Electrooxidation Of Small Organic Molecules Research Articles

Advancements in Noble Metal-Decorated Porous Carbon Nanoarchitectures: Key Catalysts for Direct Liquid Fuel Cells.

Noble-metal nanocrystals have emerged as essential electrode materials for catalytic oxidation of organic small molecule fuels in direct liquid fuel cells (DLFCs). However, for large-scale commercialization of DLFCs, adopting cost-effective techniques and optimizing their structures using advanced matrices are crucial. Notably, noble metal-decorated porous carbon nanoarchitectures exhibit exceptional electrocatalytic performances owing to their three-dimensional cross-linked porous networks, large accessible surface areas, homogeneous dispersion (of noble metals), reliable structural stability, and outstanding electrical conductivity. Consequently, they can be utilized to develop next-generation anode catalysts for DLFCs. Considering the recent expeditious advancements in this field, this comprehensive review provides an overview of the current progress in noble metal-decorated porous carbon nanoarchitectures. This paper meticulously outlines the associated synthetic strategies, precise microstructure regulation techniques, and their application in electrooxidation of small organic molecules. Furthermore, the review highlights the research challenges and future opportunities in this prospective research field, offering valuable insights for both researchers and industry experts.

Controlled synthesis of reduced graphene oxide-supported bimetallic Pt–Au nanoparticles for enhanced electrooxidation of methanol

Controlled construction of bimetallic interfaces on conductive carbon supports is extremely important for achieving better synergistic effect required for electrooxidation of small organic molecules for energy applications. Herein, controlled synthesis of reduced graphene oxide (RGO)-supported bimetallic Pt–Au nanoparticles (Pt–Au/RGO) for electrooxidation of methanol using a facile and practical approach was described. By carefully adapting sequential and simultaneous reduction steps H2PtCl6 and AuCl3were reduced on RGO support using ammonia borane (AB) and ascorbic acid (AA) as reducing agents. Three types of Pt–Au/RGO catalysts were prepared and labeled as PtAu/RGO-AB1, PtAu/RGO-AB, and PtAu/RGO-AA. The reduction process was carried at ambient conditions, without the use of surfactants, and the catalysts obtained were analyzed through various techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS). The PtAu/RGO-AB1 catalyst showed remarkable uniformity on the RGO sheets, with an average particle size of 2–3 nm. The electrochemical behavior of Pt–Au catalysts supported on reduced graphene oxide (RGO) for methanol oxidation was systematically investigated via cyclic voltammetry and chronoamperometry techniques. Among the studied catalysts, PtAu/RGO-AB1 exhibited high electrochemical active surface area (ECSA) of 92.47 m2/g, along with the highest mass and ECSA-normalized activities for the electrooxidation of methanol. PtAu/RGO-AB1 manifested exceptional resistance to accumulated CO-like species, as evidenced by its higher forward peak current density to reverse peak current density ratio (If/Ib) of 2.20. The facile and effective synthesis strategy described here provides a promising method for fabricating well-defined multi-component nanostructured electrocatalysts with potential applications for various fuel cell reactions.

Facile Synthesis of Multifunctional Ni(OH)2-supported Core-shell Ni@Pd Nanocomposites for the Electro-oxidation of Small Organic Molecules.

In the domain of proton exchange membrane fuel cells (PEMFCs), the development of efficient and durable catalysts for the electro-oxidation of small organic molecules, especially of alcohols (methanol, ethanol, ethylene glycol, et al.) has always been a hot topic. A large number of related electrocatalysts with splendid performance have been designed and synthesized till now, while the preparation processes of most of them are demanding on experimental operations and conditions. Herein, we put forward a facile and handy method for the preparation of multifunctional Ni(OH)2-supported core-shell Ni@Pd nanocomposites (Ni(OH)2/Ni@Pd NCs) with the assistance of galvanic replacement reaction (GRR) at room temperature and ambient pressure. As expected, the Ni(OH)2 substrate can prevent the aggregation of core-shell (CS) Ni@Pd nanoparticles (NPs) and inhibit the formation of COads and further prevent Pd from being poisoned. The synergistic effect between CS Ni@Pd NPs and Ni(OH)2 substrate and the electronic effect between Pd shell and Ni core contribute to the outstanding electrocatalytic performance for methanol, ethanol, and ethylene glycol oxidation in alkaline condition. This study provides a succinct method for the design and preparation of efficient Pd-based electrocatalysts for alcohol electro-oxidation.

The Impact of Water Concentration on the Electro-Oxidation of Formic Acid on Platinum

Water plays a pivotal role in several electrocatalytic reactions. In the electrooxidation of small organic molecules, water can for instance assist the oxidation of adsorbed species or inhibit the reaction through the oxidation of surface sites. This paper is the third in a series of studies aiming at evaluating the impact of water concentration on the electro-oxidation of small organic molecules on polycrystalline platinum. The study was performed in phosphoric acid electrolyte, and the water concentration was varied from 14 to 50 mol l−1. Voltammetric profiles and potential oscillations were studied at distinct [H2O]/[H3PO4] ratios and constant concentration of formic acid. There is a diminution in the catalytic activity accompanying the decrease in the water concentration. The removal of carbon monoxide demands oxygenated species and can proceed in the absence of water for ethanol and methanol, but not for formic acid. Under oscillatory regime, the impact of water concentration, it is seen that higher water concentration implies higher oscillation frequencies, shorter and less stable time-series, and sharper transitions from low to high potential, where the adsorbed carbon monoxide is oxidized by adsorbed oxygenated species. Results are discussed in connection with the voltammetric study and also compared with other parent systems.

On the electro-oxidation of small organic molecules: Towards a fuel cell catalyst testing platform based on gas diffusion electrode setups

The electrocatalytic oxidation of small organic compounds such as methanol or formic acid has been the subject of numerous investigations in the last decades. The motivation for these studies is often their use as fuel in so-called direct methanol or direct formic acid fuel cells, promising alternatives to hydrogen-fueled proton exchange membrane fuel cells. The fundamental research spans from screening studies to identify the best performing catalyst materials to detailed mechanistic investigations of the reaction pathway. These investigations are commonly performed at conditions quite different to fuel cell devices, where no liquid electrolyte will be present. We previously developed a gas diffusion electrode setup to mimic “real-life” reaction conditions and study electrocatalysts for oxygen gas reduction or water splitting. It is here demonstrated that the setup is also suitable to investigate the properties of catalysts for the electro-oxidation of small organic molecules simulating conditions of low temperature proton exchange membrane fuel cells.

The Efficiency of the Electro-Oxidation of Small Organic Molecules: Oscillations and Mechanism

Many hydrogen-carriers have been considered for the direct use in fuel cells and also in the electrochemical reform, where they are oxidized instead of water at lower potentials. We have investigated the electro-oxidation of formaldehyde, formic acid, methanol, and ethanol,[1] and of ethylene glycol, glycerol, and glucose[2] on polycrystalline platinum in acidic media, and compare the activity under conventional and oscillatory regimes. The comparison is carried out by different means and generalized by the use of simple identical experimental conditions in all cases. The activity along slow potentiodynamic curves, inferred by the peak current, decreases in the following sequence: formaldehyde ~ formic acid > methanol > ethanol ~ ethylene glycol > glucose > glycerol. The ubiquitous occurrence of potential oscillations under galvanostatic regime is associated with excursions of the electrode potentials to lower values, which noticeably decreases the overpotential of the anodic reaction, when compared to that in the absence of oscillations. Considerable enhancement in the power density was observed in an idealized fuel cell operated with those fuels when operated under oscillatory regime. Furthermore, the spontaneous periodic self-cleaning processes, present important advantages to the use of autonomous oscillations to reach both higher and long-term activities, and stability [3]. The discussion of these half-cell studies is complemented with experiments with proton exchange membrane fuel cells, namely direct liquid fuel cells (DLFCs). We have investigated the effect of temperature on DLFCs under conventional and oscillatory conditions.[4] Methanol, formic acid, ethanol, and dimethyl ether (DME) were used as fuels and identical experimental conditions were used in all cases. Some findings observed in half-cells are also observed in the DLFCs studied, but few peculiarities of the experimental configuration adopted in the later arise. Finally, mechanistic aspects underlying the observed dynamics are discussed.[1] M. V. F. Delmonde, L. F. Sallum, N. Perini, E. R. Gonzalez, R. Schlögl, H. Varela, J. Phys. Chem. C 120 (2016) 22365.[2] G. B. Melle, T. A. Ferreira, R. L. Romano, H. Varela, in preparation (2020).[3] J. A. Nogueira, P. P. Lopes, N. M. Markovic, H. Varela, Electrochem. Commun. 121 (2020) 106853.[4] J.A. Nogueira, H. Varela, Energy Fuels 34 (2020) 12995.

How decoration with Tl affects CO electro-oxidation on Pd (1 0 0) nanocubes: In situ FTIR and ab-initio insights

• Pd nanocubes were synthesized, modified by Tl and tested for CO electrooxidation. • Different amounts of Tl influence CO electrooxidation reaction on these surfaces. • CO adsorbs in a two-site geometry on clean Pd surfaces. • The adsorption geometry changes for on-top in presence of minor amounts of Tl. • DFT data reveals that high Tl coverages hinder CO adsorption on Pd. In this work we prepare Pd (1 0 0) preferentially oriented nanoparticles modified with different amounts of Tl and study the CO electro-oxidation reaction on these surfaces in alkaline medium. The analysis is based on cyclic voltammetry coupled with in situ FTIR spectroscopy, and the results are interpreted with the help of a DFT study. In situ FTIR indicates a change in the CO adsorption geometry on Pd surfaces partially covered by Tl, while DFT data reveal that for high Tl coverages CO adsorption is completely inhibited. Based on our findings, by using the proper amount of Tl, one can think in the development of Pd-based catalysts designed to present tolerance to CO poisoning, aiming their application in the electro-oxidation of small organic molecules.

Pt3Mn alloy nanostructure with high-index facets by Sn doping modified for highly catalytic active electro-oxidation reactions

Modulating the surface structure of Pt-based alloy by oxyphilic component has been proven significantly enhancement of activity and stability for electro-oxidation of small organic molecules. Inspired by these advances, the oxyphilic metal Sn is implanted into the surface of Pt3Mn concave nanocubes (CNCs) to explore the promoting effect of foreign component on stepped Pt based alloy surface in this work. Detailed characterizations of catalysts reveal that the significant surface alloying layers (Pt-Mn-Sn) are formed after the insertion of Sn. The obtained Sn/Pt3Mn catalysts present the better specific activity (SA) and mass activity (MA) compared to the unmodified Pt3Mn catalyst towards both the electro-oxidation of formic acid (FAOR) and methanol (MOR). The optimal 0.5%Sn/Pt3Mn exhibits the enhanced mass activity of 4.07 and 2.60 folds than the Pt3Mn CNCs for MOR and FAOR, respectively. In particular, the optimal 0.5%Sn/Pt3Mn catalyst performs the efficient boost of stability and CO tolerance ability due to the stabilized effect on surface structure by Sn. Further investigations indicate that the presence of oxyphilic metal Sn can efficiently protect the surface structure from disruption. The thermodynamics studies also suggest that the Sn-doped catalysts have the advantage in decreasing the reaction activation energy than that of uncorporated Sn. All results demonstrate that the doped-Sn oxyphilic metals on the surface of Pt3Mn CNCs with high-index facets (HIFs) gives the better catalytic performance for electrooxidation of small organic molecules, further providing the design strategy for the protection of HIFs.

Dual-functioning porous catalysts: robust electro-oxidation of small organic molecules and water electrolysis using bimetallic Ni/Cu foams

The simultaneous co-deposition of Cu within the matrix of Ni foams (utilizing DHBT) increases their intrinsic catalytic activity towards water electrolysis, urea oxidation reaction (UOR), and glycerol oxidation reaction (GOR) in alkaline media.

Electrocatalytic performance of inorganic nanoflakes nickel phosphates under adjusted synthetic parameters towards urea and methanol oxidation in alkaline media

Inorganic nanoflakes nickel phosphates (Ni-P) were introduced to enhance the activity of the working electrode for the electrooxidation of small organic molecules: methanol and urea. The urea proportions during the synthesis of the Ni-P material were evaluated and its impact on Ni-P morphology and structure was determined. The as-fabricated Ni-P material was studied in terms of Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscope/ energy-dispersive X-ray spectroscopy (FESEM/EDX), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface area analyses. These techniques indicate the synthesized material is Ni-P with nanoflakes morphology. Cyclic voltammetry (CV), as well as impedance spectroscopy (EIS) techniques, were investigated in the reference/working/counter electrodes system to study the electrocatalytic performance of the introduced nanoflakes phosphate material for both methanol and urea oxidation in presence of KOH aqueous medium. 0.8 M of urea was the optimum proportion found for the electrocatalytic oxidation of methanol. The synthesized phosphates showed enhanced electrocatalytic oxidation of methanol and urea at different scan rates. Besides, the EIS approves the ability of the synthesized nanoflakes phosphate to electrochemically oxidize methanol and urea. This study presents cheap electrocatalysts to help in the commercial process of fuel cells as well as water treatment from organics like urea.

Oscillatory Reaction Rates in the Electro-Oxidation of Formaldehyde on Palladium

Formaldehyde has been used as a model system to investigate the electro-oxidation of small organic molecules, mainly on platinum[1]. This reaction is extremely dependent on the control conditions (potential and current) and it is also known to display self-organized oscillations on platinum[2]. In the present work we report a study of the oscillating reaction rates in the electro-oxidation of formaldehyde on polycrystalline palladium and in aqueous sulfuric acid media. The mapping of the existence region of potential oscillations was obtained by a slow current scan. Galvanodynamic oscillations were observed to range from 0.50 to 0.85 V. Further analysis was performed by galvanostatic measurements. The amplitude of potential oscillations increases in time. The potential-increase part of the cycle is formed by a rapid increase to about 0.60 V and then a slow one to 0.85 V, followed by an abrupt drop, with an average oscillation frequency of 0.15 Hz. Both the morphology and the frequency of oscillations differ from that observed for the electro-oxidation of formaldehyde on platinum, where the electrode potential varies from 0.40 to 0.90 V, and the it increases slowly until reaching 0.60 V followed by a rapid potential increase of up to 0.90 V, and then it decreases abruptly. Oscillations on platinum under comparable conditions were also about three times faster [3]. Overall, our results suggest the surface chemistry underlying the dynamics of formaldehyde elector-oxidation on palladium and platinum is considerably different, particularly under oscillatory regime. Some mechanistic aspects of the, far less studied, palladium system will be discussed.

Enhancement of Oxidation of Formic Acid through Application of Zirconia Matrix for Immobilization of Noble Metal Catalytic Nanoparticles

Electrocatalytic activity of common noble metal (platinum, bimetallic platinum-ruthenium and palladium) nanoparticles (both unsupported and supported on Vulcan carriers) toward electrooxidation of formic acid in acid medium (0.5 mol dm–3 H2SO4) can be significantly enhanced by dispersing them over thin film of zirconia (ZrO2). The enhancement effects concern increases of the electrocatalytic current densities (normalized against the mass of noble metal catalysts) recorded under both cyclic voltammetric and chronoamperometric conditions. The observations can be rationalized in terms of the ability of zirconia nanostructures to provide active hydroxyl groups capable of inducing the removal of the inhibiting COOH or CO type adsorbates from their surfaces. The role of Vulcan carriers is in improving electronic conductivity, in addition to facilitating distribution of catalytic metal sites at the electrocatalytic interface. Regarding dissimilar mechanisms for HCOOH oxidations at Pt, PtRu and Pd nanoparticles, the activating capabilities of zirconia differ depending on the potential applied thus reflecting distinct nature of electronic or chemical interactions. Specific interactions between the zirconia support and noble metal nanoparticles are also possible, particularly in the case of Pd-based catalysts where the enhancement effects are the most pronounced. Finally, it should be emphasized that, historically, representatives of Russian school of electrochemistry, including V.S. Bagotsky, were one of the first world-wide who investigated the formic acid oxidation and emphasized the importance of metal—support interactions during electrooxidation of small organic molecules at noble metal nanoparticles.

The Impact of Water Concentration on the Electro-Oxidation of Methanol on Platinum

The electro-oxidation of small organic molecules on platinum occurs via a mechanism that includes parallel reaction pathways and steps of adsorption/desorption and oxidation. The oxidation of adsorbed carbonaceous residues usually involves the participation of adsorbed oxygenated species. In this work, the impact of water concentration on the electro-oxidation of methanol on polycrystalline platinum was investigated, using phosphoric acid as supporting electrolyte. The bulk water concentration was varied from 14 to 50 mol L−1, and the system studied under both conventional and oscillatory regimes. Changing the [H2O]/[H3PO4] ratio implies changes in both water concentration and nature and population of electrosorbing anions. The developed strategy allowed at discriminating both effects and study in-depth the contribution of water concentration itself. Bulk water concentration was shown to play a major role on the electro-oxidation of methanol, and the lower the water concentration, the higher the potential at which the reaction sets in. Chronoamperometric data evidenced that water has a stronger impact on the reaction kinetics. The reaction order with respect to the water was estimated at different applied potentials and found to decrease as the potential increases. Concerning the potential oscillations, water concentration was found to affect the oscillatory frequency, waveform and amplitude. In summary, an increase in water concentration led to an increase in the oscillatory frequency; and the amplitude reaches a maximum when [H2O] = 30 mol L−1.

Tuning of catalytic properties for electrooxidation of small organic molecules on Pt-based thin films via controlled thermal treatment

Ability to utilize structure-function relationship in the design of electrocatalysts relies on fundamental understanding of physicochemical processes at the topmost surface. It has been demonstrated that reaction rate for majority of electrochemical reactions exhibit notable dependence on geometric arrangement of surface atoms due to varying levels of binding strength between different atomic structures and adsorbate molecules. Control of surface structure at nanoscale is being investigated here through a thin film approach. The surface characteristics of electrochemically deposited Pt thin films were probed for electrooxidation of small organic molecules such as formic acid and methanol. The low-index Pt single crystal electrodes were used for reactivity benchmarking which later guided thermal annealing processes, and ultimately, fine tuning of the ratio between (1 1 1) and (1 0 0) surface facets on Pt thin films. The tailored thin film structure is responsible for significant activation of both formic acid and methanol oxidation reactions, which justifies the approach.

Regulating Surface Facets of Metallic Aerogel Electrocatalysts by Size-Dependent Localized Ostwald Ripening.

It is well known that the activity and stability of electrocatalysts are largely dependent on their surface facets. In this work, we have successfully regulated surface facets of three-dimensional (3D) metallic Au m- n aerogels by salt-induced assembly of citrate-stabilized gold nanoparticles (Au NPs) of two different sizes and further size-dependent localized Ostwald ripening at controlled particle number ratios, where m and n represent the size of Au NPs. In addition, 3D Au m- n-Pd aerogels were further synthesized on the basis of Au m- n aerogels and also bear controlled surface facets because of the formation of ultrathin Pd layers on Au m- n aerogels. Taking the electrooxidation of small organic molecules (such as methanol and ethanol) by the resulting Au m- n and Au m- n-Pd aerogels as examples, it is found that surface facets of metallic aerogels with excellent performance can be regulated to realize preferential surface facets for methanol oxidation and ethanol oxidation, respectively. Moreover, they also indeed simultaneously bear high activity and excellent stability. Furthermore, their activities and stability are also highly dependent on the area ratio of active facets and inactive facets on their surfaces, respectively, and these ratios are varied via the mismatch of sizes of adjacent NPs. Thus, this work not only demonstrates the realization of the regulation of the surface facets of metallic aerogels by size-dependent localized Ostwald ripening but also will open up a new way to improve electrocatalytic performance of 3D metallic aerogels by surface regulation.

Suppression Effect of Small Organic Molecules on Oxygen Reduction Activity of Fe/N/C Catalysts

Pyrolyzed Fe/N/C catalysts have high selectivity for catalyzing the oxygen reduction reaction (ORR) and exhibit no activity toward the electrooxidation of small organic molecules (SOMs). As such, their tolerance toward SOMs has rarely been questioned. Unexpectedly, we found that SOMs can greatly suppress the ORR activity of microporous-type Fe/N/C catalysts in alkaline medium. Such a suppression effect is strengthened as molecular polarity decreases or molecular weight increases and can be attributed to the blockage of micropore transport channels for ORR-related species by SOM adsorption. Interestingly, such a suppression effect by micropore filling disappears in the acidic medium. High tolerance to SOMs in acidic medium is attributed to the protonation of pyridinic-N, which increases the polarity of the micropore surrounding and inhibits the adsorption of low-polarity SOMs. This study is helpful to guide the synthesis of porous Fe/N/C electrocatalysts, especially when they are applied in an alkaline medium.

Ultrasonic-assisted synthesis of N-doped graphene-supported binary PdAu nanoflowers for enhanced electro-oxidation of ethylene glycol and glycerol

The design of cost-efficient catalysts for the electrooxidation of small organic molecules are highly desirable for the commercial application of direct fuel cells. Shape-controlled PdAu alloys with N-doped graphene support are highly efficient electrocatalysts for the electrooxidation of ethylene glycol and glycerol in the alkaline media. Impressively, the newly generated Pd1Au1-NF/NG catalysts prepared by a facile ultrasonic-assisted synthetic method in this work exhibit the unprecedentedly high mass activities with 12.8 and 8.7Amg −1 towards ethylene glycol and glycerol oxidation, which are 10.07- and 12.25-fold enhancements than that of commercial Pd/C catalyst (1.27 and 0.71Amg −1), respectively. This work may open a new way in enlarging the surface area and ultimately maximizing the electrocatalytic activities by tuning the morphology of metallic alloy and introducing the appropriate catalyst supports.

Structure Design and Performance Tuning of Nanomaterials for Electrochemical Energy Conversion and Storage.

The performance of nanomaterials in electrochemical energy conversion (fuel cells) and storage (secondary batteries) strongly depends on the nature of their surfaces. Designing the structure of electrode materials is the key approach to achieving better performance. Metal or metal oxide nanocrystals (NCs) with high-energy surfaces and open surface structures have attained significant attention in the past decade since such features possess intrinsically exceptional properties. However, they are thermodynamically metastable, resulting in a huge challenge in their shape-controlled synthesis. The tuning of material structure, design, and performance on the nanoscale for electrochemical energy conversion and storage has attracted extended attention over the past few years. In this Account, recent progress made in shape-controlled synthesis of nanomaterials with high-energy surfaces and open surface structures using both electrochemical methods and surfactant-based wet chemical route are reviewed. In fuel cells, the most important catalytic materials are Pt and Pd and their NCs with high-energy surfaces of convex or concave morphology. These exhibit remarkable activity toward electrooxidation of small organic molecules, such as formic acid, methanol, and ethanol and so on. In practical applications, the successful synthesis of Pt NCs with high-energy surfaces of small sizes (sub-10 nm) realized a superior high mass activity. The electrocatalytic performances have been further boosted by synergetic effects in bimetallic systems, either through surface decoration using foreign metal atoms or by alloying in which the high-index facet structure is preserved and the electronic structure of the NCs is altered. The intrinsic relationship of high electrocatalytic performance dependent on open structure and high-energy surface is also valid for (metal) oxide nanomaterials used in Li ion batteries (LIB). It is essential for the anode nanomaterials to have optimized structures to keep them more stable during the charge/discharge processes for reducing damaging volume expansion via intercalation and subsequent reduced battery lifetime. In the case of cathodes, tuning the surface structure of nanomaterials should be one of the most beneficial strategies to enhance the capacity and rate performance. In addition, metal oxides with unique defective structure of high catalytic activity and carbon materials of porous structure for facilitating fast Li+ diffusion paths and efficiently trapping polysulfide are most important approached and employed in Li-O2 battery and Li-S battery, respectively. In summary, significant progress has already been made in the electrocatalytic field, and likely emerging techniques based on NCs enclosed with high-energy surfaces and high-index facets could provide a promising platform to investigate the surface structure-catalytic functionality at nanoscale, thus shedding light on the rational design of practical catalysts with high activity, selectivity, and durability for energy conversion and storage.

Potential oscillations during electro-oxidation of ethanol on platinum in alkaline media: The role of surface sites

The electro-oxidation of small organic molecules is one of the major areas of interest in electrocatalysis due to its potential use in energy conversion. Instabilities in alkaline solution, particularly in comparison with kinetic properties in a conventional regime, are rarely reported in the literature, despite the fact that the catalytic activity is higher in this medium and the onset potential is shifted to lower values compared to acidic media. Ethanol oxidation on polycrystalline platinum exhibits oscillations under galvanostatic control. As the reaction is structure-sensitive, it is possible to study the contribution of the three platinum basal planes to the complex kinetics. We found that Pt(100) has the major influence in the overall non-linear kinetics of ethanol electro-oxidation on Pt(poly), possibly because it has the highest formation and accumulation rate of COads. Based on the differences observed in the galvanostatic transients on Pt(poly), Pt(110) and\\ Pt(100), and the absence of this behavior on Pt(111), it is possible to infer that surface sites strongly influence the kinetic scenario during the ethanol oxidation reaction.

Experimentally Determined Correlation Between Electronic and Electrocatalytic Properties in Oxidation of Small Organic Molecules for Systems Consisting of Noble Metal

It is widely accepted that catalytic and electronic properties of catalyst‘s surface are strongly related. It has been postulated that the catalyst’s center of the d-band (εd) can be used to predict the adsorption strength and dissociation energy of simple molecules adsorbed on it. However there are not many studies correlating electronic properties of catalysts determined experimentally to the catalytic activity, because usually the electronic properties of catalysts surface are calculated using DFT. In this presentation we will focus on experimental verification of the role of electronic properties on the electrocatalytic activity of selected systems containing Pt, Pd and Rh, with purposefully modified electronic properties, in electrooxidation of small organic molecules, such as ethanol and formic acid. Model systems with purposely modified electronic properties were obtained by alloying and by forming of pseudomorfic layers of one metal on the surface of other metal. As a result in the investigated catalysts the lattice parameter was modified which, together with the possible partial charge transfer, induced the changes in their electronic properties. Modification of the lattice parameter changes the degree of overlapping of band forming orbitals and, according to the d-band center theory, it can be expected that when metal lattice is contracted, the valence band becomes broader, and when metal lattice is expanded the valence band (d-band) shrinks. The changes in d-band width causes the shift of the d-band: the broadening of the valence band leads to shift of the d-band center away from Fermi level and when the d-band shrinks, the d-band center shifts in the opposite direction. The changes in electronic properties can be observed using X-ray Photoelectron Spectroscopy (XPS) and UV Photoelectron Spectroscopy (UPS), and for the same material the catalytic properties can be monitored using electrochemical methods. We used this approach to investigate how the changed electronic properties influence the catalytic activity. We focused on CO, formic acid and ethanol electrooxidation reaction. Electrooxidation of small organic molecules, such as ethanol and formic acid, on noble metals is of particular interest due to its potential application in low temperature direct ethanol/formic acid fuel cells (DEFCs/DFAFCs), and for better understanding the mechanisms of electrode reactions. In particular CO and formic acid oxidation are considered model electrode reaction, where oxidation of ethanol, albeit more complicated, is of particular interest due to its importance in DEFCs. Despite the significant work already devoted to find a good low temperature catalyst for electrooxidation of ethanol, there is no known ethanol electrooxidation reaction (EOR) catalyst, allowing for complete electrooxidation of ethanol to CO2. Even for the most active systems, incomplete and slow EOR renders the DEFCs not economically viable. Better understanding of the factors influencing the catalytic activity should allow for development of novel, more active and selective electrocatalysts, and for further development of direct, liquid fuel feed, low temperature fuel cells. This project was funded from Polish National Science Centre budget based on decision number DEC-2013/09/B/ST4/00099