Outer Helmholtz Plane Research Articles

Interface Properties of the Partially Oxidized Pt(111) Surface Using Hybrid DFT-Solvation Models.

This article reports a theoretical-computational effort to model the interface between an oxidized platinum surface and aqueous electrolyte. It strives to account for the impact of the electrode potential, formation of surface-bound oxygen species, orientational ordering of near-surface solvent molecules, and metal surface charging on the potential profile along the normal direction. The computational scheme is based on the DFT/ESM-RISM method to simulate the charged Pt(111) surface with varying number of oxygen adatoms in acidic solution. This hybrid solvation method is known to qualitatively reproduce bulk metal properties like the work function. However, the presented calculations reveal that vital interface properties such as the electrostatic potential at the outer Helmholtz plane are highly sensitive to the position of the metal surface slab relative to the DFT-RISM boundary region. Shifting the relative position of the slab also affects the free energy of the system. It follows that there is an optimal distance for the first solvent layer within the ESM-RISM framework, which could be found by optimizing the position of the frozen Pt(111) slab. As it stands, manual sampling of the position of the slab is impractical and betrays the self-consistency of the method. Based on this understanding, we propose the implementation of a free energy optimization scheme of the relative position of the slab in the DFT-RISM boundary region. This optimization scheme could considerably increase the applicability of the hybrid method.

How cations determine the interfacial potential profile: Relevance for the CO2 reduction reaction

The strong effect of the electrolyte cation on the activity and selectivity of the CO2 reduction reaction (CO2RR) can only be understood and controlled if the cation’s effect on the interfacial potential distribution is known. Using CO (the key intermediate in the CO2RR) adsorbed on Pt as a probe molecule, and combining IR spectroscopy, capacitance measurements and ab initio molecular dynamics, we show that the cation size determines the location of the outer Helmholtz plane, whereby smaller cations increase not just the polarisation but, most importantly, the polarizability of adsorbed CO (COad) and the accumulation of electronic density on the oxygen atom of COad. This strongly affects its adsorption energy, the degree of hydrogen bonding of interfacial water to COad and the degree of polarisation of water molecules in the cation’s solvation shell, all of which can deeply affect the subsequent steps of the CO2RR.

Combined Electrokinetic and Electrochemical Measurements to Study the Electric Double Layer at Electrode-Electrolyte Interface

Electrochemical techniques, such as cyclic voltammetry and chronoamperometry are generally used to understand the reaction kinetics and structure of the electric double layer (EDL) formed at the electrode-electrolyte interface. While these techniques can effectively probe the Faradaic reactions, specific adsorption processes etc., they are limited in their applicability towards measuring potential at the outer Helmholtz plane (OHP). On the other hand, electrokinetic methods are broadly used to measure potential at the slip plane, Zeta potential, which determines the nature of the diffuse layer at the interface. Depending on the ionic strength of the solution (Debye length) Zeta potential and OHP potentials can coincide. In this study, we used the electrokinetic techniques, such as streaming-current and streaming-potential methods to measure Zeta potential of solid metallic surfaces and hence attempted to bridge electrochemical and electrokinetcs in understanding of the EDLs. Figure 1a shows a novel electrochemical cell designed by our group and adapted for the electrokinetic set-up. In conventional streaming current experiment, pressure difference between the two electrolyte reservoirs drive the ionic current mostly through the slip plane. By taking the slope of current vs pressure at a given pH a Zeta potential can be calculated. We report Zeta potential of a strip of Au, our model electrode, under various conditions (varied pH and electrolyte concentration), where the solid cell set-up measurements were validated against the more conventional Zeta potential measurements of colloidal particles with dynamic light scattering approach. By incorporating electrochemical set-up, we were able to vary applied potential on the electrode to probe potential of zero charge (pzc) of gold. The surface of gold electrode was cleaned beforehand in electrochemical three-electrode set-up using cycling voltammetry. Combining the data obtained from cyclic voltammetry and electrokinetics and applying the well-tested Gouy-Chapman theory of the EDLs, we were able to calculate the ion-distribution in the diffuse layer, the diffuse layer conductivity and the charge density on the surface of the electrode. We also attempted to comment on the possible relationship between the pzc and iso-electric point. The pzc of gold was found to be dependent on the pH of the electrolyte, and it varied between 200 mV to 500 mV on SHE. Next, we will extend the method to the other interfaces of interest to electrochemical community (such as Pt). Figure 1

Ultrasensitive electrochemiluminescence immunosensor for the transcriptional co-activator p300 by using a graphene oxide monolayer and tetrahedral DNA-mediated signal amplification.

Protein p300 is a transcriptional co-activator that participates in many physiological processes including cell cycle control, differentiation and apoptosis. It serves (a) as a protein bridge that links specific transcription factors to the fundamental transcription machinery, (b) as a scaffold to complete multiple transcription cofactors, and (c) as an enzyme for acetylating histone and non-histone proteins. An ultrasensitive electrochemiluminescence (ECL) immunosensor is described herethat is based on the use of a magnetic glassy carbon electrode modified with tetrahedral DNA with hollow structure, graphene oxide (GO) and gold nanocrystals. The use of a GO monolayer allows for greater carrying capacity and warrants a wider outer Helmholtz plane. Strong and stable ECL signals were achieved due to antigen-antibody interaction by using the ECL probe Ru(phen)32+. This immunosensor has a response that covers the 0.005 to 80nM p300 concentration range and has a 1 pM detection limit. It was exploited for the determination of p300 in HeLa cell lysate and (spiked) serum. Graphical abstract Schematic presentation of an ultrasensitive Faraday-cage electrochemiluminescence immunosensor toward the transcriptional co-activator p300 analysis is presented based on a graphene oxide monolayer and tetrahedral DNA-mediated signal amplification.

Ultrasensitive mushroom-like electrochemical immunosensor for probing the activity of histone acetyltransferase

A novel mushroom-like electrochemical immunoassay for the ultrasensitive detection of histone acetyltransferase activity (HAT p300) has been established on account of the new composite graphene oxide (GO) nanolayer. The immunoassay involves immobilization of substrate peptide onto Au electrode, acetylation in lysine of substrate peptide, and the interaction between acetyl group of lysine and acetyl-antibody (AbAc) of the GO nanolayer. The GO nanolayer comprises large amounts of methylene blue molecules (MB), giving rise to large signal amplification. Only in the presence of HAT p300, an obvious electrochemical signal appears and the peak linear current is proportion to the HAT p300 concentrations ranging from 0.01 to 150 nM with a detection limit of 0.0036 nM. The great enhancement on sensitivity of the proposed mushroom-like immunosensor derives from both the constructed Faraday cage and the extended outer Helmholtz plane (OHP). Further, the immunosensor with excellent sensitivity and selectivity can be applied for the HAT p300 activity detection in Hela cell lysates, serum and urine, hinting an improved and splendid analytical performance. Briefly, this stable, simple and ultrasensitive electrochemical immunoassay has considerable promise for further applications in the HATs-interrelated epigenetic studies and drug development.

Exploring the Distribution of Zn2+ in Inner and Outer Helmholtz Planes of the Electrical Double Layer of Soil based on Wien Effect

Core Ideas Wien effect measurements assess adsorbed cations distribution over the Helmholtz planes of the electrical double layer. Assessing cation distributions in the electrical double layer improves bioavailability predictions for plant nutrients and pollutant metals. Most of the zinc adsorption takes place in the inner Helmholtz plane layer and occurs via chemical interactions. The classical electrical double layer (EDL) theory explains the interaction between ions and charged soil colloidal particles, playing an importance role in the bioavailability and toxicity of ions in soils, which are of agricultural and environmental concern. A new approach based on extrapolating measurements of suspension Wien effect is suggested to determine the adsorbed ions distribution in the different compartments of the EDL. The new approach was applied to assess Zn2+ distribution in the EDL of Zn‐saturated soil colloids. The results showed that more than 84% of Zn2+ was adsorbed via chemical interactions and located in the inner Helmholtz plane layer. The remaining Zn2+ fraction was electrically adsorbed and distributed in the outer Helmholtz plane layer (0.3 to 2.1%) and in the Gouy–Chapman diffuse layer (7.4 to 15.0%). Independently, the results of linear combination fitting of extended x‐ray absorption fine structure (EXAFS) spectra indicated that the contents of outer‐sphere Zn in one paddy soil and the boggy soil were consistent with the proportions of Zn2+ electrostatically interacting with the soil colloids based on the extrapolation of the suspension Wien effect method, while the contents of outer‐sphere Zn in a second paddy soil, the yellow cinnamon soil, and the yellow brown soil was overestimated by the EXAFS method. The approach proposed in this paper to assess specific and electrostatic adsorption deepens our understanding of metal sorption processes in soils and reinforces the adequacy of the Grahame–Stern–Gouy–Chapman model of the EDL to describe the ion distribution in the solid‐water interface.

Flexibility of inactive electrokinetic layer at charged solid-liquid interface in response to bulk ion concentration

It has been a long-lasting debate on the position of zeta potential plane within aqueous solutions. This paper reports a flexible behavior of the inactive electrokinetic layer between the outer-Helmholtz plane and zeta potential plane, so-called buffer layer, in response to bulk ion concentration. This flexibility is not only corroborated by analyzing the measured zeta potentials with resulting electrical quad-layer model (inner- and outer-Helmholtz, buffer, and diffuse layers) but also consistent with thermodynamic analysis. The model indicates that the flexible buffer layer thickness saturates to its minimum for concentrated solutions. The predicted ionic conductance agrees well with the previous experimental measurements in nanochannels. The theory provides a deep physical insight into understanding, design, and manipulation of ion transport in nanosystems.

Double-layer effect on the kinetics of CO2 electroreduction at cathodes bearing Ag, Cu, and Ag/Cu nano-arrays electrodeposited by potentiostatic double-pulse

Abstract In-doped SnO2 (ITO) cathodes bearing Ag, Cu and bimetallic Ag/Cu nanoparticulate arrays (cathode systems ITO//Ag, ITO//Cu and ITO//Ag/Cu, respectively) were prepared by a potentiostatic double-pulse technique and employed for studying the multi-step charge-transfer kinetics of CO2 electrochemical reduction (CO2ER) in propylene carbonate solution. Our results demonstrated, on one hand, that the current exchange density of the rate-determining step (rds) for the CO2 electrochemical reduction (io,rds) depends, predominantly, on the values achieved by the outer-Helmholtz plane (OHP) potential (ΔψOHP,rds) on the three cathode systems here explored. Furthermore, these results showed that a large ΔψOHP,rds (−647 mV) promoted a large io,rds (1.09 × 10−2 A⋅ cm−2) for CO2 reduction at the cathode system ITO//Cu, whereas a small ΔψOHP,rds (−168 mV) produced a small io,rds (2.05 × 10−4 A⋅ cm−2) for CO2 reduction at the cathode system ITO//Ag. In contrast, intermediate values of ΔψOHP,rds and io,rds (−333 mV, 1.09 × 10−3 A⋅ cm−2) were found for CO2 reduction on the cathode system ITO//Ag/Cu, demonstrating that the individual electrocatalytic properties of Ag and Cu can be coupled in a bimetallic array to intentionally tune the CO2ER rate in nonaqueous solvents having low proton availability.

Understanding the apparent fractional charge of protons in the aqueous electrochemical double layer

A detailed atomic-scale description of the electrochemical interface is essential to the understanding of electrochemical energy transformations. In this work, we investigate the charge of solvated protons at the Pt(111) | H2O and Al(111) | H2O interfaces. Using semi-local density-functional theory as well as hybrid functionals and embedded correlated wavefunction methods as higher-level benchmarks, we show that the effective charge of a solvated proton in the electrochemical double layer or outer Helmholtz plane at all levels of theory is fractional, when the solvated proton and solvent band edges are aligned correctly with the Fermi level of the metal (EF). The observed fractional charge in the absence of frontier band misalignment arises from a significant overlap between the proton and the electron density from the metal surface, and results in an energetic difference between protons in bulk solution and those in the outer Helmholtz plane.

Potential-resolved Faraday cage-type electrochemiluminescence biosensor for simultaneous determination of miRNAs using functionalized g-C3N4 and metal organic framework nanosheets

Here, a novel Faraday cage-type electrochemiluminescence (ECL) biosensor was presented for simultaneous determination of miRNA-141 and miRNA-21 based on the potential-resolved strategy. In this work, capture units were prepared by immobilizing hairpin DNA1 (HP1) and hairpin DNA2 (HP2) on Fe3O4 @Au nanocomposites, while g-C3N4 @AuNPs nanocomposites labelled by signal DNA1 (sDNA1) and ruthenium-based metal organic framework (Ru-MOF) nanosheets labelled by signal DNA2 (sDNA2) were used as signal units. In this proposed biosensor, signal units g-C3N4 @AuNPs-sDNA1 and Ru-MOF-sDNA2 could exhibit two strong and stable ECL emissions at − 1.4 V and + 1.5 V respectively, which could be used as effective potential-resolved signal tags. Moreover, taking advantage of the proposed Faraday cage-type model, all electrochemiluminophores in the signal units could take part in electrode reactions, the signal units became part of the electrode surface and extended the outer Helmholtz plane (OHP) of the proposed electrode, and then the detection sensitivity was improved greatly. Accordingly, dual targets miRNA-141 and miRNA-21 could be detected within the linear range of 1 fM to 10 pM, with the detection limit of 0.3 fM. Meanwhile, the proposed miRNA assay exhibited high selectivity and sensitivity, even for practical analysis in human serum. So, this potential-resolved ECL biosensor is proved to be a feasible tool for dual targets detection of miRNAs in clinical diagnosis.

Ruthenium-based metal organic framework (Ru-MOF)-derived novel Faraday-cage electrochemiluminescence biosensor for ultrasensitive detection of miRNA-141

A novel Faraday-cage electrochemiluminescence (ECL) biosensor for the sensitive detection of miRNA-141 was constructed. The capture unit was prepared by immobilizing the capture DNA (cDNA) on the functionalized magnetic nanospheres nanoFe3O4@SiO2@Au, while the signal unit was ruthenium-based metal organic framework Ru-MOF labeled by signal DNA (sDNA). The recognition scaffold was as follows: the capture unit was immobilized onto the magnetic electrode surface; the target miRNA-141 was caught; the signal unit was further hybridized; the Faraday-cage biosensor structure was formed finally. In this case, the signal unit became part of the electrode surface, the outer Helmholtz plane (OHP) of the proposed electrode was extended, all electrochemiluminophores in the signal unit could take part in the electrode reaction, and thus then the detection sensitivity was greatly improved. Taking advantage of the proposed Faraday-cage cascade, the ECL intensity was found to increase with the logarithm of miRNA-141 concentration. The linear range was wide from 1 fM to 10 pM with a limit of detection 0.3 fM. The selectivity, stability, reproducibility, precision and application of this biosensor were validated. This proposed Faraday-cage ECL biosensor has a potential prospect for clinical miRNA detection.

Ultrasensitive Faraday cage-type electrochemiluminescence assay for femtomolar miRNA-141 via graphene oxide and hybridization chain reaction-assisted cascade amplification

In this study, a novel electrochemiluminescence (ECL) biosensor for sensitive detection of femtomolar miRNA-141 was constructed on the basis of Faraday cage-type strategy via graphene oxide (GO) and hybridization chain reaction (HCR)-assisted cascade amplification. A capture probe (CP) was immobilized on Fe3O4@SiO2@Au nanoparticles as capture unit, which could catch the miRNA-141, and the immobilization of the signal unit (Ru(phen)32+-HCR/GO) was allowed via nucleic acid hybridization. The prepared biosensor exhibited two advantages for signal amplification: firstly, GO could lap on the electrode surface directly, extending Outer Helmholtz Plane (OHP) of the sensor due to the large surface area and good electronic transport property; secondly, HCR-assisted cascade amplification was designed by anchoring all HCR products on the GO surface, then embedding Ru(phen)32+ as a signal readout pathway. All these signal molecules could take part in electrochemical reactions, thus further enhancing the ECL signal drastically. Therefore, the proposed sensor constructed by integrating HCR with Faraday cage-type strategy displayed an ultrasensitive detection platform for the miRNA-141 with a low detection limit of 0.03 fM. In addition, this proposed biosensor provides a universal platform for analysis of other microRNAs.

Effect of pH on the Activity of Platinum Group Metal-Free Catalysts in Oxygen Reduction Reaction

The impact of the electrolyte’s pH on the catalytic activity of platinum group metal-free (PGM-free) catalysts toward the oxygen reduction reaction (ORR) was studied. The results indicate that the ORR mechanism is determined by the affinity of protons and hydroxyls toward multiple functional groups present on the surface of the PGM-free catalyst. It was shown that the ORR is limited by the proton-coupled electron transfer at pH values below 10.5. At higher pH values (>10.5), the reaction occurs in the outer Helmholtz plane (OHP), favoring hydrogen peroxide production. Using a novel approach, the changes in the surface chemistry of PGM-free catalyst in a full pH range were studied by X-ray photoelectron spectroscopy (XPS). The variations in the surface concentration of nitrogen and carbon species are correlated with the electron transfer process and overall kinetics. This study establishes the critical role of the multitude of surface functional groups, presented as moieties or defects in the carbonaceous ...

Quantification of Zeta-Potential and Electrokinetic Surface Charge Density for Colloidal Silica Nanoparticles Dependent on Type and Concentration of the Counterion: Probing the Outer Helmholtz Plane

Electrokinetic data were measured for dilute aqueous dispersions of amorphous silica nanoparticles of various size via capillary electrophoresis with borate buffers containing either Li+, Na+, K+, or guanidinium as a counterion. Taking the mobility-dependent relaxation effect into account (modified analytic approximation developed by Ohshima), reliable values are obtained for the electrokinetic potential and the electrokinetic charge density dependent on the type of cation and the concentration of buffer. The reliability was confirmed by comparison of the results obtained for the nanoparticles with those values obtained for the planar-limiting case (fused-silica capillary inner wall/electrolyte interface). Regarding the inner part of the electrical double layer as a (mono)layer of unspecifically adsorbed counterions, we calculate (together with data gained by Brown et al. on the same type of nanoparticles via in situ photoelectron spectroscopy and potentiometric titration) the charge density at the outer ...

Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs

Summary Low-salinity waterflooding (LSW) is ineffective when reservoir rock is strongly water-wet or when crude oil is not asphaltenic. Success of LSW relies heavily on the ability of injected brine to alter surface chemistry of reservoir crude-oil brine/rock (COBR) interfaces. Implementation of LSW in carbonate reservoirs is especially challenging because of high reservoir-brine salinity and, more importantly, because of high reactivity of the rock minerals. Both features complicate understanding of the COBR surface chemistries pertinent to successful LSW. Here, we tackle the complex physicochemical processes in chemically active carbonates flooded with diluted brine that is saturated with atmospheric carbon dioxide (CO2) and possibly supplemented with additional ionic species, such as sulfates or phosphates. When waterflooding carbonate reservoirs, rock equilibrates with the injected brine over short distances. Injected-brine ion speciation is shifted substantially in the presence of reactive carbonate rock. Our new calculations demonstrate that rock-equilibrated aqueous pH is slightly alkaline quite independent of injected-brine pH. We establish, for the first time, that CO2 content of a carbonate reservoir, originating from CO2-rich crude oil and gas, plays a dominant role in setting aqueous pH and rock-surface speciation. A simple ion-complexing model predicts the calcite-surface charge as a function of composition of reservoir brine. The surface charge of calcite may be positive or negative, depending on speciation of reservoir brine in contact with the calcite. There is no single point of zero charge; all dissolved aqueous species are charge determining. Rock-equilibrated aqueous composition controls the calcite-surface ion-exchange behavior, not the injected-brine composition. At high ionic strength, the electrical double layer collapses and is no longer diffuse. All surface charges are located directly in the inner and outer Helmholtz planes. Our evaluation of calcite bulk and surface equilibria draws several important inferences about the proposed LSW oil-recovery mechanisms. Diffuse double-layer expansion (DLE) is impossible for brine ionic strength greater than 0.1 molar. Because of rapid rock/brine equilibration, the dissolution mechanism for releasing adhered oil is eliminated. Also, fines mobilization and concomitant oil release cannot occur because there are few loose fines and clays in a majority of carbonates. LSW cannot be a low-interfacial-tension alkaline flood because carbonate dissolution exhausts all injected base near the wellbore and lowers pH to that set by the rock and by formation CO2. In spite of diffuse double-layer collapse in carbonate reservoirs, surface ion-exchange oil release remains feasible, but unproved.

Controlling the Interfacial Environment in the Electrosynthesis of MnOx Nanostructures for High-Performance Oxygen Reduction/Evolution Electrocatalysis.

High-performance, nonprecious metal bifunctional electrocatalysts for the oxygen reduction and evolution reactions (ORR and OER, respectively) are of great importance for rechargeable metal-air batteries and regenerative fuel cells. A comprehensive study based on statistical design of experiments is presented to investigate and optimize the surfactant-assisted structure and the resultant bifunctional ORR/OER activity of anodically deposited manganese oxide (MnOx) catalysts. Three classes of surfactants are studied: anionic (sodium dodecyl sulfate, SDS), non-ionic (t-octylphenoxypolyethoxyethanol, Triton X-100), and cationic (cetyltrimethylammonium bromide, CTAB). The adsorption of surfactants has two main effects: increased deposition current density due to higher Mn2+ and Mn3+ concentrations at the outer Helmholtz plane (Frumkin effect on the electrodeposition kinetics) and templating of the MnOx nanostructure. CTAB produces MnOx with nanoneedle (1D) morphology, whereas nanospherical- and nanopetal-like morphologies are obtained with SDS and Triton, respectively. The bifunctional performance is assessed based on three criteria: OER/ORR onset potential window (defined at 2 and -2 mA cm-2) and separately the ORR and OER mass activities. The best compromise among these three criteria is obtained either with Triton X-100 deposited catalyst composed of MnOOH and Mn3O4 or SDS deposited catalyst containing a combination of α- and β-MnO2, MnOOH, and Mn3O4.The interaction effects among the deposition variables (surfactant type and concentration, anode potential, Mn2+ concentration, and temperature) reveal the optimal strategy for high-activity bifunctional MnOx catalyst synthesis. Mass activities for OER and ORR up to 49 A g-1 (at 1556 mVRHE) and -1.36 A g-1 (at 656 mVRHE) are obtained, respectively.

Promoter Effects of Alkali Metal Cations on the Electrochemical Reduction of Carbon Dioxide.

The electrochemical reduction of CO2 is known to be influenced by the identity of the alkali metal cation in the electrolyte; however, a satisfactory explanation for this phenomenon has not been developed. Here we present the results of experimental and theoretical studies aimed at elucidating the effects of electrolyte cation size on the intrinsic activity and selectivity of metal catalysts for the reduction of CO2. Experiments were conducted under conditions where the influence of electrolyte polarization is minimal in order to show that cation size affects the intrinsic rates of formation of certain reaction products, most notably for HCOO-, C2H4, and C2H5OH over Cu(100)- and Cu(111)-oriented thin films, and for CO and HCOO- over polycrystalline Ag and Sn. Interpretation of the findings for CO2 reduction was informed by studies of the reduction of glyoxal and CO, key intermediates along the reaction pathway to final products. Density functional theory calculations show that the alkali metal cations influence the distribution of products formed as a consequence of electrostatic interactions between solvated cations present at the outer Helmholtz plane and adsorbed species having large dipole moments. The observed trends in activity with cation size are attributed to an increase in the concentration of cations at the outer Helmholtz plane with increasing cation size.

Real\u2013time observation of interfacial ions during electrocrystallization

Understanding the electrocrystallization mechanisms of metal cations is of importance for many industrial and scientific fields. We have determined the transitional structures during underpotential deposition (upd) of various metal cations on Au(111) electrode using time–resolved surface X–ray diffraction and step–scan IR spectroscopy. At the initial stage of upd, a characteristic intensity transient appears in the time–resolved crystal truncation rod depending on metal cations. Metal cations with relatively high coordination energies of hydration water are deposited in two steps: first, the hydrated metal cations approached the surface and are metastably located at the outer Helmholtz plane, then they are deposited via the destruction of the hydration shell. However, Tl+ and Ag+, which have low hydration energy, are rapidly adsorbed on Au(111) electrode without any metastable states of dehydration. Therefore, the deposition rate is strongly related to the coordination energy of the hydration water. Metal cations strongly interacting with the counter coadsorbed anions such as Cu2+ in sulfuric acid causes the deposition rate to be slower because of the formation of complexes.

Potential-resolved “in-electrode” type electrochemiluminescence immunoassay based on functionalized g-C3N4 nanosheet and Ru-NH2 for simultaneous determination of dual targets

Here, a novel potential-resolved “in-electrode” type electrochemiluminescence (ECL) immunosensor was fabricated based on two different types of luminant Ru-NH2 and AuNPs/g-C3N4 to realize simultaneous detection of dual targets. In this strategy, anti-CA1251 and anti-SCCA1 were immobilized on bare gold electrode as capture probes, which could catch the two corresponding target CA125 and SCCA, and the immobilization of the signal tags was allowed via the interaction between antigen and antibody. In this process, (Ru&anti-CA1252)@GO and anti-SCCA2-AuNPs/g-C3N4 could exhibit two strong and stable ECL emissions at 1.25V and −1.3V respectively, which could be used as effective signal tags. Taking advantage of “in-electrode” type ECL immunosensor, all the electrochemiluminophores near the outer Helmholtz plane are “effective” in participating in the electrochemical reactions and emitting ECL signals. Therefore, the dual targets CA125 and SCCA could be detected within the linear ranges of 0.001–100U/mL and 0.001–100ng/mL, with detection limits of 0.4mU/mL and 0.33pg/mL, respectively. All these results demonstrated that the present potential-resolved “in-electrode” type electrochemiluminescence approach provided a promising analytical method for dual targets analysis with the advantages of simple analytical procedure, small sample volume and lower cost, which made the proposed method potential for clinical detection.

Solid Phase FePC Catalysts for Increased Stability of Oxygen Reduction Reaction Intermediates at the Cathode/Electrolyte Interface in Lithium Air Batteries

Solid-phase catalysts prepared by pyrolysis of Iron(II) phthalocyanine (FePC) embedded in high-surface carbons were evaluated for the catalysis of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Li+-conducting non-aqueous electrolytes. The ORR mechanism in high donor number (DN) dimethyl sulfoxide (DMSO)-based electrolytes is markedly different from that occurs in low DN acetonitrile(MeCN)-based electrolytes. The ORR is catalyzed by the reduced Fe(I) state of Fe(II)PC. Consequently, the Fe(II)PC/Fe(I)PC redox potential relative to O2 reduction potential in each electrolyte is important for ORR catalysis. In MeCN-based electrolytes, the Fe(I)PC catalyst is formed at a higher potential than the ORR potential. Hence the catalyzed ORR occurs at the inner-Helmholtz plane of the electrode, stabilizing the superoxide ion (O2−) formed by one-electron reduction of O2, as Fe(I)PC–O2−. Indeed, LiO2 was identified in the Raman spectra of cathodes from discharged Li-O2 battery cells. In DMSO-based electrolytes, the Fe(I)PC formation potential occurs below the ORR potential and accordingly LiO2 is more stable in its solvated state in the electrolyte solution as the Li(DMSO)n–O2− ion pair. This drives the ORR at the outer-Helmholtz plane of both catalyzed and uncatalyzed electrodes in DMSO-based electrolytes. The FePC embedded carbon electrode doubled the cycle life of Li-O2 cells utilizing low DN electrolytes.