Coadsorption Of OH Research Articles

Atomic-level rhodium doping into NiO for boosting the selective electrooxidation of HMF to FFCA in neutral electrolyte

The oxidation reaction of the biomass derivative 5-hydroxymethylfurfural (HMF) holds immense promise for the sustainable synthesis of high-value chemicals. Nevertheless, achieving the selective electrooxidation of HMF to generate high value-added formyl-2-furan carboxylic acid (FFCA) intermediate remains a serious challenge. Here, the V-NiO-Rh catalyst was constructed and demonstrates an impressive FFCA selectivity of 71 % for HMF electrooxidation reaction (HMFOR) in neutral electrolyte. The designed experiments elucidate that the HMFOR mechanism is the co-adsorption of OH* and HMF* on Ni active sites. Furthermore, the theoretical calculations prove that the modulation of Ni electronic structure by single atom Rh promotes the ability of HMF adsorption and the water electrolysis to release OH*. This paper establishes a theoretical foundation for the selective synthesis of high value-added intermediates products that are challenging to obtain in alkaline media.

Theoretical Study of the NO Reduction Mechanism on Biochar Surfaces Modified by Li and Na Single Adsorption and OH Co-Adsorption

Theoretical and experimental investigations have shown that biochar, following KOH activation, enhances the efficiency of NO removal. Similarly, NaOH activation also improves NO removal efficiency, although the underlying mechanism remains unclear. In this study, zigzag configurations were employed as biochar models. Density functional theory (DFT) was utilized to examine how Li and Na single adsorption and OH co-adsorption affect the reaction pathways of NO reduction on the biochar surface. The rate constants for all reaction-determining steps (RDSs) within a temperature range of 200 to 1000 K were calculated using conventional transition state theory (TST). The results indicate a decrease in the activation energy for NO reduction reactions on biochar when activated by Li and Na adsorption, thus highlighting their beneficial role in NO reduction. Compared to the case with Na activation, Li-activated biochar exhibited superior performance in terms of the NO elimination rate. Furthermore, upon the adsorption of the OH functional group onto the Li-decorated and Na-decorated biochar models (LiOH-decorated and NaOH-decorated chars), the RDS energy barriers were higher than those of Li and Na single adsorption but easily overcome, suggesting effective NO reduction. In conclusion, Li-decorated biochar showed the highest reactivity due to its low RDS barrier and exothermic reaction on the surface.

Coadsorption of hydrazine and OH on the Ni(211) surface: A DFT study

Hydrazine (N2H4) and hydroxyl (OH) coadsorption on the Ni(211) surface is investigated using Density Functional Theory (DFT) based calculations. Effects of the vicinal steps and edges on the stability of various N2H4-OH coadsorption configurations are investigated and compared with the case of individual adsorption of the respective molecules. Stabilizing interaction between N2H4 and OH coadsorbate is found to be mediated by hydrogen-bond. The most stable interaction of N2H4-OH is found perpendicular to the step direction, with N2H4 and OH occupying the terrace and edge sites, respectively. Swapping the position of N2H4 and OH reduce the relative stability. However, placing N2H4 on edge sites stabilizes its cis-conformation with noticeable N - H bond elongation. Finally, N2H4 and OH coadsorption with N2H4 and OH coadsorbed on edge-sites is moderate in terms of overall stability but exhibits the weakest N2H4 coadsorption and longest hydrogen bond interaction distance. Nevertheless, these N2H4-OH coadsorption structures are almost equally accessible thermodynamically due to the relatively small energy differences among them (less than 0.2 eV). In an ideal extended periodic system at specific coverage used in this study, the obtained coadsorption reveals the formation of a chain-like structure between N2H4-OH linked by hydrogen bonds. The results demonstrate the importance of steps and edges in effective formations of hydrogen bond stabilizing N2H4 coadsorption with prospects of promoting proton-transfer-reaction from N2H4 to OH.

Specific adsorption of phosphate species on Ag (111) and Ag (100) electrodes and their effect at low overpotentials of the hydrogen evolution reaction

The influence of the geometry of the silver crystalline faces (111) and (100) on the adsorption/desorption processes of phosphate species as a function of potential is studied, and the surface coverages (θ) and the relaxation times (τ) are compared. A reversible process was observed for Ag(hkl)/KH2PO4 systems from j−V profiles, where a value of 0.07 ML was obtained. For Ag(111)/H3PO4, a coverage of about 0.024 ML was calculated from anodic/cathodic j−V profiles. In the case of Ag(hkl)/K3PO4 systems, highly irreversible processes were observed, resulting in different charge values from integration of anodic/cathodic peaks. For these systems, the capacitance (C(ϕ)) plots are well differentiated for the two faces, and co-adsorption of OH− was evaluated from resistance parameters. Characteristic face-specific relaxation times are obtained for each electrode by Electrochemical Impedance Spectroscopy (EIS). In addition, it was found that the onset potential of her for Ag(111) at pH=1.6 was about 100 mV more negative compared to Ag(100).

Coadsorption of hydrazine (N2H4) and OH on NiZn surface: A DFT-based study

We investigated the coadsorption of hydrazine (anti- and cis-N2H4) and hydroxyl (OH) on a Ni–Zn based alloy surface, using density functional theory (DFT) based total energy calculations. We found that the presence of Zn induces trends in N2H4 adsorption strength on sites that can be correlated with ligand-effect. On a surface with adsorbed anti- or cis-N2H4, we observe preferential OH adsorption of the bridge-sites, allowing for direct chemical interaction and subsequent N2H4 dehydrogenation. Stronger surface energetic corrugation is found in OH coadsorption with cis-N2H4 that suggests some involvement of electrostatic interaction as well.

Density Functional Theory Study of the Interactions of OH and Cl with the Pristine and Defective Surfaces of α-Fe2O3 (0001)

Fe (III) oxides have been identified as a dominant structure of the outer layer of the iron passive film formed in alkaline environment but chloride ion has been suggested to induce depassivation of these passive films under the same conditions. Here we use DFT+U to investigate the mechanism of the depassivation by studying the interactions of OH and Cl with the pristine and defective α-Fe2O3 (0001) surfaces and hematite (α-Fe2O3) is used to represent the Fe (III) oxides. On the pristine surface, the adsorption of both adsorbates can affect mostly the positions of the top two layers. The structural change increases with coverage and calculation of low coverages shows that the effects are localized. The largest effects on the surface were caused by the OH at high coverage and co-adsorption of OH and Cl, which suggests that OH could play an important role in the Cl-induced depassivation process. On the defective surfaces, Fe vacancy surface and O vacancy surface are studied. On Fe vacancy surface, Fe top site is the most stable site for both adsorbates, and the adsorption energy for the two adsorbates and structural effects caused by the adsorption are comparable to those on the pristine surface. The insertion of one Cl into the second layer of α-Fe2O3 is endothermic, with the reaction energy about 0.7 eV, which suggest that Cl is thermodynamically favorable to adsorb on the surface. Similarly on O vacancy surface, Cl is more stable on the Fe top site closer to the vacancy than in the O vacancy suggesting that the vacancy affects the Cl adsorption indirectly.

Conformational effects on hydrazine and OH coadsorption on Ni(111): A first-principles investigation

Using first-principles Density Functional Theory calculations, we investigated coadsorption of hydrazine (N2H4) and OH on Ni(111) surface. Two types of N2H4 conformations: anti and cis-conformer, with coadsorbed OH on several high symmetry sites on Ni(111) surface were studied. We found that coadsorption with cis-conformer N2H4 significantly modifies OH site preferences while such modification is less profound for coadsorption with anti-conformer N2H4. On the other way around, the cis-confomer N2H4 coadsorption becomes more stable due to the pressence of OH. We identified the electrostatic attractive dipole interaction between the coadsorbed species as the underlying mechanism for the stabilization. This electrostatic interaction is particularly strong for cis-conformer N2H4 due to its large dipole moment. We also found NH bond elongation for cis-conformer N2H4 coadsorption with OH due to the interaction between accumulated charge in OH with the H atom of N2H4. Therefore, it can be inferred that coadsorption with OH promotes the dehydrogenation reaction of N2H4 via stabilization of cis-confomer N2H4.

Density functional theory study on the effect of OH and Cl adsorption on the surface structure of α-Fe2O3

Hematite (Fe2O3) has been identified as the dominant structure of the outermost layer of the passive film formed on iron surfaces in alkaline environment but chloride has been suggested to play a major role in the depassivation of this passive film under the same conditions. Here we study the effects of OH and Cl adsorption as well as co-adsorption at different coverages on the structure of α-Fe2O3 Fe-terminated (0001) surface using DFT+U. The adsorption of both OH and Cl alters the structure of the surface, by affecting mostly the positions of the top two layers. The structural change increases with coverage for two adsorbates on a (1×1) surface and the study on a larger (2×2) surface shows that the effects are localized. The large effect of the OH and co-adsorption of OH and Cl on the surface suggests that OH could play an important role in the Cl-induced depassivation process.

Theoretical study of water gas shift reaction on Cu n Ni (n = 1–12) clusters

Density functional theory has been used to study the water-gas-shift reaction on CunNi (n = 1–12) clusters. The reaction mechanism of carboxyl has been examined. Using the energetic span model (ESM), we find that the turnover frequency-determining transition state (TDTS) is the carboxyl dissociation (COOH → CO2 + H) for CunNi (n = 1–12) and the turnover frequency-determining intermediate (TDI) is the co-adsorptions of CO and H2O on CunNi clusters for CunNi (n = 2–6, 11, 12). When it comes to CunNi (n = 1, 7–10), the turnover frequency-determining intermediate (TDI) is the co-adsorption of OH and H on CunNi clusters. Our calculation shows that the Cu8Ni cluster with the highest value of the calculated turnover frequence (TOF) exhibits high catalytic activity towards water gas shift reaction.

Theoretical investigation of the effect of OH− ions on O2 adsorption on low-index Pt surfaces in alkaline solution

The O2 adsorptions on three low-index Pt surfaces in pure water and alkaline solution were studied using molecular dynamics (MD) and the potential of mean force methods to determine the effect of OH− coadsorption on O2 adsorption. The MD results indicate that the adsorption configuration of O2 molecules showed differences on various interfaces, resulting in the variation of the stability of O2 adsorption. OH− and H2O coadsorption can affect the O2 adsorption, and represent the competitive relation of adsorption. The results indicate that the coadsorption of OH− and H2O formed a compact H-bonding network, which not only changed the adsorption configuration of O2, but also hindered the migration of O2 molecules from the solution to the adsorption layer. The results obtained in this study provide a theoretical basis for experimental research.

Mitigation of CO poisoning on functionalized Pt–TiN surfaces

It has been previously reported that the system of single Pt atoms embedded in N-vacancy (V(N)) sites on the TiN(100) surface (Pt-TiN) could be a promising catalyst for proton exchange membrane fuel cells (PEM FCs). The adsorption of molecules on Pt-TiN is an important step, when it is incorporated as the anode or cathode of PEM FCs. Utilizing first principles calculations based on density functional theory, systematic investigations are performed on the adsorption of several atomic and molecular species on the Pt-TiN system, as well as the co-adsorption of them. The favorable binding sites and adsorption energies of several molecular species, namely carbon dioxide (CO2), carbon monoxide (CO), oxygen (O2), hydrogen (H2), hydroxyl (OH), an oxygen atom (O), and a hydrogen atom (H), are explored. For each, the adsorption energy and preferred binding site are identified and the vibrational frequencies calculated. It is found that CO2, CO and H prefer the Pt top site while OH and O favorably adsorb on the Ti top site. When CO and OH are co-adsorbed on the Pt-TiN(100) surface, OH weakens the adsorption of CO. The weakening effect is enhanced by increasing the coverage of OH. A similar behavior occurs for H and OH co-adsorption on the Pt-TiN(100) surface. Because co-adsorption with OH and H species weakens the adsorption of CO on Pt-TiN, it is expected that the acid and base conditions in PEM FCs could mitigate CO poisoning on functionalized Pt-TiN surfaces.

Factors controlling the energetics of the oxygen reduction reaction on the Pd-Co electro-catalysts: Insight from first principles

We report here results of our density functional theory based computational studies of the electronic structure of the Pd-Co alloy electrocatalysts and energetics of the oxygen reduction reaction (ORR) on their surfaces. The calculations have been performed for the (111) surfaces of pure Pd, Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) alloys, as well as of the surface segregated Pd/Pd(0.75)Co(0.25) alloy. We find the hybridization of dPd and dCo electronic states to be the main factor controlling the electrocatalytic properties of Pd/Pd(0.75)Co(0.25). Namely the dPd-dCo hybridization causes low energy shift of the surface Pd d-band with respect to that for Pd(111). This shift weakens chemical bonds between the ORR intermediates and the Pd/Pd(0.75)Co(0.25) surface, which is favorable for the reaction. Non-segregated Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) surfaces are found to be too reactive for ORR due to bonding of the intermediates to the surface Co atoms. Analysis of the ORR free energy diagrams, built for the Pd and Pd/Pd(0.75)Co(0.25), shows that the co-adsorption of the ORR intermediates and water changes the ORR energetics significantly and makes ORR more favorable. We find the onset ORR potential estimated for the configurations with the O-OH and OH-OH co-adsorption to be in very good agreement with experiment. The relevance of this finding to the real reaction environment is discussed.

CO Electroxidation on Gold in Alkaline Media: A Combined Electrochemical, Spectroscopic, and DFT Study

The aim of the present work is to provide a deeper understanding of gold catalysis for CO electrooxidation in alkaline media, through a combined electrochemical, spectroscopic, and DFT study. Voltammetric and spectroscopic measurements evidence that the amount of CO irreversibly adsorbed on gold increases as the adsorption potential becomes more negative (vs SHE). This explains why higher CO coverages can be achieved in more alkaline solutions, since the value of adsorption potential vs RHE becomes more negative vs SHE with increasing pH. On the other hand, the combination of FTIRRAS experiments and DFT calculations shows that the adsorption site of irreversibly adsorbed CO on Au(111) depends on the value of the adsorption potential. It is concluded that CO adsorption on top sites takes place at all studied potentials, and hollow and bridge sites also become occupied for adsorption potentials lower and higher than 0 V vs RHE, respectively. However, it should be noted that our DFT calculations give values of the CO binding energies that are not strong enough to explain CO irreversible adsorption. This may be partly attributed to the fact that OH coadsorption is not included in the calculations. Indeed, this work presents two experimental facts that suggest that CO adsorption on gold promotes the coadsorption of OH species: (i) CO irreversibly adsorbed on Au(111) and Au(100) leads to an unusual voltammetric feature, whose charge indicates the stabilization of one OH species per adsorbed CO species; (ii) the apparent transfer coefficient of this unusual state is close to unity, suggesting that it is due to a presumed structural transformation coupled to OH adsorption. Finally, the effect of the adsorption potential on the bulk CO electrooxidation is also studied. It is found that, on Au(111), an increased occupation of CO on multifold (hollow) sites seems to result in a less efficient catalysis. However, on Au(110), an increased coverage of CO on top sites does not produce any significant change in catalysis.

A first principles study of the oxidation energetics and kinetics of realgar

Quantum-mechanical calculations allow resolving and quantifying in detail important aspects of reaction mechanisms such as spin transitions and oxygen dissociation that can be the major rate-limiting steps in redox processes on sulfide and oxide surfaces. In addition, this knowledge can help experimentalists in setting up the framework of rate equations that can be used to describe the kinetics of, e.g., oxidation processes. The unique molecular crystal structure of realgar, As 4S 4 clusters held together by van der Waals bonds, allows for a convenient quantum-mechanical (q.m.) cluster approach to investigate the thermodynamics and kinetic pathways of oxidation. The interaction of As 4S 4 clusters with oxygen and co-adsorbed ions provides a model system for understanding the molecular-scale processes that underpin empirically-derived rate expressions, and provides clues to the oxidation mechanisms of other sulfides and oxides. Two activated processes are shown to dominate the kinetics of oxidation by molecular oxygen: (i) a paramagnetic 3 O 2 to diamagnetic 1 O 2 spin transition and (ii) oxygen dissociation on the surface, in that order. The activation energies for the spin transition and O 2 dissociation step were determined to be 1.1 eV (106 kJ/mol) and 0.9 eV (87 kJ/mol), respectively, if molecular oxygen is the only reactant on the surface. In the case of As 4S 4, q.m. calculations reveal that 3 O 2 transfers its spin to the cluster and forms a low-spin, peroxo intermediate on the surface before dissociating. The adsorption of a hydroxide ion on the surface proximate to the 3 O 2 adsorption site changes the adsorption mechanism by lowering the activation energy barriers for both the spin transition (0.30 eV/29 kJ/mol) and the O 2 dissociation step (0.72 eV/69 kJ/mol). Thus, while spin transition is rate limiting for oxidation with O 2 alone, dissociation becomes the rate-limiting step for oxidation with co-adsorption of OH −. First-principles, periodic calculations of the realgar ( 1 ¯ 20 ) surface show that the energetics and structural changes that accompany oxidation of As 4S 4 clusters on the surface are similar to those involving individual As 4S 4 clusters. Thus, assuming that an As 4S 4 cluster with an adsorbed hydroxyl group is a reasonable approximation of the surface of As 4S 4 at high pH, the theoretically calculated oxidation rate (∼1 × 10 −10 mol m −2 s −1) is of the same order as empirically-derived rates from experiments at T = 298 K, pH = 8, and similar dissolved oxygen concentrations. In addition, the co-adsorption of other anions found in alkaline waters (i.e. carbonate, bicarbonate, sulfate, and sulfite) were shown to energetically promote the oxidation of As 4S 4 (on the order of 5–40 kJ/mol depending on the co-adsorbed anion, OH −, CO 3 2 - , HCO 3 - , SO 4 2 - , or SO 3 2 - , and accounting for changes in the hydration of products and reactants). The effect of the co-adsorbate on the kinetics and thermodynamics of oxidation is due to each adsorbate modifying the electronic and structural environment of the other adsorption site. Activation-energy barriers due to spin transitions are rarely discussed in the literature as key factors for controlling oxidation rates of mineral surfaces, even though the magnitude of these barriers is enough to alter the kinetics significantly. The attenuation of the activation energy by co-adsorbed anions suggests the possibility of pH− or p(co-adsorbate)-dependent activation energies that can be used to refine oxidation rate laws for sulfide minerals and other, especially semiconducting minerals, such as oxides.

Coadsorption of Trivalent Metal Ions and Anions on Strongly Acidic Cation-Exchange Resins by Bridge Bonding

The effects of anions (P(V), P(III), P(I), Se(IV), OH(-), F(-), Cl(-), SCN(-), S(IV), and CH(3)COO(-)) on the adsorption of trivalent metal ions (Fe(3+), Al(3+), Ga(3+), In(3+), and Sc(3+)) to three strongly acidic cation-exchange resins (-S)(-) of different types (porous or gel) and different exchange capacities (4.55, 3.91, and 0.96 mmol g(-1)) were studied systematically. All these metal ions showed coadsorption of OH(-), irrespective of the resins. In contrast, coadsorption of P(V), P(III), P(I), and Se(IV) was observed on the resins of the higher exchange capacities but not on the resin of the lowest exchange capacity. Stoichiometric analyses and spectroscopic (Mossbauer and infrared) studies for Fe(3+) demonstrated the presence of the coadsorbed species: [(-S)(2)Fe(OH)] and [(-S)(2)(Fe-O-Fe)(S-)(2)] for OH(-), [(-S)(2)Fe(HPO(4))Fe(S-)(2)] for P(V), and [(-S)(2)FeX](j) (X(-) = H(2)PO(3)(-), H(2)PO(2)(-), HSeO(3)(-); j > 1) for P(III), P(I), and Se(IV). No coadsorption was observed for the other anions. These findings indicate that the bridge bonding of anions between the metal ions adsorbed on the resins of the higher exchange capacities plays a crucial role for the coadsorption. Some analytical implication was also discussed.

The effect of sulfate and nitrate ions on the passivation and activation of silver in alkaline solutions

Based on the concept of a competitive adsorption of hydroxide ions with SO 4 2− and NO 3 − activating anions, some peculiarities of the anodic behavior of silver in alkaline solutions containing sulfates or nitrates are explained. At the ascending branches of the anodic peaks, a co-adsorption of OH− and SO 4 2− or NO 3 − results in the formation of mixed adsorption complexes, which are soluble better than hydroxide ones. An increase in the part of the soluble oxidation products of silver is observed if a rotating disc electrode with a ring is used. Passivation of silver is explained by a change in the electronic structure of the adsorption complexes when certain potential values are reached, while a local activation, by the destruction of these complexes at the passive state potentials between the anodic peaks. At the depassivation, pH value of the solution in pits decreases, which results in the formation of Ag2SO4 or AgNO3 salts. The presence of the salts in a deposit on the electrode is confirmed by the appearance of a C 3 cathodic peak.

Wetting of mixed OH∕H2O layers on Pt(111)

We describe the effect of growth temperature and OHH(2)O composition on the wetting behavior of Pt(111). Changes to the desorption rate of ice films were measured and correlated to the film morphology using low energy electron diffraction and thermal desorption of chloroform to measure the area of multilayer ice and monolayer OHH(2)O exposed. Thin ice films roughen, forming bare (radical39 x radical39)R16 degrees water monolayer and ice clusters. The size of the clusters depends on growth temperature and determines their kinetic stability, with the desorption rate decreasing when larger clusters are formed by growth at high temperature. Continuous films of more than approximately 50 layers thick stabilize an ordered incommensurate ice film that does not dewet. OH coadsorption pins the first layer into registry with Pt, forming an ordered hexagonal (OH+H(2)O) structure with all the H atoms involved in hydrogen bonding. Although this layer has a similar honeycomb OH(x) skeleton to ice Ih, it is unable to reconstruct to match the bulk ice lattice parameter and does not form a stable wetting layer. Water aggregates to expose bare monolayer (OH+H(2)O), forming bulk ice crystallites whose size depend on preparation temperature. Increasing the proportion of water in the first layer provides free OH groups which stabilize the multilayer. The factors influencing multilayer wetting are discussed using density functional theory calculations to compare water adsorption on top of (OH+H(2)O) and on simple models for commensurate water structures. We show that both the (OH+H(2)O) structure and "H-down" water layers are poor proton acceptors, bonding to the first layer being enhanced by the presence of free OH groups. Formation of an ordered ice multilayer requires a water-metal interaction sufficient to wet the surface, but not so strong as to prevent the first layer relaxing to stabilize the interface between the metal and bulk ice.

Thermodynamic analysis of (bi)sulphate adsorption on a Pt(1 1 1) electrode as a function of pH

A complete thermodynamic study of (bi)sulphate adsorption on Pt(1 1 1) electrodes from solutions at four different pHs (pH 0.43, 2.1, 3.1 and 4.1) is reported. The effect of pH on the sum of the Gibbs excesses of sulphate and bisulphate species, standard Gibbs energies of adsorption and formal partial charge numbers is analyzed. The results provide relevant information on the nature of species involved in the different voltammetric features. The experiments at pH 0.43 were performed in a higher base electrolyte concentration (0.5 M), that allows the study of (bi)sulphate adsorption in a broader range of concentrations. Under these conditions, two adsorption steps are clearly defined, associated to two different voltammetric features, between 0.30 and 0.60 V and between 0.65 and 0.90 V (standard hydrogen scale, SHE). Once the pH is increased, a marked decrease in absolute value of the (bi)sulphate adsorption Gibbs energy is observed, concomitant with an increasing amount of OH co-adsorption.

A density functional theory study on the water formation at high coverages and the water effect in the Fischer–Tropsch synthesis†

The O removal through water formation is an important process in the Fischer–Tropsch synthesis. In this study, both steps in water formation (O+H→OH, OH+H→H2O) are studied on the stepped Co(0001) at high coverages using density functional theory. We find the following. (i) In both O–O and O–OH co-adsorption systems, two transition states (TSs) were located for the O hydrogenation: in one TS, both O and H are on the same terrace, and in the other they are at the interface between the step edge and the terrace below. (ii) In both the O–O and O–OH co-adsorption systems, the O hydrogenation at the interface is easier (E a = 0.32 eV in the O–O system, E a = 1.10 eV in the O–OH system) than that on the same terrace (E a = 1.49 eV in the O–O system, E a = 1.80 eV in the O–OH system). (iii) In both the O–O and O–OH co-adsorption systems, only one TS for the OH hydrogenation was located, in which both OH and H are on the same terrace. (iv) Compared to the OH hydrogenation in the O–OH system (E a = 1.46 eV), the reaction in the OH–OH system (E a = 0.64 eV) is much easier. The barrier differences and the water effect on the Fischer–Tropsch synthesis are discussed. A possible route with low barriers for water formation is proposed.

Structural effects of adsorbed CN adlayers on the co-adsorption of OH − at the Pt(111) surface in sulfuric acid medium

Cyanide adlayers formed on Pt(111) were investigated at submonolayer coverages under electrochemical conditions in sulfuric acid medium. For small coverage ( θ) values, cyclic voltammetry indicates the formation of surface domains of adsorbed cyanide (islands). Great distances separate the islands in such a way that the reversible adsorption of sulfate/bisulfate ions takes place quite easily on this bare area. Simultaneously, the reversible adsorption of OH − ions occurs in the gaps between adjacent clusters of each island. Increasing the coverage of CN ads results in a progressive diminution of the distance between islands and, consequently, to a decrease in the extent of sulfate adsorption. Conversely, the higher θ CN, the larger the number of sites for OH − adsorption (higher number of rows between hexagonal clusters). Thus, the adsorption of hydroxyl species is enhanced at high cyanide coverage in this medium.