Enhanced electrocatalytic performance for methanol oxidation on Pt–TiO2/ITO electrode under UV illumination

Pt is one of the most important electrode materials employed in direct methanol fuel cell, and many efforts have been directed to improving its electrocatalytic performance. In this work, Pt–TiO₂ nanocomposites are successfully prepared by a sol–gel method. As revealed by TEM, Pt nanoparticles with an average size of 2.6 nm are well uniformly dispersed on porous TiO₂. XRD structural characterization indicates that Pt possesses a face centered cubic crystal structure while TiO₂ is in the format of both rutile and anatase phases. The electrochemical performance of as-prepared nanocomposite electrode (Pt–TiO₂/ITO) is evaluated by studying the electrocatalytic oxidation of methanol in an alkaline medium with or without UV illumination. Comparative experiments evince that the electrochemical performance of Pt–TiO₂/ITO for methanol electrooxidation is markedly improved under UV illumination. Under UV illumination, moreover, the poisoning resistance of Pt–TiO₂/ITO for methanol electrooxidation is significantly improved, as supported by the results of time-coursed current measurements.     

Pt support of multidimensional active sites and radial channels formed by SnO2 flower-like crystals for methanol and ethanol oxidation

SnO₂ nanoflowers and nanorods have been synthesized by the hydrothermal method without using any capping agent. Both types of SnO₂ nanostructures are selected as a support of Pt catalyst for methanol and ethanol electrooxidation. The synthesized SnO₂ nanostructures and SnO₂ supported platinum (Pt/SnO₂) catalysts are characterized by X-ray diffraction, scanning electron microscope and high resolution transmission electron microscope. The electrocatalytic properties of the Pt/SnO₂ and Pt/C catalysts for methanol and ethanol oxidation have been investigated systematically by typical electrochemical methods. The influence of SnO₂ morphology on its electrocatalytic activity is comparatively investigated. The Pt/SnO₂ flower-shaped catalyst shows higher electrocatalytic activity and better long-term cycle stability compared with other electrocatalysts owing to the multidimensional active sites and radial channels of liquid diffusion.     

The Ni/ZrO2 catalyst and the methanation of CO and CO2

The Ni/ZrO₂ catalyst is one of the most active systems for the methanation of CO to be employed in the hydrogen purification for PEMFC. This contribution aims to study the effect of ZrO₂ on the methanation of CO and CO₂. The catalytic behavior of Ni/ZrO₂, Ni/SiO₂, a physical mixture comprising Ni and ZrO_2, and a double-bed reactor were evaluated. The TPD of CO and CO₂, TPSR and the cyclohexane dehydrogenation reaction were carried out to describe the catalysts and the reactions. The high activity of Ni/ZrO₂ catalyst toward the methanation of CO is related to the presence of active sites on the ZrO₂ surface. The methanation of CO occurs on ZrO₂ due to its ability to adsorb CO and also because of the hydrogen spillover phenomenon. Apparently, the effect of ZrO₂ is less relevant for the methanation of CO₂. Ni/ZrO₂ is a very promising system for the purification of hydrogen.     

A theoretical analysis of methanol synthesis from CO2 and H2 in a ceramic membrane reactor

In this theoretical work the CO₂ conversion into methanol in both a traditional reactor (TR) and a membrane reactor (MR) is considered. The purpose of this study was to investigate the possibility of increasing CO₂ conversion into methanol with respect to a TR. A zeolite MR, able to combine catalytic reactions with separation properties of zeolite membranes, which allows only vapours to permeate, is considered. A mathematical model is used to simulate a traditional chemical reactor: a comparison among the model results and literature experimental data confirmed the validity of the model. Afterwards, the model is used to predict the behaviour of a zeolite MR in terms of both CO₂ conversion and methanol selectivity. The results show that it is possible to obtain both higher CO₂ conversion and methanol selectivity with respect to a TR operating at the same experimental conditions.     

Electrochemical conversion of CO2 to methanol using a glassy carbon electrode,modified by Pt@histamine-reduced graphene oxide

The electrochemical reduction of CO₂ to value-added products is one of the useful approaches to reducing the effects of global climate change. Herein, a novel electrocatalyst consisting of platinum nanoparticles on histamine-reduced graphene oxide plates (Pt@His-rGO) supported by a glassy carbon (GC) substrate for the electrochemical conversion of CO₂ to methanol has been developed. The nanocomposite was optimized in terms of pH, applied potential, CO₂ purging time and platinum loading for the highest current densities and faradaic efficiencies toward methanol production. The best results were obtained in a solution containing KNO₃ 0.1 mol L⁻¹ at the pH of 2.0, the applied potential of −0.3 V vs Ag/AgCl (KCl_sat), CO₂ purging duration of 30 min and Pt loading of 5.17 × 10⁻⁷ mol cm⁻². The faradaic efficiency of 37% was obtained for methanol production. The prepared nanocomposite requires a lower applied potential and serves as an intermediate stabilizer through the production of methanol.     

The role of CO2 embodiment in US–China trade

This study examines the influence of US–China trade on national and global emissions of carbon dioxide (CO₂). The three basic questions are as follows: (1) What amount of CO₂ emissions is avoided in the US by importing Chinese goods? (2) How much are CO₂ emissions in China increased as a result of the production of goods for export to the US? and (3) What are the impacts of US–China trade on global CO₂ emissions? Our initial findings reveal that during 1997–2003: (1) US CO₂ emissions would have increased from 3% to 6% if the goods imported from China had been produced in the US, (2) About 7%–14% of China's current CO₂ emissions were a result of producing exports for US consumers, and (3) US–China trade has increased global CO₂ emissions by an estimated 720 million metric tons. We suggest that the export of US technologies and expertise related to clean production and energy efficiency to China could be a “win–win” strategy for both countries for reducing their trade imbalance and mitigating global CO₂ emissions. Improved international accounting methodologies for assigning responsibility for CO₂ emissions must be designed to account for the dynamic nature of international trade.     

Synthesis and characterization of H5PMo10V2O40 deposited Pt/C nanocatalysts for methanol electrooxidation

Pt/C(a) catalysts are firstly prepared by modified impregnation method. In order to enhance the ability of Pt/C catalysts for methanol electrooxidation, H₅PMo₁₀V₂O₄₀ (PMV) is adsorbed on Pt/C catalysts to obtain the PMV-Pt/C catalysts. The Pt/C(a) and PMV-Pt/C are characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It is shown that Pt particles with small average size are uniformly disperesed on carbon. Cyclic voltammetry and chronoamperometry show that the PMV-Pt/C catalysts exhibit excellent catalytic activity and stability for methanol electrooxidation.     

Electrochemical characterization of the surface and methanol electrooxidation on Pt-Rh-Pd ternary alloys

Methanol adsorption and electrooxidation have been studied on Pt-Rh-Pd alloys using cyclic voltammetry and chronoamperometry. Pt-Rh-Pd electrodes were prepared by a potentiostatic electrodeposition on a gold wire from chloride solutions. Alloy bulk composition was determined by SEM/EDAX measurements. Alloy surface composition was estimated adapting Rand and Woods's method for homogenous binary noble metal alloys utilizing the potential of surface oxide reduction peak. Electrode real surface area was calculated from the charge due to surface oxide formation/reduction. Methanol was oxidized both in stripping voltammetric experiments and continuously under potentiostatic conditions from 1 M CH₃OH/0.5 M H₂SO₄ solution. The values of electron per site, surface coverage and oxidation potential were used for the characterization of methanol adsorption products. The comparison of these results with analogous data for CO₂ and CO adsorption has revealed high similarity between CO₂ and methanol adsorption products, both consisting of mainly linearly and bridge-bonded CO species, however, with a higher contribution from bridge-bonded CO in the case of methanol. Current densities obtained during continuous methanol oxidation were the highest for Pt-Rh-Pd alloys with initial bulk composition 30.6% Pt, 23.7% Rh, 45.7% Pd, being of the same order as for pure Pt electrode.     

Electrochemical reduction of CO2 in solid oxide electrolysis cells

This paper describes results on the electrochemical reduction of carbon dioxide using the same device as the typical planar nickel-YSZ cermet electrode supported solid oxide fuel cells (H₂-CO₂, Ni-YSZ|YSZ|LSCF-GDC, LSCF, air). Operation in both the fuel cell and the electrolysis mode indicates that the electrodes could work reversibly for the charge transfer processes. An electrolysis current density of ≈1 A cm⁻² is observed at 800 °C and 1.3 V for an inlet mixtures of 25% H₂-75% CO₂. Mass spectra measurement suggests that the nickel-YSZ cermet electrode is highly effective for reduction of CO₂ to CO. Analysis of the gas transport in the porous electrode and the adsorption/desorption process over the nickel surface indicates that the cathodic reactions are probably dominated by the reduction of steam to hydrogen, whereas carbon monoxide is mainly produced via the reverse water gas shift reaction.     

Hydrothermal synthesis of SnO2–V2O5 mixed oxide and electrochemical screening of carbon nano-tubes (CNT), V2O5, V2O5–CNT,and SnO2–V2O5–CNT electrodes for supercapacitor applications

Nano-scaled SnO₂–V₂O₅ mixed oxide is synthesized by a hydrothermal method in an autoclave. For comparative evaluation, V₂O₅ single oxide is prepared by a conventional process from ammonium vanadate. The capacitive behaviour of the following electrodes is studied by cyclic voltammetry in 0.1 M KCl solutions: carbon nano-tubes (CNT), V₂O₅, V₂O₅–CNT, and SnO₂–V₂O₅–CNT. At a scan rate of 100 mV s⁻¹, the SnO₂–V₂O₅–CNT electrode provides the best performance, viz., 121.4 F g⁻¹. The nano-scaled mixed oxide is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectra.     

Highly efficient CO2 bubble removal on carbon nanotube supported nanocatalysts for direct methanol fuel cell

In this paper, we investigate the CO₂ microbubble removal on carbon nanotube (CNT)-supported Pt catalysts in direct methanol fuel cells (DMFCs). The experiments involve the incorporation of near-catalyst-layer bubble visualization and simultaneous electrochemical measurements in a DMFC anodic half cell system, in which CH₃OH electro-oxidation generate carbon dioxide (CO₂) microbubbles. We observe rapid removal of smaller CO₂ bubble sizes and less bubble accumulation on a Pt-coated CNT/CC (Pt/CNT/CC, CC means carbon cloth) electrode. The improved half cell performances of the high CO₂ microbubble removal efficiency on the CNT-modified electrode (Pt/CNT/CC) were 34% and 32% higher than on Pt/CC and Pt/CP electrodes, respectively.     

nPt (Hx−2nMoO3) as a promising catalyst for the oxidation of methanol. Synthesis and electrocatalytic properties

A new method for the synthesis of the catalyst systems Pt–Mo was suggested. nPt⁰(H_x−2nMoO₃)/GC electrodes were prepared by a redox reaction between the hydrogen-containing molybdenum bronzes and potassium tetrachloroplatinate (II) in acid solutions at open circuit potential. The electrodes were characterized by CVA, SEM, X-ray microanalysis, XRD, XPS and ICP-AES. Pt⁰conglomerates formation with nonuniform distribution over the molybdenum bronzes surface has been revealed. nPt⁰(H_x−2nMoO₃)/GC electrodes showed high catalytic activity (not inferior to Pt–Ru-catalyst) in the oxidation of carbon monoxide and methanol as compared with Pt/GC-electrodes. Catalytic effect is apparently achieved by effective oxidation of strongly chemisorbed species (CO_ads, HCO_ads), which occurs at boundaries platinum – molybdenum oxide. Therefore nPt⁰(H_x−2nMoO₃) can be considered as one of perspective catalysts for DMFC.     

Anthropogenic emissions of CO2 and CH4 in an urban environment

Regular observations of atmospheric mixing-ratios of carbon dioxide and methane in the urban atmosphere, combined with analyses of their carbon-isotope composition (δ¹³C, δ¹⁴C), provide a powerful tool for assessing both the source strength and source partitioning of those gases, as well as their changes with respect to time. Intense surface fluxes of CO₂ and CH₄, associated with anthropogenic activities result in elevated levels of these gases in the local atmosphere as well as in modifications of their carbon-isotope compositions. Regular measurements of concentration and carbon-isotope composition of atmospheric CO₂, carried out in Krakow over the past two decades, were extended to the period 1995–2000 and also to atmospheric mixing-ratios of CH₄ and its carbon-isotope composition. Radiocarbon concentrations (δ¹⁴C) in atmospheric CO₂ recorded at Krakow are systematically lower than the regional background levels. This effect stems from the addition of ¹⁴C-free CO₂ into the local atmosphere, originating from the burning of fossil fuels. The fossil-fuel component in the local budget of atmospheric carbon calculated using a three-component mixing model decreased from ca. 27.5 ppm in 1989 to ca. 10 ppm in 1994. The seasonal fluctuations of this component (winter–summer) are of similar magnitude. A gradually decreasing difference between the ¹⁴CO₂ content in the local atmosphere and the regional background observed after 1991 is attributed to the reduced consumption of ¹⁴C-free fuels, mostly coal, in southern Poland and the Krakow municipal area. The linear regression of δ¹³C values of methane plotted versus reciprocal concentration, performed for the data available for Krakow sampling site, yields the average δ¹³C signature of the local source of methane as being equal to −54.2‰. This value agrees very well with the measured isotope signature of natural gas being used in Krakow (−54.4±0.6‰) and points to leakages in the distribution network of this gas as the main anthropogenic source of CH₄ in the local atmosphere.     

Hydrogenation of CO2 over Co supported on carbon nanotube,carbon nanotube-Nb2O5, carbon nanofiber,low-layered graphite fragments and Nb2O5

CO₂ hydrogenation was studied with catalysts containing 1.5–35 wt% Co supported on carbon nanotubes, nanofibers, low-layered graphite fragments and composites of carbon nanotube-Nb₂O₅. All catalytic processes with Co/supported catalysts were investigated using XRF, DSC, TGA, H₂-TPR, TEM, SEM and XPS. Based on obtained results, it is indicated that the products from CO₂ hydrogenation were CH₄ and/or CO under reaction conditions pressure of 1.5 MPa and temperature of 200–500 °C, as well as the size of the particles of Co and their phase state directly affected on the catalysts activity. 3 wt% Co catalyst supported on carbon nanotubes has shown catalytic inactivity due to amorphous state of metal. It is possible to activate them during Co crystallization after thermal treatment. It is shown, that the size of Co particles supported on carbon nanotubes is 4–6 nm. The methods of fictionalization the surface of carbon nanomaterials ensuring an additional stability of metal nanoparticles is recommended.     

Enhanced performance of supercritical CO2 treated Nafion 212 membranes for direct methanol fuel cells

Supercritical carbon dioxide (Sc-CO₂) thermal treatment to enhance performances of both Nafion 212 (NR212) commercial membranes with H-form and Na-form for direct methanol fuel cells (DMFCs) is described. XRD measurements show that the crystallinity of H-form NR212 membranes increases with increasing the treated temperature in the Sc-CO₂ system, however, the crystallinity of Na-form NR212 membranes decreases with increasing the treated temperature. Since the bigger crystallites formed after the Sc-CO₂ treatments, it improves the mechanical strength and dimensional stability of the Sc-CO₂ treated NR212 membranes with H-form and Na-form. Compared with the as-received NR212 membranes, all the Sc-CO₂ treated NR212 membranes show higher proton conductivity and better capacity of barrier to methanol crossover. From Fenton test, it can be found that the Sc-CO₂ treated NR212 membranes have better chemical stability than that of NR212 membranes. Therefore, NR212 membranes treated by the Sc-CO₂ method may be promising candidate electrolytes for DMFC applications.     

H2 adsorption in Ni and passivated Ni doped 4 Å single walled carbon nanotube

Adsorption binding energies have been calculated for Nickel-doped single-walled carbon nanotubes (CNTs). Density Functional Theory (DFT) with double numerical polarization (DNP) has been used for finding the total energies of the structures. It is found that the Nickel doped CNTs show fluctuation in the binding energies of hydrogen adsorption which is overcome by passivating the Nickel atom with two hydrogen atoms. The density of states (DOS) and Mullikan atomic charge analysis have been carried to confirm the charge transfer from Ni to the carbon atoms of the CNT. The smallest CNT (diameter ≈ 4 Å) with the chirality of (5,0) has been taken for hydrogen adsorption studies. Geometry optimization shows that Ni atom prefers bridge site rather than the centre of the hexagon. The H₂ binding energies obtained in the present study reveal that desorption would take place above room temperature in Ni doped (5,0) CNTs.     

Preparation of PtRu nanoparticles on various carbon supports using surfactants and their catalytic activities for methanol electro-oxidation

In the anodes of direct methanol fuel cells (DMFCs), Pt poisoning by CO adsorption during methanol electro-oxidation has been a serious problem. Efforts to overcome or minimize this obstacle have largely involved investigations of PtRu bimetallic catalysts. In order to prepare fine PtRu alloyed hydrosols, we used non-ionic surfactants including L121, Pluronic P123, P65, Brij 35, and Tween 20 as stabilizers in this study. The sizes of the prepared metal particles change with the surfactant used. The finest metal hydrosol is obtained when Pluronic P123 and P65 are used. The resulting metal hydrosols with Pluronic P123, Brij 35 and Tween 20 are supported on Vulcan XC-72R. PtRu/XC-72R prepared with Pluronic P123 exhibits the best catalytic activity due to better dispersion of the alloyed metal. To improve further the activity of the PtRu catalyst, the commercial Vulcan XC-72R is replaced with carbon spherule (CS), a home-made carbon support. Electrochemical analyses such as cyclic voltammetry and galvanostatic-polarization tests are performed to evaluate the prepared catalyst. PtRu/CS has a superior performance to PtRu/XC-72R in methanol electro-oxidation when Pluronic P123 is employed as the stabilizer. The higher conductivity and larger inter-particle space of the CS appear to facilitate methanol electro-oxidation.     

Steam reforming and oxidative steam reforming of methanol over CuO–CeO2 catalysts

Steam reforming (SRM) and oxidative steam reforming of methanol (OSRM) were carried out over a series of coprecipitated CuO–CeO₂ catalysts with varying copper content in the range of 30–80 at.% Cu (= 100 × Cu/(Cu + Ce)). The effects of copper content, reaction temperature and O₂ concentration on catalytic activity were investigated. The activity of CuO–CeO₂ catalysts for SRM and OSRM increased with the copper content and 70 at.% CuO–CeO₂ catalyst showed the highest activity in the temperature range of 160–300 °C for both SRM and OSRM. After SRM or OSRM, the copper species in the catalysts observed by XRD were mainly metallic copper with small amount of CuO and Cu₂O, an indication that metallic copper is an active species in the catalysis of both SRM and OSRM. It was observed that the methanol conversion increased considerably with the addition of O₂ into the feed stream, indicating that the partial oxidation of methanol (POM) is much faster than SRM. The optimum 70 at.% CuO–CeO₂ catalyst showed stable activities for both SRM and OSRM reactions at 300 °C.     

Reactivity of Ni,Cr and Zr doped ceria in CO2 splitting for CO production via two-step thermochemical cycle

This work focuses on modification and screening of ceria-based oxides for solar H₂O/CO₂ splitting via two-step thermochemical cycle. Ce_1-xM_xO_2-δ (M = Zr, Ni, Cr; x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized via sol-gel method and tested for CO₂-splitting via two-step thermochemical cycles. Reduction was conducted at 1500 °C through a ramp rate of 10 °C/min and oxidation was performed at 1000 °C isothermally. Both Ni and Cr showed low solubility in ceria and no or very limited promoting effect on CO productivity. Cr could be reduced in the first reduction step but cannot be oxidized by CO₂ in the following oxidation step. Zr doped sample showed advantages in both CO productivity and lattice stability. 15% Zr doped exhibited the best performance with the CO productivity of 315.40 μmol/g. However, the oxidation rate of Zr doped samples was much lower than that of pure ceria. Compromise between fuel productivity and fast kinetics should be made in practical application.     

Influence of CO2, CH4, and initial temperature on H2/CO laminar flame speed

The objective of this study is to investigate the impact of syngas composition by varying the H₂/CO ratio (1:3, 1:1, and 3:1 by volume), the CO₂ dilution (0%–40%), and methane addition (0%–40%) on laminar flame speed. Thus, laminar flame speeds of premixed syngas–air mixtures were measured for different equivalence ratios (0.8–2.2) and inlet temperatures (295–450 K) using the Bunsen-burner method. It was found that laminar flame speed increases with increasing H₂/CO ratio, while CO₂ dilution or CH₄ addition decreased it. The location of the maximum flame speed shifts to richer mixtures with decreasing H₂/CO ratio, while it shifts to leaner mixtures with the addition of CH₄ due to its inherent slower flame speed. The location of the maximum flame speed is also shifted towards leaner mixtures with the addition of CO₂ due to the preponderance of the reduction of the adiabatic flame temperature with increasing dilution. Comparison between experimental and numerical results shows a better agreement using a modified mechanism derived from GRI-Mech 3.0. A correlation, based on the experimental results, is proposed to calculate the laminar flame speed over a wide range of equivalence ratios, inlet temperatures, and fuel content.