Research On Nanostructured Transition Metal-based Catalyst For Advanced Water Splitting

Hydrogen has emerged as an excellent option for clean energy and potential source storage carriers due to its high energy conversion efficiency,renewability,and excellent weight energy density.As a result,the production of hydreogen using electrocatalytic water splitting,which combines the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),is regarded as a very effective,clean,and recyclable process.Currently,materials based on platinum(Pt)and iridium(Ir)are effective catalysts for HER and OER,respectively.However,their broad use is constrained by the little amount of earth reserves and the high price of precious metal components.The most promising alternatives to precious metal-based catalysts are diverse transition metals with rich electronic layer structures and variable valence.This study looked into the catalytic performance of a number of nanomaterials based on transition metals during hydroelectrolysis.Additionally,several straightforward techniques for making nano-transition metal catalysts were created,and by modifying their shape and microstructure,their water-splitting capabilities were enhanced.(1)A novel method of chemical energy-driven lithiation(CEDL)was introduced to synthesize transition metal nanostructures.By taking advantage of the slow crystallization kinetics at room temperature,more surface and boundary defects were generated and remained,which changed the atomic coordination number and tuned the electronic structure and adsorption free energy of the metals.The obtained Ni nanostructures therein exhibited excellent HER performance.In addition,the bimetal of Co and Ni showed better electrocatalytic kinetics than individual Ni and Co nanostructures,reaching 100 mA/cm2 at a low overpotential of 127 mV.The high HER performance originated from well-formed synergistic effect between Ni and Co by tuning the electronic structures.DFT simulations confirmed that the bimetallic NiCo possessed a low Gibbs free energy of hydrogen adsorption,which was conducive to enhance its intrinsic activity.CEDL method provided a general strategy that enabled simultaneous defect engineering and electronic modulation of transition metal catalysts to achieve an enhancement in HER performance.(2)Furthermore,to enhance the synergistic effect between the bimetals,the stable core-shell porous heterostructure Co@Mo/CNFs was effectively prepared by reducing Co9S8@MoS2/CNFs via chemical energy-driven lithiation method.It was found that the core-shell structure of Co9S8@MoS2/CNFs was effectively preserved after the lithium process.The boundary defects formed by lithiation can change the atomic coordination number and adjust the electronic structure of the metal.The Co-Mo heterojunctions formed a good synergistic effect and enhanced the catalytic activity.The experimental results showed that the current density could reach 100 mA/cm2 at a low overpotential of 87 mV and 400 mA/cm2 at an overpotential of 200 mV.DFT simulation confirmed that the Co@Mo bimetallic heterojunction had a low Gibbs free energy for hydrogen adsorption,which was beneficial to improve its intrinsic activity.Both defect engineering and heterostructure of transition metal catalysts were performed simultaneously to improve HER performance.(3)In order to further enhance the intrinsic activity of the material,the core-shell structure CuS@MoS2 was fisrtly prepared by a one-pot synthesis,which was then reducted by chemical energy-driven lithiation.So the Cu@Mo was obtained by this route;we found that the monolayer of MoS2 could convert to Mo cluster or single atoms in lithium process by the confining of Cu substrate.The experimental results showed that the current density can reach 100 mA/cm2 at a low overpotential of 60 mV and 400 mA/cm2 at a overpotential of 134 mV.(4)Aiming to solve the problem of low activity of transition metal in electrocatalytic oxygen evolution,heterojunction catalysts(BP-Co/CNT@NC)were synthesized by a simple solvothermal method on a Co nanoparticles-loaded nitrogen-doped carbon nanotube-carbon network(Co/CNT@NC)by pyrolysis of ZnCo-ZIF.The BP-Co heterojunction not only improved the stability of BP,but also provided a good channel for electron transfer to metal active sites during the reaction process,effectively improving the electrocatalytic oxygen evolution activity and stability of the catalyst.As expected,the optimized BP-Co/CNT@NC exhibited excellent OER performance,including a low overpotential value(370 mV)at 100 mA/cm2 in an alkaline solution,Tafel slope of 40 mV/dec and long-term stability.This strategy improved the stability of BP electrocatalysts and further expanded their electrochemical applications.