Constructing Cobalt-Based Chalcogenides Nanoarrays On Carbon Fibers And Their Application For Electrocatalytic Hydrogen Evolution

Despite many causes of haze,over-reliance on fossil fuels is considered to be the main one.In today's energy mix,fossil fuels such as coal,oil,and gas account for over 80%of the share.Hydrogen,with a high heat of combustion,is an extremely crucial clean energy.To achieve the practical utilizations of hydrogen energy need to solve many problems,one of which is how to produce fuel hydrogen efficiently.Nowadays,the overwhelming majority of industrial processes for producing hydrogen are SMR and coal gasification,which both lead to greenhouse gas CO₂ emissions.Water electrolysis with high yield and purity,is environmental friendly and reproducible.However,to reduce energy consumption,electrolysis of water often requires expensive and limited precious metals?e.g.,Pt?as HER catalytic electrode.Meanwhile,to make the cost lower,precious Pt must be placed by some cheap electrocatalysts.TMCs are one of the most efficient HER catalytic materials with low prices.In last decades,considerable efforts have been devoted to exploring TMCs HER electrocatalysts?e.g.,MoS₂ and WS₂?and have made great achievements.In fact,the element Co is over 27 times the abundance on earth of Mo and W.Therefore,more attention should be paid to study cobalt-based chalcogenides.In this thesis,we focused on constructing cobalt-based chalcogenides nanoarrays on carbon fibers and their application for electrocatalytic HER.The main research results as follow:1.Heteroatom doping is a feasible approach to adjust catalytic performance of the HER catalysts.We report a design of Fe-doped Co₉S₈ nanosheets grown on carbon cloth?Fe-Co₉S₈NSs/CC?as a hydrophilic 3D monolithic electrocatalyst for efficient HER.The water contact angle and electrochemical measurements proved that the resultant material was hydrophilic for its nano hierarchitectures and dopant Fe enhanced the catalytic capability of singular Co₉S₈.In1.0 mol L^-1 KOH,the Fe-Co₉S₈ NSs/CC possessed a relatively small Tafel slope(95.3 mV dec^-1)and required the overpotential of 83 mV to achieve 10 mAcm^-2.Meanwhile,it showed good cycle stability and durability over 20 h static test.2.MOFs can act as precursors to the design and construct of varied nanostructured materials which may be difficult to produce in other ways.We explore a calcination and hydrothermal sulfuration strategy to transform the precursor Co-MOF nanorods into CoS nanorods on carbon cloth.After that,NiCo-LDH nanosheets were decorated on CoS/CC via a one-step electrodeposition method to form the heterostructural CoS@NiCo-LDH/CC.Due to its structural and compositional merits,the as-prepared CoS@NiCo-LDH/CC exhibited remarkable electrocatalytic activity for HER.It required an overpotential of 124 mV to attain a current density of 10 mA cm^-2,and its Tafel slope was only 89 mV dec^-1.Notably,after chronopotentiometry test for 20 h,the overpotential of which decreased 18 mV instead.3.We put forward a serial ionexchange reaction and selenation strategy to prepare novel yolk-shelled Ni-Co-Se dodecahedral nanocages on carbon cloth?Y-S Ni-Co-Se/CC?.ZIF-67@LDH/CC was first synthesized by a simple ion-exchange reaction,followed by a hydrothermal selenation process to form Y-S Ni-Co-Se/CC.Moreover,the composition of the as-prepared yolk-shelled Ni-Co-Se nanocages was a mixture of Co_0.85Se and Ni_0.85Se?Co/Ni atomic ratio of about 2.42?.Due to their structural and compositional merits,the as-prepared Y-S Ni-Co-Se/CC exhibited remarkable electrocatalytic activity and long-term stability?over 80%current retention for at least 18 h?for HER.It required an overpotential of 250 mV to attain a current density of 10 mA cm^-2,which was 162 mV less than that of the Y-S Co_0.85Se/CC counterpart.