Preparation Of Pd-based Nano-composites Supported By Carbon Nanotubes And Their Electrocatalysts

Fuel cell is a power generation device that is able to convert chemical energy into electrical energy directly, and it is a kind of efficient and environmental friendly power generation technology. Under the background of resources shortage, it has important significance to research. Direct alcohol fuel cell, using alcohols as fuels and oxygen as the oxidation agent, has fuel diversity such as easy to carry, easy to store and other advantages. Pt and Pt-based catalysts are restricted due to the high cost and easy to poisoning. The price of Pd is relatively cheap, and it has high electrocatalytic activity for the alcohol oxidation in alkaline media, therefore,developing new Pd catalyst becomes the research focus. The main work in this paper is involved in the preparation of PdSnNi and PdAg catalysts, characterization of catalyst crystal structure, surface morphology and particle size by a variety of methods, and the studies on the electroactivity of catalysts for ethanol, propanol and butanol alcohol(named as C2-C4 alcohol) oxidation and activity for oxygen reduction. A membrane-less direct alcohol fuel cell was assembled using PdSnNi/MWCNT as anode catalyst and its discharge performance was tested. The main content includes the following aspects:(1) Pd/MWCNT, PdSn/MWCNT, PdNi/MWCNT and PdSnNi/MWCNT catalysts supported on MWCNT were prepared by chemical reduction method using sodium borohydride as the reducing agent. The prepared catalysts were characterized by TEM and XRD, and the electroactivity and stability for C2-C4 alcohol oxidation were tested by cyclic voltammograms and chronamperometry in alkaline media.Results showed that the PdSnNi/MWCNT catalyst performed the best activity for the oxidation of all kinds of alcohols: the biggest oxidation current density of ethanol was 83.2 mA·cm-2, the biggest oxidation current density of 1-propanol was 142.5mA·cm-2, the biggest oxidation current density of 1-butanol was 76.2 mA·cm-2. The electroactivity for the oxidation 1-propanol and 1-butanol was better than that of their respective isomer.(2) The electro-activity of Pd/MWCNT, PdSn/MWCNT, PdNi/MWCNT and PdSnNi/MWCNT catalysts for oxygen reduction reaction(ORR) was tested by cyclic voltammograms and linear potential scanning. The results showed that both inalkaline and acidic media, PdNi/MWCNT exhibited the best electroactivity for ORR,and in alkaline media, the oneset potential of ORR on PdNi/MWCNT is 0.08 V. At the rotating speed of 2000 rpm, the limiting diffusion current density of ORR on PdNi/MWCNT is 3.51 mA·cm-2. The oneset potential of PdNi/MWCNT is 0.61 V in acidic media, and the limiting diffusion current density is 4.44 mA·cm-2 at the rotating speed of 2000 rpm. PdNi/MWCNT is a good catalyst for ORR, and is expected to become the cathode material of direct alcohol fuel cell.(3) Pd/MWCNT, Pd4Ag1/MWCNT, Pd2Ag1/MWCNT and Pd1Ag1/MWCNT catalysts were prepared by chemical reduction method using sodium borohydride as the reducing agent. The prepared catalysts were characterized by TEM and XRD,and the electroactivity and stability of the catalysts for C2-C4 alcohol oxidation were tested by cyclic voltammograms under different alcohol concentrations and repeated cycle scan times in alkaline respectively. The results showed that the Pd4Ag1/MWCNT catalyst performed the best activity for the oxidation of all kinds of alcohols examined in this work: The biggest oxidation current density of ethanol is102.7 mA·cm-2, the biggest oxidation current density of 1-propanol is 162.7 mA·cm-2,and the biggest oxidation current density of 1-butanol is 84.8 mA·cm-2,Pd4Ag1/MWCNT exhibited higher electroactivity for the oxidation 1-propanol and1-butanol than that of their respective isomers.(4) A membrane-less direct alcohol fuel cell was assembled using PdSnNi/MWCNT as anode catalyst and FeCo/C-PANI as cathode catalyst. The test showed that when ethanol, propanol, isopropanol, n-butyl alcohol, isobutyl alcohol and sec-butyl alcohol were used as fuels, the open circuit voltages were 0.68 V, 0.69 V, 0.61 V, 0.50 V, 0.51 V and 0.48 V respctively. When 1-propanol was used as the fuel, the corresponding power density is the largest, which is 0.51 W g(Pd)-1.