Direct growth of carbon nanofibers to generate a 3D porous platform on a metal contact to enable an oxygen reduction reaction

Poly(1,5-diaminonaphthalene)-Grafted Monolithic 3D Hierarchical Carbon as Highly Capacitive and Stable Supercapacitor Electrodes

A holistic approach to fabricate a hierarchical electrode that consists of redox-active poly(1,5-diaminonaphthalene), 1,5 PDAN, uniformly and conformally grafted onto a 3D carbon nanotube (CNT-a-CC) electrode is set forth. The CNT-a-CC electrode was formed by direct growth of high-density CNTs on the surface of every individual microfiber, the constituent of activated carbon cloth (a-CC). Owing to the naphthalene backbone, conformal deposition of 1,5 PDAN on carbon surfaces has been readily attained via electropolymerization. This hierarchical platform with open and continuous nanochannels formed by CNTs coupled with excellent electrical connectivity between CNTs and the polymer provides a reproducible platform for electrochemical investigation. According to multiple sample analyses on CNT-a-CC, the gravimetric capacitance of 1,5 PDAN is up to 1250 F/g, and this value can be maintained up to 100 mV/s. Hierarchical organization provides a specific capacitance of 650 F/g at 2 mV/s at a 1,5 PDAN loading of 2.5 mg/cm². The conjugated ladder structure of the polymer led to strong π-π interactions between the polymer and CNT-a-CC together with mechanically robust CNT-a-CC. A capacitance retention of 94% for 1,5 PDAN has been obtained after 25,000 cycles at 100 mV/s, a significant cycle stability improvement over conventional conductive polymers such as polyaniline. This new lightweight electrode that seamlessly integrates functional species with nanochannel-like CNT-a-CC opens up a new opportunity to harness electrochemical reactions in the 3D carbon electrode for energy storage and electrocatalysis as well as electrochemical sensing.

Reproducibly creating hierarchical 3D carbon to study the effect of Si surface functionalization on the oxygen reduction reaction

We report a new method to reproducibly fabricate functional 3D carbon structures directly on a current collector, e.g. stainless steel. The 3D carbon platform is formed by direct growth of upright arrays of carbon nanofiber bundles on a roughened surface of stainless steel via the seed-assisted approach. Each bundle consists of about 30 individual carbon nanofibers with a diameter of 18 nm on average. We have found that this new platform offers adequate structural integrity. As a result, no reduction of the surface area during downstream chemical functionalization was observed. With a fixed and reproducible 3D structure, the effect of the chemistry of the grafted species on the oxygen reduction reaction has been systematically investigated. This investigation reveals for the first time that non-conductive Si with an appropriate electronic structure distorts the carbon electronic structure and consequently enhances ORR electrocatalysis. The strong interface provides excellent electron connectivity according to electrochemical analysis. This highly reproducible and stable 3D platform can serve as a stepping-stone for the investigation of the effect of carbon surface functionalization on electrochemical reactions in general.

Facile and sensitive electrochemical detection of methyl parathion based on a sensing platform constructed by the direct growth of carbon nanotubes on carbon paper

Facile and sensitive methyl parathion detection was achieved based on a novel carbon nanotube/carbon paper sensor.

Enhanced field emission from in situ synthesized 2D copper sulfide nanoflakes at low temperature by using a novel controllable solvothermal preferred edge growth route

A facile one-pot solvothermal route using the reaction of sputtered copper film and sulfur powder in ethanol solution at a low temperature of 90 °C for 12 hours has been implemented to in situ synthesize 2D hexagonal copper sulfide (CuS) nanoflakes. Their field electron emission (FE) characteristics were investigated and were found to have a close relationship with the copper film's thickness. The lowest turn on electric field (Eon) was 2.05 V μm(-1) and the largest field enhancement factor (β) was 7261 when the copper film's thickness was 160 nm. Furthermore, through a preferred edge growth route, patterned CuS nanoflakes were synthesized with the combined effect from a copper film seed layer and a passivation layer to further improve FE properties with an Eon of 1.65 V μm(-1) and a β of 8351. The mechanism of the patterned CuS nanoflake preferred edge growth is reported and discussed for the first time.

Nitrogen self-doped porous carbon from surplus sludge as metal-free electrocatalysts for oxygen reduction reactions

Nitrogen self-doped porous carbon was prepared by calcination treatment of surplus sludge, a toxic byproduct from microbial wastewater treatments, and exhibited a mesoporous structure, as manifested in scanning and transmission electron microscopic measurements. Nitrogen adsorption/desorption studies showed that the porous carbon featured a BET surface area as high as 310.8 m(2)/g and a rather broad range of pore size from 5 to 80 nm. X-ray photoelectron spectroscopic studies confirmed the incorporation of nitrogen into the graphitic matrix forming pyridinic and pyrrolic moieties. Interestingly, the obtained porous carbon exhibited apparent electrocatalytic activity in oxygen reduction in alkaline media, with the optimal temperatures identified within the range of 600 to 800 °C, where the number of electron transfers involved in oxygen reduction was estimated to be 3.5 to 3.7 and the performance was rather comparable to leading literature results as a consequence of deliberate engineering of the graphitic matrix by nitrogen doping.

Graphdiyne as a metal-free catalyst for low-temperature CO oxidation

We demonstrate by a DFT study that graphdiyne is a good, low-cost, and metal-free catalyst for low-temperature CO oxidation.

Highly efficient oxygen reduction electrocatalysts based on winged carbon nanotubes

Developing electrocatalysts with both high selectivity and efficiency for the oxygen reduction reaction (ORR) is critical for several applications including fuel cells and metal-air batteries. In this work we developed high performance electrocatalysts based on unique winged carbon nanotubes. We found that the outer-walls of a special type of carbon nanotubes/nanofibers, when selectively oxidized, unzipped and exfoliated, form graphene wings strongly attached to the inner tubes. After doping with nitrogen, the winged nanotubes exhibited outstanding activity toward catalyzing the ORR through the four-electron pathway with excellent stability and methanol/carbon monoxide tolerance. While the doped graphene wings with high active site density bring remarkable catalytic activity, the inner tubes remain intact and conductive to facilitate electron transport during electrocatalysis.