Structural Design Of Molybdenum Phosphide Electrocatalysts Toward Efficient Hydrogen Evolution Reaction

Hydrogen is the promising one of sustainable,renewable and clean energy sources,which has been regarded as one of the most promsing alternatives to reduce fossil fuel dependency.Hydrogen evolution from water electrolysis offers very effective hydrogen production,but it requires high performance electrocatalysts to reduce the overpotential for hydrogen evolution reaction（HER）.Nowadays,platinum-based catalysts are the most active electrocatalysts,but their high cost and low earth-abundance limits their applications.Therefore,it is urgent to find non-precious metals with high activity,low price and high earth-abundance to replace platinum-based catalysts.Molybdenum phosphide,showing high activity and good electrical conductivity,has proved its promise for HER.However,it is still a challenge to construct a molybdenum phosphide nanostructure which can expose rich active sites and have high activity.Base on the structure and characteristics of molybdenum phosphide,this work optimizes the HER kinetics and activity via constructing carbide-phosphide heterostructures,surface-defect engineering,hetero-atom doping,etc.1.Via simultaneously carbonization and phosphorization,we fabricated heterostructured MoC and MoP nanoparticles supported by bacterial cellulose-derived N-doped carbon（BCNC）nanofibers.As evidenced,the presence of MoC can prevent MoP from coarsening due to the strong interfacial interactions,resulting in the ultrafine nanoparticles evenly distributed in N-doped carbon nanofibers.More importantly,heterostructured MoC-MoP delivers the varied electronic-configuration to optimal binding with intermediate H,accomplishing the promoted HER kinetics.Thereby,comparing with single-component of MoC/BCNC and MoP/BCNC,the MoC-MoP/BCNC NFs exhibits high HER activity.In acid and basic electrolyte,the MoC-MoP/BCNC feature a lowη₁₀(overpotential to achieve a current density of-10mV cm^-2)of 158 and 137 mV and small Tafel slopes of 58 and 65 mV dec^-1,respectively.2.The molybdenum phosphide nanoparticles（MoP/CC）supported by carbon cloth were fabricated,and the MoP/CC was further etched by nitrogen plasma to obtain nitrogen atom doped and defect-rich MoP/CC.Etching by specific gas etchings（such as nitrogen and argon）can improve the hydrogen evolution activity of MoP.In particular,the MoP/CC after nitrogen plasma etching shows the higher activity.This is attributed to the fact that the plasma not only can etch the surface of the MoP,making its surface rich in defects,but also reducing the particle size of the MoP,thereby exposing more active sites.More importantly,nitrogen plasma treatment leads to uniform N-doping into MoP,which promotes the dissociation of H₂O,accomplishing the promoted HER kinetics.The results show that the synergistic effect of N doping and defects enhace the HER activity of MoP.In the optimal conditions,N-DR-MoP/CC has aη₁₀0 of 70 mV in alkaline electrolyte and a small Tafel slope of42 mV dec^-1.3.Via pyrolysis method,the cobalt-doped MoP based on bacterial cellulose was fabricated,which can improve the catalytic activity of HER.A series of Co-MoP/BCNC were obtained by adjusting the temperature and feeding molar ratio of n_Co/Mo.The results show that the doping of Co in MoP effectively increases the activity of HER.Under the optimal conditions,theη₁₀0 of Co-MoP/BCNC-0.05 was153 mV and the Tafel slope was 59 mV dec^-11 in the acidic electrolyte.In summary,this thesis proposed feasible strategies to optimize the structure of MoP and consequently the HER performance.It will provide a reference method and ideas for the development of highly active,stable and economical non-precious metal catalysts.