxidation potential for Br- in a given time, while FSCV is repetitively performed at a certain frequency. In the FSCV mode of CA-FSCV, a Pt UME serves as the probe to electrochemically monitor Br3- reduction for an adsorbed PBIL droplet during collision with a high temporal resolution. Based on the newly introduced CA-FSCV, we can estimate the dynamic changes in the following parameters for a short collision time: the contact radius of a PBIL droplet on a Pt UME, the concentration of Br- in the droplet, and the apparent charge transfer rate constant for electro-reduction of Br3- to Br- in the droplet, koapp. Moreover, a computational calculation using molecular dynamics is presented that can explain the change in koapp as a function of time for Br- electrolysis in a PBIL droplet. Based on the quantitative estimation of the above parameters, we suggest a more advanced mechanism for the stochastic electrochemical collision process of a PBIL droplet. These findings are important for understanding QBr2n+1/QBr half redox reactions in aqueous energy storage systems, such as Zn-Br redox flow batteries and Br-related redox enhanced electrochemical capacitors.

Stochastic Particle Approach Electrochemistry (SPAE): Estimating Size, Drift Velocity, and Electric Force of Insulating Particles.

Stochastic particle impact electrochemistry (SPIE) is considered one of the most important electro-analytical methods to understand the physicochemical properties of single entities. SPIE of individual insulating particles (IPs) has been particularly crucial for analyses of bioparticles. In this article, we introduce stochastic particle approach electrochemistry (SPAE) for electrochemical analyses of IPs, which is the advanced version of SPIE; SPAE is analogous to SPIE but focuses on deciphering a sudden current drop (SCD) by an IP-approach toward the edge of an ultramicroelectrode (UME). Polystyrene particles (PSPs) with and without different surface functionalities (-COOH and - NH3) as well as fixed human platelets (F-HPs) were used as model IPs. From theory based on finite element analysis, a sudden current drop (SCD) induced by an IP during electro-oxidation (or reduction) of a redox mediator on a UME can represent the rapid approach of an IP toward an edge of a UME, where a strong electric field is generated. It is also found that the amount of current drop, idrop, of an SCD depends strongly on both the size of an IP and the concentration of redox electrolyte. From simulations based on the SPAE model that fit the experimentally obtained SCDs of three types of PSPs or F-HP dispersed in solutions with two redox electrolytes, their size distribution histograms are estimated, from which their average radii determined by SPAE are compared to those from scanning electron microscopic images. In addition, the drift velocity and corresponding electric force of the PSPs and F-HPs during their approach toward an edge of a Pt UME are estimated, which cannot be addressed currently with SPIE. We further learned that the estimated drift velocity and the corresponding electric force could provide a relative order of the number of excess surface charges on the IPs.

Determination of Serotonin Concentration in Single Human Platelets through Single-Entity Electrochemistry.

This research introduces a method to directly detect serotonin in a single platelet through single-entity electrochemistry. Platelets isolated from human blood were analyzed by cyclic voltammetry and current-time measurements. When a single platelet collides with an ultramicroelectrode, serotonin inside the platelet is oxidized at the electrode surface, and an anodic current peak is consequently observed during measurement. The concentration of serotonin can be determined by integrating this peak current. In addition, this method can be used to determine the platelet concentration. Analysis of the collision frequency of platelets can provide information about the platelet concentration in the blood. As a result, platelet levels and serotonin concentrations in single platelets can be measured quickly and easily.

Feasibility of Voltage-Applied SERS Measurement of Bile Juice as an Effective Analytical Scheme to Enhance Discrimination between Gall Bladder (GB) Polyp and GB Cancer.

A unique surface-enhanced Raman scattering (SERS) measurement scheme to discriminate gall bladder (GB) polyp and GB cancer by analysis of bile juice is proposed. Along with the high sensitivity of SERS, external voltage application during SERS measurement was incorporated to improve sample discriminability. For this purpose, Au nanodendrites were constructed on a screen-printed electrode (referred to as AuND@SPE), and Raman spectra of extracted aqueous phases from raw bile juice samples were acquired using the AuND@SPE at voltages from -300 to 300 mV. The sample spectra resembled that of bilirubin, possessing an open chain tetrapyrrole, showing that bilirubin derivatives in bile juice were mainly responsible for the observed peaks. Discrimination of GB polyp and GB cancer using just the normal SERS spectra was not achieved but became apparent when the spectra were acquired at a voltage of -100 mV. When voltage-applied SERS spectra of bilirubin and urobilinogen (one of bilirubin's derivatives) were examined, a sudden intensity elevation occurring at -100 mV was observed for urobilinogen but not bilirubin. Based on examination of corresponding cyclic voltammograms, the potential-driven strong adsorption of urobilinogen (no faradaic charge transfer) on AuND occurring at -100 mV induced a substantial increase in SERS intensity. It was presumed that the content of urobilinogen in the bile juice of a GB cancer patient would be higher than that of a GB polyp patient, and the contained urobilinogen was sensitively highlighted by applying -100 mV during SERS measurement, allowing clear discrimination of GB cancer against GB polyp.

Stochastic Electrochemical Cytometry of Human Platelets via a Particle Collision Approach.

The quantitative analysis of human platelets is important for the diagnosis of various hematologic and cardiovascular diseases. In this article, we present a stochastic particle impact electrochemical (SPIE) approach for human platelets with fixation (F-HPs). Carboxylate-functionalized polystyrene particles (PSPs) are studied as well as a standard platform of SPIE-F-HPs. For SPIE-PSPs (or F-HPs), [Fe(CN)6]4- was used as the redox mediator, and electro-oxidation of [Fe(CN)6]4- to [Fe(CN)6]3- was conducted on a Pt ultramicroelectrode (UME) by applying a constant potential, where the corresponding oxidation current is mass-transfer-controlled. When PSPs (or F-HPs) are introduced into aqueous solution with [Fe(CN)6]4-, sudden current drops (SCDs) were observed, which resulted from the partial blockage of a Pt UME by collision of an individual PSP (or F-HP). For SPIE-PSPs (or F-HPs), we found that it is essential to enhance the migration of PSPs (F-HPs) toward a Pt UME by maximizing the steady state current associated with electro-oxidation of [Fe(CN)6]4-. This was accomplished by increasing its concentration to the solubility limit. We successfully measured the concentration of F-HPs dispersed in aqueous solution containing [Fe(CN)6]4- with a minimum detectable concentration of 0.1 fM, and the size distribution of F-HPs was also estimated from the obtained idrop distribution based on the SPIE analysis, where idrop stands for the magnitude of the current drop of each SCD. Lastly, we revealed that HPs without the fixation process (WF-HPs) are difficult to quantitatively analyze by SPIE because of their transient activation process, which results in changes from their spherical shape. The observed difficulty was also confirmed by finite element analysis, which shows that idrop can be significantly increased, as an elongated WF-HP is adsorbed on the edge of an UME.

Viologen-Bromide Dual-Redox Ionic Solid Complexes: Understanding Their Electrochemical Formation and Proton-Accompanied Redox Chemistry.

The inhibition of self-discharge in a redox-enhanced electrochemical capacitor (Redox-EC) is crucial for excellent energy retention. Heptyl viologen dibromide (HVBr2) was chosen as a strong candidate of a dual-redox species in Redox-EC due to its solid complexations during the charging process, at which HV2+ is electrochemically reduced to HV+• and form a solid complex, [HV+•·Br-], on an anode while Br- is electro-oxidized to Br3- and renders [HV2+·2Br3-] on a cathode. The solid complexes could not transfer across the separator, resulting in significant diminution of the self-discharge. In this Article, we present detailed electrochemical studies of formation of [HV2+·2Br3-] and [HV+•·Br-], their redox features, and galvanic exchange reactions between the two types of dual-redox ionic solids on a Pt ultra-microelectrode (UME) in neutral (0.33 M Na2SO4) and acidic (1 M H2SO4) solutions. Most importantly, through voltammetric and particle-impact electrochemical analyses, we found that the redox and galvanic exchange reactions of the two dual-redox ionic solid complexes involve H+ transfer, which is the key process to limit the overall kinetics of the electrochemical reactions. We also rationalize the proton-accompanied galvanic exchange reaction based on computational simulation.

Unraveling V(V)-V(IV)-V(III)-V(II) Redox Electrochemistry in Highly Concentrated Mixed Acidic Media for a Vanadium Redox Flow Battery: Origin of the Parasitic Hydrogen Evolution Reaction.

We present a mechanistic understanding of the full redox electrochemistry of V(V)-V(IV)-V(III)-V(II) and the origin of the parasitic hydrogen evolution reaction (HER) during electroreduction of either V3+ or VO2+ in a highly concentrated mixed acidic solution based on both electroanalytical and computational approaches. First, we found that the VO2+/VO2+ redox reaction is well explained by the EC/EC square scheme. We also found that V3+ is electrochemically oxidized to V4+ and subsequently undergoes a transition to stable VO2+ via hydrolysis. In the V3+/V2+ redox reaction via voltammetric analysis at scan rates greater than 0.05 V/s, the voltammograms are well explained based on a simple 1e- transfer reaction scheme. However, at the longer time scale observed in the chronoamperograms with constantly applied potentials where V3+ is electrochemically reduced to V2+, we found that a significant HER occurs because of possible formation of an electrocatalyst related to the V(II)O species, V(II)catalyst. We suggest that V(II)O is kinetically formed from V2+ via hydrolysis only when a local concentration of V2+ is high in the vicinity of a GC electrode surface, and V(II)O is adsorbed on a GC surface to form V(II)catalyst. To extend our mechanistic pathway, electroreduction of VO2+ to V(II) was also analyzed, revealing that VO2+ is electroreduced to VO+ and further reduced to VO in addition to disproportionation of VO+. Eventually, V(II)catalyst forms on a GC electrode, resulting in a significant HER. The computational calculation strongly supports the possible formation of V(II)catalyst. The calculation shows that neither V3+ nor V2+ can form stable intermediates during the HER, while V(II)O has the highest proton affinity compared with V(III)O+ and V(IV)O2+, indicating a plausible electrocatalytic property of V(II)O for the HER.

Time Transient Electrochemical Monitoring of Tetraalkylammonium Polybromide Solid Particle Formation: Observation of Ionic Liquid-to-Solid Transitions.

Energy storage systems (ESSs) using a Br-/Br2 redox reaction such as a Zn/Br redox flow battery (RFB) or a redox-enhanced electrochemical capacitor (Redox-EC) suffer from self-discharge reactions resulting in significant Coulombic loss. To inhibit the self-discharge, quaternary ammonium (Q+) and tetraalkylammonium (T+) bromide are added to form ionic liquid (QBr2 n+1) and solid (TBr3) polybromides during the ESS charging process. The electrochemical formation of liquid QBr2 n+1 and its electrochemical properties have been examined. The detailed mechanisms of ionic solid TBr3 formation, however, have not yet been explored. In this article, we analyzed the ionic liquid-to-solid phase transition of TBr3 particles using a time transient electrochemical method. We suggest the formation of ionic solid TBr3 particles via hydrated TBr3 droplets as an intermediate phase, which are generated by electro-oxidation of Br- in an aqueous TBr solution. We found the phase transition time of TBr3 particles is strongly dependent on the chemical structure of T+ and the concentration of TBr in an aqueous solution.

Controlling electric potential to inhibit solid-electrolyte interphase formation on nanowire anodes for ultrafast lithium-ion batteries.

With increasing demand for high-capacity and rapidly rechargeable anodes, problems associated with unstable evolution of a solid-electrolyte interphase on the active anode surface become more detrimental. Here, we report the near fatigue-free, ultrafast, and high-power operations of lithium-ion battery anodes employing silicide nanowires anchored selectively to the inner surface of graphene-based micro-tubular conducting electrodes. This design electrically shields the electrolyte inside the electrode from an external potential load, eliminating the driving force that generates the solid-electrolyte interphase on the nanowire surface. Owing to this electric control, a solid-electrolyte interphase develops firmly on the outer surface of the graphene, while solid-electrolyte interphase-free nanowires enable fast electronic and ionic transport, as well as strain relaxation over 2000 cycles, with 84% capacity retention even at ultrafast cycling (>20C). Moreover, these anodes exhibit unprecedentedly high rate capabilities with capacity retention higher than 88% at 80C (vs. the capacity at 1C).

Probing the speciation of quaternary ammonium polybromides by voltammetric tribromide titration.

The speciation of quaternary ammonium polybromides (QBr2n+1) was quantitatively determined by voltammetric tribromide titration on a Pt ultramicroelectrode (UME). The concentration of Br3- in a QBr2n+1-water mixed solution (QBr2n+1-WMS) was electrochemically estimated by measuring the steady state current associated with the electro-reduction of Br3- in a linear sweep voltammogram (LSV). The pBr3- titration curves of QBr2n+1-WMSs show 2-4 plateaus, each of which relates to the formation of QBr2n+1 from Br3- and Br2. The values of pBr3- at these plateaus can be regarded as corrected equilibrium constants of QBr2n+1, K'eq(n), which is Keq(n)/γ±, where γ± is a mean activity coefficient in QBr2n+1-WMS. Based on the estimated K'eq(n), fractional diagrams of QBr2n+1 were obtained, which gave information on QBr2n+1 speciation.

A self-assembled Ni(cyclam)-BTC network on ITO for an oxygen evolution catalyst in alkaline solution.

A self-assembled Ni(cyclam)-BTC film was formed on ITO in an acidic solution. Ni(cyclam)-BTC exhibited an enhanced electro-catalytic property for the oxygen evolution reaction (OER), which was strongly relevant to the Ni(iii)/Ni(iv) redox reaction activated by the potential dynamic process. A possible formation mechanism of Ni(cyclam)-BTC by self-assembly on ITO was also proposed.

Electrochemically Identified Ultrathin Water-Oxidation Catalyst in Neutral pH Solution Containing Ni2+ and Its Combination with Photoelectrode.

Water oxidation electrocatalyzed by Ni2+ under neutral conditions was investigated using various electrochemical analyses. The addition of Ni2+ in a phosphate-buffered solution catalyzed the oxidation of water, as confirmed by the detection of oxygen generation via scanning electrochemical microscopy. A combination of cyclic voltammetry, coulometric titration, and electrochemical quartz microbalance measurements identified the catalysis as heterogeneous and the catalyst as a Ni-based ultrathin (<4 nm) layer ("Ni-Pi"). Analysis of the potential- and pH-dependency of the titrated amount of charge revealed that the catalyst was deposited only under anodic polarization conditions and was removed under unpolarized conditions; the catalyst may be Ni(III) oxide, and its formation and oxidation appeared to be chemically irreversible. The diffusion-limited nature of water oxidation catalyzed by Ni2+ was closely related to the phosphate ions involved in the catalyst formation and the accompanying catalysis. Although the catalytic performance of Ni2+ alone was not remarkable, it exhibited a synergetic effect with BiVO4 for photoelectrochemical water oxidation, which can compete with Co-Pi-decorated BiVO4.

A facile room temperature chemical transformation approach for binder-free thin film formation of Ag2Te and lithiation/delithiation chemistry of the film.

The present work demonstrates a highly controllable, facile and environmentally friendly aqueous solution based synthetic method for oxide contamination-free Ag2Te thin films on desired substrates at room temperature using ion exchange induced chemical transformation of Ag/AgxO thin films. The films before and after chemical transformation reaction are characterized using an energy dispersive X-ray analyzer, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, thin film X-ray diffraction technique, high resolution transmission electron microscopy, and the selected area electron diffraction analysis technique. The as-deposited Ag2Te films show a highly crystalline nature even without thermal treatment. Furthermore, the electrochemistry for lithiation/delithiation of the Ag2Te film is studied for exploring its feasibility in the application as an anode material in a Li-ion battery. The experimentally estimated capacity of the Ag2Te electrode for Li storage is found to be about two and half fold larger than the theoretical capacity of the Ag2Te material. This implies that the binder-free Ag2Te film prepared by the current method could find a potential application in the Li-ion or other similar charge storing devices.