Anodic selective dissolution of copper alloys in chloride and carbonate melts

Abstract

The synthesis of materials with a developed electrode surface of the electropositive component of the alloy and a significant near-surface layer was performed by anodic selective dissolution of copper alloys (Cu63–Zn37, Cu40–Zn37, Cu65–Ni35, Cu35–Ni65 and Cu50–Al50). The morphological and electrochemical characteristics of the obtained electrode materials based on mesoporous copper demonstrate its prospects for catalysis substrate application, electrodeposition of materials with specified parameters, and for the low-wear anode base formation.The media was combination of lithium, sodium, potassium carbonates (30 : 30: 40 mol. %), as well as low-melting eutectic mixtures of alkali metal chlorides of various compositions (especially CsCl–KCl–LiCl (54.4 : 15.3: 30.3 wt %) in the temperature range of 623–923 K. The object of the study was copper alloys such as copper-zinc, copper-aluminum, copper-nickel. Anodic selective dissolution was performed under the following electrolysis modes: galvanostatic and potentiostatic modes; rectangular polarization; cyclic voltammetry.The values of geometric current densities were 100, 200, 300, 900, 1400 A/m2. The applied anode potential was +0.1, +0.2 and + 0.5 V (from the open circuit potential of the material). The platinum reference electrode was used. The resulting surface structures were investigated using micro- and X-ray phase analysis. The composition of frozen melt samples after electrolysis completion was studied by atomic absorption analysis. The resulting surface structures were investigated using micro- and X-ray phase analysis.The influence of the following factors on the surface structure of the final anode product was studied and discussed: composition of the studied alloy (the amount of electronegative component in the alloy, as well as its nature); electrolyte composition (chloride and carbonate melt); temperature of selective dissolution (350, 500 and 650°С)It was shown that it is possible to change the nature of the binary alloy dissolution by changing the kinetic parameters (electrolyte composition, temperature), and to obtain a mesoporous material with a developed surface, suitable for heterogeneous catalysis, structural design of electrochemical and electrical devices.a) the most perspective copper-based alloy for the formation of nanoporous and mesoporous materials in salt melts is brass Cu63–Zn37;b) the smallest average pore size had samples of brass Cu63–Zn37 in experiments with chloride melt; in galvanostatic mode the pore size was 500 nm (under given conditions – 200 A/m2, 350 °C); in potentiostatic mode – 250 nm (+0.1 V, 500 °C). With the temperature decreasing it is possible to reduce this indicator by 1.5–3.0 times;c) the square-wave potentiometry method was used to form a developed near-surface layer in several stages;g) cyclic voltammetric curves were obtained, which can be used to prognosticate and describe the stages of the anode process;e) the potentials of open circuits were obtained for the studied samples;g) by dissolution of copper-aluminum alloy in galvanostatic mode was formed the nanofiber on the surface with thread size less than 20 nm.2. The influence of the temperature, the nature of the second component of the alloy and the salt electrolyte (chloride) on the formation of the developed surface layer of the alloys under study was established:a) the increase in temperature leads to a decrease in the development of the surface layer;b) copper-nickel samples are depleting by copper due to the fact that copper is an electronegative component of the alloy in chloride melts, while the formation of developed surface layer enriched with nickel takes place;c) the increase in the content of the electronegative component leads to a decrease in the development of the surface.It was shown that it is possible to change the nature of the binary alloy dissolution by changing the kinetic parameters (electrolyte composition, temperature), and to obtain a mesoporous material with a developed surface, suitable for heterogeneous catalysis, structural design of electrochemical and electrical devices.