Surface coatings can enhance the substrate material’s properties and increase its lifetime. HEA-based materials have been extensively investigated as coating materials due to their superior hardness, excellent oxidation and corrosion resistance, effective diffusion barrier properties and wear resistance. Magnetron sputtering has been regarded as one of the most efficient methods for the deposition of HEA-based thin films. Metallic- and nitride-based HEA coatings can be easily deposited by introducing N₂ gas along with the Ar in the reaction chamber. The parameters such as target composition, bias voltage, sputtering power and notably, gas flow ratio, influence the thin film’s morphology and mechanical properties.

This update includes the literature related to the inert anodes which were published in the past decade. The metallic anodes are widely regarded as promising candidates to replace the carbon anodes due to its attractive properties like good electrical conductivity, easy to manufacture and high resistance to high thermal shocks. The metals have been tested in pure state and alloy (binary, ternary) form. The oxide scale formed on the anode surface acts as a barrier between the electrolyte and the anode, which protects the anode from being dissolved. The layer of molten fluorides is formed between the scale and the metal anode after a certain time of polarization, and the oxide scale acts as a bipolar electrode. Metal like Cu is reduced at the internal side of the scale. This paper elaborates the effects of various parameters on the performance of the anode. Cu-based alloys (Cu – Ni – Fe and Cu – Al) have shown promising results and could perform well in low-temperature electrolytes. It has been well established that the Cu content in Cu – Ni – Fe and Cu – Al alloys plays a major role in the metal dissolution as the CuO/Cu2O scales formed on the outer layer act as a sacrificial one. The corrosion rate of an anode can be reduced by decreasing the operating temperature, which is possible by using the KF – AlF3 melts. The use of suspensions can increase the purity of the produced metal by stopping the anode products to come in contact with cathode metal. Many industries including RUSAL and ELYSIS are still conducting a considerable amount of research to develop an inert anode and are expecting to have a carbon-free cell in the nearest future. The work is performed as a part of the state assignment for the science of Siberian Federal University, project number FSRZ-2020-0013. Use of equipment of Krasnoyarsk Regional Center of Research Equipment of Federal Research Center “Krasnoyarsk Science Center SB RAS” is acknowledged.

Due to environmental and economic concerns, carbon-free aluminium production has been an ultimate goal for aluminium industries. For the past few decades, a considerable amount of research has been conducted to find an inert anode material that could replace the consumable carbon anodes for aluminium electrolysis. Anodic materials such as metals, ceramics and cermets have been studied extensively. All these anode materials have their advantages and disadvantages. However, metal alloys have proven effective due to their resistance to high-temperature corrosion and ability to produce a protective oxide layer. For a successful adaptation of metallic anodes into the aluminium electrolysis cell, an electrolyte with a low-operating temperature and high alumina solubility with good electrical conductivity is required. Another significant component of the carbon-free aluminium electrolysis cell is a wettable cathode to reduce the anode-cathode distance. This review discusses the research progress on inert anodes, wettable cathodes and electrolytes.

The kinetics of anodic and cathodic processes in KF–AlF₃ and KF–AlF₃–Al₂O₃ melts obtained by means of stationary polarization and cyclic voltammetry have been studied. Studies were conducted at different cryolite ratios [CRs, (moles of KF)/(moles of AlF₃)] and different alumina contents at 700–800 °C for the Cu–Al anode and at 800 °C for the tungsten cathode. The limiting current density of oxygen evolution on the Cu–Al anode was 0.31 A cm⁻² at 700 °C and CR = 1.4. It drastically increases with CR and temperature. The limiting current density of aluminium reduction on the W cathode was in the range 0.45–0.50 A cm⁻². The cathodic process is diffusion-controlled while the anodic one shows mixed kinetics. The diffusion and mass transfer coefficients for the cathodic process (W electrode) and the mass transfer coefficient for the anodic process (Cu–Al electrode) were determined. Based on the obtained results, the electrolysis of 1.4KF–AlF₃–Al₂O₃(sat) with the Cu–Al anode and W cathode was performed. The aluminium purity was determined using an optical emission spectrometer. The XRD and SEM-EDX methods were used to study the phases formed on the anode surface.