Construction Of Two-dimensional MXene Composited Pt Electrocatalyst And Hydrogen Evolution Reaction Research

The massive consumption of fossil energy such as coal,oil and natural gas has caused global energy crisis and environmental crisis,and the development and utilization of renewable resources has become more and more urgent.Hydrogen energy can be regarded as a clean energy.At present,the large-scale production of hydrogen is mainly realized by several industrial methods,such as coal gasification,petroleum cracking and low-temperature distillation.These methods greatly increase the cost of producing hydrogen.Among them,electrocatalytic hydrolysis technology has been widely studied because of its advantages of simple process,no pollution and high purity of hydrogen products.However,in the process of water electrolysis,the slow electrode reaction kinetics and high overpotential reduce the hydrogen production efficiency.In order to speed up the reaction kinetics,it is essential to develop low-coat,high-efficiency and stable catalysts.In acidic medium,noble metal platinum is recognized as the best electrocatalyst because of its Gibbs free energy(（?）G_H^*) close to zero.However,its shortage of reserves and high cost severely limit its application.Recently,two-dimensional material MXene has become a research hotspot in electrocatalysis because of its high specific surface area,excellent electronic conductivity,good chemical stability and abundant functional groups on the surface.Furthermore,MXene can interact strongly with platinum.In this paper,two methods that can realize low platinum load are constructed by two methods:MXene composite with conductive polymer and electrostatic self-assembly with positively charged melamine into three-dimensional structure.Which is beneficial to solving the use problem of precious metals.The specific research contents are as follows:（1）Compared with other two-dimensional materials,the functional groups on the surface of MXene material can not only improve its hydrophilicity,but also provide rich active sites for catalysis.Firstly,we obtained two-dimensional Ti₃C₂T_x MXene material by etching with HCl and Li F.The method avoids the relatively dangerous hydrofluoric acid,and the preparation method can obtain single-layer or few-layer MXene nanosheets with large lateral size.The successful synthesis of this material was proved by a series of characterization.Then,we prepared the carrier compounded with two-dimensional MXene material and polypyrrole nanowire material by chemical synthesis method,and then deposited platinum（Pt）nanoparticles on its surface by electrochemical deposition method,thereby obtaining a catalyst with a mixed structure consisting of three materials with different dimensions,namely zero-dimensional（0D）platinum nanoparticles(Pt _NPs),one-dimensional（1D）PPy nanowires and two-dimensional（2D）MXene nanosheets.The PPy nanowires were compounded with MXene nanosheets,which enhanced the conductivity of the catalytic carrier and provided more active sites.The overpotential of the electrocatalyst with ultralow Pt loading(17.11μg cm^?2)is 40 m V when the current density is 10 m A cm^-2,which is very close to the commercial 20 wt%Pt/C（41 m V）.The catalyst exhibits high turnover frequencies(2.21 H₂ s^-1 in 0.5 M H₂SO₄)at 100m V and has relatively good stability due to the composite structural characteristics of 1D and2D materials.This research provides a direction for the design and development of other MXene-based electrocatalysts and more conductive polymers.（2）Taking advantage of the negative charge of functional groups on the surface of MXene,we simply treated melamine to make its surface positively charged,and then electrostatically self-assembled it with MXene into 3D crumpled morphology.Then,the nitrogen（N）doped MXene carrier was synthesized by a simple high-temperature calcination method,and atomic and nano-scale Pt was loaded on the surface,in which the loading of Pt was only 1.7 wt%.In composite materials,the electron-donating property of nitrogen improves the conductivity of the carrier,and the folds formed at the same time provide more active sites.The obtained catalyst achieves an overpotential of 63 m V at a current density of 10 m A cm^?2,higher turnover frequency value of 3.56 H₂ s^?1 and mass activity 3.52 A mg _Pt^?1 atη=200 m V,which is much higher than that of 20 wt%Pt/C(0.25 H₂ s^?1,0.25 A mg _Pt^?1).Moreover,the catalyst obtained by annealing has high stability,and hydrogen evolution reaction can continue for about 90 hours.