Controllable Preparation And Electrocatalytic Performance Of Transition Element And Biomass Carbon-based Electrocatalysts

Hydrogen energy is considered to be one of the best alternatives to traditional energy sources and resolve environmental issues due to its high combustion value,ease of storage and transportation,and no pollution.Hydrogen production from electrolysis water is considered as the most efficient method for converting renewable resources into hydrogen energy.Though precious metal-based catalysts exhibit the highest catalytic activity,the expensive cost,low reserves and poor stability have limited their widely application.Therefore,researching and developing low-cost,high-efficiency non-precious metal-based catalysts has attracted the attention of researchers.Biomass carbon materials have a wide range of applications in the energy field due to their wide range of sources and controllable chemical composition and structure.In this paper,combining with the advantages of transition elements and biomass carbon-based materials,such as cheap and easy to obtain,abundant reserves,and controllable electronic structure,transition element coupled with biomass carbon-based electrocatalytic materials with high catalytic activity and stability were prepared by using special chemical modification techniques,such as phosphorization,sulfurization and phosphorylation.The main findings obtained are as follows:?1?In this study,a binary cobalt-nickel transition metal phosphide electrocatalyst?Co_xNi_yP?was fabricated through solvothermal,pre-oxidation and low-temperature phosphating techniques,and the electrocatalytic properties of the catalysts were studied.The results showed that the organic-inorganic hybrid nanosheet catalyst Co_xNi_yP exhibited excellent HER activity in a wide pH range?0¹4?and closed to OER performance of commercial RuO₂.The HER overpotential and Tafel slopes in 0.5 M H₂SO₄ were 148 mV and39 mV/dec,respectively.The experimental and theoretical calculations showed that the excellent catalytic activity of the catalyst is mainly attributed to the two-dimensional layered nanosheet structure which promotes electron transfer.The synergistic effect between cobalt and nickel atoms in the binary metal phosphide improves the catalytic activity of the catalyst.The characteristic of easy-to-operate,controllable composition and structure of this synthesis provides new technologies for the synthesis and electrocatalytic applications of other multi-metal phosphides.?2?Considering the fact that the stability and activity of the nanosheet catalyst are not ideal,the sulfur-doped CoSe₂/CoMoO₄?S@CoSe₂/CoMoO₄?and O@CoSe₂/CoMoO₄catalysts were prepared based on the conductive CoSe₂/DETA nanobelts.When S@CoSe₂/DETA was used for electrocatalytic hydrogen evolution,the synergistic chemical coupling between CoSe₂/DETA and CoMoO₄ and the doping of sulfur induced S@CoSe₂/CoMoO₄ exhibited better catalytic activity than CoSe₂ nanobelts.Among them,S@CoSe₂/CoMoO₄ exhibited a low overpotential?177 mV?and a small Tafel slope?54mV/dec?.In addition,the O@CoSe₂/CoMoO₄ hybrid catalyst displayed outstanding OER performance,and showed lower overpotential?471 mV?and Tafel slope?43 mV/dec?that better than RuO₂,as well as higher stability and durability.?3?Due to the characteristics of abundant resources,low cost,large specific surface area,high mechanical strength,excellent electrical conductivity and stability,biomass carbon-based material can be used as a carrier to improve the stability and conductivity of the catalyst.In this study,xylose-based porous carbon supported defective molybdenum disulfide electrocatalyst?P_x-MoS₂@FPC?was prepared by coupling and phosphorization.It is found that the hybrid material not only displayed the characteristics of a molybdenum sulfide structure,but also the defective molybdenum sulfide and the introduction of carbon-based materials improve the electrical conductivity and catalytic activity of the composite.The results showed that the catalyst P₃-MoS₂@FPC demonstrated excellent electrocatalytic hydrogen evolution activity and stability in 0.5 M H₂SO₄ solution?10 mA/cm² at a low overpotential of 144 mV?.Meanwhile,the P₃-MoS₂@FPC catalyst showed outstanding methanol resistance and stability in 0.1 M KOH solution.?4?The doping of heteroatoms is beneficial to regulate the electron density of carbon atoms that bonded to heteroatoms and enhance the catalytic activity of carbon materials.In this study,the phosphorylated chitosan was used as a macromolecular skeleton.Relying on the coordination chelation between phosphate of modified chitosan and cobalt ions,cobalt-nitrogen-phosphorus porous carbon bifunctional electrocatalyst was prepared by one-step carbonization method.The results show that higher carbonization temperature?900??leads to a decrease in the specific surface area and nitrogen content of the catalyst,as well as causes a phase change of the catalyst,which induces the formation of a Co₂P phase.As a consequence,the product Co-N-P-900 displayed the best HER performance.XPS and ORR test results indicate that higher levels of pyridinium and graphitized nitrogen promote Co-N-P-700 to exhibit ORR performance superior to that of commercial Pt/C.