Preparation And Properties Of Of Electrocatalytic Nanocomposites For Highly Efficient Water Splitting

Hydrogen（H₂）,with the advantages of high energy density and carbon‐free emission,becomes a promising and renewable energy to replace traditional fuels.Water splitting driven by electricity is an effective and established technology for H₂production,involving two half‐reactions of hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）at cathode and anode,respectively.To date,the best and state‐of‐the‐art electrocatalysts for HER and OER are Pt and Ir/Ru-based oxide materials,respectively.Unfortunately,the exorbitant price and scarce crustal abundance of these noble metals limit their large-scale applications in the future.As a result,great attention has been attracted in exploring high electrocatalytic activity,inexpensive,and stable precious metal-free catalysts for the overall water splitting.In this paper,the main points are shown as follows:Bi₂Se₃ nanoflowers composed of numerous thin nanosheets were successfully synthesized by a hot-solution injection method under mild conditions.The reaction temperature,reaction time,and surfactant ratio（oleylamine/oleic acid）were conducted to investigate the influence of the phase purity and morphology.Based on the experimental results,the formation mechanism of Bi₂Se₃ nanoflowers was proposed.Bi-rich nanoparticles were formed at the beginning of the reaction,then Bi₂Se₃ nanosheets were formed on the surface of the nanoparticles owing to the reaction with exposed Bi atoms on the surface and assembled into nanoflowers.In addition,the size of nanoflowers decreased with the increasing surfactant ratio of oleamine/oleic acid due to the strong ligand binding and reduction of oleamine.Finally,Au nanoparticles were decorated onto the surface of Bi₂Se₃ nanoflowers to investigate the HER performance,which could be significantly improved by the surface plasmon resonant excitation generated on illuminated plasmonic Au nanoparticles.With the strong visible light irradiation,the overpotential at 10 mA cm^-2 was decreased from 380 to 375 mV,and the Tafel slope is decreased from 82 to78 mV dec^–1.Duo to the few reports of Bi₂Se₃ heteronanostructure as electrocatalysts for HER,Herein,a specific high-performance electrocatalyst of flower-like Bi₂Se₃decorated with MoS₂ nanosheets,has been rationally designed and successfully developed through two-step hot injection methods in colloidal system.In the second hot-injection process,in order to grow few layers and highly dispersed MoS₂nanosheets on the Bi₂Se₃ substrate for exposing more active sites,a slow reaction speed controlled by spring pump was conducted to reduce the nucleation-growth process.Compared to pristine Bi₂Se₃ and pure MoS₂,MoS₂@Bi₂Se₃ hybrid exhibited higher hydrogen evolution reaction（HER）activity with lower tafel slope of 57 mV dec^-1.Besides,the overpotential reachs 208?mV?at 10?mA cm^-2.The enhanced catalytic activity could be ascribed to the combination of increasing the active sites by vertically aligned structures,which can effectively prevent the agglomeration of MoS₂,resulting in the formation of thinner nanosheets,and improving the conductivity of the hybrid electrode by electron transfer from Bi₂Se₃ to MoS₂.For the few reports of 3D self-supporting graphene hybrids electrode as bi-functional electrocatalysts towards overall water splitting,in this work,for the first time,the synthesis of sheet-like iron doped nickel boride on 3D self-supporting graphene electrode（Fe_xNi_yB/SSG-FGS）is reported by a facile electrochemical intercalation and one step reduction approach.The SSG-FGS electrode is fabricated via electrochemical intercalation for a flexible graphene sheet（FGS）in 1 M KOH,resulting in in-situ growth self-supporting graphene（SSG）directly connected with the unexpanded FGS.The optimized Fe_xNi_yB/SSG-FGS catalyst shows very low OER overpotentials of 264 mV at 10 mA cm^-2,which is better than most of metal boride catalysts reported to date.Additionally,the assembled Fe_xNi_yB/SSG-FGS electrodes used as anode delivers a current density of 10 mA cm^-2 at 1.65 V for overall water splitting when taking NiB/SSG-FGS as cathode,which is expected to be a candidate to replace noble metal towards water electrolysis.