Electrolytic etching

Electrolytic etching is a process wherein a material (connected to a cathode) dissolves into an electrolyte solution (after passing an electric current) and the particles are then deposited on the anode. This process can be made selective by choosing the right electrolyte and adjusting the current density.

Using electrolytic etching has many advantages such as being low cost, having easy speed control by changing the electric current, and having the capability to perform processes in batches. It has many industrial applications especially in semiconductors and other electronics.

For example, electrolytic etching is used in the electrolytic exfoliation of graphene from graphite. This is to produce graphene nanosheets that are used in composite materials, molecular gas sensors, and energy storage systems. Electrolytic exfoliation is used because of its cost efficiency and scalability.

How does electrolytic exfoliation of graphene works?  First, two graphite electrodes are immersed into an electrolysis cell filled with electrolyte. The electrolyte is chosen to have both electrolytic and dispersion properties, e.g. Poly(sodium 4-styrenesulfonate). A constant current is then applied to the electrodes for several hours. Finally, the dispersion of exfoliated graphene is taken from the electrolysis cell, centrifuged, washed from the electrolyte, and dried to get graphene powder.

Aside from graphene production, electrolytic etching is also used in producing polyaniline-coated carbon fibre cloth electrodes for supercapacitors. This is because electro-etching of carbon fibre cloth increases the surface area of cloth and its hydrophilicity. In this method, carbon fiber cloth (cathode) and platinum sheet (anode) are immersed in 1M H2SO4 as electrolyte. Etching is done on 2V for 10 minutes.

Another use of electrolytic etching is in coating magnesium alloys with aluminium. Magnesium alloys are widely used in automobile engineering, aerospace, and electronics. However, there is a problem with possible corrosion. This can be solved by aluminium coating. It is done first by pre-treatment (in a short time) at lower current densities. Then, deposition is made in the longer treatment time. Aluminium disc (99.999% in purity) is used as cathode and the magnesium alloy as anode. 2:1 AlCl3–1-ethyl-3-methyl-imidazolium chloride is used as electrolyte.

Electrolytic etching is also used in producing platinum-aluminium alloys, obtaining porous silicon, and making electrodes for lithium-ion batteries. It is also used in the fabrication of precise copper micro-oils.

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Bajin Xu, Min Zhang, Guoping Ling (2014), Electrolytic etching of AZ91D Mg alloy in AlCl3–EMIC ionic liquid for the electrodeposition of adhesive Al coating

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