The Regulation Of Iridium-based Catalysts Applied On Electrochemical Oxygen Evolution Reaction

The development of the hydrogen energy economy has become increasingly attractive in the environmental energy field.The realization of high-efficiency renewable energy electrolysis of water splitting to hydrogen production technology is the key to solving a series of pollution problems driven by fossil fuels.The realization of high-efficiency electrolysis of water-splitting in acidic solutions is significant.Typically,the critical reaction step involved in water-splitting is the oxygen evolution reaction(OER),which has essential scientific research value.Designing and modifying the electrocatalytic anode Ir-based catalyst in the oxygen evolution reaction could achieve high efficiency and robust water-splitting.However,the current mechanism proposed by the scientists could not guide the design of Ir-based catalysts effectively.Therefore,the design and modification of Ir-based catalysis in acidic solution were explored in this work,and the scale relationship between the electronic properties of Ir-based catalysts and the activity of oxygen evolution reaction performance was summarized.This work mainly includes four aspects:Ir-based crystal-amorphous composite structure,Ir-based crystal,Ir-based amorphous structure,and Ir-based nanowires and nanosheet catalysts.The work contents are as follows:(1)Research on the performance of Ir-based crystal-amorphous composite structure catalysts applied to OER:The introduction of lanthanide elements in Ir-based oxdies was explored through the synthesis method of hydrothermal synthesis and low-temperature calcination in this part.The reaction temperature and reaction time were optimized combined with thermogravimetric differential thermal analysis.Ir-based amorphous and Ir-based crystalline composite catalysts were successfully prepared.A large number of(c-a)crystal and amorphous interfaces were created synergistically,achieving efficient OER performance and long-term stability.The excellent electrical conductivity of the crystalline structure and the excellent OER performance of the amorphous structure could achieve a synergistic effect in OER process.By means of XAS,XPS,etc.,the suitable electron filling number of eg orbital created by the amorphous-crystal interface was determined,and the binding energy of the metal iridium site and the reaction intermediate in the OER reaction was regulated,which achieved the excellent OER performance.(2)Research on the performance of Ir-based crystal structure applied to OER:For the first time,a new Lu2Ir2O7 pyrochlore structure was synthesized through the hydrothermal synthesis method accompanied with the low-temperature calcination.We found that Lu2Ir2O7,Eu2Ir2O7,and Pr2Ir2O7 showed different OER performance in acidic solution and alkaline solution,but all exhibit the same activity trend(Lu2Ir2O7>Eu2Ir2O7>Pr2Ir2O7)in the same solution.We determined that the higher OER performance of the catalysts in acidic solution originate from the highly active[IrO6]-[IrO6]framework brought by the surface reconstruction through the TEM and XPS analysis.We demonstrate that the highest OER performance of Lu2Ir2O7 owing to the high valence state of Ir brought by its higher Ir-O hybridization by means of XAS and DFT calculation,the linear relationship between the 2p center of O in the intrinsic properties of the three structures and its OER performance in alkaline solution was determined.The formation of the[IrO6]-[IrO6]structure is essential for the high OER activity of the Ir-based pyrochlore structure in acidic solution.(3)Research on the Ir-based amorphous structure applied to OER:For the first time,pure amorphous Lu1.25IrOx structure was synthesized through the Lu element induction.Through the electrochemical tests and characterizations in acidic solution and alkaline solution,we demonstrate that the amorphous Lu1.25IrOx structure is full of IrⅢ species,The pristine propeties of Lu1.25IrOx structure could not bring excellent OER performance.On the contrary,after the cyclic voltammetry treatment in acidic solution,Lu leaching process could result in a large number of cation vacancies,forming a large number of IrⅤ species in the catalyst,which exhibit the highest OER performance.Through the O K-edge absorption spectra in the amorphous-induced process and surface reconstruction process of the catalyst,we identified Ir d-holes in IrⅤ as a descriptor of Ir-based OER performance.(4)Research on the Ir-based nanowires and nanosheets for OER:Rb0.17IrO2 nanowires were synthesized for the first time by hydrothermal synthesis method accompanied by the lowtemperature calcination,we revealed the formation of nano-IrOx thin layer through the interfacial reconstruction in acidic solution,which could achieve the high OER performance.The DFT theoretical calculation proves that cation leaching can balance the adsorption energy of the OER reaction intermediates.Additionally,the nanosheet K0.3IrO2·H2O and Rb0.3IrO2·0.6H2O structures were synthesized for the first time,and two new 3R-type layered IrO2 structures with different lattice parameters were successfully synthesized by H ion exchange and layer exfoliation methods.The DFT calculation proves that the high concentration of the oxygen vacancies caused by the distorted 3R-type IrO2 is not conducive to the improvement of OER performance,The 3R-type IrO2 are not favourable to the OER owing to the high gap value and the high free energy barrier.This work provides a theoretical basis for exploring new Ir-based structures for OER process.