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.

The world now pushes for a low-carbon future, and international goals for greenhouse gas emission reductions have been set. Industrial processes, including metallurgical processes, make up more than a fifth of the total global emissions, and those have been rising with infrastructure development and the expansion of the middle-class worldwide. This paper focuses on two energy-intensive processes, aluminum production and metallurgical grade silicon production, and how the carbon footprints from these industrial processes have developed in recent decades. The main trend is that the increased demand for these metals has led to expanding primary production for both of them, based on energy with an increasing share of fossil-based electric power. In fact, the average carbon footprint of the energy used in aluminum and silicon production has increased by 38% and 43%, respectively, from 2000 to 2019. The change in energy mix offsets any progress in process efficiencies. This work addresses this and discusses opportunities for improvements.Graphical Abstract

Titanium diboride (TiB₂) is considered a promising material for wettable cathodes in aluminum electrolysis. The demand for wettable cathodes is associated with the development of inert anode technologies to eliminate CO₂ emissions caused by the conventional aluminum reduction process. Titanium diboride has been given special attention due to its superior properties, such as high wettability, good electrical conductivity, wear resistance, and excellent chemical stability. In this paper, we discuss different synthesis techniques used for the preparation of TiB₂ cathode material. The main methods are sintering, electrodeposition, and plasma spraying. Electrodeposition is considered to be the most reliable low-cost method for TiB₂ preparation. The vertical anode–cathode distance can be reduced by introducing wetted TiB₂ cathodes, through which specific energy consumption can be reduced significantly. For a longer lifetime, the TiB₂ cathodes should be resistant to electrolyte penetration. Further research should be conducted to understand the electrochemical behavior of TiB₂ in low-temperature electrolytes. Graphical Abstract

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.