| Energy and environment crisis are becoming the two most concerned problems in today's society because of rapid development of industrialization and urbanization.As an environment-friendly advanced oxidation technology,?photo?electrocatalysis has been widely utilized in water splitting,CO2 reduction,N2 fixation,and organic pollutant degradation.Semiconductor materials play a crucial factor in influencing the catalytic efficiency,transition metal based semiconductor materials have been widely investigated because of their excellent properties and unique crystal structure.However,transition metal based semiconductor materials cannot meet the needs of highly efficient catalysts owing to their poor conductivity and low intrinsic activity.Therefore,it is very important to design efficient and stable semiconductor materials.In this paper,transition metal based semiconductor materials were modified by heterojunction,morphology engineering,and ion doping to improve their catalytic activity.The main contents of this paper are as follows.?1?The BiVO4/WO3 composite film was prepared by the combination of hydrothermal method and successive ionic layer adsorption and reaction?SILAR?for photoelectrocatalytic?PEC?degradation of norfloxacin?NOR?under visible-light illumination.The impacts of potential,degradation process,and type of film electrode on degradation efficiency of NOR were investigated.The BiVO4/WO3 composite film electrode exhibited enhanced PEC performance with degradation efficiency of 67%at 1.0V.The superior PEC performance could be ascribed to the formation of N-N junction facilitating the interfacial charge transfer and separation rate,resulting in enhanced light-harvesting capability and electronic conductivity.The generated·O2-,·OH,and h+radicals were responsible for the PEC degradation of NOR confirmed by the radicals trapping experiments and ESR spectra.ESI-MS displayed that the piperazine ring of NOR was attacked mainly during the visible-light-driven degradation process.?2?The Sb2S3/Mo-WO3 composite film was synthesized by the combination of hydrothermal method and spin-coating technique for photoelectrocatalytic?PEC?water splitting under visible-light illumination at low input energy(1 mW cm-2).The 5%?molar ratio?Mo-WO3 film electrode exhibited optimal PEC water-splitting performance.Furthermore,the Sb2S3/5%Mo-WO3 composite film electrode spin-coated with 1.0 mL precursor?Sb-TU?achieved the highest photocurrent density of 0.42 mA cm-2,nearly 20times as high as that of 5%Mo-WO3 film electrode.The outstanding PEC water-splitting performance was mainly attributed to synergistic effect of Mo doping and deposited Sb2S3,that is,the enhanced PEC performance not only was assigned to the broadened optical spectrum but also improved electron-hole pairs separation and transfer efficiency.Density functional theory calculation?DFT?revealed that Mo doping can lower the band-gap energy of WO3 and the valance and conduction band were controlled by O 2p orbit,Mo 3d and W3d orbit,respectively,which resulted in the formation of new level and improved catalytic activity.Therefore,this work offers a new insight for designing metal elements doped into WO3 associated with transition metal sulfides for highly visible-light-induced water-splitting activity in neutral electrolyte.?3?In this work,Co3O4 films with different morphology on FTO were prepared by hydrothermal method.The Co3O4 film electrode with nanowire structure showed optimal performance for oxygen evolution reaction?OER?with an overpotential?394 mV?at 20 mA cm-2 in 1.0 mol L-11 KOH electrolyte.Subsequently,the effect of Ni doping on OER activity of Co3O4 film electrode was further studied.Among the Ni-doped Co3O4?Ni-Co3O4?with nanowire arrays,the 12%?molar ratio?Ni-Co3O4 film electrode exhibited the best activity with an overpotential of 340 mV to achieve 20 mA cm-22 and superior stability for 12 h in alkaline media,outperforming other Ni-Co3O4 film electrodes.DFT calculations demonstrated that the theoretical overpotentials of Co3O4 and Ni-Co3O4 were calculated to be 1.70 V and 0.64 V,respectively,suggesting that Ni doping can lower the oxygen evolution barrier.Therefore,this study provides a promising method for designing highly active and stable substitution for noble metal catalysts toward OER.?4?Electrochemical N2 reduction reaction?NRR?to NH3 promises an environmentally friendly and sustainable technology at ambient temperature.However,high energy barrier and the competition by hydrogen evolution reaction?HER?resulted in poor NH3 yield and low Faradaic efficiency?FE?of NRR.Herein,the FeS2 electrocatalyst was synthesized by hydrothermal method for NRR.In N2-saturated Na2SO4 electrolyte,this catalyst exhibits superior catalytic performance to achieve high NH3 yield(37.2?g h-1 mg-1cat.)and FE?11.2%?with high stability and selectivity toward NH3 at-0.5 V vs.reversible hydrogen electrode?RHE?,outperforming other NRR electrocatalysts.According to experimental results,a preferable associative distal pathway was proposed.DFT calculations revealed that NRR process can proceed preferably on Fe atom instead of S atom,and the conversion of*NH2 to*NH3 was the potential-determining step?PDS?.Therefore,this work offers a new avenue to prepare high-efficiency and highly selective transition metal-based catalysts for NRR under ambient conditions. |
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