Preparation And Electrochemical Hydrogen Evolution Properties Of Cobalt Based Sulfide And Phosphide/Graphene Composites

Hydrogen?H₂?,because of its efficiency,cleanliness and eco-friendly possibilities,has been widely regarded as efficient and clean alternatives to fossil fuels.Currently,the electrolysis of water to generate hydrogen has been considered an attractive and the most ideal energy craft.However,electrochemical hydrogen evolution reaction?HER?requires satisfied catalysts to increase energy conversion efficiency.Therefore,it is of great significance to design and develop catalysts with high performance and low cost for HER.In recent years,cobalt-based metal sulfide and phosphides,due to their unique structure and intrinsic catalytic activity,have attracted extensive interest of researchers.In this work,cobalt-based sulfide and phosphide/graphene composite electrocatalysts were successfully prepared.We analyzed the composition,morphology and structure of these electrocatalysts and studied their HER performance in different electrolytes.The main contents are as follows:1.Using thioacetamide as the sulfur source,dicyandiamide as the nitrogen source and GO as the carrier,we synthesized the precursor of nitrogen-doped reduced graphene oxide-supported cobalt sulfide nanoparticles?CoS/N-RGO?by solvothermal method.By adjusting the ratio of different nitrogen doping,we got the proper nitrogen doping ratio in RGO that the mass ratio of GO and DCDA was 1:2.Finally,the CoS/N-RGO was successfully synthesized by high-temperature calcination.Compared with CoS monomers,the CoS/N-RGO shows efficient HER performance in 0.5 M H₂SO₄ electrolyte with a low onset potential of 50.3 mV,a small Tafel slope of 74.4 mV dec^-1,a high double layer capacitance of 9.8 mF cm^-2 and long-term stability.2.Using sodium alginate?SA?and graphene oxide?GO?as raw materials,we synthesized alginate hydrogel formed by the combination of SA and GO mixed solution with Co²⁺,dehydrated by the freeze-drying process to obtain Co-alginate containing graphene aerogel.Finally,carbon core-shell containing cobalt phosphide nanoparticles embedded in graphene aerogel?CoP@C-NPs/GA?was synthesized via a phosphatization process.Further,we adjusted the mass ratio of GO and SA?mass ratio?%?=0,5,10,20;GO/SA?,when the mass ratio of GO and SA is 5%,it is found that CoP@C-NPs/GA-5 has a better microstructure morphology.The synthesized CoP@C-NPs/GA-5 exhibits efficient HER activity with small overpotentials of 120and 225 mV at current densities of 10 mA cm^-2,along with the low Tafel slopes of 57and 66 mV/dec for HER in 0.5 M H₂SO₄ and 1 M KOH electrolytes,respectively.As an extension,we also synthesized Ni₂P@C-NPs/GA-5 electrocatalysts in a similar way,and compared their HER performance,and discussed the feasible catalytic mechanism.3.NiCoP nanoparticles?NiCoP-NPs?embedded in graphene aerogel?NiCoP-NPs@GA?was successfully synthesized by sol-gel method and in-situ phosphorization process.Compared with the NiCoP bulk,the nanopores of GA played a good limited domain effect,effectively inhibited the agglomeration of NiCoP-NPs,restricted the volume of NiCoP-NPs.The Langmuir surface areas of NiCoP bulk and NiCoP-NPs@GA were 9.20 m²/g and 192.15 m²/g respectively,which confirmed that the introduction of GA significantly increased the specific surface area of NiCoP-NPs@GA.Moreover,NiCoP-NPs@GA exhibited excellent electrochemical performance,in which the NiCoP-NPs@GA exhibits outstanding stability and the small onset potentials of 34 mV and overpotentials of 109 mV at current densities of10 mA cm^-2,along with the low Tafel slopes of 63 mV/dec for HER in acidic electrolytes.In this work,bimetallic phosphides were synthesized by in situ phosphating alginate route,which provided a new idea for the synthesis of other bimetallic compound composites.