Design And Construction Of Transition Metal Phosphide-Based Carbonaceous Hybrids And Their Electrocatalytic Hydrogen Evolution Performances

Hydrogen（H₂）has always been considered as the ideal alternative for substituting fossil fuels due to its cleanliness,high-energy property and sustainability.In comparison with traditional industrial hydrogen producing methods,water electrolysis for hydrogen production is more direct and effective,without releasing greenhouse gas and toxic byproducts.Because of the polarization,the real potential of water splitting is much higher than the theoretical one,thus causing the increase of energy consumption and the decrease of efficiency.In terms of cathodic hydrogen evolution reaction（HER）,20%Pt/C is the most efficient commercial electrocatalyst to decrease its overpotential,but the shortcomings including high-cost,rare crustal abundance and inferior long-term durability restrain its large-scale application.However,transition metal phosphides possess rich resources,favorable conductivity,exhibiting promising prospect in electrocatalytic HER application,which are the potential candidates in place of precious metal-based materials.Therefore,this dissertation focuses on the structure-integrated transition metal phosphide carbonaceous hybrid HER electrocatalysts and investigates the controllability and universality of their synthesis.The main research content is as follows:（1）In the presence of NaCl hard template,electrostatic interaction-self assembly process followed by pyrolysis and phosphorization is used to fabricate MoP nanocrystals embedded in3D N-doped carbon networks（MoP/NC）.Optimize the structure,composition and performance of the catalyst through changing the experimental parameters,thus accounting for the structure-function relationship and performance superiority of MoP/NC hybrid.The optimal MoP/NC hybrid only requires the overpotential of 130 mV to deliver a current density of 10 mA cm^-2 and works continuously for 20 h with the current density retention of 88%,exhibiting the favorable electrocatalytic HER activity and stability.In addition,the hybrid of WP nanocrystals embedded in N-doped carbon networks（WP/NC）is obtained with similar steps,which not only exhibits the rationality and generality of this template synthesis,but also provides the therectical foundation for the design and construction of 3D transition metal phosphide-based carbonaceous nanomaterials.（2）A bottom-up citric-urea sol-gel method is adopted to construct FeP nanocrystals embedded in N-doped carbon nanosheets hybrid（FeP/NCNSs）.The formation process is deeply investigated.The optimal hybrid catalyst is obtained by optimizing the experimental parameters and the correlation between its architechture and performance is also systematically analyzed.To achieve the current density of 10 mA cm^-2,FeP/NCNSs hybrid possesses an overpotential of 114,205 and 409 mV,respectively,showing favorable HER activity over a broad pH range.Moreover,the preparation of Ni₂P nanocrystals embedded in N-doped carbon nanosheets could be realized by this method,which exhibits the universality of the synthesis.The synthetic route can be extended to the design and construction of other two dimensional transition metal phosphide-based carbonaceous hybrids.（3）Modify the conventional cobalt-based metal organic framework with introduction of bridge ligand.With the modified precursor,a unique low-dimensional hybrid of N-doped carbon nanowires confined CoP nanocrystals（CoP/NCNWs）is obtained through in-situ pyrolysis and phosphidation process,while an optimized pyrolysis strategy is proposed.The effects of individual component on the micro/nano-architecture and electrocatalytic performance have been systematically investigated,which reasonably accounts for structure/performance superiority of the hybrid.CoP/NCNWs only needs 95 and 154 mV in acid and alkaline,respectively,to drive a current density of 10 mA cm^-2 and achieves stable operation for 20 h,indicating the excellent HER performances in two extreme environments.Furthermore,CoP/NCNWs possesses good basic oxygen evolution performance,exhibiting favorable hydrogen/oxygen evolution bifunctional property.