Study On Preparation And Properties Of Catalysts For Direct Liquid Fuel Cells

Direct liquid fuel cell (DLFC), an energy conversion device using liquid (e.g.,methanol, ethanol, formic acid, etc.) as fuel, has received extensive attention and beenstudied widely due to many advantages such as high energy-conversion efficiency,easy storage and transportation of liquid fuel，low temperature operation, and simpleconstruction. Therefore, DLFC is a leading candidate for portable power in the future.But the high-cost and low performance of catalyst in the DLFC are the main problemsthat hamper its commercialization. In order to overcome the drawbacks, in this thesis,novel nitrogen-doped carbon and their composites materials were explored and wereapplied to the study of electro-catalytic oxygen reduction reaction (ORR) and formicacid oxidation.The main content of this thesis are presented as follows:(1) Using the copper nitrate as the source of metal and aniline as the source ofcarbon and nitrogen, the nitrogen-doped carbon support copper (Cu/N-C)nano-materials was prepared by pyrolysis at high temperature. The morphology and theelemental composition of Cu/N-C catalyst were characterized by scanning electronmicroscopy and energy dispersive spectroscopy, respectively. The electrocatalyticproperties of the Cu/N-C catalyst for ORR in acidic medium were investigated bycyclic voltammetry and linear sweep voltammetry on a rotating disk electrode. Theresults showed that the Cu/N-C catalyst had good activity for ORR. Compared to thecommercial E-TEK Pt/C catalyst, the Cu/N-C catalyst exhibited higher tolerance tocrossover of methanol and better stability.(2) The nitrogen-doped mesoporous carbon (N-MCs) was prepared by thecarbonization of ZIF-8nanoparticles (NPs) at high temperature. The the morphologyand structure of N-MCs were characterized by scanning electron microscopy andautomatic micropore and chemisorption analyzer. The results showed that the N-MCshad uniform morphology, high specific surface area (1960m2g-1) and narrow pore sizedistribution (centered at3.6nm). The electrocatalytic properties of the N-MCs catalystfor ORR in alkaline medium were investigated by cyclic voltammetry, linear sweepvoltammetry and chronoamperometry on a rotating disk electrode. Compared to thecommercial E-TEK Pt/C catalyst, the N-MCs catalyst exhibitsed better activity forORR, higher tolerance to crossover of methanol and better stability. Moreover, further kinetic studies showed that ORR on N-MCs catalyst mainly followed the four-electronprocess.(3) Pd/N-MCs composites catalyst was obtained by depositing Palladium (Pd) viaa sodium borohydride reduction method on N-MCs. The morphology and elementalcomposition of Pd/N-MCs catalyst were characterized by the transmission electronmicroscope and energy dispersive spectroscopy. The results showed that the Pd NPsare uniformly dispersed on the surface of the N-MCs. The electrocatalytic properties ofglassy carbon electrode modified by the Pd/N-MCs catalyst for formic acid oxidationwere investigated by cyclic voltammetry, linear sweep voltammetry andchronoamperometry. The results showed that the Pd/N-MCs catalyst had betterelectro-catalytic activity and stability for the oxidation of formic acid, compared toPd/C. In addition, linear sweep voltammetry studies showed that electro-catalyticoxidation of formic acid on Pd/N-MCs and Pd/C electrode both werediffusion-controlled processes, and the three dimensional porous structure ofPd/N-MCs was more benifit to the efficient diffusion and mass transfer. Comparing tothe the Pd/C. It indicated that the N-MCs was a potential candidate as a support for PdNPs in direct formic acid fuel cell.