New Class Of Carbon Materials Research Articles

Engineered Catalyst Support with Improved Durability at Higher Weight Percentage of Platinum

Proton Exchange Membrane (PEM) fuel cells are a suitable electrochemical power source for heavy duty vehicle (HDV) applications due to their high efficiency and durability. The cathode of the fuel cell uses a higher geometric loading of platinum (∼0.2 to 0.4 mgPt/cm2) for the electrocatalysis of the kinetically sluggish Oxygen Reduction Reaction (ORR) which requires higher weight percent loading of the metal (∼50%) on the carbon support to decrease the catalyst layer thickness and hence, the reactant transport losses. The conventionally used supports for platinum catalyst, such as the KetjenBlackTM type high surface area carbon (HSC) features limited mesopore area for the dispersion of Pt nanoparticles leading to increased aggregation and poor durability. Here, we show a new class of carbon materials known as the Engineered Catalyst Support (ECS) developed by Pajarito Powder with higher mesopore fraction for the dispersion of higher weight percentage of Pt nanoparticles. ECS materials can disperse up to 50% Pt by weight of the catalyst thereby enabling lower catalyst layer thickness with higher performance retained after durability test. A comprehensive set of physico-chemical and electrochemical studies in membrane electrode assembly (MEA) are reported to understand the performance and durability of Pt/ECS catalysts.

Ordered carbonaceous frameworks: a new class of carbon materials with molecular-level design.

Ordered carbonaceous frameworks (OCFs) are a new class of carbon materials with a three-dimensional ordered structure synthesized by simple carbonization of metalloporphyrin crystals with polymerizable moieties. Carbonization via solid-state polymerization results in the formation of graphene-based ordered frameworks in which regularly aligned single-atomic metals are embedded. These unique structural features afford molecular-level designability like organic-based frameworks together with high electrical conductivity, thermal/chemical stability, and mechanical flexibility, towards a variety of applications including electrocatalysis and force-driven phase transition. This feature article summarizes the synthetic strategies and characteristics of OCFs in comparison with conventional organic-based frameworks and porous carbons, to discuss the potential applications and further development of the OCF family.

Activated carbon fibers via reductive carbonization of cellulosic biomass for adsorption of nonpolar volatile organic compounds

Reductive carbonization of cellulosic fibers via nano-sized nickel catalyst in the presence of hydrogen was examined for production of activated carbon fibers (ACFs). The results showed that 99.5 % of oxygen originally presented in the biomass was removed as measured by using X-ray Photoelectron Spectroscopy (XPS), with over 63 % carbon in form of reductive species. Such reductive ACFs demonstrated high adsorption capacities for non-polar volatile organic compounds (VOCs). Particularly, the reductive ACFs absorbed benzene at a capacity that was 8 times higher than traditionally prepared carbon fibers. That can be attributed to both the reductive surface chemistry and morphology generated by the activity of the nanocatalysts. The unique network structure of the ACFs also provided a fine conductivity, that made it possible for efficient material regeneration via electrothermal desorption. The absorbed VOCs could be completely released within 1 min upon application of a moderate electrical current, and the regenerated materials could regain 100 % of its adsorption capacity even after repeated adsorption and desorption cycles. This work demonstrated for the first time the use of nanocatalyst-assisted reductive carbonization in manipulating surface properties of bio-based carbon materials, promising the production of a new class of carbon materials for industrial applications including air quality control, gas separation, and fuel storage.

High electrochemical cycling performance through accurately inheriting hierarchical porous structure from bagasse

Abstract Nature provides perfect varying models of hierarchical porous structures, but it remains a great challenge to accurately transfer these models intact to laboratory through carbonization during processing. In this study we report a new class of carbon materials whose hierarchical porous structure is accurately inherited from bagasse through a process consisting of a hydrothermal treatment with thiourea at 180 °C and then carbonization at 800 °C. The resulting composite structure consists of nanopores, supermicropores and ultramicropores with a high specific surface area of 2419 m2 g−1. The treatment with thiourea not only results in N and S doping but creates many papillae of a few hundreds of nanometer in diameter on the tubular wall. As a supercapacitor electrode working at 1 A g−1 in aqueous electrolyte, it shows a capacitance of 312 F g−1 (125 F cm−3), with 69% retention even at a very high current density of 20 A g−1. The material renders a good energy density of 11 Wh kg−1 at a power density of 125 W kg−1 and shows good cycling stability, 99.7% of initial capacitance remained after 10,000 charge/discharge cycles. As a lithium ion battery anode, it exhibited capacity of 621 mA h g-1 at 100 mA g-1 and the capacity remained at 310 mA h g-1 at 1000 mA g-1.

Production of thermally conductive carbon foams and their application in automobile transport

The report examines the possible methods of synthesis and properties of a new class of carbon materials – thermally conductive foams based on mesophase pitches and their application in automobiles to control the heat flow.

Self-Assembled 3D Graphene Monolith from Solution.

Three-dimensional (3D) graphene-assembled monoliths (GAs), especially ones prepared by self-assembly in the liquid phase, represent promising forms to realize the practical applications of graphene due to their high surface utilization and operability. However, the understanding of the assembly process and structure control of 3D GAs, as a new class of carbon materials, is quite inadequate. In this Perspective, we give a demonstration of the assembly process and discuss the key factors involved in the structure control of 3D GAs to pave the way for their future applications. It is shown that the assembly process starts with the phase separation, which is responsible for the formation of the 3D networked structure and liquid phase as the spacers avoid the parallel overlap of graphene layers and help form an interlinked pore system. Well-tailored graphene sheets and selected assembly media must be a precondition for a well-controlled assembly process and microstructure of a 3D GA. The potential applications in energy storage featuring high rate and high volumetric energy density demonstrate advantages of 3D GAs in real applications.

Theoretical investigations of sp-sp2 hybridized zero-dimensional fullerenynes

Widely recognized as the quintessential material, sp(2) hybridized carbon material with low dimensions, such as zero-dimensional fullerene, one-dimensional carbon nanotube and two-dimensional graphene, has already compiled an impressive list of superlatives. Quite recently, one-dimensional sp-sp(2) hybridized carbon tubular arrays with a wall thickness of about 40 nm and two-dimensional carbon films with the average thickness of 970 nm have been synthesized successfully. Thus, we expect that the existence of a sp-sp(2) hybridized zero-dimensional carbon allotrope is possible. A novel and stable zero-dimensional carbon allotrope (fullerenyne) with sp-sp(2) hybridization is introduced by means of density functional theory calculation and molecular dynamics confirmation. Unique porous characteristic C(96) fullernenyne with an O(h) symmetry group exhibits exceptionally high stability. We hope that the present study will lead to a further development of a broad new class of carbon materials.

Titanium carbide-derived carbon as a novel support for platinum catalysts in direct methanol fuel cell application

The improvement of direct methanol fuel cells (DMFCs) requires the development of highly active catalysts. Carbide-derived carbon (CDC) is a new class of carbon materials which are produced via selective extraction of the non-carbon compounds from metal carbides. Nanoporous carbon with a surface area of 906 m 2 g −1 and mean pore size of 3.4 nm was produced in consequence of chlorinating pure titanium carbide. This material was oxidatively treated to create the nucleation sites for the metal precursor. An increase of oxygen content in the carbon sample was observed after the functionalization step. The CDC material was subsequently loaded with 18.62 wt.% platinum, with an average particle size of 1.16 nm, by wet impregnation and chemical reduction. As a result, an enhanced electrochemical activity towards oxygen reduction was observed. The maximum power density of 50.16 mW cm −2 was achieved and is subsequently 18% higher than the value measured for commercial platinum catalyst (20 wt.% Pt) on activated carbon. This increase can be attributed to good catalyst dispersion, high surface area and small platinum cluster sizes, thus, confirming the potential of carbide-derived carbon supported catalysts for DMFC applications.

Polymeric fullerene hydrides. Birch reduction of [60] fullerene polymers from solution-based photopolymerization and free radical polymerization reactions

Fullerene polymers represent a new class of carbon materials for potential hydrogen storage applications. Poly[60]fullerene polymers were obtained by covalently linking [60]fullerene molecules in photochemical reactions. [60]Fullerene polymers were also prepared in free radical reactions of [60]fullerene with radical initiator benzoyl peroxide. The polymeric [60]fullerene materials were hydrogenated under Birch reduction conditions. The hydrides, which contain ≈3.5% (wt/wt) of hydrogen, were characterized by use of gel permeation chromatography, NMR, FT-IR, and elemental analysis. The results are compared with those of monomeric [60]fullerene hydrides.

Carbon Nanotubes

Carbon is an extraordinary element, considering the diversity of materials it forms. Ranging from sparkling gems to sooty filth, these materials have been studied and used for centuries, and carbon science was long thought to be a mature field. So when a whole new class of carbon materials—the fullerenes, such as C60—appeared in the last decade, many scientists were surprised. The consequences have reached well beyond the fullerenes themselves to include major changes in our concepts and understanding of long-known carbon materials. It is in this context that the story of carbon nanotubes starts.