Design And Performance Of MXene-based Electrocatalyst For Hydrogen Evolution Reaction

Hydrogen is one of the most promising clean energy sources because of the reserve abundance in diverse forms,the highest energy density beyond available fuels,environmental benignity,and widespread applications.The hydrogen production by electrolysis is facile and shows superiority to traditional fossil reforming ways for producing high-purity hydrogen.When coupled with renewable energy such as hydropower,photovoltaic power,and wind power,it can greatly reduce carbon emission,showing high promise in meeting incoming the global hydrogen energy economy.High energy consumption is a bottleneck problem that restricts the large-scale application of water electrolysis technology.The high dependence on a large amount of high-purity freshwater also makes it difficult to apply this technology in arid,on and offshore zones.Designing low-cost and highly efficient non-precious metal catalysts is pursued for energy-saving and low-cost water electrolysis.However,high efficiency of most reported electrocatalysts is highly sensitive to the pH conditions and chemical compositions of the water system.It brings enormous difficulties for practical use in the real water environment with complex and variable compositions.In response to these problems,this thesis systematically explored the design and fabrication of non-noble metal electrocatalysts based on two-dimensional transition metal carbides(MXene),and their application in water electrolysis under complex pH conditions and in seawater.The main results are summarized below:A molecular chemical engineering strategy was developed to efficiently stabilize the chemical structure of MXene by chemical modification of MXene surface with glucose and other biomass molecules and their in-situ interfacial polymerization.It significantly broadens the working conditions of MXene to meet the synthesis under common hydrothermal,reflux,and high-temperature conditions.Further introducing the molybdenum and sulfur source into this process creates porous nanoarrays with high activity and stability on the surface of MXene.The obtained MoS2/T3C2Tx-MXene@C electrocatalyst shows a Pt-like activity and excellent stability in 0.5 M H2SO4 for hydrogen evolution.Its activity is even superior to the electrocatalysts coupling graphene and MoS2 with a similar structure.A strategy by engineering multifunctional collaborative catalytic interface was proposed to propel the hydrogen evolution in full pH range and seawater.Collaborative catalytic interface among MXene,nitrogen-doped carbon and bimetallic carbides or rare-metal-doped phosphide was demonstrated to afford overall enhancement in electrical conductivity,exposure of reactive sites,water dissociation kinetics,H+/water adsorption and intermediate H binding capability,which satisfying highly variable chemical environment for HER under different pH conditions.The electrocatalytic performance of resultant Co0.31Mo1.69C/MXene/NC catalysts could compete with commercial Pt/C in 0.5 M H2SO4 or 1.0 M KOH but outperform it under pH 2.211.2.They also show 64 times longer life than Pt/C in seawater for hydrogen evolution.The obtained La0.17Mo0.83P/PC/MXene catalyst needs only 158 mV overpotential to reach a current density of 10 mA cm-2 in seawater,and can work stably for more than 400 h.An efficient strategy is presented to boost the thermodynamic activity of MXenes with strong light absorption in the solar spectrum for hydrogen evolution.It allows one to utilize the localized surface plasmonic resonance effect to tailor the interfacial carrier concentration and life of MXene.Remarkable photothermal effect and sub-picosecond hot electron injection of MXene with different compositions and structures were identified in the visible-near infrared region.The positive effect of the former on hydrogen evolution can be ascribed to the thermochemical effect and the reduction in the concentration polarization overpotential in the full pH range.The latter promotes the hydrogen evolution by reducing the activation energy via sub-picosecond hot electron injection from MXene.This mechanism could boost the electrocatalytic activity of various MXenes by over 5 times in the full pH range.