One-dimensional Low-Pt Nanostructured Electrocatalysts For Fuel Cell Devices

Fuel cells,especially for proton exchange membrane fuel cells,have been widely regarded as one of the most promising clean energy conversion devices.In fuel cell devices?FCs?,chemical energy from unlimited source can be converted into electric energy in high-efficiency and environment-friendly ways.Based on their outstanding advantages of convenience,high safety,and quick-start,fuel cells have been expected to come into widespread use in the areas of industry,commerce and transportation.It is well-known that both the anode and the cathode electrodes in FCs consist of Pt-based catalysts to promote the reaction rates.But platinum?Pt?is a scarce and expensive metal on earth and the stability of Pt-based catalysts has yet to be further improved,which hinder the large-scale commercial production of Pt catalysts.Therefore,designing a new type of Pt-based catalysts with high catalytic activities,low-Pt consumption and long service life has been regarded as an important research direction in FCs development.Through years of practice and research,we found that the fabrications of ultrasmall size Pt-based alloyed nanostructures,ultrasmall size Pt-based core-shell nanostructures and ultrasmall size Pt-based hollow nanostructures not only matched the development trends of low Pt loading and high Pt surface atoms utilization,but also held the superiorities of metal-doped and electronic effect for further improving catalytic activities and stabilities.With the help of amyloid fibrils,the following works were achieved,?1?the fabrications of various subnanometer PtM alloyed nanowires?NWs?,involving PtFe,PtNi,PtCo,PtRh,PtIr and PtRu NWs,with more than 10⁴ aspect ratios,?2?the fabrications of Pt-based core-shell NWs including Pd@Pt NWs and Pd@Au@Pt NWs and?3?the fabrication of superlong Pt nanotubes?NTs?with only 1 nm wall-thickness.Moreover,the synthetic mechanism of the above Pt-based nanostructures were investigated and their catalytic activities and stabilities were also tested in FCs applications.Those ultrasmall size Pt-based catalysts delivered excellent electrocatalytic performance for oxygen reduction reaction?ORR?or for methanol oxidation reaction?MOR?together with brilliant stabilities during the durability tests,which exhibited obvious advantages in both morphology and catalytic performance among all recent reports.The main contents and results of my experiments are as following:?1?we reported a general biochemic strategy to assemble varied subnanometer PtM?M=Fe,Co,Ni,Rh,Ir,Ru?alloyed NWs with more than 10⁴ aspect ratios.Our PtM NWs delivered ultrahigh electrochemical active surface areas?ECSA?,brilliant activities and outstanding durabilities for MOR.In particular,PtRh NWs exhibited a highest mass activity for MOR with 1.96 A/mg_Pt,which was greater than the recent reported typical value,1.5A/mg_Pt?Bu,Science 2016?,and 9-fold higher than that of commercial Pt/C.The mechanism of methanol dehydrogenation reaction on PtM alloys was demonstrated by density functional theory calculations and followed the order of PtRh>PtRu>PtIr>PtFe>PtCo>PtNi.This sequence was consistent with the experimental results.With regard to stabilities,there was a large activity loss of 47%after 1000 potential cycles in MOR for commercial Pt/C catalyst,and nearly exhausted before 2000 cycles.In a vast contrast,the whole kinds of PtM NWs maintained more than 90%current density after2000 potential cycles in durability tests.Therefore,the above one-dimensional?1D?ultrathin superlong PtM alloyed NWs had obvious advantages in terms of morphology,size,as well as their catalytic activity and stability for MOR.?2?Based on hydrothermal process,single-crystalline Pd NWs with ultrathin diameter of 4.8 nm were fabricated via insulin templates method.Then,we deposited 2 Au atomic layers on the surface of the prepared Pd NWs to fabricate intermediate Pd@Au NWs via mild galvanic reactions,then with the help of ascorbic acid reductant,subnanometer-thick Pt shells successfully wrapped around the Pd@Au NWs that resulted in the end-products of Pd@Au@Pt NWs.This sophisticated trinary catalysts with ultra-low Pt content delivered a prominent mass activity of 1.7 A/mg_Pt?@0.9V vs.RHE?for ORR,which was higher than the mass activity of 0.90 A/mg_Ptt observed for binary Pd@Pt NWs,and approximately 11 times higher than that of 0.16 A/mg_Ptt for traditional commercial Pt/C catalysts.In durability tests,there was a large loss of commercial Pt/C?51%?after 30,000 sweeping cycles,and nearly exhausted before 80,000 cycles.Particularly,even after 80,000 potential cycles in durability tests,Pd@Au@Pt NWs catalysts exhibited nearly no changes in both morphology and activity.Considering its superior FCs performance,specially with unprecedented stability,the Pd@Au@Pt NWs electrocatalysts appeared to be a promising candidate to facilitate the development of Pt-based catalysts in FCs.?3?As a consequence of the etching technique,numerous ultrathin Pt NTs with wall thickness of 1 nm,diameter of 5.5 nm and several micrometers length were successfully evolved from Pd@Pt NWs.This tubular catalysts with both open ends delivered ultrathigh ECSA of 91.43 m²/g_ptt which resulted from multiple Pt atoms exposed on the inner and outer surfaces that doubled Pt atoms could participate in catalytic reactions.Furthermore,the Pt NTs exhibited a mass activity of 2.09 A/mg_ptt at 0.9 V RHE for ORR,which is 2.3and 13.1 times higher than that of Pd@Pt NWs(0.91 A/mg_pt)and commercial Pt/C(0.16A/mg_pt),respectively.With regard to commercial Pt/C catalysts in durability tests for ORR,there was a loss of 22%after 10,000 sweeping cycles,and nearly loss 51%after 30,000sweeping cycles.In contrast,there were less degradation in ORR after 30,000 sweeping cycles for Pd@Pt NWs and Pt NTs that all maintained more than 70%of their initial mass activities.Not only because of the Pt materials-saving and increasing specific area,but also owing to the ideal tubular structures with both open ends,the Pt NTs exhibited the outstanding electrocatalytic performance for ORR that achieved a promoting catalysts in FCs.