Ultralow loading electroless deposition of IrOx on nickel foam for efficient and stable water oxidation catalysis

Abstract Photocatalysis and electrolysis are crucial processes for the development of a sustainable, clean energy system, since they enable solar fuel production, such as hydrogen by water splitting, as well as CO2 reduction. In these processes efficient and robust catalysts for water oxidation are required and the reduction of employed amount of noble metals is crucial to reduce costs and increase the sustainability of the technology. To obtain extremely low iridium loading on nickel foam electrodes we have employed electroless deposition by spontaneous galvanic displacement as a simple, low cost, highly scalable technique. After deposition the Ir oxidation has been achieved by annealing in air at 250 °C. By varying the deposition parameters, an optimal condition has been achieved, with an overpotential for water oxidation of 360 mV at 10 mA cm−2 in 1.0 M KOH solution. The Ni foam coverage with Ir oxide has also a positive impact on the electrode stability, strongly decreasing the degradation rate, compared to the case of bare Ni foam. The average amount of noble metal in the best performing electrode is only 35 μg cm−2 for a 1.6 mm thick Ni foam electrode. The proposed approach is highly promising for gas diffusion electrodes, and can be implemented in electrolytic cells, as well as in fuel cells

Solid-State Fabrication of Cu2O/CuO Hydroxide Nanoelectrode Array onto Graphene Paper by Thermal Dewetting for High-Sensitive Detection of Glucose

Nanostructures of Cu2O/CuO hydroxide suitable for the electrochemical determination of glucose are obtained by solid‐state dewetting of CuO layers 6, 8, and 31 nm thin deposited by sputtering onto 240 μm‐thick graphene paper. Solid‐state dewetting in nitrogen produces a partial decomposition of CuO into Cu2O and Cu. X‐ray diffraction patterns reveal the presence of high‐index crystallographic facets, which are reactive and useful toward glucose oxidation to gluconolactone. Typically, morphology studied by scanning electron microscopy reveals faceted nanoparticles with an average size below 200 nm. X‐ray photoelectron spectroscopy shows that the nanostructure surfaces of Cu2O and metallic copper exposed to natural ambient are promptly reoxidized and hydroxidized to a mixture of CuO and Cu(OH)2. Electrochemical characterization in amperometric mode reveals linear response to glucose concentration in the range from 50 to 10 × 10−3 m, sensitivity up to 83 μA cm−2 mm −1, and limit of detection up to 3.6 × 10−6 m. Good combination of low cost and simplicity of preparation with low limit of detection, high sensitivity, and wide linear range makes the proposed electrodes suitable for a variety of applications ranging from health to food and beverage industries

Perovskites and Related Structures: MOCVD Growth of Perovskite Multiferroic BiFeO 3

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Dy-Doped BiFeO3 thin films: piezoelectric and bandgap tuning

International audienceMultiferroic materials, including lead-free BiFeO3, are of specialinterest for their challenging functional properties which can suitvarious applications. This paper reports the optimization of theMOCVD process used for the deposition of epitaxial thin films ofDy-doped bismuth ferrite, Bi(1−x)DyxFeO3 (with 0 ≤ x ≤ 0.11), onconductive SrTiO3:Nb(100) single crystal substrates. Thetri-metallic precursor mixture thermal behaviour is assessed underworking conditions up to 130 °C and the impact of Dy-doping on thefilm morphology (FE-SEM), growth rate and structure (XRD and Ramanspectroscopy) is systematically reported and compared to theliterature. For Dy-doping with x ≤ 0.11, no change of symmetry hasbeen observed and all films show great homogeneity. Piezoresponseforce microscopy (PFM) and piezoresponse force spectroscopy (PFS)have been applied to investigate the ferroelectric andpiezoelectric properties of BiFeO3 and Bi(1−x)DyxFeO3 films.Ferroelectric and piezoelectric responses are good up to aDy-doping of 0.08 with a significant reduction of the opticalbandgap: 2.25 eV (for the highest doping at x = 0.11) compared to2.68 eV of pure BiFeO3 films

In situ metalation of free base phthalocyanine covalently bonded to silicon surfaces

Free 4-undecenoxyphthalocyanine molecules were covalently bonded to Si(100) and porous silicon through thermic hydrosilylation of the terminal double bonds of the undecenyl chains. The success of the anchoring strategy on both surfaces was demonstrated by the combination of X-ray photoelectron spectroscopy with control experiments performed adopting the commercially available 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine, which is not suited for silicon anchoring. Moreover, the study of the shape of the XPS N 1s band gave relevant information on the interactions occurring between the anchored molecules and the substrates. The spectra suggest that the phthalocyanine ring interacts significantly with the flat Si surface, whilst ring–surface interactions are less relevant on porous Si. The surface-bonded molecules were then metalated in situ with Co by using wet chemistry. The efficiency of the metalation process was evaluated by XPS measurements and, in particular, on porous silicon, the complexation of cobalt was confirmed by the disappearance in the FTIR spectra of the band at 3290 cm−1 due to –NH stretches. Finally, XPS results revealed that the different surface–phthalocyanine interactions observed for flat and porous substrates affect the efficiency of the in situ metalation process

Self‐Poled Heteroepitaxial Bi(1−x)DyxFeO3 Films with Promising Pyroelectric Properties

International audiencePyroelectric materials are very promising for thermal energy harvesting applications. To date, lead-based systems are the foremost studied materials in this field. A facile and simple metal organic chemical vapor deposition route is applied for the fabrication of lead-free, high quality, epitaxial Bi(1-x)DyxFeO3 (x= 0, 0.06, 0.08,0,11) thin films deposited on conductive SrTiO3:Nb (100) single crystal substrates. The films are studied by structural, morphological, compositional, and functional characterization. The correlation between the Dy-doping amount and the dielectric properties is thoroughlyinvestigated. Unipolar polarization–electric field loops and permittivity measurements show the important impact of Dy on ferroelectric, dielectric, and pyroelectric properties. Dy doping increases considerably the dielectric response, but much more thepyroelectric coefficient, up to a concentration of 8% Dy. The films are self-poled, which is an ideal situation for pyroelectric applications. The best figure of merit for pyroelectric energy harvesting, FE is 82 J/(m3K2), showing a factor increase of 2.6 as compared to the undoped film of the sample series. It constitutes a factor 4.5 improvement as compared to previous results obtained on BiFeO3 based thin films