| Electrocatalytic water splitting（EWS）has attracted much attention due to convenience and environmental protection.However,the efficiency of the EWS is limited by the high overpotentials of hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.Electrocatalysts can effectively reduce the energy barrier of HER and OER to enhance the efficiency of water electrolysis for hydrogen production.Catalytic performance of electrocatalyst is closely related to the surface interface structure.Therefore,the rational design of the surface interface structure is an effective method to improve the efficiency of electrocatalytic reaction.During catalytic reaction,the electrochemical oxidation/reduction reaction would be driven by the applied voltage,which can cause the surface self-reconstruction of electrocatalysts.Surface self-reconstruction could be not conducive to the capture of the real active sites.Currently,the prediction,elucidation and regulation of the self-reconstruction are still huge challenges in the field of electrocatalysts.In this work,the surface interface structures for efficient HER and OER were designed.Theoretical calculation and experimental verification were used to construct the surface interface structure,reveal the mechanism of surface structure evolution,and establish the relationship between the surface interface structure and catalytic efficiency.The main research details are as follows:（1）Construction of heterogeneous structure activated the hydrogen spillover on the catalyst surface for boosting HER.Mo S2@carbon quantum dots（Mo S2@CQDs）catalyst for HER with surface hydrogen spillover channel was predicted,designed and constructed by density functional theory（DFT）calculation,ab initio molecular dynamics（AIMD）simulation and experimental verification.According to DFT calculation,surface charge distribution of Mo S2@CQDs exhibited gradient decreases from carbon site on CQDs to sulfur site on Mo S2,which would cause a gradient change of hydrogen adsorption on different sites.Therefore,surface hydrogen spillover channel can be formed.The geometric configuration of Mo S2@CQDs basically remained stable during the AIMD simulations,indicating the structural stability.In the experiment,Mo S2@XCQDs（X=L,M and S）were synthesized.The corresponding characterizations of crystal structure and HER performance were carried out.The medium sized carbon quantum dots（MCQDs）could reduce the overpotential of Mo S2 by71 m V.In-situ electrochemical impedance spectroscopy（EIS）showd that Mo S2@MCQDs exhibited more surface proton adsorption charge（130.6μC）,which could confirm the formation of surface hydrogen spillover channel on the Mo S2@CQDs.（2）Geometry configuration and electronic structure were regulated through heteroatom doping for efficient OER.The geometrical and electronic structures of Mn Co2O4 were adjusted by transition metal（Fe,Ni and Zn）dopants to activate OER performance based on theoretical prediction and experimental verification.According to the DFT prediction,the volumes of Fe,Ni and Zn doped Mn Co2O4 models would shrink by 1.611,2.615 and 0.605?3,respectively.The reactivity of lattice oxygen could be activated by geometric reconstruction,providing more active sites.Transition metal dopants aslo would optimize the d-band center of Co site on the surface,which was beneficial to balance the adsorption and desorption for intermediate states.Optimized geometry and electronic structures would synergistically regulate the theoretical overpotential.Especially,Fe-Mn Co2O4 exhibited a low theoretical overpotential（0.66 V）.Based on theoretical prediction,mesoporous Fe,Ni and Zn-doped Mn Co2O4 catalysts were prepared by hydrothermal and subsequent calcination.XRD and XPS patterns were used to confirm the effect of transition metals on the geometrical and electronic structures.Fe-Mn Co2O4 showed excellent OER catalytic performance.The overpotentials of Fe-Mn Co2O4were 113,58 and 48 m V lower than those of Mn Co2O4,Ni-Mn Co2O4 and Zn-Mn Co2O4.（3）Chemical grafting strategy accelerated the surface self-reconstruction to promote OER.Ni-Co layered double hydroxides（Ni-Co LDH）and MXene quantum dots（MQDs）were used to constructure the models with different bonding modes,including the strong chemical grafting（Ni-Co LDH@MQDs）and weak electrostatic adsorption（Ni-Co LDH/MQDs）.The surface evolution process of two catalysts was predicted and studied by combining AIMD simulation,DFT calculation and experimental verification.Based on the AIMD simulations,the surface self-reconstruction process can be divided into four stages:pre-equilibrium,transformation,reconstruction and equilibrium.Compared with the reconstruction stage of Ni-Co LDH/MQDs,The reconstruction stage of Ni-Co LDH@MQDs only needed 931 fs.It is suggested that the chemically grafted MQDs can promote the surface self-reconstruction process.Based on DFT calculation,the reaction pathway of reconstructed Ni-Co LDH@MQDs would transform from adsorbate evolution mechanism to bifunctional mechanism,thereby reducing the barrier for the rate-limiting step of OER.The energy barrier of Ni-Co LDH@MQDs（0.15 e V）was lower than that of Ni-Co LDH（0.53 e V）.The prepared Ni-Co LDH@MQDs exhibited rapid surface reconstruction during OER reaction compared with Ni-Co LDH/MQDs.After surface self-reconstruction,Ni-Co LDH@MQDs possessed low overpotential and long-term stability.（4）Microenvironment modulation engineering prevented the surface self-reconstruction to relize sustainably bifunctional hydrogen and oxygen evolution.In terms of the insufficient activity and stability of transition metal phosphide in water electrolysis,carbon quantum dots were introduced to enhanced the HER and OER catalytic activity and stability of NiCoP（NiCoP@CQDs）.The effects of CQDs on the surface microenvironment and electrocatalytic performance of NiCoP were analyzed by combining DFT calculation,AIMD simulation and experimental verification.For HER,CQDs regulated the surface charge distribution and electronic structure of NiCoP,reducing the decomposition barrier of H2O and enhancing hydrogen spillover on NiCoP@CQDs surface.For OER,CQDs could regulate the d-band center of Co site to banlance the adsorption and desorption of intermediates.These would optimize the rate-determining step and reduce the theoretical overpotential.In the experiment,NiCoP supported with different types of CQDs（NiCoP@XCQDs,X=B,G and R）were synthesized.NiCoP@GCQDs showed small overpotential,fast kinetics and durable catalytic stability both in HER and OER.In-situ EIS was used to demonstrate the surface self-reconstruction of NiCoP was effectively inhibited by CQDs.In addition,a water electrolyzer assembled by NiCoP@GCQDs showed excellent performance,which was superior to the device based on precious metals（Pt||Ru O2）. |
