Study On Preparation And Electrocatalytic Performance For Polycrystalline CoP/CoP₂ And LaFe_xNi_1-xO₃ Materials

Along with the rapid increase of human demand for energy,hydrogen?H₂?,as a renewable,clean and environmentally friendly energy source,has been considered as a promising alternative to replace conventional fossil fuels in the future.Currently in the field of electrocatalysis,electrolyzed water technology used to product hydrogen is widely favored.Usually a complete electrolyzed water process is composed of two half-reactions,namely,hydrogen evolution reaction?HER?ofanode and oxygen evolution reaction?OER?of cathode.The efficiency of electrolyzed water was determined by kinetic rates of the two half-reactions.In this paper,polycrystalline CoP/CoP₂ structures and perovskite-type Fe-Ni bimetallic oxide materials were successfully prepared,which shows superior electrocatalytic performance in the process of electrolyzed water.This work report mainly includes the following two parts:?1?2-methylimidazole was used as a crosslinking agent to crosslink metal Co and phytic acid molecules,polycrystalline transition metal phosphide?CoP/CoP₂?materials was prepared by hydrothermal reaction and pyrolysis phosphate precursors.This synthetic method not only effectively controled the particle agglomeration of the metal phosphide during high-temperature pyrolysis,to maximize exposure its catalytically active sites,but also introduced a small amount of CoP₂ crystal structure.Compared with pure phase CoP,polycrystalline CoP/CoP₂ presented superior performance of electrocatalytic.Overpotentials of only 250 mV and 239 mV were required to support the current densities of 10 mA·cm^-22 and20 mA·cm^-22 for the oxygen evolution reaction and hydrogen evolution reaction,respectively.?2?The OER reaction mechanism of Fe-Ni bimetallic oxide was investigated by using AB_xB'_1-xO₃ perovskite material as the ideal framework model,for its standard cubic crystal structure.A series of different LaFe_xNi_1-xO₃?x=0,0.1,0.25?catalytic materials were prepared by sol-gel synthesis and calcinated at high temperature condition.It is found that LaFe_0.1Ni_0.9O₃ material possesses the best catalytic performance.We further analyzed,the causes of improvement for electrocatalytic activity and found that the substitution of Fe,which was taken by a suitable ratio?Fe:Ni=1:9?,stimulated the emergency of more active species during the oxygen evolution reaction.It was also confirmed that the increase of lattice oxygen and Ni^IIIII species was the key to achieving the improvement of catalytic performance.These changes,coordination form of Fe with Ni,and valence state of the active element Ni,were caused by Ni substituted by Fe randomly at B site.Furthermore,we found that La,where located at A site,can help the catalyst anti-aging compared with the transition metal oxide of amorphous state,which makes the inorganic perovskite material more tolerant than other electrocatalytic materials in practical application.