Hydrogen permeation properties of CrxCy@Cr2O3/Al2O3 composite coating derived from selective oxidation of a CrC alloy and atomic layer deposition

Metal oxides and carbides are promising tritium permeation barrier coatings for fusion reactors. However, the thermomechanical mismatch between the coating and substrate poses a threat to their interface's integrity during fabrication and operation. To address this issue, a metallic interlayer coating was introduced followed by selective oxidation in which a compact and uniform CrC amorphous alloy coating was successfully deposited on the stainless steel substrate by pulsed electrochemical deposition. A new composite coating of Cr_xC_y@Cr₂O₃/Al₂O₃ was formed by subsequent controlled oxidation conversion and atomic layer deposition. The phase, morphology, chemical state and defects of the films were analyzed and compared both before and after hydrogen exposure at 300 °C. The results show that this new kind of composite coating, based on the principles of grain boundary pinning of chromic oxide with carbide and defect healing of alumina, can remarkably improve the hydrogen permeation barrier performance of these materials.     

Atomic layer deposited thin film metal oxides for fuel production in a solar cavity reactor

Alumina thin film structures were produced by coating high surface area polymer particles via atomic layer deposition (ALD), using the polymer as a sacrificial template. Burnout of the polymer material left high surface area, high pore volume structures, with 15 nm wall thickness. Further deposition of up to 27 mol% Co and Fe was performed via ALD to produce high surface area CoFe₂O₄ particles for thermochemical water splitting. The ALD particles were thermally cycled in electrically heated lab reactors and on-sun using a concentrated solar, reflective cavity reactor. Surface area measurements of cycled ALD particles showed improved surface area retention as compared to bulk Fe₂O₃ nanopowders. Reaction rates as high as 15.2 and 9.8 μmol/s/g were observed, on-sun, for H₂O and CO₂ splitting respectively. Thermochemical cycling in a concentrated solar cavity reactor showed an order of magnitude increase in solar utilization efficiency between ALD particles and bulk Fe₂O₃ nanopowders.     

Proton incorporation in yttria-stabilized zirconia during atomic layer deposition

This work elucidated the proton-incorporation mechanism in ALD YSZ¹. Isotope ²H₂O was used as an oxidant to trace proton incorporation. The ratio of ZrO₂ to Y₂O₃ ALD cycles was varied from 1:1 to 5:1. TEM confirmed that the ALD YSZ films grew as fully crystallized columnar grains in the cubic ZrO₂ phase. SIMS indicated that the Y³⁺ and ²H⁺ concentrations were linearly correlated, indicating yttria-deposition-induced proton incorporation. XPS confirmed an appreciable amount of Y(OH)₃ proportional to the ²H⁺ content in the ALD YSZ, as was also detected by SIMS. Oxide ion vacancies created by the replacement of ZrO₂ with relatively small amounts of Y₂O₃ provided additional vacancies for proton incorporation, resulting in steeper [²H⁺]/[Y³⁺] slopes.     

Ru-decorated Pt nanoparticles on N-doped multi-walled carbon nanotubes by atomic layer deposition for direct methanol fuel cells

We present atomic layer deposition (ALD) as a new method for the preparation of highly dispersed Ru-decorated Pt nanoparticles for use as catalyst in direct methanol fuel cells (DMFCs). The nanoparticles were deposited onto N-doped multi-walled carbon nanotubes (MWCNTs) at 250 °C using trimethyl(methylcyclopentadienyl)platinum MeCpPtMe₃, bis(ethylcyclopentadienyl)ruthenium Ru(EtCp)₂ and O₂ as the precursors. Catalysts with 5, 10 and 20 ALD Ru cycles grown onto the CNT-supported ALD Pt nanoparticles (150 cycles) were prepared and tested towards the electro-oxidation of CO and methanol, using cyclic voltammetry and chronoamperometry in a three-electrode electrochemical set-up. The catalyst decorated with 5 ALD Ru cycles was of highest activity in both reactions, followed by the ones with 10 and 20 ALD Ru cycles. It is demonstrated that ALD is a promising technique in the field of catalysis as highly dispersed nanoparticles of controlled size and composition can be deposited, with up-scaling prospects.     

Application of dense nano-thin platinum films for low-temperature solid oxide fuel cells by atomic layer deposition

Nano-thin platinum (Pt) films with a dense microstructure for low-temperature solid oxide fuel cells (LT-SOFCs) were fabricated by atomic layer deposition (ALD) and were characterized in terms of their micro-structural properties and electrochemical performance. Pt thin films with a purity level of ∼99% were achieved by controlling the O₂ pulsing time. The agglomeration behavior of the ALD Pt thin films was characterized by the annealing temperature, becoming extremely severe above 550 °C. An LT-SOFC with a 25 nm thick dense ALD Pt cathode layer exhibited a peak power density of ∼110 mW/cm² at 450 °C.     

High stability and activity of Pt electrocatalyst on atomic layer deposited metal oxide/nitrogen-doped graphene hybrid support

A novel nanostructured support of ZrO₂/nitrogen-doped graphene nanosheets (ZrO₂/NGNs) hybrid was synthesized successfully by atomic layer deposition (ALD) technology to significantly improve the activity and stability of Pt electrocatalyst. Electrochemical test shows that Pt–ZrO₂/NGNs catalyst has 2.1 times higher activity towards methanol oxidation reaction (MOR) than Pt/NGNs catalyst, due to the promotion by ZrO₂ to the MOR on Pt surface. Pt–ZrO₂/NGNs catalyst has higher electrochemical surface area (ECSA) and better oxygen reduction reaction (ORR) activity than Pt/NGNs catalyst. Pt–ZrO₂/NGNs catalyst has also demonstrated 2.2 times higher durability than that of Pt/NGNs. The enhanced activity and durability were attributed to the unique triple-interaction of ZrO₂–Pt–NGNs. These findings indicate that metal oxide-metal-support is a promising catalyst structure for low temperature fuel cells.     

Pt nanoparticles sputter-deposited on TiO2/MWCNT composites prepared by atomic layer deposition: Improved electrocatalytic activity towards the oxygen reduction reaction and durability in acid media

Acid-treated multi-walled carbon nanotubes (MWCNTs) were decorated with TiO₂ using the atomic layer deposition (ALD) technique followed by uniform distribution of platinum nanoparticles (PtNPs) through magnetron sputtering. Surface analyses were performed by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical decontamination and characterization of the Pt-TiO₂/MWCNT electrodes were carried out by CO stripping followed by cyclic voltammetry in acid media. The oxygen reduction reaction (ORR) was studied in O₂-saturated 0.05 M H₂SO₄ solution using the rotating disk electrode (RDE) method. Durability of the prepared catalysts was examined by repetitive potential cycling. Electrochemical data obtained was analyzed and compared to that of the commercial Pt/C catalyst. It was revealed that the Pt-TiO₂/MWCNT catalysts possess higher ORR activity and better durability as compared to that of the commercial Pt/C.     

Atomic layer deposition of Pt nanocatalysts on graphene oxide nanosheets for electro-oxidation of formic acid

This study describes an atomic layer deposition (ALD) approach for the fabrication of Pt nanocatalysts supported on graphene oxide (GO) sheets and their electrocatalytic performance in electro-oxidation of formic acid. The ALD process for forming the Pt atomic layer involves two self-limiting reactions and, thus, induces the decoration of ALD-Pt on the edges of GO sheets with the presence of dangling bonds and oxygen functionalities. The resultant ALD-Pt catalyst on GO sheets offers better catalytic activity, CO tolerance, and long-term stability than those on commercial carbon support. On the basis of the results, the ALD approach described here can be applied to the design of novel catalytic materials for a variety of energy-storage applications, for example, high-performance fuel cells.     

Improved performance of Cu(In,Ga)Se2-based submodules with a stacked structure of ZnO window prepared by sputtering

In this study, performance improvement of CIGS-based submodules using a sputtered ZnO:5.7 wt% Ga₂O₃ (5.7GZO) as window layers is reported. Preheating treatment at 200°C for 15 min is applied to the parts before the deposition of GZO window layers. This contributes to increase the optical transparency (%T) of GZO window considering the %T of about +5% and to improve the J_sc of about +4 mA/cm². Deposition of a high-resistivity, intrinsic ZnO (i-ZnO) thin layer on the Zn(O,S,OH)_x buffer layer before 5.7GZO window deposition contributes to improve the properties of pn hetero-junction quality and increase the optical transparency, V_oc and FF.