Study On Synthesis Of Co₉S₈-based 2D Materials And Electrocatalytic Performance For Hydrogen Evolution Reaction

Environmental pollution caused by large-scale fossil fuel combustion,global warming and energy crisis has been the focus of the world.Hydrogen is considered to be an ideal energy carrier to replace traditional fossil fuels due to its high energy density,excellent combustion performance,and cleanness.Water electrolysis is a promising hydrogen production method that converts renewable energy into hydrogen molecules.Noble metals?e.g.,Pt,Pd,and Ru/Ir oxide?are the most effective electrocatalysts for facilitating electrocatalytic water splitting,but their higher costs and rarity are major hurdles for large-scale practical applications.Thus,designing high-performance,inexpensive,and robust electrocatalysts for the hydrogen evolution reaction?HER?based on earth-abundant elements is still at the frontier of electrocatalysis research.Transition metal sulfides and their composites are inexpensive,rich in raw materials,and good stability,while also exhibit high performance in the field of hydrogen production from electrolysis of water.In this paper,a novel two-dimensional?2D?nanocomposite?Co₉S₈/NSG?was successfully fabricated by the simultaneous formation of cobalt sulfide?Co₉S₈?triangular nanosheets and N,S-doped graphene?NSG?using monomolecular cobalt-thiourea with grapheme as the precursor via a facile low-temperature and one-step direct pyrolysis in organic amine solvents.The Co₉S₈/NSG was used for the study of electro catalytic hydrogen evolution in acidic media.Adding graphene carrier can effectively regulate the morphology and improve the performance of electrocatalytic hydrogen production.At the same time,the morphology and properties can be controlled by changing the pyrolysis temperature.The optimal composite Co₉S₈/NSG-220 achieved an onset overpotential of 147 mV,a Tafel slope of 97 mV dec^-1,and a good stability with no obvious decay of current after 16 h for the hydrogen evolution reaction?HER?.Based on the experimental investigation and density functional theory?DFT?calculations,the mutual activation effects induced by the electron transfer across the active interface constructed between NSG and Co₉S₈was a key factor in the superior catalytic performance of the HER.The tightly bound sheet-on-sheet structure significantly enhanced the intrinsic catalytic activity by mutual activation effects between the compounds.The above method demonstrates the effect of"one plus one greater than two"in the electrocatalytic process.In addition,the HER performance could be further optimized by doping a moderate ratio of molybdenum?molybdenum-cobalt molar ratio of 5%?into the synthesis system with an onset overpotential of 129 mV,a Tafel slope of 85 mV dec^-1,and a superior stability with substantially no loss of the current density after 16 h for HER.This monomolecular precursor pyrolysis method provides a novel research thought for promoting rational design and optimization of new high-performance functional materials.Two-dimensional nanocomposite(Ni_1.8Co_7.2S₈/NSG)of bimetallic sulfide nanosheets Ni_1.8Co_7.2S₈ grown vertically on N,S codoped graphene?NSG?were prepared by a simple one-step solvothermal method.The Ni_1.8Co_7.2S₈/NSG was used for the study of electro catalytic hydrogen evolution in alkaline media.Within the achieved hierarchical architecture,the interconnected network and the vertical channels formed between the close-contact NSG and Ni_1.8Co_7.2S₈ nanosheets can effectively improve the conductivity of the material and the utilization rate of the catalytic active site.Compared with Co₉S₈ and Ni_1.8Co_7.2S₈ materials,Ni_1.8Co_7.2S₈/NSG shows higher HER performance with an overpotential of 207 mV to reach 10 mA cm^-2 and a low Tafel slope of 92 mV dec^-1 as well as a superior stability with substantially no loss of the catalytic activity of the electrode material after 16 h for HER.This synthesis method provides a new idea for the further development of functional composites composed of non-noble metal sulfides for electrochemical energy conversion systems.