Theoretical Design,Preparation And Performance Study Of Electrocatalyst For Oxygen Evolution Reaction Based On Activity Descriptor

As a secondary clean energy,hydrogen energy is known as the"ultimate energy in the 21st century".The development and utilization of hydrogen energy can fundamentally solve energy and environmental problems,and then meet the needs of modern human society.Green hydrogen mainly refers to the use of renewable energy to obtain hydrogen by electrolysis of water,and the oxygen evolution reaction（OER）occurring at the anode of the electrolytic water equipment involves a multi-electron transfer process,and the kinetic reaction is slow,which is a key factor restricting the efficiency of the entire hydropower electrolysis device.At present,the main stable commercial OER catalyst is iridium-based catalyst,which is expensive,scarce reserves and other disadvantages limit the large-scale application of water electrolysis equipment.In recent years,the two-dimensional carbon-based nanomaterials,which can provide potential reaction sites and abundant adjustable electronic structures,and the RuO₂-based materials,which are cheaper than the precious metal iridium and have excellent OER catalytic activity,have become the frontiers and hot spots in the development of efficient OER electrocatalysts.Although many carbon-based OER catalytic materials have been reported,carbon-based materials provide a rich tunable electronic structure,but also bring great challenges to the design of catalysts.The evolution mechanism of the active site in the real oxygen evolution reaction environment and the theoretical design strategy of the catalyst are still unclear.In addition,RuO₂-based materials have both high activity and poor stability,and the reactivity-stability tradeoff problem that needs to be solved has hindered the design of efficient stabilized catalysts.In recent years,with the rapid development of density functional theory（DFT）in the field of material design,the concept of activity descriptor relates the electronic structure information of materials with theoretical/experimental activity,which provides an effective method for understanding the source of catalytic activity and the establishment of structure-activity relationship,and further provides a powerful guide for the design and synthesis of efficient electrocatalysts.Therefore,this paper takes carbon-based and RuO₂-based materials as the main body,aiming at the key problems such as unclear theoretical design method and urgent improvement of activity and stability of OER electrocatalyst.With the assistance of DFT calculation,The active configuration,electronic structure properties and OER activity origin of non-noble metal carbon-based atomically dispersed catalytic materials and non-noble metal doped RuO₂-based materials were systematically analyzed and screened,and a variety of activity descriptors suitable for carbon-based and RuO₂-based materials were proposed.Then,under the guidance of activity descriptors,carbon based and RuO₂-based OER electrocatalysts used in alkaline and acid electrolyzer equipment were synthesized by experiments,and the structure-activity relationship between catalytic activity and electronic structure properties was explored.The main research contents are as follows:1.Through theoretical simulation,the activity source and activity control mechanism of oxygen electrode reaction of atomically dispersed catalysts with bimetallic sites were understood from two aspects of active structure evolution and electronic structure calculation.Based on the electronic structure information obtained by DFT calculation,the activity descriptors,d-orbital spin state gap（?ξ）and active site symmetry（?d）,are constructed,which can well describe the change trend of bimetallic site intrinsic OER and oxygen reduction reaction（ORR）activity.2.Based on the symmetry descriptor of active site proposed in Content 1,the influence of symmetry on OER reactivity and reaction mechanism was systematically analyzed,and an OER electrocatalyst based on g-C₃N₄ with an asymmetric structure of metal and four nitrogen atom coordination（MN₄）active site was proposed.Compared with the symmetric active sites,the asymmetric active sites showed a dynamic oxygen adsorption reaction mechanism and higher theoretical activity.OER electrocatalyst with outstanding intrinsic activity was synthesized by experiments under the guidance of activity descriptor and applied to alkaline electrolyzer equipment.A series of relevant experiments and DFT calculations verified the guiding role of symmetry descriptors in the design of carbon-based OER electrocatalysts and explored the structural-activity relationship between the structure of MN₄active site and OER activity based on symmetry descriptors.3.Although highly efficient carbon-based catalytic materials were synthesized under the guidance of symmetry descriptors for alkaline electrolytic cell equipment,their stability under strong acid and high potential conditions is still poor,and it is difficult to use in proton exchange membrane electrolytic cell（PEMWE）equipment with higher efficiency and lower energy consumption.Therefore,more stable metal oxide materials in acidic system were selected as the carrier to continue to explore the relationship between OER activity and electronic structure information of materials.By calculating the charge distribution and d orbital electron cloud information in the structure model of RuO₂/Ir O₂ based materials and using DFT,the energy band center and charge state activity descriptors of metal and lattice oxygen are proposed,and the electronic structural property regions with high OER activity are determined.The relationship between metal doping strategies on the electronic structure and catalytic activity of active Ru species in RuO₂ structure was explored.4.Based on the theoretical exploration of metal doping strategies to improve the OER activity and stability of RuO₂-based materials,a theoretical stability evaluation method,namely the free energy of metal dissolution reaction,was further proposed for RuO₂-based materials,which was then combined with the theoretical activity evaluation method.A theoretically efficient and stable co-doped RuO₂ material with niobium and molybdenum was selected from a variety of non-precious metals.Its moderate price and d-orbital distribution regulate the adsorption capacity of active ruthenium species to oxygen-containing intermediates,improve the OER activity,and only 1.44V voltage can reach the current density of 10 m A cm^-2 under acidic conditions.To reach 1 A cm^-2 in PEMWE equipment requires only 1.76 V voltage and shows excellent stability.In addition,a lattice control strategy is proposed and verified by combining theoretical simulations and experiments.The lattice spacing of（110）crystal faces can be used as a descriptor to effectively correlate the activity and stability of RuO₂-based materials.