Fabrication And Electrocatalytic Properties Of Porous Two-dimensional Nanosheets

With the industrialization of society and the increasing demand for energy,environmental pollution and the depletion of fossil energy sources are becoming increasingly prominent,making it urgent to develop new environmentally friendly and sustainable energy sources.Among the many new energy sources,hydrogen has a significant role in the"double carbon"strategy due to its high energy density,eco-friendliness and ease of preparation.Electrocatalytic hydrogen production is a low-cost,non-polluting and promising hydrogen production technology,which is conducive to the industrial production of green hydrogen.However,the slow reaction kinetics and high energy potential of the anodic oxygen evolution reaction（OER）in electrocatalytic hydrogen production severely restrict the cathodic hydrogen evolution reaction（HER）,so there is an urgent need to develop efficient catalysts to improve the catalytic activity of HER or to use fast kinetic reactions（e.g.glycerol oxidation reaction）to indirectly/directly reduce the negative impact of OER.Based on this,a variety of porous two-dimensional nanocatalysts with the large electrochemical active area,fast electron transfer and stable structure have been prepared and applied to electrocatalytic hydrogen production or glycerol oxidation reaction（GOR）through rational composition design and morphological modulation in this paper.The main research contents are as follows:1.Unconventional ferroelectricity exhibited by Bi-based nanosheets presents potential opportunities in catalytic fields,whereas the polarization characteristic remains controversial in electrocatalysis.Herein,we report a novel ferroelectric catalyst of polarized Bi₂Fe₄O₉ nanosheets（polarized Bi₂Fe₄O₉ NSs）through the corona poling method after hydrothermal and calcination processes,exhibiting super catalytic activity for water splitting controlled by ferroelectric switching based on the adjusted d-band center and special two-dimensional（2D）structure.The ferroelectric polarization depending on high voltage greatly enhances the activity of polarized Bi₂Fe₄O₉ NSs for HER with a 98 m V positive shift of overpotential compared to the unpolarized Bi₂Fe₄O₉NSs in alkaline conditions.Meanwhile,the Tafel slope decreases from 104.5 m V dec^-1to 83.7 m V dec^-1 due to the forward poling,and the charge transfer resistance(R_ct)also decreases greatly after polarization attributing to the effect of the Schottky barrier between electrode and electrolyte.After long-term stability tests,the polarized Bi₂Fe₄O₉NSs exhibit excellent durability for hydrogen production.Our results show that the effect of ferroelectric polarization of Bi₂Fe₄O₉ NSs enhances the electrocatalytic hydrogen evolution.2.In this work,we have used an efficacious piezoelectric method to significantly increase the catalytic water splitting activity without affecting the morphology as well as the components by altering the bulk charge separation state inside the material.The obtained Cu Co₂O₄ nanosheets（Cu Co₂O₄ NSs）are performed by corona polarization apparatus,which significantly enhanced ferroelectricity relative to that before polarization increased the physical charge separation and piezoelectric potential energy,enhancing the green hydrogen production.The polarized Cu Co₂O₄ NSs show excellent HER with an ultralow overpotential of 78.7 m V at 10 m A cm^-2and OER with an ultralow overpotential of 299 m V at 10 m A cm^-2 under alkaline conditions compared to that of Cu Co₂O₄ NSs without polarization.Moreover,the Tafel slopes of polarized Cu Co₂O₄NSs during the HER and OER process are 86.9 m V dec^-1 and 73.1 m V dec^-1,respectively,much lower than commercial Pt/C(88.0 m V dec^-1)or Ru O₂(78.5 m V dec^-1)catalysts,indicating a faster kinetics rate.In particular,polarized Cu Co₂O₄ NSs are identified as promising catalysts for water electrolysis with robust stability,offering outstanding catalytic performance and excellent energy efficiency.3.Pd-based catalysts have received wide attention due to their outstanding anti-CO poisoning property,whereas the structural instability limits their application.The hierarchical porous Pd Ru Cu nanosheets（HP Pd Ru Cu NSs）with large electrochemically active surface areas,abundant active sites,and stable structures are synthesized through continuous access to CO gas.HP Pd Ru Cu NSs exhibit excellent HER catalytic activity with an ultralow overpotential of 25 m V at 10 m A cm^-2and a Tafel slope of 87.5 m V dec^-1 in alkaline media.Meanwhile,the peak mass activity and specific activity of HP Pd Ru Cu NSs for GOR are 1083 m A mg_Pd^-1 and 38.8 A m^-2,respectively,superior to that of Pd Ru nanosheets（Pd Ru NSs）,Pd nanosheets（Pd NSs）,and commercial Pd black.The introduction of Ru and Cu atoms facilitates the C-C bond cleavage and the complete oxidation of glycerol to CO₂,as well as the accelerated oxidation/removal of the poisonous CO_ads in between.