Regulation Of Local Electronic State In MOFs Derivatives For Water Splitting

Hydrogen,as an environment-friendly and renewable resource,has been considered as the fossil fuel alternative due to its high gravimetric energy density,high energy density and the abundant resource.Water splitting currently is the most effective and economic way to produce hydrogen on a large scale.To exploit efficient and low-cost electrocatalysts is the key to reduce high energy consumption.This research realized the development of a series of MOFs(Metal-Organic Frameworks)derivatives with highly electrocatalytic activities.By taking the MOFs as templates,the mechanism of controlling catalytic activity through the method of“local electron-state regluation”was investigated,and the“structure-activity relationship”between microstructure and catalytic activity was also clarified to guide the designing of high-efficient electrocatalysts.The specific contents and results are outlined:(1)Through the method of“interface engineering”,the mechanism of controlling intrinsic catalytic activity by the interface sturcture was revealed,and a catalyst with highly efficient bifunctional of electrolytic water also was prepared.Taking the Co-based MOFs of ZIF-67(Zeolitic Imidazolate Framework-67)as the initial template,a composite of Co P/CN@Mo S₂which containing the interface of Co P/CN/Mo S₂ was constructed.When the applied overpotential was 144 m V(p H=0)and 149 m V(p H=14),the driving current density can be reach to 10 m A·cm^-2 during the HER(Hydrogen Evolution Reaction)process.On the alkaline OER(Oxygen Evolution Reaction),the over potential required to drive the same current density was 289 m V.In addition,when driving the electrocatalytic overall water splitting,the applied potential was just 1.61 V(vs.RHE).Combined with theoretical calculations,it was shown that the interface coupling effect induces the transfer of localized electrons,which can optimize the adsorption/desorption ability of the active site to the intermediate products during the water splitting process,in turn to accelerate the reaction kinetics and improve the catalytic activity.(2)Based on the regluation of local electronic state through the method of"interface engineering",by the idea of hetero-interface building and configuration optimizing,the catalytic activity of transition metal compounds can be greatly enhanced,also the“structure-activity effect”was revealed.Taking ZIF-67 as template to construct a 3D hollow nanostructure which containing the interface of(Co,Ni)Se₂ and Ni Fe LDH.On the alkaline OER process,the required overpotential for driving current density of 10 m A·cm^-2 was 277m V.In addition,a simplified model of structural unit of Ni-O-Co-O-Fe-O-Ni was proposed to describe the reconfiguration of the local electrons.The different ability of forming?-electrons between O 2p electrons and the t_2gorbital of Fe,Co and Ni,which leads to the redistributing of localized electrons with the tendency toward the uniformly and lower energy state.Thereby optimizing their adsorption capacity for oxygen-containing species in the OER process and promoting the catalytic activity.This study provided a realistic basis for the preparation of noble metal free catalysts with highly efficient OER activity.(3)Inspired by the regulation of local electronic state and the dynamic description of electronic transfer with theoretical model,this study would focus on the methodology,by proposing the strategy of the"host-guest modification"to explore a universal method to fabricate efficient catalyst.The hollow structure of Ni Co P/C that deriving from ZIF-67serving as the host,and amorphous Fe OOH was introduced as the guest to modify the surface,and then obtained the composite of Ni Co P/C@Fe OOH.In the alkaline medium,when the driving current density was 10 m A·cm^-2,the required overpotential for the composite was271 m V.In addition,the electrons in the composite spontaneous transferred from Fe OOH to Ni Co P,indicating the existence of reconstruction among the electrons at the interface.Further expanding the host material to a single 3d and 3d/4d metal elements co-existence structure,the corresponding obtained composites of Co P@Fe OOH and Mo-Co P@Fe OOH both exhibited the enhanced OER activity.Further,established a theoretical model to describe the reconstruction of local electronic state,and the mechanism of the catalytic activity enhancement was revealed.This study would provide a universal method for the preparation of high efficient OER catalysts(4)Combing with the method of regulation of the local electronic state,as well as the controlling of half-reaction on the anode of water splitting,it would an efficient way to overcome the problem of high energy consumption caused by the OER.Specifically,using urea as an additive,a low-energy half-reaction of UOR(Urea Oxidation Reaction)was introduced to replace the OER process and kept the HER unchanged.In addition,a one-step solvothermal method was adopted to accurately prepare the bimetallic MOFs derivatives of Mn/Ni-BDC.Due to the different electronegativity of Mn⁴⁺and Ni^2+/3+,the local electrons of O^2-tending to shift to the Mn,which led to the weakening of the coordination ability between the oxygen and Ni,thereby realizing the activation of the Ni site,and was favour to optimize the adsorption capacity for urea oxidation intermediates(*NH,*CO),in turn to promote the catalytic activity of UOR.In the alkaline medium with urea,when driving current density of10 m A·cm^-2,the applied potential was only 1.317 V,which lays the foundation for the practical application of water-to-hydrogen production.Based on the results,optimized novel materials of MOFs derivatives with excellent electrocatalytic performance and low-energy-consumption of water-to-hydrogen production could be realized by the guidance of“local electronic state regulation”.The four strategys of“interface engineering”,“heterostructure interface construction”,“host-guest modification”and“asymmetric coordination”were proposed to realize the regluation of local electronic configuration,and in turn to effective improve the catalytic activity of water splitting.It will make great contribution to the development of hydrogen production industry.