Porous MnO 2 as a non-noble metal oxygen reduction reaction (ORR) electrocatalyst was prepared by a simple sonochemical route. The as-prepared porous MnO 2 exhibited higher electrocatalytic activity , superior stability and better methanol tolerance than commercial Pt/C catalyst in alkaline media. Furthermore, the ORR proceeded via a nearly four-electron pathway. Cyclic voltammetry (CV) and rotating-disk electrode (RDE) measurements verified that the ORR enhancement was attributed to the porous structure and good dispersity, which facilitated sufficient transport of ions, electrons, O 2 and other reactants in the process of ORR. The results indicated that a facile and feasible sonochemical route could be used to prepare highly active porous MnO 2 electrocatalyst for ORR, which might be promising for direct methanol fuel cells.
A porous MnO 2 /CeO 2 composite catalyst was prepared via the template method for the catalytic decomposition of formaldehyde (HCHO). The physical and chemical properties of the catalysts were intensively characterized via X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller analysis, temperature programmed reduction system and X-ray photoelectron spectroscopy. The catalytic activity and stability for HCHO oxidation were measured via a fixed bed reactor, and the effects of physical and chemical properties of the catalysts on their catalytic performance were investigated. The results showed that the porous MnO 2 /CeO 2 catalyst had abundant 3D pore structures, a large specific surface area, an amorphous structure, and an abundance of lattice oxygen species. Thus, the MnO 2 /CeO 2 catalyst had high catalytic activity and stability for HCHO decomposition. This catalyst completely decomposed HCHO at 90 °C and maintained a 99% HCHO conversion rate over 72 h. The highly porous structure reduced the diffusion resistance in the reaction process and improved the efficiency of catalytic decomposition of HCHO. Doping with CeO 2 improved the low temperature oxidation activity and catalytic stability of the porous MnO 2 /CeO 2 catalyst. The porous MnO 2 /CeO 2 composite was an effective agent for the removal of harmful HCHO from the air.
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