Synthesis Of Two-dimensional Molybdenum-based Nitrogen (phosphide) And Study Of Its Electrocatalytic Water Splitting Performanc

The rational development and utilization of energy is a global focus.The use of fossil fuels not only causes periodic energy shortages,but also has a negative impact on the environment.Developing clean energy is the key to overcoming these issues.The H2 has a high combustion value with the water as combustion product,making it an efficient and clean fuel.Electrocatalytic water splitting is one of the sustainable ways to produce H2.The process requires a high overpotential to be driven.At present,precious metals(Pt for HER,RuO2 or IrO2 for OER)are the most effective electrocatalysts,but they are limited by scarcity and high cost.Transition metals(Mo,Co etc.)have incompletely filled outer d electronic structures,so it is of practical significance to develop transition metals as catalysts.Through morphology control and heterojunction engineering,the electronic structure of the interface can be adjusted to form a highly active catalytic site.Combining the advantages of 2D materials and heterojunctions,a new method for constructing two-dimensional transition heterostructures is proposed to achieve efficient water electrolysis.The main research contents are as follows:A porous two-dimensional CoO/Co5.47N/Mo2N heterojunction was constructed by using Co-Co LDH nanosheets as the substrate and cobalt source.The Co-Co LDH nanosheet was firstly synthesized,and a ZIF-67/Co-Co LDH was formed based on partially replacing Co with 2-methylimidazole in a methanol system.Further,PMo12 was introduced to form POM/ZIF-67/Co-Co LDH,which was subjected to hightemperature nitriding treatment to obtain a porous CoO/Co5.47N/Mo2N nanosheet heterojunction.The heterojunction of Co5.47N and Mo2N in can form the high active sites.The porous structure formed by high-temperature treatment accelerates the mass transfer process,and the two-dimensional structure also allows for the maximum exposure of catalytic sites.The advantages enable CoO/Co5.47N/Mo2N excellent HER performance.When the current density is 10 mA cm-2,the overvoltage is 37 mV(without ir correction).The electrolytic cell assembled with CoO/Co5.47N/Mo2N as the cathode and Mo/Ni2P/Fe2P as the anode can provide a current density of 10 mA cm-2 with a working voltage of only 1.47 V,and can be driven by solar panels to produce hydrogen(Pt/C‖RuO2 is 1.58 V).By using Co(OH)2 nanosheets as the substrate,the Ni was introduced into the synthesis to obtain Co/Ni ZIF-67/Co(OH)2 composite.The PMo 12 was further introduced by the water bath method to obtain PMo12/Co-Ni ZIF-67/Co(OH)2.After high-temperature treatment in ammonia atmosphere,the Mo0.84Ni0.16/Co5.47N/Mo2N catalyst was obtained.The optimized catalyst exhibits good HER and OER performance under alkaline conditions.The Mo0.84Ni0.16/Co5.47N/Mo2N needed an overpotential of 65 mV for HER and 241 mV for OER in 1.0 M KOH(10 mA cm-2).The electrolytic cell assembled with Mo0.84Ni0.16/Co5.47N/Mo2N as the cathode and anode requires a working voltage of 1.55 V(1.57 V for Pt/C‖RuO2)to provide a current density of 10 mA cm-2.Water splitting requires matching of efficient OER and HER catalysts.Based on the synthesis of HER catalyst,a highly active OER catalyst was constructed by using NiFe LDH as precursor.In ethanol solvent,the NiFe/PMo12 precursor was obtained by the impregnation and evaporation route.The ratios of Ni,Fe,and Mo were adjusted by controlling the reaction time.After phosphating,the two-dimensional phosphating Mo/Ni2P/Fe2P was obtained.The two-dimensional heterogeneous structure and multielement synergy of the catalyst result in good OER activity.When the current density is 10 mA cm-2,the OER overpotential of Mo/Ni2P/Fe2P in 1.0 M KOH is 201 mV.There is the low overpotential at high current density with good stability.