Preparation And Electrochemical Properties Of Nickel-based Complex Oxide Thin Films

The development and promotion of clean energy are an important way to create the sustainable society.Electrochemical water splitting is considered to be one of the most promising strategies to generate hydrogen.However,the slow OER reaction process of water splitting inhibits the reaction rate,making the problem of seeking renewable energy has been turned into a problem of seeking high-efficiency energy-saving catalysts.When looking for high-performance and low-cost OER catalysts,compared with the hard-to-obtain and expensive precious metal catalysts,the earth-rich transition metal perovskite oxides have attracted widespread attention as catalysts.The main work of this thesis is to use pulsed laser deposition to deposit single crystal and amorphous perovskite LaNiO₃thin films on different substrates,and to study its OER performance by changing its growth conditions.We use the relationship between electrical conductivity and electrocatalysis to explore the electrochemical properties of the film by regulating the growth conditions of the single crystal films.With the change of the growth temperature and the gradient of oxygen partial pressure,when the temperature reaches 550?,the growth partial pressure of oxygen growth is 200 m Torr,and the partial pressure of oxygen is 100 Torr during annealing and cooling,the obtained LaNiO₃/Sr Ti O₃ single crystal films have the best electrical conductivity and the best electrochemical catalytic performance.In addition to the growth conditions,we also studied the effects of the electrocatalysis when the growth of LaNiO₃ thin films on different substrates(Sr Ti O₃<001>,Sr Ti O₃<011>,Sr Ti O₃<111>and La Al O₃),which change the lattice constant of LaNiO₃ films from generate stress,to improve the electrocatalytic performance of LaNiO₃ films.In addition,we also discussed the amorphous LaNiO₃ thin film,and studied its electrocatalytic performance by adjusting the growth oxygen partial pressure.In the process of exploration,it was found that when the oxygen partial pressure under a low condition(vacuum to 1 m Torr),with the increase of oxygen partial pressure,the OER performance of amorphous films also increased.However,as the partial oxygen pressure continuous to increase(10 to 200 m Torr),the electrocatalytic performance of amorphous films decreases accordingly.The Tafel slope calculation also shows that the amorphous LaNiO₃ films have the best electrochemical activity when the oxygen partial pressure is1 m Torr.After further investigating the effect of oxygen partial pressure changes on the OER performance of amorphous films,it was discovered that the oxygen vacancies and theNiorbital filling present a competitive mechanism.Under the low condition of the oxygen partial pressure,the improvement of OER performance can be attributed to the Ni³⁺/Ni²⁺ratio increasing with the increase of oxygen partial pressure,while when the growth oxygen partial pressure continued to increases,the OER performance is controlled by the dominant oxygen vacancy.The competition between the two mechanisms led to the optimization of OER activity,with oxygen partial pressure of 1 m Torr and current density of up to 1038?A cm^-2(defined by the current density at 1.6 V vs RHE).When we investigated the electrochemical properties of LaNiO₃ single crystal and amorphous thin films,we found that compared with single crystal epitaxial LaNiO₃,the current density of amorphous LaNiO₃ increased by 9 times,showing superior OER activity.And for the amorphous film,it is different from the stable performance of the single crystal film in the electrocatalytic test.As the number of OER test turns increases,the amorphous film exhibits amorphous self-adaptability,and the OER performance will first increase with the number of turns continue to increase and then decreas.Compared with single crystal films,amorphous LaNiO₃ films have higher OER activity.The current density of amorphous LaNiO₃ is increased by 9 times,showing superior OER activity and specific amorphous self-adaptability.