Gold Cathode Research Articles

Solution processed alkali-metal and alkaline-earth-metal compounds as the efficient electron injection layer in organic light-emitting diodes

To enable the use of high work-function metals as the cathode in organic light emitting diodes (OLEDs), different types of alkali-metal and alkaline-earth-metal based compounds are examined as the electron injection layer (EIL). All the studied compounds can improve the device performance for aluminum, gold, and silver cathodes. Potassium hydroxide (KOH) and potassium carbonate (K2CO3) are employed as EIL for the first time in OLEDs. The performance of the device with sodium hydroxide (NaOH)/silver cathode almost doubles the conventional barium/aluminum device’s efficiency. By examining the work-function of EIL-modified metals through Kelvin Probe, a general correlation between the device performance and cathode work-function is revealed. The image-charge effect is found to be a contributor to the reduction of the metal work-function.

All‐Carbon‐Electrode‐Based Endurable Flexible Perovskite Solar Cells

AbstractEndured, low‐cost, and high‐performance flexible perovskite solar cells (PSCs) featuring lightweight and mechanical flexibility have attracted tremendous attention for portable power source applications. However, flexible PSCs typically use expensive and fragile indium–tin oxide as transparent anode and high‐vacuum processed noble metal as cathode, resulting in dramatic performance degradation after continuous bending or thermal stress. Here, all‐carbon‐electrode‐based flexible PSCs are fabricated employing graphene as transparent anode and carbon nanotubes as cathode. All‐carbon‐electrode‐based flexible devices with and without spiro‐OMeTAD (2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene) hole conductor achieve power conversion efficiencies (PCEs) of 11.9% and 8.4%, respectively. The flexible carbon‐electrode‐based solar cells demonstrate superior robustness against mechanical deformation in comparison with their counterparts fabricated on flexible indium–tin oxide substrates. Moreover, all carbon‐electrode‐based flexible PSCs also show significantly enhanced stability compared to the flexible devices with gold and silver cathodes under continuous light soaking or 60 °C thermal stress in air, retaining over 90% of their original PCEs after 1000 h. The promising durability and stability highlight that flexible PSCs are fully compatible with carbon materials and pave the way toward the realization of rollable and low‐cost flexible perovskite photovoltaic devices.

The beam coherence simulation of 1-dimensional nano-scale photocathode under high power laser irradiation

1-dimensional (1D) nano-scale photocathode with back-illumination is a promising technology for producing highly coherent electrons which may allow us to realize 4-dimensional space-time analysis of atomic structures. By simulation, we evaluated the coherence of electrons generated from gold cathode by taking into account laser-induced heating effect. The laser irradiation conditions for different cathode thickness were derived from 1D-Two Temperature Model (TTM). We also investigated the coherence of the beam by beam tracking simulation including conventional extracting electric field. Our result indicates that the beam coherence at the acceleration electron where the sample to measure is located is not sensitive to the initial beam coherence on the cathode surface.

NMR Study of the Reductive Decomposition of [BMIm][NTf2 ] at Gold Electrodes and Indirect Electrochemical Conversion of CO2.

Potential controlled electrolyses of [BMIm][NTf2 ] ionic liquid were performed at a gold cathode under nitrogen atmosphere. The structures of the major conversion products of the BMIm+ cation were elucidated on the basis of 1D and 2D nuclear magnetic resonance (NMR) analyses and gas chromatography (GC) analysis of the volatile compounds. Recombination of the imidazol-2-yl radicals, generated at the electrode by single electron transfer, leads to neutral diastereomeric dimers in equal proportions, with a faradaic efficiency of 80 %, while disproportionation of these radicals and/or reaction with hydrogen atoms adsorbed at the electrode generates a neutral monomer with 20 % faradaic efficiency. Both pathways also yield the N-heterocyclic carbene imidazolin-2-ylidene, which is involved in fast proton exchange with the parent BMIm+ cation. The reductive decomposition products of the BMIm+ cation are no longer detected if the pre-electrolysed sample is reacted with CO2 , which undergoes an indirect reduction and generates the carboxylate adduct.

Effect of Enhanced Ion Transfer in Process-Induced Electrochemical Corrosion on Surface Morphology and Tribological Properties

The presence of both gold and polycrystalline silicon in a given microelectromechanical systems (MEMS) device can profoundly impact surface properties through an electrochemical reaction occurring during micro-fabrication processing. Tests show a mechanistically similar increase in surface roughness with an increased ratio of gold (cathode) to silicon (anode) surface area, and with prolonged galvanic reaction time. This is attributed to increased ion transfer due to either increased electrochemical current or increased reaction time. Furthermore, microdevices with greater process-induced surface damage were found to have lower contact adhesion. The increased surface roughness decreases the intermolecular forces that contribute to adhesion due to increased average asperity separations. Results are interpreted in light of the principle galvanic corrosion mechanism and the effect on the primary nanoscale intermolecular forces. [2016-0172]

Plasmon resonance-enhanced photocathode by light trapping in periodic concentric circular nanocavities on gold surface

In this paper, we report the design and characterization of a new surface plasmon polariton (SPP) nanocavity on the surface of gold film to enhance the efficiency of metallic photocathodes. The plasmonic surface increases absorption over normal metals, and due to the localization of fields, this results in complete elimination of reflection from the metal surface. Here, a periodic array of concentric circular nanocavities on the gold surface was designed to exhibit multiband plasmonic resonances at 600nm, 710nm and 800nm. We theoretically report on the enhancement of relative quantum efficiency from gold cathode up to 70 times compared to a flat surface, by use of nanostructured plasmonic surfaces to trap, localize, and enhance optical fields. The proposed structure have a number of useful practical features such as broadband or multiband absorption and broad angular bandwidth. The symmetry in the proposed structure eliminates any polarization dependence within the structure.

In Situ Infrared Spectroscopy Study of PYR14TFSI Ionic Liquid Stability for Li–O2 Battery

In situ infrared subtractive normalized Fourier transform infrared spectroscopy (SNIFTIRS) experiments were performed simultaneously with the electrochemical experiments relevant to Li-air battery operation on gold cathodes in ionic liquid PYR14TFSI based electrolyte. Ionic liquid anion was found to be stable, while the cation PYR14+ was found to decompose in studied conditions. In oxygen saturated LiTFSI containing PYR14TFSI electrolyte carbon dioxide and water were formed at potential 4.3 V either with or without previous oxygen electro-reduction reaction. However in deoxygenated LiTFSI contacting ionic liquid no formation of CO2 or water was observed, suggesting oxygen presence to be crucial in carbon dioxide production.

Hierarchical nanoporosity enhanced reversible capacity of bicontinuous nanoporous metal based Li-O2 battery.

High-energy-density rechargeable Li-O2 batteries are one of few candidates that can meet the demands of electric drive vehicles and other high-energy applications because of the ultra-high theoretical specific energy. However, the practical realization of the high rechargeable capacity is usually limited by the conflicted requirements for porous cathodes in high porosity to store the solid reaction products Li2O2 and large accessible surface area for easy formation and decomposition of Li2O2. Here we designed a hierarchical and bicontinuous nanoporous structure by introducing secondary nanopores into the ligaments of coarsened nanoporous gold by two-step dealloying. The hierarchical and bicontinuous nanoporous gold cathode provides high porosity, large accessible surface area and sufficient mass transport path for high capacity and long cycling lifetime of Li-O2 batteries.

Catalytic Activity of Au/MWNTs Nanocomposite on Oxygen Reduction Reaction and Application on Li-O2 Batteries

Li-air batteries have recently captured scientific interest for the much higher theoretical energy density than conventional Li ion batteries. However, some major problems still limit the practical realization of Li-O2 batteries, including the reversible capacity (and energy density), side reactions occurred on cycling, low energy efficiency due to the hysteresis between charge and discharge (up to 2V). The use of proper electrocatalysts on porous cathodes is regarded as the key to reduce the overpotential of the charge process, including precious metals [1-3], metal oxides [4-6] and MOFs [7]. Bruce et al. [8] demonstrated that porous gold cathodes in dimethyl sulfoxide (DMSO) electrolyte were able to maintain the high ratio of Li2O2 in the charge products, resulted in only a 5 % capacity loss after 100 charge cycles. However, the high cost of gold limits the application of porous gold in Li-O2batteries. In this work, a facile method was used to synthesize the Au/MWNT nanocomposite was used instead of porous gold cathode in the DMSO electrolyte with 0.1 M LiClO4. The MWNTs were degassed before the immersion in H2O2, resulted in hydrophilic surface with –OH and –COOH groups. Then, the reaction between 1.5 mM HAuCl4 and 1.5 mM tetrakis(hydroxylmethyl)phosphornium chloride alkaline solution was allowed to take place in the presence of the treated MWNTs, led to Au/MWNT nanocomposite (d = 2.1 nm) with the Au loading of 29 wt. %. The catalytic activity of the nanocomposite on oxygen reduction reaction (ORR) was investigated by cyclic voltammetry and RRDE experiments, which demonstrated that the nanocatalyst exhibits a stronger ORR catalytic performance than those reduced by ethylene glycol, and the MWNTs substrate is also better than Vulcan XC72R. Moreover, the number of electron for the ORR on the nanocatalyst was determined as 2.4, corresponding to the reduction product of H2O2, which also suggests that Li2O2 is probably the major ORR product in the Li-O2battery if the nanocatalyst is used. A nickel foam cathode sprayed with Au/MWNTs catalyst (1.6 mg/cm2) was assembled in a Swagelok cell, together with a Li disk and a Nylon 66 filter membrane. The Li-O2 battery was cycled between the final discharge potential of 2.2 V and charge potential of 4.0 V vs. Li/Li+ in 0.1 M LiClO4DMSO electrolyte, from which the specific capacity for the Au/MWNT nanocatalyst was determined as 1293 mAh/g, larger than the porous gold reported by Bruce et al. [8], indicating that the nanogold catalysts possess much stronger catalytic property than bulk gold, and is expected to be used in Li-air batteries at low cost. ACKNOWLEDGEMENTS The work was supported by the National Natural Science Foundation of China (Grant No. 21163004) and Guangxi Natural Science Foundation (Grant No. 2013GXNSFAA 019029). REFERENCES Y. C. Lu, et al. Electrochem. Solid-State Lett., 13 (6): A69 (2010).H. D. Lim, et al. Science, 6: 3570 ( 2013).X. J. Li, et al. ACS Appl. Mater. Interf., 6, 12409 (2014).C. W. Sun, et al. J. Mater. Chem. A, 2, 7188(2014).Z. L. Jian, Angew. Chem. Int. Ed., 126, 452 (2014).J. J. Xu, et al. Angew. Chem. Int. Ed., 125, 3979 (2013).D. F. Wu, et al. Adv. Mater. 26, 3258(2014).Z. Q. Peng, Science, 337, 563(2012).

Diagnosing x-ray power and energy of tungsten wire array z-pinch with a flat spectral response x-ray diode.

Fast z-pinch is a very efficient way of converting electromagnetic energy to radiation. With an 8-10 MA current on primary test stand facility, about 1 MJ electromagnetic energy is delivered to vacuum chamber, which heats z-pinch plasma to radiate soft x-ray. To develop a pulsed high power x-ray source, we studied the applicability of diagnosing x-ray power from tungsten wire array z-pinch with a flat spectral response x-ray diode (FSR-XRD). The detector was originally developed to diagnose radiation of a hohlraum in SG-III prototype laser facility. It utilized a gold cathode XRD and a specially configured compound gold filter to yield a nearly flat spectral response in photon energy range of 0.1-4 keV. In practice, it was critical to avoid surface contamination of gold cathode. It is illustrated that an exposure of an XRD to multiple shots caused a significant change of response. Thus, in diagnosing x-ray power and energy, we used each XRD in only one shot after calibration. In a shot serial, output of FSR-XRD was compared with output of a nickel bolometer. In these shots, the outputs agreed with each other within their uncertainties which were about 12% for FSR-XRD and about 15% for bolometer. Moreover, the ratios between the FSR-XRD and the bolometer among different shots were explored. In 8 shots, the standard deviation of the ratio was 6%. It is comparable to XRD response change of 7%.

Aqueous and Nonaqueous Sodium-Air Cells with Nanoporous Gold Cathode

ABSTRACT Two types of sodium-air cells, i.e., nonaqueous and mixed aqueous-nonaqueous (abbreviated as ‘aqueous’) cells, have been compared to elucidate factors limiting performances of nonaqueous air cells and how the aqueous electrolyte is effective to reliving these limitation. The two cells have the same configuration consisting of a nanoporous gold (NPG) air electrode and a ceramic separator of fast sodium ion conductor, NASICON. Only the selection of catholyte, either alkyl carbonate-based nonaqueous solution of NaClO4 or aqueous solution of NaOH, is different. All performances are demonstrated to be better for the aqueous one. Lower overpotential of aqueous cell leads to better round-trip efficiency. A large resistance relevant to oxygen reduction reaction in the nonaqueous cell is relieved by changing the catholyte to the aqueous electrolyte, affording higher rate capability and power density. The aqueous electrolyte is also effective to remove the limitation of the discharge capacity defined by the volumetric amount of air electrode, as has been claimed in previous studies on aqueous Na-air cells. Furthermore, the aqueous cell is demonstrated to be robust and less sensitive and to atmosphere. The NPG electrode works reversibly in the half-cell reaction of the aqueous cell, while an electrodeposition of metallic Na on the anode during charging requires an improvement.

Sulfide Modification of Dye-Sensitized Solar Cell Gold Cathodes for Use with Cobalt Polypyridyl Mediators

[Co(bpy)3]2+/3+-type complexes have emerged as promising alternatives to the traditional I–/I3– electrolyte used in dye-sensitized solar cells (DSSCs). One of the many advantages these complexes exhibit is their ability to undergo reduction on Au cathodes rather than the more expensive Pt. However, in our experience irreproducibility of fabricated Au cathodes has been a longstanding issue due to variations in charge-transfer resistance (RCT) for the Co2+/3+ couple. These variations manifest themselves as poor fill factors in the current–voltage measurements. In an effort to increase electronic coupling between the Co complex and the Au surface (and thereby reduce RCT), a simple surface modification with sulfide ion has been developed. XPS measurements indicate the modification is stable after exposure to mediator solution. Cyclic voltammetry shows a drastic increase in reversibility for the Co2+/3+ electrochemistry, especially under typical DSSC mediator conditions. A commensurate enhancement in the fill factor is observed in subsequent J–V measurements. The results provide a straightforward method of yielding more reproducible Au cathodes to be used in combination with [Co(bpy)3]2+/3+-type mediators.

A Rotating Ring Disk Electrode Study of the Oxygen Reduction Reaction in Lithium Containing Dimethyl Sulfoxide Electrolyte: Role of Superoxide

We have employed the rotating ring disk electrode (RRDE) technique to study the oxygen reduction reaction (ORR) on gold and glassy carbon cathodes in dimethyl sulfoxide (DMSO) electrolytes containing lithium salts. At the gold ring electrode at 3.0 V vs. Li/Li+ (0.1 M LiPF6) soluble superoxide radical anion undergoes oxidation to O2 under convective-diffusion conditions. For both glassy carbon and gold cathodes, typical oxygen reduction current-potential curves are sensitive to rotation speed and undergo a maximum and further electrode passivation by formation of Li2O2 while the Au ring electrode currents follow the same peak shape with detection of soluble superoxide at the ring downstream in the electrolyte solution. Unlike the behavior in acetonitrile-lithium solutions, LiO2 is more stable in DMSO and can diffuse out in solution and be detected at the ring electrode. While in cyclic voltammetry both time and potential effects are convoluted, we have carried out RRDE chrono-amperometry experiments at the disk electrode with detection of superoxide at the Au ring so that thus potential and time effects were clearly separated. The superoxide oxidation ring currents exhibit a maximum at 2.2 V due to the interplay of O2− formation by one-electron O2 reduction, Li2O2 disproportionation and two-electron O2 reduction.

In situ observation of electrolytic H2 evolution adjacent to gold cathodes

The early stages of gas evolution during electrolytic hydrogen production on Au electrodes are characterized by in situ transmission electron microscopy. The results demonstrate that reaction product molecules initially dissolve into solution and then nucleate near, but not on, the electrodes. The gas subsequently wets the electrodes and its successive evolution is governed by triple phase boundary line motion.

Infrared Spectroscopy Studies on Stability of Dimethyl Sulfoxide for Application in a Li–Air Battery

In situ infrared subtractive normalized Fourier transform infrared spectroscopy (SNIFTIRS) experiments performed simultaneously with the electroreduction of oxygen on gold and platinum cathodes in LiPF6 dimethyl sulfoxide (DMSO) electrolyte have shown that the solvent is stable with respect to nucleophilic attack by the electrogenerated superoxide radical anion. However, long-term experiments with KO2 solutions in DMSO have shown a slow formation of dimethyl sulfone. Evidence of dimethyl sulfone formation by anodic oxidation of DMSO above 4.2 V (Li/Li+) in the presence of trace water has been obtained on gold. On platinum, this unwanted reaction in the charging cycle of a lithium–air battery takes place at lower potentials, i.e., 3.5 V.

A stable cathode for the aprotic Li–O2 battery

Rechargeable lithium-air (O2) batteries are receiving intense interest because their high theoretical specific energy exceeds that of lithium-ion batteries. If the Li-O2 battery is ever to succeed, highly reversible formation/decomposition of Li2O2 must take place at the cathode on cycling. However, carbon, used ubiquitously as the basis of the cathode, decomposes during Li2O2 oxidation on charge and actively promotes electrolyte decomposition on cycling. Replacing carbon with a nanoporous gold cathode, when in contact with a dimethyl sulphoxide-based electrolyte, does seem to demonstrate better stability. However, nanoporous gold is not a suitable cathode; its high mass destroys the key advantage of Li-O2 over Li ion (specific energy), it is too expensive and too difficult to fabricate. Identifying a suitable cathode material for the Li-O2 cell is one of the greatest challenges at present. Here we show that a TiC-based cathode reduces greatly side reactions (arising from the electrolyte and electrode degradation) compared with carbon and exhibits better reversible formation/decomposition of Li2O2 even than nanoporous gold (>98% capacity retention after 100 cycles, compared with 95% for nanoporous gold); it is also four times lighter, of lower cost and easier to fabricate. The stability may originate from the presence of TiO2 (along with some TiOC) on the surface of TiC. In contrast to carbon or nanoporous gold, TiC seems to represent a more viable, stable, cathode for aprotic Li-O2 cells.

Selective Conversion of CO2 to CO with High Efficiency Using an Inexpensive Bismuth-Based Electrocatalyst

The wide-scale implementation of solar and other renewable sources of electricity requires improved means for energy storage. An intriguing strategy in this regard is the reduction of CO2 to CO, which generates an energy-rich commodity chemical that can be coupled to liquid fuel production. In this work, we report an inexpensive bismuth-carbon monoxide evolving catalyst (Bi-CMEC) that can be formed upon cathodic polarization of an inert glassy carbon electrode in acidic solutions containing Bi(3+) ions. This catalyst can be used in conjunction with ionic liquids to effect the electrocatalytic conversion of CO2 to CO with appreciable current density at overpotentials below 0.2 V. Bi-CMEC is selective for production of CO, operating with a Faradaic efficiency of approximately 95%. When taken together, these correspond to a high-energy efficiency for CO production, on par with that which has historically only been observed using expensive silver and gold cathodes.

Surface electron–hydronium ion-pair bound to silver and gold cathodes: A density functional theoretical study of photocatalytic hydrogen evolution reaction

Noble metal catalysts, such as silver and gold, play a significant role in photocatalytic water splitting to hydrogen for their high efficiency and environmentally-friendly nature. In this paper, a surface electron–hydronium ion-pair (EHIP) was proposed as an intermediate for photocatalytic hydrogen evolution reaction (HER) on silver and gold cathodes based on density functional theory (DFT) calculations. The EHIP is in the configuration of H3O+(H2O)ne−, where the hydronium H3O+ and the electron is separated by water layers. The electron bound in the EHIP can first be excited under light irradiation, subsequently inducing a structural relaxation into a hydrated hydrogen atom. Eventually, two hydrogen atoms recombine into a hydrogen molecule in the thin layer close to the electrode surface, e.g. at the outer Helmholtz plane (OHP). Additionally, Raman spectra of the interfacial EHIP species are calculated, which is in support of the presence of EHIP intermediates in the process of photocatalytic HER on silver and gold cathodes.

A Reversible and Higher-Rate Li-O 2 Battery

The rechargeable nonaqueous lithium-air (Li-O(2)) battery is receiving a great deal of interest because, theoretically, its specific energy far exceeds the best that can be achieved with lithium-ion cells. Operation of the rechargeable Li-O(2) battery depends critically on repeated and highly reversible formation/decomposition of lithium peroxide (Li(2)O(2)) at the cathode upon cycling. Here, we show that this process is possible with the use of a dimethyl sulfoxide electrolyte and a porous gold electrode (95% capacity retention from cycles 1 to 100), whereas previously only partial Li(2)O(2) formation/decomposition and limited cycling could occur. Furthermore, we present data indicating that the kinetics of Li(2)O(2) oxidation on charge is approximately 10 times faster than on carbon electrodes.

On the use of radioisotopes to study the possible synthesis by magnetron sputtering of bimetallic nanoparticles

An approach using physical vapor deposition technology to produce nanoparticles (NPs) containing radioactive atoms and the methodology to transfer them in pure water is investigated. NPs are synthesized by magnetron sputtering at high pressure and radioactive atoms are loaded on magnetron cathodes prior to sputtering. The technique was tested for gold cathode loaded with 57/58 Co and 195/196 Au. Linked to biological vector molecules, the nanoparticles can be used to enhance diagnostic sensitivity in medical imaging or to treat cancer. Sizes and morphologies of the NPs were analyzed by electron microscopy, UV-Visible spectroscopy and atomic absorption spectroscopy. Results show well dispersed NPs with sizes varying between 5 and 10 nm. Activities of these NPs were measured with a CAPINTEC well counter and a High Purity Germanium detector system. Centrifugation analyses also demonstrate that the choice of the activated metal which can be alloyed with NPs plays an important role in the synthesis. This was confirmed by the Au–Co phase diagram that shows that cobalt cannot be included efficiently in the gold NPs conversely to gold.