Bifunctional Effects Research Articles

Catalysis of Methanol Oxidation on Bimetallic Ir/Pt(poly) Electrodes.

Oxidation of methanol was studied in alkaline solution on bimetallic Ir/Pt(poly) catalysts prepared by the spontaneous deposition of Ir on polycrystalline Pt. Nano-scale surface properties of Ir/Pt(poly) catalysts were revealed by ex situ Atomic Force Microscopy imaging. Modified electrodes were characterized in situ electrochemically by cyclic voltammetry in 0.1 M KOH. Investigations of the methanol oxidation in the same alkaline solution showed that Ir/Pt(poly) electrode obtained after 1 minute Ir deposition, which is equivalent to 80% Ir coverage, showed improved activity with respect to both constitutive metals. The observed synergism on the methanol oxidation activity was ascribed to both bifunctional and electronic effects that are induced by the presence of spontaneously deposited Ir. The origin of the synergism and the possible methanol oxidation pathways were discussed on the basis of the activities of the Ir/Pt(poly) electrodes for the oxidation of the most probable reaction intermediates, CO and formaldehyde, in the same alkaline solution.

Enhancement of Bifunctional Effect for LiNO3/glyme Electrolyte by Using Dual Solvent System for Li-O2 Batteries

Recently, LiNO3-based electrolytes using tetraglyme (G4) solvent (LiNO3/G4) have attracted increasing attention for non-aqueous rechargeable Li-air (O2) batteries (LAB) because of the bifunctional effect of NO3− anion as both redox mediator (RM) at air electrode and additive to form Li2O layer on the surface of Li metal negative electrode (NE), which suppresses Li dendrite growth and electrolyte decomposition. However, the dissociation degree of LiNO3 salt was quite low, which causes to low ionic conductivity and the above effects of NO3− would not work effectively in the electrolyte. In this study, we tried to apply dual solvent system to the LiNO3/G4 electrolyte. Namely, acetonitrile and dimethyl sulfoxide (DMSO) with relatively high dielectric constant and low viscosity were mixed with G4 solvent to increase the number per volume and mobility of Li+ and NO3− as carrier ions for reduction of the large overpotential during charge process and enhancement of the power density. The DMSO mixed electrolyte greatly reduced the large charge overpotential and relative stable operation for the LAB (Li ∣ O2) cells. Furthermore, the Li2O passivation layer formed by NO3− anion effectively suppressed the electrolyte decomposition at Li metal NE. These effects were enhanced especially at higher rate of discharge/charge operation.

Pd modified Ni nanowire as an efficient electro-catalyst for alcohol oxidation reaction

Developing highly efficient and economically viable electro-catalyst is very crucial research topic nowadays for achieving affordable direct alcohol fuel cells. Nano-structural architecture plays a crucial role in the catalytic activity. Herein we are reporting, a cost effective one-dimensional (1D) nano structured electro-catalyst for improved methanol oxidation reaction. Pd modified Ni nanowire catalyst towards methanol electro oxidation were prepared by a simple galvanic replacement reaction. Exclusive nano-wire morphology achieved through a wet chemical reduction method without employing any capping agents or surfactants. Pd modified Ni nano-wires exhibited a supreme catalytic activity and durability towards methanol electro-oxidation. The distinctive 1D morphology and strong metal support interaction (SMSI) between Pd and NiO along with the bifunctional effects of Pd and Ni attributed to the enhanced catalytic activity. The amount of precious Pd metal was reduced by 90 wt% with enhanced catalytic efficiency. Ethanol electro-oxidation study showed an improved catalytic activity with mass activity of 1479.79 mA/mg Pd.

Highly efficient methanol oxidation on durable PtxIr/MWCNT catalysts for direct methanol fuel cell applications

Development of highly active and durable Pt based anode materials with higher utilization of Pt is quite crucial towards the commercial viability of direct methanol fuel cells (DMFCs). Herein, multi-walled carbon nanotube supported PtxIr nanostructures (PtxIr/MWCNT) are successfully prepared by one-pot wet chemical reduction without any surfactants. The role of Ir content and its bi-functional mechanism on kinetics of methanol oxidation reaction (MOR) was studied. The MOR on PtxIr/MWCNT follows Langmuir-Hinshelwood mechanism by successive oxidative removal of CO. The co-existence of IrO2 plays a vital role as catalytic promotor. Amongst, Pt2Ir/MWCNT shows enhanced electrocatalytic activity (mass activity (MA), 933.3 mA/mgPt) and durability (13.8% loss of MA after 5000 potential cycles) thru the well-balanced electronic and bi-functional effects. This study implies that the optimized composition of Pt2Ir/MWCNT exhibits efficient methanol oxidation and could be a potential catalyst for direct methanol fuel cells.

Niobium increasing the electrocatalytic activity of palladium for alkaline direct ethanol fuel cell

Palladium and niobium in 1: 0, 3: 1, 2: 1 and 1: 1 carbon black electrocatalysts, respectively, were prepared by a chemical reduction method. The Pd1Nb1/C electrocatalyst showed a maximum power density of 27 mW cm−2 at 60 °C in the ethanol direct alkaline fuel cell (ADEFC) experiment. The residues of products formed in 60 °C of ADEFC operation were analyzed by FT-Raman and Pd1Nb1/C presented higher carbonate formation than the other products using the different electrocatalysts. In addition, the electrocatalysts of Pd1Nb1/C exhibited a more negative onset potential for both the CO stripping experiment and the ethanol oxidation reaction. Nb also increased the exchange current density by ethanol oxidation using the different electrocatalysts. We suggest that higher hydrophilicity, greater number of defects and oxygenated species promote bifunctional and electronic effects, improving the electrocatalytic activity of Pd. Therefore, Nb is an interesting co-catalyst for ADEFC Pd-based electrocatalysts.

Electrochemical Oxidation of Methanol and Ethanol at Rh@Pt and Ru@Pt Catalysts

The influence of the amount of Pt deposited onto Rh and Ru nanoparticles on the oxidation of methanol and ethanol has been compared in H2SO4(aq) at ambient temperature and in a proton exchange membrane (PEM) cell at 80 °C. In H2SO4(aq), Rh@Pt and Ru@Pt show similar enhancements in activities over Pt for both methanol and ethanol oxidation. However, differences in the optimum Pt coverage indicate that compression of the Pt lattice by Rh plays a dominate role, while ligand effects are more important for Ru@Pt. In the PEM cell, the Ru core enhanced activities significantly for both methanol and ethanol, while activities were suppressed by the Rh core. This may arise from dominance of ligand and/or bifunctional effects for the Ru@Pt catalyst at 80 °C. Data from the PEM cell showed that the stoichiometry for ethanol oxidation at Ru@Pt was higher than for Rh@Pt, indicating a higher selectivity for the complete oxidation to CO2.

Half-Sphere Shell Supported Pt Catalyst for Electrochemical Methanol Oxidation

Bi-functional effect, elevated mass transport and increased durability have been combined within one catalyst for electrochemical methanol oxidation reaction. It has niobium (Nb) doped titanium dioxides (TiO2) nanosized half-sphere shell (HSS) as the substrate material deposited with small amount of Pt nanoparticles. These specially designed HSS nanostructure has significantly increased surface areas which are suitable for Pt nanoparticles to be deposited onto them to form the catalyst denoted as Pt/Nb-TiO2 HSS. It exhibits a remarkably high methanol oxidation activity of 0.21 V vs RHE which is 0.05 V lower than HiSPEC10000 PtRu/C catalyst, due to the substrate’s strong metal support interactions effect, bi-functional effect and the special structure. These HSS nanostructures have also increased the methanol diffusion and mass transport within the anode to give a maximum power output of 0.0931 W of cathode polarization in miniature direct methanol fuel cell (DMFC). It also acts as protection shells, which minimises the dissolution of Pt metal nanoparticles to prevent its diffusion through the membrane.

The effect of support on Pd1Nb1 electrocatalysts for ethanol fuel cells

Pd1Nb1/C on different kinds of carbon black were prepared by a modified sol-gel method. The alkaline direct ethanol fuel cell (ADEFC) performance was performed first with the Pd1Nb1 electrocatalysts and then by varying the fuel concentration. In CV, Pd1Nb1/Printex 6L (50:50 wt%) exhibited 2.2 times higher mass activity than that of the Pd/C (Alfa Aesar); their mass activities were 1300 and 590 mA mgPd−1, respectively. The best performance for the ADEFC was obtained using Pd1Nb1/Printex 6L, which yielded a maximum power density and cell voltage of 28 mW cm−2 and 1.17 V, respectively. The Pd1Nb1/Printex 6L electrocatalyst exhibited a more negative onset potential for the CO stripping reaction. We suggest that the higher hydrophilicity (contact angle) and higher degree of disorder of Printex 6L (Raman) corroborates these results. In addition, both bifunctional and electronic effects operated on the electrocatalyst due to the presence of metal oxides and alloys of PdNb (XRD), respectively, in the synthesized electrocatalysts. Therefore, it was notable that the support has an essential role—as important as the cocatalyst—in the electrocatalytic performance.

Bifunctional effect of laser-induced nucleation-preferable microchannels and in situ formed LiF SEI in MXenes for stable lithium-metal batteries

A bifunctional effect of laser-induced aligned lithiophilic microchannels and in situ formed LiF-enriched SEI on lithium deposition is proposed by using fs laser on the MXene membrane. Stable Li plating/stripping is achieved at 20 mA cm−2 in an asymmetric cell.

A New Type of Strong Metal-Support Interaction Caused by Antimony Species

Interactions between metals and supports are of fundamental interest in heterogeneous catalysis, Noble metal particles supported on transition metal oxides (TMO) may undergo a so-called strong metal-support interaction via encapsulation. This perspective addresses catalytic properties of the metal catalysts in the SMSI state which can be explained on the basis of complementary studies. The electronic geometric and bifunctional effects originating from strong metal-support interactions (SMSI) that are responsible for the catalyst’s activity, selectivity, and stability are key factors that determine performance. A series of Pd-Sb supported on different metal oxide (i.e. SiO2, γ-Al2O3, TiO2, and ZrO2) were prepared by the impregnation method. The catalysts were characterized by N2 adsorption (BET-SA and pore size distribution), TEM (transmission electron microscope), TPR (temperature-programmed reduction), CO-chemisorption, the structural characterization of Pd (dispersity, surface area), interaction between Pd and Sb2O3 and also the influence of the nature of the support were investigated. SiO2 supported Pd catalyst exhibited the highest surface area (192.6 m2/g) and pore volume (0.542 cm3/g) compared to the other supported oxides catalysts. The electron micrographs of these catalysts showed a narrow size particle distribution of Pd, but with varying sizes which in the range from 1 to 10 nm, depending on the type of support used. The results show almost completely suppressed of CO chemisorption when the catalysts were subjected to high temperature reduction (HTR), this suppression was overcome by oxidation of a reduced Pd/MeOx catalysts followed by re-reduction in hydrogen at 453 K low temperature reduction (LTR), almost completely restored the normal chemisorptive properties of the catalysts, this suppression was attributed by SbOx species by a typical SMSI effect as known for other reducible supports such as TiO2, ZrO2, CeO2, and Nb2O5.

Enhanced Anti-melanoma Efficacy of a Pim-3-Targeting Bifunctional Small Hairpin RNA via Single-Stranded RNA-Mediated Activation of Plasmacytoid Dendritic Cells.

Melanoma is the most serious type of skin cancer. The immunosuppressive tumor microenvironment and aberrant expression of some proto-oncogenes are the main cause of melanoma development. We have constructed a single-stranded RNA (ssRNA)–Pim-3–small hairpin RNA (shRNA) dual-function vector, which activates the toll-like receptor (TLR)7 to stimulate the antitumor immune response through ssRNA fragments and simultaneously silences the proto-oncogene Pim-3 to intensify apoptosis of the tumor cells via shRNA. Here, we found that therapy with the ssRNA-Pim-3-shRNA dual-function vector not only promotes the apoptosis and inhibits the proliferation of B16F10 melanoma cells by inhibiting the expression of Pim-3 but also enhances the activation of CD8+ T cells and natural killer (NK) cells and simultaneously reduces the proportion of intratumoral regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs). Together, these features effectively inhibit the growth of melanoma. Intriguingly, the bifunctional therapeutic effect that reverses the tumor immunosuppressive microenvironment is dependent on the activation of plasmacytoid dendritic cells (pDCs) and the secretion of type I interferon (IFN). Our study suggests that ssRNA-Pim-3-shRNA dual-function therapy is expected to become a promising therapeutic strategy for melanoma and other solid tumors with immunosuppressive microenvironment.

Ru@Pt/C core-shell catalyst for SO2 electrocatalytic oxidation in electrochemical Bunsen reaction

Although SO2 is a highly toxic industrial pollutant, it can be used as a potential source of hydrogen and H2SO4 in the presence of water. This characteristic of SO2 is widely applied in desulfurization of industrial flue gas, hybrid-sulfur cycle and sulfur-iodine cycle. The main way to advance this technology is to develop a suitable electrocatalyst. So far researches on electrocatalysts for liquid phase oxidation of SO2 mainly focus on noble metal, which have excellent corrosion resistance and catalytic activity in acidic environment. In order to improve the performance of Pt-catalysts in SO2 electrocatalytic oxidation and reduce the use of Pt, a series of Ru@Pt/C core-shell catalysts with different Ru/Pt molar ratios were synthesized by microwave-assisted alcohol reduction. Reduction in the size of Pt shell is beneficial to increase the catalytic activity brought by the electronic effect. The bi-functional effect of Ru and Pt is more pronounced in the case of low Pt coverage. Ru only plays an auxiliary role and does not have the property of direct catalytic oxidation of SO2. The results showed that the optimal mass activity was achieved when Ru/Pt was 1:1. While when Ru/Pt was 3:1, the unit mass activity of Pt was the highest, which was 3.97 times of Pt/C.

Niobium Enhances Electrocatalytic Pd Activity in Alkaline Direct Glycerol Fuel Cells

AbstractPdxNby/C binary electrocatalysts supported on Printex 6 L carbon black were prepared by using an adapted chemical reduction method with sodium borohydride. The electrocatalysts were characterized by using SEM, TEM, XRD, EDS, ICP‐MS, water contact angle and Raman spectroscopy. The best performance for the alkaline direct glycerol fuel cell (ADGFC) was obtained by using Pd1Nb1/C, which yielded a maximum power density of 27 mW cm−2 at 70 °C. Residues of products formed from the glycerol oxidation were analyzed by using FT‐Raman and high‐performance liquid chromatography (HPLC). The Pd1Nb1/C electrocatalyst exhibited a more negative onset potential for the CO oxidation reaction and a higher conversion rate of glycerol to carbonate. We suggest that the higher hydrophilicity, higher degree of disorder, and bifunctional effects enhanced the electrocatalytic activity of Pd, as Nb facilitated the oxidation of adsorbed CO in Pd and increased the transfer rate of electron from Pd to carbon black support Therefore, Nb is a promising co‐catalyst for Pd‐based electrocatalysts for ADGFCs.

Simultaneous focusing and rotation of a bifunctional thermal metamaterial with constant anisotropic conductivity

We show that a constant anisotropic conductivity tensor can lead to two different functionalities at the same time, thermal focusing or a shielding effect together with a rotating effect. This design is of practical applications, as in energy harvesting and dissipation devices, and it is desirable to concentrate or to shield the thermal energy from a selected direction. We demonstrate that it is possible to control the way that heat flows within a medium to achieve the bifunctional effect solely through a suitable balance among the three material parameters of a homogeneous medium. It is seen that the diagonal entries of the conductivity tensor will govern the thermal focusing or shielding effect, while the off diagonal terms control the rotational effect. To fabricate the designed anisotropic material, we show that the material can be realized via the construction of a layered medium with two alternating isotropic constituents. Theoretical analysis and numerical calculations based on finite element calculations are presented to validate the performance of the design. The use of uniform conductivity to manage heat conduction brings exciting new advances for practical applications, with which one can manipulate thermal energy and offer unprecedented control of heat conduction at the same time.

A Kinetic Analysis of the CO Electro-Oxidation Reaction on Pt Bimetallics: Understanding the Interplay of Bifunctional and Electronic Effects

The CO electro-oxidation reaction has been one of the most thoroughly studied reaction mechanisms in electrocatalysis, mostly due to its role as a model reaction for the oxidation of larger organics like methanol and ethanol, each of which have important renewable energy applications in direct alcohol fuel cells. Bimetallics of Pt-M (where M is an oxophilic modifier such as Ru or Sn) have been shown extensively to have improved CO tolerance compared to pure Pt. The reason for this enhancement is often attributed to some combination of bifunctional (oxophilic metal provides OH to remove poisoning CO on Pt) and electronic (oxophilic metal weakens the CO binding strength on the Pt sites) effects. However, it has been difficult to determine the extent to which these different effects are operative in a given system. In this work, we perform a kinetic analysis of the CO electro-oxidation reaction in order to elucidate the roles of bifunctional and electronic effects. We look specifically at the classic Pt-Ru bimetallic system, and determine that the rates of bifunctional coupling are generally lower than the rates of coupling on Pt sites electronically modified by Ru. This indicates that, at least for the Pt-Ru system, the electronic effects that weaken CO binding on Pt are more operative than the bifunctional effect. This implies that that the prospects for bifunctional gains in general may be more limited than once thought, and that a more rational design parameter for bimetallic materials may be the electronic effects between the two components.

Insights into Compositional and Structural Effects of Bimetallic Hollow Mesoporous Nanospheres toward Ethanol Oxidation Electrocatalysis.

A one-pot soft-templating method is reported to fabricate nanosized bimetallic PdAg hollow mesoporous nanospheres (HMSs) for electrocatalytic ethanol oxidation reaction (EOR). The synthesis relies on the "dual-template" surfactant of dioctadecyldimethylammonium chloride that drives in situ growth of mesoporous frameworks on the surface of vesicles into the HMSs with radially opened mesochannels. The synthetic protocol is extendable to engineer elemental compositions and hierarchical nanostructures of PdAg nanoalloys. This system thus provides a direct yet solid platform to understand catalytic add-in synergies of PdAg HMSs toward electrochemical EOR. By evaluating compositional and structural features separately, bimetallic Pd65Ag35 HMSs display the highest EOR activity with a mass activity of 4.61 A mgPd-1. Mechanism studies indicate that synergistically electronic and bifunctional effects as well as structural advantages of Pd65Ag35 HMSs kinetically optimize the removal of poisoning carbonaceous intermediates and accelerate the diffusion processes (the rate-determining step), and thus promote the EOR performance accordingly.

Bifunctional Dye Molecule in All‐Inorganic CsPbIBr2 Perovskite Solar Cells with Efficiency Exceeding 10%

Inorganic lead halide perovskites are attracting increasing attention due to their much better thermal stability than the organic–inorganic hybrid perovskite materials. Thus, the low power conversion efficiency (PCE) is a key issue for the inorganic lead halide perovskite solar cells (PSCs). This is mainly due to their wider bandgap and larger energy loss (Eloss) in the devices. Herein, for solving this issue, a dye molecule‐assisted engineering using the dye of 5,15‐bis(2,6‐dioctoxyphenyl)‐10‐(bis(4‐hexylphenyl)‐amino‐20‐4‐carboxyphenylethynyl)porphyrinato]zinc(II) (YD2‐o‐C8) is demonstrated. Results indicate that this molecule has a bifunctional effect, not only as a co‐sensitization layer for CsPbIBr2 with broader absorption spectrum but also reduces the Eloss by interface passivation. Specifically, the light absorption range of the photoactive layer is broadened from 600 to nearly 680 nm. At the same time, the interfacial charge recombination is highly reduced. After optimizing, the champion PCE is enhanced from 7.02% to 10.13%, and record‐high open‐circuit voltage (VOC) of 1.37 V and short‐circuit currents (JSC) of 12.05 mA cm−2 are achieved. This study opens a simple and efficient way to improve the efficiency of inorganic PSCs.

Lamellar platinum–rhodium aerogels with superior electrocatalytic performance for both hydrogen oxidation and evolution reaction in alkaline environment

Hydrogen oxidation and evolution reactions (HOR and HER) in alkaline media are very kinetically sluggish, which becomes one of major barriers for the breakthrough of anion exchange membrane fuel cells. Thus, developing highly active and economically competitive HOR/HER electrocatalysts for alkaline electrolytes is of critical importance to realize future hydrogen economy. Herein, we for the first time report a new class of platinum-rhodium nanoalloy aerogel (PtRh NAA) via a facile and controllable strategy as exceptional HOR/HER electrocatalysts in alkaline environment. The as-synthesized PtRh NAA features unique lamellar architecture, hierarchical pores system and abundant low-coordinated sites. Benefiting from the combined structural and electronic effects as well as bifunctional synergetic effects, the lamellar PtRh NAA delivers an excellent HOR specific activity of 1.25 mA cm−2Pt+Rh, which is 5.5 times higher than that of the commercial Pt/C (0.225 mA cm−2Pt). Meanwhile, its HER overpotential at −10 mA cm−2 can be lowered to −55 mV, representing one of the highest HER activity so far. Moreover, no obvious deactivations are observed even after 5000 potential cycles for both HOR and HER, exhibiting excellent operation stability. These findings open a new field to design more advanced aerogels with high electrocatalytic performance.

Bifunctional resonance effects of classical electromagnetically induced transparency and Fano response using a terahertz metamaterial resonator.

A terahertz metamaterial resonator consisting of two rectangular strips embedded in a closed-ring resonator is designed and investigated in this paper that can simultaneously generate the classical electromagnetically induced transparency effect and two Fano resonance modes. The formation of the transparent window and the Fano dips can be attributed to the coupling of the localized resonance modes between the closed-ring resonator and the two embedded rectangular strips. The effect of embedded rectangular strip sizes on the transmitted performance is discussed, and it is found that the resonant performance of the transparent window and Fano effect depends mainly on the length of the rectangular strips in the longitudinal direction. Based on this, two different device applications related to the embedded rectangular strips are discussed. The metamaterial proposed here could open up new avenues toward the control of terahertz waves in many technology-related areas.

AuPd/C core–shell and alloy nanoparticles with enhanced catalytic activity toward the electro-oxidation of ethanol in alkaline media

Carbon-supported Pd, Au@Pd core–shell and Au1–xPdx-alloyed nanoparticles were prepared by a chemical reduction method and characterized by different experimental techniques, including X-ray powder diffraction, transmission electron microscopy, scanning-transmission electron microscopy using bright-field and high-angle annular dark field detectors and X-ray energy dispersive spectroscopy. The catalytic mass activity toward ethanol oxidation was assessed by cyclic voltammetry and chronoamperometry at room temperature. The measurements showed that the addition of Au enhances remarkably the electrocatalytic activity of the material, due to the bifunctional effect of Au1–xPdx/C alloys, and the synergetic effect on Au@Pd/C, resulting in a dissolution resistance of core–shell catalysts at potentials of 1.5 V versus reversible hydrogen electrode. In situ Fourier transform infrared spectroscopy measurements showed that the mechanism for ethanol oxidation depends on the electrocatalyst structure and morphology. Acetate was identified as the main product of ethanol electro-oxidation on the studied electrocatalysts. However, the presence of a core–shell structure on Au@Pd/C resulted in enhanced ethanol oxidation selectivity toward CO2. The improvement of activity is attributed to the interaction between Pd shell and Au core.