Study On Methanol Oxidation Reaction Using Multi-walled Carbon Nanotubes Supported Pt-based Catalyst

The continuous growth of global energy demand has raised concerns about energy security and living environment.In the past two decades,people have been trying to develop new energy technologies.Among them,direct methanol fuel cells（DMFCs）are considered to be one of the most promising alternative energy sources in the future due to their simple structure,compact design,high energy density and energy conversion efficiency.However,as the core of direct methanol fuel cells,Pt-based catalysts still have problems such as high cost,short service life and easy poisoning,which hinder the large-scale commercial application of DMFCs.In this paper,from the perspective of regulating the surface composition and electronic structure of Pt-based electrocatalysts,the following three aspects have been carried out to improve the catalytic activity,enhance the anti-toxicity and stability:（1）In this system,PtFe alloy with high catalytic performance supported on nitrogen-doped carbon（NC）modified multi-walled carbon nanotubes（MWCNTs）was successfully prepared by synergistic regulation of surface composition and electronic structure.Compared with the original Pt/C catalyst（0.38 mA/μg）,the MOR mass activity（MA）of Pt₁Fe₃@NC/MWCNTs catalyst（0.86 mA/μg）with an appropriate amount of Fe³⁺addition increased by 2.26 times.In addition,the CO oxidation onset potential of Pt₁Fe₃@NC/MWCNTs catalyst is lower than that of Pt/C catalyst（0.71 V and 0.80 V）.The Pt₁Fe₃@NC/MWCNTs（21.16%）catalyst has a lower chronoamperometry test drop rate than Pt/C（47.81%）at a constant current of 0.75 V for 2000 s.Benefiting from the optimal surface composition,the corrosion resistance of MWCNTs,the strong electron interaction between PtFe alloy and MWCNTs,and the nitrogen-doped carbon（NC）layer,the Pt₁Fe₃@NC/MWCNTs catalyst exhibits better MOR performance and CO poisoning resistance.This study will open up a new perspective for the design of efficient electrocatalysts in the DMFCs field.（2）The Fe will fall off due to the effect of hydrogen evolution corrosion reaction in acidic solution for a long time,resulting in insufficient stability of the catalyst.On the basis of the previous system,the stability of the catalyst was further improved.In this work,multi-walled carbon nanotubes（MWCNTs）supported PtCoalloy catalysts with good MOR performance and stability were successfully prepared by combining low temperature adsorption and high temperature reduction.Compared with the commercial Pt/C catalyst,the MOR mass activity（MA）and area specific activity（SA）of the Pt₁Co₃@NC/MWCNTs sample with the optimal Co²⁺addition amount increased by 1.93 and 2.45 times,respectively.The current density reduction rate（9.34%）of Pt₁Co₃@NC/MWCNTs after 2000 s chronoamperometry test at 0.75 V（vs RHE）is much lower than that of Pt/C catalyst（43.06%）.In addition,we used accelerated durability test（ADT）to obtain the catalyst activity decline rate（25.73%and 48.69%）,and the results further confirmed that the catalyst had good stability.The improved MOR activity and durability of Pt₁Co₃@NC/MWCNTs catalyst is attributed to the moderate surface composition,the optimal electronic interaction between PtCoalloy and MWCNTs,and the protection of N-doped carbon（NC）shell.It has potential application value in the design and preparation of efficient and stable electrocatalysts for DMFCs.（3）At present,PtRu bimetallic nanomaterials have been recognized as the best anti-CO poisoning methanol oxidation reaction（MOR）electrocatalyst.Based on the previous system,Ru transition metal was introduced to further adjust the electronic structure of Pt to enhance the anti-toxicity of the catalyst.We successfully synthesized Pt₁Co_xRu₁@NC/MWCNTs trimetallic alloy catalyst with good MOR performance and CO poisoning resistance.The electrochemical test results show that the MOR mass activity of Pt₁Co₃Ru₁@NC/MWCNTs sample with moderate Co²⁺doping amount is0.78 mA/μg,which is 1.81 times higher than that of commercial PtRu/C（0.43 mA/μg）catalyst.Secondly,the CO oxidation onset potential of Pt₁Co₃Ru₁@NC/MWCNTs catalyst is lower than that of PtRu/C catalyst（0.497 V and 0.561 V）,indicating that it has better resistance to CO poisoning.Compared with commercial PtRu/C catalyst（45.8%）,Pt₁Co₃Ru₁@NC/MWCNTs has a lower current density decrease rate（25.7%）after 2000 s CA test at 0.75 V（vs RHE）.This is attributed to the protection of the NC layer,the PtCoRu trimetallic coordination effect and the interaction between PtCoRu alloy and MWCNTs.This system provides a new theoretical guidance for accurately adjusting the surface composition and enhancing the activity,anti-toxicity and stability of multi-metal alloy nanocatalysts.