Synthesis Of Transition Metal/Carbon Based Composites And Their Application In Electrocatalytic Water Decomposition

Nowadays,with the consumption of fossil fuels and natural resources,the two major problems of energy crisis and environmental degradation have become more and more serious,so people are paying more and more attention to the development of sustainable and environmentally friendly energy.At present,electrochemical water splitting,as a non-fossil fuel-based technology,has attracted more and more attention due to its high energy conversion efficiency and has stimulated in-depth research for the production of low-cost and high-purity hydrogen.Noble metal electrocatalysts,such as Pt,Pd,and Ir,are considered to be the pioneers of HER catalysts.It is still the best HER catalyst,with almost zero overpotential and excellent long-term durability.However,the cost of such precious materials is very high,and they lack long-term stability and/or are not affected by fuel oxidation molecules,thus hindering their large-scale application and commercialization.It is of great significance for the design,use and production of highly efficient and cost-effective non-precious HER electrocatalysts to replace traditional noble metal catalysts.Recently,non-noble metal materials,such as transition metal carbides,nitrides,chalcogenides,phosphides,metal alloys,and heteroatom-doped carbon nanostructures,have been potential candidates for HER catalysts.Transition metal carbides and nitrides have become promising materials due to their unique metal-carbon chemical bond and similar noble metal d-state density near the Fermi level,have attracted widespread attention.In addition,the metal-N active center can effectively improve the electrocatalytic performance because of its Pt-like electrical structure and enhanced electronic conductivity.With the development of theoretical calculation capabilities in recent years,theoretical simulations can accurately optimize the structure of catalysts,such as the incorporation of transition metals and noble metals.Theoretical calculations have proved that the surface electronic structure of nanomaterials and carbon and metal can be effectively adjusted.Coupling,resulting in lower adsorption energy of hydrogen and related electrochemical intermediate products,thereby reducing the overvoltage of the electrocatalyst.It is worth noting that by doping nitrogen into carbon,the resulting N-doped carbon(NC)obviously exhibits an optimized and enhanced electronic structure.Different types of nitrogen doping will also have various effects on electrochemical reactions and catalytic reactions.Therefore,we synthesized a series of electrocatalysts based on transition metal/carbon-based composite materials.The electrocatalytic hydrogen evolution and electrocatalytic oxygen evolution performances of these prepared nanomaterials in electrolyte were studied.The main contents are as follows:1.Using a simple in-situ method and direct high-temperature annealing of WOx/aniline hybrid nanoparticles,WN-W2C nanocrystals coated in a nitrogen-doped carbon matrix were synthesized.Electrochemical measurement results show that the WN-W2C-2R nanocomposite with the highest nitrogen content has the best HER activity in 0.5 M H2SO4 electrolyte,when the current density is 10 mA cm-2 the overpotential is only 242 mV,showing good electrochemical hydrogen evolution performance.The durability and long-term cycle stability tests show that the catalyst has good stability and catalytic performance after 5000 cycles and a 10-hour long-term stability test.This discovery provides a new idea for the synthesis of high-performance,inexpensive and durable hydrogen production catalysts in acid media.2.Nitrogen-doped graphene can promote the transfer of electrons from the alloy core to the graphene carbon to promote catalytic performance,and on the other hand,it can protect the metal core from acid and alkali corrosion to improve cycle stability.Electrochemical tests show that S-4 with the highest nitrogen doping amount exhibits the best HER activity,and its overpotential is only 42 mV when the current density is 10 mA cm-2,which is almost close to the 20 wt%Pt/C catalyst The electrocatalytic performance of Pt-based electrocatalysts,and after a 10 thousands cycles test,its electrocatalytic performance has not significantly deteriorated,so it can become a cheap substitute for Pt-based electrocatalysts in HER.Nitrogen doping can increase H*adsorption sites,and proper amount of precious metal Pd doping can optimize the electronic structure of the alloy.PdNiCo alloy cores can transfer more electrons to the graphene shell than pure Co metal cores,thereby enhancing C-H bonds and greatly reducing the free energy of adsorption of active hydrogen protons at a point,thereby further enhancing HER activity.3.A simple hydrothermal method was used to synthesize cobalt-doped MoS2 nanosheet structures similar to sea urchins.By adding different amounts of Co,we synthesized a series of doped MoS2 nanomaterials.It is used as an electrocatalyst in a three-electrode test system.The catalyst exhibits the dual functional activity of hydrogen evolution and oxygen evolution in both acidic and alkaline media.The trace amount of Co doping in MoS2 can effectively adjust its electronic structure,thereby improving the HER activity of MoS2,and at the same time contributing additional catalytic active sites for OER,thereby exhibiting a good full water decomposition in acidic and alkaline media.Dual functionality.This dual-function Co-doped MoS2 will be very meaningful for the entire water splitting application.On the carbon cloth substrate,sea urchin-like cobalt-doped MoS2 nanoparticles are self-assembled to form a flexible film by deposition,and they were applied to all water decomposition of two electrodes.This results show that its good catalytic activity and excellent cycling stability prove it's wide practical application value.