Synthesis Of Group IB Metal-based Catalysts And The Study Of Their Electrocatalytic Properties

Due to the continuous consumption of non-renewable fossil fuels,the severe energy crisis and environmental pollution urge our society to find more sustainable and environmentally friendly energy conversion systems to meet the huge global energy de:mand.Various electrochemical energy conversion systems including oxygen reduction(ORR)and carbon dioxide reduction(CO2RR)have been intensively investigated to replace fossil fuels and reduce environmental pollution.However,the biggest challenge for ORR and CO2RR is the low energy conversion efficiency.Electrocatalysts with high activity,durability and high selectivity are the keys to improve the energy conversion efficiency.Group IB metals have attracted extensive attention because of their advantages such as low cost and easy availability.Nanomaterials based on group IB metals including metals,metal compounds and alloys have been widely applied in the fields of CO2RR and ORR.However,the catalytic activity and durability of the catalysts still need to be further improved.This dissertation introduces preparation of phosphate derived silver(PD-Ag),copper atomic clusters supported on N-doped porous carbon matrix(Cu ACs/NPC)and silver phosphate crystals with different shapes.The scanning electron microscopy(SEM),X-ray powder diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and other instruments were used to characterize the morphology and structure of these three materials.Besides,the catalytic performance of these catalysts for CO2RR and ORR as well as corresponding catalytic mechanism was investigated by electrochemical workstation.The detailed research contents and results are shown as follows:(1)Phosphate derived silver(PD-Ag)catalyst was fabricated from Ag3PO4 precursor by a quick facile electroreduction method.The PD-Ag with coral-like surface can selectively reduce CO2 to CO,affording a current density of-2.93 mA cm-2 with a maximum faradaic efficiency(FE)of 97.3%at an operating potential of-0.7 V(vs.RHE).It is demonstrated that a 19-fold increase of the electrochemically active surface area(ECSA)is obtained for PD-Ag compared to polycrystalline Ag(Ag foil).Furthermore,the PD-Ag shows excellent stability with a stable current density and a constant CO FE(97%)in 0.5 M KHCO3 electrolyte during the 10-hour electrolysis.Comparative experiments of PD-Ag and silver foil as well as silver nanoparticles prove that the enhancement of the electroactivity results from its coral-like surface,not only serving plenty of active sites,but also producing CO2-intermediate at a lower overpotential.(2)Copper atomic clusters supported on N-doped porous carbon matrix(Cu ACs/NPC)were synthesized by a facile pyrolysis method assisted with ZIF-8.It exhibits a high selectivity for CO with the maximum faradaic efficiency(FE)of 93.2%at the low potential of-0.5 V(vs.RHE).The corresponding CO partial current density reaches to-5.09 mA cm-2 with 46-fold and 1159-fold enhancement in comparison with Cu nanoparticles dispersed on N-doped porous carbon matrix(Cu NPs/NPC)and bulk Cu dispersed on N-doped porous carbon matrix(Bulk Cu/NPC),respectively.Further results demonstrate that the favorable structure of Cu atomic clusters on the support has large surface active sites to enhance the CO2 adsorption for excellent performance.Additionally,in-situ X-ray absorption spectroscopy(XAS)reveals that Cu ACs/NPC has a tunable chemical state,which can be easily switched between air-stable Cu2+ and highly reductive Cu0 for efficient CO2 reduction to CO.A combination of the favorable structure and the tunable chemical state thus results in the excellent CO2RR performance.(3)Silver phosphate(Ag3PO4)catalysts with different shapes including cubes,rhombic dodecahedra and tetrapods were synthesized by a simple chemical precipitation method.Among them,rhombic dodecahedral silver phosphate crystals show the best ORR performance in terms of the onset potential(Eonet)and half-wave potential(E1/2)which are 0.93 V(vs.RHE)and 0.79 V(vs.RHE),respectively.Moreover,limiting current density for the rhombic dodecahedra can reach to 6.68 mA cm-2 under 1600 rpm.The improved electrocatalytic performance can be attributed to its exposed(110)crystal plane which facilitates the adsorption and further reduction of oxygen molecules on the silver surface.In addition,the rhombic dodecahedral silver phosphate crystals show excellent stability by the 12-hour I-T test in an alkaline electrolyte solution.The methanol poisoning resistance test also proves that the catalyst has strong methanol resistance and can be applied to methanol fuel cells.