Performance Of Pt/C Doped With Ni, Co, Fe, Mo, W For Oxygen Electro-Redution In Alkaline Media

Driect methanol fuel cell (DMFC) is viewed as one of the most promisingmobile power sources due to the merits of methanol fuel such as the abundantsource, the inexpensive price, the low poison, the convenient transportation andstorage and the high energy efficiency. However, the present proton exchangemembrane direct methanol fuel cells (PEM-DMFC) are facing with the mainobstacles such as the electrooxidated inefficiency of methanol and methanolcross,over. Benefited from the alkaline media, the reaction activities of cathodeand anode are greatly improved. The reaction over potential is lower. Thedirection of electro-osmosis and methanol cross-over is opposite, and the rate ofmethanol cross-over is reduced. The cell power density and generatingefficiency may higher than that of PEM-DMFC. Therefore AEM-DMFC hasbeen paid more attention increasingly as a result of its advantages.Most study of cathodic electrocatalytic materials in alkaline media is focused on Pt/C and Ag/C catalysts. The activity and methanol-tolerance isinsufficient, the reaction over potential is higher, advantages of AEM-DMFC arenot displayed. Therefore it is important to develop the new electrocatalysts forcathode.The bonding d electron numbers of Ni, Co, Fe, Mo, W decrease in turn, thed electronic structure of nano-Pt and the Pt-Pt distance can be modified bydoped with these transition metal, and the activity and methanol-tolerance canbe modulated. In this work, carbon supported Pt-M(M=Ni,Co,Fe,Mo,W)catalysts were prepared by the colloidal method and characterized by XRD, EDS,XPS. Potentiodynamic was carried out to measure the performance of theoxygen electro-reduction on the electro-catalysts.The results indicate that Pt-based alloys appear circular shape and distributehomogeneously on the carbon, the particle size is homogeneous and about 2～4nm. The crystalline form is platinic face-centered cubic and most of crystalplane is Pt(111), the doped metal elements don't form simple substance and existas Pt-M alloy formation. The morphosis of Pt are Pt⁰ and Pt⁴⁺ and the morphosisof Ni are NiO and Ni₂O₃ on the surface of the Pt-Ni/C catalyst.The relation of catalytic activity of Pt-M/C and the doped metal amountsexhibits parabolic curve shape, i.e. "volcano" shape. With the increasing in thealkali concentration, the onset over potential for oxygen electro-reduction onPt-M/C and Pt/C increase, and the maximal reaction currents of the oxygenelectro-reduction decrease. In the same alkaline media, the order of the activities of Pt-based alloys isPt₅₀Mo₅₀/C＞Pt₅₀Fe₅₀/C＞Pt₅₀Ni₅₀/C＞Pt₅₀Co₅₀/C＞Pt/C＞Pt₅₀W₅₀/C, and the order ofthe methanol-toerlance is Pt₅₀Mo₅₀/C＞Pt₅₀Co₅₀/C＞Pt₅₀Fe₅₀/C＞Pt₅₀Ni₅₀/C＞Pt/C＞Pt₅₀W₅₀/C. With the addition, Mo can enhance the activities and methanol-tolerance of Pt/C for oxygen electro-reduction markedly. Fe,Co,Ni can improverelatively, but W element reduces the activities and methanol-tolerance of Pt/C.The prime reason of Mo, Fe, Co-promoted Pt/C is the departuring of bonding delectron of Pt; The doped Ni atoms add new activity centers on Pt/C catalyst.The maximal current of Pt₅₀Mo₅₀/C catalyst can reach 107 mA/mg and the onsetover potential for oxygen electro-reduction is less 200 mV than Pt/C in 0.1mol/L KOH solution, and the maximal current to be a Pt 1.35 times; Themaximal current of Pt₅₀Mo₅₀/C catalyst in 0.1 mol/L KOH+0.5 mol/L CH₃OHsolution decreases 3.7% and the oxygen electro-reduction onset potential shifts0.05 V negatively, when compared with the non-methanol situation. But themaximal current of Pt/C decreases 27% and the oxygen electro-reduction onsetpotential shifts 0.05 V negatively. The methanol-tolerance of Pt₅₀Mo₅₀/C issuperior. The effect of pH for activity of Pt₅₀Mo₅₀/C is weakly, The maximalcurrent of Pt₅₀Mo₅₀/C catalyst in 0.5 mol/L, 1.0 mol/L, 2.0 mol/L KOH solutiononly decreases 6%, 22% and 41% respectively, wich is far less than 16%, 39%and 62% of Pt/C, when compared with the 0.5 mol/L KOH solution situation.Pt₅₀Ni₅₀/C has the same high activity stability as Pt/C.