Investigation Of Hybrid Anode Catalysts For Alkaline Direct Alcohol Fuel Cells

Fuel cell is an electrochemical device that converts the chemical energy from the fuel and oxidant into electricity directly through an electrochemical reaction.It is a kind of green energy because of its high energy conversion efficiency,low noise and low pollution.Direct alcohol fuel cells(DAFCs)have been paid more and more attention due to its high energy density.But there are many problems about DAFCs,such as the cross-over effect of methanol molecular,low cost performance of electrode catalysts and so on.It is well known that Pt-based materials are the best eletrocatalysts for alcohol oxidation reactions.However,they are so expensive,and can be easily poisoned by carboneous intermediates(such as CO).So there are two main directions for the development of DAFCs anode catalysts.One of them is to enhance the CO tolerance of Pt-based materials.Another is to choose non-noble metals which possess good catalytic performance for alcohol oxidation.In this thesis,Pt-based ternary hybrid composites and Ni-based layered double hydroxides(LDHs)were prepared to catalyze methanol and ethanol oxidation reactions,respectively.Platinum/exfoliated Ni-Al layered double hydroxides(LDHs)/reduced graphene oxide(rGO)ternary composite(Pt/LDH/rGO)as a highly active electrocatalyst for efficient methanol oxidation reactions(MORs)was fabricated by a facile self-assembly method with controlling electrostatic interactions between precursors.The introduction of 2D atomic layers of Ni-Al LDH sheet is of vital importance for the removal of poisonous carbonaceous intermediates on Pt surface in the methanol oxidation process due to its outstanding performance in dissociative absorption of water molecules.Structural characterizations show that the active Pt particles with a size range of 3?5 nm are uniformly dispersed on the LDH 2D platelets and the rGO sheet acts as a conductive supporter for the Pt/LDH composites.An in-situ reactivation process for recovery of Pt activity is proposed in virtue of different working potential ranges between Ni-Al LDH and Pt in alkaline solution.Under periodic reactivation,the activity of Pt can be fully recovered without renewing the reaction solution.Electrochemical tests show that the as-prepared ternary composite exhibits better activity and durability towards MOR than the commercial Pt/C catalyst.Ni-Al LDH/FTO and Ni-Fe LDH/FTO were prepared by a potentiostatic electrodepositon method in the colloids of Ni-Al LDH and Ni-Fe LDH nanosheets,respectively.Structural characterizations show that when the deposition potential is-2 V(vs.Pt),a thin film of LDH nanosheets would spread over the surface of FTO.Electrochemical tests show that Ni-Al LDH/FTO has superior activity and durability to Ni-Al LDH nanosheets and Ni-Al LDH-CO3 2-for ethanol oxidation reaction(EOR)in alkaline environment.The good performance of Ni-Al LDH/FTO can be attributed to the enhancement of conductivity and dispersion of LDH platelets by FTO substrate.Based on the similar reasons,Ni-Fe LDH/FTO presents better activity and durability than Ni-Fe LDH nanosheets and Ni-Fe LDH-CO32-for oxygen evolution reaction(OER)in alkaline environment.