The Preparation Of Pt-Based Alloy Cocatalysts And Its Influence On CdS’s Performance In Hydrogen Evolution From Water Splitting Under Visible Light

The use of solar photocatalystic decomposition of water for hydrogen generation is one of the effective ways to solve future energy crisis and environmental pollution problems,so it has been widely studied by scholars.Cadmium sulfide（Cd S）has become one of the most popular materials owing to its excellent advantages of perfect energy band gap（about 2.4 e V）and suitable conduction band position.However,severe photocorrosion characteristics and high recombination rate of photo-induced carriers restrict its application and development.At present,the Pt nanoparticles as co-catalyst loaded on the surface of Cd S has proven to be a very effective method to improve the photocatalytic hydrogen generation activity.However,due to scarcity and high cost of Pt,it can not be widely used in the field of photocatalytic hydrogen generation,so it is extremely important to find a catalyst with low platinum content and high activity.Preliminary studies have shown that Pt-based alloys can not only significantly increase catalytic activity,but also reduce the amount of Pt used and the cost of the catalyst.If Pt-based alloy nanoparticles are treated by dealloying technology,the utilization rate of Pt can be improved,and the unsaturated Pt atoms obtained will become the catalytic active centers,then can further improve the catalytic performance.In this paper,using Cd S as base catalyst to investigate the effects of Pt-based alloys and its dealloying on Cd S’s performance in photocatalytic decomposition of water for hydrogen generation under visible light irradiation.The specific research content is as follows:1.Effect of PtNi_x and its dealloying on Cd S’s performance in photocatalytic hydrogen generationPtNi_x alloy nanoparticles（NPs）were synthesized via solvothermal method and loaded on the surface of Cd S by photo-induced deposition method.Under 300 W Xe light（λ≥420 nm）irradiation,（NH₄）₂SO₃ was used as hole sacrifial reagent,the photocatalytic decomposition of water for hydrogren generation was performed.The results showed that the hydrogen generation activity of Pt₃Ni/Cd S was 40.03 mmol·h^-1·g^-1（QE=44.9%,λ=420 nm）,which was 1.8 times higher than that of Pt/Cd S and 2 times higher than that of Ni/Cd S.In addition,Pt₃ Ni alloy NPs was added to excssive HNO₃ for dealloying treatment.When the Pt₃ Ni alloy were dealloying for 10 h,the hydrogren generation activity of d-Pt₃Ni-10h/Cd S reached 46.13 mmol·h^-1·g^-1（QE=52.7%,λ=420 nm）,which was 1.2 times higher than that of Pt₃Ni/Cd S and 2.1 times higher than that of Pt/Cd S,indicating that dealloying technology could further improve the hydrogren generation performance of Cd S.The improved photocatalytic activity was due to surface unsaturaton of Pt atoms in a metastable structure after dealloying,which enhanced the ability to capture electrons and thus promoted the effective separation of carriers.Electrochemical results showed that Cd S modified by PtNi_x NPs could not only enhance the current density of hydrogen evolution,but also reduce the overpotential of hydrogen evolution.SEM and TEM showed that Cd S and Pt₃ Ni alloy presented leaf shape and polyhedron morphology,respectively.PL spectrum and I-T curves showed that d-Pt₃Ni-10h/Cd S photocatalyst had the weaker fluorescence intensity,the longest flouorescence lifetime and the strongest photocurrent intensity,which indicated that d-Pt₃Ni-10 h NPs modified Cd S could improve effectively the separation efficiency of photogenerated carriers and minimize their recombination,thus improve the hydrogen generation activity.2.Effect of Pt Co_x and its dealloying on Cd S’s performance in photocatalytic hydrogen generationIn this chapter,Co element is introduced as the second metal of Pt-based alloy,Pt Co_x alloy NPs were synthesized by solvothermal method and modified to the surface of Cd S as a co-catalyst.Under visible light irradiation,the hydrogen production rate of Pt₃Co/Cd S was 45.09 mmol·h^-1·g^-1（QE=46.0%,λ=420 nm）,which was 1.8 times as much as that of Pt/Cd S and 2.7 times as much as that of Co/Cd S.After Pt Co_x NPs were dealloyed treatment,the hydrogen production activity of d-Pt₃Co-HNO₃/Cd S reached 48.66 mmol·h^-1·g^-1（QE=54.4%,λ=420 nm）,which was apparently higher than that of Pt₃Co/Cd S,1.9 times as much as that of Pt/Cd S and 2.9 times as much as that of Co/Cd S,suggesting that dealloying technology could further enhance the hydrogen production performance of Cd S.The higher photocatalytic activity of d-Pt₃CoHNO₃/Cd S due to that the dealloying can expose more active sites of Pt and capture more electrons,thus can effectively suppress photo-generated electron-holes.Electrochemical results showed that the electrochemical hydrogen evolution activity is consistent with the photocatalytic hydrogen production activity.XPS spectrum showed that the Schottky potential energy was formed between Pt₃ Co NPs and Cd S,which was beneficial to the photocatalytic decomposition of water for hydrogen production.PL spectrum and I-T curves showed that d-Pt₃Co-HNO₃/Cd S photocatalyst had the weaker fluorescence intensity and the strongest photocurrent intensity,suggesting that the photo-generated carriers were effectively separated and the photocatalytic performance was significantly improved.3.Effect of PtNi_x Coy and its dealloying on Cd S’s performance in photocatalytic hydrogen generationIn order to reduce the cost of the catalyst,introducing Ni and Co element,PtNi_x Coy ternary alloy NPs were synthesized by solvothermal method.The effects of PtNi_x Coy alloy and its dealloying on the photocatalytic hydrogen production performance of Cd S were investigated under visible light irradiation.The hydrogen production rates of Pt Ni₂Co/Cd S and Pt Ni Co₂/Cd S were 35.42 mmol·h^-1·g^-1 and 34.93 mmol·h^-1·g^-1,respectively,which were significantly higher than those of single metal Pt/Cd S,Ni/Cd S and Co/Cd S.After dealloying,the hydrogen production rates of d-Pt Ni₂Co/Cd S and d-Pt Ni Co₂/Cd S were 41.52 mmol·h^-1·g^-1and 44.94 mmol·h^-1·g^-1,respectively,which were apparently higher than those of Pt Ni₂Co/Cd S and Pt Ni Co₂/Cd S.Electrochemical results showed that PtNi_x Coy NPs could increase the current density of hydrogen evolution and decrease the overpotential of hydrogen evolution.XRD patterns showed that PtNi_x Coy NPs tended to deposit preferentially on（002）crystal surface of Cd S during photocatalytic decomposition of water for hydrogren generation reaction.UV-Vis spectrum showed that PtNi_x Coy/Cd S enhanced the absorption of visible light in the range of 550-800 nm.PL spectrum and I-T curves showed that d-Pt Ni₂Co/Cd S and d-Pt Ni Co₂/Cd S had the weaker fluorescence intensity and the strongest photocurrent intensity,suggesting that photoelectron-hole composite wass minimized and photocatalytic activity was the highest.