Studies And Applicaitons Of Electrodeposition By Noble Metal Materials In The Confined Space Of A Glass Conical Pipette

Monitoring the growth process and reaction process of materials in real time is an important way to optimize the material synthesis conditions as well as to explore the reaction mechanism.Confined space not only restricts the growth of materials in space but also endows materials with unexpected properties due to its internal confinement effect.Glass nanopipettes,with excellent rigidity and controllable pore size,can be easily prepared.Due to the complex mechanism of controlled synthesis of micro-and nanomaterials,it is necessary to monitor the synthesis process in real time.Based on the confinement electrodeposition of pipettes,the material deposition process can be monitored through electrical signals,and the morphology of the material can be controlled by changing electrochemical parameters.Furthermore,the conical glass pipette is an ideal site for evaluating the catalytic performance of individual micro-and nanoparticle materials.It can reveal the heterogeneity of the catalytic ability of materials at the individual particle level in a closed bipolar environment,and it can be used as the micro-and nano-bipolar electrode（BPE）to reveal various electrochemical reaction mechanisms,which can solve the difficulties of BPE signal acquisition as well as monitor the reaction process on the BPE,making it an ideal site for analyzing and revealing the catalytic performance of materials.Based on this,this paper investigates the electrodeposition process and mechanism of precious metal materials in the confined space of two solution systems,non-homogeneous and homogeneous,using a submicron-sized conical glass pipette as a tool.The growth process of silver wires in non-homogeneous phase and the bipolar reaction process of gold particles in homogeneous phase are monitored by electrochemical signals,and the application of the gold particles on BPE is initially explored.The main content and conclusions are as follows:（1）Based on the liquid-liquid interface（LLI）of the micropipette,silver wires have been electrodeposited in the confined domain by a redox reaction of Ag NO₃ and Fc at the orifice.The i-t curves characterized the growth state of the silver wires,and the higher the rate of current increased,the faster the electron transfer and the faster the growth of the silver wires;conversely,the slower the growth of the silver wires.The surfactant was not beneficial for the linear deposition of silver wires at the interface.The main driving force for the growth of silver wires into linear structures was the theoretical current difference between the water-oil phase,which was mainly caused by the concentration difference between Ag NO₃ and Ferrocene（Fc）.According to the Butler-Volmer electrode kinetic equation,the standard rate constants of Ag⁺and Fc can be deduced to be of the same order of magnitude.The combination of the conical pipette and metallic material using LLI makes both of them have better application prospects in sensing detection and mechanism research.（2）Further studies using four different ferrocene derivatives as reducing agents verified that the properties of the reactants are also an important factor affecting the theoretical current difference in the water-oil phase and that the lower the standard reduction potential the more elongated the silver wire deposited.Gold wires were also successfully deposited in micron tubes by using the more reductive Dimethylferrocene（DFc）,indicating the general applicability of the present method.The difference between the i-t curves when silver wires were deposited by micropipettes with different shapes was obvious.The current increase rate is faster in the pipette with a large cone angle,and the silver wires will grow faster and,vice-versa,more slowly.If the spatial restriction disappears completely,silver wires are more difficult to form at the interface instead.Electrochemical analysis in the confined space allows monitoring of the metallic wire growth process and customizing the wire to the requirements.（3）With L-ascorbic acid（AA）inside the micropipette as the reducing agent and HAu Cl₄outside the pipette as the metal source,the electrodeposition process of gold microparticles in the confined space was studied by applying different potentials and the deposition process was verified by simulation using finite element simulation（FEM）.It is found that Au Cl₄^-would be distributed farther inside the micropipette under a high positive voltage drive,while it can not enter the pipette under negative voltage.Due to the special conical structure of the pipette,after being blocked by gold particles,the gold particles at voltages as low as 1.0 V can be polarized into a confined wireless gold BPE,and a signal cycle with three characteristic phases appears.The occurrence of hydrogen evolution reaction（HER）at the cathode of gold BPE was confirmed by changing the p H of AA,and the electrolysis of gold at the anode was confirmed by replacing the bulk solution.A simple electrochemical method is used to obtain micron-scale gold BPE with low potential excitation in a confined conical pipette,which facilitates the expansion of micro-and nano-BPE applications.（4）In-depth studies have been performed for the self-switching repetitive current variations and the generation of individual spike signals that appear in（3）.After a steady low baseline current in phase I,a series of positive spike signals caused by the rupture/generation of a single H₂ nanobubble are recorded,representing the onset of phase II.Simultaneously,the dissolution of the gold blocked in the orifice will generate a new channel,increasing the baseline current in phase III,where gold synthesis occurs again,leading to the onset of another cyclic reaction.This is the mechanism of self-switching repetition due to the deposition and polarization of gold particles,and the FEM also confirms this reaction process mechanism.Furthermore,the integrated charges of all spike signals in phase II correspond to the consumption of anodic gold,confirming that a single spike corresponds to a single H₂generation process.This work monitors both the self-switching repetitive bipolar reaction of gold particles and the HER of individual H₂ nanobubbles,making the conical pipette an ideal tool to further reveal the heterogeneity of catalytic ability at the single-particle level.