Nanoporous Graphitic-C3N4@Carbon Metal-Free Electrocatalysts for Highly Efficient Oxygen Reduction

Based on theoretical prediction, a g-C3N4@carbon metal-free oxygen reduction reaction (ORR) electrocatalyst was designed and synthesized by uniform incorporation of g-C3N4 into a mesoporous carbon to enhance the electron transfer efficiency of g-C3N4. The resulting g-C3N4@carbon composite exhibited competitive catalytic activity (11.3 mA cm–2 kinetic-limiting current density at −0.6 V) and superior methanol tolerance compared to a commercial Pt/C catalyst. Furthermore, it demonstrated significantly higher catalytic efficiency (nearly 100% of four-electron ORR process selectivity) than a Pt/C catalyst. The proposed synthesis route is facile and low-cost, providing a feasible method for the development of highly efficient electrocatalysts.

Direct electrochemical formation of alloyed AuPt nanostructured electrocatalysts for the oxidation of formic acid

The formation of highly anisotropic AuPt alloys has been achieved via a simple electrochemical approach without the need for organic surfactants to direct the growth process. The surface and bulk properties of these materials were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and electrochemically by cyclic voltammetry to confirm alloy formation. It was found that AuPt materials are highly active for both the model hydrogen evolution reaction and the fuel cell relevant formic acid oxidation reaction. In particular for the latter case the preferred dehydrogenation pathway was observed at AuPt compared to nanostructured Pt prepared under identical electrochemical conditions which demonstrated the less preferred dehydration pathway. The enhanced performance is attributed to both the ensemble effect which facilitates CO(ads) removal from the surface as well as the highly anisotropic nanostructure of AuPt.

Perpendicularly oriented MoSe2/graphene nanosheets as advanced electrocatalysts for hydrogen evolution

By increasing the density of exposed active edges, the perpendicularly oriented structure of MoSe2 nanosheets facilitates ion/electrolyte transport at the electrode interface and minimizes the restacking of nanosheets, while the graphene improves the electrical contact between the catalyst and the electrode. This makes the MoSe2/graphene hybrid perfect as a catalyst in the hydrogen evolution reaction (HER). It shows a greatly improved catalytic activity compared with bare MoSe2 nanosheets.

Graphene-oxide-supported ultrathin Au nanowires: efficient electrocatalysts for borohydride oxidation

We report stable ultrathin Au nanowires supported on reduced graphene oxide with outstanding electrocatalytic activity for borohydride oxidation. Electrochemical impedance spectroscopy measurements showed abnormal inductive behavior, indicative of surface reactivation. DFT calculations indicate that the origin of the high activity stems from the position of the Au d-band center.

A noble and single source precursor for the synthesis of metal-rich sulphides embedded in an N-doped carbon framework for highly active OER electrocatalysts

Here, we demonstrate a green and environment-friendly pyrolysis route for the synthesis of metal-rich sulphide embedded in an N-doped carbon (NC) framework in the absence of sulphide ions (S2-). The metal-chelate complex (tris(ethylenediamine) metal(II) sulfate) serves as a new and single source precursor for the synthesis of earth abundant and non-precious hybrid structures such as metal-rich sulphides Co9S8@NC and Ni3S2@ NC when M-II = Co2+ and Ni2+ and counter sulphate (SO42-) ions are the source of S. Both the hybrids show superior OER activity as compared to commercial RuO2.

Effects of treatment in different atmosphere on Pt3Sn/C electrocatalysts for ethanol electro-oxidation

Pt3Sn/C catalyst was prepared by a modified polyol process and treated in air, H-2/Ar, and Ar atmosphere, respectively. XRD analyses indicate that all of these catalysts have face-centered cubic (fcc) crystal structure. Temperature-programmed reduction (TPR) experiments show that more Sn exists in zero-valence in the Ar-treated PtSn catalyst than in the others. Cyclic voltammetry (CV), chronoamperometry (CA) experiments, and the performance tests of direct ethanol fuel cell (DEFC) indicate that the catalytic activity of PtSn/C for ethanol oxidation was affected significantly by the chemical state of Sn in catalyst particles. The as-prepared PtSn/C gives the higher power density, while Ar-treated PtSn/C shows the lower cell performance. It seems that the multivalence Sn rather than the zero-valence Sn in the PtSn catalyst is the favorable form for ethanol oxidation. Energy dispersion X-ray analysis (EDX) of the PtSn/C-as prepared and PtSn/C (after stability test) shows the active species (platinum, tin, and oxygen) composition changed to a different extent. Further attempt to improve the catalyst stability is needed.

Preparation and characterization of PtSn/C anode electrocatalysts for direct ethanol fuel cell

Highly active PtSn/C catalyst was prepared by a polyol method. The catalyst was reduced in H-2/Ar atmosphere at 600 degreesC for 2 h in order to obtain different metallic phase. TEM images show uniform dispersion of spherical metal nanoparticles with average diameters of 1.8 and 3.9 nm for the as-prepared and treated catalysts, respectively. UV-vis spectrophotometry is employed to monitor the preparation process and the results indicate that Pt-Sn complex formed once the precursors of Pt and Sn were mixed together. The structure properties of the samples were characterized using X-ray diffraction. The results show that after reduction, the catalyst tends to form PtSn alloy. TPR experiment results show that Sn exists in multivalent state in the as-prepared sample while only zero-valence Sn was detected in the treated sample, while it could not be excluded that the multivalent tin existed in the treated sample. Cyclic voltammetry (CV) technique and single direct ethanol fuel cell (DEFC) tests indicate that the as-prepared catalyst possesses superior catalytic activity for ethanol oxidation to the treated sample. The results suggest that Pt and multivalent Sn are the active species for ethanol oxidation. (C) 2004 Elsevier B.V. All rights reserved.

Preparation of highly active Pt/C cathode electrocatalysts for DMFCs by an improved aqueous impregnation method

An improved aqueous impregnation method was used to prepare 40 wt% Pt/C electrocatalysts. TEM analysis of the samples showed that the Pt particles impregnated for a short time have a very narrow size distribution in the range of 1-4 nm with an average size of 2.6 nm. UV-vis spectroscopy measurements verified that the redox reaction between PtCl62- and formaldehyde took place with a slow rate at ambient temperature via a two-step reaction path, where PtCl42- serves as an intermediate. The use of the short-time-impregnated 40 wt% Pt/C as cathode electrocatalysts in direct methanol fuel cells yields better performance than that of commercial 40 wt% Pt/C electrocatalyst. Experimental evidence provides clues for the fundamental understanding of elementary steps of the redox reactions, which helps in guiding the design and preparation of highly dispersed Pt catalyst for fuel cells.

Green synthesis of highly stable platinum nanoparticles stabilized by amino-terminated ionic liquid and its electrocatalysts for dioxygen reduction and methanol oxidation

Preparation of monodispersed platinum nanoparticles with average size 2.0 nm stabilized by amino-terminated ionic liquid was demonstrated. The resulting platinum nanoparticles (Pt-IL) retained long-term stability without special protection. The Pt-IL nanoparticles exhibited high electrocatalytic activity toward reduction of oxygen and oxidation of methanol. Rotating disk electrode voltammetry and rotating ring-disk electrode voltammetry confirmed that the Pt-IL films could catalyze an almost four-electron reduction of dioxygen to water.

Gold/platinum hybrid nanoparticles supported on multiwalled carbon nanotube/silica coaxial nanocables: Preparation and application as electrocatalysts for oxygen reduction

A simple approach combining sonication and sol-gel chemistry was employed to synthesize silica coated carbon nanotube (CNTs) coaxial nanocables. It was found that a homogeneous silica layer can be coated on the surface of the CNTs. This method is simple, rapid, and reproducible. Furthermore, gold nanoparticle supported coaxial nanocables were facilely obtained using amino-functionalized silica as the interlinker. Furthermore, to reduce the cost of Pt in fuel cells, designing a Pt shell on the surface of a noble metal such as gold or silver is necessary. High-density gold/platinum hybrid nanoparticles were located on the surface of I-D coaxial nanocables with high surface-to-volume ratios. It was found that this hybrid nanomaterial exhibits a high electrocatalytic activity for enhancing oxygen reduction (low overpotential associated with the oxygen reduction reaction and almost four-electron electroreduction of dioxygen to water).

Alternate assemblies of polyelectrolyte functionalized carbon nanotubes and platinum nanoparticles as tunable electrocatalysts for dioxygen reduction

A novel method based on electrostatic layer-by-layer self-assembly (LBL) technique for alternate assemblies of polyelectrolyte functionalized multi-walled carbon nanotubes (MWNTs) and platinum nanoparticles (PtNPs) is proposed. The shortened MWNTs can be functionalized with positively charged poly(diallyldimethylammonium chloride) (PDDA) based on electrostatic interaction. Through electrostatic layer-by-layer assembly, the positively charged PDDA functionalized MWNTs (PDWNTs) and negatively charged citrate-stabilized PtNPs were alternately assembled on a 3-mercaptopropanesulfonic sodium (NIPS) modified gold electrode and also on other negatively charged surface, e.g. quartz slide and indium-tin-oxide (ITO) plate, directly forming the three-dimensional (3D) nanostructured materials. This is a very general and powerful technique for the assembling three-dimensional nanostructured materials containing carbon nanotubes (CNTs) and nanoparticles. Thus prepared multilayer films were characterized by ultraviolet-visiblenear-infrared spectroscopy (UV-vis-NIR), scanning electron microscopy (SEM) and cyclic voltammetry (CV). Regular growth of the mutilayer films is monitored by UV-vis-NIR.

Electrochemical chlorine sensor with multi-walled carbon nanotubes as electrocatalysts

It has been reported for the first time that an electrochemical gas sensor mdified with multi-walled carbon nanotubes (MWNTs) film as elctrocatalyst was fabricated for the determination of chlorine (Cl-2).Here, MWNTs and graphite were compared with each other in terms of their electrochemical properties using cyclic voltammetry. Cl-2 gas was allowed through the cathode surface of the sensor and the resulting galvanic effects were monitored. Results indicated that both of the MWNTs and graphite have the electrocatalytic activity for the reduction of Cl-2 while the MWNTs-modified electrode exhibited a higher accessible surface area in electrochemical reactions, excellent sensitivity, stable response, reproducibility and recovery for the determination of Cl-2.