| As a mature technology,alkaline water splitting is considered as one of the ideal ways to produce hydrogen because of its advantages such as clean and pollution-free.In order to realize the large-scale application of alkaline water splitting,the development of catalysts with excellent performance for alkaline hydrogen evolution reaction(HER)is a major scientific problem that needs to be solved.Although noble metal catalysts have the highest HER activity,their high cost and scarcity hinder their large-scale application.Therefore,it is important to develop non-precious metal catalysts with high activity and high stability.Molybdenum-based materials show excellent HER activity in water splitting,but their performance still needs to be improved.In this thesis,metal foam supported nickel sulfide and molybdenum sulfide composite catalysts(MoS2/Ni3S2/NF),nickel molybdate catalysts(NiMoO4-xH2O-300)and copper and molybdenum carbide composite catalysts(Cu/Mo2C)were developed for alkaline HER using molybdenumbased materials.The research contents in this thesis are as follow.1.MoS2/Ni3S2 composite catalyst(MoS2/Ni3S2/NF)was generated on nickel foam by a facial one-step hydrothermal method.XRD,Raman,XPS,SEM were used to characterize the catalyst,and it was proved that electron transfer occurred between MoS2 and Ni3S2.MoS2/Ni3S2 contained a large number of gaps,which favorably exposed the internal active sites of the catalyst.The synergy between the MoS2 and Ni3S2 improves the HER performance.In 1 M KOH,MoS2/Ni3S2/NF has an overpotential of 97 mV at the current density of 10 mA cm-2,a low Tafel slope of 40.1 mV dec-1,long-lasting lifetime over 6 hours at a current density of 100 mA cm-2.2.NiMoO4·xH2O nanoneedle arrays were grown on copper foam by hydrothermal method,and annealed at temperatures of 150,300 and 450℃ to regulate the exposure of specific crystal faces of NiMoO4-xH2O.The nanoneedle array and the pore structure on the surface of nanoneedle ensures a high electrochemically active surface area.The NiMoO4·xH2O-300 catalyst obtained by annealing at 300℃ had the highest active crystal plane content and the highest alkaline HER activity.NiMoO4·xH2O-300 has an overpotential of 56 mV at a current density of 10 mA cm-2,a Tafel slope of 25.3 mV dec-1,and long-lasting lifetime more than 50 hours at a current density of 100 mA cm-2.The reasons for the high HER performance of NiMoO4·xH2O-300 are large electrochemically active surface area,low charge transfer impedance and high active crystal plane content.3.Nickel foam-supported Anderson-type polyoxometalates(POMs)were synthesized by a simple immersion method.The nickel foam-supported Cu/Mo2C composite catalysts were synthesized by using POMs as metal sources and melamine as carbon sources and reducing agents.In addition,we synthesized POMs with Mn,Fe,Co,Ni,Zn,and Cu as the central atoms to prove the universality of the precursor path.By controlling the mass of melamine,we studied the phase evolution during synthesizing Cu/Mo2C.Cu/Mo2C has excellent alkaline HER performance,with overpotentials of 24 mV and 178 mV corresponding to 10 mA cm-2 and 1000 mA cm-2 current densities,respectively,Tafel slope of 51.3 mV dec-1,and long-lasting lifetime more than 150 hours at high current densities,which is better than most molybdenum carbide-based catalysts.In addition,Cu/Mo2C also has efficient HER performance and stability in simulated seawater.By using in situ surface enhanced infrared absorption spectroscopy(ATR-SEIRAS)to study the interfacial water structure,the results show that the excellent performance of Cu/Mo2C originate from the optimization of the interfacial water structure by positively charged Cu crystals,which reduces the rigidity of the interfacial water and accelerates the transfer of the reaction intermediate OH*/H2O.This work developed an alkaline HER catalyst with excellent performance and demonstrated that the performance of the catalyst can be improved by optimizing the interfacial water structure. |
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