Preparation And Performance Study Of MXene-based Non-noble Metal Catalyst

Fuel cells have shown great prospects because of their high conversion efficiency and low carbon emissions with the urgent demand for clean energy in the world.Compared with proton exchange membrane fuel cells,alkaline anion exchange membrane fuel cells have faster reaction kinetics that provide the possibility to use low-cost non-precious metal catalysts.At present,non-precious metal catalysts mainly include M-N-C catalysts and heteroatom-doped carbon materials.M-N-C catalysts are expected to instead of Pt/C catalysts but keeping the high catalytic activity.However,the preparation process of high temperature treatment inevitably leads to the physical accumulation of active particles of M-N-C catalysts and affects the catalytic performance of the catalysts.MXene,as a new type of 2D nanomaterial,could be used as support for non-precious metal catalysts due to its good electrical conductivity,excellent corrosion resistance and large specific surface area.Its unique physicochemical properties could also improve the catalytic activity and stability of catalysts.In this paper,three M-N-C@MXene materials were prepared as high-performance non-precious metal oxygen reduction catalysts based on zeolites imidazole framework（ZIF）by in situ growth and high-temperature pyrolysis.In this paper,we prepared single layer Ti₃C₂T_x-MXene by HCl and LiF.Co/Zn-N-C@Ti₃C₂T_x catalyst was prepared by in situ growth of ZIF-67/ZIF-8 and pyrolysis at high temperature.Co/Zn-N-C derived from ZIF-67/ZIF-8 provides abundant active sites such as Co-N and Zn-N and effectively avoids the re-stacking of MXene nanosheets.The half-wave potential and limiting diffusion current density of Co/Zn-N-C@Ti₃C₂T_x catalyst at 1600rpm were 0.847V and 6.13m A cm^-2,respectively.After 30000s chronoamperometry test,the current of Co/Zn-N-C@Ti₃C₂T_x catalyst was 95.17%of the initial value,which was significantly higher than the 79.79%of Pt/C catalysts.At the same time,it has excellent methanol resistance.The peak power density of fuel cell reaches 51.4 m W cm^-2 based on Co/Zn-N-C@Ti₃C₂T_x catalyst at 60℃.Few layers of Mo₂TiC₂-MXene were prepared by HF and Fe element was doped in the synthesis process of ZIF-8.Fe-NC@Mo₂TiC₂ composite catalyst was prepared by heat treatment at 900℃in argon atmosphere.The phase characterization showed that Fe-NC@Mo₂TiC₂ not only had abundant Fe-N_x active sites,but also had some Mo-N sites.The catalytic performance of Fe-NC@Mo₂TiC₂catalyst was improved obviously due to the existence of Mo-N sites.The half-wave potential and initial potential of Fe-NC@Mo₂TiC₂ catalyst were 0.884V and 0.967V,respectively,which were significantly better than those of Pt/C catalyst.Methanol tolerance of Fe-NC@Mo₂TiC₂ catalyst was also much better than commercial Pt/C.After 30000s chronoamperometry test,the current of Fe-NC@Mo₂TiC₂catalyst decreased by only4.2%,while Pt/C catalyst decreased by 28.4%.This indicated that Fe-NC@Mo₂TiC₂catalyst had better long-term durability than Pt/C catalyst.The effect of three-dimensional composite support on the catalytic performance of M-N-C catalyst was also studied.The Mo₂TiC₂-rGO_3D composite support with three-dimensional structure was prepared by hydrothermal method.Cu and Ni were doped in the process of in-situ growth of ZIF-8 and Cu-Ni-NC@Mo₂TiC₂-rGO_3Dcatalyst was prepared.In the oxygen reduction reaction test,Cu-Ni-NC@Mo₂TiC₂-rGO_3Dcatalyst had higher catalytic activity than Cu-Ni-NC@Mo₂TiC₂-rGO_2D.This indicated that the porous structure and large specific surface area of the 3D composite support can effectively improve the catalytic performance of the catalyst.After 2500 cycles of accelerated aging test,the half-wave potential of Cu-Ni-NC@Mo₂TiC₂-rGO_3D catalyst decreased by 10m V,which was much lower than that of Pt/C catalyst by 25m V,proving its excellent stability.In addition,Cu-Ni-NC@Mo₂TiC₂-rGO_3D catalyst also showed excellent to CO and methanol poisoning resistance.