Rapid Batch Preparation Of Prussian Blue Analogues/Derivatives And Their Oxygen Evolution Reaction Performance

The two major challenges to the sustainable development of modern economy are increasingly serious environmental pollution and energy shortage.In order to solve these two problems,it is of great significance to develop renewable and sustainable energy to replace traditional energy.Due to its high energy density and environmentally friendly characteristics,hydrogen is a promising clean energy,which can provide impetus for the development of human society in the future,and has been widely studied in the past decades.In order to produce hydrogen economically and efficiently,people have made great efforts and explored some key technologies,among which hydrogen production by electrolysis of water has great prospects because of its high energy conversion efficiency.The process of hydrogen production by electrolysis of water is composed of two half-reactions,the cathodic hydrogen evolution reaction（HER）and the anodic oxygen evolution reaction（OER）.The oxygen evolution reaction is considered as a rate-limiting step,which seriously hinders the improvement of the overall efficiency of electrochemical hydrogen production.Therefore,it is of great significance to develop cheap,efficient and stable electrocatalysts to improve the performance of OER and promote the production of hydrogen from electrolytic water.In the past few decades,advanced catalysts designed for energy related electro-oxidation reactions have received extensive attention.Taking OER as an example,noble metal free（pre-）catalysts usually need to undergo a pre-oxidation process before OER catalysis to generate catalytic active high-value species in situ.It is found that OER mainly occurs at high valence metal sites,and the enrichment of catalytic high valence metal sites is very important to accelerate the OER process.This kind of high valence active species is the real catalytic active site.However,most of the high valence transition metal ions are thermodynamically unstable,which limits the design and manufacture of efficient catalysts for direct OER catalysis.Therefore,it is a promising method to improve the activity of OER to promote the pre-oxidation reaction by in-situ formation of active high valence species.As a typical metal organic framework material,Prussian blue analogues（PBA）have the advantages of open framework structure,controllable metal ion composition,high cycle stability and low cost.Therefore,it is of great significance to develop a rapid batch synthesis route to synthesize PBA as an effective precursor of PBA derivative catalyst for the design and optimization of OER electrocatalyst.High entropy materials（HEM）are expected to make new progress in energy storage and conversion technology due to their excellent mechanical properties,high temperature stability and high chemical stability.By combining PBA material with high entropy material,the author explored a new kind of high entropy amorphous cyanide oxide,and achieved high efficiency and ultra-stable OER performance.The main contents of this thesis include:1.The authors proposed a rapid batch synthesis route for preparing Prussian Blue Analogue（PBA）nanocubes with adjustable composition and uniform particle size.Using this method,four kinds of electrocatalysts,Co Co PBA,Co Fe PBA,Fe Fe PB and Ni Fe PBA were synthesized as effective pre-catalysts for OER,and a series of characterization were carried out.The four catalysts all have typical nanocube morphology,and the preparation time is short and the yield is large,which can reach gram level.Taking Co Co PBA as an example,the OER performance of the catalyst and the pre-oxidation process in the catalytic process were studied.Co Co PBA has the advantages of rich surface active sites,good charge transfer behavior and pre-oxidation reaction from Co²⁺to Co³⁺,which can realize the rapid generation and accumulation of catalytic active Co³⁺sites.Based on the above advantages,Co Co PBA shows significant OER activity.The catalyst can reach a current density of 10 m A cm^-2 at a potential of 329 m V and 195.8 m A cm^-2 at a potential of 1.8 V vs.RHE.Compared with the other three catalysts,Co Co PBA has the smallest overpotential,the largest anode current density,the smallest Tafel slope and excellent intrinsic activity.In addition,after long-term OER operation of the catalyst,the OER performance of Co Co PBA nanocube showed a 5.5 times improvement,which proved that there was an accumulation process of high-valent active species.In addition,the obvious surface reconstruction phenomenon of Co Co PBA can be identified by the catalytic scanning electron microscope（SEM）image,which proves the key role of pre-oxidation process in promoting OER.This work provides a general method for the rapid and batch preparation of PBA-based materials,and clarifies the pre-oxidation process promoting OER catalysis,which can provide useful guidance for the design and optimization of advanced catalysts for energy-related electrooxidation reactions in the future.2.The authors synthesized a kind of high entropy amorphous oxycyanide（HE-CNO）porous nanocube pre-catalyst,which can undergo a rapid pre-oxidation process and produce a large amount of accumulated active substances.Thanks to its amorphous characteristics,high porosity and catalytic ensemble effect,HE-CNO has efficient and ultra-stable OER performance.The catalyst can reach a current density of 10 m A cm^-2 with only 328 m V over potential,and shows excellent stability for up to 72 hours.The I-t stability of the catalyst was tested at 400 m V,and the structural reconstruction of HE-CNO pre-catalyst during OER operation was studied.The mass activity of HE-CNO increased from 12.0 A g^-1 to 181.0 A g^-1,indicating that there was an obvious activation process in the first 20 hours.After the activation stage,the OER activity of HE-CNO decreased significantly after 72 hours of catalytic process,and the mass activity decreased to 146 A g^-1.It is worth noting that the catalytic performance of this high entropy catalyst is still 12.2 times higher than that of the original catalyst,which proves the ultra-stable OER performance of this high entropy catalyst.The discovery of this pre-catalyst can provide a basis for the design of advanced catalysts to promote water cracking,and the explanation of pre-oxidation process can also provide ideas for the optimization of catalysts.