Mass production of Nickel@Carbon nanoparticles attached on single-walled carbon nanotube networks as highly efficient water splitting electrocatalyst

Herein, we develop a direct current arc discharge method which enables large-scale synthesis of nickel@carbon attached single-walled carbon nanotube networks as an electrocatalyst for highly efficient water splitting. Mass amount of Ni@C/SCN (～80 g) could be easily obtained. After optimization, the catalyst exhibits a superior performance of electrochemical water splitting, which allows a current density of 10 mA cm^?2, with an overpotential of only 260 mV for OER and 198 mV for HER. The electrolyzer can achieve a current density of 10 mA cm^?2 at 1.8 V.     

Crossed FeCo2S4 nanosheet arrays grown on 3D nickel foam as high-efficient electrocatalyst for overall water splitting

Great efforts in developing low-cost, highly efficient and stable electrocatalysts are to tune the chemical compositions and morphological characteristics for enhancing efficiency of water splitting. In this communication, FeCo₂S₄ nanosheet was grown in situ on nickel foam (FeCo₂S₄/NF) via a facile hydrothermal sulfidization method and served as a high-efficient bifunctional electrocatalyst for overall water splitting. As-synthesized FeCo₂S₄/NF self-supported electrode delivers 20 mA cm^?2 at an overpotential of 259 mV toward OER and 10 mA cm^?2 at an overpotential of 131 mV toward HER in alkaline media. Moreover, when used as both anode and cathode in a two-electrode electrolyzer, only a small cell voltage of 1.541 V is needed to afford a current density of 10 mA cm^?2 for overall water splitting. Bifunctional electrode FeCo₂S₄/NF also revealed a distinguished electrochemical durability during a 12 h stability test at 1.63 V, which would provide a promising water splitting installation for commercial hydrogen production.     

Nickel foam-supported NiFe layered double hydroxides nanoflakes array as a greatly enhanced electrocatalyst for oxygen evolution reaction

In this work, nickel-iron layered double hydroxides nanoflakes are grown on nickel foam by a facile in-situ complexation precipitation method. The fabricated nickel-iron layered double hydroxides/nickel foam with special 3D structure with large electrochemical activated surface area is proposed as a greatly enhance electrode material for oxygen evolution reaction. The electrochemical properties of the as-fabricated nickel-iron layered double hydroxides/nickel foam electrode are evaluated using 1 mol L^?1 KOH as electrolyte. The obtained electrochemical results show that the fabricated nickel-iron layered double hydroxides/nickel foam electrode exhibits a low overpotential of 245 mV at current density of 10 mA cm^?2 with small Tafel slope of 27 mV dec^?1. Also, it displays a much longer durability of 20 h with very small decay of 0.02% as compared with 3D nickel foam, IrO₂ and the related catalysts reported. Therefore, this study indicates that the nickel-iron layered double hydroxides/nickel foam is a promising electrode material for oxygen evolution reaction due to its facile preparation method, low cost and environmentally friendly nature.     

Highly efficient,large surface area and spherically shaped Pt particles deposited electrolytically synthesized graphene for methanol oxidation with impedance spectroscopy

Graphene was synthesized via electrochemical exfoliation technique of graphite rod in Poly (sodium 4-styrenesulfonate) solution. Laser Raman and X-ray Diffraction Spectroscopies were used to confirm the defects and crystal nature of graphene. The surface wettability studies based on water contact angle, further differentiates the affinity of as-prepared graphene and pristine graphite towards water. Modified Glassy carbon (GC) electrodes were prepared by electro-deposition of Platinum (Pt) on bare and graphene coated GC, denoted as GC/Pt and graphene/Pt modified GC respectively. The morphology and chemical composition of the thus synthesized graphene and graphene/Pt modified electrodes were investigated by High resolution transmission electron microscopy, Scanning electron microscopy and Energy dispersive spectroscopy. The electrochemically active surface area of the electro-deposited spherically shaped Pt particles was calculated to be 63.96 m² g^?1 and 25.10 m² g^?1 on graphene/Pt and GC/Pt, respectively. The electro-catalytic performance of modified electrodes for methanol oxidation was envisaged by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. Graphene/Pt modified GC electrode showed higher oxidation peak current (42.90 mA cm^?2) than GC/Pt modified electrode (16.24 mA cm^?2) in forward scan of methanol oxidation because of the uniform distribution of spherically shaped Pt particles on graphene. The reaction path for methanol oxidation at different potentials was elucidated by means of Electrochemical Impedance Spectroscopy.     

Facile synthesis of laminated porous WS2/C composite and its electrocatalysis for oxygen reduction reaction

The Vulcan XC-72R modified WS₂ nanocomposite (WS₂/C）was prepared by solid reaction process combined with sonication. The as-prepared WS₂/C nanocomposite presents a laminated porous structure by SEM and TEM characterization. The electrochemical experiments show that the onset potential and the limiting-current density of WS₂/C is 0.78 V and 4.99 mA cm^?2, respectively, which is much higher than, WS₂ (3.12 mA cm^?2) and Vulcan XC-72R (2.79 mA cm^?2). The number of transfer electrons in ORR at the WS₂/C nanocomposite electrode is 3.70, which is close to four-electron process. Besides, the current density of WS₂/C nanocomposites remained at 90% after 20,000 s, indicating its superior electrochemical stability. All these facts reveal that the as-prepared WS₂/C nanocomposite can be regarded as a promising cathode ORR catalyst for fuel cell.     

Phosphorus-doped nickel sulfides/nickel foam as electrode materials for electrocatalytic water splitting

Hydrogen production from electrocatalytic water splitting is viewed as one of the most promising methods to generate the clean energy. In this work, we successfully prepared an electrode material by growing phosphorus-doped Ni₃S₂ (PNi₃S₂) on nickel foam substrate (NF) under hydrothermal conditions. The phosphorus-doping has an obvious effect on the morphology of Ni₃S₂ on the surface of the nickel foam, which probably results in more active sites, higher electrical conductivity and faster mass transfer. The resulting electrode material displays excellent electrocatalytic activities and stability towards both OER (oxygen evolution reaction) and HER (hydrogen evolution reaction). A relatively low overpotential of 306 mV is required to reach the current density of 100 mA cm^?2 for OER and 137 mV at 10 mA cm^?2 for HER in 1 M KOH solution. When PNi₃S₂/NF was used in an electrolyzer for full water splitting, it can generate a current density of 10 mA cm^?2 at 1.47 V with excellent stability for more than 20 h.     

High electrocatalytic performance of a graphene-supported PtAu nanoalloy for methanol oxidation

Homogeneously distributed PtAu nanoalloy anchored to graphene (PtAuNA/G) was synthesized via a simple one-step electrochemical deposition process, in which Pt and Au ions and graphene oxide was simultaneously electro-reduced on the glassy carbon electrode. The morphology evolution of PtAuNA/G synthesized with different deposition times was characterized via field-emission scanning electron microscopy. X-ray diffraction and transmission electron microscopy was applied to confirm the alloy structure. The electrodeposition conditions, including the deposition time, were further optimized to explore the morphological evolution of PtAuNA/G. Based on cyclic voltammetry and chronoamperometry results, it was found that PtAuNA/G can efficiently catalyze the oxidation of methanol in alkaline media with dramatically enhanced electrocatalytic activity (7.268 mA cm^?2, 3.83 times higher than that of commercial carbon-supported Pt nanoparticles, 1.894 mA cm^?2), along with a considerably improved tolerance to poisoning (current decline: 69% vs 99.89%). These results indicate a great potential for PtAuNA/G in fabricating high-performance direct methanol fuel cells.     

Surface modification of aligned TiO2 nanotubes by Cu2O nanoparticles and their enhanced photo electrochemical properties and hydrogen generation application

In this work, we report the synthesis of cuprous oxide (Cu₂O) nanoparticles modified vertically oriented aligned titanium dioxide (TiO₂) nanotube arrays through wet chemical treatment of TiO₂ nanotubes and their multi-functional application as enhanced photo electrochemical and hydrogen generation. The synthesized samples were characterized by X-ray diffraction, SEM, TEM, and UV–Vis spectroscopy. The structural characterization revealed that the admixed Cu₂O nanoparticles on the TiO₂ surface did not alter its crystalline structure of vertically oriented aligned TiO₂ nanotube. The photocatalytic performance and hydrogen generation of as synthesized Cu₂O nanoparticles modified aligned TiO₂ nanotube was found to highly depend on the Cu₂O content. The optical characterizations reveal that the presence of Cu₂O nanoparticles extends its absorption into the visible region which improves the photocurrent density in comparison to pristine aligned TiO₂ nanotubes electrodes due to enhanced photoactivity and better charge separation. The optimum photocurrent density and hydrogen generation rate has been found to be 3.4 mA cm^?2 and 127.5 μmole cm^?2 h^?1 in 1 M Na₂SO₄ electrolyte solution under 1.5 AM solar irradiance of white light with illumination intensity of 100 mW cm^?2.     

Co Nanoparticles@N-doped carbon coated on carbon Nanotube@Defective silica as non-noble photocathode for efficient photoelectrochemical hydrogen generation

The development of photoelectrodes capable of light-driven hydrogen evolution from water with non-noble metals is an important approach for the storage of solar energy in the form of a chemical energy carrier. In this study, we report Co nanoparticles@N-doped carbon coated on carbon nanotube@defective-silica (CNTs@Co@NC/D-SiO₂), which are composed of Co nanoparticles@N-doped carbon as electrocatalyst, defective-silica as photocatalyst and carbon nanotube as conductive substrates. The obtained non-noble photocathode possesses the high performance for efficient photoelectrochemical hydrogen evolution reaction. When evaluated for hydrogen evolution reaction electrocatalysis, CNTs@Co@NC/D-SiO₂ exhibits a small onset overpotential of 104 mV (J = 1 mA cm^?2), a Tafel slope of 69.1 mV dec^?1 and outstanding long-term cycling stability. The P type semiconductor characteristics of CNTs@Co@NC/D-SiO₂ due to defective-silica with carrier concentration of 3.53 × 10¹⁹ cm^?3 is measured, which produces a significant positive shift of overpotential of 40 mV (J = 10 mA cm^?2) under 100 mW cm^?2 simulated sunlight irradiation. These findings provide a straightforward and effective route to produce cheap and efficient photo-electro-catalyst for water splitting.     

Syntheses of nickel sulfides from 1,2-bis(diphenylphosphino)ethane nickel(II)dithiolates and their application in the oxygen evolution reaction

In this work, four heteroleptic Ni(II)dppe dithiolates complexes, [Ni(NED)(dppe)] (Ni-NED), [Ni(ecda)(dppe)] (Ni-ecda), [Ni(i-mnt)(dppe)] (Ni-i-mnt) and [Ni(cdc)(dppe)] (Ni-cdc) (dppe = 1,2-bis(diphenylphosphino)ethane; NED = 1-nitroethylene-2,2-dithiolate; ecda = 1-ethoxycarbonyl-1-cyanoethyelene-2,2-dithiolate; i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and cdc = cyanodithioimidocarbonate), have been synthesized and characterized by analytical and spectroscopic techniques (Elemental analysis, vibrational, electronic absorption and multinuclear NMR spectroscopy). Structural characterization of all the four complexes by single crystal X-ray diffraction study suggests distortion in regular square planar geometry at Ni(II) center by coordination with two phosphorus of the dppe and two sulfur of the dithiolate ligands, respectively. The decomposition of all four complexes have been done to produce nickel sulfides and the resulting nickel sulfides have been utilized for electrocatalytic oxygen evolution reaction (OER). The nickel sulfide obtained by decomposing Ni-cdc shows best activity with overpotential η = 222 mV at j = 10 mA cm^?2 and a Tafel slope of 44.2 mV dec^?1 while other catalysts shows η > 470 mV at j = 5 mA cm^?2 and η > 600 mV at j = 10 mA cm^?2 at loading of 1.3 mg cm^?2.     

The composite electrolyte with an insulation Sm2O3 and semiconductor NiO for advanced fuel cells

Novel Sm₂O₃?NiO composite was prepared as the functional electrolyte for the first time. The total electrical conductivity of Sm₂O₃?NiO is 0.38 S cm^?1 in H₂/air condition at 550 °C. High performance, e.g. 718 mW cm^?2, was achieved using Sm₂O₃?NiO composite as an electrolyte of solid oxide fuel cells operated at 550 °C. The electrical properties and electrochemical performance are strongly depended on Sm₂O₃ and NiO constituent phase of the compositions. Notably, surprisingly high ionic conductivity and fuel cell performance are achieved using the composite system constituting with insulating Sm₂O₃ and intrinsic p-type conductive NiO with a low conductivity of 4 × 10^?3 S cm^?1. The interfacial ionic conduction between two phases is a dominating factor giving rise to significantly enhanced proton conduction. Fuel cell performance and further ionic conduction mechanisms are under investigation.     

Electrochemical synthesis of Li-doped NiFeCo oxides for efficient catalysis of the oxygen evolution reaction in an alkaline environment

Oxygen evolution reaction (OER) is an essential reaction for overall electrochemical water splitting. In this present study, we adopt a facile electrochemical deposition method to synthesize the Li-doped NiFeCo oxides for OER in an alkaline medium. The scanning electron microscopy, X-ray diffraction, Brunauer-Emmet-Teller method and X-ray photo-electron spectroscopy provides the information of morphology, structure, specific surface area and electronic state of the electrocatalysts respectively. Investigates the electrochemical properties by the thin-film technique on a rotating disk electrode and in a single-cell laboratory water electrolyzer connects with electrochemical impedance spectroscopy. Among the catalysts under investigation, Ni_0·9Fe_0·1Co_1·975Li_0·025O₄ exhibits the highest activity towards oxygen evolution reaction, and explains the activity by the oxygen binding energy; such knowledge can be helped to develop better catalyst. We achieve onset over potential 220 mV and receive 10 mA cm^?2 current density at over potential 301 mV with Tafel slope 62 mV dec^?1 in 1 M KOH solution. The results are similar to recently published catalysts in the literature. In water electrolyzer, the Ni_0·9Fe_0·1Co_1·975Li_0·025O₄ modified nickel foam anode exhibits a current density of 143 mA cm^?2 at a cell voltage of 1.85 V in 10 wt% KOH and a temperature of 50 °C.     

Enhanced electrocatalytic activity of NiO nanoparticles supported on graphite planes towards urea electro-oxidation in NaOH solution

Nickel oxide nanoparticles are fabricated onto graphite planes [NiO/Gt] by chemical precipitation of Ni(OH)₂ particles with consecutive calcination at 400 °C. The formed electrocatalysts are characterized using X-ray diffraction (XRD) and Transmission electron microscopy (TEM). TEM images demonstrate the deposition of NiO nanoparticles on graphite surface through their crystallite lattice fringes with spacing values of 2.45 Å (111), 2.10 Å (200) and 1.48 Å (220). The electrocatalytic activity of NiO/Gt electrocatalyst is examined towards urea electro-oxidation in NaOH solution using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Urea oxidation peak current density is observed at NiO/Gt electrocatalyst containing 15 wt% NiO [NiO/Gt?15] at a potential value of +640 mV (Ag/AgCl) with a current density value of 17.63 mA cm^?2. The loading amount of NiO in the prepared electrocatalyst significantly affects its electrocatalytic performance. NiO/Gt?15 exhibits the highest urea oxidation current density with the desired stability. The lower Tafel slope, charge transfer resistance and the higher exchange current density and diffusion coefficient values of urea molecules at NiO/Gt?15 surface elect its application as a promising electrocatalyst material during urea oxidation reaction in fuel cells.     

Nickel selenide nanostructures as an electrocatalyst for hydrogen evolution reaction

Electrochemical water splitting has gained momentum for the development of alternative energy sources. Herein, we report the synthesis of two different nickel selenide nanostructures of different morphology and composition employing hydrothermal method. NiSe₂ nanosheets were obtained by the anion-exchange reaction of Ni(OH)₂ with Se ions for 15 h. On the other hand, NiSe nanoflakes were synthesized by the direct selenization of nickel surface with the reaction time of 2 h. Tested as an electrocatalyst for hydrogen evolution reaction, NiSe₂ nanosheets and NiSe nanoflakes can afford a geometric current density of 10 mA cm^?2 at an overpotential of 198 mV and 217 mV respectively. The measured Tafel slope values of NiSe nanoflakes are 28.6 mV dec^?1, which is three times lower as compared with NiSe₂ nanosheets (72.1 mV dec^?1). These results indicates the HER kinetics of NiSe nanoflakes are at par with the state-of-the-art Pt/C catalyst and also complimented with the short synthesis time of 2 h. Further, both nickel selenides exhibit ultra-long term stability for 30 h as evident from constant current chronopotentiometry and electrochemical impedance spectroscopy results.     

NiO hollow microspheres as efficient bifunctional electrocatalysts for Overall Water-Splitting

Development of efficient, earth-abundant and low-cost electrocatalyst for effective water electrolysis is highly demanding for production of sustainable hydrogen energy. In this paper, we report the cost-effective synthetic protocol for porous NiO hollow spheres in large scale through a simple spray drying strategy, using aqueous nickel ammonium carbonate complex solution, followed by calcination. The synthesized NiO hollow spheres calcined at 300 °C (NiO-300) are porous, made of nanoparticles in size range of 10–16 nm with a size range of 2.5–4 μm and total surface area of 120 m²/g. The NiO-300 exhibited excellent bifunctional electrocatalytic water splitting characteristic, both OER, and HER, in basic solution. NiO-300 modified glassy carbon electrode showed superior water electrolysis kinetics and to achieve 10 mA cm^?2 current density, it required 370 mV overpotential for OER and 424 mV overpotential for HER in 1 M KOH. It is also worked well with cost-effective plastic chip electrode. An assembled two-electrode system by pairing NiO modified plastic chip electrode as both anode and cathode in a 1.0 M KOH electrolyte for overall water splitting exhibit clear bubble formation at 1.6 V potential.     

Electrochemically synthesized polypyrrole/MWCNTs-Al2O3 ternary nanocomposites supported Pt nanoparticles toward methanol oxidation

As known, a good support enhances the activity and durability of any catalyst. In the current study, polypyrrole (PPY)/nanocomposite (MWCNTs and Al₂O₃) films were fabricated by electrochemical polymerization of pyrrole solution with a certain amount of nanoparticles on titanium substrates and were used as new support materials for Pt catalyst. The modified electrodes were characterized by Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) techniques. High catalytic activity and long-time stability toward methanol oxidation of Pt/PPY–MWNTs-αAl₂O₃ catalyst have also been verified by cyclic voltammetry results and chronoamperometric response measurements. This catalyst exhibits a vehemently high current density (345.03 mA cm^?2) and low peak potential (0.74 v) for methanol oxidation. Other electrochemical measurements (electrochemical impedance spectroscopy (EIS), CO stripping voltammetry and Tafel test) clearly confirmed that Pt/PPY–MWNTs-αAl₂O₃/Ti electrode has a better performance toward methanol oxidation compared to the other electrodes and that can be used as a promising electrode material for application in direct methanol fuel cells (DMFCs).     

Controllable synthesis of PtPd nanocubes on graphene as advanced catalysts for ethanol oxidation

PtPd nanocubes (NCs) were uniformly deposited on the reduced graphene oxides (RGOs) via a one-pot solvothermal reduction. These PtPd NCs were enclosed with (100) facet. Their size can be tuned from 11 to 27 nm by controlling their composition. Under the optimum atomic ratio of Pt/Pd (1:5), the as-prepared RGO-supported PtPd NCs show a superior catalytic efficiency of ethanol oxidation reaction (EOR) with a specific activity of 2.3 mA cm^?2 and a mass activity of 1.08 A mg^?1 Pt, far above those for the RGO-supported Pt nanoparticles (0.3 mA cm^?2 for specific activity and 0.018 A mg^?1 Pt for mass activity). Besides, these EOR catalysts exhibit a high CO-tolerance without significant current decay during steady-state polarization at 0.6 V over 4000 s. Their durability is also remarkable with only 8.9% loss of their electrochemical surface area (ECSA) after 10 000 cycles of voltammetric test.     

Optimization on the electrochemical properties of La2NiO4+δ cathodes by tuning the cathode thickness

The electrochemical properties of La₂NiO_4+δ electrodes were investigated as a function of the electrode thickness based on three-electrode half cells. The electrocatalytic activity of the electrodes with the varied thicknesses ranging from 5 to 30 μm was surveyed by electrochemical impedance spectroscopy technique under open-current voltage conditions. The cathodic polarization curves of these electrodes were also inspected. The results indicated that the electrochemical properties of these electrodes were highly dependent on their thickness. The polarizations of involved electrode reaction processes displayed different variations with changing the electrode thickness. Tuning the electrode thickness was confirmed to be effective for optimizing the electrochemical properties. Among the investigated electrodes, the electrode with a thickness of ～20 μm achieved the optimal properties. At 800 °C in air, this electrode exhibited a polarization resistance of 0.24 Ω cm², an exchange current density of 201 mA cm^?2 and an overpotential of 40 mV at 200 mA cm^?2. On this ground, an anode-supported single cell with ～20 μm thick La₂NiO_4+δ cathode was fabricated. At 800 °C and using hydrogen fuel, this single cell attained a maximum powder density of 500 mW cm^?2.     

Towards activation of amorphous MoSx via Cobalt doping for enhanced electrocatalytic hydrogen evolution reaction

Amorphous molybdenum sulfide (a-MoS_x) has been shown as one of the most promising catalysts in acidic electrolytes towards hydrogen evolution reaction (HER). Its intrinsic electrocatalytic activity can be further enhanced via doping and cropping the electronic structure.In this study, one-step electro-deposition was employed to fabricate MoS_xCo_y/TNAs hybrid electrodes using TiO₂ nanotube arrays as support. The microstructure and chemical composition of the samples were characterized via X-ray diffraction (XRD), scanning electron microscope (SEM), tunneling electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). The electrochemical properties of the samples were investigated through linear sweep voltammetry (LSV), cyclic voltammetry (CV), Tafel curves, and electrochemical impedance spectroscopy (EIS). According to experimental results, MoSCo structure was formed after Co²⁺ was incorporated into MoS_x, resulting in increases in both unsaturated Mo and S atoms acting as the active sites that lead to enhancement of intrinsic electrocatalytic activity. The pseudo-capacitance of MoS_xCo_y/TNAs (x = 1.70, y = 0.25) reached 46 mF cm^?2, a 31.4% improvement over 35 mF cm^?2 of MoS_x/TNAs. The onset hydrogen evolution potential, overpotentials at current densities of ?10 mA cm^?2 and –20 mA cm^?2 were recorded at ?92 mV, ?173 mV, and ?209 mV, respectively, reduction of 30 mV, 24 mV, and 28 mV than ?112 mV, ?197 mV, and ?237 mV of MoS_x/TNAs, respectively. This electrode was subjected to 1000-cycle testing and demonstrated stable electrochemical activity, illustrating excellent stability.     

Pt nanoparticles modified Au dendritic nanostructures: Facile synthesis and enhanced electrocatalytic performance for methanol oxidation

A facile and simple method is presented for the synthesis of bimetallic composites, Pt nanoparticles modified dendritic Au nanostructures (PtNPs/DGNs), in which dendritic Au was deposited on a glassy carbon electrode via a potentiostatic method and sphere-like Pt nanoparticles were decorated on Au substrates through a chemical reduction reaction. The compositions, morphologies, and structures of the PtNPs/DGNs were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. Results indicated that bimetallic composites were successfully synthesized and spherical Pt nanoparticles were dispersed evenly on dendritic Au substrates. The number of Pt nanoparticles on Au surface was regulated by controlling the chemical reduction deposition time, allowing the electrocatalytic properties of the composite towards methanol oxidation to be tuned. Electrochemical measurements, including cyclic voltammetry and chronoamperometry, were performed to investigate the electrochemical properties and electrocatalytic behaviors of the PtNPs/DGNs towards methanol oxidation. Pt nanoparticles partially covered dendritic Au exhibited dramatically enhanced electrocatalytic activity (3.947 mA cm^?2), which was 2.65 times that of commercial carbon-supported Pt nanoparticles (1.487 mA cm^?2), along with much improved poisoning tolerance (current decline: 70.85% vs 99.36%). These enhanced performances were likely caused by the large active electrochemical area of the bimetallic nanocomposites and the change in the electronic structure of Pt when the Au surface was modified with fewer Pt nanoparticles.