Study On The New Metal Alloy Photocatalytic Cocatalyst

Hydrogen as a clean and efficient energy sources, is an important way tosolve the energy shortages and environmental pollution problems. Currently,hydrogen is mainly derived from fossil fuel refining (about96%), however thisway not only can not solve the energy shortage, but also brings seriousenvironmental pollution problems. Photocatalytic water splitting using solarenergy to obtain clean hydrogen can effectively solve the above problems. Asthe hydrogen demand is increasing, improveing the activity of hydrogenproduction and developing new technologies for hydrogen production have getmore and more attention. Among the semiconductor photocatalytic materials,the band gap of CdS is2.4eV, CdS is a highly active catalytic activity withvisible light photocatalyst, but pure CdS photocatalytic has a low photocatalyticactivity. Co-catalyst plays a very important role in photocatalytic water splittingreaction system. It can greatly improve the activity of hydrogen production. In this paper, in order to get a new type of high activity of photocatalytic watersplitting, study the influence of cocatalyst’s crystal morphology inphotocatalytic water splitting activity. Preparation methods of differentmorphologies Pt, Pd single metal and alloy nanoparticles and the activity ofelectro-catalytic oxidation are explored. By loading different morphologies ofcocatalyst, to study the impact on the photocatalytic water splitting activity. Themain contents and results are as follows:(1) Chemical reduction method and hydrothermal method are used forpreparing the shape controlled platinum nanoparticles. Sphere, cube and cubeoctahedron Pt nanoparticles were successfully prepared, based on theinvestigation on the influences of experimental parameters including thereaction time, reducing agent concentration and so on. Studied theelectrocatalytic oxidation activity of platinum nanoparticles, compared cubeoctahedral Pt with commercial Pt/C, cube octahedron Pt nanoparticles havelarger current density and higher electrical activity. The specific morphology Ptnanoparticles prepared by chemical reduction method loaded on the catalyst,get composite photocatalyst Pt/CdS. Studied the effect of cocatalystmorphology to the photocatalytic water splitting activity. Pt/CdS with cubemorphology Pt cocatalyst have a higher photocatalytic water splitting activity,was approximately1.3times higher than that of Pt/CdS with cube octahedralmorphology Pt cocatalyst. Indicating the {100} faces of Pt nanoparticles have ahigher activity than {111} faces. (2) A facile and simple chemical reduction method has been developedfor the fabrication of Pd nanoparticles. Sphere and different siz of cubes Pdnanoparticles were successfully prepared by controlling the amount of KBr ascapping agent. It is found that in the absence of Br-, spherical nanoparticleswere prepared. The existence of Br-makes the particles grow along <100>direction, leads to the formation cube morphology with six {100} planes. Withthe increase of amount of Br-, the particle size is increased, and a small amountof rodlike is generated. Electro-catalytic oxidation activity of Pd nanoparticleswith different morphologies was studied using cyclic voltammetry method inethanol solution. Pd nanoparticles with {100} crystal faces have a highersurface energy can provide more active sites, so Pd nanoparticles with cubemorphology showed39times higher Electro-catalytic oxidation activity thanthat of spherical. The Pd nanoparticles with specific morphology as co-catalystloading on traditional catalyst CdS, get composite photocatalyst Pd/CdS. Cubicmorphology Pd nanoparticles as a co-catalyst, because of the strong adsorptionability of photo-generated electrons, greatly improved the photocatalytic watersplitting activity, which is2.2times than that of sphere. The result evidence thatthe crystal face have a great influence of adsorption and desorption activity ofthe catalyst.(3) Pt-Pd bimetal cocatalysts were carried out using a hydrothermalmethod. In particular, it was found that molar ratio of platinum and palladiumhas a great influence in morphology. When the molar ratio is1:1, it is cube Pt-Pd alloy, particle size is about15nm. When the molar ratio is1:2, cubemorphology for20nm is obtained. When the molar ratio of platinum andpalladium is2:1, with the reduction of the palladium, only a few cubes areformed, most nanoparticles are irregular polyhedron. When the proportion of Ptfurther increases to3:1, there is almost no cube, most nanoparticles areirregular morphology. After loading on the catalyst CdS, get Pt-Pd/CdScomposite photocatalyst. When the molar ratio of Pt: Pd is1:2, photocatalyticactivity is the lowest, hydrogen production rate is about600μmol/h. When themolar ratio of Pt:Pd is1:1, exhibiting a higher photocatalytic water splittingactivity, the rate of hydrogen production is about1120μmol/h. When the molarratio of Pt:Pd is2:1, with the increase of the amount of platinum, the activehydrogen is further increased to approximately1910μmol/h. When the molarratio of Pt:Pd increased to3:1, the hydrogen production rate decreased to1300μmol/h.