Study On Co-Based Nano-catalysts For Hydrogen Generation From Sodium Borohydride Hydrolysis

With the rapid development of socio-economic and people's growing demand for energy,it is of great significance to look for a clean,safe,efficient and sustainable energy system.Hydrogen which is a new,clean and renewable energy draws much attention.As an effective carrier of hydrogen,proton exchange membrane fuel cells can convert chemical energy directly into electric energy and produce only water.However,it is difficult to use the hydrogen as fuel for fuel cells mainly because of the lack of safe and efficient hydrogen storage technology as well as convenient way to supply hydrogen,NaBH4 with the advantages of high theoretical hydrogen storage capacity,high energy density,safety and credibility,has become a hot research of hydrogen storage materials.The hydrolysis and dehydrogenation reaction of NaBH4 is a convenient and safe hydrogen generation technology and most of the study devote to find an efficient catalyst for it.Although,as the dominant catalyst,the noble metals(e.g.Pt,Pd,Ru,Rh,etc.)have superior catalytic activity for the hydrolysis reaction of NaBH4,the high cost,limited reserves and lots of demand have limited their widespread application.Therefore,the discovery of an inexpensive and excellent performance catalyst for NaBH4 hydrolysis is an urgent problem.Compared with the noble metal catalysts,Co-based catalyst draws more attention because of its good catalytic activity and low costs.In this paper,we carried out a series of studies about preparation,characterization and catalytic activities for NaBH4 hydrolysis of the Co-based catalyst.Specific studies are as follows:1.Co@Pt-PEDOT:PSS/MWCNTs nanocatalyst:Co@Pt core-shell nanoparticles was constituted by a Co core and a layer of Pt shell,and supported on multi-walled carbon nanotubes(MWCNTs)modified by poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)(PEDOT:PSS)by a facile strategy.The carrier catalyst was compounded through a kind of simple method.Co was prepared by chemical reduction of Co colloidal and Pt was replaced by a galvanic replacement.Transmission electron microscopy and X-ray diffraction were used to characterize the morphology and the structure of Co@Pt-PEDOT:PSS/MWCNTs catalysts,moreover,X-ray photoelectron spectroscopy were used to analyse the element valence.These well-supported and low-Pt-content nanostructures provide more surface active sites,and then catalytic activities for the NaBH4 hydrolysis reaction was advanced greatly.The maximum hydrogen generation rate is 6900 mL/(min-g)at 298 K.The activation energy of the hydrolysis for Co@Pt-PEDOT:PSS/MWCNTs catalysts is found to be 47.3 kJ·mol-1.2.CuCoNi nanosheets catalyst:The well dispersed magnetically recyclable tri-metallic nanosheets with non-noble metallic elements have been successfully synthesized via a facile one-step in situ procedure using sodium borohydride(NaBH4)as the reducing agent.Transmission electron microscopy and X-ray diffraction were used to characterize the morphology and the structure of CuCoNi nanosheets catalysts,moreover,X-ray photoelectron spectroscopy were used to analyse the element valence.The 2-D metal nanosheets exhibit higher catalytic activities for hydrolytic dehydrogenation of NaBH4 than those traditional mono-metallic,bimetallic and trimetallic alloy nanoparticles.The synergetic interaction between Co and Ni in CuCoNi nanosheets may play a critical role in the enhanced catalytic activity.Furthermore,the kinetic studies indicate that the catalytic hydrolysis of NaBH4 by the CuCoNi nanosheets is first order,with the activation energy measured to be 40.6 kJ·mol-1.3.Ru-M bimetallic nanocatalyst:A simple and green method has been demonstrated to successfully prepare Ru-M(M = Fe,Co,Ni)NPs with tunable composition(nominal Ru/M atomic ratios of 4:1,1:1,and 1:4)in aqueous solution under mild conditions.All Ru-M NPs with a small size of 3-5 nm show a Ru fcc structure,suggesting the bimetallic formation(alloy and/or partial core-shell),examined by transmission electron microscopy(TEM),and X-ray diffraction(XRD)analysis.The catalytic activities of Ru-M NPs in the hydrolytic dehydrogenation of NaBH4 reveal that Ru-Co NPs with a ratio of 3:1 show the best catalytic activity and even better than that of pure Ru NPs when normalized to Ru molar amount.The Co oxidation state in Ru-Co NPs has been suggested to be responsible for the corresponding catalytic activity for hydrolytic dehydrogenation of NaBH4.This strategy for the synthesis of Ru-M NPs is simple and environmentally benign in aqueous solution with the potential for scale-up preparation and the in situ catalytic reaction.