Showing papers on "Platinum published in 2012"
TL;DR: The first synthesis of NiMo nitride nanosheets on a carbon support (NiMoNx/C) is reported, and the high HER electrocatalytic activity of the resulting NiMoNX/C catalyst with low overpotential and small Tafel slope is demonstrated.
Abstract: Hydrogen production through splitting of water has attracted great scientific interest because of its relevance to renewable energy storage and its potential for providing energy without the emission of carbon dioxide. Electrocatalytic systems for H2 generation typically incorporate noble metals such as Pt in the catalysts because of their low overpotential and fast kinetics for driving the hydrogen evolution reaction (HER). However, the high costs and limited world-wide supply of these noble metals make their application in viable commercial processes unattractive. Several non-noble metal materials, such as transition-metal chalcogenides, carbides, and complexes as well as metal alloys have been widely investigated recently, and characterized as catalysts and supports for application in the evolution of hydrogen. Nitrides of early transition-metals have been shown to have excellent catalytic activities in a variety of reactions. One of the primary interests in the applications of nitrides in these reactions was to use them in conjunction with low-cost alternative metals to replace group VIII noble metals. For example, the function of molybdenum nitride as a catalyst for hydrocarbon hydrogenolysis resembles that of platinum. The catalytic and electronic properties of transition-metal nitrides are governed by their bulk and surface structure and stoichiometry. While there is some information concerning the effect of the bulk composition on the catalytic properties of this material, there is currently little known about the effects of the surface nanostructure. Nickel and nickel–molybdenum are known electrocatalysts for hydrogen production in alkaline electrolytes, and in the bulk form they exhibited exchange current densities between 10 6 and 10 4 Acm , compared to 10 3 Acm 2 for Pt. Jaksic et al. postulated a hypo-hyper-d-electronic interactive effect between Ni and Mo that yields the synergism for the HER. Owing to their poor corrosion stability, few studies in acidic media have been reported.With the objective of exploiting the decrease in the overpotential by carrying out the HER in acidic media, we have developed a low-cost, stable, and active molybdenum-nitride-based electrocatalyst for the HER. Guided by the “volcano plot” in which the activity for the evolution of hydrogen as a function of the M H bond strength exhibits an ascending branch followed by a descending branch, peaking at Pt, we designed a material on the molecular scale combining nickel, which binds H weakly, with molybdenum, which binds H strongly. Here we report the first synthesis of NiMo nitride nanosheets on a carbon support (NiMoNx/C), and demonstrate the high HER electrocatalytic activity of the resulting NiMoNx/C catalyst with low overpotential and small Tafel slope. The NiMoNx/C catalyst was synthesized by reduction of a carbon-supported ammonium molybdate [(NH4)6Mo7O24·4H2O] and nickel nitrate (Ni(NO3)2·4H2O) mixture in a tubular oven in H2 at 400 8C, and subsequent reaction with NH3 at 700 8C. During this process, the (NH4)6Mo7O24 and Ni(NO3)2 precursors were reduced to NiMo metal particles by H2, and then they were mildly transformed to NiMoNx nanosheets by reaction with ammonia. The atomic ratio of Ni/Mo was 1/4.7 determined by energy dispersive X-ray spectroscopy (EDX) on the NiMoNx/ C sample. The transmission electron microscopy (TEM) images, as shown in Figure 1a, display NiMo particles that are mainly spherical. The high-resolution TEM image, as shown in the inset of Figure 1a, corroborated the presence of an amorphous 3 to 5 nm Ni/Mo oxide layer (see Figure S4 in the Supporting Information for resolved image), whereas NiMoNx is characterized by thin, flat, and flaky stacks composed of nanosheets with high radial-axial ratios (Figure 1b and Figure S5 in the Supporting Information for a magnified image). Figure 1c shows that some of the nanosheets lay flat on the graphite carbon (as indicated by the black arrows), and some have folded edges that show different layers of NiMoNx sheets (white arrows). The thickness of the sheets ranged from 4 to 15 nm. The average stacking number of sheets measured from Figure 1b is about [*] Dr. W.-F. Chen, Dr. K. Sasaki, Dr. J. T. Muckerman, Dr. R. R. Adzic Chemistry Department, Brookhaven National Laboratory Upton, NY 11973 (USA) E-mail: ksasaki@bnl.gov
1,135 citations
TL;DR: In this paper, the authors provide an overview of the fundamentals underlying the reduction of oxygen on platinum and its alloys, and report the ORR activity of Pt5La for the first time, which shows a 3.5-to 4.5fold improvement in activity over Pt in the range 0.9 to 0.87 V.
Abstract: The high cost of low temperature fuel cells is to a large part dictated by the high loading of Pt required to catalyse the oxygen reduction reaction (ORR). Arguably the most viable route to decrease the Pt loading, and to hence commercialise these devices, is to improve the ORR activity of Pt by alloying it with other metals. In this perspective paper we provide an overview of the fundamentals underlying the reduction of oxygen on platinum and its alloys. We also report the ORR activity of Pt5La for the first time, which shows a 3.5- to 4.5-fold improvement in activity over Pt in the range 0.9 to 0.87 V, respectively. We employ angle resolved X-ray photoelectron spectroscopy and density functional theory calculations to understand the activity of Pt5La.
995 citations
TL;DR: The resultant POMC with a small amount of P doping is demonstrated as a metal-free electrode with excellent electrocatalytic activity for oxygen reduction reaction (ORR), coupled with much enhanced stability and alcohol tolerance compared to those of platinum via four-electron pathway in alkaline medium.
Abstract: Phosphorus-doped ordered mesoporous carbons (POMCs) with different lengths were synthesized using a metal-free nanocasting method of SBA-15 mesoporous silica with different sizes as template and triphenylphosphine and phenol as phosphorus and carbon sources, respectively. The resultant POMC with a small amount of P doping is demonstrated as a metal-free electrode with excellent electrocatalytic activity for oxygen reduction reaction (ORR), coupled with much enhanced stability and alcohol tolerance compared to those of platinum via four-electron pathway in alkaline medium. Interestingly, the POMC with short channel length is found to have superior electrochemical performances compared to those with longer sizes.
834 citations
TL;DR: It is found that NG supported with 5 wt % Fe nanoparticles displayed an excellent methanol crossover effect and high current density in an alkaline solution, and Fe-incorporated NG showed almost four-electron transfer processes and superior stability in both alkaline and acidic solutions, which outperformed the platinum and NG-based catalysts.
Abstract: The high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has hindered the practical application of fuel cells. Thanks to its unique chemical and structural properties, nitrogen-doped graphene (NG) is among the most promising metal-free catalysts for replacing platinum. In this work, we have developed a cost-effective synthesis of NG by using cyanamide as a nitrogen source and graphene oxide as a precursor, which led to high and controllable nitrogen contents (4.0% to 12.0%) after pyrolysis. NG thermally treated at 900 °C shows a stable methanol crossover effect, high current density (6.67 mA cm–2), and durability (∼87% after 10 000 cycles) when catalyzing ORR in alkaline solution. Further, iron (Fe) nanoparticles could be incorporated into NG with the aid of Fe(III) chloride in the synthetic process. This allows one to examine the influence of non-noble metals on the electrocatalytic performance. Remarkably, we found that NG supported with 5 wt % Fe nanoparticles displayed ...
558 citations
TL;DR: Researchers have revealed electronic interactions between platinum and ceria that go well beyond known effects and lead to excellent catalytic activity.
Abstract: Oxide materials typically used as supports for the active metal nanoparticles of heterogeneous catalysts are known to influence catalytic activity through strong metal–support interactions. Researchers have now revealed electronic interactions between platinum and ceria that go well beyond known effects and lead to excellent catalytic activity.
545 citations
TL;DR: It is found that WC and W(2)C are both excellent cathode support materials for ML Pt, exhibiting HER activities that are comparable to bulk Pt while displaying stable HER activity during chronopotentiometric HER measurements.
Abstract: This work explores the opportunity to substantially reduce the cost of hydrogen evolution reaction (HER) catalysts by supporting monolayer (ML) amounts of precious metals on transition metal carbide substrates. The metal component includes platinum (Pt), palladium (Pd), and gold (Au); the low-cost carbide substrate includes tungsten carbides (WC and W2C) and molybdenum carbide (Mo2C). As a platform for these studies, single-phase carbide thin films with well-characterized surfaces have been synthesized, allowing for a direct comparison of the intrinsic HER activity of bare and Pt-modified carbide surfaces. It is found that WC and W2C are both excellent cathode support materials for ML Pt, exhibiting HER activities that are comparable to bulk Pt while displaying stable HER activity during chronopotentiometric HER measurements. The findings of excellent stability and HER activity of the ML Pt–WC and Pt–W2C surfaces may be explained by the similar bulk electronic properties of tungsten carbides to Pt, as is ...
452 citations
TL;DR: In this paper, the particle size, composition, and shape effect for the monodisperse and homogeneous platinum alloy electrocatalysts that have been synthesized by organic solution approaches are studied.
Abstract: In the past decade, significant advancement has been made in the development of electrocatalysts for energy conversion and storage. Among various approaches, alloying Pt with 3d transition metals has shown great potential in tailoring the atomic and electronic structures of catalytically active materials toward improved catalytic performance. Here, we provide a brief overview of the recent advancements in the design and synthesis of electrocatalysts for the oxygen reduction reaction. Our focus is placed on the systematic studies of particle size, composition, and shape effect for the monodisperse and homogeneous platinum alloy electrocatalysts that have been synthesized by organic solution approaches.
393 citations
TL;DR: In this paper, a MnCo2O4-graphene hybrid material was used as the cathode catalyst for Li-O2 batteries with a non-aqueous electrolyte.
Abstract: We employ a MnCo2O4–graphene hybrid material as the cathode catalyst for Li–O2 batteries with a non-aqueous electrolyte. The hybrid is synthesized by direct nucleation and growth of MnCo2O4 nanoparticles on reduced graphene oxide, which controls the morphology, size and distribution of the oxide nanoparticles and renders strong covalent coupling between the oxide nanoparticles and the electrically conducting graphene substrate. The inherited excellent catalytic activity of the hybrid leads to lower overpotentials and longer cycle lives of Li–O2 cells than other catalysts including noble metals such as platinum. We also study the relationships between the charging–discharging performance of Li–O2 cells and the oxygen reduction and oxygen evolution activity of catalysts in both aqueous and non-aqueous solutions.
383 citations
TL;DR: The use of N,N-dimethylformamide (DMF) as both solvent and reductant in the solvothermal synthesis of Pt alloy nanoparticles (NPs), with a particular focus on Pt-Ni alloys, is reported on.
Abstract: Platinum alloy nanoparticles show great promise as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes. We report here on the use of N,N-dimethylformamide (DMF) as both solvent and reductant in the solvothermal synthesis of Pt alloy nanoparticles (NPs), with a particular focus on Pt–Ni alloys. Well-faceted alloy nanocrystals were generated with this method, including predominantly cubic and cuboctahedral nanocrystals of Pt3Ni, and octahedral and truncated octahedral nanocrystals of PtNi. X-ray diffraction (XRD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), coupled with energy dispersive spectroscopy (EDS), were used to characterize crystallite morphology and composition. ORR activities of the alloy nanoparticles were measured with a rotating disk electrode (RDE) technique. While some Pt3Ni alloy nanoparticle catalysts showed specific activities greater than 1000 μA/cm2Pt, alloy catalysts prepared with a nominal composition of PtNi disp...
370 citations
TL;DR: It is demonstrated that adding a small amount of gold to palladium and forming highly uniform nanoparticle cores make the platinum monolayer electrocatalyst significantly tolerant and very promising for the automotive application of fuel cells.
Abstract: Platinum is used as a cathode in fuel cells but undergoes dissolution during potential changes, hindering commercial application in electric vehicles. Sasaki et al. report a new class of stable electrocatalysts that consist of platinum monolayers on palladium–gold alloy nanoparticles.
TL;DR: The highly sensitive and time-resolving dissolution monitoring enables the distinction between anodic and cathodic dissolution processes during potential transient and chronoamperometric experiments, and the precise quantification of the amount of dissolved Pt.
Abstract: Platinum stability: Dissolution of Pt, which is one major degradation mechanism in, for example, hydrogen/air fuel cells, was monitored under potentiodynamic and potentiostatic conditions. The highly sensitive and time-resolving dissolution monitoring enables the distinction between anodic and cathodic dissolution processes during potential transient and chronoamperometric experiments, and the precise quantification of the amount of dissolved Pt.
TL;DR: In this paper, a comparison of ORR reaction mechanisms between acidic and alkaline conditions is elucidated, and the primary advantage of performing ORR in alkaline media is found to be the enhanced activation of the peroxide intermediate on the active site that enables the complete fourelectron transfer.
Abstract: Complex electrochemical reactions such as Oxygen Reduction Reaction (ORR) involving multi-electron transfer is an electrocatalytic inner-sphere electron transfer process that exhibit strong dependence on the nature of the electrode surface. This criterion (along with required stability in acidic electrolytes) has largely limited ORR catalysts to the platinum-based surfaces. New evidence in alkaline media, discussed here, throws light on the involvement of surface-independent outer-sphere electron transfer component in the overall electrocatalytic process. This surface non-specificity gives rise to the possibility of using a wide-range of non-noble metal surfaces as electrode materials for ORR in alkaline media. However, this outer-sphere process predominantly leads only to peroxide intermediate as the final product. The importance of promoting the electrocatalytic inner-sphere electron transfer by facilitation of direct adsorption of molecular oxygen on the active site is emphasized by using pyrolyzed metal porphyrins as electrocatalysts. A comparison of ORR reaction mechanisms between acidic and alkaline conditions is elucidated here. The primary advantage of performing ORR in alkaline media is found to be the enhanced activation of the peroxide intermediate on the active site that enables the complete four-electron transfer. ORR reaction schemes involving both outer- and inner-sphere electron transfer mechanisms are proposed.
TL;DR: In this article, a reduced graphene oxide (RGO)-supported platinum (Pt) catalyst was prepared by simple ethylene glycol (EG) reduction and used for hydrogenation of nitroarenes.
TL;DR: In this article, a new inorganic solid state electrocatalyst for the hydrogen evolution reaction (HER) was reported, which is a highly crystalline layered ternary sulfide copper-molybdenum-sulfide (Cu2MoS4) catalyst.
Abstract: A new inorganic solid state electrocatalyst for the hydrogen evolution reaction (HER) is reported. Highly crystalline layered ternary sulfide copper-molybdenum-sulfide (Cu2MoS4) was prepared by a simple precipitation method from CuI and [MoS4]2− precursors. In aqueous solution and over a wide pH range (pH 0 to 7), this Cu2MoS4 showed very good catalytic activity for HER with an overvoltage requirement of only ca. 135 mV and an apparent exchange current density of 0.040 mA cm−2 (Tafel slope of ca. 95 mV per decade was found irrespective of the pH value). This Cu2MoS4 catalyst was found to be stable during electrocatalytic hydrogen generation. Therefore, it represents an attractive alternative to platinum.
TL;DR: In this article, the effect of cathode platinum loading on oxygen transport resistance in a fuel cell electrode was determined by measuring limiting current in fuel cells over a wide range of platinum loadings (0.03 to 0.40 mgPt/cm2).
Abstract: The effect of cathode platinum loading on oxygen transport resistance in a fuel cell electrode was determined by measuring limiting current in fuel cells over a wide range of platinum loadings (0.03 to 0.40 mgPt/cm2). The measurements show that the electrode oxygen transport resistance is inversely proportional to platinum loading or, equivalently, platinum surface area, and is mathematically similar to a 12 s/cm resistive film coating the active platinum sites. At low platinum loading this anomalous resistance significantly reduces the partial pressure of oxygen at the platinum surface and seriously degrades fuel cell performance at high power conditions. The magnitude of this film-like resistance is equivalent to ~35 nm of bulk-like ionomer but only 4–10 nm, assuming uniform coating, is present in the electrode. Alternatively, 380 nm diameter agglomerates with 20 nm of ionomer coating their external surface would create the same resistance, but such agglomerates are not apparent in SEM micrographs. As a result, the source of this resistance remains unknown, and further investigations are required to understand and mitigate it.
TL;DR: The potential at which the hydrogen peroxide reduction and oxidation reactions are equally likely to occur reflects the intrinsic affinity of the platinum surface for oxygenated species, hereby defined as the "ORR-corrected mixed potential" (c-MP).
Abstract: Understanding the hydrogen peroxide electrochemistry on platinum can provide information about the oxygen reduction reaction mechanism, whether H2O2 participates as an intermediate or not. The H2O2 oxidation and reduction reaction on polycrystalline platinum is a diffusion-limited reaction in 0.1 M HClO4. The applied potential determines the Pt surface state, which is then decisive for the direction of the reaction: when H2O2 interacts with reduced surface sites it decomposes producing adsorbed OH species; when it interacts with oxidized Pt sites then H2O2 is oxidized to O2 by reducing the surface. Electronic structure calculations indicate that the activation energies of both processes are low at room temperature. The H2O2 reduction and oxidation reactions can therefore be utilized for monitoring the potential-dependent oxidation of the platinum surface. In particular, the potential at which the hydrogen peroxide reduction and oxidation reactions are equally likely to occur reflects the intrinsic affinity of the platinum surface for oxygenated species. This potential can be experimentally determined as the crossing-point of linear potential sweeps in the positive direction for different rotation rates, hereby defined as the “ORR-corrected mixed potential” (c-MP).
TL;DR: With activities comparable to the commercial Pt catalyst, enhanced poisoning tolerance and lower cost, Pt-Zn and Pt(3)Zn NCs are a promising new family of catalysts for direct methanol fuel cells.
Abstract: We report the first synthesis of highly monodisperse Pt(3)Zn nanocrystals (NCs). Shape-controlled synthesis generates cubic and spherical Pt-Zn NCs. Reaction temperature is the key to incorporate Zn into Pt, even in the absence of a strong reducing agent. The Pt-Zn NCs are active toward methanol oxidation, with the spherical NCs exhibiting higher activity than the cubic NCs. The Pt-Zn alloy phase can be transformed into the Pt(3)Zn intermetallic phase, upon annealing. The intermetallic Pt(3)Zn shows better performance than the alloy phase Pt-Zn. Besides the activity toward methanol oxidation, Pt-Zn NCs show excellent poisoning tolerance. With activities comparable to the commercial Pt catalyst, enhanced poisoning tolerance and lower cost, Pt-Zn and Pt(3)Zn NCs are a promising new family of catalysts for direct methanol fuel cells.
TL;DR: In this paper, a carbon supported platinum electrode in a bismuth saturated solution at a carefully chosen potential is capable of oxidizing glycerol to dihydroxyacetone with 100% selectivity.
Abstract: A carbon supported platinum electrode in a bismuth saturated solution at a carefully chosen potential is capable of oxidizing glycerol to dihydroxyacetone with 100% selectivity. In the absence of bismuth, the primary alcohol oxidation is dominant. Using a combination of online HPLC and in situ FTIR, it is shown that Bi blocks the pathway for primary oxidation but also provides a specific Pt–Bi surface site poised for secondary alcohol oxidation.
TL;DR: In this article, a novel synthesis procedure is devised to obtain nitrogen-doping in hydrogen-exfoliated graphene (HEG) sheets, which is used as catalyst support for dispersing platinum and platinum-cobalt alloy nanoparticles.
Abstract: A novel synthesis procedure is devised to obtain nitrogen-doping in hydrogen-exfoliated graphene (HEG) sheets. An anionic polyelectrolyte–conducting polymer duo is used to form a uniform coating of the polymer over graphene sheets. Pyrolysis of graphene coated with polypyrrole, a nitrogen-containing polymer, in an inert environment leads to the incorporation of nitrogen atoms in the graphene network with simultaneous removal of the polymer. These nitrogen-doped graphene (N-HEG) sheets are used as catalyst support for dispersing platinum and platinum–cobalt alloy nanoparticles synthesized by the modified-polyol reduction method, yielding a uniform dispersion of the catalyst nanoparticles. Compared to commercial Pt/C electrocatalyst, Pt–Co/N-HEG cathode electrocatalyst exhibits four times higher power density in proton exchange membrane fuel cells, which is attributed to the excellent dispersion of Pt–Co alloy nanoparticles on the N-HEG support, the alloying effect of Pt–Co, and the high electrocatalytic activity of the N-HEG support. A stability study shows that Pt/N-HEG and Pt–Co/N-HEG cathode electrocatalysts are highly stable in acidic media. The study shows two promising electrocatalysts for proton exchange membrane fuel cells, which on the basis of performance and stability present the possibility of replacing contemporary electrocatalysts.
TL;DR: A natural self-regeneration step for urea derived graphitic carbon nitride with platinum nanoparticles is found by simply opening the system to air in the dark under ambient conditions, following its solar-driven hydrogen production.
TL;DR: In this article, the authors used sum frequency generation (SFG) to explore the mechanism of the enhancement of selectivity of a 1-ethyl-3methylimidazolium tetrafluoroborate (EMIM-BF4)-coated silver catalyst.
Abstract: Lowering the overpotential for the electrochemical conversion of CO2 to useful products is one of the grand challenges in the Department Of Energy report, “Catalysis for Energy”. In a previous paper, we showed that CO2 conversion occurs at low overpotential on a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4)-coated silver catalyst in an aqueous solution of EMIM-BF4. One of the surprises in the previous paper was that the selectivity to CO was better than 96% on silver, compared with ∼80% in the absence of ionic liquid. In this article, we use sum frequency generation (SFG) to explore the mechanism of the enhancement of selectivity. The study used platinum rather than silver because previous workers had found that platinum is almost inactive for CO production from CO2. The results show that EMIM-BF4 has two effects: it suppresses hydrogen formation and enhances CO2 conversion. SFG shows that there is a layer of EMIM on the platinum surface that inhibits hydrogen formation. CO2, however, can react...
TL;DR: The first examples of BMes(2)-functionalized NHC chelate ligands have been achieved and their Pt(II) acetylacetonate complexes have been synthesized and fully characterized.
Abstract: The first examples of BMes2-functionalized NHC chelate ligands have been achieved. Their Pt(II) acetylacetonate complexes have been synthesized and fully characterized. These NHC-chelate Pt(II) compounds display highly efficient blue or blue-green phosphorescence in solution (Φ = 0.41–0.87) and the solid state (Φ = 0.86–0.90). Highly efficient electroluminescent devices based on these new Pt(II) compounds have also been fabricated.
TL;DR: This review is devoted to silica-noble metal core-shell nanostructures and outlines the main methods used for the preparation and surface modification ofsilica particles and presents the major strategies for the formation of metal nanoshells on the modified silica particles.
TL;DR: Through an analysis of the thermolysis of the binder and composite material, it is determined that the high surface area of an electrode, as determined by nitrogen adsorption, is consistent with but not sufficient for high performing electrodes.
Abstract: Several techniques for fabricating functionalized graphene sheet (FGS) electrodes were tested for catalytic performance in dye-sensitized solar cells (DSSCs). By using ethyl cellulose as a sacrificial binder, and partially thermolyzing it, we were able to create electrodes which exhibited lower effective charge transfer resistance (<1 Ω cm2) than the thermally decomposed chloroplatinic acid electrodes traditionally used. This performance was achieved not only for the triiodide/iodide redox couple, but also for the two other major redox mediators used in DSSCs, based on cobalt and sulfur complexes, showing the versatility of the electrode. DSSCs using these FGS electrodes had efficiencies (η) equal to or higher than those using thermally decomposed chloroplatinic acid electrodes in each of the three major redox mediators: I (ηFGS = 6.8%, ηPt = 6.8%), Co (4.5%, 4.4%), S (3.5%, 2.0%). Through an analysis of the thermolysis of the binder and composite material, we determined that the high surface area of an e...
01 Jan 2012
TL;DR: In this article, the ORR-corrected mixed potential (c-MP) is defined as the crossing point of linear potential sweeps in the positive direction for different rotation rates.
Abstract: Understanding the hydrogen peroxide electrochemistry on platinum can provide information about the oxygen reduction reaction mechanism, whether H(2)O(2) participates as an intermediate or not. The H(2)O(2) oxidation and reduction reaction on polycrystalline platinum is a diffusion-limited reaction in 0.1 M HClO(4). The applied potential determines the Pt surface state, which is then decisive for the direction of the reaction: when H(2)O(2) interacts with reduced surface sites it decomposes producing adsorbed OH species; when it interacts with oxidized Pt sites then H(2)O(2) is oxidized to O(2) by reducing the surface. Electronic structure calculations indicate that the activation energies of both processes are low at room temperature. The H(2)O(2) reduction and oxidation reactions can therefore be utilized for monitoring the potential-dependent oxidation of the platinum surface. In particular, the potential at which the hydrogen peroxide reduction and oxidation reactions are equally likely to occur reflects the intrinsic affinity of the platinum surface for oxygenated species. This potential can be experimentally determined as the crossing-point of linear potential sweeps in the positive direction for different rotation rates, hereby defined as the "ORR-corrected mixed potential" (c-MP).
TL;DR: The potential benefits of using terdentate over bidentate ligands in the construction of organometallic complexes as organic light-emitting diode (OLED) emitters offering better color purity are highlighted, and the molecular origins of the differences between the two are explored.
Abstract: This study highlights the potential benefits of using terdentate over bidentate ligands in the construction of organometallic complexes as organic light-emitting diode (OLED) emitters offering better color purity, and explores in detail the molecular origins of the differences between the two. A pair of closely related platinum(II) complexes has been selected, incorporating a bidentate and a terdentate cyclometallating ligand, respectively, namely, Pt(4,6-dFppy)(acac) (1) {4,6-dFppy = 2-(4,6-difluorophenyl)pyridine metalated at C(2) of the phenyl ring} and Pt(4,6-dFdpyb)Cl (2) {4,6-dFdpyb = 4,6-difluoro-1,3-di(2-pyridyl)benzene, metalated at C(2) of the phenyl ring}. The emission properties over the range of temperatures from 1.2 to 300 K have been investigated, including optical high-resolution studies. The results reveal a detailed insight into the electronic and vibronic structures of the two compounds. In particular, the Huang-Rhys parameter S that serves to quantify the degree of molecular distortion in the excited state with respect to the ground state, though small in both cases, is smaller by a factor of 2 for the terdentate than the bidentate complex (S ≈ 0.1 and ≈0.2, respectively). The smaller value for the former reflects the greater degree of rigidity induced by the terdentate ligand, leading to a lesser contribution of intraligand Franck-Condon vibrational modes in the green spectral range of the emission spectra. Consequently, an enhanced color purity with respect to blue light emission results. The high rigidity and the short Pt-C bond in Pt(4,6-dFdpyb)Cl also serve to disfavor nonradiative decay pathways, including those involving higher-lying dd* states. These effects account for the greatly superior luminescence quantum yield of the terdentate complex in fluid solution, amounting to φ(PL) = 80% versus only 2% found for the bidentate complex.
TL;DR: The electron transfer processes are accompanied by electron recombination, which is a major cause of efficiency loss in DSSCs and other solar cells.
Abstract: Since 1991, much progress has been made in the development of dye-sensitized solar cells (DSSCs). When compared to traditional silicon solar cells, DSSCs possess several unique advantages, such as simpler fabrication procedures, higher plasticity, higher transparency, and a greater variety of colors. Generally, a DSSC can be described by three components: a photoanode (i.e. , a dye-sensitized mesoporous semiconductor film); an electrolyte containing a redox couple; and a counter electrode (CE). Figure 1 is a schematic drawing of a DSSC. Under illumination, a sensitizer molecule (S) jumps to an excited state (S*), and the unstable S* releases a photoelectron (e ) that injects into the conduction band (CB) of the semiconductor, leaving behind a sensitizer hole (S) [actually, the excited state (S*) may relax to the ground state without release of a photoelectron, but this is not the main process] . These processes occur according to Formulae (1) and (2). Next, the photoelectrons in the CB are collected by the substrate (SB), flow through the external circuit, and reach the CE [Formulae (3) and (4)] . The oxidation state of the electrolyte (Ox) is reduced to the reduction state (Red ) by electrons at the CE, as shown in Formula (5). Meanwhile, S is regenerated by Red , which is oxidized to Ox according to Formula (6) until a circuit circle is completed. The electron transfer processes are accompanied by electron recombination. The recombination processes occur between the photoelectrons (CB) and the sensitizer holes [Formula (7)] and between the photoelectrons and Ox of the redox couple [Formula (8)] . Recombination is a major cause of efficiency loss in DSSCs and other solar cells.
TL;DR: In this article, a one-pot green method to synthesize Pt and Pd nanoparticles was reported, where two natural aromatic polymers, lignin and fulvic acid, were used as reducing and stabilising agents at moderate temperature (80 °C) in water and under aerobic conditions.