Study On The Construction Of Black Phosphorenebased Composites And The Photoelectrocatalytic Properties

The increasing energy demands of modern society and the environmental pollution caused by the burning of fossil fuels have forced researchers to explore new renewable energy storage and conversion systems.A fuel cell is an electrochemical device that converts the chemical energy of a fuel directly into electrical energy.This conversion process has several unique advantages over the multi-step process involved in combustion-based conventional heat engines,such as energy conversion independent of the"Carnot cycle",high efficiency and low emissions.These features make the fuel cell an attractive energy conversion device for future transport and portable power supplies,with significant long-term economic and environmental benefits.Ethanol is a clean,renewable energy source that produces a high mass energy density from complete oxidation,is easy to transport,and can be an ideal fuel source for fuel cell.The difficulty of breaking carbon-carbon bonds during the catalytic oxidation of ethanol to carbon dioxide is a challenge in direct ethanol fuel cell catalyst research.To achieve ethanol-based fuel cells,one of the key s is the need to design electrocatalysts that are efficient,low cost and resistant to intermediate poisoning.The development of fuel cell catalysts is mainly hampered by the high cost and low reserves of the precious metal Pt.As Pd is 50 times more abundant on earth,it can be an alternative to Pt in the development of highly efficient electrocatalysts.In order to obtain further efficient electrocatalysts,on the one hand,an alloying strategy is adopted to optimize the composition,size and structure of the Pd-based catalysts.On the other hand,the introduction of carrier materials promotes the dispersion of noble metal nanoparticles,thus generating more active sites.In this paper,two-dimensional semiconductor black phosphorene was used as carrier to prepare new composite electrocatalytic materials by taking advantage of its large specific surface area and band gap tunable properties.However,the disadvantage of black phosphorene is its poor environmental stability.In this study,the organic macrocyclic molecule cucurbit[6]uril（CB[6]）was innovatively added as a functional additive to modify the black phosphorene carrier using its organic moiety.The main research and conclusions of this paper are as follows:（1）Black phosphorus crystals were prepared from analytically pure red phosphorus by chemical vapor deposition,and layer ed black phosphorus nanosheets were obtained by liquid phase exfoliation.The macrocyclic hos t compound CB[6]was introduced as an auxiliary material and a new method for anchoring noble metal to semiconductor was proposed.Two-dimensional black phosphorus nanosheets（BPNSs）modified with CB[6]were synthesized by a simple solvothermal method and palladium nanoparticles（Pd NPs）were anchored to the BP-CB[6]surface by chemical reduction to obtain the composite Pd/BP-CB[6].Electrochemical test results show that Pd/BP-CB[6]has an electrochemically active area（ECSA）of 60m²g^-1 and a mass activity of 1420 m A·mg _Pd^-1 in 1 M KOH+1 M C₂H₅OH solution to catalyze the oxidation of ethanol,which is 4.1 times higher than that of commercial Pd/C(20 wt%,350 m A·mg Pd^-1).This indicates that the Pd/BP-CB[6]catalyst has good ethanol electrooxidation（EOR）activity in alkaline media.（2）The synergistic effect of electrocatalysis and photocatalysis also contributes to the activity and stability of EOR.In the visible light-assisted electrocatalytic EOR,the peak current density of the Pd/BP-CB[6]electrode under visible light irradiation reached 1900 m A·mg Pd^-1,which is 1.34 times higher compared to the dark environment,and the excellent cycling stability was also demonstrated.The results of CA,CP and EIS further corroborated that visible light irradiation improved the surface of the Pd/BP-CB[6]electrode charge separation efficiency and promoted the charge transfer on the electrode surface.（3）The bimetallic synergy was exploited to introduce Ag into the Pd lattice to form an alloy catalyst,and a one-pot hydrothermal method was used to prepare a Pd-Ag/BP alloy catalyst with black phosphorus nanosheets as the carrier s.The synergistic interaction between the bimetals facilitated the formation of-OH groups during the oxidation of ethanol and contributed to the further oxidation of intermediate CO _ads.The ECSA of Pd-Ag/BP was tested in 1 M Na OH and resulted in 56.9 m²g^-1.The mass activity of 1280m A·mg _Pd^-1 for catalytic oxidation of ethanol in 1 M KOH+1 M C₂H₅OH solution is 3.7 times higher than that of commercial Pd/C(20 wt%,350m A·mg _Pd^-1).（4）The alloy/semiconductor composite catalyst was applied to catalyze the oxidation of ethanol with the assistance of visible light,with Pd-Ag/BP exhibiting a mass activity of 1670 m A·mg Pd^-1,which is 1.3 times higher compared to the dark environment.The results of photoelectric tests such as CA and CP indicated a faster charge transfer rate at the electrode interface with the assistance of visible light.The diffusion coefficient of this Pd-Ag/BP electrode w as improved under visible light irradiation,which is beneficial to the catalytic performance of EOR.The experimental results show that the Pd/BP-CB[6]catalyst prepared in this study functionalized the surface of BP by introducing the organic macrocyclic compound CB[6],and contributed to the dispersion of precious metals.The composite provided a large elec trochemically active area and showed high mass activity in the ethanol oxidation reaction.The alloy/semiconductor composite catalyst Pd-Ag/BP can significantly modulate the electronic structure of Pd,which should have a positive impact on the catalytic a ctivity and stability.The synergistic effect of photocatalysis and electrocatalysis improved the electron transport kinetics of both composite catalysts during EOR by introducing visible light irradiation.