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The ability to prepare controllable nanocatalysts is of great interest for many chemical industries. Atomic layer deposition (ALD) is a vapor phase technique enabling the synthesis of conformal thin films and nanoparticles (NPs) on high surface area supports and has become an attractive new route to tailor supported metallic NPs. Virtually all the studies reported, focused on Pd NPs deposited on carbon and oxide surfaces. It is, however, important to focus on emerging catalyst supports such as boron nitride materials, which apart from possessing high thermal and chemical stability, also hold great promises for nanocatalysis applications. Herein, the synthesis of Pd NPs on boron nitride (BN) film substrates is demonstrated entirely by ALD for the first time. X-ray photoelectron spectroscopy indicated that stoichiometric BN formed as the main phase, with a small amount of BNxOy, and that the Pd particles synthesized were metallic. Using extensive transmission electron microscopy analysis, we study the evolution of the highly dispersed NPs as a function of the number of ALD cycles, and the thermal stability of the ALD-prepared Pd/BN catalysts up to 750 °C. The growth and coalescence mechanisms observed are discussed and compared with Pd NPs grown on other surfaces. The results show that the nanostructures of the BN/Pd NPs were relatively stable up to 500 °C. Consequent merging has been observed when annealing the samples at 750 °C, as the NPs’ average diameter increased from 8.3 ± 1.2 nm to 31 ± 4 nm. The results presented open up exciting new opportunities in the field of catalysis.
A conductive SnO2 layer and small quantities of IrO2 surface cocatalyst enhance the catalytic efficiency of nanoporous Fe2O3 electrodes in the oxygen evolution reaction at neutral pH. Anodic alumina templates are therefore coated with thin layers of SnO2, Fe2O3, and IrO2 by atomic layer deposition. In the first step, the Fe2O3 electrode is modified with a conductive SnO2 layer and submitted to different postdeposition thermal treatments in order to maximize its catalytic performance. The combination of steady‐state electrolysis, electrochemical impedance spectroscopy, X‐ray crystallography, and X‐ray photoelectron spectroscopy demonstrates that catalytic turnover and e− extraction are most efficient if both layers are amorphous in nature. In the second step, small quantities of IrO2 with extremely low iridium loading of 7.5 µg cm−2 are coated on the electrode surface. These electrodes reveal favorable long‐term stability over at least 15 h and achieve maximized steady‐state current densities of 0.57 ± 0.05 mA cm−2 at η = 0.38 V and pH 7 (1.36 ± 0.10 mA cm−2 at η = 0.48 V) in dark conditions. This architecture enables charge carrier separation and reduces the photoelectrochemical water oxidation onset by 300 mV with respect to pure Fe2O3 electrodes of identical geometry.
We report a new and versatile colloidal route towards the synthesis of nanoalloys with controlled size and chemical composition in the solid solution phase (without such phases segregations as core-shell...
This work investigates the n-Si photoanodes corrosion protection by Atomic Layer Deposition (ALD) of a TiO 2 film. A specific electrochemical experimental sequence (including successive rest potential measurements and voltammetries under illumination or not) has been established to study the stability of the electrodes in KOH. Depending on the deposition conditions (precursor composition and temperature), the electrochemical properties of the layers are different. The photoanodes coated using titanium tetraisopropoxide (TTIP) at low temperature exhibit a low photocurrent (j ph ) that is progressively enhanced during the electrochemical sequence and their stability decreases. When using tetrakis(dimethylamido)titanium (TDMAT), the j ph is almost constant and the film prevents from corrosion. The characterizations show that the ALD parameters drive the microstructure of the layer that is found critical for the electrochemical response. A hydrogen doping occurring during the open circuit potential measurements under illumination is evidenced by IR spectroscopy. It is mainly localized at the grain boundaries and pores of the layers as well as in the n-Si and it modifies the charge transfer at the electrode/solution junction and the hydrogen diffusion weakens the film causing the Si corrosion. The different charge transfer mechanisms are finally proposed depending on the ALD conditions and the film thickness.
Iron oxide (rust) is an attractive contender as a water oxidation anode material due to its stability and abundance. The limitations associated with its low catalytic activity and electrical conductivity are overcome by combining it with tin oxide and iridium oxide in a nanoporous geometry. More details can be found in article number https://doi.org/10.1002/admi.201801432 by Sandra Haschke, Julien Bachmann, and co‐workers.
The sunlight’s intermittent nature is one of the issues limiting widespread harvesting of solar energy for power infrastructures. A leading approach is to store as chemical fuels the energy produced by this discontinuous renewable energy source. The development of photoelectrochemical cells (PECs) used to produce H2 and O2 from water photo-splitting has, therefore, attracted a great deal of interest. Nowadays, the efficiency of the photoelectrochemical cells (PEC) ranges from 12 to 18% depending on the materials and the type of cells (single- or multiple-junction) while the theoretical limit is 24.4 and 30% for tandem and multi-junction cells, respectively. High efficiency at a high cost has been shown from multi-junction cells but no sufficient improvements leading to a market compliant PEC have been reported yet. The photoelectrochemical technology remains at a low technology readiness level (TRL 1 to 2) and the main issue is the actual production cost of H2. To solve this question, it is mandatory to reduce significantly the costs and to increase the photoconversion efficiency. Many research groups are currently investigating different routes to fabricate PECs that could respond to the market demand. To improve efficiency, stability and price, one has, of course, to select a cost-effective photosensitive materials and the appropriate cell design. It has been recently shown that micro- or nanostructuring and/or surface functionalization of the photoelectrodes can lead to higher performances. Among the numerous approaches and techniques that have been used since nanosciences and nanotechnologies have emerged, atomic layer deposition (ALD) has recently demonstrated its high effectiveness to fabricate both two- and three-dimensional (2D, 3D) nano-objects. Energy storage and production are part of the fields of applications in which ALD has shown highly promising perspectives. It will be shown in this presentation that, during the last five years, ALD has been effectively integrated in various fabrication strategies of photoelectrodes. After a brief introduction on the various methods of surface micro- and nanostructuring methods, a short description of the ALD process will be presented. The goal of this presentation is to report the different types of uses of ALD in the field of solar fuel production: active materials, surface state passivation and corrosion protection. A special attention will be drawn on the recent results obtained in our laboratory where a rapid, inexpensive two-step method for structuring n-type (100) Si surfaces with micron-sized cavities, the process is based on the photoelectrochemical etching (PEE) of the Si surface and its subsequent alkaline etching. This method produces a layer of random macropores over a large area, which renders the Si surfaces antireflective over the visible spectrum. We demonstrate that such surfaces can be conformably coated by anatase TiO2 layers by atomic layer deposition (ALD) and that they can be used as stable photoanodes producing enhanced photocurrents under simulated sunlight with respect to their planar counterparts. These TiO2-protected Si microstructured surfaces were highly stable in strongly alkaline solutions and were used as photoanode for several hours under simulated sunlight. Such photoanodes surfaces showed 50 % photocurrent enhancements and ~400 mV negative shift of onset potential without any co-catalysts, demonstrating their high potential for solar energy conversion applications [3]. [1] N. S. Lewis and D. G. Nocera, Proc. Natl. Acad. Sci. 103, 15729 (2006). [2] A. Fujishima and K. Honda, Nature 238, 37 (1972). [3] L. Santinacci, M. W. Diouf, M. K. S. Barr, B. Fabre, L. Joanny, F. Gouttefangeas, and G. Loget, ACS Appl. Mater. Interfaces, 8, 24810 (2016)
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