Synthetic And Electrocatalytic Hydrogen Evolution Reaction Of Catalysts For Titanic-Based Materials

At present,the long-term use of fossil fuels such as coal and petroleum has led to the greenhouse effect,causing global warming.Additionally,the non-renewable nature of these energy sources has prompted widespread mention of hydrogen energy as the most promising clean energy of the 21st century.In order to achieve sustainable development,hydrogen energy,a green,safe,and non-polluting new energy source,has gained significant attention.Water electrolysis for hydrogen production(HER)is an efficient method that can rapidly generate high-purity hydrogen gas on a large scale without any pollution.However,the majority of electrocatalysts used in this process employ precious metals,which are expensive and have low yields.This greatly limits the development of the hydrogen energy industry.Therefore,developing an efficient,stable,and cost-effective electrocatalyst is a crucial breakthrough to address these challenges.In this study,a series of titanium-based catalytic materials are prepared for the hydrogen evolution reaction under both acidic and alkaline conditions.The research is divided into three parts,focusing on investigating and analyzing the catalytic active sites of these titanium-based catalysts and the influence of modulating the electronic structure on the catalytic activity and stability of HER.The first part of the study designed three titanium-copper intermetallic compounds with different titanium-to-copper ratios.Due to their unique crystal structure and distinct coordination environments,these compounds would generate a variety of active sites for the hydrogen evolution reaction(HER).Experimental investigations on their HER catalytic activity confirmed that TiCu4 exhibited the highest activity among the three compounds and demonstrated excellent catalytic stability.In the subsequent density functional theory(DFT)analysis,it was revealed that hybridization occurred between titanium and copper atoms in TiCu4,altering its electronic structure.This modification affected the distribution of Fermi energy levels and generated a significant number of antibonding states,thereby enhancing its catalytic efficiency.Subsequently,a TiCu4 model was constructed for simulating hydrogen atom adsorption on its surface.The results confirmed that the hydrogen adsorption energy(ΔGh*)was close to the optimal position(ΔGH*=0).Based on these findings,it can be concluded that adjusting the elemental ratio in the design of bimetallic intermetallic compounds can alter their electronic structure and contribute to enhancing their electrocatalytic HER performance.This provides valuable insights for the design of more bimetallic catalysts.In the second part,after studying the micron-scale titanium-copper intermetallic compound as a titanium-based catalyst,it was found that a large amount of material was required for the working electrode.To address this issue,a solution was to prepare supported catalysts.After reviewing extensive literature,it was discovered that MXene,a unique 2D layered nanomaterial with physical and chemical diversity,could serve as a catalyst support.Different preparation methods introduced different terminal functional groups,and through physical characterization and experimentation,it was determined that MXene with OH groups exhibited optimal activity.Subsequently,the study investigated whether using MXene as a support could enhance the performance of the supported metal.The loading method involved the high-temperature H2 reduction of copper metal salt onto the MXene support.Comparative analysis of the HER performance of these materials with the previous section confirmed that even with a very low copper loading(0.05 mg),the catalytic activity exceeded that of Cu metal obtained using a pellet method(30 mg).The study demonstrated that the support could enhance the catalyst’s activity due to the smaller particle size,larger surface area,and increased number of active sites when the nanoscale metal particles were loaded on the support.The next part of the study will investigate whether other metals can be loaded onto the MXene support and enhance their catalytic activity.In the third part,addressing the issue of non-uniform particle size and agglomeration of the metal-loaded titanium-based MXene material mentioned above,an electrochemical in situ reduction method.which is a mild reduction approach,was employed to improve the situation.A comparison was made with the H2 high-temperature reduction method.In this section,two methods were used to reduce PtCl4 onto the MXene surface,resulting in two types of Pt-loaded titanium-based catalyst materials.Through high-resolution transmission electron microscopy(HRTEM)observations of the material surface,it was found that the particle size of Pt nanoparticles in MX_PtCl4(approximately 3 nm)was much smaller compared to MX_Pt(>5 nm),while the particle size of commercial Pt/C(approximately 3 nm)was similar to MX_PtCl4.Investigation of their catalytic activity revealed that MX_PtCl4(5%loading)outperformed Pt/C(20%loading)in both acidic and alkaline conditions.Based on these findings,the electronic structure was studied,and DFT calculations were conducted.It was discovered that when MXene was used as the support,the support effect would "push" the surface electrons of MXene toward the Pt nanoparticles,altering the electronic structure of the metal particles,enhancing the electron density of states,and changing the adsorption energy(ΔGH*)of critical adsorbates,thus improving the catalytic activity.However,carbon black,when used as a support,did not exhibit a support effect and instead affected the stability of Pt/C in acidic and alkaline environments.Ultimately,the research demonstrated that titaniumbased MXene,as a support,could enhance the HER catalytic activity of the supported metal while exhibiting good stability in acidic and alkaline conditions.