CO Electro-oxidation Reaction Research Articles

Electrooxidation of CO on Platinum Nanoparticles Supported on NiO Thin Films

In this article, we report on a robust experimental model to investigate strong metal–support interactions (SMSI) and their effect on electrocatalytic reactions in the absence and presence of direct contact between the nanoparticles (NPs) and the metal oxide thin film. Specifically, we describe beneficial interactions between Ni0.9O thin film supports and PtNPs toward the CO electrooxidation reaction. The metal oxide layer (Ni0.9O) is prepared by atomic layer deposition and characterized using X-ray photoelectron spectroscopy (XPS). PtNPs, containing an average of either 55 (Pt55) or 140 (Pt140) atoms, were synthesized using a dendrimer encapsulation method. The results indicate negative shifts of ∼100 and ∼60 mV of the CO electrooxidation peak potential when Ni0.9O thin films are in contact with Pt55 NPs and Pt140 NPs, respectively. Additionally, the oxygen evolution reaction (OER) is suppressed only when the PtNPs are in contact with the Ni0.9O thin film. Density functional theory (DFT) calculations indicate that both the CO electrooxidation enhancement and suppression of the OER can be attributed to a 1.23 eV decrease of the CO* binding energy and a 0.35 eV increase of the OH* binding energy at a NiO(111)/Pt55 NP interface compared to isolated Pt55 NPs.

Pt-O-Cu anchored on Fe2O3 boosting electrochemical water-gas shift reaction for highly efficient H2 generation

Electrochemical water–gas shift (EWGS) reaction is an emerging technology with energy-saving and environmental-friendly advantages to produce high-purity hydrogen form the waste gas containing CO. However, it remains a significant challenge to design superior activity and highly durable EWGS electrocatalysts, particularly with low content of noble metals. Herein, a series of Pt-xCu/Fe2O3 (x = 0, 2, 5) catalysts are synthesized by the complexation precipitation method to construct coupling sites between Pt and CuOx, aiming to optimize the adsorption of CO and the activation of OH–. The obtained 2.5Pt-2Cu/Fe2O3 catalyst presents a unique Pt-O-Cu structure, delivering a much lowest onset potential, high specific activity, and excellent mass activity (1.5 A·mgPt-1) at 0.73 V (vs. RHE), which is over 15 and 3 times that of commercial Pt/C (20%) and unmodified Pt/Fe2O3 catalyst, respectively. Meanwhile, the in-situ X-ray absorption results demonstrate that the facilitated interaction among the Pt-O-Cu structure promotes the high durability of the 2.5Pt-2Cu/Fe2O3 catalyst and the operability at high potential. More importantly, the moderate binding of CO and moderate activation of OH* are suggested for boosting the reactivity in the CO electro-oxidation reaction. In particular, the fabricated Pt||2.5Pt-2Cu/Fe2O3, employed in coupling the HER and CO electro-oxide reaction, shows a remarkable hydrogen production of about 98 mmolH2·h−1·mgPt−1 at 0.8 V (vs. RHE). This work also definitely confirms the possibility of the catalyst being applied to produce hydrogen under practical conditions with different concentrations of CO, even being applied in the purification of trace CO in a hydrogen-rich atmosphere.

Direct Evidence for the Decisive Role of OH* Activation in CO Electro-Oxidation Reaction

Direct Evidence for the Decisive Role of OH* Activation in CO Electro-Oxidation Reaction

Revised Zero-Dimensional Model for a Solid Oxide Fuel Cell with Mo-Doped Ceria Anode Using Syngas as Fuel

A zero-dimensional model was implemented to simulate the performance of a solid oxide fuel cell (SOFC) with Mo-doped ceria (CMO) anode using humidified (3%v/v water) syngas (50%v/v H2 – 50%v/v CO) as fuel. The model was validated preliminarily using polarization data (cell voltage vs current density, ΔEcell vs j, curves) generated experimentally at 800ºC using a SOFC supported on the electrolyte (a 20 mm diameter, 250 μm thickness yttria-stabilized zirconia, YSZ, disc) with a 14 mm diameter CMO-YSZ|CMO anode and a 14 mm diameter LSM (lanthanum strontium manganite)|LSM-YSZ cathode, that was connected to a Gamry Reference 3000 potentiostat/galvanostat/ZRA using platinum mesh and wires. Open circuit voltage was modeled using a Nernst equation corrected by H2 and CO electrooxidation reactions selectivity at the anode, which was determined through the resolution of relevant mass balances as a function of the SOFC thermodynamics and kinetics.

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.

The electrochemical interface of the cathode in high temperature PEM fuel cells

One of the most challenging areas towards the optimization of fuel cell technology is the development of catalytic layers with active, extended and stable electrochemical interfaces giving the ability to operate under a variety of operational conditions. In this work, the effect of parameters such as the amount of H3PO4 and Pt loading was examined regarding the formation of the electrochemical interface of an operating cathodic electrode in a high temperature PEM Fuel Cell. Electrodes beased on commercial 30 wt% Pt/C and H3PO4 imbibed TPS polymer electrolyte membrane were employed. Based on the thickness and catalyst loading of the catalytic layer, there is an optimum amount of acid in relation to the partial pressure of steam (pH2O) produced at the cathode that leads to uniform wetting of the catalyst avoiding catalyst poisoning and/or blocking due to flooding of the electrode. Interestingly high pH2O causes a decrease in H2 evolution reaction rate and increase in H2 adsorption coverage, implying stronger Had bonding with the Pt surface. Moreover, this work describes the development of a reliable procedure for quantitative evaluation of the real electrochemical active surface area (ECSA) of high temperature Pt electrodes by the combined analysis of CO stripping experiments and the simultaneous CO2 recording by means of online mass spectrometry. Regardless of the H3PO4 or Pt loading in the cathodic electrode, increase of steam's partial pressure progressively causes the degradation the Pt/C|H3PO4 electrochemical interface. At pH2O > 10 kPa, the ECSA decreased in all cases, but more intensely for high amounts of Η3PΟ4 within the electrode structure. The charge of the peak in the cyclic voltammogram did not completely correspond to the CO electrooxidation reaction. This difference is attributed to side oxidation reactions taking place within the same potential window as with the COad electrooxidation and depends on conditioning time (CO adsorption time), temperature and humidity.

Understanding the interplay of bifunctional and electronic effects: Microkinetic modeling of the CO electro-oxidation reaction

In this work, we build a microkinetic (MK) model of the CO electro-oxidation reaction using density functional theory (DFT) calculations and scaling relations to understand the interplay between bifunctional mechanisms and electronic modification. A single-site model is first used to identify trends in activity under different operating conditions. The model is then extended to include two site types to understand the surface characteristics necessary for bifunctional activity. For these general cases, we show that the “optimal” adsorption energetics change as a function of the applied potential. We then perform a case study by explicitly modeling both site types in platinum-ruthenium alloy models to assess whether bifunctional or electronic effects are most operative. We find that if these materials indeed remain metallic alloys, then electronic effects are likely dominant, with the sole active sites being electronically-modified Pt sites. Ru sites are spectators that favorably perturb the electronic structure of Pt.

Modulating the oxophilic properties of inorganic nanomaterials for electrocatalysis of small carbonaceous molecules

Abstract Modulating the oxophilic properties of inorganic nanomaterials has become a powerful approach to achieve high catalytic performance of electrocatalytic reaction in fuel cells. This review introduces the recent progress on the methods of engineering the oxophilic properties of nanomaterials and their corresponding applications in electrocatalysis. Key engineering methods are summarized, including decorating oxophilic atoms and nanoclusters on host metal based nanocatalysts, engineering the oxophilic composition of nanocatalyst surfaces, and utilizing oxophilic materials as support for nanocatalysts. The critical role of the oxophilic properties of these nanocatalysts in CO electrooxidation, alcohol electrooxidation, and formic acid electrooxidation reactions are highlighted. Perspectives on engineering the oxophilic properties of nanomaterials and their influence on electrocatalysis are presented.

A Kinetic Analysis of the CO Electro-Oxidation Reaction on Pt Bimetallics: Understanding the Interplay of Bifunctional and Electronic Effects

The CO electro-oxidation reaction has been one of the most thoroughly studied reaction mechanisms in electrocatalysis, mostly due to its role as a model reaction for the oxidation of larger organics like methanol and ethanol, each of which have important renewable energy applications in direct alcohol fuel cells. Bimetallics of Pt-M (where M is an oxophilic modifier such as Ru or Sn) have been shown extensively to have improved CO tolerance compared to pure Pt. The reason for this enhancement is often attributed to some combination of bifunctional (oxophilic metal provides OH to remove poisoning CO on Pt) and electronic (oxophilic metal weakens the CO binding strength on the Pt sites) effects. However, it has been difficult to determine the extent to which these different effects are operative in a given system. In this work, we perform a kinetic analysis of the CO electro-oxidation reaction in order to elucidate the roles of bifunctional and electronic effects. We look specifically at the classic Pt-Ru bimetallic system, and determine that the rates of bifunctional coupling are generally lower than the rates of coupling on Pt sites electronically modified by Ru. This indicates that, at least for the Pt-Ru system, the electronic effects that weaken CO binding on Pt are more operative than the bifunctional effect. This implies that that the prospects for bifunctional gains in general may be more limited than once thought, and that a more rational design parameter for bimetallic materials may be the electronic effects between the two components.

Calculations of the pH-Dependent Onset Potential for CO Electrooxidation on Au(111).

CO electrooxidation on the Au(111) surface exhibits an onset potential that depends strongly on the pH of the electrolyte. In alkaline solution, the onset potential for CO electrooxidation is found, experimentally, to be 0.5 V lower than in acidic media on the reversible hydrogen electrode scale. This phenomenon is explained here with density functional theory which is used to calculate adsorbate binding energies including the electric double layer of the Au(111)/aqueous interface. Our model consists of a charged Au(111) slab and implicit solvation for the electrolyte. The double reference method is used to determine the potential-dependent CO electrooxidation reaction energetics. A microkinetic model, based upon the calculated reaction energetics, confirms the lower onset potential in alkaline media. Our results show that there are three factors contributing to the lower onset potential in base: (1) stronger CO adsorption, (2) attraction between adsorbed CO and OH-, and (3) the high concentration of OH- in base.

Origins of Less Noble Behavior by Au during CO Adsorption

The behavior of CO interaction with gold in electrochemical environment is presented in this work by means of SERS technique. The results shows spectroscopic evidences that the adsorbed CO promotes the formation of oxidic species even at potentials where is not thermodynamically favorable (lower than 0.6 V vs. RHE), explaining the low overpotential CO electrooxidation reaction onset (@ ca. 0.2 V). At high potentials (<1.3 V), the CO displays an anomalous behavior, persisting adsorbed on the surface at high coverage oxide film which allow us to use the CO molecule as a probe and get information about the electrode surface on the course of the reaction as well as suggesting gold oxide as an active catalyst in small organic alcohol oxidation.

Uncovering the real active sites of ruthenium oxide for the carbon monoxide electro-oxidation reaction on platinum: The catalyst acts as a co-catalyst

The poisoning of platinum electroactive surfaces by the adsorption of CO is a critical hindrance for the development of fuel cells. Combining Pt with (hydrous) ruthenium oxide has been shown to enhance the CO electro-oxidation reaction on the electrocatalyst. However, how the co-catalyst surface provides oxygenated species to remove CO adsorbed on platinum is still an undiscussed matter. Here we show that an indispensable intermediate form of RuO2, catalyzed by Pt, is responsible for the removal of CO on Pt at low potential. In order to unravel the synergetic effect of ruthenium oxide and platinum towards CO electro-oxidation, ruthenium oxide nanosheets (RuO2(ns)) with monoatomic thickness were deposited onto the surface of polycrystalline Pt, glassy carbon and polycrystalline Au rotating disk electrodes. Combined with the well-defined electrochemical behavior of RuO2(ns), these model electrodes enabled to investigate both (i) the synergetic effect of ruthenium oxide towards the electro-oxidation of CO on Pt and (ii) the influence of the metal substrate (Pt or Au) towards the electrochemical behavior of RuO2. When deposited on the smooth Pt surface, RuO2(ns) were found to fully interact as a co-catalyst for the electro-oxidation of (monolayer adsorbed and bulk) CO on Pt, without blocking the electroactive surface of Pt. The addition of RuO2(ns) lead to two distinct synergetic effects for the bulk electro-oxidation of CO on Pt. Upgrading the general understanding, an interdependency between RuO2 and Pt is observed for the ‘low potential’ electro-oxidation of bulk CO (onset at 0.65V vs. RHE).

Carbon-supported Pt nanoparticles with (100) preferential orientation with enhanced electrocatalytic properties for carbon monoxide, methanol and ethanol oxidation in acidic medium

The relationship between atomic arrangement (morphology) and catalytic activity/selectivity in heterogeneous catalysis is an actual hot research topic concerning a range of reactions. This article evaluates one-pot synthesized carbon-supported Pt nanoparticles with preferential Pt(100) orientation prepared with an environmentally friendly shape-directing agent and compares this with Pt/C polycrystalline towards CO, methanol and ethanol electrooxidation reactions. The preferentially cubic nanomaterial (Pt-(100)) interacts differently with CO molecule and presents distinct hydrogen adsorption/desorption characteristics. Pt/C polycrystalline exhibits a CO-stripping profile with one peak at 0.86 V in contrast to three peaks between 0.75 and 0.86 V and a pre-peak at about 0.4–0.6 V for the Pt/C-(100), which may be associated to the unique surface characteristics of the cubic material. The onset potentials towards carbon monoxide, methanol and ethanol electro-oxidation reactions on Pt/C-(100) are 22%, 21% and 54% lower than on Pt/C polycrystalline. The ratio between the forward per backward peak current densities for the electrooxidation of ethanol and methanol are higher on Pt/C-(100), which suggests that Pt(100) domains are more tolerant to undergo poisoning by the intermediates/by-products formed in these reactions. Proton exchange membrane fuel cells fed with pure hydrogen and with a H2/CO mixture show superior performance using Pt/C-(100) as anode in comparison to Pt/C polycrystalline catalyst. These results evidence that controlling the morphology of Pt nanoparticles is a key factor to improve the catalytic activity of the polymer electrolyte fuel cell fueled with fuels that involve the electro-oxidation of CO.

Distributed-Charge Transfer Model Analysis of SDC-based IT-SOFCs for the Electrochemical Oxidation of Syngas and Biogas

Introduction Applications based on Solid Oxide Fuel Cells (SOFC) for distributed production of energy require the cell to operate both with traditional hydrocarbons (CH4, LPG) and biomass-derived fuels (biogas). Several benefits in terms of lifetime and thermo-mechanical resistance are achieved by decreasing the operating temperature to 500-700°C (IT-SOFC). On the one hand, the use of hydrocarbons leads traditional Ni-based anodes to deactivate due to coke formation; on the other hand, lower temperatures ask for electrolytes different from YSZ, mostly based on Ce oxides. Novel cells and materials are then required. In this work, IT-SOFCs based on Samarium doped Ceria (Sm0.2Ce0.8O1.9, SDC) electrolytes and Cu/Pd/CZ80 anodes are investigated for applications with syngas mixtures and CO2/CH4 mixtures. A physically-based, numerical model of the IT-SOFC was applied to analyze the experimental results and kinetic equations were derived for the electro-chemical reactions: in the presence of syngas, the occurrence of a co-oxidation route is proved, wherein H2 and CO are electro-oxidized contemporarily. Materials and Methods SDC electrolyte-supported cells with 15 wt% Cu, 0.15 wt% Pd, 15 wt% CZ80 (CZ80 20 wt% CeO2, 80 wt% ZrO2) composite anodes and LSCF cathodes were prepared by die-pressing. SDC powders mixed with graphite were pressed with pure SDC. The bilayer was calcined in air (1400°C, 3 h) producing a porous SDC scaffold (150 μm) supported on a dense SDC electrolyte (380 μm). The porous scaffold was impregnated with Cu/Pd/CZ80-based solutions and then the cathode (40 μm) was deposited. Polarization and EIS measurements were collected between 600 and 700°C with syngas mixtures (2.3 – 0.4 H2/CO ratio), H2/N2 mixtures (from 97 to 30% H2 v/v), CO/CO2 mixtures (from 97 to 50% CO v/v) and synthetic biogas (75% CH4/25% CO2). The EIS tests were performed at the OCV. A model was applied to analyze both the EIS spectra and the polarization curves. The model is one-dimensional, charge-distributed, Dusty-Gas, dynamic and heterogeneous and allows to predict the cell voltage based on physically-sound conservation equations for mass, charge and energy. The model includes molecular kinetic schemes for the anodic catalytic reactions (CO2 reforming of CH4, WGS) and for the electrocatalytic reactions (H2 and CO electro-oxidation, O2 reduction). Appropriate correlations account for the presence of the electronic current leakage in the electrolyte. Results and Discussion The IT-SOFCs were first tested in syngas mixtures at varying the H2/CO ratio: no variation was found passing from 2.3 to 0.4 ratio (Fig. 1a). Analogous observations were done with the EIS spectra. These results suggested that both the H2 electro-oxidation and the CO electro-oxidation occurred simultaneously in the presence of syngas. A model analysis of the polarization and EIS curves was performed to prove the activation of the co-oxidative route for CO and H2. The IT-SOFCs were thus tested in H2/N2 mixtures at varying H2 concentration to derive a power-law kinetic rate equation for the electro-oxidation of H2. The polarization curves (Fig. 1b) showed a decrease of the extracted current at decreasing H2 partial pressure. As well, an increase of the polarization resistance at decreasing H2 content was observed in the EIS tests (Fig. 1c). Coherently with the use of SDC, which is a MIEC electrolyte and activates a leakage current, the measured OCVs were smaller than the Nernstian ones. Application of the charge distributed model revealed the axial variation of the leakage current in the electrolyte and in the electrodes. To complete the kinetic investigation, EIS and polarization tests with CO/CO2 mixtures were performed to derive a power-law rate for the CO electro-oxidation reaction. A picture similar to that of the H2/N2 tests was observed. The rate equations and their parameters (reaction orders, activation energies and rate constants) were derived based on the best simulation of the impedance spectra. Once these rates were extracted, the experiments with syngas mixtures were simulated on a fully predictive basis: the close match of the simulations confirmed that the co-oxidative scheme could rationalize the data. Simulations based on different reactive schemes (H2 oxidation + WGS, CO oxidation + RWGS) failed in achieving a satisfactory description, suggesting that the parallel oxidation of H2 and CO was the only adequate scheme. Conclusions By means of model analysis of experimental polarization and impedance curves, we show that, in the presence of syngas, the electro-oxidation of H2 and that of CO occur simultaneously in a novel, Ni-free, IT-SOFCs based on Samaria-doped Ceria. The activation of a co-oxidative route is a most distinguishing feature of Ce-based cells, compared to traditional SOFCs. Figure 1

Performance and transient behavior of the kW-grade PEMFC stack with the Pt[sbnd]Ru catalyst under CO-contained diluted hydrogen

In the study, a self-made kW-class 40-cell proton exchange membrane fuel cell (PEMFC) stack, with an active area of 112.85 cm2 for each membrane electrode assembly and with the anodic PtRu catalyst, was tested under different simulated reformate gases of different CO concentrations and different hydrogen concentrations. The performances and the transient voltages of the stack and the individual cells under different CO/N2/H2 mixtures were studied. The results show that increasing the CO concentration or decreasing the H2 concentration of the CO-contained reformate gas negatively affects the performance of the PEMFC stack. Moreover, the PEMFC stack with the PtRu anodic catalyst can tolerate a CO concentration of up to 50 ppm under non-diluted H2. However, it can only tolerate 10 ppm CO under diluted H2. The CO tolerance decreases dramatically with an increase in the H2 dilution level. In addition, increasing the CO concentration in diluted H2 or decreasing the H2 concentration in CO-contained H2 accelerates the occurrence of potential oscillation. The potential oscillation is owing to the interactions of CO electro-oxidation and adsorption reactions on the catalyst. This work is also the first to report that the potential oscillation phenomenon initially occurs at the upstream cells of the stack.

CO electro-oxidation reaction on Pt nanoparticles: Understanding peak multiplicity through thiol derivative molecule adsorption

The electro-oxidation of CO adsorbed on Pt nanoparticles is an important reaction in fuel cells. Despite extensive research, the underlying concept for peak multiplicity is not yet clearly understood. We investigated CO electro-oxidation features by scan-rate-dependent Tafel analysis and a model system experiment based on adsorption of 3-mercaptopropionic acid (3-MPA). The results suggest that the first main oxidation peak corresponds to the competition between OH adsorption and the interaction between adsorbed CO and OH. Modifying the Pt surface with 3-MPA can reduce the OH coverage, which in turn reduces the width of the first peak. However, the peak potential is not significantly dependent on OH coverage. Considering that the free surface is large enough for OH adsorption on Pt at high potential, the second peak shows few features that depend on OH coverage; the second peak is mainly influenced by the Pt-CO interaction.

Synthesis and evaluation of CO electro-oxidation activity of carbon supported SnO2, CoO and Ni nano catalysts for a PEM fuel cell anode

Fuel contaminants especially CO which have poisoning effect on anodic catalysts, are the main barriers to commercialization of PEM fuel cell technology. Many efforts have been done to discount the CO poisoning effect on anodic catalysts. The non-noble metal elements capability for CO electro-oxidation per-se has not been fully evaluated. In this paper, properties of non-noble metal catalysts for CO electro-oxidation were studied. To do this, carbon supported nano-catalysts of SnO2, Ni and CoO were synthesized via the borohydride reduction method. Their electrochemical activity for CO electro-oxidation was evaluated in an in-house made half-cell using a new electrochemical test procedure based on recording CV current under continuous CO gas flow over the catalyst surface. Then, electrochemical tests on the synthesized catalysts and commercial Pt20/C were performed. The max current charge obtained from CO electro-oxidation with commercial Pt20/C was 13,200 μA per mg of metal at 0.74 V and for SnO2/C, CoO/C and Ni/C were 630, 450 and 140 μA per mg of metal, respectively. These amounts were obtained at 0.58, 0.43 and 0.26 V. Results proved the capability of CoO/C and SnO2/C to perform the CO electro-oxidation reaction at low potentials in a PEM fuel cell anode condition.

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

Oxidation of Small Organic Molecules on Noble Metals and Pseudomorphic Layers of Noble Metals

Ethanol, due to its low toxicity and relatively high energy density, is a promising candidate to be used in fuel cells. It is mainly obtained from biomass, thus its oxidation does not influence the total CO2 amount in the biosphere. However incomplete and slow electrooxidation of ethanol impedes the commercialization of low-temperature ethanol fuel cells. Electrocatalytic oxidation of ethanol is a complex, multi-step process with not completely understood mechanism. Factors influencing the catalytic activity of many systems towards ethanol electrooxidation are still unclear, and effective catalyst for ethanol electrooxidation has not been discovered yet. Most systems used for electrocatalytic oxidation of ethanol contain platinum-group metals in the form of nanoparticles, but even for those systems high overpotentials and incomplete oxidation of ethanol is observed. Another factor influencing the catalytic activity towards ethanol oxidation is poisoning of catalysts’ surface by products of incomplete oxidation. In particular for Pt, a quick decrease in surface activity during ethanol electrooxidation has been observed, which is related to surface poisoning by strongly adsorbed CO, a by-product of ethanol electrooxidation reaction. Adsorption of CO inhibits further electrooxidation of ethanol, and as a result high electrode potential is required to oxidize ethanol, as the surface CO must be oxidized first. To overcome the problem of surface poisoning by CO, bi-metallic surfaces, such as Pt-Ru and Pt-Sn were proposed, due to the fact, that the second metal provides adsorbed OH groups, required to oxidize the adsorbed CO, at lower potential than Pt. This so-called “bifunctional mechanism” was firstly described for methanol electrooxidation on Pt-Ru by Watanabe and Motoo in 1975. However in the case of ethanol electrooxidation the presence of Ru or Sn on Pt surface, despite yielding higher current density, leads to even further decrease in CO2 yield, increase the amount of acetic acid produced. This shift in product distribution significantly decrease the maximum amount of energy, which can be obtained from ethanol electrooxidation in conditions relevant to fuel cells on Pt-Sn or Pt-Ru, as it is impossible to oxidize acetic acid in those conditions, making oxidation of ethanol effectively a 4-electron process. It is thus imperative to develop new catalysts more active towards C-C bond scission, which is impossible without good understanding of the factors influencing catalytic activity in general. It is postulated, that electronic properties are in part responsible for catalytic activity of a given material. Theoretical DFT calculations suggest that chemisorption energy, activation barrier and energy of dissociation of small molecules on metal surface can be correlated to the d-band center of gravity of that metal (so called d-band center theory). This holds true for many systems and reactions it is possible that for more complex system other factors, not included in the d-band center theory, can play a significant role. For instance for more complex reactions, such as oxidation of simple alcohols, the relation between electronic and electrocatalytic properties are much more complicated, because those reactions are multi-step processes and the change of electronic properties may influence the elementary reactions to a different degree. One of the model systems allowing for studying the relation between catalytic and electronic properties of transition metals are pseudomorphic layers. Such systems consist of one metal (substrate) on which another metal is deposited forming a thin layer, usually a monolayer. It has been discovered, that in those systems the top atom layer mimics the crystallographic structure and lattice parameter of the substrate. Possible examples of such systems are monocrystal substrate with a monolayer of other metal or core-shell nanoparticles. Pseudomorphic layers allow to introduce and study changes in electronic properties due to modification of lattice parameter of the topmost layer and changes resulting from possible partial charge transfer between topmost layer and substrate material. At the same time, if pseudomorphic layer provides full coverage of the substrate’s surface, non-electronic effects, such as above mentioned bi-functional mechanism, can be eliminated. We focused on correspondence between electronic properties of noble metals (especially Pt and Pd) and their pseudomorphic layers observed using X-ray Photoelectron Spectroscopy (XPS) and UV Photoelectron Spectroscopy (UPS) and catalytic activity towards CO, formic acid and ethanol electrooxidation reactions. Catalytic activity was investigated using electrochemical methods. Oxidation of formic acid was selected as a model electrode reaction while oxidation of CO is a crucial step in electrooxidation of ethanol on noble metals. This project was funded from Polish National Science Centre budget based on decision number DEC-2013/09/B/ST4/00099

Optimization of alkaline catalytic inks for three-electrode electrochemical half-cell measurements

Recent development on new anionic exchange membranes for alkaline membrane fuel cells has led to an increase on electrocatalyst testing measurements in three-electrode half-cells in alkaline media. However, there is not yet any commercial alkaline ionomer widely used, comparing to Nafion® in acidic media. In this work, two different commercial alkaline ionomers (I2 from Acta and Fumion® FAA-3 from Fumatech) are tested. Different catalyst: ionomer ratios are employed in order to adjust the ink composition for a correct evaluation of the catalyst activity. For this purpose, a commercial 20 wt.% Pt/C catalyst was tested for CO electrooxidation and oxygen reduction reaction in thin layer RDE configuration.