Preparation And Electrochemical Properties Of Nickel-Based Noble-Metal-Free Three Dimensional Electrode

The increasing global energy demand and accompanying climate change are driving scientists to search for sustainable and environmentally friendly alternative sources of energy to replace exhaustible fossil fuels.Recently,the electrocatalytic water splitting for generating hydrogen and oxygen has attracted extensive attention because this process provides a promising approach for the generation of sustainable,secure,and clean hydrogen-fuel energy.In this regard,developing electrochemical energy storage devices which can transfer and store electricity is an essential step towards resolving energy crisis.Among various energy storage devices,supercapacitors stands out with great appliation prospect,for showing an intermediate energy density and power density bridging batteries and conventional dielectric capacitors.Hence,there is a significant need of developing materials for electrodes,which are capable of efficiently catalyzing water splitting as well as storing energy in supercapacitors.Recently,as an economical and efficient alternative to expensive metal precursors,nickel-based electrocatalysts in the form of nickel foam（NF）,alloys,nitrides,phosphides,oxides,and metal organic frameworks（MOFs）have exhibited superior electrocatalytic activity and stability toward oxygen evolution reaction（OER）,hydrogen evolution reaction（HER）,and energy storage aspecct.In this work,I synthesized a series of Ni-based nano/micro-materials and studied their performance as electrode materials in supercatacitors and water spliting reactions.The obtained Ni-based catalysts showed excellent electrochemical performance,proving to be ideal candidates as catalytic electrode materials.The details are summarized as follows:Firstly,we report a simple one-step method for fabricating three-dimensional（3D）biphasic Ni₁₂P₅-Ni₂P nanorod arrays by direct phosphorization of commercially nickel foam（Ni foam）in tube furnace for different growth time.In the reaction system,sodium hypophosphite（NaH₂PO₂）was used as an effective phosphorus source,whereas Ni foam was used as nickel source as well as substrate for the growth of Ni-P.When used as a 3D electrode for OER,the obtained Ni-P nanorods with 2h phosphatization treatment displayed highest activity.The nanorods are also highly active for electrocatalyzing the HER in alkaline media.In addition,the bifunctional Ni-P catalysts enabled a highly performed overall water-splitting in 1.0 M KOH electrolyte.This work provided a valuable reference for the preparation of nickel phosphide electrode materials with special morphologies.Based on the first work,nickel phosphide（Ni-P）was simply combined with NiCo LDH via electrodeposition,forming core-shell nanorods array on Ni foam and further used for pseudocapacitive electrode.Owing to the splendid synergistic effect between Ni-P and NiCo LDH nanosheets,the hybrid electrode exhibited significantly enhanced performance for supercapacitors.Additionally,this work demonstrated that Nickel-based phosphide showed great potential application value in the field of energy storage.Finally,a unique method is used to in-situ grow well-ordered Ni Fe-MOF-74 on Ni foam by inducing Fe²⁺in solution and directly used as the electrocatalysts for OER.In our reaction system,Fe²⁺could be slowly oxidized to Fe³⁺with the assistance of water and oxygen.Through redox-etching Ni foam by Fe³⁺,Ni²⁺was slowly released from the surface of Ni foam,resulting in the in-situ and uniform growth of NiFe-MOF-74 on Ni foam.Benefited from the synergistic cooperation of the intrinsic open porous structure of MOF-74,in-situ formed MOF arrays as well as the synergy effect of Ni and Fe,the outstanding water oxidation activities was achieved in alkaline electrolyte.