| With the continuous increase in the proportion of renewable energy,such as wind power and photovoltaic in the power system,the strong unpredictability,intermittency and volatility of renewable energy have brought great challenges to the safe and stable operation of the power system.Water electrolysis technology is an ideal technology to convert renewable electricity into long-storable hydrogen energy.Water electrolysis includes two kinds of half-reactions,hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）,in which any sluggish half-reaction will decrease its overall energy efficiency.To overcome this barrier,it is extremely significant to rationally construct an electrode with high efficiency in water electrolysis.Generally,iridium dioxide and platinum noble metals have the most excellent OER and HER activity,respectively;but the high price of these catalysts limits their wild application.Moreover,the OER process involves multi-step proton-coupled electron transfer and high energy barrier,resulting in slow OER kinetic process and low intrinsic activity;and its high reaction potential will continuously oxidize the electrode material,resulting in the uncertainty of the actual OER active species.Meanwhile,the gas production in HER cathode is twice than that in OER anode,resulting in bubbles covering the electrode surface,which seriously reduces the utilization rate of active sites,thus restricting the supply and transmission of reactants,thereby increasing the energy consumption of the water electrolysis system.Therefore,it is highly desirable to develop non-noble metal electrocatalysts for water electrolysis with low-cost,high activity,high durability and bubble regulation.Based on the above problems,the main contents of this paper include:1)In view of the dispute over the actual catalytic active species of the transition metal compound oxygen evolution electrode,an electrochemical reconstruction electrode of non-metallic compounds was constructed.By means of the physicochemical characterization,electrochemical characterization and stability test,it was clear that the electrode would oxidize and etch non-metallic elements at the OER reaction potential,resulting in irreversible structural reconstruction.It was confirmed that nickel based hydroxyl oxide was the actual species with stable OER activity.Then,the oxygen vacancy content of the reconstructed electrode was adjusted by the non-metallic category.Besides,the relationship between the oxygen vacancy content and the performance of water electrolysis was also clarified by electrochemical tests.2)Based on the fact that oxygen vacancies widely exist in transition metal based reconstruction electrodes,in order to further reveal the effect on oxygen vacancy defect,a surface reconstruction electrode of molybdenum/sulfur two-element electrochemical etching was constructed.Moreover,the interaction mechanism of oxygen vacancy content on electronic density of states and adsorption free energy of oxygen species in the process of water electrolysis and its coupling effect on OER performance were revealed by the density functional theory and first principles simulation calculation.3)The gradient pore bubble transport regulating electrode was prepared by lamination pressing method and hydrothermal synthesis method.The effect of electrode pore structure on bubble desorption rate and desorption size was revealed.The bubble force balance was used to clarify the bubble transport regulating mechanism.The effect of electrode pore structure on material transport and HER performance was also analyzed.4)Based on the view that the electrode structure can strengthen bubble desorption and accelerate the supply of substrate,an open-structured spiral fiber electrode with the bubble sliding behavior was designed by mechanical rotation method and solvent thermal synthesis method.Studying the influence of electrode structure on the growth of catalytic crystal.visualizing the influence of electrode structure on bubble desorption.Revealing the bubble directional sliding mechanism with the help of force balance analysis.The particle image velocimetry system was used to trace and detect the distribution of liquid flow field near the electrode;and the influence of electrode structure on HER performance and the utilization of electrochemical active sites was also characterized.5)Based on the excellent preparation strategy of OER and HER catalysts in this paper,a water electrolysis device with gradient hydrophobic coating and trapezoidal foam metal structure was further constructed.Combined with visualization analysis and force analysis,the influence mechanism of wettability and structure for the water electrolysis electrode on bubble behaviors was clarified.The corresponding performance parameters of gradient hydrophobic trapezoidal electrode under different current and voltage conditions were compared by electrochemical means.The main conclusions of the study are as follows:（1）Nickel based non-metallic compound OER pre-catalytic electrode was prepared by hydrothermal synthesis and vapor deposition.The active species with excellent OER performance was identified as amorphous Ni OOH by electrochemical surface reconstruction method,and the reconstructed electrode Ni2P2S6/CC-SR with rich active oxygen vacancies was constructed by adjusting the non-metallic category of pre-catalytic electrode.Therefore,the bimetallic compound surface etching reconstructed electrode Ni2P2S6/CC-SR also showed good OER catalytic activity,requiring only 219 m V overpotential at 10 m A cm-2.（2）An surface reconstruction electrode（Ni Mo3S4/CC-SR）of the electrochemical etching on molybdenum and sulfur elements constructed by hydrothermal synthesis and sulfuration reaction had the highest oxygen vacancy content（60.3%）.Subsequently,the first principle simulation calculation exhibited that with the increase of oxygen vacancy content in Ni OOH（101）crystal plane model corresponding to the reconstructed electrode,the valence band center of Ni 3d orbit shifted to the positive direction and the adsorption free energy of electrode rate determining step decreased,indicating that the adsorption capacity of OER electrode for oxygen species was optimized.The electrochemical test results showed that there was a positive correlation between the oxygen vacancy content and the electrochemical performance;besides,the reconstruction electrode（Ni Mo3S4/CC-SR）with molybdenum/sulfur element had the highest OER catalytic activity.The current density of 10 m A cm-2 could be obtained only at the overpotential of 207 m V.（3）Based on the electrode substrate with gradient pore structure,a Ni3S2/Mo S2electrode for HER loaded with porous sufficient nanosheets was constructed.The results of visualization and bubble transport control mechanism analysis showed that the bubble in the SML/NF-HE gradient pore electrode with the decreased pores from the inside to the outside would be continuously cut due to the reduction of bubble adhesion from the inside to the outside,thus showing the smallest bubble desorption size,thereby exposing more electrode catalytic active sites,and finally realizing high-efficiency electrochemical hydrogen evolution.Only 83 m V overpotential was required to reach the current density of-10 m A cm-2.（4）Mo S2⊥CFB hydrogen evolution electrode with an open-structured spiral fiber was prepared by mechanical rotation and solvothermal synthesis method.This electrode had an excellent microenvironment for catalyst crystal growth,and nanosheet catalysts were densely and uniformly grown inside and outside the electrode.Moreover,Mo S2⊥CFB hydrogen evolution electrode showed the most excellent bubble desorption characteristics and liquid substrate supply capacity due to its bubble unidirectional sliding characteristics.Therefore,when the overpotential is 0.4 V,the current density for hydrogen evolution is 3.7 times higher than that of the plane electrode Mo S2⊥CC electrode.（5）An water electrolysis device with the gradient hydrophobic coating and trapezoidal foam metal structure was constructed.Due to the existence of gradient hydrophobic structure and trapezoidal structure,the bubbles above the electrode surface would undergo continuous oriented infiltration and migration from the end to the root of the PTFE clamp under the joint driving of the double Laplace pressure difference,thus realizing the oriented infiltration,migration and automatic separation/capture of hydrogen/oxygen bubbles.The electrolytic voltage required to achieve the current densities of 10 m A cm-2 and 100 m A cm-2 were only 1.52 V and 1.68 V,respectively. |
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