Design,Synthesis,and Electrocatalytic Performance Of Noble Metal Free Nanocatalyst For Water Splitting

Hydrogen,high mass-specific energy density and clean energy,is considered as a rational substitute for fossil fuels.Owing to low cost and high-purity product,electrochemical water splitting becomes a potential hydrogen generation technology,which involves two electrochemical half reactions,hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.However,the practical application of water splitting performs the large overpotential and the unfavorable thermodynamics,owing to sluggish kinetics involving four electron transfer.Hence,even now the researchers need to develop appropriate electrocatalyst,in order to decrease the activation energy and increase the conversion efficiency.Up to now,the state-of-the-art HER and OER electrocatalysts are Pt-based materials and the oxides of Ru or Ir,respectively.Nevertheless,the scarcity and high cost hinder widespread deployment of precious metal materials.Extensive efforts have been devoted to nonprecious electrocatalysts including transition-metal compounds,such as sulfides,phosphides,carbides,nitrides and oxides.However,the activity and durability of most noble-metal-free electrocatalytic materials remain far from satisfactory.In the thesis,we have designed and prepared a series of non-precious metal catalysts for electrochemical water splitting,and enhanced the activity and stability of materials through heteroatom doping,special morphology and carbon coating.The main research contents are given as follows:The non-precious FeP nanocubes were prepared within 35 min by acid etching the electrodeposited Fe/FeOOH/FeP precursors at room temperature.The FeP nanocubes possessed unique nanoporous structures on the surface and inside,which were beneficial to expose more active sites and effectively accelerate the mass transfer.Therefore,the as-synthesized nanoporous FeP cubes exhibited favourable catalytic HER activity with low overpotential to approach 10 mAcm^-2 in both acid and alkaline media,as well as long-term stability in acid solution.Fe₃C catalysts have been intensively studied due to their low cost,superior catalytic performance and stability as electrode material in place of precious metal materials.We acquired the molybdenum-doped iron carbide nano-materials after calcination utilized zinc-iron-molybdenum trimetal composites as templates.The doping of molybdenum could adjust the electronic structure,which was conducive to the improvement of catalyst performance.At the same time,the structure of carbon coating could increase the conductivity and stability.The Mo-Fe/Fe₃C material showed favourable OER performance in alkaline media,and it could maintain its original activity after 24 hours of continuous testing.We synthesized yolk-shelled CoP@Fe-CoP/N-doped-carbon micro-polyhedras?CoP@FeCoP/NC YSMPs?by the anion-exchange reaction from ZIF-67micro-polyhedras?ZIF-67 MPs?as templates and the subsequent phosphorization.Owing to large active surface area of yolk-shelled construction,interaction between metal phosphides and synergistic effect between phosphides and carbon matrix,the as-obtained CoP@FeCoP/NC YSMPs have exhibited superior hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?catalytic performance in an alkaline electrolyte,needing overpotentials as low as 143 mV and 236 mV?for HER and OER?,respectively,to drive the current density of 10 mA cm^-2.When a two-electrode water splitting device is conducted with the as-prepared catalyst,a low cell voltage is only 1.68 V under 10 mA cm^-2 and it shows outstanding stability after continuous run for 20 h.