Study On Preparation Of Transition Metal Phosphides(Sulfides) And The Regulations Of Their Electrocatalytic Performances

Hydrogen fuel has attracted much attention due to its high theoretical energy density,promising large-scale applications and environmental friendliness.As an efficient way to produce hydrogen fuel,currently,water electrolysis is a hot research topic.However,a major challenge is to accelerate the sluggish oxygen evolution reaction(OER)kinetics.So far,layered NiFe double hydroxide represents the best OER activity among all Ni and Co-based oxides.Nevertheless,the low electronic conductivity seriously impedes the electron transfer from the catalyst surface to the carrier electrode,thus limiting its whole catalytic activity.Also,its complete mechanism and structural characteristics are not fully understood.On the other hand,platinum electrode has been used as the counter electrode for hydrogen evolution reaction due to its good stability and high conductivity.Recent studies show that the Pt electrode can be slowly dissolved and regenerate on the working electrode along with the long-time hydrogen evolution reaction(HER)test.However,to date,the relationship between the Pt deposition and the intrinsic properties of the working electrode remains elusive.The main contents of this thesis are as follows:(1)To improve the catalytic performance of pure nickel phosphite,monodispersed ternary(Ni1-xFex)12P5 nanocrystalline with tunable Ni/Fe ratios are prepared as highly efficient OER electrocatalysts.X-ray photoelectron spectroscopy(XPS)studies reveals that enhanced charge transfer from the foreign metal(Fe)to the host(Ni)to P atoms and a strong synergistic effect exist in the composite(Ni1-xFex)12P5 electrocatalysts,thus rendering the as-prepared(Ni1-x,Fex)12P5 nanocrystalline compounds with a Ni/Fe ratio of 0.51/0.49,the highest OER activity with a small onset potential of 125 mV,a low Tafel slope of 39 mV dec-1,and a low overpotential of 216 mV,to achieve 20 mA cm-2 in an alkaline medium electrolyte.(2)To explain the internal relationship between Pt regeneration and the inherent properties of working electrode,layered 2H-WS2 nanosheets with varying degrees of edge sites are prepared via hydrothermal method to study the edge selectivity of in situ electrochemical Pt deposition.It is revealed that the layered WS2 nanosheets with rich exposed edges show much stronger interaction with Pt atoms because the terminated S22-or S 2-ligands on the edge exhibit much lower binding energy for Pt atoms compared with the apical S2-ligands on the terrace surface.The Pt atoms are easier to regenerate on the edge sites rather than the terrace sites.The in situ electrochemical Pt-deposited WS2 nanosheets with rich exposed edges can act as a highly active hybrid electrocatalyst to accelerate HER kinetics and exhibit commercial Pt-like HER performance,especially in the alkaline media.