| Currently,the ever-increasing energy crisis and environmental pollution problems caused by consuming traditional fossil materials have hindered the sustainable development of human society.Therefore,the search for renewable alternative energy sources has become a critical issue.Because of the advantages of high energy density and being free of carbon emissions,hydrogen is widely considered an ideal source of clean energy of the future.Nowadays,water electrolysis is one of the most effective ways to develop and utilize hydrogen energy on a large scale.The electrolysis process includes the oxygen evolution reaction(OER)and the hydrogen evolution reaction(HER)occurring on the anode and cathode,respectively.Despite many works have been performed to lower the overpotentials applied to the electrodes,it remains a challenge to develop a bifunctional catalyst which can match the benchmark performance of precious metals electrocatalysts(e.g.,Pt for HER,IrO2/RuO2 for OER).Therefore,it is of great significance to explore non-precious,efficient and durable electrocatalysts as electrode materials for both the HER and OER reactions,instead of precious metals used in industrial fields.In this thesis,a three-dimensional transition metal foam is used as the substrate,and the embroidered spherical structure composed of nanosheets is formed on the substrate surface by a hydrothermal method.At the same time,the response relationship between different preparation processes and electrochemical performance was also explored.The main research contents are as follows:(1)The 3D hydrangea-like microspheres made of nickel-vanadium double hydroxide nanosheets are firstly prepared on the Ni-Co foam(NCF)followed by the hydroxides exchange with(MoS4)2-ions to form a Chevrel-phase of Ni-V-Mo sulfide.Benefiting from the 3D holey nanostructures with a large surface area,low adsorption free energy values and fast electronic transport,the overpotentials of the optimized Ni8V2(Mo3S4)11/NCF catalyst for HER and OER at a current density 10 mA cm-2 are as low as 129 mV and 330 mV,respectively.The amount of H2 and O2 generated at a current density of 10 mA cm-2 are about 517 and 342 ?mol h-1,which is very competitive with most advanced research results reported for non-noble metal electrodes in alkaline medium.The Chevrel-phase chalcogenide also features excellent long-term stability under prolonged HER and OER cycling conditions.Our results suggest that Chevrel-phase materials are promising as low cost and efficient bifunctional electrocatalysts for overall water splitting in alkaline electrolytes.(2)In this work,the iron-doped NiV LDHs nanosheet arrays are fabricated on the nickel-iron foam by one-step hydrothermal method,and then the "embroidered" structure assembled with nanosized NiVFe LDHs is transformed into the high-performance phospho-nitride electrocatalyst(N-NiVFeP/NFF)by the N2-PH3 plasma doping,the three-dimensional(3D)structure of NiVP with Fe and N doping is achieved.The resulting N-NiVFeP/NFF shows excellent HER and OER performances under industry-relevant conditions.Indeed,the overpotentials of HER and OER in 1 M KOH electrolyte solution are only 79 and 229 mV at a current density of 10 mA cm-2,as well as the small Tafel slopes of 78.6 mV dec-1 and 72.6 mV dec-1.Particularly,the N-NiVFeP/NFF exhibits superior electrocatalytic performances which are indicated by the smaller overpotentials than Pt/C and RuO2 with a high current density and long-term stability operated with a low or high current density for more than 100 hours.This work provides an innovative approach for engineering bifunctional electrocatalysts with the simultaneous cation and anion atoms doping,which will open new way for fabricating advanced energy materials. |
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