| Direct formic acid fuel cell (DFAFC) is an important new energy technology, withthe advantages of high energy convertion efficiency, minmal pollution emission and hugecommercial potentials. Platinum alloys have been becoming one of focus in the anodecatalytic materials for DFAFC due to their high catalytic activity, and the catalyticmechanism of formic acid is always a research hotspot in DFAFC field. In this paper, ourresearch was performed closely around the key issues in DFAFC. Both the microstructurecharacteristics of surfaces for the carbon-supported anode catalytic materials (Pt(111)/C,Pt-Sn(111)/C, Pt-Mn(111)/C and Pt-Sn-Mn(111)/C), and the mechanism of adsorption anddissociation of those specieses (formic acid, CO and H2O) on the surfaces were analyzedusing first-principle theory based on density functional theory (DFT). From the theoreticallevel? the electrocatalytic mechanism of formic acid on the surface of platinum alloymaterials, the mechanism of anti-poisoning towards CO and the improvement mechanismof catalytic materials in the case of different dopings were disscussed. The optimizedperformance of those materials was explored using first-principle method, which canpresent theoretical basis and support for anode catalytic materials in DFAFC. The mainresearch contents and results are presented as follows?In this paper, the adsorption model of HCOOH, H2O and CO at four types of site onPt(111)/C surface was investigated using DFT and self-consistent periodic calculation. Theadsorption energy, frequency, electric charge and density of states before and afteradsorption on Pt(111)/C surface were also studied. The results show that the adsorption ofPt(111)/C towards formic acid is weak. The site with maximum adsorption energy isfcc-Pt3site with the value of46.5kJ·mol1. The maximum adsorption energy of CO is155.9kJ·mol1, which indicates that the catalytic materials with pure platinum has weakeranti-poisoning ability towards CO and easily results in the degradation of electrodeelectrocatalytic activity.The microstructure of material Pt-Sn(111)/C and the catalytic mechanism of formicacid on Pt-Sn(111)/C surface were studied using GGA-PW91algorithm. The results showthat the adsorption energies of formic acid at the eight types of site increase obviously.Fcc-Pt3is the optimal adsorption site with the value of86.8kJ·mol1. After Sn doped,Fermi level shifts to right, the conduction band broadens, and the valence band andconduction band lower slightly. The adsorption energy of CO on Pt-Sn(111)/C decreasesthrough two ways. The adsorption energy of site with direct participation of Sn decreasesobviously, while the value is only equal to a half of that before doping. Those reultssuggests that the mechanism of anti-poisoning towards CO with the PtSn systemprimaryly relates to the mechanism of the adsorption energies towards CO as directlyweakened. In this paper, the microstructure of Pt-Mn(111)/C and the catalytic mechanism offormic acid on Pt-Mn(111)/C surface were studied using GGA-PW91algorithm. Theresults show that the adsorption energies of formic acid at eight sites increase obviously.Bridge-PtMn and hcp-Pt2Mn are the optimal adsorption sites, their values are119.9and117.2kJ·mol1, respectively. It suggests that the adsorption energy of formic acid onPt-Mn(111)/C surface increases through two ways. It is also found that the adsorptionenergy of site with direct participation of Mn increases obviously, and the value is threetimes than that before doping. The distance between d-band centre and Fermi levelshortens, and the delocalization of valence band and conduction band strengthens after Mndoped. But the adsorption energy of CO decreases slightly, which is obviously differentfrom the adsorption system of Pt-Sn(111)/C. In the doped system with Mn, the adsorptionenergy of H2O increases obviously and produces OH(ads)easily. After Mn doped, theanti-poisoning ability towards CO is improved. So, it is speculated that the process is thebifunctional mechanism.The microstructure of Pt-Sn-Mn(111)/C and the catalytic mechanism of formic acidon Pt-Sn-Mn(111)/C surface were simulated by GGA-PW91algorithm. The reults showthat the adsorption energies of formic acid at five sites increase obviously. Hcp-PtSnMn,fcc-PtSnMn and top-Mn are the optimal adsorption sites, and their values are118.2,115.3and112.1kJ·mol1, respectively. It indicates that the adsorption energy of site with directparticipation of Mn increases obviously. After Mn and Sn doped, the distance betweend-band centre and Fermi level shortens. Compared with Pt-Mn(111)/C surface, thePt-Sn-Mn(111)/C surface shows more d-band centre change. It suggests that theadsorption energies of CO at five sites on Pt-Sn-Mn(111)/C surface decreases through twoways. The adsorption energies at the sites with Sn decrease more obviously while anothergroup decreases less obviously. According to those results, it is believed that both theweakened mechanism of the adsorption energies of CO at the sites with Sn and thebifunctional mechanism at the sites with Mn exist on Pt-Sn-Mn(111)/C surface.In this paper, the anode material Pt-M/C(M=Sn, Mn) of DFAFC was studied bytheoretical research method. The improvement characteristics and mechanism of elementslike Sn and Mn were presented, and the materials was successfully modified by DFTcalculation. And it can provide a theoretical reference for the design and development ofthe anode catalyst materials in DFAFC. |
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