Preparation And Performance Of MOFs-based Electrocatalysts For Oxygen Evolution Reaction

Electrochemical water splitting is an efficient way to obtain clean and renewable hydrogen energy.Developing oxygen evolution reaction（OER）electrocatalysts with abundant reserves,low-cost,high catalytic activity,and good stability are crucial to the wide application of water electrolysis.As an emerging type of electrocatalyst,metal-organic frameworks（MOFs）possess large specific surface area,tunable pore size,and structural diversity.In this paper,a series of novel MOFs-based electrocatalyst materials were designed and prepared.The synthesized products were characterized by XRD,SEM,TEM,FT-IR,Raman,XPS and nitrogen adsorption-desorption tests.The electrocatalytic performances of these materials towards oxygen evolution reaction were investigated,and the catalytic mechanisms were explored.The main points are as follows:1.Two-dimensional Fe Ni-MOF（Fe（py）₂Ni（CN）₄）with different particle morphologies including nanobox,nanocube,nanoplate and nanosheet is controllably synthesized by a microemulsion method.The morphology-dependent electrocatalytic properties of these Fe Ni-MOF nanocrystals are investigated towards oxygen evolution reaction（OER）.The Fe Ni-MOF nanoboxes exhibit the best OER performance in 1.0M KOH electrolyte due to the higher intrinsic activity of the exposed crystal faces of the nanoboxes and the increased catalytic active sites exposed by their hollow structure,with an overpotential of 285 m V at a current density of 10 m A cm^-2and a Tafel slope of 50.9 m V dec^-1.Meanwhile,the nanobox catalyst exhibits good durability during the 36 h stability test.By studying the intermediates in the OER process,it is revealed that the real OER catalytically active species are metal hydroxides and oxyhydroxides evolved from Fe Ni-MOF.This work provides a feasible strategy for designing and synthesizing high-performance MOFs electrocatalysts by tuning the morphology of MOFs to optimize the electrochemical performance.2.A low-crystallinity Co Fe-PBA（Co₃[Fe（CN）₆]₂）catalyst is prepared by a mild solvothermal treatment.The reduced crystallinity of Co Fe-PBA with increased disordered structure enables more exposed active sites and higher metal valence states,which leads to enhanced OER catalytic activity of Co Fe-PBA.The Co Fe-PBA electrocatalyst delivers a low overpotential of 298 m V at the current density of 10 m A cm^-2 and a small Tafel slope of 44.5 m V dec^-1 in alkaline medium.Directly improving OER performance of MOFs by a simple solvothermal treatment demonstrated in this work provides a new strategy for the performance improvement of MOFs catalysts without destroying the intrinsic structure of MOFs.3.A composite electrocatalyst of Fe Ni-MOF and r GO is prepared by a simple in-situ synthesis strategy.Benefiting from the introduction of r GO and the optimization of MOF morphology,the Fe Ni-MOF/r GO composite exhibits enhanced electrical conductivity and more open active sites.Under alkaline condition,the composite exhibits good OER catalytic activity and long-term stability,with an overpotential of 263 m V at a current density of 10 m A cm^-2,a Tafel slope of 56.7 m V dec^-1,as well as good stability during 24 h OER tests.This study provides a feasible strategy for the construction of high-performance MOFs/r GO composite electrocatalysts.4.Fe Ni-LDH/MOF composite nanostructures are successfully fabricated by partially converting Fe Ni-LDH nanosheets grown on carbon cloth（CC）into MOF（Ni[Fe（CN）₅NO]）nanoparticles by a sacrificial template method.The MOF nanoparticles are in situ decorated on the surface of Fe Ni-LDH nanosheets,providing abundant open active sites and mass transfer channels for electrocatalysis.As a result,the Fe Ni-LDH/MOF/CC as a self-supporting electrode exhibits excellent OER catalytic performance with an overpotential of 263 m V at a current density of 100 m A cm^-2 and a Tafel slope of 50.2 m V dec^-1.In addition,the catalyst exhibits good durability during the 24 h OER test.This work provides an efficient route for the preparation of high-performance LDH and MOFs composite electrocatalytic materials.