Study On The Regulation Of Electrochemical Oxygen Evolution Performance Of IrO₂ Composite Catalyst

The air and water pollution poblems caused by consumption of fossil energy and emission of pollutants have already been the focuses of social concern.The electrochemical reactions show promising application in producting hydrogen through the transformation of solar and wind energy and solving the air pollution problem via optimizing the energy structure.Meanwhile,the application of advanced oxidation environment,especially the anodic reaction which has a strong oxidation ability,directs the way to degrade refractory pollutants in water.Therefore,anodic electrocatalysis has great application potential in sustainable energy conversion as well as solving environmental pollution problems.IrO2 is widely used in electrochemistry and regarded as one of the most active and stable oxygen reaction reaction?OER?catalysts.With an eye to the basic scientific issues in electrochemical anode reaction,we explored the regulation of IrO2 catalyst OER reaction performance in acidic environment for better in-depth understanding of the science of anode reaction and realizing the wide application of electrochemical technology in green chemistry and environmental pollution solutions,and the main research results as listed as follows:?1?Study on the effect of metallic Ir on OER activity of traditional IrO2.The metallic iridium is usually found during IrO2,but failed to be further discussed.Here we prepared Ir-IrO2 catalyst,and found the presence of Ir influence the activity of IrO2.As evidenced by characterizations,the metallic iridium is buried by IrO2,but can influence the electron distribution of IrO2,and multi-valence of iridium is found during electrochemical reaction,as a result the OER activity is improved.A low onset over-potential of merely 203 mV and a Tafel slope of 53mv dec-1 were obtained for the prepared catalyst Ir-IrO2₀.5AF.In addition,Ir-IrO2₀.5AF catalyst retained high activity for long time under constant potential polarization.The enhanced performance is attributed to the introduction of lower valence Ir as hydrogen acceptor:hydrogen transfers from-OOH intermediate in OER to adjacent H acceptor site,forming intermediate with lower Gibbs free energy,and resulting in higher activity.The present study emphasizes the important role of composition with lower valence in establishing H acceptors and contributes a variety of opportunities toward rational designing of efficient and stable electro-catalysts.?2?Study on the effect of nano morphology on OER performance of IrO2.The Cu2O nanowire was used as template for hydrothermally growing iridium electrochemical catalyst,after removing the template,the Ir-IrO2 nanotube was formed.The nanotube morphology enlarge the electrochemical surface area,more active sites,and improved OER activity when comparing to IrO2.?3?Enhanced OER performance via interface engineering of nano IrO2 supported on two-dimensional birnessite material.The location of Ir is achieved by the chemical adsorption of Ir on Mn-O hanging bond at the birnessite surface and the further transferred to IrO2 nano-crystal in hydrothermal reaction.The coordination of Ir-O-Mn is formed on the interface,and lattice mismatch leads to lattice distortion in IrO2.At the same time,the different bonding strength of Ir-O and Mn-O leads to charge transfer between nano IrO2 and the birnessite.realizing the interaction between catalyst and the support.With peak shifting in?101?facet and without shifting in?110?facet,XRD diffraction results reveal that the c-axis is shorten and IrO2 crystal is distorted.The XPS spectrum results indicate that there is electron transfer from Ir to the substrate,resulting in higher iridium oxidation state than Ir?.The IrO2 crystal distortion and Ir oxidation state change are further confirmed by XAS spectrum.On account of these electronic manipulations being favorable to the oxygen evolution reaction,the as-synthesized composite exhibited excellent OER activity and stability.The electrochemical surface area,mass activity and intrinsic activity of IrO2/Mn-Co?2:1?-birnessite is about 2,6,and 2 times higher than IrO2.The improved catalytic nature was followed by the enhancement in the electrochemical active surface area,mass specific activity and intrinsic activity.Moreover,the Tafel slope of 42 mV dec-1 reveals better reaction kinetics for IrO2/Mn-Co?2:1?-bimessite than many previously reported catalysts despite the low precious noble metal content in the as-synthesized composite.Conclusively,we have proven that the catalyst-support interaction holds vital importance in the rational design of electrochemical catalysts.?4?Research on the catalyst-support effect on OER performance of twisted MnO2 nano-sheet supported IrO2.We report an effective strategy to lower Ir consumption and boost OER performance in acid by loading IrO2 onto MnO2,in which the IrO2 crystals are well dispersed,and undergo a so-called z-extension Jahn-Teller distortion in the octahedral structure.Here,we introduce Mn oxide as substrate by making use of its large surface area,strong acidic resistance,and low electrical resistivity.Layered ?-MnO2 can be chemical synthesized effectively and conveniently when mixing Mn2+precursor and alkaline solution containing hydrogen peroxide.In this way,through a simple hydrothermal method by mixing Iridium and Manganese precursor together,MnO2 with thin and flexible features could be tightly overlain by the Ir oxide nanoparticles.Such combination can afford the composite catalyst?1?largely exposed IrO2 active sites in that they are tightly anchored by MnO2,preventing undesired aggregates,?2?strong corrosion resistance against acid as IrO2 covers the surface,?3?low electrical resistivity based on the intimate connection between the active electro-chemical catalyst and substrate,and?4?an optimal modification to IrO2 electron structure as a result of the coupling between the two materials.These merits together endue the IrO2-MnO2 catalyst exceptional OER performance in acid solution,resulting in a low onset potential?200 mV?,distinct increase in durability,while the consumption of Iridium is only 30-40%molar ratio.