Synthesis And Electrocatalytic Performance Of Nickel-based Materials Derived From Metal-Organic Frameworks

It's urgent to develop all kinds of clean and renewable energy due to the decrease of fossil fuel which accompanied with serious environmental pollution.Hydrogen is widely considered to be a sustainable and abundant energy carrier which has tremendous potential to resolve the energy crisis.In the process of electrolytic hydrogen production,the kinetic process of oxygen evolution reaction?OER?is very slow because it involves the transport of four electrons,and a high potential is needed to overcome the reaction barrier,thereby driving the water decomposition reaction.Therefore,it is of great significance to develop low cost,highly efficient and environmentally friendly electrocatalyst for OER.Graphitized carbon can in-situ derive from metal-organic frameworks?MOFs?during the calcination process,nitrogen,phosphorus,and other elements can be incorporated into the carbon skeleton.Thus,MOFs derivatives are very promising substitutes for noble metal-based electrocatalysts.In this thesis,nitrogen-containing and nitrogen-free organic ligands were respectively used to synthesize two different precursors of nickel-based MOFs by solvothermal method.The precursors were calcined differently to obtain graphene-supported carbon-confined Ni2P nanocrystals?Ni2P@C/G?and nitrogen-doped carbon confined nickel/graphene composite?Ni@NC/G?.The structure of the two samples was characterized by the corresponding test methods,and the OER electrocatalytic performance of the two catalysts was also studied.The mechanism of Ni₂P@C/G during OER process was further explored.The main results are as follows:?1?Using trimesic acid as organic ligand,a nickel-based precursor was prepared by solvothermal method,then Ni₂P@C/G was obtained through a two-step calcination process.In addition,using 2-methylimidazole as organic ligand,a nickel-based precursor containing nitrogen was synthesized by solvothermal method.This precursor was subjected to a one-step carbonization treatment at different temperatures to obtain Ni@NC/G.The phase,morphology,graphitization degree,element content,specific surface area and other propeties of Ni2P@C/G and Ni@NC/G were characterized.?2?Ni₂P@C/G exhibits excellent electrocatalytic performance for OER which only requires 285 mV to reach a current density of 10 mA cm^-2,Tafel slope is as low as 44 mV dec^-1,and has outstanding durability.Its performance is better than that of commercial IrO₂ and rivals most recently reported non-noble metal based OER electrocatalysts.Further mechanism investigations suggest that the Ni₂P nanocrystals inside the graphitized carbon layer can be oxidized during OER process,and the in-situ generated NiOOH can act as reactive sites to enhance the electrocatalytic activity for OER.?3?Ni@NC/G obtained by different carbonization temperatures were tested for electrocatalytic performance.The results show that Ni@NC/G-550 has the best OER catalytic activity with a remarkably decreased overpotential(291 mV at10 mA cm^-2)and a considerably low Tafel slope(74 mV dec^-1),which can be comparable to commercial IrO₂.