Mesoporous Carbon Films Research Articles

Ultrafine CoFe Alloy Nanoparticles Confined in Highly Ordered Mesoporous Carbon Films as Catalysts for the Oxygen Evolution Reaction

Ultrafine CoFe Alloy Nanoparticles Confined in Highly Ordered Mesoporous Carbon Films as Catalysts for the Oxygen Evolution Reaction

Sensitive chemoselectivity of cellulose nanocrystal films

Cellulose nanocrystals (CNCs), self-assembled into a chiral nematic structure film, create an advanced platform for the fabrication of remarkable sensing, photonic and chiral nematic materials. Despite extensive progress in the knowledge of functions of CNCs, their chemoselectivity has rarely been reported. Here, we report a brand-new perspective of CNCs in chemoselectivity, which shows sensitive selectivity even between isomers of monosaccharides and disaccharides by generating discernible crystal patterns. This sensitive selectivity of glucose homologs is attributed to the selective carbohydrate–carbohydrate interactions (CCIs) through generating hydrogen bonds between CNC units and the glucose homologs, endowing a remarkable color variation of the CNC films. Moreover, the CCIs are distinct for different immersion times and concentrations of glucose homologs, verified through Fourier Transform Infrared Spectroscopy (FTIR) spectra. Based on the sensitive CCIs, pristine CNC films are then used as templates to generate chiral mesoporous carbon films with tunable specific surface areas by assembly of CNC suspensions and the glucose homologs. We envision that the sensitive chemoselectivity of CNC films as well as precise structure modulation could provide insights into the recognition of carbohydrates and the preparation of mesoporous carbon in numerous practical applications. A pristine chiral nematic cellulose nanocrystal film with sensitive chemoselectivity to glucose homologues and even isomers of monosaccharides and disaccharide are prepared through self-assembly. For different kinds of glucose homologs, distinct crystal morphologies are formed due to the selective carbohydrate–carbohydrate interactions. Besides, the highly ordered left-helical layered structure of pristine cellulose nanocrystal film could be used as templates for the precise construction of delicate nanostructures.

Large-Pore Ordered Mesoporous Turbostratic Carbon Films Prepared Using Rapid Thermal Annealing for High-Performance Micro-pseudocapacitors.

Carbonization by rapid thermal annealing (RTA) of precursor films structured by a brush block copolymer-mediated self-assembly enabled the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based micro-supercapacitors within minutes. The large pore size of the fabricated films facilitates both rapid electrolyte diffusion for carbon-based electric double-layer capacitors and conformal deposition of V2O5 without pore blockage for pseudocapacitors. The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to produce microphase-segregated carbon precursor films on a variety of substrates. Ultrafast RTA processing (∼50 °C/s) at elevated temperatures (up to 1000 °C) then generated stable, conductive, turbostratic MPC films, resolving a significant bottleneck in rapid fabrication. MPC prepared on stainless steel at 900 °C demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm2 and 126 F/cm3 (at 0.8 mA/cm2 using 6 M KOH as the electrolyte), respectively, and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V2O5 deposition yielded pseudocapacitors with 10-fold increase in energy density (20 μW h cm-2 μm-1) without adversely affecting the high power density (450 μW cm-2 μm-1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performance carbon-based micro-pseudocapacitors.

Laser-assisted synthesis of carbon coatings with cobalt oxide nanoparticles embedded in gradient of composition and sizes

We report on a new laser-assisted method for the synthesis of composite coatings consisting of cobalt oxide-embedded porous carbon with gradient of composition and sizes. Uniform carbon thin films containing cobalt oxide nanoparticles (CoO NPs) of various concentrations and sizes are obtained by Combinatorial Matrix-Assisted Pulsed Laser Evaporation (C-MAPLE) followed by a post-annealing treatment. Specifically, simultaneous pulsed laser irradiation of two concentric cryogenic targets was applied for gradient thin films assembling on solid substrates. Both targets contained environmentally friendly phloroglucinol/glyoxylic acid organic precursors and a template dissolved in an ethanol-chloroform mixture, whereas one of them enclosed, in addition, cobalt nitrate salt. Due to angular dispersion and crossing of the two vapor plumes during co-deposition process, thin composite polymeric nanocoatings containing Co nitrate salt were obtained. After subsequent thermal annealing treatment of samples at 600 °C, mesoporous carbon films exhibiting CoO NPs gradient distribution were then directly obtained onto the substrates. Carbon matrix formation was supported by EDX analyses and characteristic D, G and 2D bands present in the Raman spectra. Co NPs concentration varied from 3 to 32 wt% on the substrates with a minimum at furthest interaction point of the Co salt containing plume and substrate, while carbon concentration significantly decreased from 91 to 63 wt%. Oxygen amount was relatively constant at about 6 wt% for all coatings. The CoO NPs are homogenously dispersed in the carbon matrix whereas a tendency for aggregation is observed for high loadings. In addition, the CoO NPs size gradient distribution ranged from 3 to 8 nm with the minimum size correlating the minimum concentration.

Precisely Controlled Vertical Alignment in Mesostructured Carbon Thin Films for Efficient Electrochemical Sensing.

Two-dimensional carbon materials, incorporating a large mesoporosity, are attracting considerable research interest in various fields such as catalysis, electrochemistry, and energy-related technologies owing to their integrated functionalities. However, their potential applications, which require favorable mass transport within mesopore channels, are constrained by the undesirable and finite mesostructural configurations due to the immense synthetic difficulties. Herein, we demonstrate an oriented monomicelle assembly strategy, for the facile fabrication of highly ordered mesoporous carbon thin films with vertically aligned and permeable mesopore channels. Such a facile and reproducible approach relies on the swelling and fusion effect of hydrophobic benzene homologues for directional monomicelle assembly. The orientation assembly process shows precise controllability and great universality, affording mesoporous carbon films with a cracking-free structure over a centimeter in size, highly tunable thicknesses (13 to 85 nm, an interval of ∼12 nm), mesopore size (8.4 to 13.5 nm), and switchable growth substrates. Owing to their large permeable mesopore channels, electrochemical sensors based on vertical mesoporous carbon films exhibit an ultralow limit of detection (50 nmol L-1) and great sensitivity in dopamine detection.

Colloidal bimetallic platinum–ruthenium nanoparticles in ordered mesoporous carbon films as highly active electrocatalysts for the hydrogen evolution reaction

Ordered mesoporous carbon films with high surface area, good electrical conductivity and an improved distribution of NPs with tunable composition show high electrocatalytic activity in HER.

Ultrafine Cobalt‐Doped Iron Disulfide Nanoparticles in Ordered Mesoporous Carbon for Efficient Hydrogen Evolution

AbstractDesigning earth‐abundant and efficient electrocatalysts to replace noble metals is highly desired for the hydrogen evolution reaction (HER) in water electrolysis. In this study, we constructed a self‐supported electrode with ordered mesoporous carbon film coated carbon fibers as a substrate and Co doped FeS2 nanoparticles as catalytically active phase for the HER. The ordered mesoporous carbon served as nanoreactor to restrict the growth of sulfide particles and prevent them from agglomeration, leading to the formation of ultrafine and highly dispersed sulfide of ∼5 nm, which enables the exposure of abundant active sites. Meanwhile, the Co atom doping enhanced the adsorption of the catalyst towards hydrogen, thereby improving its intrinsic activity. As a result, the electrode exhibited outstanding catalytic activity for the HER in acid electrolyte, manifesting a current density of 10 mA cm−2 at an overpotential of 92 mV and a small Tafel slope of 59 mV dec−1.

Photoelectrocatalytic H2 and H2O2 Production Using Visible-Light-Absorbing Photoanodes

Hydrogen and hydrogen peroxide have been photoelectrocatalytically produced by electrocatalytic reduction using simple carbon electrodes made by depositing a mesoporous carbon film on carbon cloth. Visible-light-absorbing photoanodes have been constructed by depositing mesoporous CdS/TiO2 or WO3 films on transparent fluorine-doped tin oxide (FTO) electrodes. Both produced substantial photocurrents of up to 50 mA in the case of CdS/TiO2 and 25 mA in the case of WO3 photoanodes, and resulting in the production of substantial quantities of H2 gas or aqueous H2O2. Maximum hydrogen production rate was 7.8 µmol/min, and maximum hydrogen peroxide production rate was equivalent, i.e., 7.5 µmol/min. The same reactor was employed for the production of both solar fuels, with the difference being that hydrogen was produced under anaerobic and hydrogen peroxide under aerated conditions. The present data promote the photoelectrochemical production of solar fuels by using simple inexpensive materials for the synthesis of catalysts and the construction of electrodes.

Mesoporous carbon film via spin coating soft templating method for supercapacitor electrode

Mesoporous carbon (MPC) films were prepared by using spin coating self-assembly soft templating method onto titanium (Ti) foils as substrates. Carbon precursor of resorcinol (R), formaldehyde (F) and a surfactant of triblock copolymer Pluoronic F127 (F127) which may act as a structure directing agent (SDA) for the pore structure geometry tuning were used in the preparation of the mesoporous carbon films. The samples were then carbonised to obtain the final product of MPC films. The mesostructure was characterised by thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FESEM) and electrochemical analyses. The MPC film showed excellent electrochemical property for supercapacitor application by achieving specific capacitance value of 15.23 mF cm-2 at the scan rate of 5 mV s−1 in 1.0 M potassium chloride (KCl) neutral aqueous electrolyte which was approximately 88 times higher than as prepared samples. F127/RF carbon film also displayed outstanding cycle stability with 98% capacitance retention after 1000 cycles. This has proven that the synthesised MPC film-coated titanium foil may be a promising candidate for high performance electric double layer capacitors (EDLC).

Ordered mesoporous carbon in solid-phase microextraction for analysis of volatile organic compounds in water samples

An ordered mesoporous carbon (OMC) film supported on graphite fiber was prepared by a dip-coating method combined with a solvent evaporation induced self-assembly (EISA) strategy.

Outstanding hydrogen evolution performance of supported Pt nanoparticles: Incorporation of preformed colloids into mesoporous carbon films

Platinum is the best catalyst known so far for the hydrogen evolution reaction (HER) in acidic environments, but it is also a scarce and expensive resource. Maximizing its performance per metal atom is essential in order to reduce costs. The deposition of small Pt nanoparticles (2–3 nm) onto electrically conductive, highly accessible and stable carbon supports leads to active catalysts. However, blocking of pores and active sites by Nafion, which acts as a binding species, reduces the catalytic activity. Moreover, inaccessible Pt located in micropores diminishes an efficient exploitation of the noble metal.We report a new synthesis approach to ordered mesoporous carbon (OMC) coatings with preformed Pt nanoparticles. The particles are exclusively located inside the mesopores. Furthermore, no Nafion binder is needed. As a consequence, the PtNP/OMC catalyst film outperforms Pt/C catalysts reported in literature particularly at high current densities. PtNP/OMC catalyst films with a geometric Pt loading of 1.6 µgPt/cm2 achieve a current density of −100 mA/cm2 at an overpotential of ca. −70 mV.

Dependence of power conversion properties of the hole-conductor-free mesoscopic perovskite solar cells on the thickness of carbon film

Abstract Effect of film thickness of mesoporous carbon on power conversion properties of the hole-conductor-free mesoscopic perovskite solar cells is studied by varying the volume of carbon paste. It is observed that, with increment of the film thickness, perovskite crystallites become smaller; As for the performance parameters, open-circuit voltage (VOC) drops slowly; while short-circuit current density (JSC) and fill factor (FF) rise at first, and then decrease after the film thickness surpasses about 22 μm. The slight decrease in open-circuit voltage (VOC) is due to heavier recombination brought by smaller crystallite size of perovskite. The upgraded short-circuit current density is due to accelerated charge-extracting rate across the interface between perovskite and mesoporous carbon, as revealed by the transient photocurrent (TPC) decay measurement. As for the improved fill factor, it is ascribed to the increased conductivity of the mesoporous carbon film. Besides, shelf-stability of the devices is tested. Stability up to 112 days (relative humidity of 40–70%, no encapsulation) are observed for these carbon based mesoporous perovskite solar cells, even though the mesoporous carbon is as thin as ∼4 μm. The sound stability shows that the TiO2 nanoparticle-bonding carbon film could provide effective barrier against H2O/O2.

Mesoporous carbon film inlaid with Li3V2(PO4)3 nanoclusters through delaying sol-gel method for high performance lithium-ion hybrid supercapacitors

A one-pot sol-gel method was modified through delaying gel curing by compositing Li3V2(PO4)3 with carbon. As a result, mesoporous carbon film inlaid with Li3V2(PO4)3 nanoclusters (named as LVP-C) was prepared to serve as cathode for the “non-consumable electrolyte type” and “internal serial hybrid type” Lithium-ion hybrid supercapacitor (LIHS). The LVP-C17 composite exhibited a considerably high initial discharge capacity of 128 mAh g−1 at 0.2C-rate, which was extremely close to the theoretical specific capacity. The BET specific surface area of the LVP-C17 composite is as high as 53.65 m2 g−1 and the Barret-Joyner-Halenda (BJH) pore-size-distribution curve displays that the pore sizes of the composite are mainly below 10 nm. The Raman test of the LVP-C17 composite mainly exhibits the graphitized carbon (SP2 hybridization) and a smaller R value (0.86), from which it can be inferred that the electronic conductivity of the composite is improved. The LIHS was designed by using LVP-C17 as cathode and active carbon (AC) as anode (LVP-C17//AC LIHS), which exhibited a higher energy density of 24 Wh kg−1 at a power density 405 W kg−1, with 77% specific capacitance retention after 1000 cycles in a wider voltage range of 0–2.7 V. Furthermore, even at higher power density of 2.03 kW kg−1, the energy density provided by the device can still retain 12.4 Wh kg−1. The device combines the electrochemical performance advantages of lithium-ion batteries (LIBs) with supercapacitors (SCs) and is comparable to the energy density and power density of currently commercially available Ni/MH batteries.

Three‐Dimensional Cathode Constructed through Confined‐Growth of FeP Nanocrystals in Ordered Mesoporous Carbon Film Coated on Carbon Cloth for Efficient Hydrogen Production

AbstractEfficient, stable, and affordable electrocatalysts are essential for large‐scale hydrogen generation through water electrolysis. Nanosized catalyst particles integrated with a conductive current collector are highly desirable candidates yet quite challenging to synthesize. In this study, we prepared a self‐supported electrode constructed with FeP nanocrystals confined in the pores of ordered mesoporous carbon‐coated carbon cloth (FeP@OMC/CC) for efficient hydrogen evolution reaction (HER). The synergistic effect of ultrafine FeP nanocrystals, ordered mesoporous configuration and highly conductive carbon fiber framework endowed the self‐supported electrode with enriched active sites, accelerated charge and mass transport and strong mechanical stability. Consequently, the as‐synthesized FeP@OMC/CC electrode exhibited remarkable HER performance with a low overpotential (10 mA cm−2 at an overpotential of 51 mV), small Tafel slope (39 mV dec−1), and superior structural and electrochemical stability (over 20 h under an overpotential of 70 mV), which is one of the highest electrocatalytic performance observed among all nonprecious materials.

Effect of Ba Content on the Activity of La1-x Ba x MnO3 Towards the Oxygen Reduction Reaction.

The electrocatalytic activity of La1‐xBaxMnO3 nanoparticles towards the oxygen reduction reaction (ORR) is investigated as a function of the A‐site composition. Phase‐pure oxide nanoparticles with a diameter in the range of 40 to 70 nm were prepared by using an ionic liquid route and deposited onto mesoporous carbon films. The structure and surface composition of the nanoparticles are probed by XRD, TEM, EDX, and XPS. Electrochemical studies carried out under alkaline conditions show a strong correlation between the activity of La1‐xBaxMnO3 and the effective number of reducible Mn sites at the catalysts layer. Our analysis demonstrates that, beyond controlling particle size and surface elemental segregation, understanding and controlling Mn coordination at the first atomic layer is crucial for increasing the performance of these materials.

Soft-templated mesoporous RuPt/C coatings with enhanced activity in the hydrogen evolution reaction

Platinum is the most active catalyst for the electrolytic hydrogen evolution reaction (HER). Yet, it is expensive as well as scarce and therefore needs to be used most efficiently. In order to reduce the amount of necessary Pt we propose a synthesis approach to alloyed RuPt nanoparticles which retain the enhanced catalytic activity of Pt. These particles are dispersed on an electrically conductive, highly accessible and stable carbon coating. The synthesis route relies on the co-deposition of molecular Ru and Pt precursors together with a carbon precursor with micelles as structure directing pore templates. The films adhere without the use of binding agents like Nafion, which can decrease catalytic activity by blocking of pores and active surface sites. Carbonization in reducing atmosphere (H2/Ar) leads to ordered mesoporous carbon films with a controlled morphology and a very high electrical conductivity. The films exhibit well-dispersed small nanoparticles.The presented RuPt catalyst films show a four times higher activity per Pt in the hydrogen evolution reaction compared to conventional Nafion-based Pt/C reference catalysts. Moreover, the synthesis approach represents a generic approach to ordered mesoporous carbon coatings containing metal nanoparticles.

Matrix-Assisted Pulsed Laser Evaporation: A novel approach to design mesoporous carbon films

We report on a fast synthesis method of porous carbon films on solid substrates. Thin carbon micro-structures tailored by processing conditions were synthesized for the first time by Matrix-Assisted Pulsed Laser Evaporation. The procedure consists of pulsed laser irradiation of a cryogenic target composed of phloroglucinol/glyoxylic acid organic precursors dissolved in different mixtures of solvents. An excimer UV KrF* pulsed laser was employed inside a vacuum chamber for material expulsion from the target and immobilization on a solid facing collector. By modifying laser energy or target solvents, thin polymeric coatings of hundreds of nanometers with various cross-linking degrees were obtained at room temperature in 10 min only. No drying or thermo-polymerization step is required even for high boiling point solvents such as dymethyl sulfoxide (DMSO). After thermal treatment, mesoporous carbon films exhibiting diverse nano-morphologies and surface areas up to 705 m2 g−1 determined by Kr adsorption were then directly obtained onto various collectors. Processing and assembling mechanisms of phenolic resins were investigated and two competing mechanisms, e.g., target absorption of laser wavelength and subsequent molecules transfer/interactions are accounted for the growth of high quality films as highlighted by several techniques.

Facile synthesis of mesoporous carbon from furfuryl alcohol-butanol system by EISA process for supercapacitors with enhanced rate capability

A smart, efficient and cost-effective strategy using modified evaporation induced self-assembly (EISA) is employed to synthesize mesoporous carbon (MC) with excellent textural parameters. Furfuryl alcohol is utilized as an alternative source of carbon precursor for the first time in EISA process in place of conventional EISA precursor, namely resol. Further n-Butanol, used as a co-structure directing agent during synthesis plays a crucial role in formation of a high surface area mesoporous carbon. The resulting carbon synthesized by modified EISA process shows a high specific surface area with large pore volume and more of ordered graphitic carbon. Wettability studies reveal that the surface functionalized mesoporous carbon film surface exhibits superior hydrophilic properties in comparison with non-functionalized mesoporous carbon film surface. It delivers a high specific capacitance of 151 F g−1 at a high current density of 50 A g−1 and shows excellent rate capability with 93% capacitance retention. It also exhibits good cyclic stability with capacitance retention of 96% after 10,000 cycles and delivers a stable energy density of 2.7 W h kg−1 by retaining a power density of 2516 W kg−1. The excellent electro-chemical performance of mesoporous carbon reported in the present study is attributed to the presence of high surface area of MC with large interconnected mesopores that allows unhindered flow of the electrolyte ions to the active surface sites. Benchmark studies reveal that the electro-chemical performance of mesoporous carbon being reported in this study is better than carbon electrode based commercial supercapacitors. Thus, the simple and unique strategy employed in the present study can be extended to synthesize carbon materials for other energy storage applications.

Elucidating Structure-Activity Relationships for the Oxygen Reduction Reaction at Mn-Based Perovskites

Transition metal oxides such as perovskites (ABO3) are becoming an important class of materials in the context of oxygen electrocatalysis for alkaline fuel cells and metal-air batteries.1,2 Although these materials have been extensively investigated in the field of solid oxide fuel cells, their properties as oxygen electrocatalysts at room temperature are far from being fully rationalised. Establishing structure-activity relationships based on the electronic structure of the B-site, widely recognised as the main active site, is one of the key challenge in this field. Such information is extremely important towards designing catalysts with optimal B-site orbital occupancy, coordination number and metal-oxygen bond length. In a recent study, we have shown that LaMnO3 exhibits over two orders of magnitude higher activity towards the ORR than other lanthanide perovskites (e.g. Co, Fe, Cr and Ni).3 Our analysis show that the origin of this high activity is linked to changes in the redox state at the Mn sites at potentials close to the formal ORR potential, leading to an increase in electron population at the key active site. In this contribution, we shall focus on the structure-activity relationship of a family of LaxCa1-xMnO3 nanoparticles, assessing their activity as a function of the Mn-valency. We will provide a detailed analysis of the bulk and surface structure employing X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). Studies employing rotating ring-disc electrodes of the nanoparticles supported on mesoporous carbon films show that their activity towards the ORR are among the highest reported for transition metal oxides.4 We finally establish that the mean ORR activity of surface Mn sites increases as the Mn valency decreases.5 These studies highlight the need for independent assessment of key aspects such as the extent of A-site surface segregation and average Mn valency in order to establish consistent structure-activity relationships.

Highly Active Binder-Free Catalytic Coatings for Heterogeneous Catalysis and Electrocatalysis: Pd on Mesoporous Carbon and Its Application in Butadiene Hydrogenation and Hydrogen Evolution

Heterogeneous catalysis performed in wall-coated reactors and electrocatalysis require homogeneous catalytic coatings with high surface area and good accessibility of the active sites. Conventional coating methods necessitate the use of binder components that often block pores and active sites, which limits catalytic efficiency, and utilization of expensive active metals. We report an approach for the direct and binder-free synthesis of chemically, mechanically, and thermally stable catalytic coatings based on ordered mesoporous carbon films employed as catalyst support. The synthesis relies on the codeposition of a structure-directing agent and small clusters of polymeric carbon precursors along with ionic metal species on a substrate. A sequence of thermal treatments converts the polymer into partly graphitized carbon, decomposes the structure-directing agent, and converts the metal precursor into highly active nanoparticles. Syntheses and catalytic applications are exemplarily demonstrated for palladiu...