Preparation Of Transition Metal-based Nanomaterials And Their Electrocatalytic Methanol Oxidation Studies

In recent years,increasing energy demand and increasing environmental awareness have encouraged researchers to develop advanced,efficient and environmentally friendly energy conversion devices and storage technologies.Direct methanol fuel cell(DMFC)have been regaerded as one of the most competitive new energy saving conversion devices in the field of energy conversion in the future due to its advantages such as low-temperature operation,low pollution emission,simple structure,high energy conversion efficiency,convenient storage and safe transportation of methanol.Platinum(Pt)-based noble metal catalysts are considered to be one of the most efficient and widely used electrocatalysts at present,but their high cost,low reserves and susceptibility to reaction intermediates have seriously hindered their large-scale commercial application.Transition metal catalysts have been attracted much attention in the field of electrocatalytic methanol oxidation due to their abundant reserves,simple preparation and efficient electrocatalytic activity.Therefore,based on the current research direction in the field of electrocatalysis,we designed and prepared transition metal-based nanostructured electrocatalyst with low-cost,high catalytic performance and high stability.In this thesis,two transition metal-based catalyst materials were systematically studied and applied for in alkaline methanol oxidation reaction(MOR).Based on the design of non-noble metal nanoarray materials,the surface structure of the catalyst was optimized and controlled through heterogeneous interface construction strategy,which effectively improved the electrocatalytic activity and stability of the catalyst in alkaline medium.The following research work was has been carried out:1.The Ni-Mo precursor nanoarray was synthesized by a simple hydrothermal method,and annealed in the atmosphere of argon to produce bimetallic oxide(NiMoO₄),and further nitridation in the atmosphere of ammonia,Ni-MoN composites nanorod arrays(Ni-MoN NR/NF)were prepared in situ on the nickel foam substrate as a electrode for alkaline methanol oxidation reaction.As results,there is a strong electron interaction between Ni and Mo after the introduction of N element,which optimizes the electronic structure.Compared with NiMoO₄ nanorods(NiMoO₄ NR/NF),the electrocatalytic performance of Ni-MoN NR/NF generated by nitriding has been significantly improved,which showed a lower oneset potential(1.35 V vs.RHE),a higher current density(374m A cm^-2@1.724 V vs.RHE),and a lower Tafel slope(40 m V dec^-1).This work has a certain reference significance for the development of non-noble metal nanomaterial catalysts for electrocatalytic methanol oxidation.2.This work reported an atomic layer deposition method to prepare NiO on self-supported Co₃O₄ nanoneedle array grown on porous nickel foam substrate(NiO-Co₃O₄ NA@NF)as anodic catalyst for MOR reaction in alkaline medium.The catalyst of the composite can be optimized by adjusting the number of deposition cycles of atomic layer deposition.The synergistic effect between NiO and Co₃O₄ components as well as the specific 3D nanoarray structure,which improves the electrocatalytic methanol oxidation performance of as-prepared NiO-Co₃O₄ NA@NF.As a result,NiO-Co₃O₄NA@NF catalyst showed a low onset potential(1.27 V vs.RHE),at the same time,the current density reached 174 m A cm^-2 at the potential was 1.524 V(vs.RHE).In addition,the current density remains 93%after 7000 s,and the structure was intact,showing high electrochemical stability and structural stability.This work not only designed and prepared a transition metal-based electrode material with high performance and stability,but also proposed a simple and general atomic layer deposition modification method,which has reference value for the development of transition metal oxide nanocomposite materials.