Clean Rhodium Research Articles

Clean rhodium nanoparticles prepared by laser ablation in liquid for high performance electrocatalysis of the hydrogen evolution reaction.

Rhodium nanoparticles (NPs) were prepared by a one-step, green and facile procedure consisting in laser ablation of a bulk Rh target immersed in pure water (W–Rh-NPs) or ethanol (E–Rh-NPs). When embedded in mesoporous carbon based inks, both W–Rh-NPs and E–Rh-NPs show excellent activity towards the hydrogen evolution reaction in acidic media, operating close to the thermodynamic potential with 85–97% faradaic yields and low Tafel slopes of 50–54 mV per decade in the low overpotential region (η < 20 mV). A superior activity of W–Rh-NPs with respect to E–Rh-NPs is ascribed to the absence of surface carbon reducible species derived from the synthesis in organic solvent, and thus confirms the importance of the use of water as the preferred medium for laser synthesis of clean nanocrystals in liquid environment. These results provide an important contribution to the impelling need for the preparation of nano-catalysts based on energy critical materials by clean, sustainable and low cost routes.

Water Production Reaction on Rh(110)

By means of scanning tunneling microscopy and density functional theory calculations, we studied the water formation reaction on the Rh(110) surface when exposing the (2 x 1)p2mg-O structure to molecular hydrogen, characterizing each of the structures that form on the surface during the reaction. First the reaction propagates on the surface as a wave front, removing half of the initial oxygen atoms. The remaining 0.5 monolayers of O atoms rearrange in pairs, forming a c(2 x 4) structure. Second, as the reaction proceeds, areas of an intermediate structure with c(2 x 2) symmetry appear and grow at the expense of the c(2 x 4) phase, involving all the oxygen atoms present on the surface. Afterward, the c(2 x 2) islands shrink, indicating that complete hydrogenation occurs at their edges, leaving behind a clean rhodium substrate. Two possible models for the c(2 x 2) structure, where not only the arrangement but also the chemical identity is different, are given. The first one is a mixed H + O structure, while the second one resembles the half-dissociated water layer already proposed on other metal surfaces. In both models, the high local oxygen coverage is achieved by the formation of a hexagonal network of hydrogen bonds.

Boron Nitride Nanomesh

A highly regular mesh of hexagonal boron nitride with a 3-nanometer periodicity and a 2-nanometer hole size was formed by self-assembly on a Rh(111) single crystalline surface. Two layers of mesh cover the surface uniformly after high-temperature exposure of the clean rhodium surface to borazine (HBNH)3. The two layers are offset in such a way as to expose a minimum metal surface area. Hole formation is likely driven by the lattice mismatch of the film and the rhodium substrate. This regular nanostructure is thermally very stable and can serve as a template to organize molecules, as is exemplified by the decoration of the mesh by C60 molecules.

Tricyclohexylphosphine Adsorbed on Rhodium

Tricyclohexylphosphine (TCHP) adsorbates on rhodium, prepared both from solution and by sublimation in UHV are studied by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). XPS and IRAS are used to investigate the molecular orientation of the adsorbates and the coordination to the surface. TPD is used to study the stability of the adsorbates. Molecular surface interactions causing chemical shifts in the core level spectra of the adsorbates on rhodium are investigated using multilayer films and adsorbates on gold as references. In the solution deposition procedure, freshly evaporated rhodium samples are shortly exposed to air, resulting in oxygen covered surfaces. The P(2p) core level XPS spectrum shows only one type of phosphorus with a P(2p3/2) binding energy about 2.7 eV higher than when adsorbed on gold. This is in agreement with molecular adsorption through oxygen to the surface. To study the interaction of TCHP with clean rhodium we also prepared a TCHP adsorbate by an in situ sublimation process in UHV. One dominating state of phosphorus is observed with a P(2p3/2)binding energy about 2.6 eV lower than when adsorbed from solution, but close to what was found when adsorbed on gold. This indicates formation of a soft donor/acceptor bond due to a direct coordination of the molecule through the phosphorus lone pair orbital to the rhodium surface. The soft donor/acceptor and oxygen bridging to rhodium lead to a large electronic reorganization of the phosphorus atom, which manifests itself as substantial infrared peak shifts of the cyclohexyl modes, especially the CH2 stretches. Combined IRAS and TPD measurements show molecular desorption at 465 K for the UHV prepared monolayer, which is consistent with strong chemisorption to the rhodium surface.

The selectivity of hydrazine oxidation on a polycrystalline rhodium surface

Abstract The surface reactions of coadsorbed hydrazine and atomic oxygen have been examined by means of temperature-programmed reaction spectroscopy (TPRS) on a clean polycrystalline rhodium surface over the 90 to 1450 K temperature range. Nitrogen and water are the primary oxidation products observed. In addition, the usual hydrazine decomposition products N2, NH3, H2 and N2H2 are observed. Nitrogen oxides (NO and N2O) were not observed even in the presence of excess oxygen. Preadsorbed atomic oxygen initiates hydrazine oxidation below 140 K indicating that adsorbed hydrazine is quite reactive on a clean rhodium surface. Large initial coverages of coadsorbed hydrazine and atomic oxygen result in the formation of nitrogen and water below 200 K. We suggest that the NN bond in hydrazine remains intact resulting in “direct” N2 formation during this low-temperature oxidation process. An analogous “direct” N2 formation process has been previously reported during hydrazine decomposition on iridium; we have also reported a similar process during hydrazine decomposition on rhodium. For lower hydrazine coverages, two higher temperature water desorption peaks at 270 and 360 K are observed. The water peak at 270 K is limited by reaction of H, O and OH while the water peak at 360 K appears to be limited by surface reaction between coadsorbed oxygen and a NHy surface intermediate. With increasing initial oxygen coverages the yield of water increases, while the yield of hydrazine decomposition products (NH3, H2 and N2H2) decreases. The selectivity of nitrogen formation during hydrazine oxidation below 250 K is controlled by direct reaction processes which leaves the NN bond in hydrazine intact. In this temperature range, hydrogen-oxygen reactions are the dominant mode of interaction with the adsorbed atomic oxygen. Above 250 K, nitrogen-nitrogen recombination is strongly favored over a broad range of temperatures and coverages. No evidence for a nitrogen-oxygen surface was observed even in the presence of excess adsorbed oxygen clearly suggesting the predominance of N atom recombination over N + O atom surface reaction even in the presence of excess adsorbed atomic oxygen.

The selectivity of hydrazine oxidation on a polycrystalline rhodium surface

The surface reactions of coadsorbed hydrazine and atomic oxygen have been examined by means of temperature-programmed reaction spectroscopy (TPRS) on a clean polycrystalline rhodium surface over the 90 to 1450 K temperature range. Nitrogen and water are the primary oxidation products observed. In addition, the usual hydrazine decomposition products N 2, NH 3, H 2 and N 2H 2 are observed. Nitrogen oxides (NO and N 2O) were not observed even in the presence of excess oxygen. Preadsorbed atomic oxygen initiates hydrazine oxidation below 140 K indicating that adsorbed hydrazine is quite reactive on a clean rhodium surface. Large initial coverages of coadsorbed hydrazine and atomic oxygen result in the formation of nitrogen and water below 200 K. We suggest that the NN bond in hydrazine remains intact resulting in “direct” N 2 formation during this low-temperature oxidation process. An analogous “direct” N 2 formation process has been previously reported during hydrazine decomposition on iridium; we have also reported a similar process during hydrazine decomposition on rhodium. For lower hydrazine coverages, two higher temperature water desorption peaks at 270 and 360 K are observed. The water peak at 270 K is limited by reaction of H, O and OH while the water peak at 360 K appears to be limited by surface reaction between coadsorbed oxygen and a NH y surface intermediate. With increasing initial oxygen coverages the yield of water increases, while the yield of hydrazine decomposition products (NH 3, H 2 and N 2H 2) decreases. The selectivity of nitrogen formation during hydrazine oxidation below 250 K is controlled by direct reaction processes which leaves the NN bond in hydrazine intact. In this temperature range, hydrogen-oxygen reactions are the dominant mode of interaction with the adsorbed atomic oxygen. Above 250 K, nitrogen-nitrogen recombination is strongly favored over a broad range of temperatures and coverages. No evidence for a nitrogen-oxygen surface was observed even in the presence of excess adsorbed oxygen clearly suggesting the predominance of N atom recombination over N + O atom surface reaction even in the presence of excess adsorbed atomic oxygen.

Hydrazine decomposition on a clean rhodium surface: A temperature programmed reaction spectroscopy study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHydrazine decomposition on a clean rhodium surface: A temperature programmed reaction spectroscopy studyJagdish Prasad and John L. GlandCite this: Langmuir 1991, 7, 4, 722–726Publication Date (Print):April 1, 1991Publication History Published online1 May 2002Published inissue 1 April 1991https://doi.org/10.1021/la00052a021RIGHTS & PERMISSIONSArticle Views338Altmetric-Citations51LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (457 KB) Get e-Alerts Get e-Alerts

Diimide formation on rhodium surfaces: a temperature-programmed reaction spectroscopy study

Diimide (N 2 H 2 ) formation has been detected as a gas-phase product over the 180-500 K temperature range from a clean rhodium surface during decomposition of both hydrazine and ammonia. The diimide was identified on the basis of mass spectrometry of the parent ion (30 amu) and a single-dehydrogenation fragmentation product (29 amu) that is 6% of the parent. The formation of diimide was confirmed chemically for both precursors by observing substantial increases in yield in the presence of coadsorbed hydrogen and a substantial decrease in the presence of coadsorbed oxygen. Adsorbed NH from N 2 H 4 or NH 3 decomposition is proposed as a potential surface intermediate

Reconstructive adsorption of H [sbnd]Rh(110)—a multiphase study

The adsorption of hydrogen on a clean rhodium(110) surface develops—with increasing coverage—a number of commensurate phases (1 × 3-H, 1 × 2-H, 1 × 3-2H, 1 × 2-3H, 1 × 1-2H). Low Energy Electron Diffraction (LEED) was used to investigate both the phase diagram and the position of adsorbate and substrate atoms. Hydrogen adsorption not only weakens the multilayer relaxation but also causes a slight reconstruction of the rhodium substrate which is reduced with increasing coverage. At low coverages hydrogen atoms occupy threefold co-ordinates sites with a Rh-H bond length of 1.84 A ± 0.1 A and a hydrogen radius of 0.54 A ± 0.1 A. At higher coverages repulsive interactions between adjacent hydrogen atoms make adatoms move up to allow for maximum horizontal distances. Coverage dependent transition temperatures and angular beam profile analyses allow the determination of the phase diagram. The critical temperatures for the primitive phases 1 × 3-H and 1 × 2-H are TC = 132 ± 5 K and TC = 150 ± 5 K, respectively. The 1 × 3-H phase transforms to lattice gas disorder through a continuous phase transition, whereas in the case of the 1 × 2-H phase, a reversible transition to an incommensurate phase is observed. For the non-primitive phases TC is near or above the desorption boundary and thermal desorption is a competing process to the order-disorder transition. Order-order transitions are of first order as observed for the transitions of the primitive phases 1 × 3-H to 1 × 2-H as well as for the non-primitive phases 1 × 3-2H to 1 × 2-3H.

ChemInform Abstract: HYDROGEN CYANIDE SYNTHESIS FROM METHANE AND AMMONIA ON CLEAN RHODIUM

Chemischer InformationsdienstVolume 16, Issue 18 Preparative Organic Chemistry ChemInform Abstract: HYDROGEN CYANIDE SYNTHESIS FROM METHANE AND AMMONIA ON CLEAN RHODIUM D. HASENBERG, D. HASENBERGSearch for more papers by this authorL. D. SCHMIDT, L. D. SCHMIDTSearch for more papers by this author D. HASENBERG, D. HASENBERGSearch for more papers by this authorL. D. SCHMIDT, L. D. SCHMIDTSearch for more papers by this author First published: May 7, 1985 https://doi.org/10.1002/chin.198518081AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume16, Issue18May 7, 1985 RelatedInformation

The reaction of nitrous oxide with rhodium

A clean rhodium filament at room temperature is highly reactive towards nitrous oxide. The oxygen atom of the N 2O molecule is adsorbed with a sticking probability of 0.45 whilst the nitrogen atoms appear in the gas phase as molecular nitrogen. The room temperature uptake of oxygen is about 5 × 10 14 atom cm −2 and is independent of nitrous oxide pressure in the range 3.5 × 10 −8 to 1.1 × 10 −6 torr. The adsorption curve is of typical form with an initial region of essentially constant sticking probability. For the first 80% of adsorption at room temperature the shape is satisfactorily accounted for if molecules are able to visit 4–5 adsorption sites whilst held in a weakly-bonded precursor state.

Activated chemisorption of molecules

Dissociative chemisorption of polyatomic gases on crystal surfaces has long been reported as a slow process. Using molecular beam techniques, we have investigated the adsorption of methane on clean rhodium surfaces and provided a clue to the mechanism of activation.

Oxygen reduction studies at smooth pre-reduced ruthenium and rhodium electrodes in 85% orthophosphoric acid

Summary Cathodic reduction of oxygen has been studied on bright oxide-free rhodium and ruthenium electrodes in purified 85% orthophosphoric acid as a function of temperature. Tafel slopes on reproducibly clean rhodium electrodes are close to RT/F ; on ruthenium the corresponding value is about 2RT/F . The Tafel slope on ruthenium did not have the theoretical temperature-dependence. A similar effect was previously noted on gold and iridium electrodes under the same conditions 5 . On rhodium an apparent increase in Tafel slope occurs at higher current densities. This may indicate a change in mechanism. Ruthenium behaves like iridium 5 in the presence of impurities: These result in deactivated electrodes with lower Tafel slopes. The exchange current on rhodium was about 2 orders of magnitude less than that on platinum (slope also RT/F ) 6 under the same conditions. The value of i 0 on ruthenium was similar to that noted on iridium (about 10 −11 A cm −2 ) under the same conditions. Oxygen reduction is first-order on these metals. Activation energies at the reversible potential were determined to be 22.0±1.5 kcal on rhodium, similar to the value (22.9 kcal) reported on platinum 6 , and 11.7±0.5 kcal on ruthenium, somewhat less than the value (12.6 kcal) on iridium 5 . The suggested rate-determining step on these metals is O 2 + H + + e − → − O 2 H ads On rhodium, it occurs under Temkin adsorption conditions in the potential range where medium coverages of adsorbed O and OH radicals (from water oxidation) are present on the electrode. On ruthenium, high coverages of these radicals occur, and adsorption is Langmuirian.

Oxygen reduction studies at smooth pre-reduced ruthenium and rhodium electrodes in 85% orthophosphoric acid

Cathodic reduction of oxygen has been studied on bright oxide-free rhodium and ruthenium electrodes in purified 85% orthophosphoric acid as a function of temperature. Tafel slopes on reproducibly clean rhodium electrodes are close to RT/F; on ruthenium the corresponding value is about 2RT/F. The Tafel slope on ruthenium did not have the theoretical temperature-dependence. A similar effect was previously noted on gold and iridium electrodes under the same conditions5. On rhodium an apparent increase in Tafel slope occurs at higher current densities. This may indicate a change in mechanism. Ruthenium behaves like iridium5 in the presence of impurities: These result in deactivated electrodes with lower Tafel slopes. The exchange current on rhodium was about 2 orders of magnitude less than that on platinum (slope also RT/F)6 under the same conditions. The value of i0 on ruthenium was similar to that noted on iridium (about 10−11 A cm−2) under the same conditions. Oxygen reduction is first-order on these metals. Activation energies at the reversible potential were determined to be 22.0±1.5 kcal on rhodium, similar to the value (22.9 kcal) reported on platinum6, and 11.7±0.5 kcal on ruthenium, somewhat less than the value (12.6 kcal) on iridium5. The suggested rate-determining step on these metals is O2 + H+ + e− → − O2Hads On rhodium, it occurs under Temkin adsorption conditions in the potential range where medium coverages of adsorbed O and OH radicals (from water oxidation) are present on the electrode. On ruthenium, high coverages of these radicals occur, and adsorption is Langmuirian.

156. Decomposition of n-propane and n-butane on clean rhodium films.: R. W. Roberts, J. Phys. Chem., 66, Sept. 1962, 1742–1743.

156. Decomposition of n-propane and n-butane on clean rhodium films.: R. W. Roberts, J. Phys. Chem., 66, Sept. 1962, 1742–1743.

REACTIONS OF SATURATED HYDROCARBONS WITH CLEAN RHODIUM FILMS

REACTIONS OF SATURATED HYDROCARBONS WITH CLEAN RHODIUM FILMS

DECOMPOSITION OF n-PROPANE AND n-BUTANE ON CLEAN RHODIUM FILMS

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDECOMPOSITION OF n-PROPANE AND n-BUTANE ON CLEAN RHODIUM FILMSRichard W. RobertsCite this: J. Phys. Chem. 1962, 66, 9, 1742–1743Publication Date (Print):September 1, 1962Publication History Published online1 May 2002Published inissue 1 September 1962https://doi.org/10.1021/j100815a506RIGHTS & PERMISSIONSArticle Views11Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (295 KB) Get e-Alerts

Reaction of ethane with a clean rhodium film

I HAVE observed that when ethane at low pressure (1.2 × 10−2 torr) comes in contact with a 27° C. rhodium film which was prepared in ultra-high vacuum (1 × 10−9 torr), it will decompose to yield gaseous methane and an adsorbed residue with a composition of CH1.5. Others1,2 have observed this cracking reaction to occur at temperatures above 160° C. on metal surfaces of unknown cleanliness.

Reaction of Ethane with a Clean Rhodium Film

I HAVE observed that when ethane at low pressure (1.2 × 10−2 torr) comes in contact with a 27° C. rhodium film which was prepared in ultra-high vacuum (1 × 10−9 torr), it will decompose to yield gaseous methane and an adsorbed residue with a composition of CH1.5. Others1,2 have observed this cracking reaction to occur at temperatures above 160° C. on metal surfaces of unknown cleanliness.

Temperature Scale and Thermionic Emission from Rhodium

When rhodium is heated to incandescence in an atmosphere of air or oxygen, a coating forms on its surface. This is shown by a change in the emissivity. When the temperature is increased sufficiently this coating suddenly disappears, and when the temperature is lowered it reappears. This coating is probably an activated adsorption of oxygen, or an oxide of rhodium. It is found experimentally that the temperature and partial oxygen pressure at which the coating disappears are related by the Clausius-Clapyron equation: (d loge P)/dT=L/RT2.P is the partial oxygen pressure, T the absolute temperature, and L the heat of vaporization of the surface. The electron work function of a clean rhodium surface is found to be [open phi]=4.80 volts, and A = 33 amp./cm2/degree2.