In the glassware of a chemistry laboratory, the gradual growth of a reddish-brown metallic
layer on the surface of the cathode always triggers the marvel of the observer as the electric
current passes through the blue solution. This copper-centered electrolysis process is not
only a classic example of understanding electrochemical reactions, but also a key technology
indispensable to modern industrial production. In this paper, we will explore the whole
process of copper electrolysis, revealing the mystery of metal morphology transformation
under the action of electric field.
The microscopic picture of copper electrolysis
In the electrolytic system composed of copper sulfate solution, the moment of energization
that opens the microscopic world of ion migration. Anode copper plate (purity ≥ 99%) in
the current under the action of oxidation reaction (Cu → Cu ² ⁺ + 2e-), the release of copper
ions to the cathode migration. At the same time, H⁺ and OH- in the solution are driven by
the electric field to the two poles respectively, forming a complete charge transport network.
Cathodic process: Cu²⁺ captures electrons to be reduced to metallic copper, and the deposition
rate is positively correlated with the current density. When the current density is controlled at
0.5-2A/dm², a dense coating can be formed; more than 3A/dm² produces dendritic crystallization.
Anode dynamics: copper atoms continuously enter the solution in the form of ions, and the
anode surface shows uniform dissolution characteristics. However, when the impurity content
exceeds 0.3%, the anode will be passivated, resulting in an abnormal increase in tank voltage.
Full Record of Experimental Phenomena
Visual change
0-5 minutes: red spots appear on the surface of cathode, and traces of anode
dissolution are clearly visible.
15 minutes: the thickness of plating layer reaches 20μm, showing metallic luster.
30 minutes: the solution changes from bright blue to blue-green, and the anode
shrinks about 1mm.
Physical parameter change
Solution temperature rises 3-5°C (Joule heating effect)
pH decreased from initial 2.5 to 1.8 (H⁺ concentration increased)
Conductivity increases by 15% (change in ion mobility)
Analysis of special phenomena-
Edge effect: thicker deposition layer at the edge of the electrode (uneven
distribution of current density)
Bubble interference: anodic side reaction of oxygen precipitation leads to pockmarks
in the plated layer
Color layering: Tyndall effect formed by solution concentration gradient
Technical specifications for industrial-grade electrolytic copper
Raw material pretreatment standard
The anode copper plate should be calendered→acid washing→polished with surface
roughness≤Ra1.6.
Electrolyte preparation: Cu²⁺ concentration of 40-50g/L, sulfuric acid concentration of 180-200g/L
Additive system: gelatin 0.01-0.03g/L+thiourea 0.001-0.005g/L
Copper cathode purity: ≥99.99% (ASTM B115 standard)
Plating bonding force: no shedding by 90 degrees bending test
Surface roughness: mirror plating Ra ≤ 0.05μm
Teaching experiment operation guide
Basic experimental program
Reagent: copper sulfate pentahydrate (AR grade) 50g, concentrated sulfuric acid (98%) 10mL
Device: DC power supply (0-12V), pure copper electrode (2 × 5cm), glass tanks
Steps:
(1) Prepare 200mL electrolyte (CuSO₄-5H₂O 250g/L + H₂SO₄ 50g/L)
(2) Setting voltage 3V, initial current about 0.5A
(3) Record electrode changes every 5 minutes for a total duration of 30 minutes
Phenomenon Observation Points
Directionality of the growth of the deposited layer (preferentially extending in the direction of the current)
Quantitative relationship between anodic dissolution rate and plating thickness
Corresponding law between solution color change and copper ion concentration
Data recording template
Time (min) Cathode weight gain (g) Anode weight loss (g) Solution temperature (°C)
5 0.12 0.15 26
15 0.38 0.42 29
30 0.75 0.81 32
V. Technological innovation and development trend
Pulse electrolysis technology
Adopting square wave current with adjustable duty cycle, the density of the deposited layer can be increased by
30%, which is especially suitable for the manufacture of copper interconnections for precision electronic components.
Ultra-pure water electrolysis system
Obtain nano-sized copper powder (particle size 50-100nm) by ultra-potential electrolysis in pure water
environment for 3D printing conductive ink.
Green Process Improvement
Electrolyte closed loop recycling system (metal recovery >99.5%)
Biodegradable additive development (replacing traditional cyanide)
Photovoltaic-powered electrolysis unit (reduces carbon footprint)
Golden Rules for Safe Operation
Personal Protection
Wear an acid mask (when handling concentrated sulfuric acid)
Use acid and alkali resistant gloves (made of butyl rubber)
Lab coats need to be impermeable
Emergency treatment program
Electrolyte splash: Immediately rinse with 5% sodium bicarbonate solution.
Electrode short circuit: cut off the power supply before treatment
Abnormal gas production: turn on the forced ventilation system
Waste management
Neutralization of waste liquid: add milk of lime to adjust pH to 6-8
Recycling of sedimentary sludge: copper content >90% can be directly returned to the furnace
Sorting of waste electrodes: the metal part goes to the non-ferrous metal recycling channel.
Copper electrolysis technology is like a microcosmic precision choreography, where each ion performs
an orderly transformation under the command of an electric field. From basic knowledge in laboratory
glassware to large-scale production on the factory floor, this technology continues to drive progress in
materials science. When we harvest the polished copper layer at the cathode, we not only complete the
morphological transformation of the metal, but also realize the depth of human control over the nature
of matter. Understanding the inner logic of this process will open the door to advanced manufacturing.