Design And Performance Study Of Graphene-based Catalysts For Direct Methanol Fuel Cells

Direct methanol fuel cell(DMFC)has attracted increasing attention as the ideal renewable energy conversion device.However,it still suffers from two major limitations:the heavy use of precious metal platinum and the sluggish kinetics of methanol oxidation catalytic reaction(MOR),which have prevented its large-scale commercialization.Therefore,it is essential to design and develop effective methanol oxidation catalysts.In this dissertation,we have designed and prepared a variety of catalysts with different compositions and morphologies using graphene carbon materials as supports to enhance the electrochemical performance.The rational construction of the catalysts reduces the content of noble metals,achieves the improvement of catalytic activity and stability,and also strengthens their resistance to CO poisoning.Additionally,the combination of experiments and theoretical calculations reveals the electrocatalytic mechanism of methanol oxidation.The main studies are as follows:1.In this work,multi-dimensional ternary composite electrocatalysts of Pt/Ni(OH)2/NG have been synthesized with 0D Pt nanoparticles on the 2D Ni(OH)2 nanosheets supported by 3D porous nitrogen-doped graphene hydrogel,and with a low amount(4.26 wt%)of Pt.Notably,the multi-dimensional porous structure design,abundant hydroxyl species and mutual interactions of ternary catalysts endowed the excellent electrocatalytic performance.The novel Pt/Ni(OH)2/NG catalysts exhibited the superior mass activity of 2.99 A mg-1Pt for MOR,which was about 2.8 and 4.8 times higher than that of commercial PtRu/C and Pt/C,respectively.Furthermore,both the long-term durability and stability of Pt/Ni(OH)2/NG electrocatalysts were significantly improved.2.We presented a new co-catalysis structure tuning strategy of doping PtM(M=Cu,Co,Fe)alloys and transition metal hydroxides onto nitrogen-doped graphene to construct PtM/Ni(OH)2/NGO ternary hybrid electrocatalysts.The hierarchical structural engineering and optimized chemical components contributed to the efficient methanol oxidation performance.The unique dendritic PtM alloys regulated the electronic structure of Pt and accelerated the electron transfer in the catalytic reaction.Moreover,the PtM alloy and Ni(OH)2 synergistically catalyzed the methanol oxidation,which highly promoted the anti-CO poisoning ability by removal of carbonaceous intermediates on Pt active sites,and also showed the superior mass and specific activity in alkaline media.3.The porous graphene with morphology-controlled TiO2 supported Pt nanoparticles(UV-Pt@TiO2/graphene)as efficient catalysts for methanol oxidation reaction were investigated via situ UV-photo-assisted reduction strategy.Both experimental results and DFT theoretical calculations showed that the TiO2 nanorods(TONR)with the optimal(001)and(110)facets effectively strengthened the Pt trapping ability,enhanced the adsorption of methanol molecules,and weakened CO intermediates poisoning compared to TiO2 nanocrystals(TONC).Importantly,in both acid and alkaline electrolytes,the UV-Pt@TONR/GN catalysts exhibited superior catalytic activity(1945.63 mA mg-1Pt/3165 mA mg-1Pt)and long-term durability for MOR.The outstanding catalytic properties were intrinsically attributed to well-hierarchical structure and strong metal-support interactions,which facilitated the tuning of surface properties and electronic structures,promoted charge transfer and synergistically boosted methanol electrooxidation.This work indicates the importance of catalyst morphology/facet tuning for catalytic performance enhancement and provided a feasible idea for DMFC catalyst design and construction.4.The non-precious metal catalysts of the well-defined Ni/NiO heterostructures supported by graphene(Ni/NiO/RG)were designed via a delicate interface engineering technique,especially the modulation of metal/metal oxide interface could improve the methanol oxidation reaction kinetics and broaden the previous studies.The successful construction of the Ni/NiO interface contributed to abundant accessible active sites,attenuated CO poisoning effect and enhanced methanol oxidation kinetics.Thus,the catalyst exhibited excellent catalytic activity and stability for MOR in an alkaline solution,outperforming most of the reported non-precious metal catalysts.Meanwhile,the change of free energy during the MOR was investigated by DFT calculations,further demonstrating the promotion of the Ni/NiO interface to the catalytic kinetics of methanol oxidation.5.Combined with the modulation of nanomaterial structure and components,the hierarchical PBA-derived sulfide heterostructures supported by N-doped graphene(FeNi2S4/NiS-NG)as efficient catalysts have been developed for the methanol oxidation reaction.Benefiting from the merits of hollow nanoframes structure and heterogeneous sulfide synergy,FeNi2S4/NiS-NG composite not only possessed abundant active sites to boost the catalytic properties,but also alleviated the CO poisoning effect during the process exhibiting favorable kinetic behavior toward MOR.Additionally,the catalyst showed competitive electrocatalytic stability,with a current density of over 90%after 2000 consecutive CV cycles.This study offers promising insights into the rational modulation of the morphology and components of precious metal-free catalysts.