New-type Antiperovskite Nitrides Electrocatalysts For Water Splitting

Considering the poor conductivity and low activity of the current electrocatalysts,with the performance orientation,this dissertation has developed series of low-cost,highly active and stable antiperovskite nitrides electrocatalysts for water electrolysis,which is achieved by the highly conductive and composition-tunable properties of antiperovskite nitrides.Besides,this dissertation has focused on the correlationship between the electronic structure of the electrocatalysts and their electrocatalytic activity to unveil the key foctors affecting the performance of antiperovskite nitrides and guide the design of highly effective antiperovskite nitride electrocatalysts.The main contents and results of this dissertation are presented as follow:（1）A facile method of vaporing to coprecipitate and nitridation is employed to synthesize series of nickel-based antiperovskite nitrides（ANNi₃）with different A-site metals for alkaline hydrogen evolution reaction（HER）electrocatalysts.The HER performance of ANNi₃electrocatalysts have been systematically compared.It has been found that Cd NNi₃ shows the best HER activity among all the ANNi₃ with 100 m V of the overpotential to reach 10 m A cm^-2.Besides,Cd NNi₃ presents the lowest overpotential（88 m V）at a specific current density of 0.5m A cm^-2_ECSA and the smallest intrinsic Tafel slope of 68 m V dec^–1.According to the XPS and HER measurements,the ANNi₃ with higher content of Ni⁰ would have higher HER activity.（2）The surface evolution of the nickel-based antiperovskite ANNi₃ in the operating condition toward alkaline HER has been investigated.It has been found that a Cd-doped Ni O layer is formed at the surface of the post-HER Cd NNi₃ in alkaline electrolyte.XPS measurement results of the post-HER ANNi₃ strongly prove the surface oxidized reconstruction of ANNi₃ during the alkaline HER.The alkali-treated ANNi₃ electrocatalysts also present the similar results of the post-HER ANNi₃.This indicates that the surface reconstruction of the ANNi₃ during alkaline HER is caused by the oxidized corrosion of the alkaline electrolyte.The effect of different A-stie metals on HER mechanism is investigated according to the surface evolution on the post-HER ANNi₃.The surface evolution of ANNi₃ in the alkaline HER operating condition is beneficial to the identification of their real active site,which can forcefully guide the contruction of electrocatalytic model and the investigation of electrocatalytic mechanism of the antiperovskite nitrides in alkaline electrolyte.（3）A groundbreaking strategy of the In-site substitution by Cu with different degree in In NNi₃ is employed to tune its lattice parameter and the electronic structure of the active metal Ni and further optimize the interaction between the adsorbed intermediates and electrocatalysts surface.In this way,series of new-type Cu_xIn_1-xNNi₃（0≤x≤1）antiperovskite electrocatalysts with high conductivity,excellent HER activity and desirable durability are developed in this dissertation.The best-developed Cu_0.4In_0.6NNi₃ needs merely 42 m V to reach 10 m A cm^-2toward HER and exhibits a small Tafel slope of 51 m V dec^-1,which surpasses most of the non-noble metal-based HER electrocatalysts.This study has offered an innovative strategy of altering the composition in the nickel-based antiperovskite nitrides to optimize their electrocatalytic activity,which offers a new approach for expanding the application of antiperovskite nitrides in electrochemical energy fields.（4）New-type Cu NCo_3-xV_x（0≤x≤1）antiperovskite electrocatalysts have been prepared by hydrothermal coprecipitation and nitridation method.The composition-tuning strategy has first been used to optimize the electrocatalytic activity of Co-based antiperovskite nitrides via partical substitution of Co in Cu NCo₃ by V.After optimizing the component,the obtained Cu NCo_2.4V_0.6 electrocatalyst needs merely 235 m V of the overpotential to reach an oxygen evolution reaction（OER）current density of 10 m A cm^-2,which is comparable to that of the precious Ir/C（232 m V）.XANES,HR-TEM and XPS measurements on the post-OER electraocatalysts indicates that the antiperovskite nitrides occurred an oxidized reconstruction during the OER process.It has been found that the V substitution can lead to the formation of Co³⁺-riched surface,which lead to the enhanced OER performance.