Controllable Synthesis Of Transition Metal Phosphides And Their Applications In Water Electrolysis

Facing the threats of worsening environmental pollution and energy shortage,researchers are motivated to seek green and renewable energy as an alternative to fossil fuels.H₂,as an important energy carrier to power future,possess a high gravimetric energy density without carbon emission.Electrocatalytic water splitting,as a sustainable H₂ production technology,is essential to the development of the future hydrogen economy.However,the water electrolysis is an energetically uphill chemical process where the sluggish kinetics limits the two half reactions（oxygen evolution reaction OER and hydrogen evolution reaction HER）.Up to now,noble-metal such as Pt/C and Ir O₂ are widely utilized for HER and OER,but they cannot be economical and long-term effective catalysts for practical applications.Therefore,it is a hot research topic to design low-cost,high-efficiency and durable bifunctional catalyst for the overall water splitting.The potential of transition metal phosphides（TMPs）in electrochemical reaction attract tremendous attention because of favorable HER performance and potential for OER.The metal-organic frameworks（MOFs）are smart choice as precursors for electrocatalysts because of the complex structure and rich coordination centers.This dissertation focuses on the controllable preparation of TMPs by optimizing the morphology,chemical composition and electronic structure,being highly effective and stable catalysts for overall water splitting.The main research contents are as follows:（1）C coated CoP hollow microporous nanocages（C-Co P-1/12）is synthesized by calcination of Prussian blue analog precursor and further phosphorization treatment.Under alkaline condition,the C-Co P-1/12 exhibits splendid electrocatalytic performances with a low overpotential of 173 m V for HER and 333 m V for OER at a current density of 10 m A cm^-2.The C-Co P-1/12 shows high electrocatalytic performance for overall water splitting with a low potential of only 1.650 V for the driving current density of 10 m A cm^-2,and behave remarkably stability for least 24 h.The engineering of phosphating is the critical step for the synthesis of pure phase Co P with hollow nanoarchitecture.By compared with the Co₂P,the Co P possess lower water dissociation barrier and favorable?*value acrossing theoretical calculations,resulting in superior electrocatalytic performance.Such impressive water splitting performance is mainly attributed to the collective effects of metal phosphide with unique electronic structure,the shortened electron transport paths,and the conductive C coating.（2）The NiCoP NRs/CP were firstly synthesized by hydrothermal method,and following the phosphorization.The resulting Ni Co P NRs/CP displayed extraordinary electrocatalytic performances in 1.0 M KOH,reaching a current density of 10 m A cm^-2 at the overpotential of 49.5 m V for HER and 263 m V for OER.When evaluated as both the cathode and anode,the Ni Co P NRs/CP required the potential of 1.575 V at a current density of 10 m A cm^-2,along with outstanding durability for at least 50 h.The Ni Co P NRs with ideal-sized nanorods morphology are more favorable for exposing rich catalytically active sites.The strong intimate contact between well-ordered Ni Co P nanorods and the conductive carbon paper enhances structural stability and conductivity.The improved charge transfer between metal atoms in the Ni Co P NRs/CP provides two electron-donating active sites,further improving the electrocatalytic performance.（3）An unconventional heterostructure composed of metal organic network（Fe Ni-PBA）and nickel cobalt carbonate hydroxide is fabricated by ion inducing,which is further phosphatized to obtain hammer-like Fe,Ni-P@Ni Co P/CP as highly effective catalyst for p H-universal HER and alkaline water electrolysis.To deliver a current density of 10 m A cm^-2,the as-synthesized Fe,Ni-P@Ni Co P/CP exhibits versatile HER electroactivity with very low overpotentials of 50.9,70.5 and 52.3 m V in acidic,neutral and alkaline media,respectively.Moreover,the Fe,Ni-P@Ni Co P/CP displays admirable OER activity,with an overpotential of only 237 m V for 10 m A cm^-2 in 1.0 M KOH.Impressively,the alkaline water electrolyzer device using Fe,Ni-P@Ni Co P/CP as both the cathode and anode only requires potentials of 1.532 and 1.893 V to reach a current density of 10 and 100 m A cm^-2,respectively,along with outstanding durability for at least 50 h.The collective effects of the unconventional heterostructure and unique electronic structure dramatically improving electrocatalytic activity.