High-Performance Ammonia Protonic Ceramic Fuel Cells Using a Pd Inter-Catalyst

This study reports the performance and durability of a protonic ceramic fuel cells (PCFCs) in an ammonia fuel injection environment. The low ammonia decomposition rate in PCFCs with lower operating temperatures is improved relative to that of solid oxide fuel cells by treatment with a catalyst. By treating the anode of the PCFCs with a palladium (Pd) catalyst at 500 °C under ammonia fuel injection, the performance (peak power density of 340 mW cm⁻² at 500 °C) is approximately two-fold higher than that of the bare sample not treated with Pd. Pd catalysts are deposited through an atomic layer deposition post-treatment process on the anode surface, in which nickel oxide (NiO) and BaZr_0.2Ce_0.6Y_0.1Yb_0.1O_3–δ (BZCYYb) are mixed, and Pd can penetrate the anode surface and porous interior. Impedance analysis confirmed that Pd increased the current collection and significantly reduced the polarization resistance, particularly in the low-temperature region (≈500 °C), thereby improving the performance. Furthermore, stability tests showed that superior durability is achieved compared with that of the bare sample. Based on these results, the method presented herein is expected to represent a promising solution for securing high-performance and stable PCFCs based on ammonia injection.     

Fabrication of Supported AuPt Alloy Nanocrystals with Enhanced Electrocatalytic Activity for Formic Acid Oxidation through Conversion Chemistry of Layer‐Deposited Pt2+ on Au Nanocrystals

The exploitation of nanoconfined conversion of Au‐ and Pt‐containing binary nanocrystals for developing a controllable synthesis of surfactant‐free AuPt nanocrystals with enhanced formic acid oxidation (FAO) activity is reported, which can be stably and evenly immobilized on various support materials to diversify and optimize their electrocatalytic performance. In this study, an atomic layer of Pt²⁺ species is discovered to be spontaneously deposited in situ on the Au nanocrystal generated from a reverse‐microemulsion solution. The resulting Au/Pt²⁺ nanocrystal thermally transforms into a reduced AuPt alloy nanocrystal during the subsequent solid‐state conversion process within the SiO₂ nanosphere. The alloy nanocrystals can be isolated from SiO₂ in a surfactant‐free form and then dispersedly loaded on the carbon sphere surface, allowing for the production of a supported electrocatalyst that exhibits much higher FAO activity than commercial Pt/C catalysts. Furthermore, by involving Fe₃O₄ nanocrystals in the conversion process, the AuPt alloy nanocrystals can be grown on the oxide surface, improving the durability of supported metal catalysts, and then uniformly loaded on a reduced graphene oxide (RGO) layer with high electroconductivity. This produces electrocatalytic AuPt/Fe₃O₄/RGO nanocomposites whose catalyst‐oxide‐graphene triple‐junction structure provides improved electrocatalytic properties in terms of both activity and durability in catalyzing FAO.     

Study of nickel passivation in a borate medium

The adsorption of borate ions at the nickel and/or nickel oxide-electrolyte electrochemical interface was studied at various concentrations and pH values in lithium and borate solutions. First, the passivation range of nickel was estimated using cyclic voltammetry. The nickel passive layer formation kinetics (transfer resistance, capacitance of passive film formed, adsorption capacitance), as well as the semiconducting properties of this oxide layer, were studied using electrochemical impedance spectroscopy (E.I.S.). These electrochemical techniques were used in conjunction with adsorption measurements performed with an electrochemical quartz crystal microbalance (E.Q.C.M.) and with surface analyses (Auger spectroscopy). The nickel oxide showed type p semiconducting properties and was depleted at, corrosion potential. Moreover, very little borate adsorption was observed during the different tests. This may have been the result of the negative surface charge, in the pH and potential conditions applied.     

Ultrathin Ultralow-Platinum Catalyst Coated Membrane for Proton Exchange Membrane Fuel Cells

Catalyst coated membrane (CCM) is the core component of proton exchange membrane fuel cells and is routinely fabricated by spraying Pt/C slurries onto membrane, resulting in low activity and thick catalyst layer (CL, 5–10 µm) with an unaffordable Pt loading of 0.2–0.4 mg cm⁻² and a large mass transfer resistance at cathode. Highly active ultrathin ultralow-Pt CL (UUCL) is urgently required, but remains rare. Herein, wet-chemical direct growth of UUCLs on both sides of membrane to achieve integrated ultrathin ultralow-Pt catalyst coated membranes (UUCCMs) with a cathodic CL thickness of 79.7 ± 15.0 nm and a Pt loading of 20.2 ± 1.6 µg cm⁻² is reported. The key to this unique fabrication is the release of proton from membrane to regioselectively initiate the growth of interconnected Pd nanoneedle clusters array on membrane, followed by high-density deposition of Pt nanoparticles on Pd (Pt/Pd UUCLs). The single cell of UUCCMs exhibits the highest mass peak power density of 59.9 W mg_Pt,Cathode⁻¹ in the literature. The exceptional activity originates from high electrochemically active surface area, remarkable oxygen reduction reaction activity closely correlated with strain, and electronic effect at Pt/Pd interface, as well as improved mass transfer and optimal water management.     

Novel synthesis of quaternary nanocomposites based on chemical vapor grown graphene for photocatalytic hydrogen evolution

Pd-Pt/graphene-TiO₂ nanocomposites were synthesized via a facile ultrasonic and hydrothermal method. For the functionalization of graphene, large area graphene obtained by chemical vapor deposition method was oxidized by 3-chloroperoxybenzoic acid. The functionalized graphene oxide was decorated with TiO₂. And then, Pt and Pd nanoparticles were dispersed on graphene surface, simultaneously. The characterizations of “as-prepared” samples were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), Raman, specific surface area (BET) and with energy dispersive X-ray (EDX). The photocatalytic activity of the Pd-Pt/graphene-TiO₂ nanocomposite catalyst was evaluated by H₂ evolution under UV light. Pd-Pt/graphene-TiO₂ (Pd-Pt/G-TiO₂) exhibited higher photocatalytic activities than control experimental group samples (TiO₂, G-TiO₂, Pd/G-TiO₂ and Pt/G-TiO₂) under UV light irradiation.     

Catalytic properties of Pt cluster-decorated CeO2 nanostructures

Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO₂ nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO₂ surfaces have a clean surface and clean interface between Pt and CeO₂. Different growth behaviors of Pt on the two types of CeO₂ nanocrystals were observed, with epitaxial growth of Pt on CeO₂ nanooctahedra and random growth of Pt on CeO₂ nanorods. The structures of the Pt clusters on the two different types of CeO₂ nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The support-dependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO₂ nanorods showed much higher activity compared with Pt/CeO₂ nanooctahedra because of the higher concentration of oxygen vacancies in the CeO₂ nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO₂ nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.     

Surface poisoning in the nucleation and growth of palladium atomic layer deposition with Pd(hfac)2 and formalin

Palladium (Pd) atomic layer deposition (ALD) can be performed with Pd(hfac)₂ (hfac = hexafluoroacetyl-acetone) and formalin as the reactants. For Pd ALD on oxide surfaces, the nucleation of Pd ALD has been observed to require between 20 and 100 ALD cycles. To understand the long nucleation periods, this study explored the surface reactions occurring during Pd ALD nucleation and growth on hydroxylated Al₂O₃ substrates. In situ Fourier transform infrared (FTIR) spectroscopy on high surface area nanopowders was used to observe the surface species. The adsorption of Pd(hfac)₂ on hydroxylated Al₂O₃ substrates was found to yield both Pd(hfac)* and Al(hfac)* surface species. The identity of the Al(hfac)* species was confirmed by separate FTIR studies of hfacH adsorption on the hydroxylated Al₂O₃ substrates. Isothermal loss of the Al(hfac)* species revealed second-order kinetics at 448-523 K with an activation barrier of E_d = 39.4 kcal/mol. The lack of correlation between Al(hfac)* and AlOH* species during the loss of Al(hfac)* species suggested that the Al(hfac)* species may desorb as Al(hfac)₃. After Pd(hfac)₂ exposure and the subsequent formalin exposure on hydroxylated Al₂O₃ substrates, only hfac ligands from Pd(hfac)* species were removed from the surface. In addition, the formalin exposure added formate species. The Al(hfac)* species was identified as the cause of the long nucleation period because Al(hfac)* behaves as a site blocker. The surface poisoning by Al(hfac)* species was corroborated by adsorbing hfacH prior to the Pd(hfac)₂ exposures. The amount of Pd(hfac)* species after Pd(hfac)₂ exposures decreased progressively versus the previous hfacH exposure. Pd ALD occurred gradually during the subsequent Pd ALD cycles as the Al(hfac)* species were slowly removed from the Al₂O₃ surface. Ex situ transmission electron microscopy analysis revealed Pd nanoclusters that grew in size and dispersion with increasing number of Pd ALD cycles. These nanoclusters eventually coalesced to form a continuous Pd ALD film. Surface poisoning by the hfac ligands may help to explain the nucleation difficulties for metal ALD on oxide substrates using β-diketonate reactants.     

Benefits of Zr addition to oxidation resistance of a single-phase (Ni,Pt)Al coating at 1373 K

A single-phase (Ni,Pt)Al coating with lean addition of Zr was prepared by co-electroplating of Pt-Zr composite plating and subsequent gaseous aluminization treatments. Isothermal and cyclic oxidation behavior of the Zr-doped (Ni,Pt)Al coating samples was assessed at 1373 K in static air in comparison with plain nickel aluminide (NiAl) and normal (Ni,Pt)Al coatings. Results indicated that Zr-doped (Ni,Pt)Al coating demonstrated a lower oxidation rate constant and reduced tendency of oxide scale spallation as well as surface rumpling, in which the enhanced oxidation performance was mainly attributed to the segregation of Zr at oxide scale grain boundaries and the improved Young’s modulus of the coating. Besides, the addition of Zr effectively delayed oxide phase transformation of Al₂O₃ from θ phase to α phase in the early oxidation stage and coating degradation of β-NiAl to γ'-Ni₃Al in the stable oxidation stage.     

Role of Ti out-diffusion from a Pt/Ti bi-layer on the crystalline growth of (Ba,Sr)TiO3: A transmission electron microscopy investigation

We investigated the influence of the Ti out-diffusion in Pt/TiO_x/SiO₂/Si substrates (0 ≤ x ≤ 2), having different thicknesses of Pt and TiO_x layers, on the crystalline growth of (Ba,Sr)TiO₃ (BST) deposited by pulsed laser deposition. By means of X-ray diffraction and transmission electron microscopy, we show that the orientation of BST clearly depends on the presence and quantity of Ti having migrated up to the Pt surface, and on its possible oxidation prior to BST deposition, which was controlled by the atmosphere (vacuum or oxygen) of the pre-heating stage of the BST deposition process. Whereas BST has no preferential orientation if grown on a bare Pt surface, a strong (111) orientation of BST is obtained for a limited diffusion of titanium oxides on the Pt surface just before BST deposition. However, the (111) orientation is lost if this seeding titanium oxide layer on Pt is too thick just before BST deposition. Also, the formation of protrusions was evidenced at the BST/Pt interface and associated with the oxidation of Ti within the Pt layer.     

Electrocatalytic action of nano-SiO2 with electrodeposited nickel matrix

The present work focuses on the electrocatalytic effect of nano-SiO₂ on nickel electrodeposition and chemical interaction between nano-SiO₂ and nickel in composite coating. The electrochemical behavior from n-SiO₂/Ni composite brush plating system and quick nickel solution are investigated using cyclic voltammetry. The interaction between n-SiO₂ particles and matrix metal nickel is researched by X-ray photoelectron spectrometry. The results show that the n-SiO₂ take part in the electrode reaction during nickel electrocrystallization and can catalyze the nickel electrodeposition. The unsaturated bond of oxygen on n-SiO₂ particles surface can capture some of the absorbed nickel atoms and form nickel–oxygen chemical bond. It is proved that the chemical binding interaction exists in the interface between nanoparticles surface and matrix metal nickel.     

Influence of iron additives on the corrosion resistance of Al<Subscript>87</Subscript>Gd<Subscript>5</Subscript>Ni<Subscript>8</Subscript> amorphous metal alloy

Based on the results of voltammetric investigations, we have shown that the partial replacement of nickel by 4 at. % Fe in Al₈₇Gd₅Ni₈ amorphous alloy leads to a decrease in the corrosion currents and an increase in the polarization resistance, which demonstrates the higher corrosion resistance of Al₈₇Gd₅Ni₄Fe₄ alloy. Using the method of electrochemical impedance spectroscopy, we have studied the durability and protective capacity of passivation oxide layers at electrodes made of this alloy in 0.1 M NaCl aqueous solution. We have also selected an impedance model of the formation of interfaces oxide–0.1 M NaCl and amorphous metal alloy–0.1 M NaCl. We have established that active diffusion redox reactions, described by the Warburg element, take place at the interface oxide film–0.1 M NaCl. The diffusivities of anions from the solution into the surface oxide layer have been calculated. Finally, we show that, with increase in the time of electrochemical reaction in 0.1 M NaCl aqueous solution, diffusion decreases due to the compaction of the surface oxygen-containing layers.     

A study of the passivating oxide layer on fine nickel particles

The surface oxide layer of fine nickel particles has been investigated by high- resolution electron microscopic observation,, electron diffraction, X-ray diffraction, X-ray photo- electron spectroscopy and temperature-programmed gas desorption experiment. The thickness of the oxide layer formed on the particles was about 2 nm. The oxide layer was composed of innermost NiO, and outermost Ni(OH)₂ and amorphous nickel carbonate-hydroxide. The oxide layer give a good thermal stability to fine nickel particles.     

Pt Nanoparticle Assisted Homogeneous Surface Engineering of Polymer-Based Bulk-Heterojunction Photocathodes for Efficient Charge Extraction and Catalytic Hydrogen Evolution

To fabricate a high-efficiency bulk-heterojunction (BHJ)-based photocathode, introducing suitable interfacial modification layer(s) is a crucial strategy. Surface engineering is especially important for achieving high-performance photocathodes because the photoelectrochemical (PEC) reactions at the photocathode/electrolyte interface are the rate-limiting process. Despite its importance, the influence of interfacial layer morphology regulation on PEC activity has attracted insufficient attention. In this work, RuO₂, with excellent conductivity, capacity and catalytic properties, is utilized as an interfacial layer to modify the BHJ layer. However, the homogeneous coverage of hydrophilic RuO₂ on the hydrophobic BHJ surface is challenging. To address this issue, a Pt nanoparticle-assisted homogeneous RuO₂ layer deposition method is developed and successfully applied to several BHJ-based photocathodes, achieving superior PEC performance compared to those prepared by conventional interface engineering strategies. Among them, the fluorine-doped tin oxide (FTO)/J71:N2200(Pt)/RuO₂ photocathode generates the best photocurrent density of −9.0 mA cm⁻² at 0 V with an onset potential of up to 1.0 V under AM1.5 irradiation.     

A two-step approach to synthesis of Co(OH)<Subscript>2</Subscript>/γ-NiOOH/reduced graphene oxide nanocomposite for high performance supercapacitors

A two-step approach was reported to fabricate cobaltous hydroxide/γ- nickel oxide hydroxide/reduced graphene oxide (Co(OH)₂/γ-NiOOH/RGO) nanocomposites on nickel foam by combining the reduction of graphene oxide with the help of reflux condensation and the subsequent hydrothermal of Co(OH)₂ on RGO. The microstructural, surface morphology and electrochemical properties of the Co(OH)₂/γ-NiOOH/RGO nanocomposite were investigated. The results showed that the surface of the first-step fabricated γ-NiOOH/RGO nanocomposites was uniformly coated by Co(OH)₂ nanoflakes with lateral size of tens of nm and thickness of several nm. Co(OH)₂/γ-NiOOH/RGO nanocomposite demonstrated a high specific capacitance (745 mF/cm² at 0.5 mA/cm²) and a cycling stability of 69.8% after 1000 cycles at 30 mV/cm². γ-NiOOH/RGO//Co(OH)₂/γ-NiOOH/RGO asymmetric supercapacitor was assembled, and maximum gravimetric energy density of 57.3 W?h/kg and power density of 66.1 kW/kg were achieved. The synergistic effect between the highly conductive graphene and the nanoflake Co(OH)₂ structure was responsible for the high electrochemical performance of the hybrid electrode. It is expected that this research could offer a simple method to prepare graphene-based electrode materials.     

Nanostructured positively charged bioactive TiO<Subscript>2</Subscript> layer formed on Ti metal by NaOH,acid and heat treatments

Nanometer-scale roughness was generated on the surface of titanium (Ti) metal by NaOH treatment and remained after subsequent acid treatment with HCl, HNO₃ or H₂SO₄ solution, as long as the acid concentration was not high. It also remained after heat treatment. Sodium hydrogen titanate produced by NaOH treatment was transformed into hydrogen titanate after subsequent acid treatment as long as the acid concentration was not high. The hydrogen titanate was then transformed into titanium oxide (TiO₂) of anatase and rutile by heat treatment. Treated Ti metals exhibited high apatite-forming abilities in a simulated body fluid especially when the acid concentration was greater than 10 mM, irrespective of the type of acid solutions used. This high apatite-forming ability was maintained in humid environments for long periods. The high apatite-forming ability was attributed to the positive surface charge that formed on the TiO₂ layer and not to the surface roughness or a specific crystalline phase. This positively charged TiO₂ induced apatite formation by first selectively adsorbing negatively charged phosphate ions followed by positively charged calcium ions. Apatite formation is expected on the surfaces of such treated Ti metals after short periods, even in living systems. The bonding of metal to living bone is also expected to take place through this apatite layer.     

Microstructural analysis of Pd/Pt/Au/Pd ohmic contacts to InGaP/GaAs

Microstructural evolution during the annealing of Pd/Pt/Au/Pd p-ohmic contacts (with and without a thin layer of Zn) to InGaP/GaAs HBTs has been studied using transmission electron microscopy (TEM). Metal layers were deposited by electron beam evaporation directly onto the InGaP emitter layer with the intention of consuming the InGaP during annealing to contact the heavily C-doped p-type GaAs (3×10¹⁹ cm⁻³) base layer below. Initial reaction between Pd and Pt and InGaP formed a five-component amorphous layer (Pd, Pt, In, Ga and P), which crystallized to (Pt_xPd_1−x)5(In_yGa_1−y)P (0≤x, y≤1) at the interface between Pt and the amorphous layer. Annealing at temperatures ≥415°C caused complete decomposition of the InGaP and partial decomposition of the GaAs base layer, producing a contact consisting of (Pt_xPd_1−x)5(In_yGa_1−y)P, PtAs₂ and PdGa. The attainment of low contact resistances did not depend on the presence of Zn. Minimum values of 0.10−0.12 Ω mm were achieved after annealing at 415–440°C for contacts both with and without Zn. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reduced Graphene Oxide Nanohybrid–Assembled Microneedles as Mini‐Invasive Electrodes for Real‐Time Transdermal Biosensing

A variety of nanomaterial‐based biosensors have been developed to sensitively detect biomolecules in vitro, yet limited success has been achieved in real‐time sensing in vivo. The application of microneedles (MN) may offer a solution for painless and minimally‐invasive transdermal biosensing. However, integration of nanostructural materials on microneedle surface as transdermal electrodes remains challenging in applications. Here, a transdermal H₂O₂ electrochemical biosensor based on MNs integrated with nanohybrid consisting of reduced graphene oxide and Pt nanoparticles (Pt/rGO) is developed. The Pt/rGO significantly improves the detection sensitivity of the MN electrode, while the MNs are utilized as a painless transdermal tool to access the in vivo environment. The Pt/rGO nanostructures are protected by a water‐soluble polymer layer to avoid mechanical destruction during the MN skin insertion process. The polymer layer can readily be dissolved by the interstitial fluid and exposes the Pt/rGO on MNs for biosensing in vivo. The applications of the Pt/rGO‐integrated MNs for in situ and real‐time sensing of H₂O₂ in vivo are demonstrated both on pigskin and living mice. This work offers a unique real‐time transdermal biosensing system, which is a promising tool for sensing in vivo with high sensitivity but in a minimally‐invasive manner.     

Temperature programmed desorption study of the oxide layer formed by the interaction of polycrystalline nickel with oxygen

In a 100 l exposure of oxygen, an oxide layer was formed on a nickel surface, this surface was heated and maintained at 623 K to dissociate the oxide, then by exposure to 5 l oxygen, a small amount of oxygen was adsorbed again. From the Temperature Programmed Desorption spectrum of this O₂/Ni surface it can be concluded that the original oxide layer on the nickel surface was not a stoichiometric nickel (II) oxide, but may be a compound of a variety of oxides such as nickel (II) oxide, nickel (III) species and excess oxygen.     

Silicide formation with nickel and platinum double layers on silicon

Diffusion effects and silicide formation in double layers of electron-gun-evaporated thin films of nickel and platinum on 〈100〉 and 〈111〉 silicon substrates were studied by megaelectronvolt backscattering spectrometry, transmission electron microscopy and glancing angle X-ray diffraction as a function of heat treatment (200–900 °C) for both sequences of thin films. It was found for the Si/Ni/Pt(Si/Pt/Ni) system that Ni₂Si(Pt₂Si) starts growing first. When all the nickel (platinum) has been consumed by this compound growth, platinum (nickel) diffuses through the Ni₂Si(Pt₂Si) layer and accumulates at the SiNi₂Si(SiPt₂Si) interface. This platinum (nickel) diffusion seems to be a grain boundary diffusion.For 〈100〉 Si/Ni/Pt samples with thin platinum layers it has been shown that platinum acts as a marker for the moving species in the transition from Ni₂Si to NiSi. For thick platinum layers it was observed that similar processes occur, leading to essentially a four-layered silicide where the layers are alternately rich in nickel and rich in platinum (450 °C, 20 min). In the silicide for the 〈100〉 Si/Pt/Ni system the distribution of nickel and platinum is approximately the reverse of the asdeposited distribution (about 450 °C, 20 min). In the further evolution of the profiles the elemental distribution becomes smooth and flat for both sequences of the layers (750 °C, 20 min). We suggest the existence of a ternary of the type SiNi_1?xPt_x.     

Nickel oxide sol-gel films from nickel diacetate for electrochromic applications

Nickel diacetate tetrahydrate, [Ni(acetate)₂·4H₂O] and nickel diacetate dimethylaminoethanol, [Ni(acetate)₂(dmaeH)₂] were successfully used to deposit NiO_x thin films on conductive glass substrates by sol-gel techniques for large area electrochromic applications. Homogeneous one layer films 100 nm thick were deposited by spin coating 0.5 M [Ni(acetate)₂·4H₂O] in dmaeH at 1000 rpm and by dip coating methods. The NiO_x films were characterised by X-ray diffraction, transmission electron microscopy and atomic force microscopy. The thin film electrochromic performances were characterised by means of optical (transmittance) and electrochemical (cyclic voltammetry) methods. On early cycling NiO_x thin films present an activation period, related to an increase in capacity. The electro-optical data show an increase in the electrochromic response (i.e. an increase in contrast and colouration efficiency) upon cycling. Following this initial activation period a steady state is reached in which the thin films reversibly switch from transparent to brown. The anodically coloured NiO_x thin films are therefore suitable for use in a complete electrochromic cell with tungsten oxide as the cathodic colouring layer. However, the films are not fully stable with long cycling.