Study On Electrocatalytic Performance Of Organic Modified Phosphide In Ammonia Synthesis

Ammonia（NH₃）is an indispensable nitrogen source in today’s society.Meanwhile,with the intrinsic properties of high hydrogen density and low liquefying pressure,NH₃is deemed to be one of the carbon-free energy carriers in the future.However,the traditional Haber-Bosch method（under the conditions of 400–500°C,10-30 MPa）still being used industrially to synthesize ammonia.Electrochemical nitrogen reduction reaction（NRR）emerges as a promising alternative to convert N₂ to NH₃ under ambient conditions,which not only can use water as a hydrogen source but also can be powered with renewable energy sources.However,its practical applications are still challenging,since the utilization of non-polar N₂ is rather limited due to its inert nature and extremely low solubility in most solvents.In addition,the competition effect of hydrogen evolution（HER）in the reaction process can not be neglected.Therefore,designing new catalysts with outstanding N₂-fixing ability and selectivity has become urgent tasks in this field.With the excellent electrical conductivity,transition metal phosphates（TMPs）have been widely used in electrocatalysis.However,due to the high hydrogen affinity,limited N₂supply,and water poisoning occurs easily on the bulk TMP,the FE and NH₃ yield are rather negligible.Based on the above situation,the following studies were carried out in this thesis focusing on the surface molecular modification of TMPs nanoarrays:（1）Nickel phosphide nanoarray（Ni₂P/CP）was prepared on carbon paper by hydrothermal method and phosphating,and then modified with octadecanethiol to construct hydrophobic self-assembled monolayer（C18@Ni₂P/CP）on the surface of Ni₂P/CP.C18@Ni₂P/CP offers an NH₃ yield of 1.13×10^-10 mol s^-1 cm^-2 and a FE of7.73%at–0.1 V vs.reversible hydrogen electrode（RHE）in 0.1 M Na₂SO₄,with excellent stability and selectivity.（2）Cobalt phosphide nanoarray（Co P/TM）was prepared on titanium mesh by hydrothermal method and phosphating,and then modified with octadecanethiol to construct hydrophobic self-assembly monolayer（C18@COP/TM）on Co P/TM surface.Such C18@Co P/TM offers an NH₃ yield of 1.44×10^-10 mol s^-1 cm^-2 and a FE of 14.03%at–0.2 V vs.RHE in 0.1 M Na₂SO₄.Notably,C18@Co P/TM demonstrates excellent durability as well.Density functional theory（DFT）calculations suggest that modifying Co P with octadecanethiol leads to regulated surface electronic structure,which further promotes the catalytic formation of NH₃.