Laser Assisted Synthesis Of Ni-based Compound And Its Electrochemical Performances

Ni-based compounds are considered as one of the most promising materials for pseudocapacitor and methanol oxidation,owing to the low cost,environmental friendliness,high theoretical capacitance and excellent catalytic activity.However,the poor conductivity,large volume expansion and serious aggregation of Ni-based compound during electrochemical reaction limit its practical applications.Developing novel synthesis strategy in doping of impurities,surface modification and optimal structural design to improve electrochemical performances of Ni-based compounds,is a hot topic in pseudocapacitor and methanol oxidation.Laser ablation in liquids(LAL)and laser irradiation in liquids(LIL)have been demonstrated as an effective and eco-friendly technology to fabricate kinds of nanomaterials with controllable component,structure morphology and size.Meanwhile,nanomaterials produced by LAL and LIL have unique properties such as small size,highly active and charged surface.Based on those advantages,a series of Nickel-based compounds have been synthesized by LAL or LIL in this paper.Moreover,as-synthesized Nickel-based compounds used as electrode materials for supercapacitors and non-platinum catalysts for methanol oxidation display excellent performance.The study contents and results are listed as following:(1)Ni3+ doped cobalt-nickel layered double hydroxides as high performance electrode material for supercapacitorsNi3+ doped cobalt-nickel layered double hydroxides(Co-Ni-LDHs)were synthesized by ablating Ni taget in CoCl2 aqueous solution.The existence of Ni31 ions in Co-Ni-LDHs reduced the conductive resistance and increased the mobility of surface charge and transfer rate of electrolyte.As a result,Ni31 doped Co-Ni-LDHs displayed maximum specific capacitances of 2275 F/g and 1450 F/g at the current density of 1 A/g and 20 A/g,respectively,indicating a high rate specific capacitance.Moreover,the capacitance retention was up to 80%after 1800 cycles at the current density of 6 A/g,manifesting good cycling stability.Moreover,Different trivalent ion(Ni31,Co3+)doped LDH was also prepared by changing ablation target and solution.(2)Hierarchical mesoporous NiCo2O4@Mn3O4 core-shell nanowire arrays on nickel foam with enhanced supercapacitor performanceHierarchical mesoporous NiCo2O4@Mn3O4 nanowires arrays on nickel foam were prepared via hydrothermal reaction and LAL for supercapacitor applications.The as-prepared electrodes exhibited specific capacitances of 1100 F/g and 750 F/g at the current density of 5 A/g and 30 A/g,respectively,and the capacitance retention was up to 62.48%after 2000 cycles at the current density of 2 A/g,indicatingexcellent rate capability and superb cycling stability.The outstanding electrochemical performance was attributed to the effective conductive transport path between component materials,reduced electron and ion transport pathways,enhanced surface area,and facile electrolyte infiltration into the hierarchical mesoporous structure.The hierarchical mesoporous design may provide a universal approach for the development of new electrode materials for high-performance pseudocapacitors.(3)Ultrafine nickel nanoparticles modified reduced graphene oxide as efficient non-platinum catalysts for methanol oxidationSynthesis of low-cost,highly-active and durable non-platinum metal catalysts for methanol oxidation reaction(MOR)is always full of challenge.Here,Ni nanoparticles modified reduced graphene oxide(Ni/rGO)as an efficient non-platinum catalyst were synthesized by laser ablation of Ni target in graphene oxide(GO)solution and the following in situ reduction process.It found that GO played an important role to restrict the growth and aggregation of ultrafine nickel colloids in the process of laser ablation.The resulting Ni/rGO catalyst showed advantageous in active sites and charge transport resulting from the small particle size(2.3±0.4 nm),uniform dispersion and electronic effect arising from the electron interactions between reduced graphene oxide(rGO)and Ni.The obtained Ni/rGO exhibited the ultrahigh catalytic mass activity of 1600 mA/mg,methanol saturation concentration(4 M),which was superior to that of the reported Ni-based catalysts.Remarkably the mass activities of Ni/rGO before and after 1000 cycles exceeded that of the commercial Pt/C catalyst,indicating excellent catalytic activity and stability.(4)Laser assisted synthesis of NiO nanoparticles modified heteroatom S,N dual-doped carbon nanocubes as efficent electrocatalyst for methanol oxidationDoped nanocarbon materials(e.g.,carbon nanotubes,graphene)are considered as effective electrocatalyst supports for fuel cells.In the current paper,we reported a novel approach to synthesize nitrogen,sulfur-dual doped multi-walled carbon nanotubes(CNT)as a highly efficient support for NiO nanoparticles catalysts.The NiO modified S,N dual-doped carbon nanotubes(NiO/N,S-CNT)were successfully prepared by laser irradiating the solution of nickel acetate,thiourea and CNT.Under laser irradiation,the CNT were heated to decompose thiourea as the sole source of nitrogen and sulfur,meanwhile triggered the chemical reactions locally,resulting fine NiO NPs attached tightly to NiO/N,S-CNT.The doped nitrogen and sulfur atoms not only provided uniformly dispersed anchoring sites for the formation of NiO nanoparticles on the surface of CNTs but also enhanced the electron transfer interaction between NiO nanoparticles and the N,S-CNT support.The electrochemical properties of the catalysts demonstrated that the as-prepared NiO/N,S-CNT exhibited much higher electrocatalytic activity(2200 mA/mg),long-term durability(the mass activity kept 65.8%after 40000 s)and methanol saturation concentration(13 M)for the methanol oxidation reaction(MOR)compared to the undoped NiO/CNT.In addition,we had successfully synthesized other heteroatom-doped graphite such as N,S doped graphene by LIL.