Electrochemical catalytic activity for oxygen reduction reaction of nitrogen-doped carbon nanofibers

The electrocatalytic activity of nitrogen-doped carbon nanofibers (N-CNFs), which are synthesized directly from vaporized acetonitrile over nickel-iron based catalysts, for oxygen reduction reaction (ORR), was investigated. The nitrogen content and specific surface area of N-CNFs can be controlled through the synthesis temperature (300-680 degrees C). The graphitization degree of N-CNFs also are significantly affected by the temperature, whereas the chemical compositions of nitrogen species are similar irrespective of the synthesis conditions. From measurement of the electrochemical double layer capacitance, the surface of N-CNFs is found to have stronger interaction with ions than undoped-carbon surfaces. Although N-CNFs show higher over-potential than Pt catalysts do, N-CNFs were observed to have a noticeable ORR activity, as opposed to the carbon samples without nitrogen doping. The activity dependency of N-CNFs on the content of the nitrogen with which they were doped is discussed, based on the experiment results. The single cell of the direct methanol fuel cell (DMFC) was tested to investigate the performance of a membrane-electrode assembly that includes N-CNFs as the cathode catalyst layer.     

Recent progress in electrochemical reduction of carbon monoxide toward multi-carbon products

The increasing CO₂ emissions and accompanying climate challenges have boosted the exploration of candidate pathways for storing and utilizing renewable carbon resources. Electrochemical CO₂ reduction (ECO₂R) has been proven as a promising technology for artificial carbon fixation. Nevertheless, the unsatisfactory multi-carbon (C₂₊) product selectivity hinders its widespread use. Recently, the indirect route via electrochemical CO reduction (ECOR) to C₂₊ products has become a potential alternative through the combination with ECO₂R. In this review, we briefly summarize the most recent and instructive research in the ECOR development process from advanced ECOR catalysts and reaction mechanisms. Furthermore, the challenges and outlooks based on current understanding in this field are expounded. These insights and perspectives offer meaningful guidance for grasping ECOR and designing relevant catalysts with enhanced C₂₊ product selectivity.     

Pinpoint and bulk electrochemical reduction of insulating silicon dioxide to silicon

Silicon dioxide (SiO(2)) is conventionally reduced to silicon by carbothermal reduction, in which the oxygen is removed by a heterogeneous-homogeneous reaction sequence at approximately 1,700 degrees C. Here we report pinpoint and bulk electrochemical methods for removing oxygen from solid SiO(2) in a molten CaCl(2) electrolyte at 850 degrees C. This approach involves a 'contacting electrode', in which a metal wire supplies electrons to a selected region of the insulating SiO(2). Bulk reduction of SiO(2) is possible by increasing the number of contacting points. The same method was also demonstrated with molten LiCl-KCl-CaCl(2) at 500 degrees C. The novelty and relative simplicity of this method might lead to new processes in silicon semiconductor technology, as well as in high-purity silicon production. The methodology may be applicable to electrochemical processing of a wide variety of insulating materials, provided that the electrolyte dissolves the appropriate constituent ion(s) of the material.     

F-doped carbon hollow nanospheres for efficient electrochemical oxygen reduction

Journal of Materials Science - Herein, a metal-free catalyst F-CHNS-900 has been prepared through a one-step pyrolysis of polytetrafluoroethylene and ZnCl2 at 900 °C. According to the...     

Synthesis of Pt nanocrystals with different shapes using the same protocol to optimize their catalytic activity toward oxygen reduction

Engineering the shape and thus surface structure of Pt nanocrystals is an effective strategy for optimizing their catalytic activities toward various reactions. However, different protocols are typically used to produce Pt nanocrystals with distinctive shapes, making it difficult to directly compare their catalytic activities owing to the complication of surface contamination. Here we demonstrate that Pt nanocrystals with a variety of shapes, including those enclosed with low- or high-index facets, can be synthesized using the same protocol by simply adjusting the concentration of reducing agent and/or the reaction time. Specifically, when the reducing agent was used at a relatively low concentration, Pt truncated cubes, cuboctahedrons, truncated octahedrons, and octahedrons were produced sequentially upon the increase in reaction time. When 67% more reducing agent was used, Pt cubes and concave cubes were obtained consecutively as the reaction time was prolonged. Our quantitative analysis suggests that the diversity of shape and difference in size can be resulted from the difference in reduction kinetics. In evaluating their structure–activity relationship for oxygen reduction, it was established that the high-index facets on Pt concave cubes possessed a specific activity of 6.3 and 1.3 times greater than those of Pt cubes and octahedrons exposed by {1?0?0} and {1?1?1} facets, respectively. This work not only offers a general method for the synthesis of Pt nanocrystals having diverse shapes and thus different types of facets but also highlights the significance of reduction kinetics in controlling the structure evolution of other metal nanocrystals.     

Light-switchable catalytic activity of Cu for oxygen reduction reaction

The surface reactivity of metals is fundamentally dependent on the local electronic structure generally tailored by atomic compositions and configurations during the synthesis. Herein, we demonstrate that Cu, which is inert for oxygen reduction reaction (ORR) due to the fully occupied d-orbital, could be activated by applying a visible-light irradiation at ambient temperature. The ORR current is increased to 3.3 times higher in the potential range between −0.1 and 0.4 V under the light of 400 mW·cm⁻², and the activity enhancement is proportional to the light intensity. Together with the help of the first-principle calculation, the remarkably enhanced electrocatalytic activity is expected to stem mainly from the decreased metal–adsorbate binding by photoexcitation. This finding provides an additional degree of freedom for controlling and manipulating the surface reactivity of metal catalysts besides materials strategy.     

Vacuum-assisted synthesis of tiny Au nanoparticles entrapped into mesoporous carbon matrix with superior catalytic activity for 4-nitrophenol reduction

In this work, we report a vacuum-assisted approach to synthesize tiny Au nanopartciles (Au NPs) entrapped into mesoporous carbon matrix (denoted as Au@MC). The tiny Au NPs are stably entrapped within the mesoporous structure and possess a small particle size (～2.64?nm). The composite also exhibits a high specific surface area (～421?m² g^?1), which may provide convenient transportation and diffusion for substrate molecules. Thus, Au@MC exhibits superior catalytic activity and reusability for 4-nitropheno (4-NP) reduction. The vacuum-assisted synthesis with unique nanostructure is expected to be applied in the preparation of other catalysts.     

Metallocorrole-based porous organic polymers as a heterogeneous catalytic nanoplatform for efficient carbon dioxide conversion

Metallocorrole macrocycles that represent a burgeoning class of attractive metal-complexes from the porphyrinoid family,have attracted great interest in recent years owing to their unique structure and excellent performance revealed in many fields,yet further functionalization through incorporating these motifs into porous nanomaterials employing the bottom-up approach is still scarce and remains synthetically challenging.Here,we report the targeted synthesis of porous organic polymers(POPs)constructed from custom-designed Mn and Fe-corrole complex building units,respectively denoted as CorPOP-1(Mn)and CorPOP-1(FeCl).Specifically,the robust CorPOP-1(Mn)bearing Mn-corrole active centers displays superior heterogeneous catalytic activity toward solvent-free cycloaddition of carbon dioxide(CO₂)with epoxides to form cyclic carbonates under mild reaction conditions as compared with the homogeneous counterpart.CorPOP-1(Mn)can be easily recycled and does not show significant loss of reactivity after seven successive cycles.This work highlights the potential of metallocorrole-based porous solid catalysts for targeting CO₂ transformations,and would provide a guide for the task-specific development of more corrole-based multifunctional materials for extended applications.     

Oxygen reduction activity of carbon nitride supported on carbon nanotubes

Fuel cells offer an alternative to burning fossil fuels, but use platinum as a catalyst which is expensive and scarce. Cheap, alternative catalysts could enable fuel cells to become serious contenders in the green energy sector. One promising class of catalyst for electrochemical oxygen reduction is iron-containing, nanostructured, nitrogen-doped carbon. The catalytic activity of such N-doped carbons has improved vastly over the years bringing industrial applications ever closer. Stoichiometric carbon nitride powder has only been observed in recent years. It has nitrogen content up to 57% and as such is an extremely interesting material to work with. The electrochemical activity of carbon nitride has already been explored, confirming that iron is not a necessary ingredient for 4-electron oxygen reduction. Here, we synthesize carbon nitride on a carbon nanotube support and subject it to high temperature treatment in an effort to increase the surface area and conductivity. The results lend insight into the mechanism of oxygen reduction and show the potential for carbon nanotube-supported carbon nitride to be used as a catalyst to replace platinum in fuel cells.     

In-line catalytic purification of carbon dioxide used in analytical-scale supercritical fluid extraction

Supercritical fluid extraction analyses are often compromised by trace impurities present in the solvent carbon dioxide. These impurities, commonly used as lubricants in the specialty gas industry, can produce significant background levels, increasing limits of detection and quantification. This problem is especially severe when electron capture detection (ECD) is used for trace concentrations of analytes (e.g., polychlorinated biphenyls and chlorinated pesticides). In this study, an in-line catalyst-based purification system was successfully employed to remove ECD-responsive contaminants from CO2. Low-purity (98%) "Bone Dry" CO2 was purified to levels cleaner than a very-high-purity grade of CO2 specified at less than 10 ppt ECD-responsive contaminants. Purification was successfully applied to extremely sensitive on-column experiments as well as higher flow rate off-line experiments. In addition to lowering limits of detection and quantification, significant cost savings can be realized by purifying inexpensive, low-purity CO2 instead of relying on much more expensive, prepurified CO2.     

A concept for immobilizing catalytic complexes on electrodes: cubic phase layers for carbon dioxide sensing

Liquid crystalline cubic phases formed with monoolein and Myverol have been used as matrixes to host a catalytic complex of nickel(II) and 1-hexadecyl-1,4,8,11-tetraazacyclotetradecane for the reduction of carbon dioxide. The structures of the cubic phases, both with and without the catalyst, were established using small-angle X-ray scattering. The catalytic reduction of carbon dioxide was performed using thin mercury film and glassy carbon electrodes modified with cubic phases containing the catalyst. The linear dependence of the catalytic reduction current on the carbon dioxide concentration allowed use of the modified electrodes as sensing devices both in solution and in the gas phase. The high reproducibility of the measurements makes this method of monitoring carbon dioxide levels attractive compared to other methods based on modified electrodes.     

Correction to: Technical principles of atmospheric carbon dioxide reduction and conversion: economic considerations for some developing countries

Clean Technologies and Environmental Policy -     

Highly efficient multi-metal catalysts for carbon dioxide reduction prepared from atomically sequenced metal organic frameworks

The precise control on the combination of multiple metal atoms in the structure of metal-organic frameworks(MOFs)endowed by reticular chemistry,allows the obtaining of materials with compositions that are programmed for achieving enhanced reactivity.The present work illustrates how through the transformation of MOFs with desired arrangements of metal cations,multi-metal spinel oxides with precise compositions can be obtained,and used as catalyst precursor for the reverse water-gas shift reaction.The differences in the spinel initial composition and structure,determined by neutron powder diffraction,influence the overall catalytic activity with changes in the process of in s itu formation of active,metal-oxide supported metal nanoparticles,which have been monitored and characterized with in situ X-ray diffraction and photoelectron spectroscopy studies.     

纳米金增强掺磷四面体非晶碳膜的电化学活性

采用电沉积法在过滤阴极真空电弧技术合成的掺磷四面体非晶碳(ta-C∶P)薄膜表面沉积纳米金团簇,制备纳米金修饰的掺磷非晶碳(Au/ta-C∶P)薄膜电极。利用X射线光电子能谱、拉曼光谱、扫描电子显微镜和电化学伏安法表征ta-C∶P和Au/ta-C∶P的微观结构、表面形貌和电化学行为。结果表明,-80V的脉冲偏压更利于磷原子进入碳的网络,并明显增加薄膜的电导率和电化学活性。纳米金团簇可增加ta-C∶P电极的有效面积,提高对铁氰化钾氧化还原反应的活性和电极可逆性,增强对多巴胺的催化活性。研究结果揭示ta-C∶P和Au/ta-C∶P薄膜在电分析及生物传感器方面的潜在应用。     

Coordination engineering of cobalt phthalocyanine by functionalized carbon nanotube for efficient and highly stable carbon dioxide reduction at high current density

Coordination engineering can enhance the activity and stability of the catalyst in heterogeneous catalysis.However,the axial coordination engineering between di...     

Economic value of improved quantification in global sources and sinks of carbon dioxide

On average, about 45 per cent of global annual anthropogenic carbon dioxide (CO(2)) emissions remain in the atmosphere, while the remainder are taken up by carbon reservoirs on land and in the oceans-the CO(2) 'sinks'. As sink size and dynamics are highly variable in space and time, cross-verification of reported anthropogenic CO(2) emissions with atmospheric CO(2) measurements is challenging. Highly variable CO(2) sinks also limit the capability to detect anomolous changes in natural carbon reservoirs. This paper argues that significant uncertainty reduction in annual estimates of the global carbon balance could be achieved rapidly through coordinated up-scaling of existing methods, and that this uncertainty reduction would provide incentive for accurate reporting of CO(2) emissions at the country level. We estimate that if 5 per cent of global CO(2) emissions go unreported and undetected, the associated marginal economic impacts could reach approximately US$20 billion each year by 2050. The net present day value of these impacts aggregated until 2200, and discounted back to the present would have a mean value exceeding US$10 trillion. The costs of potential impacts of unreported emissions far outweigh the costs of enhancement of measurement infrastructure to reduce uncertainty in the global carbon balance.     

Facile synthesis of Au nanoparticles supported on polyphosphazene functionalized carbon nanotubes for catalytic reduction of 4-nitrophenol

Carbon nanotubes (CNTs) functionalized with cyclotriphosphazene-containing polyphosphazenes (PZS) were found to cause the facile immobilization of Au nanoparticles on the surface. The PZS functional layers not only improved the dispersion of CNTs in aqueous solution but also used as a platform for subsequent immobilization of Au nanoparticles. The functionalized CNTs and the Au@PZS@CNTs nanohybrids were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, X-ray diffraction, thermogravimetric analysis, Atomic absorption spectrum, and X-ray photoelectron spectroscopy. The results showed that the PZS layers with thickness of about 25 nm were formed uniformly on CNT surfaces by polycondensation between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol, and that high density of homogeneously dispersed spherical Au nanoparticles with average size of 6 nm was immobilized on their outer surface. Meanwhile, the catalytic activity and reusability of the Au@PZS@CNTs nanohybrids were investigated by employing the reduction of 4-nitrophenol into 4-aminophenol by NaBH₄ as a model reaction.     

Mechanism for electrochemical synthesis of diamond-like carbon

Some unusual features of the low-temperature electrochemical synthesis of diamond-like carbon are described. It is shown that the electrochemical synthesis of carbon is catalyzed by transition metals, and the formation of a film on the electrode is preceded by the formation of a colloidal solution and a carbon gel. Pis’ma Zh. Tekh. Fiz. 23, 40–45 (May 12, 1997)