Adsorption of hydrogen on Pt(1 1 1) and Pt(1 0 0) surfaces and its role in the HOR

Hydrogen adsorption isotherms, evaluated by combination of cyclic voltammetry and chronoamperometry, are reported on Pt(1 1 1) and Pt(1 0 0) surfaces in 0.1 M HClO₄. We found that at E > 0.05 V Pt(1 1 1) and Pt(1 0 0) are only partially covered by the adsorbed hydrogen (H_ad). On both surfaces, a full monolayer of the adsorbed hydrogen is completed at −0.1 V, i.e. the adsorption of atomic hydrogen is observed in the hydrogen evolution potential region. We also found, that the activity of the hydrogen oxidation reaction is mirrored by the shape of the hydrogen adsorption isotherms, implying that H_ad is in fact a spectator in the HOR.     

Microwave-irradiated synthesized platinum nanoparticles/carbon nanotubes for oxidative determination of trace arsenic(III)

Platinum nanoparticles/carbon nanotubes (Pt_nano/CNTs) were rapidly synthesized by microwave radiation, and applied for the oxidative determination of arsenic(III). The transmission electron microscopy (TEM) revealed the size of synthesized Pt nanoparticles with nominal diameter of 15 ± 3 nm. Pt_nano/CNTs modified glassy carbon electrode (Pt_nano/CNTs/GCE) exhibited better performance for arsenic(III) analysis than that of Pt nanoparticles modified GCE (Pt_nano/GCE) by electrochemical deposition or Pt foil electrode. Excellent reproducibility of the Pt_nano/CNTs/GCE was obtained with the relative standard deviation (RSD) of 3.5% at 20 repeated analysis of 40 μM As(III), while the RSD was 9.8% for Pt_nano/GCE under the same conditions. The limit of determination (LOD) of the Pt_nano/CNTs/GCE was 0.12 ppb, which was 1–2 orders of magnitude lower than that of Pt_nano/GCE or Pt foil electrode.     

A spectroscopic proof of a surface equilibrium between on top and bridge bonded CO at Pt(1 1 0) in acid solution

According to most of works in the literature, adsorbed carbon monoxide at Pt(1 1 0) electrodes in acid media presents only linear bonded (CO_L) so-called, atop geometry. In the present work, the formation of bridge bonded carbon monoxide (CO_B) is shown via in situ infrared FT spectra, measured on a Pt(1 1 0) electrode covered with 25% CO, in HClO₄ solutions. For the first time, the inter conversion between atop and bridge bonded CO at potentials in the hydrogen adsorption region is reported in acid solution. Band intensity and band center frequency indicate dipole–dipole coupling effects in spite of the low CO total coverage.     

Voltammetric analysis of the co-adsorption of cyanide and carbon monoxide on a Pt(1 1 1) surface

Carbon monoxide has been adsorbed at controlled potential on a Pt(1 1 1) electrode, which was pre-covered with cyanide up to saturation. From the results obtained, it has been deduced that CO occupies platinum sites between CN molecules with no distortion of the pre-adsorbed cyanide layer. The anodic stripping of CO does not induce modifications of the CN adlayer either. These observations allow the estimation of θ_CO rather accurately by means of the coulometric method.     

pH effect on electrocatalytic reduction of CO2 over Pd and Pt nanoparticles

Adsorbed hydrogen participates in electrocatalytic reduction of CO₂ and competitive hydrogen evolution reaction (HER) simultaneously, and its reaction pathway greatly affects the activity and selectivity of CO₂ reduction. In this work, we investigate pH effect on electrocatalytic reduction of CO₂ over Pd and Pt nanoparticles (NPs) with a similar size in a pH range from 1.5 to 4.2. Pt NPs completely contribute to HER in the pH range. Over Pd NPs, Faradaic efficiency for CO production at − 1.19 V (vs. reversible hydrogen electrode) varies from 3.2% at pH of 1.5 to 93.2% at pH of 4.2, and current density for CO production reaches maximum at pH of 2.2. The significant enhancement of Faradaic efficiency and current density for CO production over Pd NPs at high pH values is attributed to decreased kinetics of hydrogen evolution reaction by increasing hydrogen binding energy and lowered adsorption affinity of CO-like intermediate compared to Pt.     

Direct electrochemistry study of glucose oxidase on Pt nanoparticle-modified aligned carbon nanotubes electrode by the assistance of chitosan–CdS and its biosensoring for glucose

Aligned carbon nanotubes (ACNTs) electrode has been developed for the direct protein electrochemistry and enzyme-biosensor study involving two types of nanoparticles. Pt nanoparticles (Pt_nano) were electro-modified on the ACNTs’ each tube, greatly increasing the electrode surface area for locating protein and also its electronic transfer ability. Glucose oxidase (GOD) with chitosan (CS) and CdS nanoparticles electrochemically coated on each tube of ACNTs–Pt_nano by the electrodeposition reaction of CS when pH value passing its pKa. The CdS nanoparticles between ACNTs electrode and GOD have stimulated the GOD’s direct electron transfer during its redox reaction of FAD/FADH₂. The CS–GOD–CdS/ACNTs–Pt_nano electrode also offer sensitive response to the substrate of glucose with detection limit of 46.8 μM (S/N = 3) and apparent Michaelis–Menten constant of 11.86 mM.     

Unique CO-tolerance of Pt–WOx materials

Well-defined tungsten-oxide-supported platinum nanoparticles (Pt/WO_x) were elaborated by impregnation-reduction of a platinum salt onto commercial monoclinic WO₃. Field-emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM) revealed that the Pt particles are well-distributed on the oxide support, present a narrow particle size distribution centered on ca. 2–3 nm and a low degree of agglomeration. Carbon black was added to ensure electronic percolation in the electrodes during the electrochemical measurements. CO_ads electrooxidation currents were monitored at potentials as low as 0.1 V vs. RHE on Pt/WO_x, demonstrating high CO-tolerance compared to carbon-supported Pt or PtRu catalysts.     

Electrochemical behavior of CO2 reduction on palladium nanoparticles: Dependence of adsorbed CO on electrode potential

The electrochemical reduction of CO₂ is strongly influenced by both the applied potential and the surface adsorption status of the catalyst. In this work a gas diffusion electrode (GDE) coated with Pd nanoparticles/carbon black (Pd/XC72) was used to study the electrochemical reduction of CO₂. Cyclic voltammetric (CV) analysis of Pd/XC72 between 1.5 V and − 0.6 V (vs. RHE) shows the formation of intermediates and the blocking of hydrogen absorption on the Pd nanoparticles (NPs) under a CO₂ atmosphere. The relationships between the Faradaic efficiency/current density and the applied potential reveal that the onset potential of CO formation is around − 0.4 V. Moreover, the presence of adsorbed CO was confirmed through CV analysis of Pd/XC72 under CO₂ and CO/He atmospheres. This demonstrates that H atoms and CO intermediates co-adsorb on the surface of the Pd NPs at an applied potential of around − 0.4 V. When the applied potential is more negative than − 0.6 V, adsorption of CO intermediates on the surface of the Pd NPs becomes dominant.     

Hydrogen oxidation reaction on thin platinum electrodes in the polymer electrolyte fuel cell

A method for measuring the kinetics of the hydrogen oxidation reaction (HOR) in a fuel cell under enhanced mass transport conditions is presented. The measured limiting current density was roughly 1600 mA cm_Pt^? 2, corresponding to a rate constant of the forward reaction in the Tafel step of 0.14 mol m^? 2 s^? 1 at 80 °C and 90% RH. The exchange current density for the HOR was determined using the slope at low overvoltages and was found to be 770 mA cm_Pt^? 2. The high values for the limiting and exchange current densities suggest that the Pt loading in the anode catalyst can be reduced further without imposing measurable voltage loss.     

A topographic view of the Pt(1 1 1) surface at the electrochemical interface in the presence of carbon monoxide

In this communication we present topographic images of the Pt(1 1 1) surface in CO saturated 0.1 M HClO₄, obtained by scanning tunneling microscopy.The topography presents two different structures, depending on the CO adsorption potential (E_ad = 0.15 V or E_ad = 0.5 V vs RHE). For adsorption at 0.15 V the system presents a heterogeneous appearance, which totally covers the surface and impedes the observation of steps on the substrate surface. When CO is adsorbed at 0.5 V large clusters forming chains along the steps are observed. These aggregates can be, tentatively, correlated with the H-bonded water structure suggested earlier on the basis of FTIR spectroscopy. The clusters have inhibitory effects on CO oxidation.     

Electron-deficient adduct site in the ring opening of methylcyclopentane (MCP) on tungsten-oxide-supported Pt,Ir and Pt–Ir catalysts

The activities of Pt/WO₂, Ir/WO₂ and Pt–Ir/WO₂ toward the conversion of methylcyclopentane (MCP) were investigated. The catalysts were prepared using impregnation and co-impregnation methods and were characterized by SEM, XRD, N₂-sorption and TEM investigations. The most active catalyst toward the conversion of MCP, irrespective of the temperature, was Ir/WO₂. The order of the reactivity was Ir/WO₂ > Pt–Ir/WO₂ > Pt/WO₂. Strong metal–support interactions (SMSI) were observed for all the catalysts over the entire investigated temperature range. At 400 °C, the Pt and Pt–Ir showed 100% selectivity toward ring-enlargement reactions associated with the presence of electron-deficient adduct sites on the reducible acidic WO₂ support. Ring opening occurred over all the catalysts in three positions, resulting in the formation of 2-methylpentane (2-MP), 3-methylpentane (3-MP), and n-hexane (n-H). Difficulty in breaking the secondary – tertiary carbon bonds was observed predominantly on the Ir catalyst, which opens the MCP ring via a selective mechanism.     

WO3 decorated carbon nanotube supported PtSn nanoparticles with enhanced activity towards electrochemical oxidation of ethylene glycol in direct alcohol fuel cells

This paper describes the concept of the utilization of metal oxide (WO₃) modified multi-walled carbon nanotubes (MWCNT) for supporting and activating PtSn nanoparticles (PtSn/WO₃-MWCNT and PtSn/MWCNT) for ethylene glycol oxidation. The resulting nanocomposite was developed and characterized using electrochemical and microscopic (TEM, SEM−EDS) techniques, as well as XRD analysis. The electrocatalytic currents measured under voltammetric and chronoamperometric conditions were greater than those found with the commercially available Vulcan-supported Pt₃Sn nanoparticles, which were used as reference catalysts. In situ FTIR spectroscopy was used to detect the formation of oxidation intermediates or products during the ethylene glycol oxidation. Combining the transition metal oxide species with Pt-based nanoparticles can generate OH groups at low potentials. These groups participate in the oxidation of passivating CO adsorbates on the Pt surface, and can also potentially break CH bonds. Further, the effectiveness of synthesized catalyst has been assessed through testing both catalysts in the single fuel cell. A single fuel cell with a PtSn/WO₃-MWCNT anode gave a better performance than one with a pristine PtSn/Vulcan anode, with a current density of around 79.8 mA cm⁻² and an output power density of 20.5 mW cm⁻².     

A solid-state pH sensor based on WO3-modified vertically aligned multiwalled carbon nanotubes

In this communication, a novel solid-state pH sensor based on WO₃/MWNTs nanocomposite electrode will be reported. WO₃ nanoparticles were homogeneously coated on vertically aligned MWNTs by magnetron sputtering. Potentiometric pH response of the WO₃/MWNTs electrode in Britton–Robinson buffers revealed a linear working range from pH 2 to12 with a slope of about ?41 mV pH^?1 and a response time less than 90 s. The stability of the electrode remained over a month. Moreover, the WO₃/MWNTs electrode displayed excellent anti-interference property. Compared to conventional pH sensors, the pH sensor based on WO₃/MWNTs nanocomposite electrode also showed excellent reproducibility, high stability and superb selectivity.     

O2 surface concentration change and its implication on oxygen reduction mechanism and kinetics at platinum in acidic media

O₂ concentration near Pt surface during oxygen reduction reaction (ORR) in 0.1 M HClO₄ has been monitored by rotating ring-disk electrodes system. At 0.8 V < E < 1.0 V (vs. RHE), O₂ concentration near Pt surface increases with potential accompanying with the decrease of ORR current at the disk electrode; O₂ concentration in the negative-going scan is larger than that at the same potential in the positive-going scan, while ORR current shows the opposite trend at ω > 400 rpm. At E > 0.8 V accumulation of O_ad|OH_ad at Pt disk electrode with ORR time is evident, revealing that O_ad|OH_ad formation rate is faster than that for the removal of OH_ad to H₂O under such conditions. At relatively lower rotation speed and faster scan rate, the cathodic current during ORR in the negative-going scan can be larger than that in the positive-going scan with a current peak at ca. 0.8 V, which is attributed to the superimposition of ORR current increase due to change of O₂ concentration near the surface and the additional reduction of O_ad|OH_ad formed from decomposed O₂ at higher potentials.     

Oxygen reduction reaction activities of Ni/Pt(111) model catalysts fabricated by molecular beam epitaxy

Oxygen reduction reaction (ORR) activities were evaluated for clean Pt(111) and Ni/Pt(111) model catalysts fabricated by molecular beam epitaxy. Exposure of clean Pt(111) to 1.0 L CO at 303 K produced linear-bonded and bridge-bonded CO-Pt IR bands at 2093 and 1858 cm^? 1. In contrast, 0.3-nm-thick Ni deposited on Pt(111) at 573 K (573 K-Ni_0.3 nm/Pt(111)) produced broad IR bands for adsorbed CO at around 2070 cm^? 1; the separation of reflection high-energy electron diffraction (RHEED) streaks is slightly wider for 573 K-Ni_0.3 nm/Pt(111) than for the clean Pt(111). For 823 K-Ni_0.3 nm/Pt(111), the separation of the RHEED streaks is the same as that for the Pt(111), and a single sharp IR band due to adsorbed CO is located at 2082 cm^? 1. The results suggest that for the 823 K-Ni_0.3 nm/Pt(111), a Pt-enriched outermost surface (Pt-skin) was formed through surface segregation of the substrate Pt atoms. ORR activities for the 573 K- and 823 K-Ni_0.3 nm/Pt(111) as determined from linear sweep voltammetry curves were five times and eight times higher than that for clean Pt(111), respectively, demonstrating that Pt-skin generation is crucial for developing highly active electrode catalysts for fuel cells.     

Room Temperature COad Desorption/Exchange Kinetics on Pt Electrodes—A Combined In Situ IR and Mass Spectrometry Study

The room temperature desorption and exchange of CO in a saturated CO adlayer on a Pt electrode, at potentials far below the onset of oxidation, was investigated by isotope labeling experiments, using a novel spectroelectrochemical setup, which allows the simultaneous detection of adsorbed species by in situ IR spectroscopy and of volatile (side) products and reactants by online mass spectrometry under controlled electrolyte flow conditions. Time‐resolved IR spectra show a rapid, statistical exchange of pre‐adsorbed ¹³CO_ad by ¹²CO_ad in ¹²CO containing electrolyte; mass spectrometric data reveal first‐order exchange kinetics, with the rate increasing with CO partial pressure. The increasing CO_ad desorption rate in equilibrium with a CO containing electrolyte is explained by a combination of an increasing CO_ad coverage upon increasing the CO pressure, and a decrease of the CO adsorption energy with coverage, due to repulsive CO_ad–CO_ad interactions.     

Influence of Pt and Au nanophases on electrochromism of WO3 in nanostructure thin-film electrodes

We report electrochromic properties of WO₃ in Au–WO₃ and Pt–WO₃ nanostructure thin-film electrodes prepared by co-sputtering deposition method. The nanostructure electrodes consisted of Au or Pt metallic nanophase and a tungsten oxidative phase, indicating the formation of crystalline metallic nanophases in the amorphous oxide matrix. In particular, due to metallic nanophases, the modified electrochromic properties of WO₃ were observed in the Au–WO₃ and Pt–WO₃. The nanostructure electrodes showed a reverse optical modulation with respect to applied potentials in H₂SO₄ solution compared to that of pure WO₃ electrode. However, due to an excellent electrocatalytic activity of platinum for methanol electrooxidation at 25 °C, the electrochromism of the Pt–WO₃ in contrast with that of the Au–WO₃ was affected by the potentials for methanol electrooxidation in 2 M CH₃OH and 0.5 M H₂SO₄.     

Titanium-supported nanoporous bimetallic Pt–Ir electrocatalysts for formic acid oxidation

Novel titanium-supported nanoporous network bimetallic Pt–Ir/Ti electrocatalysts (S1:Pt₅₉Ir₄₁/Ti, S2:Pt₄₄Ir₅₆/Ti, S3:Pt₂₂Ir₇₈/Ti) have been successfully fabricated by the hydrothermal process. The nanoparticles of Pt and Ir were deposited on the titanium substrates in the presence of formaldehyde as a reduction agent. The electrocatalytic activity of these electrocatalysts towards formic acid oxidation in 0.5 M H₂SO₄ + 0.5 M HCOOH solutions was investigated using cyclic voltammograms (CVs), linear sweep voltammograms (LSVs), chrono amperometry and electrochemical impedance spectroscopy (EIS). The CVs of S1, S2 and S3 exhibit two anodic peaks in the forward scan and one anodic peak in the reverse scan which are similar to the pure Pt. Their LSVs show that the three samples present significantly high current densities of formic acid oxidation compared to the Pt electrode. It is observed from the chrono amperometric measurements at potential 600 mV that the sample S2 delivers a steady-state current density that is 545 times larger than that for the pure Pt electrode. EIS analysis shows that the impedances on both the imaginary and real axes of S1, S2 and S3 are much lower than those of the pure Pt. Among the three samples (S1, S2 and S3), S2 exhibits the highest electrocatalytic activity towards the formic acid oxidation.     

Tuning the hydrogen and hydroxyl adsorption on Ru nanoparticles for hydrogen electrode reactions via size controlling

Controlling the particle size of catalyst to understand the active sites is the key to design efficient electrocatalysts toward hydrogen electrode reactions including hydrogen oxidation and evolution (HOR/HER). Herein, the hydrogen and hydroxyl adsorption on Ru/C could be effectively tuned for HOR/HER by simple controlling the particle sizes. It is found that the metallic Ru (Ru⁰) is the active site for HOR/HER, while oxidized Ru (Ru^x+) will hinder the adsorption and desorption of hydrogen on the catalyst. For the HOR, catalyst with small particles is more efficient, due to it is a three-phase interface reaction of gas on the surface of the catalyst. For the HER, the metallic state of Ru is crucial. The deconvolution of hydrogen peaks indicates that the catalytic sites with low hydrogen binding energy (HBE) shoulder the majority of the HOR activity. CO stripping curve further demonstrates that the stronger hydroxyl species (OH_ad) affinity is beneficial to promote the HOR performance. The results indicate that the design of efficient HOR/HER catalyst should focus on the balance between particle size and metallic states.     

Surface spectators and their role in relationships between activity and selectivity of the oxygen reduction reaction in acid environments

We use the rotating ring disk (RRDE) method to study activity–selectivity relationships for the oxygen reduction reaction (ORR) on Pt(111) modified by various surface coverages of adsorbed CN_ad (Θ_CNad). The results demonstrate that small variations in Θ_CNad have dramatic effect on the ORR activity and peroxide production, resulting in “volcano-like” dependence with an optimal surface coverage of Θ_CNad = 0.3 ML. These relationships can be simply explained by balancing electronic and ensemble effects of co-adsorbed CN_ad and adsorbed spectator species from the supporting electrolytes, without the need for intermediate adsorption energy arguments. Although this study has focused on the Pt(111)–CN_ad/H₂SO₄ interface, the results and insight gained here are invaluable for controlling another dimension in the properties of electrochemical interfaces.