Rh Films Research Articles

Hydrogen adsorption study on nanostructured Ag–Rh films grown by supersonic cluster beam deposition

Following recent literature work, an interesting result on hydrogen sorption by Ag–Rh clusters was reported which do not follow the common understanding of hydrogen absorption in bulk alloys. Thus, nanostructured Ag–Rh films with a composition of 75% Ag–25% Rh were grown by supersonic cluster beam deposition onto microbalance quartz crystals in order to measure hydrogen absorption. The films were exposed to H2 gas to study hydrogen absorption at different partial pressure. The Ag–Rh films were then characterized by XPS and AFM. The Ag/Rh atomic ratio was found to be 75/25 by XPS. Surface roughness was determined by AFM to be 3 nm RMS in all the films. In disagreement with the quoted literature report, no hydrogen absorption was observed in our Ag–Rh films up to 5.3×103Pa of hydrogen pressure. The response of the balance was checked and validated by measuring hydrogen absorption on 10 and 100 nm Pd films. The hydrogen absorption by Pd yielded an atomic H/Pd ratio of ∼0.65 in agreement with our prior measurements.

Compression‐molded soy protein concentrate film incorporated with natural antioxidant: Storage stability and their effectiveness to improve the quality of fish products during refrigeration

The aim of the present research was to investigate aging stability of compression-molded soy protein concentrate (SPC) film activated with red grape extract (RGE) (10%w/w SPC) and its effect as a food packaging material under refrigerated conditions. After 90 days at 25 ± 2°C and 65 ± 2% RH, control and active SPC films, kept unchanged transparency and color parameters, visual appearance, and water vapor permeability. Tensile properties varied significantly over time due to physical and chemical aging. The in vitro antioxidant activity of films dropped with time, remaining high after 90 days. SPC active film delayed bacterial growth and preserved mackerel chunks color parameters during storage. Samples packed with active SPC films received similar scores by a sensory panel to those packed with polyethylene, up to 15th d. The results demonstrated the potential of SPC-based films as bio-based alternatives for enhancing the quality of fish products during refrigeration storage. Practical applications The combined film obtained by adding RGE to the SPC formulation turned out to an effective packaging for food preservation. Our results open new perspectives to SPC-RGE films as innovative environmentally safe packaging that can effectively delay the lipid oxidation and microbial growth in fish products, prolonging the shelf life and contributing to reduce the food spoilage and waste.

Noble metal alloy thin films by atomic layer deposition and rapid Joule heating

Metal alloys are usually fabricated by melting constituent metals together or sintering metal alloy particles made by high energy ball milling (mechanical alloying). All these methods only allow for bulk alloys to be formed. This manuscript details a new method of fabricating Rhodium–Iridium (Rh–Ir) metal alloy films using atomic layer deposition (ALD) and rapid Joule heating induced alloying that gives functional thin film alloys, enabling conformal thin films with high aspect ratios on 3D nanostructured substrate. In this work, ALD was used to deposit Rh thin film on an Al2O3 substrate, followed by an Ir overlayer on top of the Rh film. The multilayered structure was then alloyed/sintered using rapid Joule heating. We can precisely control the thickness of the resultant alloy films down to the atomic scale. The Rh–Ir alloy thin films were characterized using scanning and transmission electron microscopy (SEM/TEM) and energy dispersive spectroscopy (EDS) to study their microstructural characteristics which showed the morphology difference before and after rapid Joule heating and confirmed the interdiffusion between Rh and Ir during rapid Joule heating. The diffraction peak shift was observed by Grazing-incidence X-ray diffraction (GIXRD) indicating the formation of Rh–Ir thin film alloys after rapid Joule heating. X-ray photoelectron spectroscopy (XPS) was also carried out and implied the formation of Rh–Ir alloy. Molecular dynamics simulation experiments of Rh–Ir alloys using Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) were performed to elucidate the alloying mechanism during the rapid heating process, corroborating the experimental results.

Polyaniline-coated mesoporous Rh films for nonacidic hydrogen evolution reaction

Hydrogen evolution reaction (HER) from water electrolysis in alkaline and neutral media provides a possibility to produce pure hydrogen fuel on a large scale. Therefore, the exploration of highly efficient non-Pt HER electrocatalysts is of great significance. Herein, polyaniline (PANI)-coated mesoporous Rh film on Ni foam is controllably fabricated by a micelle-assisted replacement reaction and the subsequent surface modification. Profiting from the synergetic effect of interconnected mesoporous structure, high electrical conductivity of PANI and the modified electronic structure of Rh, the synthesized mRh@PANI film exhibits superior HER electrocatalytic activity and durability in alkaline and neutral electrolytes. To reach a current density of 50 mA cm−2, low overpotentials of 37 and 69 mV are required in 1 M KOH and 1 M PBS solutions, respectively.

Boosting electrochemical nitrogen fixation by mesoporous Rh film with boron and sulfur co-doping

Electrochemical nitrogen reduction reaction (NRR) has been regarded as one of the most promising alternative strategies for nitrogen fixation, and the design of efficient NRR catalysts is the critical factor. Herein, boron and sulfur co-doped mesoporous Rh film on Ni foam (B, S-mRh/NF) is developed for electrochemical ammonia synthesis. The boron and sulfur co-doping, the B, S-mRh/NF, can inhibit competitive hydrogen evolution reaction effectively. Owing to binder-free mesoporous structures, binder-free characteristic, and multicomponent alloy, the B, S-mRh/NF displays a high NH3 yield of 11.88 μg/h/cm2 at −0.1 V and Faraday efficiency of 38.42% at −0.05 V in neutral electrolyte. This work offers an effective strategy for the rational design of nonmetal-doped porous Rh electrocatalysts with self-supported structure, which would be highly potential for the electrochemical ammonia synthesis.

Atomic layer deposition of rhodium and palladium thin film using low-concentration ozone.

Rhodium (Rh) and palladium (Pd) thin films have been fabricated using an atomic layer deposition (ALD) process using Rh(acac)3 and Pd(hfac)2 as the respective precursors and using short-pulse low-concentration ozone as the co-reactant. This method of fabrication does away with the need for combustible reactants such as hydrogen or oxygen, either as a precursor or as an annealing agent. All previous studies using only ozone could not yield metallic films, and required post treatment using hydrogen or oxygen. In this work, it was discovered that the concentration level of ozone used in the ALD process was critical in determining whether the pure metal film was formed, and whether the metal film was oxidized. By controlling the ozone concentration under a critical limit, the fabrication of these noble metal films was successful. Rhodium thin films were deposited between 200 and 220 °C, whereas palladium thin films were deposited between 180 and 220 °C. A precisely controlled low ozone concentration of 1.22 g m−3 was applied to prevent the oxidation of the noble metallic film, and to ensure fast growth rates of 0.42 Å per cycle for Rh, and 0.22 Å per cycle for Pd. When low-concentration ozone was applied to react with ligand, no excess ozone was available to oxidize the metal products. The surfaces of deposited films obtained the RMS roughness values of 0.30 nm for Rh and 0.13 nm for Pd films. The resistivities of 18 nm Rh and 22 nm Pd thin films were 17 μΩ cm and 63 μΩ cm.

On the Promotion of Catalytic Reactions by Surface Acoustic Waves.

Surface acoustic waves (SAW) allow to manipulate surfaces with potential applications in catalysis, sensor and nanotechnology. SAWs were shown to cause a strong increase in catalytic activity and selectivity in many oxidation and decomposition reactions on metallic and oxidic catalysts. However, the promotion mechanism has not been unambiguously identified. Using stroboscopic X‐ray photoelectron spectro‐microscopy, we were able to evidence a sub‐nanosecond work function change during propagation of 500 MHz SAWs on a 9 nm thick platinum film. We quantify the work function change to 455 μeV. Such a small variation rules out that electronic effects due to elastic deformation (strain) play a major role in the SAW‐induced promotion of catalysis. In a second set of experiments, SAW‐induced intermixing of a five monolayers thick Rh film on top of polycrystalline platinum was demonstrated to be due to enhanced thermal diffusion caused by an increase of the surface temperature by about 75 K when SAWs were excited. Reversible surface structural changes are suggested to be a major cause for catalytic promotion.

Study on the influence of the thickness of nanostructured rhodium films toward electrooxidation of adsorbed carbon monoxide

Carbon-supported rhodium thin films with various thicknesses are grown by varying the number of laser pulses, Nlp (from 5000 to 50,000) under 2 Torr of He background atmosphere using the pulsed laser deposition method. The thin films are characterized for their morphological features and structural properties. It is observed that smooth dense 2D nanosheets of Rh are obtained with 5000 Nlp, whereas higher Nlp yields to highly porous Rh films. X-ray photoelectron spectroscopy reveals that both metallic Rh and Rh3+ are present at the surface of the Rh films. Nevertheless, the amount of metallic Rh increased as the Nlp increased. The influence of the thickness of the Rh films on the tolerance to CO, a poison that strongly adsorbs on the surface of catalysts in fuel cells reactions, was investigated through anodic stripping voltammetry. It is found that Rh film deposited with 50,000 Nlp exhibits the highest electroactive surface area (27.90 cm2 vs. 1.20 cm2 of Pt), the lowest onset potential of CO electrooxidation (0.47 V vs. 0.60 V Pt), and a net charge corresponding to electrooxidation of the CO adlayer of 424 μC cm−2 (vs. 358 μC cm−2 of Pt). Such high tolerance to CO poisoning is explained on the basis of the elevated porosity and roughness of the Rh surface. Indeed, a roughness factor of 90.5 for Rh against about 3.8 for Pt grows under analogous deposition conditions of pressure and number of laser pulses.

Solid-state synthesis, magnetic and structural properties of interfacial B2-FeRh(001) layers in Rh/Fe(001) films

Here we first report results of the start of the solid-state reaction at the Rh/Fe(001) interface and the structural and magnetic phase transformations in 52Rh/48Fe(001), 45Rh/55Fe(001), 68Rh/32Fe(001) bilayers from room temperature to 800 °C. For all bilayers the non-magnetic nanocrystalline phase with a B2 structure (nfm-B2) is the first phase that is formed on the Rh/Fe(001) interface near 100 °C. Above 300 °C, without changing the nanocrystalline B2 structure, the phase grows into the low-magnetization modification αlʹ (MSl ~ 825 emu/cm3) of the ferromagnetic αʹ phase which has a reversible αlʹ ↔ αʺ transition. After annealing 52Rh/48Fe(001) bilayers above 600 °C the αlʹ phase increases in grain size and either develops into αhʹ with high magnetization (MSh ~ 1,220 emu/cm3) or remains in the αlʹ phase. In contrast to αlʹ, the αhʹ ↔ αʺ transition in the αhʹ films is completely suppressed. When the annealing temperature of the 45Rh/55Fe(001) samples is increased from 450 to 800 °C the low-magnetization nanocrystalline αlʹ films develop into high crystalline perfection epitaxial αhʹ(001) layers, which have a high magnetization of ~ 1,275 emu/cm3. αhʹ(001) films do not undergo a transition to an antiferromagnetic αʺ phase. In 68Rh/32Fe(001) samples above 500 °C non-magnetic epitaxial γ(001) layers grow on the Fe(001) interface as a result of the solid-state reaction between the epitaxial αlʹ(001) and polycrystalline Rh films. Our results demonstrate not only the complex nature of chemical interactions at the low-temperature synthesis of the nfm-B2 and αlʹ phases in Rh/Fe(001) bilayers, but also establish their continuous link with chemical mechanisms underlying reversible αlʹ ↔ αʺ transitions.

Enhancing catalytic activity of rhodium towards methanol electro-oxidation in both acidic and alkaline media by alloying with iron

The methanol electrooxidation catalysts in the form of Rh and FeRh thin films were prepared by magnetron sputtering deposition. To activate the FeRh catalyst, the as-prepared FeRh films were cycled in 0.1 M HClO4 electrolyte in potential window from −0.25 V to 0.8 V (vs. Ag/AgCl). The dissolution of Fe atoms during the cycling leads to the formation of Rh-skeleton surface. Obtained FeRh catalysts exhibit significantly enhanced activity to methanol electrooxidation in both acidic and alkaline environments comparing to pure Rh catalyst. The optimal concentration of Fe is found to be 50%. Electrochemical impedance spectroscopy investigations show the higher rate of methanol dehydrogenation as well as better tolerance to CO intermediates poisoning of the FeRh catalysts. This study demonstrates that Rh-based catalysts can be considered as alternative to Pt-based catalysts.

The influence of current density and bath temperature on electrodeposition of rhodium film from sulfate–phosphate aqueous solutions

Rhodium films were electrodeposited galvanostatically on copper–zinc alloy substrates from sulfate–phosphate aqueous solutions, in order to obtain a smooth, dense, and thick Rh film for electrical contacts. The influence of current density and bath temperature on phases, crystal structure, microstructure, and deposition rate of the film was studied. The phases and crystal structure, as well as microstructure of the film were determined by X-ray diffraction and scanning electron microscopy, respectively. The results showed that the current density and bath temperature had a significant influence on electrodeposition of rhodium film. The particles or aggregates on the surface evolved from fine to coarse and large with the increase of current density and bath temperature. By adjusting the deposition conditions, the optimized current density and bath temperature were 6.4–12.7 mA cm−2 and 50 °C, respectively. The film was composed of polycrystalline phase with monometallic form. The film was uniform and dense at low current density. The thickness of the film was up to 1.38–2.1 μm. At the optimal temperature of 50 °C, the surface of the film was smooth and fine. At the same time, the electrodeposition mechanism of the film was discussed. Rhodium films were electrodeposited from sulfate–phosphate aqueous solutions. The influence of current density and bath temperature on electrodeposition of the film was studied, and at the same time, the electrodeposition mechanism of the film was addressed.

Estimating the Interrelation between the Rate of Atomic Layer Deposition of Thin Platinum-Group Metal Films and the Molecular Mass of Reactant Precursors

The published data on the atomic layer deposition of thin platinum-group metal (Ru, Rh, Pd, Os, Ir, and Pt) films with the use of different reactant precursors and second reactants (O2, O3, H2, etc.) are generalized in the context of microelectronic technologies. A procedure for analyzing the data on the atomic layer deposition kinetics is discussed. The rate of atomic layer deposition of metallic ruthenium is not higher than 0.15 nm/cycle. An inverse dependence of the limiting atomic layer deposition growth rate on the precursor molecular mass is established. The rates of atomic layer deposition of thin films of all the remaining metals in the group range between 0.03–0.07 nm/cycle, which is lower than the values for a monolayer of these metals by several times. The methodology and ways of enhancing the reliability of the kinetic data on the atomic layer deposition are discussed, including the need for taking into account the sample surface types and effects of nucleation delays at the initial growth stages of the thin platinum-group metal film. The possible occurrence of chemical deposition reactions with intermediate products involved at the pulsed injection of the reactants is considered.

A Spectroscopic Study on the Electrochemical Nitrogen and Nitrate Reduction Reactions on Rhodium and Ruthenium Surfaces

Ammonia is one of the most promising carbon-free alternative energy storage media for several reasons, including its high weight fraction of hydrogen (17.65%), ease of decomposition to produce high-purity hydrogen, ease of liquefaction at room temperature, and low transportation cost.1 The N2 reduction reaction (NRR) is an attractive approach to synthesizing ammonia with renewable electrical energy by using water and nitrogen as the reactants.2-3 Rh and Ru are promising N2 reduction reaction electrocatalysts, given their suitable nitrogen adsorption energy and low overpotential. However, the N2 reduction reaction pathway on these surfaces is still unclear, as there is a lack of information about the reaction intermediates. In this study, we employed surface-enhanced infrared absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanisms of nitrogen reduction on Rh and Ru. A Rh nanofilm deposited on the Si prism by a chemical deposition method was used as the working electrode. Figure 1a shows the IR spectra collected in the first CV segment in N2-saturated KOH solution with the spectrum at 0.4 V as the reference. The bands at 3250 and 1612 cm-1 attribute to the O-H stretching and H-O-H bending of water molecules. Those bands intensity increase significantly as a result of the change in the adsorption configuration of water molecules upon decreasing the potential. A weak band at 1865 cm−1 emerged below −0.2 V, and the band intensity increased as the potential became more negative, which was assigned to the adsorbed H atoms. An obvious band at ~2020 cm−1 was attributed to the N=N stretching of end-on adsorbed N2HX (1≤X≤2) on the Rh surface. These bands were clearly revealed in a single spectrum at 0 and −0.4 V, shown in Figure 1b. The potential dependence of the N=N stretching band absorption and frequency are given in Figure 1c, as well as the IR absorption potential dependence of hydrogen on the Rh surface. When the potential fell from 0.2 V to −0.05 V, the band intensity of N2HX was significantly enhanced, peaking at −0.05 V, which suggested that the coverage of the adsorbed N2HX species on the Rh surface was boosted in this potential range. Simultaneously, the frequency of the N=N stretching band was blue-shifted from 1997 cm−1 at 0.2 V to 2034 cm−1 at −0.05 V, due to the weakened adsorption strength of the N2HX species on the Rh surface. The highest N2HX coverage was achieved between 0 and −0.2 V. When the potential further decreased from −0.2 to −0.4 V, the N=N stretching band intensity decreased, indicating less coverage of the adsorbed N2HX species. Figure 1d presents the DEMS data collected during the NRR in an alkaline electrolyte with Rh/C as the electrocatalyst. As occurred during nitrate reduction, the pulse DEMS signal of H2 (m/e = 2) was detected at potentials below 0 V as the HER occurred on the Rh surface. The pulse DEMS signal of N2H2 (m/e = 29) was also detected with H2, but its intensity was much lower than that of H2 (m/e=2), and the signal of N2H2 (m/e = 30) was undetectable. Similar spectroscopic studies on Ru surface will be also discussed. Figure 1. (a) FTIR spectra during the first segment from 0.4 to −0.4 V on Rh film electrode in N2-saturated 0.1 M KOH solution. The reference spectrum was taken at 0.4 V. (b) Single spectrum at 0 V (black line) and −0.4 V (red line) in the range of 1250−3000 cm−1. (c) Potential dependence of the N=N stretching band IR absorption (black dot) and frequency (red triangle), derived from (a). The potential dependence of the hydrogen IR absorption magnified by a factor of two (pink dot) is also given. (d) DEMS of H2 (m/e = 2) and N2H2 (m/e = 29, 30) on Rh/C during a scan from 0.4 to −0.8 V in N2-saturated 1 M KOH solution. Potential scan rate: 5 mV s−1. References Lipman, T.; Shah, N., Ammonia as an Alternative Energy Storage Medium for Hydrogen Fuel Cells: Scientific and Technical Review for Near-Term Stationary Power Demonstration Projects, Final Report. UC Berkeley Transportation Sustainability Research Center 2007.Giddey, S.; Badwal, S. P. S.; Kulkarni, A., Int. J. Hydrogen. Energ. 2013, 38, 14576-14594.Guo, C. X.; Vasileff, A.; Qiao, S., Energ. Environ. Sci. 2017. Figure 1

The observation of inherent spin Seebeck effect in Rh/YIG hybrid structure

Rhodium (Rh) is a 4d metal possessing a large spin orbit coupling strength and spin-Hall conductivity with a very small magnetic susceptibility, implying an insignificant magnetic proximity effect (MPE). We report here the observation of longitudinal spin Seebeck effect (LSSE) using Rh as a normal metal. A Rh film was sputtered on nanometer thick YIG films of highly crystalline nature and extremely low magnetic damping to obtain Rh/YIG hybrid structure. A clear thermal voltage Vth (SSE voltage) was obtained when a temperature gradient was applied on the Rh/YIG hybrid. The Rh film showed a very weak anomalous Hall resistance and the magneto-resistive testing clearly ruled out the magnetization of the Rh films via MPE. The anisotropic magnetoresistance (AMR) revealed a clear spin hall magnetoresistance (SMR) signal in Rh film implying a purely intrinsic spin current generation, free from any parasitic magnetic effects. The work can open a new window in the study of pure and uncontaminated spin current, generated in ferromagnetic insulators, using Rh as spin current detector.

A comparative study on TWC reactions over Rh thin films and supported Rh nanoparticles under lean conditions

On a FeCrAl metal foils honeycomb fully-covered by 7 nm-thick Rh film (Rh/SUS), the stoichiometric NOCOC3H6O2H2CO2H2O reaction exhibited high turnover frequencies (TOF) more than 25-fold greater compared with those for a reference supported Rh nanoparticle catalysts (Rh/ZrO2), which were coated on a cordierite honeycomb substrate using a conventional slurry coating. As a result, these two types of honeycombs showed comparable catalyst performance at the stoichiometric air-to-fuel ratios (A/F). The Rh/SUS significantly improved the NO conversion to N2 under lean conditions (14.60 < A/F ≤ 15.10) as compared with Rh/ZrO2. Most of the metallic Rh surface of Rh/SUS remained unchanged compared with Rh/ZrO2 when the atmosphere was changed from stoichiometric (A/F = 14.6) to lean (A/F > 14.6), where oxidized Rh should be thermodynamically stable. Metallic Rh formed on Rh/SUS was gradually oxidized on exposure to excess O2, whereas Rh on ZrO2 was readily oxidized to less-active Rh2O3. The resistance of metallic Rh against oxidation is considered to be a possible reason for the enhanced NO conversion efficiency under lean conditions.

Investigation of Gilbert damping of a tetragonally distorted ultrathin Fe0.5Co0.5 epitaxial film with high magnetic anisotropy

We have investigated the Gilbert damping, α, of a tetragonally distorted, perpendicular magnetic anisotropic (PMA) ultrathin Fe0.5Co0.5 film grown on a Rh-buffered MgO(100) substrate fabricated by magnetron sputtering at room temperature by means of the time-resolved magneto-optical Kerr effect. We obtained the highest PMA value of 0.573 MJ/m3 ever reported for the Fe0.5Co0.5/Rh film. The PMA strongly depends on the lattice distortion which originates from the epitaxial growth in the large lattice misfit system of Fe0.5Co0.5 and Rh. We have estimated an unusually high value of α = 0.041 ± 0.002 for a 1 nm thick Fe0.5Co0.5 film. Based on the microstructural observation and the first-principles calculation, we conclude that the large α in the ultrathin Fe0.5Co0.5 film comes from the minority-spin electron transition around the Fermi level mediated by the spin-orbit interaction, which is caused by the large lattice distortion.

The promotion of CO dissociation by molybdenum oxide overlayers on rhodium

A considerable promotional effect of MoOx species observed at high pressures on the catalytic activity of rhodium initiated the present UHV model study. The MoOx overlayers formed on Rh films (0.15–20.0ML) supported by TiO2(110) substrate were characterized by AES, TPD, work function (WF) measurements and CO adsorption. On the mixed oxide support produced by depositing 1.2ML Mo onto TiO2(110), a new recombinative CO desorption state was observed with Tp=700K, assigned as β-CO and related to the promotional effect of MoOx species diffused onto Rh particles of 1.0ML coverage. The development of β-CO needs 0.5–0.7ML threshold Rh coverage, attributable to particle size effect and geometric factors governing the CO adsorption. The β-CO state with Tp=725–742K could also be detected on Rh films covered by MoOx moiety formed by the oxidation of Mo overlayers in O2. Remarkably, recombinative CO desorption with Tp=700K could be observed on the Rh nanoparticles covered by MoOzCy produced from pure Mo deposits by CO adsorption, too. In harmony with the promotional effect of MoOx overlayer found at high pressures, it is established that the dissociation of CO is maximal at 0.2–0.3ML Mo coverage, attributed to the presence of active sites at the oxide-metal interface. The low desorption peak temperature (700K) of associative CO desorption observed in the presence of MoOx and MoOzCy overlayers indicates a low activation energy for the reactions of Oa and Ca atoms, allowing high reaction rates for these intermediates. The MoOx species exerted both promotion and inhibition effects on CO adsorption at sub-monolayer coverages, but above 1ML it completely suppressed the reactivity of rhodium layers towards CO, suggesting that its surface concentration is a critical factor.

ATR-SEIRAS study of formic acid adsorption and oxidation on Rh modified Au(111–25 nm) film electrodes in 0.1 M H2SO4

Rh modified Au(111–25nm) film electrodes prepared by electron beam evaporation and galvanostatic deposition were employed to study adsorption and electro-oxidation of formic acid (HCOOH) in 0.1M sulfuric acid solution using in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). When HCOOH was introduced at the hydrogen adsorption potential range, CO was formed and adsorbed in atop (COL) and bridge (COB) configurations, co-adsorbing with water molecules. Formation of formate together with COL and COB was detected when HCOOH was introduced at 0.30V, while only formate was observed at 0.55V. The HCOOH oxidation on Rh film electrode in acidic media is significantly affected by the surface oxides and adsorbed CO and proceeds, not excluding a possible direct oxidation of HCOOH to CO2, via two indirect oxidation pathways involving dissociative adsorption of HCOOH with the formation of main reactive intermediate formate and mostly blocking CO intermediate.

(Invited) Observing Photochemical Charge Transport at Particle Based Tandem Junctions for Overall Water Splitting

Photochemical charge generation, separation, and transport across particle interfaces are central to photoelectrochemical water splitting, a pathway to hydrogen from solar energy. Here we use surface photovoltage spectroscopy (SPS) to probe these processes in films of BiVO4 and Rh:SrTiO3 particles on fluorine doped tin oxide (FTO) or p-doped silicon wafers. Particle films were made by drop-coating of premade particle suspensions in water followed by thermal annealing. Photochemical charge separation in the films was measured as a function of layer thickness and illumination intensity, and in the presence of sacrificial electron donors. The formation of Tandem junctions is clearly observed and to result in a maximum photovoltage of up to -150 mV under 0.3 mW cm-2 illumination. Charge separation is limited by light absorption and by slow electron transport. Overall Water Splitting with visible light an a quantum efficiency of 0.61% at 400 nm was observed with a direct contract tandem photocatalysts made of ruthenium-loaded Rh:SrTiO3 nanocrystals and of BiVO4 microcrystals. The activity and stability of this system depends on the temperature employed for generating the tandem junction. The ability to measure the built-in potential in particle junctions promotes the development of particle-based systems for artificial photosynthesis. Figure 1

ITER first mirror mock-ups exposed in Magnum-PSI

The goal of this work was to investigate coated first mirrors under very harsh erosion conditions. Mock-up mirrors were exposed to high-flux hydrogen/argon plasma in the linear plasma facility Magnum-PSI. Rhodium (Rh) and molybdenum (Mo) coated mirrors of different coating thicknesses, with or without water cooling, exhibited different responses to this exposure. Failures of Rh films were demonstrated for 5 micron thick film, 1 micron film revealed 10% decrease in the specular reflectivity only in the exposed area. In comparison, water cooled Mo mock-ups showed a significant diffuse reflectivity on the entire surface leading to more than 50% specular reflectivity losses in the visible range. The losses for non-cooled Mo samples did not exceed 7% in the whole studied wavelength range of 250–2500 nm. Three phenomena were proposed to explain these results. First the mechanical properties of the films as characterized by scratch and hardness measurements as well as residual stress analysis measured by x-ray diffraction. Rh films showed a high compressive stress value of 2.5 ± 0.4 GPa leading to poor adhesion of the thick films deposited on stainless steel substrate due to the high amount of available energy per area stored in the unbuckled film i.e. J m−2. It was confirmed by ANSYS simulation that the von Mises stress for the Rh coating was twice as high as that for the Mo coating due to different mechanical properties. Moreover, the maximum stress for thick Rh film (261 MPa) was higher than the critical buckling stress calculated with a buckle clamped Euler column model demonstrating the failure mode of the film. The second phenomenon was roughening of the mirror surface which was flux and temperature dependent, i.e. at low temperatures the surface would roughen randomly without any oriented surface morphology and at higher temperatures the surface diffusion constants would dominate the process and smoothen the surface. The last phenomenon was the significant oxidation and carbidization of the Mo surface even on the non-exposed area, as detected by x-ray photoelectron spectroscopy, leading also to a decrease in the reflectivity in the entire measured range, which was not observed for Rh film.