Synthesis And Electrocatalytic Performance Of The Ni/Co Bimetal-Organic Frameworks And Their Derivatives

As an effective method for hydrogen production,electrochemical water splitting provides a new route to solve the global energy crisis and environmental pollution.However,the efficiency of hydrogen production is severely hindered by the anodic oxygen evolution reaction（OER）due to its high energy barrier.Therefore,it is urgent to develop efficient catalysts to reduce the overpotential of the OER process.Transitional metal-organic frameworks（MOF）and their derivatives are a new kind of porous materials with controllable structures and large specific surface areas,which exhibit promising performance in OER catalysis.In this thesis,a series of bimetallic N-Ni_xCo_y-MOF materials were fabricated by combining nickel and cobalt ions with organic ligands such as 1,4-naphthalenedicarboxylic acid and 4,4’-bipyridine.Metal phosphides and sulfides derived from the N-Ni_xCo_y-MOF were then prepared and applied as OER catalysts.The main works are as follows:1)N-doped bimetallic N-Ni_xCo_y-MOF spheres were fabricated by the facile oil bath method.Then,N-Ni_xCo_y-P bimetallic phosphides were synthesized by low-temperature phosphating.It was shown that the introduction of N atoms could efficiently increase the conductivity and improve the OER performance of the catalysts.Among these N-Ni_xCo_y-P phosphides,N-Ni₂Co₃-P exhibited the best OER catalytic performance with an overpotential of 290.0 m V at 10 m A cm^-2 in alkaline electrolyte.The Tafel slope of N-Ni₂Co₃-P was 60.85 m V dec^-1,indicating the excellent electrochemical reaction kinetics.Comparative experiments showed that the complete phosphorization might lead to the collapse of the MOF precursors,lower the electrical conductivity and reduce the active sites of the catalysts,resulting in poor OER performance.2)N-doped bimetallic N-Ni_xCo_y-S sulfide hollow spheres were synthesized by a facile hydrothermal reaction using N-Nix Coy-MOF and thioacetamide as the precursors and sulfur source,respectively.In the OER test,N-Ni₁Co₄-S showed the lowest overpotential which was just 282.5 m V at 10 m A cm^-2 in 1 M KOH solution due to the synergistic effect between Ni and Co elements,the faster electron transfer rate and the larger specific surface area provided by the hollow structure.And the TOF of the N-Ni₁Co₄-S was 0.59 s^-1 which was the highest among these N-Ni_xCo_y-S samples.Besides,N-Ni₁Co₄-S exhibited good stability for 36 h at a large current density of 50 m A cm^-2.The characterization of N-Ni₁Co₄-S after OER indicated that the metal oxide/hydroxides derived from the oxidation of the sulfides might be the actual active sites in OER process.