Preparation of Transition Metal-based Nanomaterials and Electroatalytic Performance for Water Splitting

Author:Ma Xing Xing

Supervisor:tang ji lin


Degree Year:2019





Water splitting is of crucial importance for exploiting renewable energy conversion and storage systems.Designing efficient bifunctional electrocatalysts for both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)is in desperate need for the development of overall water-splitting devices.Platinum(Pt)-based and Iridium(Ir)-based materials represent the classical high-performance catalysts for HER and OER,respectively.However,scarcity and high cost of noble metal materials restrict their widespread application.The design of cost-efficient earth-abundant catalysts with superior performance for the electrochemical water splitting is highly desirable.We developed a series of electrocatalysts for HER and OER based on non-noble transition metal.1.NiCoP@Cu3P heterostructure was fabricated on Cu-foam(NiCoP@Cu3P/CF)by a simple and effective approach for the first time.It presents high catalytic performance for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)due to the synergistic active sites,large electrochemical surface area,small charge-transfer resistance,efficient mass transport and electron transfer.The optimized NiCoP@Cu3P/CF exhibits a pretty low overpotential of 54 mV at 10 mA cm-2,small Tafel slope of 72 mV dec-1 serving as HER electrocatalyst and also exhibits low overpotential of 309 mV at 10 mA cm-2,extremely small Tafel slope of 42 mV dec-1 serving as OER electrocatalyst in 1 M KOH.2.Dense CuxO nanowires were fabricated on three dimensional Cu foam(CF),which consists of mixed Cu2O phase and CuO phase as electrochemical active sites.Importantly,through the characterization of morphology and chemical composition,we found that Cu2O and CuO can transform to each other during electrochemical reduction or oxidation process.And Cu2O and CuO serve as active center for HER and OER respectively,and the transformation is beneficial to the catalytic performance.In alkaline solution,overpotentials as small as 135 mV and 315 mV to reach 10 mA cm-2 current density and small Tafel slope of 135 mV dec-1 and 63 mV dec-1 are achieved on the CuxO NWs/CF catalyst for HER and OER,respectively.And it also shows long-term stability for both HER and OER.3.An Fe-doped CoNiMoOx/NF microcuboid structure was fabricated on Ni foam which act as substrate and nickel source.The outer layer of the microcuboid structure consisted of amorphous structure and nanoparticles with a diameter of tens nanometers and.The structure has a large specific surface area which can ensure abundant active sites.And the nanoparticles contain two crystal compound of CoMoO4 and CoMo3O8.The large number of interfaces produced by the mixed crystal structure of CoMoO4 and Co2Mo3O8 by hydrogen reduction can produce abundant active sites;Both the synergistic effect between Co and Ni elements and the low oxidation state of Mo can optimizes the surface metal electron distribution of the material,which can improves the catalytic activity of single active site.The introducing of Fe electrocatalytic significantly improved the OER electrocatalytic activity of the metal molybdate that make it be a bifunctional electrocatalyst for water splitting.Fe-CoNiMoOx/NF exhibits excellent HER and OER catalytic activity and stability.To achieve current densities of 10 and 100 mA cm-2,the overpotentials required for HER and OER are 25 mV,78 mV and 221 mV,269 mV in 1 M KOH,respectively.