Nonlinear Dynamic Behaviors And Regulation Law Of Electrode Reaction Of Manganese Electrodeposition

Manganese is an important strategic resource in China.However,the manganese electrodeposition has disadvantages including high energy consumption,low current efficiency and heavy pollution.Energy saving and emission reduction are the focus issue of current research.During the electrodeposition process,the multiple valence state changes of manganese and coupling of multiple chemical reactions have resulted in rich and complex nonlinear kinetic behaviors at the electrode/solution interface.Nonlinear behaviors of electrochemical oscillation and metal fractal growth cause the electrolysis process unstable,unmanageable,and increased extra consumption.Therefore,a systematical study in terms of the physicochemical processes on the electrode/solution interface is necessary and beneficial to reveal the electrode reaction mechanism and elaborate the interface reaction dynamics,so as to control the electrode reaction process more effectively and regulate the entire electrolysis process more efficiently.In this work,the influence of three external control methods of electrolytic additives,electrolytic power supply,and electrode materials on manganese electrodeposition were identified,depending on the theory of non-equilibrium thermodynamics and nonlinear kinetics.In detail,the dynamic behaviors of the electrode process were analyzed and revealed in order to realize the directional transformation and precise regulation of manganese electrodeposition process.The research work mainly includes the following parts:(1)Sodium oleate(NaOL)was introduced as an electrolytic additive,and the electrochemical-chemical combined analysis method was employed to investigate the influence of NaOL on anode electrochemical oscillation,anode oxygen evolution reaction activity and cathode deposition of manganese.The results shown that Mn SO₄electrolyte with 6.0×10^-5 mol·L^-1 NaOL reduced the anode potential and the potential oscillation frequency,so that the potential oscillation attractor was more regular than without NaOL.At the same time,the OER overpotential of the lead alloy anode with NaOL was 68 m V lower than that without NaOL at 40?,and the formation of by-product manganese oxide anode slime was also suppressed.A mechanism of NaOL regulating electrochemical oscillation was proposed,and the influence of NaOL on the cathode hydrogen evolution reaction activity,electrolytic cell pressure,energy consumption and current efficiency were analyzed and discussed.The results shown that NaOL has no significant effect on the morphology and crystal form of manganese deposits on the cathode.But manganese dendrites at the edge of the cathode was reduced,current efficiency was increased by 1.9%,and electrolysis energy consumption was reduced by 2.4%.(2)For the electrolytic power supply mode,pulse current and chaotic circuit current were introduced as the new electrolysis power supply,and the influence of the external control electric signal on the manganese electrodeposition process was studied.Compared with direct current,the average anode potential under pulse current was 33⁶0 m V lower,and the corresponding potential oscillation attractor was more orderly,which had a good energy-saving effect.Especially,Mn²⁺was oxidized more fully in Mn SO₄ solution,and less loose and poorly conductive Mn OOH intermediates were formed at 500 Hz,which made the anodic deposited Mn O₂ layer dense and smooth.Thus,the anode metal substrate had a better corrosion resistance than direct current electrodeposition.Compared with direct current electrolysis,the cathode manganese deposition current efficiency increased by 3.11³.77%,the energy consumption reduced by 5.30⁸.17%,and the cathode obtained relatively flat and uniform?-Mn by using pulse electrodeposition for 2⁸ h.For chaotic circuit power supply,two types of chaotic circuit power supply systems were designed,namely hyperchaotic circuit(HCC)system and amplitude modulation and frequency modulation chaotic circuit(AM&FMCC)system.The results showed that the anode potential oscillation behavior has been suppressed to a certain extent by using HCC.The average oscillation period was increased by 5.6 s,and the average oscillation amplitude was reduced by 38 m V,which would help reduce the generation of anode slime and the additional energy consumption during the electrolysis process.At the same time,the surface anodic Mn O₂was smooth and compact,which improved the oxygen evolution reaction activity and corrosion resistance of the lead alloy anode.However,the average current efficiency was only 61.92%with HCC and it was necessary to further explore the method for increasing the actual output value of chaotic current.For AM&FMCC,the anode potential oscillation experienced a trend from scratch to obvious change as the input chaotic voltage amplitude frequency increased.Meanwhile,the peak current density of anodic Mn²⁺oxidation enlarged and the generated Mn O₂ anode slime thickened with the increase of AM&FMCC frequency.The average current efficiency of cathode deposited manganese was only 35%after 250 Hz electrolysis,indicating the chaotic current output by AM&FMCC also needs to be further improved.(3)For the electrode material,the polyacrylonitrile-based carbon fiber material was applied as the anode for manganese electrodeposition process.The electrode reaction characteristics,cell voltage,energy consumption,current efficiency and cathode manganese deposition during the electrolysis process were comprehensively discussed after analyzing the basic chemical composition and microscopic morphology of carbon fiber material.The results shown that the polyacrylonitrile-based carbon fiber anode had excellent electrocatalytic activity that the OER overpotential was reduced by 112 m V compared with the lead alloy anode at a cathode current density of 350 A·m^-2.Furthermore,the generation of by-product anode slime was reduced by 80%,thus,the Mn²⁺concentration and deposition rate in the electrolyte was more uniform,resulting significantly reduced fractal structure of manganese dendrite,thereby improving the quality and stability of cathode manganese products.Furthermore,compared with Pb alloy anode,the average cell voltage was reduced by 150 m V,energy consumption was reduced by 8.36%,and current efficiency was increased by 4.3%by using the carbon fiber anode under constant current electrolysis.In addition,the corrosion resistance and stability of carbon fiber electrodes were better than commercial carbon plate electrodes.Comparing with carbon plate anode,the current efficiency of carbon fiber anode increased by 5.45%,energy consumption decreased by 10.34%,and anode mass loss decreased by 46.5%after 8 hours of electrolysis.In summary,the influence of three external control methods of electrolytic additives,electrolytic power supply and electrode materials on the manganese electrodeposition were employed for controlling the nonlinear behavior of electrode reactions,improving current efficiency,and reducing lenergy consumption and pollution emissions.This provides new ideas and new paths to high-efficiency and energy-saving operation for the electrolysis process.