Hybrid Carbon Supports Composed of Small Reduced Graphene Oxide and Carbon Nanotubes for Durable Oxygen Reduction Catalysts in Proton Exchange Membrane Fuel Cells.

We demonstrated highly active and durable hybrid catalysts (HCs) composed of small reduced graphene oxide (srGO) and carbon nanotubes (CNTs) for use as oxygen reduction reaction (ORR) catalysts in proton exchange membrane fuel cells. Pt/srGO and Pt/CNTs were prepared by loading Pt nanoparticles onto srGO and CNTs using a polyol process, and HCs with different Pt/CNT and Pt/srGO ratios were prepared by mechanically mixing the two components. The prepared HCs consisted of Pt/CNTs well dispersed on Pt/srGO, with catalyst HC55, which was prepared using Pt/srGO and Pt/CNTs in a 5:5 ratio, exhibiting excellent oxygen reduction performance and high stability over 1000 cycles of the accelerated durability test (ADT). In particular, after 1000 cycles of the ADT, the normalized electrochemically active surface area of Pt/HC55 decreased by 11.9%, while those of Pt/srGO and Pt/C decreased by 21.2% and 57.6%, respectively. CNTs have strong corrosion resistance because there are fewer defect sites on the surface, and the addition of CNTs in rGO further improved the durability and the electrical conductivity of the catalyst. A detailed analysis of the structural and electrochemical properties of the synthesized catalysts suggested that the synergetic effects of the high specific surface area of srGO and the excellent electrical conductivity of CNTs were responsible for the enhanced efficiency and durability of the catalysts.

Polyol-Mediated Synthesis of V2O5-WO3/TiO2 Catalysts for Low-Temperature Selective Catalytic Reduction with Ammonia.

We demonstrated highly efficient selective catalytic reduction catalysts by adopting the polyol process, and the prepared catalysts exhibited a high nitrogen oxide (NOX) removal efficiency of 96% at 250 °C. The V2O5 and WO3 catalyst nanoparticles prepared using the polyol process were smaller (~10 nm) than those prepared using the impregnation method (~20 nm), and the small catalyst size enabled an increase in surface area and catalytic acid sites. The NOX removal efficiencies at temperatures between 200 and 250 °C were enhanced by approximately 30% compared to those of the catalysts prepared using the conventional impregnation method. The NH3-temperature-programmed desorption and H2-temperature-programmed reduction results confirmed that the polyol process produced more surface acid sites at low temperatures and enhanced the redox ability. The in situ Fourier-transform infrared spectra further elucidated the fast absorption of NH3 and its reduction with NO and O2 on the prepared catalyst surfaces. This study provides an effective approach to synthesizing efficient low-temperature SCR catalysts and may contribute to further studies related to other catalytic systems.

Small Reduced Graphene Oxides for Highly Efficient Oxygen Reduction Catalysts.

We demonstrated highly efficient oxygen reduction catalysts composed of uniform Pt nanoparticles on small, reduced graphene oxides (srGO). The reduced graphene oxide (rGO) size was controlled by applying ultrasonication, and the resultant srGO enabled the morphological control of the Pt nanoparticles. The prepared catalysts provided efficient surface reactions and exhibited large surface areas and high metal dispersions. The resulting Pt/srGO samples exhibited excellent oxygen reduction performance and high stability over 1000 cycles of accelerated durability tests, especially the sample treated with 2 h of sonication. Detailed investigations of the structural and electrochemical properties of the resulting catalysts suggested that both the chemical functionality and electrical conductivity of these samples greatly influence their enhanced oxygen reduction efficiency.