Interface And Structure Regulation Of Transition Metal Oxide-based Water Splitting Catalyst

Hydrogen as an environmentally friendly clean energy can reduce people’s dependence on traditional fossil energy,reduce environmental pollution,and the global greenhouse effect.In hydrogen production technology,electrocatalytic water splitting is considered to be a very industrially promising technology due to its mild conditions,high hydrogen purity,safety,and effectiveness.Precious metal-based catalysts are usually used to reduce the energy consumption of water splitting.However,their scarce resources,high prices,and instability limit their large-scale application in water splitting.The development of non-precious metal catalysts with high catalytic activity is essential for the electrocatalytic water splitting.This thesis takes high-abundance transition metal oxide-based catalysts as the research object.Based on the analysis of the electrocatalytic water splitting reaction mechanism,constraints and performance optimization strategies,mainly through the nanostructure of the catalyst,designing the multi-phase interface structure,regulating electronic structure,and inducing amorphization to develop high-performance transition metal oxide-based catalysts,and study its performance and catalytic mechanism in hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）and overall water splitting.The specific work is reflected in the following aspects:（1）The number of active sites,the free energy of water dissociation,and hydrogen adsorption in the catalyst are the three main factors that affect the activity of alkaline hydrogen evolution reaction（HER）.At present,it is still difficult to control these three factors at the same time.In this study,based on the idea of triple-phase interface structure design and synergistic catalysis.We demonstrate a novel triple-phase interface designed Ni O/Ru@PNS electrode that includes Ru nanoparticles and Ni O layer in situ grown on porous nickel scaffold（PNS）with galvanostatic replacement reaction and in situ electro-oxidation process,respectively.The results show that the triple-phase interface design of Ni O/Ru@PNS electrode achieves the synchronous modulation of the three factors mentioned above.The Ni O/Ru@PNS electrode only requires an overpotential of 39 m V at a current density of-10 m A cm^-2 and exhibits better performance than the commercial Pt/C catalyst when the current density is greater than-75 m A cm^-2.The theoretical calculation results further show that the Ni O layer can significantly reduce the reaction energy barrier of the Volmer step in the HER process,and Ru nanoparticles can promote the Heyrovsky step.Because the hydrogen intermediates and electron can be easily transported through the triple-phase interfaces,such a triple-phase interface structure exhibits highly efficient synergistic catalysis.Our studies demonstrated that the design of the triple-phase interface structure enhances the synergistic catalysis among the various components and provides a feasible solution for constructing a highly efficient metal oxide-based catalyst.（2）Generally,transition metal oxides catalysts have shown high activity for the OER in alkaline medium,however,they are generally inactive for HER.In this study,Co O showed excellent HER catalytic activity through the design of the nanowire structure array and the doping strategy of aliovalent fluorine anion.Hydrothermal and heat treatment methods were used to grow in situ on carbon cloth to obtain F anion-doped Co O nanowire arrays（F-Co O/CC）.HER performance tests show that F-Co O/CC only needs an overpotential of 52.8 m V to drive a current density of-10 m A cm^-2 in an alkaline solution,and the performance exceeds commercial Pt/C catalyst at higher current densities and can maintain the stability of structure and performance for a long time.Theoretical calculation results show that the substitution of F anions for O ions increases the charge distribution of Co sites,reduces the valence state of Co,facilitates water dissociation,weakens the adsorption of Co sites to hydrogen,and enhances the intrinsic activity of Co O.At the same time,F-doped Co O can significantly reduce the intrinsic band gap of Co O,increase its electronic conductivity,and accelerate the electron supply and charge transfer of the catalytic reaction.This strategy of using nanowire arrays structure design and anion doping to control the electronic structure enhances the basic HER activity of transition metal oxides and provides a reference for the development of industrial low-cost catalysts.（3）The development of bifunctional HER and OER catalysts that can be used in alkaline solutions is necessary for overall water splitting.Here,the F-Co O/CC prepared above is used as the research object,and the anodization-induced amorphous transformation is used to improve the OER activity of the F-Co O/CC.Combined with the excellent HER activity of the F-Co O/CC,an overall water splitting catalyst with bifunctional is obtained.First,F-Co O/CC electrodes were anodized（activated）to form an amorphous shell.The amorphous shell enhances the OER activity with an overpotential of only 237.7 m V at 10 m A cm^-2,which is superior to the commercial Ir O₂ catalyst.At the same time,due to the self-limiting nature of the amorphous shell,it exhibits excellent durability during testing.Research analysis shows that the etching of F anions is the determinant of the amorphous form of the F-Co O surface.A large amount of Co³⁺and OH species formed in the amorphous shell enhance the OER activity of the catalyst.Also,when F-Co O/CC and activated F-Co O/CC is used as cathode and anode respectively for overall water splitting,the system only needs a voltage of 1.53 V to achieve a current density of 10 m A cm^-2.It is better than the Pt/C-Ir O₂ catalytic system.In this work,the use of nanowire array design,ion doping control,and amorphous strategy will upgrade the transition metal oxide to a bifunctional catalyst,which provides an effective reference for the development of metal oxide-based bifunctional catalyst in the future.In this work,the anodic oxidation induced amorphous structure was used to enhance the OER performance of the transition metal oxide-based catalyst and was also applied to the overall water splitting,which provides a reference for the development of bifunctional catalysts.