Preparation And Catalytic Performance Of Cobalt-Based Borides(Phosphides,Nitrides)

Industrial development and technological progress have brought the problems of environmental pollution and energy shortages.Catalytic technologies rely on efficient catalysts provide opportunities for clean energy and conversion/degradation of pollutants.Hydrogen has the smallest molecular weight,and it is also one of the most promising elements at present.For example,the water splitting to produce H2 and reduction of nitro-hydrogenation to obtain low-toxic,high-value-added amino-compounds have become the current research hotspots.Noble metals are of most effective catalysts,but its high cost and low reserves limit the practical application.Thus,the development of high-efficiency,low-cost non-noble metal catalysts is the key for the application of relevant reactions/techniques.Cobalt is cheap and can combine with varieties of anions(boron,nitrogen,phosphorus)to achieve rich and varied structures,and finally,to form Co-based borides(phosphides,nitrides)with precious metal-like structures.Based on the important influence of the structure on performance of the material,this theme aim to develop an effective method for the structural regulation of Co-based borides(phosphides,nitrides)to improve their performance in hydrogen production via catalytic water splitting and nitro-amino conversion reactions.The research contents of this paper mainly includes the following three aspects:Firstly,we have selected Co(NO3)2-6H2O as Co source,and modified CNTs used as carriers to obtain cobalt oxide/CNTs precursor by hydrothermal method.The Co-B/CNTs materials was obtained by using NaBH4 as a boron source through controlled heat treatment of cobalt oxide/CNTs precursors under N2 protection conditions,and can be used as a catalyst for hydrogen production by water splitting.The test results show Co-B/CNTs material has good HER performance.At the current density of 10 mA cm-2,the overpotential is 190 mV and 284 mV under acidic and alkaline electrolyte conditions,respectively,which proves that borides have potential in the field of electrocatalysis.Secondly,we also explored and synthesized a bifunctional catalyst COP/NCS with excellent performance.The Co-HQ precursor with a sheet structure was successfully prepared at room temperature through the coordination of 8-hydroxy quinoline(8-HQ)with Co(NO3)2-6H2O(Co-HQ precursor).The cobalt phosphide embedded in lamellar carbon(CoP/NCS)can be obtained by the calcination of precursor under N2 protection in the presence of NaH2PO2 as the phosphorus source.The CoP/NCS can be used as a high-efficiency catalyst for HER and OER with good stability.The ?10 of HER and OER are 71 mV and 254 mV,respectively.To reach a current density of 10 mA cm-2,the voltage is only 1.63 V for overall water splitting.Finally,based on the above study,we continued to explore the reaction conditions in the coordination of cobalt with 8-HQ to obtain complexes with specific morphology.It is shown that a spherical Co-HQ-S precursor can be obtained by solvothermal reaction of Co2+ and 8-HQ.After further heating treatment under NH3 atmosphere,the cobalt nitride(Co4N)embedded into N-doped carbon(NC)spheres can be formed.The analysis indicates that the small-size Co4N is evenly distributed in the carbon spheres,forming a structure similar to"Dragon Fruit".The Co4N/NC composite can be used as a highly efficient and stable catalyst to catalyze the conversion of p-nitrophenol to p-aminophenol.The 0.2 mM p-nitrophenol solution(30 mL)can be 100%converted in only 4 min in the presence of 5 mg of Co4N/NC.The Co4N/NC also has good cycle stability,and the conversion efficiency can still reach more than 90%after 5 times of catalytic reaction with easy separation ability by applied magnetic field.