Study On The Synthesis And Electrocatalytic Water Splitting Performance Of Molybdenum-based Compounds

Hydrogen is a non-polluting clean energy source with broad development prospects.Electrochemical water splitting is an ideal route for obtaining hydrogen in pure form.During water splitting,Hydrogen Evolution Reaction(HER)occurs at cathode,and Oxygen Evolution Reaction(OER)occurs at anode,and the overall efficiency depends primarily on the electrocatalysts which were used in the catalytic process.Currently,Platinum(Pt)based catalysts exhibit the highest electrochemical HER performance.Because of the scarcity and high cost of Pt,the industrial implementation is extremely unrealistic thing.On the other side,oxygen evolution reaction is a four electron transfer process,whose high energy barrier result kinetically sluggishness,hence OER hinders the rate of water splitting to a marked extent.Ir and Ru based oxides exhibit the best catalytic performance for OER,but unsteadiness greatly prohibits the large-scale application.Hence,it's a hot research topic to design electrocatalysts which were inexpensive as well as exhibit high electrochemical performance in hydrogen energy production.Molybdenum(Mo)based compounds drawn much attention due to the merits like high earth-abundance,low-cost,and excellent catalytic performance in elelctrochemical water splitting.Molybdenum dioxide(MoO2),a wide bandgap semiconductor transition metal oxide exhibits high electrocatalytic performance over a wide pH range due to its notable low electrical resistivity.In addition,bimetallic oxides poccess suitable Gibbs adsorption free energy for intermediates.In comparison to single metal oxides,bimetallic oxides exhibit superior performance towards OER.Herein,based on this research background,through the microstructural design and component regulation,novel polypyrrole coated nitrogen doped MoO2 nanorods(PPy@N-MoO2)and cobalt-molybdenum bimetallic oxide nanosheets(Co@Co2Mo3O8@CoMoO4)were developed.The respective electrochemical HER and water splitting reaction performances were deduced in detail.The main content includes the following aspects:(1)Through the hydrothermal reaction of molybdenum trioxide and hypoxanthine,a nanorod morphological precursor was obtained.When this precursor was pyrolyzed under inert atmosphere,nitrogen doped molybdenum dioxide nanorods(N-MoO2)were obtained.In the next step,polypyrrole was uniformly coated on the surface of N-MoO2 nanorods for making the final product,PPy@N-MoO2.Being the catalyst for electxocatalytic hydrogen evolution reaction,PPy@N-MoO2 has the following merits:Nitrogen doping modify the electronic structure of MoO2 and optimized the absorption and desorption of hydrogen;One-dimensional nanorod structure inherited from precursor promotes the transfer rate of proton.Polypyrrole with conjugated structure could greatly improve the conductivity,thus the electron transfer rate between electrolyte and electrocatalyst was increased and the kinetics of the reaction were promoted.In addition,polypyrrole acts as protective layer,which inhibits MoO2 from corrosion,thus the stability of the catalyst was improved.In summary,the controlled structural and component designing contributed significantly to the excellent electrocatalytic performance of this novel catalyst both in alkaline and acidic solutions.When the current density reaches 10 mA cm-2,the overpotential is 146 mV and 188 mV,with Tafel slope of 71 mV dec-1 and 75 mV dec-1 in alkaline and acidic media respectively.(2)The hydrothermal reaction of phosphomolybdic acid hydrate with cobalt acetate and subsequent high-temperature treatment in an inert atmosphere yielded a cobalt-molybdenum bimetallic oxide(Co@Co2Mo3O8@CoMoO4)nanosheets.The synergy between Co,Co2MO3O8 and CoMoO4 in nanosheets promoted the electrocatalytic performance.The coexistence of high valent Mo(VI)and the low valent Mo(IV)can balance the charge distribution during the catalytic reaction.The electrocatalytic results towards water splitting reaction indicated that the Co@Co2Mo3O8@CoMoO4 catalyst exhibits excellent performance.When the current density reaches 10 mA cm-2,the overpotential is 270 mV for OER and 242 mV for HER respectively.