Formic acid oxidation

A graphene nanoplatelet (GNP)-supported Ir–Zn catalyst (Ir–Zn/GNP) was fabricated by H2 reduction to discover an alternative for non-platinum and non-palladium catalysts as an anode catalyst in direct formic acid fuel cell (DFAFC). The obtained Ir–Zn/GNP catalyst with ratio of Ir:Zn = 50:50 (Ir50Zn50/GNP) exhibited better electrocatalytic activity than GNP-supported iridium catalyst (Ir/GNP) for formic acid oxidation. Although the oxidation peak current density of Ir50Zn50/GNP was slightly lower than that of Ir/GNP, the oxidation peak potential shifted more negatively (193 mV) than Ir/GNP with higher value of the ratio of forward scan to reverse the scan peak current (If/Ib). The presence of Zn also enhanced the power density and current generation with increased performance stability in a passive DFAFC cell tests. The improvement of the electrochemical performance was ascribed to the ensemble effect where the addition of Zn could modify the Ir atom arrangement, thereby promoting th...

By taking advantage of the non-equilibrium synthetic conditions, the cathodic corrosion method was used to prepare a selected a number of alloys of which solid-solution alloys do not exist under ambient conditions. To illustrate our finding we present the preparation at room temperature of PtBi and PtPb alloy nanoparticles with various compositions. These alloys have shown benchmark mass activity and durability towards the formic acid oxidation. The improvement in the catalytic activity is explained based on the composition of the metal alloys, the reduced particle size and, quite importantly, the level of cleanliness of the catalyst obtained by this method.

The electrocatalytic reactivity of Pt nanoparticles supported on high-pressure-high-temperature diamond particles towards adsorbed CO, methanol and formic acid oxidation is investigated employing differential electrochemical mass spectrometry (DEMS). Surface treatment of diamond particles, employed as dimensionally stable electrocatalyst supports, leads to materials with surfaces featuring mainly hydrogen (HDP) or oxygen-based functional groups (ODP). Pt nanoparticles with average diameter below 5 nm were generated by impregnation of the modified diamond particles. The voltammetric responses associated with the oxidation of adsorbed CO appeared unaffected by the surface termination of the diamond support. However, significant differences were observed for methanol oxidation in acid solutions, with Pt/HDP producing smaller current densities than Pt/ODP and a commercially available Pt catalyst (Pt/E-TEK). DEMS studies show higher conversion efficiencies to CO 2 for Pt/ODP and Pt/E-TEK, while Pt/HDP exhibited values of approximately 90%. Evidence of formic acid generation as intermediate during methanol oxidation was obtained on all catalysts. Significant differences in the current density associated with the oxidation of formic acid were also observed, with Pt/HDP also providing the lowest current densities. The ensemble of the experimental data suggests that adsorbed HCOO ads species is the key intermediate in methanol oxidation, and its subsequent oxidation to CO 2 is strongly affected by the average surface termination of the diamond support.

Formic acid oxidation was studied on platinum-coated bismuth deposits on glassy carbon substrate. The catalyst was prepared by a two-step process using chronocoulometry, i.e. controlled amount of Bi was electrodeposited onto glassy carbon followed by electrodeposition of Pt layer. The amount of Pt was constant while the amount of Bi vary to correspond the molar ratio of Pt:Bi = 1:0.1 or 1:1 or 1:10. AFM characterization of the electrode surface indicates that Pt is deposited preferentially on previously formed Bi particles, but cyclic voltammetry revealed Bi leaching meaning that Bi was not completely occluded by Pt. In order to obtain stable electrode surface, deposits were subjected to potential cycling up to 1.2 V vs. SCE in supporting electrolyte, prior to use as catalysts for formic acid oxidation. On this way the electrodes composed of Bi core occluded by Pt and Bioxide surface layers were obtained. The Pt(Bi)/GC electrodes exhibit enhanced electrocatalytic activity in comparison to Pt/GC for formic acid oxidation which depends on composition and surface morphology. High currents and onset potential shifted to negative values indicate a significant increase in direct path what is explained through ensemble effect induced by Bi-oxide species interrupting Pt domains. Electronic modification of Pt both by surface and sub-surface Bi can play some role as well. Significantly prolonged potential

The oxidation of formic acid was studied at supported Pt catalyst (47.5 wt%. Pt) and a low-index single crystal electrodes in sulfuric acid. The supported Pt catalyst was characterized by the TEM and HRTEM techniques. The mean Pt particle diameter, calculated from electrochemical measurements fits well with Pt particle size distribution determined by HRTEM. For the mean particle diameter the surface averaged distribution of low-index single crystal facets was established. Comparison of the activities obtained at Pt supported catalyst and low-index Pt single crystal electrodes revealed that Pt(111) plane is the most active in the potential region relevant for fuel cell applications.

The present study explores the synthesis, characterization, and comparative electrocatalytic evaluation of heterofunctionalized palladium/magnetite (iron oxide) nanoparticles (Pd/IONPs) with diverse morphologies for formic acid (FA) oxidation to enhance catalytic activity. Various morphologies, including dumbbell, hybrid, branched, and core−shell-like structures were synthesized and characterized using transmission electron microscopy (TEM), selected area electron diffraction (SAED), and vibrating sample magnetometer (VSM). In addition, polyvinylpyrrolidone (PVP)-coated Pd nanobars were synthesized and used as a control catalyst to compare the performance of the heterostructured Pd/IONPs. The electrocatalytic activity of these particles was investigated via cyclic voltammetry (CV) to reveal structure−function relationships in heterogeneous catalysts. Among the different morphologies, branched Pd/octopod-shaped IONPs demonstrated superior catalytic activity and carbon monoxide (CO) poisoning tolerance in FA oxidation. This is attributed to the high-energy {113} facets in the arms of the IONP octopods, which facilitated the attachment of many Pd atoms and promoted a synergistic catalytic effect. The increased exposure of active sites on these facets enabled more efficient FA oxidation pathways, as evidenced by a higher ratio of anodic direct oxidation peak current density (I a1) to anodic indirect oxidation peak current density (I a2) and greater endurance against CO poisoning measured as the ratio of I a1 to cathodic direct oxidation peak current density (I b). These findings highlight the critical role of NP morphology in catalyst design for advancing energy conversion and storage technologies.

Carbon materials with developed porosity are usually used as supports for platinum catalysts. Physico-chemical characteristics of the support influence the properties of platinum deposited and its catalytic activity. In our studies, we deposited platinum on carbon fibrous like materials obtained from platanus seeds - achenes. The precursor was chemically activated with different reagents: NaOH, pyrogallol, and H2O2, before the carbonization process. Platinum was deposited on all substrates to study the influence of the substrate properties on the activity of the catalyst. Carbon materials were characterized by nitrogen adsorption/desorption isotherms measurements, X-ray diffraction, and scanning electron microscopy. It was noticed that the adsorption characteristics of carbon support affected the structure of platinum deposits and thus their activity.

TiO 2 and Ti-W mixed oxide photocatalysts, with W/Ti molar ratios in the 0-5% range, were prepared through a simple sol-gel method, followed by annealing at 500 or 700 • C, and their photoactivity was tested in the photo-oxidation of formic acid in the aqueous phase under ambient aerobic conditions. XRPD analysis evidenced that in the presence of tungsten the anatase phase was stable even after calcination at 700 • C, with a progressively larger surface area and smaller particle dimensions with increasing tungsten content. Tungsten can both enter the titania lattice, as demonstrated by HAADF-STEM analysis, and also segregate as amorphous WO 3 on the photocatalysts surface, as suggested by XPS analysis. The best performing Ti/W oxide photocatalyst is that containing 1.0 mol% W/Ti, mainly due to the tungsteninduced stabilization effect of the anatase phase, whereas electron transfer from TiO 2 to WO 3 , though compatible with the here performed EPR measurements, appears to have no beneficial effect in the investigated reaction, likely due to the low energy level of the conduction band of WO 3 , from which electrons cannot efficiently transfer to adsorbed dioxygen.

The formic acid oxidation (FAO) reaction is studied on platinum in acid solutions using a specially designed flow cell and different experimental techniques, such as open circuit potential decay, chronoamperometry, voltammetric stripping, HCOOH concentration pulses and rotating disc electrode. It allows for the first time the evaluation of the surface coverage of irreversibly adsorbed reaction intermediates on steady state conditions. It is found that the unique species adsorbed irreversibly is CO (E < 0.5 V). It is demonstrated that at higher potentials the adsorption of the intermediate species involved in the FAO is highly reversible and their decomposition is the rate determining step. From the analysis of the results and taken into account available spectroscopic measurements, a new reaction mechanism is proposed, which is compatible with all the known experimental evidences and allows the interpretations of previous unexplained results.

The electrochemical characteristics of a mixture of Pt-black and WC powders and its catalytic activity for methanol and formic acid oxidation were investigated in acid solution. XRD and AFM measurements revealed that the WC powder employed for the investigation was a single-phase material consisting of crystallites/spherical particles of average size of about 50 nm, which were agglomerated into much larger particles. Cyclic voltammetry showed that the WC underwent electrochemical oxidation, producing tungstate species. In the case of the mixed Pt + WC powders, the tungstate species were deposited on the Pt as a thin film of hydrous tungsten oxide. Enhanced hydrogen intercalation in the hydrous tungsten oxide was observed and it was proposed to be promoted in mixed powders by the presence of hydrogen adatoms on bare Pt sites. The determination of Pt surface area in the Pt + WC layer by stripping of underpotentially deposited Cu revealed that the entire Pt surface was accessible for u...

The catalytic activity of platinum (Pt) nanoparticles (NPs) towards methanol electrooxidation in alkaline media was demonstrated to be dependent on their interactions with their nanostructured ceria support. Ceria nanorods (NRs) with diameters of 5 to 10 nm and lengths of 15 to 50 nm as well as ceria NPs with diameters of 2 to 6 nm were applied as supports for similarly sized Pt NPs with diameters of 2 to 5 nm. Cyclic voltammetry data showed that Pt NPs supported on ceria NPs exhibited a 2-to-5-fold higher catalytic current density versus ceria NRs. X-ray photoelectron spectroscopic data indicated that Pt NPs deposited onto ceria NRs were disproportionally composed of oxidized species (Pt 2+ , Pt 4+ and Pt-O-M) rather than Pt 0 while Pt NPs on ceria NPs mainly consisted of Pt 0. Stronger metal-support interactions between Pt NPs and ceria NRs are postulated to induce preferential oxidation of Pt NPs and consequently decrease the catalytic sites and overall activity.

In this research, a water-in-oil microemulsion method with HCl as a capping agent was applied to synthesize carbon supported Pt catalysts. Varying the concentration of HCl caused changes in the shape of obtained nanoparticles, i.e. preferential growth of certain facets. Addition of catalyst support in the synthesis process facilitated the cleaning procedures necessary to remove the surfactant residues. Prepared catalyst powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis indicated the influence of HCl addition on the crystallite size and crystal habit. TEM revealed that addition of higher amounts of the capping agent led to the formation of a noticable amount of particles with concave cubic or branched-like structures. Influence of the catalyst particles shape on its electrochemical properties was tested in the oxidations of CO ads , ammonia and formic acid. The latter one was examined in terms of both activity and stability of as prepared and oxide-annealed (electrochemically treated) catalysts. The results clearly demonstrate that even small changes in the nanoparticle surface structure give rise to distinct modifications in their properties. Concave cubic particles, in comparison to other catalysts, show improved catalytic properties and the contribution of their preferentially oriented {100} facets is electrochemically detectable.

TiO 2 and Ti-W mixed oxide photocatalysts, with W/Ti molar ratios in the 0-5% range, were prepared through a simple sol-gel method, followed by annealing at 500 or 700 • C, and their photoactivity was tested in the photo-oxidation of formic acid in the aqueous phase under ambient aerobic conditions. XRPD analysis evidenced that in the presence of tungsten the anatase phase was stable even after calcination at 700 • C, with a progressively larger surface area and smaller particle dimensions with increasing tungsten content. Tungsten can both enter the titania lattice, as demonstrated by HAADF-STEM analysis, and also segregate as amorphous WO 3 on the photocatalysts surface, as suggested by XPS analysis. The best performing Ti/W oxide photocatalyst is that containing 1.0 mol% W/Ti, mainly due to the tungsteninduced stabilization effect of the anatase phase, whereas electron transfer from TiO 2 to WO 3 , though compatible with the here performed EPR measurements, appears to have no beneficial effect in the investigated reaction, likely due to the low energy level of the conduction band of WO 3 , from which electrons cannot efficiently transfer to adsorbed dioxygen.

Carbon materials with developed porosity are usually used as supports for platinum catalysts. Physico-chemical characteristics of the support influence the properties of platinum deposited and its catalytic activity. In our studies, we deposited platinum on carbon fibrous like materials obtained from platanus seeds - achenes. The precursor was chemically activated with different reagents: NaOH, pyrogallol, and H2O2, before the carbonization process. Platinum was deposited on all substrates to study the influence of the substrate properties on the activity of the catalyst. Carbon materials were characterized by nitrogen adsorption/desorption isotherms measurements, X-ray diffraction, and scanning electron microscopy. It was noticed that the adsorption characteristics of carbon support affected the structure of platinum deposits and thus their activity.

A graphene nanoplatelet (GNP)-supported Ir–Zn catalyst (Ir–Zn/GNP) was fabricated by H2 reduction to discover an alternative for non-platinum and non-palladium catalysts as an anode catalyst in direct formic acid fuel cell (DFAFC). The obtained Ir–Zn/GNP catalyst with ratio of Ir:Zn = 50:50 (Ir50Zn50/GNP) exhibited better electrocatalytic activity than GNP-supported iridium catalyst (Ir/GNP) for formic acid oxidation. Although the oxidation peak current density of Ir50Zn50/GNP was slightly lower than that of Ir/GNP, the oxidation peak potential shifted more negatively (193 mV) than Ir/GNP with higher value of the ratio of forward scan to reverse the scan peak current (If/Ib). The presence of Zn also enhanced the power density and current generation with increased performance stability in a passive DFAFC cell tests. The improvement of the electrochemical performance was ascribed to the ensemble effect where the addition of Zn could modify the Ir atom arrangement, thereby promoting th...

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO2 nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO2 nanotubes (TiO2 NTs) with strictly defined geometry were produced by anodization of Ti foil and Ti mesh in a mixture of glycerol and water with ammonium fluoride electrolyte. The above mentioned catalytically active metal nanoparticles (NPs) were located mainly on the top of the TiO2 NTs, forming ‘rings’ and agglomerates. A part of metal nanoparticles decorated also TiO2 NTs walls, thus providing sufficient electronic conductivity for electron transportation between the metal nanoparticle rings and Ti current collector. The electrocatalytic activity of the TiO2 NTs/Ti foil, decorated by Pt, Pd and/or Pd + Pt NPs was investigated by cyclic voltammetry (CV) and new Pd/TiO2 NTs/Ti mesh catalyst was additionally tested in a direct formic acid fuel cell (DFAFC). The res...

A graphene nanoplatelet (GNP)-supported Ir–Zn catalyst (Ir–Zn/GNP) was fabricated by H2 reduction to discover an alternative for non-platinum and non-palladium catalysts as an anode catalyst in direct formic acid fuel cell (DFAFC). The obtained Ir–Zn/GNP catalyst with ratio of Ir:Zn = 50:50 (Ir50Zn50/GNP) exhibited better electrocatalytic activity than GNP-supported iridium catalyst (Ir/GNP) for formic acid oxidation. Although the oxidation peak current density of Ir50Zn50/GNP was slightly lower than that of Ir/GNP, the oxidation peak potential shifted more negatively (193 mV) than Ir/GNP with higher value of the ratio of forward scan to reverse the scan peak current (If/Ib). The presence of Zn also enhanced the power density and current generation with increased performance stability in a passive DFAFC cell tests. The improvement of the electrochemical performance was ascribed to the ensemble effect where the addition of Zn could modify the Ir atom arrangement, thereby promoting th...

The electrochemical characteristics of a mixture of Pt-black and WC powders and its catalytic activity for methanol and formic acid oxidation were investigated in acid solution. XRD and AFM measurements revealed that the WC powder employed for the investigation was a single-phase material consisting of crystallites/spherical particles of average size of about 50 nm, which were agglomerated into much larger particles. Cyclic voltammetry showed that the WC underwent electrochemical oxidation, producing tungstate species. In the case of the mixed Pt + WC powders, the tungstate species were deposited on the Pt as a thin film of hydrous tungsten oxide. Enhanced hydrogen intercalation in the hydrous tungsten oxide was observed and it was proposed to be promoted in mixed powders by the presence of hydrogen adatoms on bare Pt sites. The determination of Pt surface area in the Pt + WC layer by stripping of underpotentially deposited Cu revealed that the entire Pt surface was accessible for u...

TheelectrooxidationbehaviorofformicacidonPt鄄Ru/GCelectrodewasinvestigatedbyCV,multi鄄 potentialstepsandSERS.ItwasfoundthatformicacidcoulddissociatespontaneouslyonPt鄄Ru/GCelectrodeasit dissociatedonroughPtelectrode,producestrongabsorptionintermediateCOandreactiveintermediate-COO-.The resultsdemonstratedthatRucouldimprovetheelectrocatalyticactivityofformicacidonPt鄄Ru/GCelectrode.Asthe ratioofPtandRuindespositionsolutionchangedfrom10颐1to1颐 1,theoxidationpotentialofCOshiftednegatively about60mV(from0.41Vto0.35V).ComparedtoroughPtelectrode,theoxidationpotentialofCOonPt鄄Ru/GC(1颐1) shiftednegatively200mV.TheseresultsindicatethatSERSishopefultobeacomprehensivespectroscopytoolof investigatingtheelectrocatalyticreactionmechanism.

Carbon materials with developed porosity are usually used as supports for platinum catalysts. Physico-chemical characteristics of the support influence the properties of platinum deposited and its catalytic activity. In our studies, we deposited platinum on carbon fibrous like materials obtained from platanus seeds - achenes. The precursor was chemically activated with different reagents: NaOH, pyrogallol, and H2O2, before the carbonization process. Platinum was deposited on all substrates to study the influence of the substrate properties on the activity of the catalyst. Carbon materials were characterized by nitrogen adsorption/desorption isotherms measurements, X-ray diffraction, and scanning electron microscopy. It was noticed that the adsorption characteristics of carbon support affected the structure of platinum deposits and thus their activity.

Direct ethanol fuel cells (DEFCs) are considered the most suitable direct alcohol fuel cell (DAFC) in terms of safety and current density. The obstacle to DEFC commercialization is the low reaction kinetics of ethanol (C2H5OH) oxidation because of the poor performance of the electrocatalyst. In this study, for the first time, graphene nanoplates (GNPs) were coated with sulfated zirconium dioxide (ZrO2) as adequate support for platinum (Pt) catalysts in DEFCs. A Pt/S-ZrO2-GNP electrocatalyst was prepared by a new process, polyol synthesis, using microwave heating. Field emission scanning electron microscope (FESEM) imaging revealed well-dispersed platinum nanoparticles supported on the S-ZrO2-GNP powder. Analysis of the Fourier transform infrared (FTIR) spectrometry confirmed that sulfate modified the surfaces of the sample. In X-ray diffraction (XRD), no effect of S-ZrO2 on the crystallinity net in Pt was found. Pt/S-ZrO2-GNP electrode outperformed those with unsulfated counterparts...

The electrochemical characteristics of a mixture of Pt-black and WC powders and its catalytic activity for methanol and formic acid oxidation were investigated in acid solution. XRD and AFM measurements revealed that the WC powder employed for the investigation was a single-phase material consisting of crystallites/spherical particles of average size of about 50 nm, which were agglomerated into much larger particles. Cyclic voltammetry showed that the WC underwent electrochemical oxidation, producing tungstate species. In the case of the mixed Pt + WC powders, the tungstate species were deposited on the Pt as a thin film of hydrous tungsten oxide. Enhanced hydrogen intercalation in the hydrous tungsten oxide was observed and it was proposed to be promoted in mixed powders by the presence of hydrogen adatoms on bare Pt sites. The determination of Pt surface area in the Pt + WC layer by stripping of underpotentially deposited Cu revealed that the entire Pt surface was accessible for u...

The electrochemical characteristics of a mixture of Pt-black and WC powders and its catalytic activity for methanol and formic acid oxidation were investigated in acid solution. XRD and AFM measurements revealed that the WC powder employed for the investigation was a single-phase material consisting of crystallites/spherical particles of average size of about 50 nm, which were agglomerated into much larger particles. Cyclic voltammetry showed that the WC underwent electrochemical oxidation, producing tungstate species. In the case of the mixed Pt + WC powders, the tungstate species were deposited on the Pt as a thin film of hydrous tungsten oxide. Enhanced hydrogen intercalation in the hydrous tungsten oxide was observed and it was proposed to be promoted in mixed powders by the presence of hydrogen adatoms on bare Pt sites. The determination of Pt surface area in the Pt + WC layer by stripping of underpotentially deposited Cu revealed that the entire Pt surface was accessible for u...

The direct formic acid fuel cell (DFAFC) is one of the most promising direct liquid fuel cells. Pd is the most active catalyst towards formic oxidation, however, it suffers from CO-like poisoning and instability in acidic media. Blending formic acid with ethanol is known to synergistically enhance the Pt catalytic activity of Pt. However, it has not been studied in the case of Pd. In this study, ethanol/formic acid blends were tested, aiming at understanding the effect of ethanol on the formic acid oxidation mechanism at Pd and how the direct and indirect pathways could be affected. The blends consisted of different formic acid (up to 4 M) and ethanol (up to 0.5 M) concentrations. The catalytic activity of a 40% Pd/C catalyst was tested in 0.1 M H 2 SO 4 + XFA + YEtOH using cyclic voltammetry, while the catalyst resistance to poisoning in the presence and absence of ethanol was tested using chronopotentiometry. The use of these blends is found to not only eliminate the indirect pathway but also slowly decrease the direct pathway activity too. That is believed to be due to the different ethanol adsorption orientations at different potentials. This study should open the door for further studying the oxidation of FA/ethanol blends using different pHs and different Pd-based catalysts. Scheme 1 Formic acid oxidation pathways (direct, indirect, and formate) on Pd catalyst surface.

Direct ethanol fuel cells (DEFCs) show a huge potential to power future electric vehicles and portable electronics, but their deployment is currently limited by the unavailability of proper electrocatalysis for the ethanol oxidation reaction (EOR). In this work, we engineer a new electrocatalyst by incorporating phosphorous into a palladium-tin alloy and demonstrate a significant performance improvement toward EOR. We first detail a synthetic method to produce Pd2Sn:P nanocrystals that incorporate 35 % of phosphorus. These nanoparticles are supported on carbon black and tested for EOR. Pd2Sn:P/C catalysts exhibit mass current densities up to 4.89 A mgPd-1 , well above those of Pd2Sn/C, PdP2/C and Pd/C reference catalysts. Furthermore, a twofold lower Tafel slope and a much longer durability are revealed for the Pd2Sn:P/C catalyst compared with Pd/C. The performance improvement is rationalized with the aid of DFT calculations considering different phosphorous chemical environments. Depending on its oxidation state, surface phosphorus introduces sites with low energy OHadsorption and/or strongly influences the electronic structure of palladium and tin to facilitate the oxidation of the acetyl to acetic acid, which is considered the EOR rate limiting step.

Este trabalho propõe estudar ânodos baseados em Pt e PbO x frente à reação de oxidação do ácido fórmico. Os materiais estudados foram sintetizados por uma metodologia sol-gel adaptada. Estudos voltamétricos mostraram que o processo de oxidação ocorre em potenciais extremamente baixos. Este bom desempenho foi comprovado por meio de curvas de polarização e cronoamperometrias. The performance of Pt-PbO x-based catalysts to promote the formic acid oxidation is described here. All materials were synthesized by a modified sol-gel method. Voltammetric studies showed that the Pt-PbO x /C anode starts the oxidation process at extremely low potentials. Quasi-stationary polarization experiments and current vs. time measurements confirmed this affirmation.

Pt atoms attract electrons from neighboring atoms. Ru atoms attract hydroxide ligands. These two characteristics respectively weaken the bonding and recovering of the Pt site from CO oxidation and then facilitate the FAO in ternary PdPtRu NCs.

M w 55000, Sigma Aldrich), and potassium hydrogen carbonate (KHCO 3 , 99.99%, Acros Organics) were used as received. Thiophenol (99%, Acros Organics), ethylene glycol (EG, Fisher Chemical), ethanol (190 proof), and acetone were used without further purification. De-ionized (DI) water was used for preparing all aqueous solutions. Synthesis of silver benzenethiolate (AgBT) nanoboxes The synthesis started with the preparation of ternary silver halide (AgCl 0.5 Br 0.5) nanocubes by following the procedure reported elsewhere. 1,2 In a typical preparation of AgCl 0.5 Br 0.5 nanocubes, 2.5 g of PVP was first dissolved in 12 mL of EG in a 50-mL three-necked flask with the assistance of vigorous stirring. To this solution was added 10.2 mg of NaCl and 18.4 mg of NaBr powders. The solution was purged with nitrogen gas and then a nitrogen blanket maintained the inert atmosphere above the solution. The flask was covered with an aluminum foil to prevent any possible undesirable light-induced reactions. The solution was then heated up to 60 o C and maintained at this temperature until all salts were dissolved. 1 mL EG solution of 0.34 mol/L AgNO 3 was added to the warm solution at a rate of 1 mL/min using a syringe pump. Mixing AgNO 3 with halide ions triggered the precipitation reaction to form AgCl 0.5 Br 0.5 nanocubes. The reaction lasted 2 hours to ensure the completion of nanocube growth. The nitrogen atmosphere, the temperature of 60 0 C, and magnetic stirring of 300 rpm (with a stir bar of 19.1 mm × 9.5 mm) were maintained throughout the entire synthesis. The product solution was transferred to a 50-mL centrifuge tube, followed by the addition of 20 mL of ethanol. The solution was then sequentially vortexed and centrifuged at 6000 rpm for 20 min. The supernatant was discarded, and the nanocubes settled at the bottom of the centrifuge tube were re-dispersed in 20 mL of ethanol. The new dispersion was centrifuged again at 6000 rpm for 10 min. The recovered nanocubes were dispersed in 5 mL of ethanol for preparing AgBT nanoboxes. A solution of thiophenol (HBT, 0.049 M) was prepared by mixing thiophenol and ethanol at 1:200 (V/V) ratio. 15 mL of the thiophenol solution was then added to the dispersion of AgCl 0.5 Br 0.5 nanocubes, followed by

In order to investigate 111e toper underpolential deposition (upd) on gold sin~'lc crystals, V~oray surtaee ditTraciion (XRSD~ measurements were I~rformed under in-silu conditions. At'tot tbrmation of a complete Cu upd layer, Cu was tbund to adsorb in a commensurate p(I × !) structure in lburfold hollow sites with a vertical distance of 1.4 ,g, from the Au(100) surface. The coverage obtained by XRSD was (65 5: 8)%. The structure of the Cu uixl layer was studied as a function of applied potential and of the Cu-ion concentration in solution. The Cu-ion concentration did not affect the structure of the Cu upd layer. As a lunction of the applied potential, it was possible to investigate the formation of the Cu upd layer by XRSD. From a comparison between the XRSD results and the cyclic voltammetry, the formation of an ionic adlayer is inferred for the Cu upd on Au(100) in perchloric acid.

In order to investigate 111e toper underpolential deposition (upd) on gold sin~'lc crystals, V~oray surtaee ditTraciion (XRSD~ measurements were I~rformed under in-silu conditions. At'tot tbrmation of a complete Cu upd layer, Cu was tbund to adsorb in a commensurate p(I × !) structure in lburfold hollow sites with a vertical distance of 1.4 ,g, from the Au(100) surface. The coverage obtained by XRSD was (65 5: 8)%. The structure of the Cu uixl layer was studied as a function of applied potential and of the Cu-ion concentration in solution. The Cu-ion concentration did not affect the structure of the Cu upd layer. As a lunction of the applied potential, it was possible to investigate the formation of the Cu upd layer by XRSD. From a comparison between the XRSD results and the cyclic voltammetry, the formation of an ionic adlayer is inferred for the Cu upd on Au(100) in perchloric acid.

The catalytic activity of platinum (Pt) nanoparticles (NPs) towards methanol electrooxidation in alkaline media was demonstrated to be dependent on their interactions with their nanostructured ceria support. Ceria nanorods (NRs) with diameters of 5 to 10 nm and lengths of 15 to 50 nm as well as ceria NPs with diameters of 2 to 6 nm were applied as supports for similarly sized Pt NPs with diameters of 2 to 5 nm. Cyclic voltammetry data showed that Pt NPs supported on ceria NPs exhibited a 2-to-5-fold higher catalytic current density versus ceria NRs. X-ray photoelectron spectroscopic data indicated that Pt NPs deposited onto ceria NRs were disproportionally composed of oxidized species (Pt 2+ , Pt 4+ and Pt-O-M) rather than Pt 0 while Pt NPs on ceria NPs mainly consisted of Pt 0. Stronger metal-support interactions between Pt NPs and ceria NRs are postulated to induce preferential oxidation of Pt NPs and consequently decrease the catalytic sites and overall activity.

Improving the electrocatalytic activity for formic acid oxidation of bimetallic Ir-Zn nanoparticles decorated on graphene nanoplatelets To cite this article: Khairul Naim Ahmad et al 2020 Mater. Res. Express 7 015095 View the article online for updates and enhancements.

Asymmetric stripping peaks for sub-monolayer Ag films deposited on RuO, single crystal electrodes have been observed for (110) and (001) surfaces where both Ru and 0 sites are available on the ideal surface. Interpretation of this observation in terms of irreversible and quasi-reversible adsorption of silver leads to an interaction coefficient g close to-4 which may result in the formation of Ag islands (new phase) due to the strong attractive lateral forces. On the other hand, a symmetric Ag stripping peak is characteristic for the RuO, (111) surface where only Ru sites are available on the ideal surface. This indicates a reversible adsorption process for which the value of g was determined to be-1. The weaker lateral attraction forces seem to be associated with the different geometrical arrangement of Ag adatoms on different crystallographic faces of the RuO, single crystals rather than with increased substrate-adatom interactions since no major shifts in the peak potential were observed.

The formic acid oxidation reaction (FAOR) is one of the key reactions that can be used at the anode of low-temperature liquid fuel cells. To allow the knowledge-driven development of improved catalysts, it is necessary to deeply understand the fundamental aspects of the FAOR, which can be ideally achieved by investigating highly active model catalysts. Here, we studied SnO 2-decorated Pd nanocubes (NCs) exhibiting excellent electrocatalytic performance for formic acid oxidation in acidic medium with a SnO 2 promotion that boosts the catalytic activity by a factor of 5.8, compared to pure Pd NCs, exhibiting values of 2.46 A mg −1 Pd for SnO 2 @Pd NCs versus 0.42 A mg −1 Pd for the Pd NCs and a 100 mV lower peak potential. By using ex situ, quasi in situ, and operando spectroscopic and microscopic methods (namely, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine-structure spectroscopy), we identified that the initially well-defined SnO 2-decorated Pd nanocubes maintain their structure and composition throughout FAOR. In situ Fourier-transformed infrared spectroscopy revealed a weaker CO adsorption site in the case of the SnO 2decorated Pd NCs, compared to the monometallic Pd NCs, enabling a bifunctional reaction mechanism. Therein, SnO 2 provides oxygen species to the Pd surface at low overpotentials, promoting the oxidation of the poisoning CO intermediate and, thus, improving the catalytic performance of Pd. Our SnO x-decorated Pd nanocubes allowed deeper insight into the mechanism of FAOR and hold promise for possible applications in direct formic acid fuel cells.

This work investigates the mechanisms by which Sn and Ru can improve or inhibit the site-specific catalytic activity of Pt (neighboring or distant from foreign atoms) at bimetallic surfaces. For this purpose, we decorated Pt stepped surfaces (non-equivalent sites) by site-selective electrodeposition of different coverages of either Sn or Ru on (110) Pt steps, forming Snsteps/Pt(hkl) and Rusteps/Pt(hkl) bimetallic surfaces, and we used CO adlayer electro-oxidation as a surface probe reaction, monitored by in situ FTIR and cyclic voltammetry techniques. The results showed that both Sn and Ru selectively accelerated the reaction pathway of CO electro-oxidation only at the (111) Pt terrace sites, but importantly played different underlying roles in favoring activity at these active sites. In case of Snsteps/Pt(hkl) catalysts, the CO adlayer oxidation started at lower potentials than on Rusteps/Pt(hkl), but Sn only improved the activity at sites on atoms of the first rows of (111) Pt terraces, while the catalytic benefit of Ru seemed to extend further along the (111) Pt terraces. Compared to unmodified Pt surfaces, Ru did not influence the activity at the line of the (110) Pt steps, while Sn slightly inhibited the activity there, which characterized a slight contrasting effect in catalytic activity at the (111) terraces compared to the (110) step sites. In this regard, the chemical modification by irreversible deposition of either Sn or Ru at lines of Pt steps on a stepped Pt surface interestingly resulted in a non-uniform synergistic effect or balancing of energies involving different site-specific catalytic activities at non-equivalent Pt surface sites. Since the electro-oxidation of CO takes place at the (111) Pt terrace sites away from Sn or Ru, and because COads behaves as an immobile species during its oxidation, it is reasonable to assume that the classical bifunctional mechanism completely fails as a model to interpret the enhancement of catalytic activity towards CO electro-oxidation at Snsteps/Pt(hkl) or Rusteps/Pt(hkl)

In order to deepen the knowledge about the origin of the CO pre-oxidation process and the intrinsic catalytic activity of Pt superficial steps toward CO oxidation were performed a series of CO stripping experiments on stepped Pt electrodes in acidic medium. For the occurrence of CO pre-oxidation, it was found that it arises (reproducibly) whenever four interconnected conditions are simultaneously fulfilled: (1) CO adsorption at potentials lower than about 0.2 V; (2) on surfaces saturated with CO ads ; (3) in presence of traces of CO in solution; (4) in presence of surface steps. If any of these four conditions is not satisfied, the CO pre-oxidation pathway does not appear, even though the steps on the electrode surface are completely covered by CO. By controlling the removal of the CO adlayer (voltammetrically), we show that once the CO adlayer has been partially oxidized, the (111) terrace sites of stepped surfaces are released earlier than the (110) step sites. Moreover, if (110) steps are selectively decorated with CO, its oxidation occurs only at potentials ~150 mV higher than the CO pre-oxidation peak. Our results systematically demonstrate that step sites are less active to oxidize CO than those ones responsible for the CO pre-oxidation process. Once the sites responsible for the CO pre-oxidation are made free, there is no apparent motion of the remaining adsorbed CO layer, suggesting that the activation of the surface controls

As part of a mechanistic study of the electrooxidation of C1 molecules we have systematically investigated the dissociative adsorption/oxidation of formaldehyde on a polycrystalline Pt film electrode under experimental conditions optimizing the chance for detecting weakly adsorbed reaction intermediates. Employing in situ IR spectroscopy in an attenuated total reflection configuration (ATR-FTIRS) with p-polarized IR radiation to further improve the signal-to-noise ratio, and using low reaction temperatures (3 °C) and deuterium substitution to slow down the reaction kinetics and to stabilize weakly adsorbed reaction intermediates, we could detect an IR absorption band at 1660 cm(-1) characteristic for adsorbed formyl intermediates. This assignment is supported by an isotope shift in wave number. Effects of temperature, potential and deuterium substitution on the formation and disappearance of different adsorbed species (COad, adsorbed formate, adsorbed formyl), are monitored and quan...

The electrocatalytic activity of a spontaneously tin-modified Pt catalyst, fabricated through a simple ''dip-coating'' method under open-circuit conditions and characterized using surface analysis methods, was studied in electrooxidation reactions of a preadsorbed CO monolayer and continuous oxidation of methanol, formic acid, and formaldehyde in the potentiodynamic and potentiostatic modes. The catalytic activity of the tinmodified Pt surface is compared with that of a polycrystalline Pt electrode. Spontaneously Sn-modified Pt catalyst shows a superior activity toward adsorbed CO oxidation and thus can be promising for PEFC applications. The methanol oxidation rate is not enhanced on the Sn-modified Pt surface, compared to the Pt electrode. Formic acid oxidation is enhanced in the low potential region on the Sn-modified surface, compared to the Pt electrode. The formaldehyde oxidation rate is dramatically increased by modifying tin species at the most negative potentials, where anodic formaldehyde oxidation is completely suppressed on the pure Pt electrode. The results are discussed in terms of poisoning CO intermediate formation resulting from dehydrogenation of organic molecules on Pt sites, and oxidation of poisoning adsorbed CO species via the surface reaction with OH adsorbed on neighboring Sn sites.

A graphene nanoplatelet (GNP)-supported Ir-Zn catalyst (Ir-Zn/GNP) was fabricated by H 2 reduction to discover an alternative for non-platinum and non-palladium catalysts as an anode catalyst in direct formic acid fuel cell (DFAFC). The obtained Ir-Zn/GNP catalyst with ratio of Ir: Zn=50:50 (Ir 50 Zn 50 /GNP) exhibited better electrocatalytic activity than GNP-supported iridium catalyst (Ir/GNP) for formic acid oxidation. Although the oxidation peak current density of Ir50Zn50/GNP was slightly lower than that of Ir/GNP, the oxidation peak potential shifted more negatively (193 mV) than Ir/GNP with higher value of the ratio of forward scan to reverse the scan peak current (If/Ib). The presence of Zn also enhanced the power density and current generation with increased performance stability in a passive DFAFC cell tests. The improvement of the electrochemical performance was ascribed to the ensemble effect where the addition of Zn could modify the Ir atom arrangement, thereby promot...

This paper describes an electrochemical method for measuring dilute levels of chloride using an underpotentially deposited (UPD) Ag adlayer on polycrystalline Au substrates as a sensing agent. Specifically, chloride ions adsorb onto the Ag UPD adlayer and effect changes in the electrochemical deposition and stripping characteristics of the silver film. Cyclic voltammograms (CVs) of the native Au/Ag(UPD) electrode in 0.1 M H 2 SO 4 (aq) exhibit a primary stripping peak for the Ag UPD adlayer at 550 mV vs Ag +/0 , and chloride adsorption onto the Au/Ag-(UPD) surface effects a peak shift to ∼600 mV vs Ag +/0 , depending on the amount of adsorbed Cl-, as affected by the Clconcentrations and contact times employed in the derivatization. The chloride-treated electrodes also exhibit a stripping peak at 275 mV that is not observed on the native substrate and increases in intensity with Clconcentration and derivatization time. The integrated charge density for this latter stripping peak relative to that for the primary stripping peak at 550-610 mV provides a useful metric for quantifying adsorbed Cllevels, and these values allow measurement of Clconcentrations in dilute aqueous solutions. For Clconcentrations between 0.5 and 100 µM, the kinetics of Cladsorption followed a transient Langmuir adsorption model and allowed measured surface coverages to be used for determining Clsolution concentrations. Using contact times of 1 min for Cladsorption, the electrodes showed a linear response across Clconcentrations of 0.5-20 µM.

It was demonstrated that some foreign meta monolayers formed by underpotential deposition have pronounced catalytic effects on the oxidation of formic acid on platinum_ The explanation of these effects was sought within the framework of existing data on the formic acid oxidation and the underpotential deposition. It was found that the catalytic effect of foreign metal monolayers originates in the decrease of hydrogen adsorption thus preventing the formation of the main poisoning species*2QH. At the same time these experiments confir_m the previously post.ulated mechanism of formation of the p'oisoning species involving adsorbed hydrogen_ of ACademician kg. FIXK&&~~ 80th birthday.

A graphene nanoplatelet (GNP)-supported Ir-Zn catalyst (Ir-Zn/GNP) was fabricated by H2 reduction to discover an alternative for non-platinum and non-palladium catalysts as an anode catalyst in direct formic acid fuel cell (DFAFC). The obtained Ir-Zn/GNP catalyst with ratio of Ir: Zn = 50:50 (Ir50Zn50/GNP) exhibited better electrocatalytic activity than GNP-supported iridium catalyst (Ir/GNP) for formic acid oxidation. Although the oxidation peak current density of Ir50Zn50/GNP was slightly lower than that of Ir/GNP, the oxidation peak potential shifted more negatively (193 mV) than Ir/GNP with higher value of the ratio of forward scan to reverse the scan peak current (If/Ib). The presence of Zn also enhanced the power density and current generation with increased performance stability in a passive DFAFC cell tests. The improvement of the electrochemical performance was ascribed to the ensemble effect where the addition of Zn could modify the Ir atom arrangement, thereby promoting the oxidation through dehydrogenation pathway. However, extremely high Zn content would inhibit oxidation capability because Zn atoms might reduce the Ir catalytic sites. A new alternative for non-Pt and non-Pd anode catalysts for DFAFC applications was successfully achieved.