Design,Synthesis And Water Oxidation Properties Of Iron Group Elements Materials

The Energy and environment have become two difficult problems in the sustainable development of the world.The development of clean,non-pollution and sustainable energy has attracted increasing attetion.Hydrogen is a green and renewable energy,which is an effective way to solve the world energy crisis in the future.Water splitting is an effective way to produce hydrogen.Water splitting involves two half reactions-a hydrogen evolution reaction and an oxygen evolution reaction.Compared with the hydrogen evolution reaction,the oxygen evolution reaction is the bottleneck of water splitting.At present,noble metals?Ru,Ir?oxides have good oxygen evolution performance.However,the low abundance and high price restrict noble metals application in industrial production.Therefore,it is urgent to find non-precious and stable catalyst to replace the precious metal catalyst.At first,we studied the effect of defects on the oxygen evolution ability.The electrocatalytic water oxidation catalysts with hollow nanocube Ni-Fe double hydroxide and manganese doped porous nickel oxide nanosheets were designed and synthesized.Secondly,the photocatalytic ability of CoP to produce oxygen in dye sensitized system was carried out.Finally,the photoelectrochemical water oxidation of organic metal complex was loaded on the surface of the BiVO₄ photoelectrode was studied.The main contents are as follows:1.In this study,etching from Cu₂O template,amorphous Ni-Fe bimetal hydroxides with hollow nanocubes are synthesized.The resulting sample of Ni_0.75Fe_0.25?OH?_x exhibits excellent activity and good durability for water oxidation,which affords a overpotential of 310 mV at current density of 10 mA cm^-22 in alkaline solution.The enhanced activity attributed to 1)according to the pH dependence of the redox peaks,Pourbaix slope¹16 mV/pH is obtained,and it suggests a two proton-one electron transfer that has been thought to be instrumental for the evolution of molecular oxygen;2)The oxygen vacancy in the Ni_0.75Fe_0.25?OH?_x sample contributes to the adsorption of water.3)The unique hollow amorphous structure of the Ni_0.75Fe_0.25?OH?_x sample gives it a large specific surface area and more active sites.The well-maintained hollow morphology and amorphous structure metal hydroxide obtained by novel and facile route can be extended to design other efficient electrochemical water oxidation catalysts.2.Identifying active sites of oxygen evolution reaction?OER?catalysts is essential for studying water oxidation mechanisms.Herein,the active site of nickel oxide nanosheets by manganese modulation is investigated in electrocatalytic oxygen evolution system.The intrinsic catalytic activity Ni³⁺(t⁶_2ge_g¹)and Jahn-Teller active Mn³⁺(t³_2ge_g¹)species,which act synergistically to promote the elctrocatalytic oxygen evolution reaction.X-ray absorption near edge structure ?XANES?indicates that the Ni³⁺and Mn³⁺in Ni_0.75Mn_0.25.25 nanosheets should result from nickel vacancies and oxygen vacancies,respectively.Density functional theory?DFT?calculations indicate that the Ni and Mn act synergistically to promote the forming O-O bond.Our work provides a comprehensive understanding the active site of porous nickel oxide nanosheets by manganese modulation and rational design of electrocatalysts with precisely engineered structures and electrical properties.3.Metal phosphides are good electrocatalysts and photocatalysts for hydrogen production.We use Co-Co PBA as a template to obtain CoP by low-temperature phosphating,low-temperature vulcanization to form CoS_2,and low-temperature calcination to obtain Co₃O₄.At first,we studied the photocatalytic water oxidation performance of CoP,CoS₂ and Co₃O₄ in[Ru?bpy?₃]²⁺-Na₂S₂O₈ dye sensitization system.The oxygen generation kinetics curve indicated that CoP had the largest oxygen production.Through the characterization of high transmission electron microscopy,we found an amorphous structure was formed on the surface of CoP after photocatalytic reaction.In addition,we studied the electrocatalytic oxygen production of CoP,CoS₂ and Co₃O₄ in 1 M KOH solution.A series of electrochemical tests have shown that CoP has the best electrocatalytic performance and good stability.Based on the above results,we believe that the high photocatalytic and electrocatalytic activity of CoP is due to the formation of metal phosphide and metal?hydrogen?oxide core-shell structure during the catalytic reaction,which facilitates the transfer of electrons in photocatalysis and electrocatalysis.4.Bismuth vanadate?BiVO₄?has been regarded as a promising photoanode material for photoelectrochemical?PEC?water splitting owing to its low cost,and small band gap energy?².4 eV?.A simple process is developed for preparing a new type of low-cost metal-organic coordination composed of tannic acid coordinated with Co ions?TACo?as an efficient cocatalyst to eliminate the surface trapping states and suppress the charge-carrier recombination on BiVO₄photoanodes.For the BiVO₄/TACo photoanode,a high photocurrent density of 4.8mA cm^-2 at 1.23 V?vs.RHE,AM 1.5 G?,which approximately 3-fold higher than that of bare BiVO₄.Systematic studies reveal that the enhanced water oxidation performance on BiVO₄/TACo photoanode can be ascribed to the synergistic effect of following factors:?i?The photogenerated holes are directly transferred to TACo layer;?ii?The transferred holes can directly oxidied Co²⁺to generate Co³⁺active sites,which could directly oxidize H₂O to molecular O₂.