Synthesis Of Selenium Vacancy Enriched Ni_0.85Se_1-x Nanowire Arrays For Electrocatalytic Alkyne Semihydrogenation

Alkenes are important building blocks for the production of polymers,drugs,fine chemicals,etc.Selective semihydrogenation of alkynes to alkenes has long been one of the fundamental reactions in chemical production.To date,the semihydrogenation of alkynes still faces several major challenges:low selectivity caused by overhydrogenation,safety issues caused by the use of hydrogen（H₂）and other inorganic and organic hydrogen sources,and the high cost of precious metal Pd catalysts.Recently,using water as the hydrogen source for electrocatalytic hydrogenation reaction has attracted widespread attention due to its mild reaction conditions,good controllability,and no need of additional reducing agents.However,the development of low-cost transition metal selenides as the electrocatalysts for electrocatalytic highly selective semihydrogenation of alkynes using water as the hydrogen donor remains untouched.In this thesis,self-supporting Ni_0.85Se nanowire arrays(denoted as Ni_0.85Se_1-x NWs)with rich Se vacancies were synthesized as a cathode to enable the transfer semihydrogenation of alkynes with high conversion efficiency and excellent selectivity,using surface-absorbed active hydrogen（H*）as hydrogen donor.The main contents are as follows:1.Using the self-supported Ni_0.85Se NWs as the starting precursors,selenium vacancy enriched Ni_0.85Se_1-x NWs with adjustable selenium vacancies in Ni_0.85Se_1-xcould be synthesized by an facile oxidative etching treatment of diluted H₂O₂ at different etching times.Scanning electron microscope,X-ray diffraction and electron paramagnetic resonance results indicated the successful synthesis of Ni_0.85Se_1-x NWs.2.At-1.2～-1.3 V vs.Hg/Hg O,the conversion yield of 4-aminophenylacetylene（1a）could be reached to 97%with 99%selectivity of 4-aminostyrene（2a）after 3 h.2a selectivity could be achieved over 95%over a wide potential window of-1.05～-1.3 V vs.Hg/Hg O,which did not vary with prolonging the reaction time.After running for six cycles at the optimal potential（-1.2 V vs.Hg/Hg O）,no obvious decline of catalytic activity and selectivity and no apparent changes of the morphology of Ni_0.85Se_1-x were observed,showing the good electrocatalyst stability.Control experiments proved that H*generated by water electrolysis was the key intermediate for the semihydrogenation of alkyne.Theoretical calculation results showed that:1)the presence of Se vacancies caused the d-band center to be closer to the Fermi level,which enhanced the adsorption of H₂O and alkynes substrate over Ni_0.85Se_1-x and accelerated the electron transfer from catalyst to the substrates.Additionally,the introduction of Se vacancies lowered the activation energy of the hydrogen evolution reaction and boosted the generation of H*,thereby promoting the semihydrogenation process of alkynes;2)relatively weaker adsorption of alkenes compared to alkynes and the thermodynamically unfavorable over-hydrogenation step were crucial for producing alkene with high selectivity.3.Broad substrate scopes consisting of the aryl terminal/internal alkynes and aliphatic alkynes with high conversion yields and outstanding selectivity highlighted the promising prospect of our method.Interestingly,deuterated alkenes with up to 99%deuterium incorporation can also be delivered with D₂O as the deuterated donor.