Preparation Of Hierarchical Nano-porous Materials Applied In Water Splitting

With the development of industrial society,cleaner energy production technology is becoming more and more important.Electrolytic water technology has attracted many researchers'attention because it can help store renewable energy such as solar energy and produce high purity oxygen and hydrogen.There are two semi-reactions in electrolytic water,that is,hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.At present,Pt/C?HER?and RuO₂?OER?,have been recognized as excellent electrocatalysts,but the large-scale application is impeded by the scarcity and high cost associated with precious metals.The development of efficient non-precious metal catalysts to drive proton reduction and oxygen evolution at lower overpotential and higher reaction rates is essential for the large-scale popularization of electrolytic water technology.With the advantages of high specific surface area,rich active sites and adjustable mass transfer rate,hierarchical nanostructured materials are promising catalysts,which have attracted much attention in many fields due to their unique structure and excellent performance.In this paper,the relationship between hierarchical nanostructure catalysts and their performance is studied.The main results are as follows:?1?MoS₂ has a low theoretical free energy of hydrogen adsorption,but its active sites are mainly concentrated on the edge,and the poor conductivity further inhibits its HER performance.The P-MoS₂ hierarchical structure was synthesized by using MoO₃nanorods as sacrifice template.This material has excellent catalytic performance for hydrogen evolution reaction,and the overpotential is only 98 mV at a current density of 10 mA·cm^-2 in 1 M KOH electrolyte,It is much lower than MoS₂ two-dimensional nanosheets,and this strategy provides a new idea for optimizing the performance of MoS₂ by using phosphorus-doped and sacrifice template to obtain hierarchical structure.?2?The catalytic activity of CoSe₂ for oxygen evolution reaction has been difficult to improve.The design of hierarchical structure is a feasible strategy to improve catalytic performance,we designed a controlled-selenylation self-templating strategy for synthesizing hierarchical structural oxygen-modified O-CoSe₂-HNT electrocatalyst.Benefitted from advanced structural design,the hierarchical structural O-CoSe₂-HNT catalyst with oxygen-rich surface exhibits the highest OER activity with the lowest overpotential of 252 mV to achieve the current density of 10 mA·cm^-22 with respect to CoSe₂?356 mV?,IrO₂?330 mV?,and RuO₂?280 mV?.After 2000 cycles and35 h chronoamperometry,the OER performance of O-CoSe₂-HNT catalyst shows no obvious degradation,suggesting good stability.There is little change in morphology,crystal structure and chemical components.?3?Finally,the concept of constructing hierarchical structure is introduced into overall water splitting.Two-dimensional Mn-CoP nanosheets were synthesized by using ZIF-67 as template.The catalyst exhibits good electrocatalytic performance for both HER and OER,the catalyst shows higher catalytic activity with small overpotential of 148 mV to achieve the current density of 10 mA·cm^-22 in 0.5 M H₂SO₄,and exhibits oxygen evolution catalytic performance comparable to that of RuO₂ in 1M KOH.