The Structure Design Of PtNi Bimetallic Cocatalysts And Its Influence On CdS For Photocatalytic Water Splitting Reaction Under Visble Light

Faced with fossil energy depletion and increasing energy demand,and the resulting serious environmental pollution,climate warming and other issues,the world has invested a lot of scientific research to develop new clean energy.Among all the candidates,as a new renewable energy,hydrogen with high energy density and environmental friendly,has been regarded as a promising carbon-free source energy carrier in the future.Solar photocatalytic hydrogen production from water splitting is one of the possible ways using solar energy.Ever since Fujishima and Honda reported photoelectrochemical?PEC?water splitting using a TiO₂ electrode in 1972,many researchers have intensively studied water splitting using semiconductor photoelectrodes or photocatalysts.However,the activity of photocatalysts is low,the response range to sloar spectrum is narrow and some narrow-band semiconductor photocatalysts have less stability and photocorrosion phenomenon.This thesis use Cd S as base catalyst and Pt-based bi-metal as co-catalyst,aiming at increasing photocatalytic activity and reducing the cost of catalyst.The following is the details:1.Effect of structural parameters on CdS's activity for hydrogen production from water splitting under visible lightIt is well known that specific surface area or particle size,crystallinity,crystalline phase and morphology have influence on photocatalytic activity of CdS,and these factors determine the bandgap structure,the light response range,the charge separation and transfer rate,and the reaction rate of the active sites.CdS photocatalytic nanomaterials with nanospheres,nanorods and nano/micro leaves were synthesized using different Cd and S source by hydrothermal or solvothermal method,then H₂PtCl₆was reduced by NaBH₄ to form Pt nanoparicles and loaded on the surface of CdS.The highest H₂production activity of Pt/CdS is 47.77 mmol/h/g when the loading amount of Pt is 1.2wt%and L-CdS was used.The structure and morphology of various CdS samples were characterized,and the key parameters affecting the hydrogen production of CdS visible light were discussed.The results show that L-CdS has the strong and sharp peaks in?002?facet and we infer that the?002?crystal facet may be a high index crystal facet of L-CdS and finally result in a high catalytic activity.2.The preparation of PtNi bimetallic nanoparticles and its influence on hydrogen production activity of CdS in the photocatalytic water splitting reaction.In recent years,the preparation of PtNi bimetallic has become a hotspot in the field of photoelectric catalysis.Many methods have been developed for the preparation of PtNi bimetallic.In general,the choice of synthesis conditions such as metal precursors,solvents,reducing agents,capping agents,reaction temperature and time will affect the structure of bimetallic nanoparticles.However,it is only the first step to synthesize PtNi bimetallic nanoparticles as a co-catalyst for photocatalytic water splitting reaction,and also it need to be deposited on the CdS surface by photo-reduction.Therefore,it is necessary to carefully select the metal precursor salt,solvent,reducing agent,capping agent in the preparation process.Not only to obtain the expected structure of PtNi,but also to ensure that the solvent,reducing agent,capping agent can be separated from the PtNi surface in the follow-up process.It have to say that this is a contradiction.In this paper,the preparation of PtNi alloy nanoparticles was carried out with ethylenediamine as solvent and N,N-dimethylformamide as solvent and reducing agent respectively without capping agent.PtNi alloy nanoparticles were prepared by solvothermal and co-reduction synthesis method,using Pt?acac?₂ and Ni?acac?₂ as precursors,ethylenediamine as solvent,NaBH₄ as reducing agent and PVP as stabilizer,and then deposited on the surface of L-CdS by photo-reduction.PtNi/CdS hydrogen production rate reaches to the highest 48.96 mmol/h/g when the loading amount is 3wt%,PtNi molar ratio is 1:3.The result is mainly due to the synergistic effect of bimetallic which can enhance electron transfer rate and further reduce photogenerated electron-hole recombination rate.PtNi nanopolyhedra were prepared by solvothermal and co-reduction synthesis method,using Pt?acac?₂ and Ni?acac?₂ as precursors,N,N-dimethylformamide as solvent and reducing agent,and then deposited on the surface of L-CdS by photo-reduction.PtNi/CdS hydrogen production rate reaches to the highest 56.55 mmol/h/g when the loading amount is 4wt%,PtNi molar ratio is 3:1,which is much better than monometallic counterparts.The result is mainly due to the synergistic effect of bimetallic which can enhance electron transfer rate and further reduce photogenerated electron-hole recombination rate.