Geping Yin

Durability Study of Pt ∕ C and Pt ∕ CNTs Catalysts under Simulated PEM Fuel Cell Conditions

The durability of carbon black supported Pt (Pt/C) and multiwalled carbon nanotubes supported Pt (Pt/CNTs) catalysts for potential application in polymer electrolyte membrane fuel cells are investigated using an accelerated durability test. The electrochemical surface area of Pt/C degrades by 49.8% during the 192-h test time, compared with 26.1% for Pt/CNTs, which is due to Pt particle growth and Pt loss from the support in the form of Pt ions and Pt particles. Transmission electron microscopy and X-ray diffraction analysis show that Pt particles in Pt/CNTs present higher sintering resistance. X-ray photoelectron spectroscopy characterization indicates that CNTs in Pt/CNTs are more resistant to electrochemical oxidation than carbon black in Pt/C. It can be concluded that Pt/CNTs are more stable under electrochemical operation, which can be attributed to specific interaction between Pt and the support and the higher resistance of the support to electrochemical oxidation.

Carbonized Nanoscale Metal–Organic Frameworks as High Performance Electrocatalyst for Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is one of the key steps in clean and efficient energy conversion techniques such as in fuel cells and metal-air batteries; however, several disadvantages of current ORRs including the kinetically sluggish process and expensive catalysts hinder mass production of these devices. Herein, we develop carbonized nanoparticles, which are derived from monodisperse nanoscale metal organic frameworks (MIL-88B-NH3), as the high performance ORR catalysts. The onset potential and the half-wave potential for the ORR at these carbonized nanoparticles is up to 1.03 and 0.92 V (vs RHE) in 0.1 M KOH solution, respectively, which represents the best ORR activity of all the non-noble metal catalysts reported so far. Furthermore, when used as the cathode of the alkaline direct fuel cell, the power density obtained with the carbonized nanoparticles reaches 22.7 mW/cm2, 1.7 times higher than the commercial Pt/C catalysts.

Polyelectrolyte-Induced Reduction of Exfoliated Graphite Oxide: A Facile Route to Synthesis of Soluble Graphene Nanosheets

Here we report that poly(diallyldimethylammonium chloride) (PDDA) acts as both a reducing agent and a stabilizer to prepare soluble graphene nanosheets from graphite oxide. The results of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and Fourier transform infrared indicated that graphite oxide was successfully reduced to graphene nanosheets which exhibited single-layer structure and high dispersion in various solvents. The reaction mechanism for PDDA-induced reduction of exfoliated graphite oxide was proposed. Furthermore, PDDA facilitated the in situ growth of highly dispersed Pt nanoparticles on the surface of graphene nanosheets to form Pt/graphene nanocomposites, which exhibited excellent catalytic activity toward formic acid oxidation. This work presents a facile and environmentally friendly approach to the synthesis of graphene nanosheets and opens up a new possibility for preparing graphene and graphene-based nanomaterials for large-scale applications.

Electrostatic Self‐Assembly of a Pt‐around‐Au Nanocomposite with High Activity towards Formic Acid Oxidation

Pt-around-Au nanocomposite is synthesized using the electrostatic selfassembly method. This catalyst shows significantly improved activity towards formic acid oxidation. The possible reason is the efficient spillover of HCOO from Au to the surrounding Pt NPs, where HCOO is further oxidized to CO2.

Ultrahigh stable carbon riveted Pt/TiO2–C catalyst prepared by in situ carbonized glucose for proton exchange membrane fuel cell

Highly active Pt/TiO2–C catalyst has been synthesized by a microwave-assisted polyol process. The obtained Pt/TiO2–C sample was characterized by XRD, EDAX, HRTEM, XPS, and electrochemical measurements. The results show that the Pt/TiO2–C catalyst possesses substantially enhanced stability and identical activity in comparison with Pt/C prepared by the same procedure. Furthermore, carbon riveted Pt/TiO2–C composite with a novel structure based on in situ carbonization of the glucose was designed and synthesized. The results of TEM and electrochemical measurements indicate that the carbon riveted Pt/TiO2–C catalyst has much greater stability than Pt/TiO2–C and Pt/C with similar activity. The significantly enhanced stability for carbon riveted Pt/TiO2–C catalyst is ascribed to: (1) the excellent stability of anatase TiO2; (2) the strong metal-support interaction between Pt and TiO2; (3) the anchoring effect of the carbon layers formed during the carbon riveting process. These findings indicate that carbon riveted Pt/TiO2–C is a promising catalyst for proton exchange membrane fuel cells which are under long term operation.

A Novel Structural Design of a Pt/C-CeO2 Catalyst with Improved Performance for Methanol Electro-Oxidation by β-Cyclodextrin Carbonization

Although the direct methanol fuel cell (DMFC) is considered to be a promising power source for portable electronic devices and electric vehicles, [ 1–8 ] some obstacles, such as the low methanol electrooxidation kinetics from the poisoning of intermediates during the oxidation processes and methanol crossover from anode to cathode, still exist and impede its commercialization. [ 7 , 9–13 ] Aiming at the CO poisoning issues, the most widely accepted strategy is to develop Pt-based alloys such as Pt-Sn, [ 14–20 ] Pt-Ni, [ 21–23 ] or Pt/ metal oxide composite catalysts such as Pt-TiO 2 [ 24–26 ] based on the bifunctional mechanism and the electronic effect, [ 27–31 ] and the latter is also related to other factors including the size and shape of metal oxide nanocrystals, the surface areas, and the support effect. [ 32–35 ] Among various possible metal oxide supports, cerium oxides (CeO 2 ) are of particular interest due to higher oxygen storage capacity and much lower price, as well as the good mechanical resistance and anticorrosion ability in acidic media, which may signifi cantly promote methanol oxidation and reduce the catalyst preparation cost. Therefore, to explore the possibility of employing CeO 2 as a co-catalyst in methanol electro-oxidation is very necessary and meaningful. However, due to the low electron conductivity of CeO 2 at the cost of catalytic performance, it necessarily deserves the investigation of the structural design of catalysts to weaken the sideeffects resulting from the low electron conductivity and the lack of attachment of Pt and CeO 2 . Recently, many researchers have investigated the CeO 2 as a co-catalyst for methanol or other alcohol oxidation, [ 36,37 ] but very few papers have focused on the structural design of CeO 2 -based catalysts to enhance the electron conduction and synergistic effect. Xia [ 38 ] and co-workers synthesized the Pt/CeO 2 hybrid nanostructure catalyst in the aqueous phase through electrostatic attraction between negatively charged PtCl 4 2precursors and the positively charged surface of 6-aminohexanoic acid (AHA)-stabilized CeO 2 nanocrystals, and it exhibited a higher resistance to poisoning during the catalytic reduction of p -nitrophenol into p -aminophenol by

Carbon nanotubes decorated with Pt nanoparticles via electrostatic self-assembly: a highly active oxygen reduction electrocatalyst

Carbon nanotubes (CNTs) are noncovalently functionalized with poly(allylamine hydrochloride) (PAH) and then employed as the support of Pt nanoparticles. X-Ray photoelectron spectroscopy confirms the successful functionalization of CNTs with PAH. The negatively charged Pt precursors are adsorbed on positively charged PAH-wrapping CNTs surface via electrostatic self-assembly and then in situ reduced in ethylene glycol. X-Ray diffraction and transmission electron microscope images reveal that Pt nanoparticles with an average size of ∼2.6 nm are uniformly dispersed on CNT surface. Pt/PAH-CNTs exhibit unexpectedly high activity towards oxygen reduction reaction, which can be attributed to the large electrochemical surface area of Pt nanoparticles. It also shows enhanced electrochemical stability due to the structural integrity of PAH-CNTs. This provides a facile approach to synthesize CNTs-based nanoelectrocatalysts.

Recent progress in nanostructured electrocatalysts for PEM fuel cells

Polymer electrolyte membrane (PEM) fuel cells are attracting much attention as promising clean power sources and an alternative to conventional internal combustion engines, secondary batteries, and other power sources. Much effort from government laboratories, industry, and academia has been devoted to developing PEM fuel cells, and great advances have been achieved. Although prototype cars powered by fuel cells have been delivered, successful commercialization requires fuel cell electrocatalysts, which are crucial components at the heart of fuel cells, meet exacting performance targets. In this review, we present a brief overview of the recent progress in fuel cell electrocatalysts, which involves catalyst supports, Pt and Pt-based electrocatalysts, and non-Pt electrocatalysts.

Three dimensional N-doped graphene/PtRu nanoparticle hybrids as high performance anode for direct methanol fuel cells

A three-dimensional (3D) N-doped graphene aerogel with porous structures and uniformly distributed PtRu NPs (N-GA/PtRu) is constructed by a simple, rapid and eco-friendly method. The N-GA/PtRu exhibits an unprecedented performance towards the methanol electrochemical oxidation reaction. Notably, N-GA/PtRu can be directly used as the anode of direct methanol fuel cells by simple physical pressing without the need for any binders or additives.

Nanosized core/shell silicon@carbon anode material for lithium ion batteries with polyvinylidene fluoride as carbon source

A nanosized anode material for lithium ion batteries with silicon as core and amorphous carbon as shell was synthesized by dispersing nanosized silicon in polyvinylidene fluoride solution and a subsequent pyrolysis process. The amorphous nature of the carbon in the composite was detected by X-ray diffraction and Raman spectroscopy. The core/shell structure was further identified by transmission electron microscopy. High reversible capacity and acceptable rate capability were exhibited compared with pristine silicon. The reversible capacity of the silicon@carbon nanocomposite at 50 mA g−1 after 30 cycles is 1290 mAh g−1 with a capacity retention of 97%. A stable reversible capacity of 450 mAh g−1 was delivered even at 1000 mA g−1. These improvements are attributed to the amorphous carbon shell, which suppresses the agglomeration of nanosized silicon, reduces the cell impedance, buffers the volume changes and stabilizes the electrode structure during charge/discharge cycles.