Nano-sized Ag Research Articles

A theoretical study on the size and morphology dependency of integral melting enthalpy and entropy of nanomaterials

Due to the fact that the melting process of nanomaterials is carried out with the continuous change of melting temperature, previous equations of differential melting enthalpy and entropy are unable to reflect their thermodynamic behaviors of actual melting process. On the basis of our previous work, theoretical calculations were conducted on the size and morphology dependent integral melting enthalpy and entropy of nano-sized Au, Ag and Sn and reasonable agreements with experimental results were observed. In addition, the integral melting enthalpy and entropy were also compared with the corresponding differential quantities. The differences between integral and differential melting enthalpy are mainly determined by the surface area and the interfacial tension, and the melting entropy by the surface area and the temperature coefficient of interfacial tension. The findings are able to deepen our understanding of the size and morphology dependent melting thermodynamics of nanomaterials and to further develop the thermodynamic theory of phase transitions of nanomaterials.

Improved visible-light activities of g-C3N4 nanosheets by co-modifying nano-sized SnO2 and Ag for CO2 reduction and 2,4-dichlorophenol degradation

Graphitic carbon nitride (g-C3N4) usually exhibits weak photocatalytic activity for CO2 reduction and pollutant degradation. Herein, the visible-light activities of g-C3N4 nanosheets are successfully improved by co-modifying SnO2 and Ag, with ∼10-time and ∼8-time improvement respectively for CO2 conversion and 2,4-dichlorophenol (2,4-DCP) degradation as compared to the pure g-C3N4. Mainly based on the transient-state surface photovoltage responses, transient-state photoluminescence spectra and electrochemical analyses, it is confirmed that the improved photoactivities are attributed to the synergistic effect of the prolonged charge lifetime and the provided catalytic function by modifying SnO2 and Ag, respectively. In addition, the synergistic effect is also feasible by replacing Ag with Au. This work will provide an effective strategy for designing high-activity g-C3N4 based photocatalysts.

Applications of silver nanocatalysts for low-temperature oxidation of carbon monoxide

Silver (Ag) is the best catalyst for many catalytic oxidation reactions. It is highly active for total oxidation of carbon monoxide (CO) at a lower temperature. The performance of silver catalysts depending upon their structure, surface active sites, and various Ag-O interactions. The other factors effects on the silver catalysts performances are synthesis method, treatment and reaction conditions and sizes of various Ag nanoparticles. The role of various silver species Ag0/Ag+ has examined and Ag0 as an active species originated to increases the catalytic activity at ambient conditions. The nano-sized Ag catalysts have concerned much interest because of their distinctive catalytic activity for different reactions. The silver catalysts highly dispersed over various support would be constructive for the best activity in CO oxidation at low temperatures. The particle size has certain effects on the catalytic performances of supported Ag catalysts. For active supports, the lattice oxygen presence in the support and electron transform among the silver‐oxygen and transition metals play a major role in the catalytic process. There are huge research articles are present on this matter, but very few numbers of review papers are available on this issue. So this is a gap fulfilled by this manuscript.

Effect of Thermally Evaporated Silver Nanoparticles on the Surface Morphology and Stability of Electrodeposited Lithium Metal Anode

Due to the extra-high capacity (3860 mAhg-1) and the lowest electrochemcial equilibrium potential (-3.040 VSHE), lithium metal has been considered as a promising candidate for high-energy lithium ion battery anode [1]. However, the undesired dendrite growth results in detrimental effects in the cell performance, such as cell short-circuit, low coulombic efficiency, and dead lithium, which have hampered widespread exploits of lithium metal-based batteries. Therefore, in recent year, numerous strategies to prevent or mitigate the problematic dendrite growth, including protective layers on Li metal surface, solid electrolytes, artificial solid electrolyte interphase (SEI) layer and so forth has been reported. Among them, one of the effective methods is to provide heterogeneous lithiophilic nucleation sites on the surface of current collectors as first suggested by Yan et al., [2]. They found that heterogeneous metal seeds, which have solubility of lithium in binary phase diagram, could induce selective deposition of lithium on its surface. Recently, Hou et al., reported lithiophilic Ag nanoparticles as nucleation sites by using electroless deposition for stable electrodeposition of lithium [3]. However, from a heterogeneous nucleation point of view, the morphology of electrodeposited lithium metal will be strongly affected by uniformity of nucleation seed layers, in other words, the more uniform distribution of nucleation seeds, the more stable morphology of lithium. In this study, we introduce a thermal evaporation method to deposit Ag nanoparticles as well-distributed nucleation sites. The Ag seeds with various evaporation thicknesses (1, 3 and 5 nm) were deposited on the commercial copper foils (thickness ≈ 25 um) to study the effect of evaporation thickness on the morphology of electrodeposited lithium metal. To electrodeposit lithium on Ag-seeded Cu foil and investigate the electrochemical properties of deposited Li metal electrodes, CR 2032-type coin cells were assembled in an Ar-filled glove box (CE: Li strip, WE: Ag-seeded Cu foil, and Celgard separator). We used 1M lithium bis(trifluoromethane)sulfonamide (LiTFSI) dissolved in 1,3-dioxolane/1,2-dimethoxyethane (DOL/DME, 1:1 by volume) as electrolyte without any additives. Figure 1 shows SEM surface morphologies of a pristine copper foil and Ag-seeded Cu foils with different evaporation thicknesses of Ag. After evaporation of Ag 1 nm on the pristine Cu foil (Fig. 1-(a)), it is showed that nano-sized Ag particles uniformly distributed on the surface of Cu foil (Fig. 1-(b)). In addition, from Fig. 1-(b) to Fig. 1-(d) it is clearly confirmed that the sizes of Ag particles increased with increasing evaporation thicknesses. Figure 2 shows the morphologies of electrodeposited lithium on Ag-seeded layers with different evaporation thickness. Figure 2-(a) shows SEM image of lithium metal deposited on a pristine Cu foil, which has well-known dendritic structure. In case of electrodeposited lithium on the Ag 1 nm-seeded Cu foil (Fig. 2-(b)), it also shows dendrites on its surface although heterogeneous nucleation sites are provided. However, the morphology of lithium on the Ag-3nm seeded Cu foil has distinct differences in shape and size of lithium deposits (Fig. 2-(c)). The width size of lithium deposits was smaller than those of Ag 1 nm-seeded Cu foil and pristine Cu foil, and they have interlacing vine-like structure. Further increased evaporation thickness of Ag nucleation layer to 5 nm leads to large morphological changes of electrodeposited lithium metal (Fig. 2-(d)). It shows highly dense structure with less pore and flat surface, meaning that dendrite-free lithium film was deposited. In summary, we used thermally evaporated Ag nanoparticles as heterogeneous nucleation sites to electroplate uniform lithium metal. From the results, it was concluded that through a facile thermal evaporation controllable and well-distributed heterogeneous nucleation metal seeds can be formed on the commercial Cu current collectors, leading to a dendrite-free deposition of lithium.

Synergistic Effect of Ag and ZnO Nanoparticles on Polypyrrole-Incorporated Epoxy/2pack Coatings and Their Corrosion Performances in Chloride Solutions

In this study, two formulae (F1 and F2) of epoxy/2pack coatings incorporated with polypyrrole (PPy)-conducting polymer were produced from bisphenol-A type of epoxy resin (DGEBA) with the addition of Ag and ZnO nanoparticles. The synergism effect of Ag and ZnO nanoparticles on the mechanical and corrosion resistance properties was reported. The curing agent 2,4,6-tris (dimethylaminomethyl) phenol (ARADUR 3282-BD) was used under optimized stoichiometry values. The nanoparticles ratio in different wt.% were first dispersed in solvent by the sonication process and then added to epoxy/PPy composition. All the coated steel panels were cured at room temperature in a controlled dust free environment for 7 days in order to obtain a hard and intact coating. The dispersion of nano-size ZnO and Ag pigments was investigated using scanning electron microscopy (SEM) and its composition through an energy dispersive X-ray (EDX) technique. Conventional techniques and nano-indentation were also performed to observe the effect of ZnO and Ag synergism content on the hardness and modulus of elasticity at nano scale. The corrosion behavior of the coated samples was investigated at room temperature in 3.5% NaCl solution using electrochemical impedance spectroscopy (EIS). The synergism effect of nanoparticles along with PPy resulted in an enhancement of mechanical and corrosion-resistant properties.

Electrospun Nanocomposite Ag–ZnO Nanofibrous Photoanode for Better Performance of Dye-Sensitized Solar Cells

Electrospun nanocomposite Ag–ZnO nanofibers have been prepared by an electrospinning technique and characterized using x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), and ultraviolet–visible (UV–Vis) spectroscopy. The prepared composite Ag–ZnO nanofibers were used as a photoanode for dye-sensitized solar cells (DSSCs) after pretreatment with TiCl4. Among the fabricated DSSCs, that using the nanocomposite Ag–ZnO nanofibers as the photoanode material showed higher power conversion efficiency of 5%, compared with the value of 3.19% when using pure ZnO nanofibers as the photoanode. The enhanced efficiency of this DSSC can be attributed to the surface plasmon resonance (SPR) phenomenon of the nanosize Ag particles on the surface of the ZnO nanofibers.

Enhanced photocatalysis, photoluminescence, and anti-bacterial activities of nanosize Ag: green synthesized via Rauvolfia tetraphylla (devil pepper)

In the current study, we have built up a novel, green approach technique for the synthesis of silver nanoparticles (Ag NPs) from Rauvolfia tetraphylla leaves extract. The synthesized nanoparticles were thoroughly characterized using different analytical techniques like X-ray diffraction, Fourier transform infrared spectroscopy, UV–Vis spectroscopy (UV–Vis), scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscope analysis. It is confirmed as a cubic phase with average particle size about 40 nm with a spherical shape. Further, the characterized material was inspected for the photocatalytic degradation of most common environmental pollutants (carcinogenic organic dyes) like Methylene blue (M.B), Rhodamine B (Rh. B) and Rose bengal (R.B) with degradation efficiency of 81, 55 and 80% respectively. In addition, it was examined by optical property (photoluminescence) with blue emission by the excitation at 370 to 400 nm, which is useful for blue LEDs (light emitting diode). Furthermore, it also shows the superior anti-bacterial activity against gram-positive bacterias such as Pseudomonas aeruginosa, Escherichia coli and Klebsiella aerogenes and gram-negative bacteria Staphylococcus aureus. Ag NPs synthesized using Rauvolfia tetraphylla leaf extract exhibited a good photocatalytic and antibacterial activity. Hence, it’s a first to report the synthesis of Ag NPs using natural reducing agent Rauvolfia tetraphylla leaf extract for Luminescence and Dye degradation applications.

Antibacterial and structural properties of mesoporous Ag doped calcium borosilicate glass-ceramics synthesized via a sol-gel route

Structural, electrical, bioactivity and antibacterial properties of mesoporous Ag doped calcium borosilicate glass-ceramics are reported. A simple sol-gel route was used to synthesize the mesoporous glass-ceramics. N2 adsorption–desorption studies reveal the mesoporous structure of the samples. The embedment of nano-sized Ag metallic particles in glass matrix was confirmed for Ag doped sample calcined at 600 °C by X-ray diffraction, UV–visible, and transmission electron microscopic analyses. Ac conductivity is used to study the electrical relaxation processes. Ag nanoparticle-embedded sample reveal nearly constant loss behaviour, whereas silver ions alone embedded sample show universal dielectric relaxation behaviour. Ag doped samples exhibit good antibacterial properties without compromising the bone-like apatite layer formation. The antibacterial effect against Gram negative bacteria is higher for Ag doped sample calcined at 600 °C which exhibits a dominant nearly constant dielectric loss feature.

Effects of annealing on microstructure and mechanical properties of rapidly solidified Cu-3 wt% Ag-1 wt% Zr

Cu-3 wt% Ag-1 wt% Zr alloy with excellent thermal stability is prepared by rapid solidification technique. The microstructure and mechanical properties as a function of annealing temperatures are investigated. The results indicate that the Cu-3 wt% Ag-1 wt% Zr alloy exhibits a homogeneous microstructure with uniformly distributed nano-sized Ag precipitates and micron-sized Cu4AgZr particles. Moreover, the average grain size is 7 µm without any plastic processing. When annealed at and below 700 °C, Ag will precipitate out only by a continuous way, but together with a discontinuous way at 800 °C. Furthermore, no significant coarsening of micron-sized Cu4AgZr particles and grains is observed even when exposed at 900 °C for 4 h, which results in the excellent mechanical properties of the alloy after annealing at high temperatures. However, the dissolution of micro-sized Cu4AgZr particles results in the abnormal grain growth when annealed at 925 °C, which leads to the decrease of hardness and strength.

Electrochemical migration of nano-sized Ag interconnects under deionized water and Cl−-containing electrolyte

With the trend of miniaturization of electronic products, the applications of fine-pitch interconnect have extended in high performance intelligent electronic devices. Thus, electrochemical migration (ECM) would be a concern in fine-pitch scale interconnects under the environment of temperature, humidity and biased voltage. This study investigated ECM behavior of fine-pitch nano-sized Ag interconnects prepared by screen-printing and sputtering methods in deionized water and Cl−-containing electrolytes. The ECM induced short-circuit was caused by dendrite formation between the cathode and anode. The ECM time to short circuit decreased with reducing pitch size for both samples but the sputtered samples exhibited better ECM resistance than printed ones due to continuous and consolidated structures of sputtered interconnects. In addition, different microstructure evolution of interconnects were found in different electrolytes and corresponding ion transport mechanism during ECM was discussed. When Cl−-containing electrolyte with concentration higher than 554 ppm was introduced, no more dendrite formation between the Ag interconnects was found and the ECM of Ag was suppressed. Instead, AgCl particles were formed at anode of interconnects and continued to grow accompanying with consumption of Ag interconnects, finally leading to open-circuit failure.

Microstructure characterization and thermoelectric properties of Sr0.9La0.1TiO3 ceramics with nano-sized Ag as additive

Sr0.9La0.1TiO3 thermoelectric ceramics with different contents of nano-sized Ag metal particles as additive were prepared by conventional solid state reaction method, and the influences of Ag adding content on the microstructure and thermoelectric properties were investigated. XRD characterization confirmed that the main phase was perovskite Sr0.9La0.1TiO3, along with a small amount of metal Ag phase. SEM images showed that all of the samples were dense, and the results of TEM indicated that the Ag particles accumulated at the grain boundaries to form a percolating network, contributing to increasing the electrical conductivity. Raman spectra of Sr0.9La0.1TiO3/xAg samples before and after annealing in Ar+C atmosphere showed a great difference, resulting from the creation of oxygen vacancies and changes in the TiO bond vibration and rotation mode. With increasing Ag adding content, the absolute value of Seebeck coefficient increased. Ag addition caused an increase in carrier concentration and acted as electrical connections between the grains, which improved the electrical conductivity and reduced the thermal conductivity to 1.4–3.4 W/m/K. Finally, the maximum ZT value of ZT883K = 0.30 was obtained for x = 20 wt% samples.

The Preparation of Graphene Oxide-Silver Nanocomposites: the Effect of Silver Loads on Gram-Positive and Gram-Negative Antibacterial Activities.

In this work, silver nanoparticles (Ag NPs) were decorated on thiol (–SH) grafted graphene oxide (GO) layers to investigate the antibacterial activities in Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Pseudomonas aeruginosa). The quasi-spherical, nano-sized Ag NPs were attached to the GO surface layers, as confirmed by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The average size of GO-Ag nanocomposites was significantly reduced (327 nm) from those of pristine GO (962 nm) while the average size of loaded Ag NPs was significantly smaller than the Ag NPs without GO. Various concentrations of AgNO3 solutions (0.1, 0.2, and 0.25 M) were loaded into GO nanosheets and resulted in the Ag contents of 31, 43, and 65%, respectively, with 1–2 nm sizes of Ag NPs anchored on the GO layers. These GO-Ag samples have negative surface charges but the GO-Ag 0.2 M sample (43% Ag) demonstrated the highest antibacterial efficiency. At 10 ppm load of GO-Ag suspension, only a GO-Ag 0.2 M sample yielded slight bacterial inhibition (5.79–7.82%). As the GO-Ag content was doubled to 20 ppm, the GO-Ag 0.2 M composite exhibited ~49% inhibition. When the GO-Ag 0.2 M composite level was raised to 100 ppm, almost 100% inhibition efficiencies were found on both Staphylococcus aureus (S.A.) and Pseudomonas aeruginosa (P.A.), which were significantly higher than using pristine GO (27% and 33% for S.A. and P.A.). The combined effect of GO and Ag nanoparticles demonstrate efficient antibacterial activities.

Detection of nanoparticles in Dutch surface waters

Nano-enabled consumer products are a likely source of nanoparticles in the environment and a number of studies have shown the release of nanoparticles from commercial products. Predicted environmental concentrations have been calculated but there is a need for real measurement data to validate these calculations. However, the detection of engineered nanoparticles in environmental matrices is challenging because of the low predicted environmental concentrations which may be in the ng/L range. In this study nanosized Ag, CeO2 and TiO2 have been measured in multiple surface water samples collected along the rivers Meuse and IJssel in the Netherlands using single-particle ICP-MS as measurement technique. Validation of the analytical method showed its capability to quantitatively determine nanoparticles at low concentrations. Concentration mass detection limits for Ag, CeO2 and TiO2 were 0.1ng/L, 0.05ng/L and 10ng/L respectively. Size detection limits for Ag, CeO2 and TiO2 were 14, 10 and 100nm. The results of the study confirm the presence of nano-sized Ag and CeO2 particles and micro-sized TiO2 particles in these surface waters. n-Ag was present in all samples in concentrations ranging from 0.3 to 2.5ng/L with an average concentration of 0.8ng/L and an average particle size of 15nm. n-CeO2 was found in all samples with concentrations ranging from 0.4 to 5.2ng/L with an average concentration of 2.7ng/L and an average particle size of 19nm. Finally, μ-TiO2 was found in all samples with a concentration ranging from 0.2 to 8.1μg/L with an average concentration of 3.1μg/L and an average particle size of 300nm. The particle sizes that were found are comparable with the particle sizes that are used in nanomaterial applications and consumer products. The nanoparticle concentrations confirm the predicted environmental concentrations values in water for all three nanoparticles.

Asymmetric ITO/Ag/ZTO and ZTO/Ag/ITO anodes prepared by roll-to-roll sputtering for flexible organic light-emitting diodes

We report highly transparent and flexible asymmetric InSnO (ITO)/Ag/ZnSnO (ZTO) and ZTO/Ag/ITO multilayer anodes prepared by roll-to-roll sputtering for use as electrodes in flexible organic light-emitting diodes (OLEDs). The electrical, optical, mechanical, and morphological properties of the asymmetric ITO/Ag/ZTO and ZTO/Ag/ITO films were comprehensively compared. Due to the presence of the nano-sized Ag interlayer, the roll-to-roll sputtered asymmetric electrodes exhibited very low sheet resistance and good mechanical flexibility. Despite the similar electrical and optical properties of the ITO/Ag/ZTO and ZTO/Ag/ITO multilayers, the performance of flexible OLEDs fabricated with ITO/Ag/ZTO was better than that of OLEDs fabricated with ZTO/Ag/ITO; this is because hole injection from the multilayer is closely related to the work function of the top oxide layer. The successful operation of flexible OLEDs on asymmetric ITO/Ag/ZTO anodes indicates that roll-to-roll sputtered ITO/Ag/ZTO multilayers are a viable alternative to brittle ITO films for use as highly flexible and transparent electrodes.

Structural properties of electrodeposited Cu-Ag alloys

Cu-Ag alloys are promising materials for electrical interconnections due to their combination of high conductivity and superior mechanical strength. In the present work, Cu-Ag alloys were electrodeposited from a cyanide-free electrolytic bath and different Ag percentages, ranging from 3 to 15 at.%, were obtained by controlling the deposition conditions. Electrochemical processes occurring during Cu-Ag deposition were investigated by means of cyclic voltammetry. Structural properties were examined by TEM and XRD and hardness was assessed by microindentation. TEM observations revealed the presence of nano-sized Ag precipitates at low Ag content, and the composition of the Cu-rich and Ag-rich phases in high-Ag alloys was deduced from XRD measurements. As-deposited alloys exhibited high hardness values and the contribution of solid-solution hardening was highlighted.

Infield superconducting properties of nano-sized Ag added Cu0.5Tl0.5Ba2Ca2Cu3O10−δ

Infield superconducting properties of {(Ag)x/CuTl-1223}; (x = 0, 0.5, 1.0, 2.0 and 4.0wt %) nanoparticles-superconductor composites were investigated under different applied magnetic field up to H = 8T. The increase in critical temperature {Tc(0)} and decrease in normal state resistivity (ρo) were observed with increasing contents of Ag nanoparticles in CuTl-1223 superconducting matrix. The value of Tc°nset (K) remained almost unaffected by applying external magnetic field, but a decreasing trend in Tc (0) was observed by increasing the value of external applied magnetic field. The transition region below Tc°nset (K) showed Arrhenius behavior due to thermally activated flow of magnetic vortices. Enhancement in flux flow activation energy (Uo) and suppression in transition width (ΔT) of CuTl-1223 phase with addition of Ag nanoparticles showed the improvement in flux pinning strength of superconductor.

Nanostructural Characterization of Low Resistance Joints Using Ag Pastes for GdBa2Cu3O7-x Coated Conductors

GdBa2Cu3O7-x coated conductors were splice jointed by a face-to-face manner using a paste containing nano-sized Ag particles under a pressure of about 50 MPa at 150 °C for 1 hr. The low electrical resistance of 6 nΩ at the joint was attained. Nanostructural characterizations of the starting Ag paste and the jointed region of the coated conductors were carried out using scanning electron microscopy and transmission electron microscopy. The size of the Ag particles in the starting pastes were confirmed to be a few tens of nanometers in diameter. The size of Ag particles became larger during the jointing process. Both the surfaces of the stabilizing Ag layers were partially bonded by the Ag particles. No oxides or other elements were detected in the region of the bonding parts.

Interaction of silver and gold nanoparticles in mammalian cancer: as real topical bullet for wound healing— A comparative study

The present study evaluates in vitro cytotoxic effects and the mode of interaction of biologically synthesized Ag and Au nanoparticles (NPs) using Brassica oleracea L. var. capitata f. rubra (BOL) against HT-1080 cancer cells and bacterial cells as well as their wound healing efficacy using a mouse model. UV-visible spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray analysis have ascertained the formation of nano-sized Ag and Au particles. Fourier transform infrared analysis has confirmed that polyphenol and amide groups in BOL act as capping as well as reducing agents. The free radical scavenging activity under in vitro conditions is found to be higher for the Ag NPs when compared to the Au NPs. Acridine orange-ethidium bromide dual staining and comet assay have indicated that the cytotoxic effects are mediated through nuclear morphological changes and DNA damage. The intracellular localization of Ag and Au NPs in HT-1080 cells and their subsequent effect on apoptosis and necrosis were analyzed by flow cytometry while the mode of interaction was established by scanning electron microscopy under field emission mode and by bio-transmission electron microscopy. These methods of analysis clearly revealed that the Ag and Au NPs have easily entered and accumulated into the cytosol and nucleus, resulting in activation of inflammatory and apoptosis pathways, which in turn cause damage in DNA. Further, mRNA and protein expression of caspase-3 and caspase-7, TNF-α, and NF-κB have provided sufficient clues for induction of intrinsic and extrinsic apoptosis and inflammatory pathways in Ag NP- and Au NP-treated cells. Evaluation of wound healing properties of Ag and Au NPs using a mouse model indicates rapid healing of wounds. In addition, no clear toxic effects and no nuclear abnormalities in peripheral blood cells are observed. Ag NPs appear to be a better anticancer therapeutic agent than Au NPs. Nonetheless, both Ag NPs and Au NPs show potential for promoting topical wound healing without any toxic effects. Graphical abstract Schematic representation of biological synthesis of Ag and Au NPs and its application on cancer and wound healing.

High oxygen reduction reaction activity of C-N/Ag hybrid composites for Zn-air battery

A novel nitrogen-doped biomass carbon/silver (C-N/Ag) composite has been synthesized by a simple method, wherein the precursor of soymilk simultaneously serves as carbon and nitrogen sources, reductant and substrate. The structure, morphology and valence state of samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectra. Results show the formation of nano-sized Ag homogenously disperses on the surface of mesoporous substrate, and the self-reduction role mainly attributes to the presence of unsaturated carbon bonding. Electrochemical properties were characterized by galvanostatic discharge and impedance spectra techniques. The sample prepared with 1 mmol AgNO3 solution, activated by 0.1 M KOH and annealed at 900 °C shows excellent oxygen reduction reaction activity and good electrochemical durability in alkaline medium. The onset potential, limiting diffusion current density and electron transfer number are 0.93 V, 6.26 mA cm−2 and 4.00, respectively, superior to those of 60 wt.% Ag/C and comparable to 20 wt.% Pt/C catalysts correspondingly. The discharge performance of Zn-air batteries is better than that of 20 wt% Pt/C.

Electrocatalytic CO2 Reduction on Nanosized Ag Dendrites Electrodeposited on Indium Doped SnO2 Electrodes Immersed in Aprotic Medium

Electrochemical reduction of CO2 by means of metallic nanostructures (i.e. Ag, Au, Cu), sp2 carbon derivatives (i.e. graphite oxide, graphene) and their combinations is considered as a promising pathway for aiding to decrease the effects of the global warming. However, the electrochemical reduction of CO2 contained in aqueous medium requires large overpotentials with a significant competition with the H2 evolution reaction, thus resulting in low faradaic efficiencies. On the other hand, reactivity of metallic nanostructures is strongly dependent from the size and the aspect ratio in nanoparticles and nanorods, respectively, as well as from the crystalline faces exposed to the electrolytic medium. In order to overcome this trouble, we studied the electrocatalytic CO2 electroreduction in aprotic medium by employing nanosized Ag dendrites, which were previously electrodeposited on In-doped SnO2 (ITO) electrodes by means of a double-pulse potential (DPP) technique (deposition conditions were defined by means of cyclic voltammetry (CV) technique). These experiments were carried out in a three-electrode cell containing aqueous 0.1M KNO3+1mM AgNO3. In this sense, the presence of dendritic nanostructures on the silver-modified ITO electrodes (ITO/Ag) was confirmed by scanning electron microscopy. CV results showed that the electrical charge associated to the Ag dissolution is clearly dependent from the growth time (duration ~ms) and independent from the nucleation time (duration ~sec). This result demonstrated that the Ag deposition is kinetically-controlled by one-electron transfer. Furthermore, CV results demonstrated that the thermodynamic potential for the Ag reduction E°Ag+|Ag was observed at -0.32 vs. Ag|AgCl (3M NaCl) during the first scan but, it becomes less cathodic at E°Ag+|Ag= -0.08 vs. Ag|AgCl (3M NaCl) during the successive scans; thus confirming that the dendritic shape of the Ag deposits is promoted immediately after some seeds of metallic atoms are confined on the ITO surface. Complementarily, electrochemical CO2 reduction in a three-electrode cell containing propylene carbonate + 0.1M Bu4NPF6 was confirmed on the as-prepared ITO/Ag electrodes by means of linear voltammetry (LV). In this way, two reduction peaks were localized at -0.3 and -0.5V vs. Ag|AgCl (0.01M AgNO3 + 0.1M Bu4NCl in MeCN), which can be associated to the semireactions 1 and 3, respectively. Electrochemical contribution from the ITO substrate was absent during the CO2 reduction reaction. (1) CO2 + e- → CO2 · - (slow)(2) CO2 + CO2 · - → (CO2)2 · - (3) (CO2)2 · - + e- → -OOC-COO· -