Study On Bubble Nucleation And Growth Behavior Based On Scanning Electrochemical Cell Microscope Technology

Electrolyzed water is considered to the greenest and environmentally friendly hydrogen production method.In order to improve the efficiency of hydrogen production by electrolysis of water and reduce economic costs,researchers mainly optimize the electrolysis water catalyst from the following two aspects:The first aspect is to find HER or OER catalysts that are inexpensive and have good intrinsic catalytic activity,such as transition metal oxides,sulfides,double hydroxides and alloys.The other is to optimize the morphology and structure of the catalyst,such as designing and synthesizing nanosheets,nano-porous and other three-dimensional structures which can provide more active sites.However,no matter how to optimize the composition of the material or the structure of the material,another factor that affects the efficiency of electrolysis water cannot be avoided,that is,the problem of bubble adsorption on the catalyst surface.Generally,in the process of water electrolysis,the anode will produce a lot of oxygen bubbles,and the cathode will produce a lot of hydrogen bubbles.The catalytic active sites on the surface of the electrode are often covered by bubbles,resulting in a decrease in the catalytic performance of the electrode.Therefore,studying the bubble nucleation,growth and detachment behavior at the solid-liquid interface can help design a catalyst structure that is easier for bubble nucleation and detachment and improve the efficiency of water electrolysis.The research on interface micro and nano bubbles originated from the hypothesis of submicron bubbles proposed by Parker.Since Luo et al.used the atomic force microscope to observe the nanobubble at the solid-liquid interface for the first time,more and more researchers have begun to explore its properties.At present,the main methods used to explore micro-nano bubbles are atomic force microscope,optical microscope,dark field microscope and total internal reflection fluorescence microscope.Although these technologies can image micro and nano bubbles,they cannot obtain more chemical information in real time.Here,we used scanning electrochemical cell microscope technology to study the nucleation and growth process of hydrogen bubbles and oxygen bubbles on the electrode surface,and explored the effect of surfactants on the nucleation and growth of hydrogen bubbles.The main results are as follows:（1）Based on scanning electrochemical cell microscopy technology,explored the effect of perfluorooctanoic acid（PFOA）,cetyltrimethylammonium bromide（CTAB）and silicone defoamer（siloxane）on the nucleation of individual H₂bubble generated by electrocatalytic proton reduction.Cyclic voltammetry test results show that all three types of surfactants can reduce the critical concentration required for hydrogen nucleation,and the greater the surfactant concentration,the more obvious the reduction effect.Among them,the effect of organosilicon defoamer siloxane is the most obvious.Both the microscopic and macroscopic constant voltage hydrogen evolution test results show that the three types of surfactants can promote the nucleation of hydrogen bubbles and improve the hydrogen evolution efficiency of Pt.（2）Based on scanning electrochemical cell microscopy technology,the nucleation and growth behavior of oxygen on the surface of platinum（Pt）,gold（Au）,glassy carbon（GC）,conductive glass（ITO）,stainless steel 304（SS 304）and Ni（OH）₂/Ni nanosheet catalysts under alkaline conditions were studied respectively.Microscopic cyclic voltammetry test results show that oxygen bubbles behave differently on different catalyst surfaces.The bubble nucleation current and nucleation voltage of different areas on the surface of each material are counted.It is found that the properties of different areas on the surface of the GC electrode are almost the same,and the catalytic performance of different areas of Ni（OH）₂/Ni materials is quite different.By comparing the peak current,nucleation voltage and current onset potential in the cyclic voltammetry curve,the difficulty of oxygen bubble nucleation growth on the surface of six materials was qualitatively analyzed.It was found that the minimum voltage required for the nucleation and growth of oxygen bubbles on the surface of the SS 304 material,and the lowest critical concentration required for the nucleation and growth of oxygen bubbles on the GC surface.