Preparation of Mo-based Catalyst and Electrocatalysis Application in Hydrogen Evolution Reaction and Nitrogen Reduction Reaction

Author:Ren Xiang

Supervisor:wei qin

Database:Doctor

Degree Year:2019

Download:239

Pages:112

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Energy is the cornerstone of human development and an important support for social progress.At present,most of the main energy sources in society come from fossil fuels such as coal,oil,and natural gas,but these fossil fuels not only face the decline in reserves and non-renewable factors,but also cause environmental pollution and threaten human health.Therefore,the development of energy with high efficiency and sustainable development is an urgent problem for social and human progress.At the same time,the development of chemical energy to meet industrial needs is also an important support in current industrial progress.As a clean and efficient renewable energy,hydrogen has attracted widely attentions.Its combustion product is water,which achieves zero pollution effect,and the hydrogen energy has high heat value and wide sources.It is an ideal alternative energy source for fossil fuels.Hydrogen production from electrocatalytic water splitting is considered to be an effective method.Ammonia,as an important chemical product,has wide range of applications.The increasing consumption of ammonia promotes the development of new nitrogen fixation technology,while the development of electrocatalytic nitrogen fixation technology makes the industrialization process of ammonia at a higher level.In this doctoral dissertation,we mainly focus on the morphology-maintained preparation and performance modification of Mo-based nanomaterials,which can realize the preparation and characterization of functional nanomaterials,as well as the application of electrocatalytic hydrogen evolution and electrocatalytic nitrogen reduction.The achieved main results are as follows:1.Preparation of amorphous FeMoS4 nanorod array for hydrogen evolution:Firstly,the crystal FeOOH nanorod array was grown on bare carbon cloth by hydrothermal reaction,and then transformed into amorphous FeMoS4 nanorod array by ion exchange strategy in ammonium thiomolybdate solution.The catalyst exhibits good hydrogen evolution performance.In 1.0 M phosphate buffer saline,only 204 mV overpotential is needed to achieve 10 mA cm-2 current density,which is much better than that of the precursor FeOOH nanorod.The free energy calculated by density functional theory also shows the excellent hydrogen evolution performance of FeMoS4 nanorod.2.Preparation of amorphous CoMoS4 nanosheet array for hydrogen evolution:Firstly,Co(OH)F nanosheet array was grown on bare carbon cloth by hydrothermal reaction,and then transformed into amorphous CoMoS4 nanosheet array by ion exchange strategy in ammonium thiomolybdate solution.The CoMoS4 nanosheet array exhibits good hydrogen evolution performance.In 1.0 M phosphate buffer saline,the current density of 10 mA cm-2 can be achieved by 183 mV overpotential,which is much better than that of the precursor Co(OH)F nanosheet.The free energy calculated by density functional theory also shows the excellent hydrogen evolution performance of CoMoS4 nanosheets.3.Preparation of Mo2N nanorod catalyst and its electrocatalytic reduction of nitrogen:At first,MoO2 nanorod material was synthesized,then Mo2N nanorod catalyst was obtained by high temperature nitridation process.Ammonia production and Faraday efficiency of catalyst materials at different potentials were measured in 0.1 M HCl.The results show that the nitrogen reduction efficiency of Mo2N catalyst is 4.5%and the ammonia yield is 78.4μg h-1 mgcat.-1 at -0.3 V.The efficiency of Mo2N catalyst is better than that of most of the catalytic nitrogen reduction materials reported at room temperature and pressure.Density functional theory calculations show that the free energy barrier of the reduction process of MoO2 decreases significantly after nitridation process.4.Preparation of Mo2C nanorod catalyst and its electrocatalytic reduction of nitrogen:Mo2C nanorod catalyst was synthesized by multi-step method.The Mo2C nanorod catalyst exhibits excellent nitrogen reduction performance and good stability and selectivity at ambient temperature and pressure.Ammonia production and Faraday efficiency of Mo2C catalyst at different potentials were measured in 0.1 M HCl.The results show that the nitrogen reduction efficiency of Mo2C catalyst is 8.13%,and the ammonia yield is 95.1μg h-1 mgcat.-1 at -0.3 V.The Faraday efficiency and ammonia yield of Mo2C catalyst are better than most reported electrocatalytic nitrogen reduction catalysts.Moreover,the mechanism of the electrocatalytic process of nitrogen reduction was further discussed by density functional theory calculation.