Preparation Of Ultrafine Ruthenium-iridium Alloy Nanocrystals And Their Synergistic Catalytic Mechanism For Water Splitting

Proton exchange membrane（PEM）electrolysis of water for hydrogen production is one of the hotspots in hydrogen energy research.Aiming at the common bottleneck problem of the anodic oxygen evolution reaction（OER）in the process of water electrolysis,the kinetic process is very slow and the energy consumption is high.Using a controllable polyol thermal reduction reaction system,a series of ruthenium-iridium alloy nanocrystalline electrocatalytic materials with different compositions were synthesized.The electrocatalytic performance of oxygen evolution in acidic water is improved through effective control methods such as electronic coupling effect and geometric coordination effect between various active components in the alloy.The thesis mainly focuses on the composition design of high-performance low-iridium catalysts in acidic water,the regulation of nanophase structure,and the construction of new electrolysis systems assisted by supporting electrolytes.The related research work provides theoretical and technical support for the commercial application of proton exchange membrane（PEM）electrolysis of water for hydrogen production.The main findings obtained are as follows:（1）Using a controllable polyol synthesis system,using Ru Cl₃ and H₂Ir Cl₆ as precursors,a one-step alcohol thermal reduction method was used to successfully prepare a Ru Ir binary alloy nanocrystalline catalyst with a typical dendritic structure,with a particle size of about 1.6 nm.There are two-phase composite structures of hexagonal close-packed（hcp）and face-centered cubic（fcc）in alloy nanocrystals,which form a coherent relationship through the mechanism of epitaxial growth of specific crystal planes.The composite structure catalyst has a preferred orientation of（0 00 1）crystal plane,and a highly active amorphous Ir Ox oxide layer exists on the surface.When the atomic ratio of Ru to Ir is 6:4,the overpotential of the alloy catalyst at a current density of 10 m A cm^-2 is only 192 m V,and the continuous electrolysis operation for 30 h has no obvious activity decay,and the performance is significantly better than that of the commercial Ir O₂catalyst.The synergistic catalytic effect of the two-phase coherent structures of hcp and fcc in Ru Ir alloy nanocrystals is the main reason for the accelerated oxygen evolution kinetics.Using a combination of theoretical calculations and experimental studies,the strong electronic/geometric coordination effect between Ir and Ru atoms is further demonstrated,which is helpful to break the frontier scientific challenge of restricting the relationship between the activity and stability of oxygen evolution catalysts.（2）In the electrolytic acid water reaction system,the performance of the alloy is further improved by adding Na Cl catalyst promoter.Furthermore,a new method of electrolysis assisted by supporting electrolyte is proposed.After adding 0.6M Na Cl in the dielectric environment,the OER overpotential of Ru Ir alloy was further reduced by42 m V,and the stability was improved by 33%.The improved catalytic performance can be attributed to the specific adsorption of Cl^-species at the oxygen vacancies in the lattice of the catalyst surface,which optimizes the chemisorption energy of the oxygen evolution product,promotes the kinetic mechanism of water dissociation and product desorption,and reduces the reaction energy barrier.In addition,the chemisorbed Cl species on the lattice oxygen vacancies stabilize the surface structure of the catalyst and achieve charge balance,hindering the dissolution of active metals and structural collapse,thereby enhancing the stability of the catalyst.This provides a useful attempt for a new acidic water electrolysis method.（3）On the basis of Ru Ir binary alloys,a series of Ru Ir M ternary alloys were prepared by introducing a third metal with high oxyphilicity（M=Ce,Nb and W）.Through the regulation of the electronic/geometric structure of the multi-component alloy by the third metal component,the adsorption capacity and adsorption sites of the oxygen-containing intermediates are optimized,and the kinetic process of oxygen evolution is accelerated.In addition,the introduction of dopant metal strengthens the chemical adsorption of oxygen anions,further stabilizes the chemical structure of the catalyst surface,and further improves the stability of the catalyst.Compared with the Ru Ir binary alloy,the overpotential of Ru Ir Nb ternary alloy catalyst is reduced by 9 m V and the stability is improved by 11%.The DFT calculation results show that the theoretical overpotential of Ru Ir W is 0.13 V lower than that of Ru Ir binary alloy.This finding further confirms that the multi-alloying effect of highly oxyphilic metals is an effective method to break the mutually restrictive relationship between the activity and stability of oxygen evolution catalysts.