Preparation And Electrocatalytic Performance Study Of Two-dimensional Noble Metal-based Catalysts

Electrocatalytic water splitting is considered as one of the most promising hydrogen production strategies due to its high reaction efficiency,relatively pure reactants,and environmentally-friendly characteristics.Among them,the strategy to improve the oxygen evolution reaction OER(Oxygen Evolution Reaction)activity of transition metal oxides and hydroxides usually depends on the optimization of their electronic structures,which can be effectively modified by adding transition metals to iridium-based oxides.Compared with single metal,the bimetallic design can not only reduce the noble metal load,but also provide a valid strategy to adjust the electronic structure,thus improving the intrinsic activity of the catalyst.At the same time,replacing the OER reaction at the anode with the hydrogen oxidation reaction HzOR(Hydrazine Oxidation Reaction),which has a lower thermodynamic potential,is an effective strategy to reduce the electrolysis voltage.Similar to traditional water electrolysis,hydrazine-assisted water electrolysis hydrogen production is based on the existing cathodic HER(Hydrogen Evolution Reaction)reaction and the use of hydrazine oxidation reaction at the anode.Compared with the OER reaction,the hydrazine oxidation reaction has significant thermodynamic advantages,greatly reducing the voltage required for electrolytic hydrogen production.Hydrazine hydrate has extremely high toxicity and is often residual in various industrial wastewater.Therefore,designing a HzOR catalyst with high activity and adaptability to various electrolytic environments is not only beneficial for the application of hydrazine oxidation assisting hydrogen evolution systems,but also for the effective treatment of wastewater.It is a challenging and attractive task.The catalytic activity of electrocatalysts often depends on the intrinsic activity of the catalytic active sites and the number of catalytic active sites.The unique morphology of two-dimensional(2D)layered materials has advantages in exposing the number of catalytic active sites,while precious metal materials have shown superior intrinsic activity compared with non-precious metals in previous studies.In addition,some design and regulation strategies such as carrier optimization,defect engineering,construction of heterogeneous interfaces,doping,etc.can also affect the surface properties of catalysts and influence their catalytic activity.Therefore,how to prepare excellent 2D layered catalysts with precious metals reasonably and effectively has become the focus of this study.Based on this,this article explores two types of precious metal layered materials and applies them to three typical catalytic reactions,namely,HER,OER,and HzOR reactions,specifically including the following works:(1)Rh/RhOx nanosheets with a Rh-O-Rh interface were prepared by strong alkaliassisted thermal synthesis and subsequent H2 reduction treatment.The electrocatalyst showed excellent performance for HER under all pH conditions,outperforming Pt/C and most HER catalysts currently available.Specifically,the current density of 10 mA cm-2 was achieved for HER under electrolyte conditions of 1.0 M potassium hydroxide,1.0 M PBS,and 0.5 M sulfuric acid with only overpotentials of 17,39,and 31 mV,respectively.At the same time,the catalyst also showed excellent working stability under long-term HER reaction,successfully constructing a 2D precious metal oxide catalyst with advantages in HER.(2)Based on the previous work,the catalytic performance of two-dimensional ruthenium oxide nanosheets was explored in the oxidation of hydrazine and applied as a bifunctional catalyst in an OHzS system.In the OHzS system,under the conditions of 1.0 M potassium hydroxide,1.0 M PBS,0.5 M sulfuric acid electrolyte,and a certain concentration of N2H4,the voltage only needs to be 0.068,0.268,and 0.348 V,respectively,to achieve a current density of 10 mA cm-2.In addition,the Rh/RhOx promotion mechanism was further explained by density functional theory(DFT).The presence of O atoms can effectively activate Rh on the surface of Rh/RhOx,reducing the entire reaction barrier,which is one of the important reasons for the excellent performance of Rh/RhOx-500 catalyst.(3)A CoIr bimetallic nanosheet was prepared by alkali-assisted mechanochemical method and applied in oxygen evolution reaction(OER).The optimal Ir0.3Co0.7Ox nanosheet showed further improved catalytic performance under the regulation of Co while maintaining a 1T phase.In a 1 M KOH solution,the Ir0.3Co0.7Ox current density reached 10 mA cm-2 with only an overpotential of 186 mV,and the Tafel slope was about 33.7 mV dec-1,which was much better than commercial IrO2 and most current OER catalysts.In addition,the synthesized Ir0.3Co0.7Ox maintained good performance after 160 hours of operation.The excellent activity of Ir0.3Co0.7Ox can be attributed to the introduction of Co species with different lattice sizes,producing metal vacancies.The ultra-thin two-dimensional nanosheet structure exhibited a large specific surface area and provided more active sites effectively.