| Direct Formic Acid Fuel Cells(DFAFCs)have attracted more and more attention due to their safety,high power density,and the ability to working with high concentrated formic acid.Platinum(Pt)-based electrocatalysts for anodic formic acid oxidation reaction(FAOR)play crucical roles in detreming the performance of DFAFCs.Therefore,it is highly desired to exploring effficeint Pt-based electrocatalysts for FAOR.Although plenty of works have been devoted to improving the activity and stability of Pt-based electrocatalysts,very few works have been conducted to regulating the the pathway of FAOR on Pt-based electrocatalysts.Realzing FAOR in dierct pathway can effectively improve the effciency of formic acid oxidation,as well as to boost the DFAFCs performance.Herein,we designed and prepared platinum-based electrocatalysts by regualting the atomic structure and metallic valence,aiming to realzie FAOR indirect pathway.(1)A triangle assembly of Pt single-atom structure was constructed by using C3N4 as template.The obtained Pt-C3N4@CNT electrocatalyst exhibits promising ctivity and the selectivity for FAOR.A total direct reaction pathway was realized for FAOR on Pt-C3N4@CNT electrocatalyst,with a high mass activity of 1910 A g-1Pt and a high specific activity of 7.9 A m-2 at a potential of 0.44 V.These values are 17.40 and 2.60 times higher than that of Pt nanoparticels loaded CNT mateiral(Pt@CNT,110 A g-1 Pt and 3.1 A m-2),respectively.CO stripping voltammetries show that the adsorption of CO on the surface of Pt-C3N4@CNT is geratly inhibited.A single fuel cell using Pt-C3N4@CNT as anode electrocatalyst delivers a high power density of 206.46 mW mg-1.Differential charge density diagrams show that,compared with Pt@CNT,Pt-C3N4@CNT has a lower electron density around Pt atoms,which is benificial for desorption of CO.DFT calculations show that Pt-C3N4@CNT is prone to following a direct dehydrogenation process,which is a thermodynamicall favorable pathway for FAOR.Mechanism studeis show that the superior selectivity of Pt-C3N4@CNT can be attributed to synergistic effect between the adjacent Pt atoms in the triangle assembly structure,which is beneficial to the direct oxidation of HCOOH to CO2.Also,the downshift of d-band center of the Pt in Pt-C3N4@CNT contributes to the desorption of CO.(2)Pt-PtO/C electrocatalysts with different ratio of oxidation states Pt/metallic Pt were successfully prepared by adjusting the reduction time.An optimized PtOx/C-5 electrocatalyst with a reduction time of 5 mins exihibits highest activity and selectivity for FAOR,with a high mass activity of 83.21 A g-1Pt at a potential and a high specific activity of 0.84 A m-2 at 0.48 V.CO stripping voltammetries show that the CO is easily oxidized at PtOχ,while the metallic Pt is prone to be poinsed by CO.The Pt-PtO/C electrocatalysts has a strong anti-poisoning ability against CO,thus effectively regualting the pathway of FAOR.The direct pathway for FAOR can be realized by adjusting the valence state of Pt in Pt-based catalysts.In summary,we have designed and prepared Pt-C3N4@CNT and Pt-PtO/C as high performance FAOR electro catalysts for DFAFCs.Atomic structure and averge valence of Pt can effectively change the pathway of FAOR.Experimental results and theoretical calculations offer deep understanding of the mechanism of FAOR at Pt-based electrocatalysts for the development of high performance DFAFCs. |
