Synthesis Of Hollow Structure PBA And Its Derivatives And OER Electrocatalytic Properties

As an important clean energy,hydrogen energy has attracted wide attention of the whole society.Electrochemical water splitting is an effective way to obtain hydrogen energy.Due to its slow reaction kinetics,oxygen evolution(OER)has become a bottleneck reaction that limits the energy efficiency of water splitting.Designing efficient OER catalysts has become an important research direction in recent years.Structure design and composition control are two important ideas for developing high performance catalyst materials.Hollow nanostructures can provide more catalytic active sites and promote the mass transmission,which is conducive to the improvement of electrocatalytic performance.Cheap transition metal-based catalysts have become a research hotspot in the field of electrocatalysis due to their availability of raw materials,variety,and excellent performance.Prussian blue analogues(PBAs)usually contain two or more transition metal elements,and the synergy between the different elements usually results in better catalytic performance.More importantly,a variety of derived materials can be obtained by simple treatment of PBAs.These derived materials not only inherit the composition advantages of PBAs,but also improve their electrical conductivity after derivative treatment.In addition,it is easy to obtain hollow structure PBAs and their derivatives through reasonable design.In this paper,we designed three kinds of PBAs with hollow structures by anion exchange reaction or cation exchange reaction.The related materials were derived to improve the catalytic performance of OER effectively.1.Using ZIF-67 hollow spheres as precursor,a hierarchical hollow structure CoFe PBA was obtained by anion exchange method.The material was subjected to a series of heat treatments in a nitrogen atmosphere.The effects of heat treatment temperature on the morphology,structure and composition of materials were investigated by systematic characterization of the samples.The sample treated at 350℃ showed the best OER catalytic performance among all samples.In 1 M KOH electrolyte,the overpotential is only 291 mV when the current density is 10 mA cm-2.This is because the sample not only maintains the hollow structure of the precursor well,but also transforms into a multi-component composite material under suitable heat treatment conditions.The presence of alloys and metal elements brings more catalytic active sites and improves the conductivity of materials.2.Prismatic hollow CoNiFe PBAs with different contents of Co and Ni were prepared by anion exchange method using acetate hydroxide as precursor.CoNiFe PBAs was phosphating at 350℃ and the corresponding derived materials were obtained.The influence of cobalt and nickel content on material size was investigated by morphological characterization.When the ratio of cobalt to nickel is 3:1,the precursor has the smaller size.The corresponding CoNiFe PBA and its phosphide also have the smaller size,and show excellent electrocatalytic performance.The reasons for the difference in the performance of electrocatalytic OER were analyzed based on the size of materials and the content of metal elements.3.A hollow cubic structure MnFe PBA was synthesized by the regulation of sodium citrate.A cubic hollow MnCoFe PBA was prepared by cation exchange method.MnFe PBA and MnCoFe PBA were phosphating at 400℃.The effects of Co on the morphology and electrocatalytic properties of the materials were studied.MnCoFe PBA maintains the hollow structure of MnFe PBA,and the introduction of cobalt metal provides more active sites.The phosphating product of MnCo Fe PBA showed better catalytic activity and stability when used as OER catalyst.