## 3 Electrodeposition
### Electrolytes  
The electrodeposition of high-entropy alloys is carried out from aqueous or organic electrolytes (Table 1) with relatively low concentrations of metal ions, typically in the range of 0.01-0.1 M, usually in the form of chlorides and/or sulfates [16; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48]. Acidic aqueous solutions are most commonly used; however, both acidic and alkaline baths may contain citrate ions, added either as sodium [29; 35; 43; 45; 48] or ammonium [26; 44] salts, and sometimes as citric acid [26; 29; 51], to help align the deposition potentials of the constituent metals and to suppress the precipitation of hydroxides or basic salts in alkaline environments. Metals such as tungsten, molybdenum, vanadium, or rhenium are introduced as sodium or ammonium oxyanion salts. It is worth noting that acidic aqueous chloride [32; 46] or mixed chloride-sulfate-citrate baths [55] have been used to successfully deposit HEAs containing 10-20 at% Al, despite the fact that aluminum typically does not undergo reduction at the cathode in aqueous media. Aqueous solutions often contain various additives [22; 25; 26; 27; 28; 29; 30; 32; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48], such as sodium hypophosphite NaH\({}_{2}\)PO\({}_{2}\) and ascorbic acid C\({}_{6}\)H\({}_{8}\)O\({}_{6}\) to prevent the oxidation of Fe\({}^{2+}\) to Fe\({}^{3+}\), ammonium salts and/or boric acid H\({}_{3}\)BO\({}_{3}\) to act as buffers, alkali metal chlorides (NaCl, KCl) to improve electrolyte conductivity, sulfanilic acid C\({}_{6}\)H\({}_{2}\)NSO\({}_{3}\) as an anti-stress agent, formic acid HCOOH, gelatin, or saccharin C\({}_{7}\)H\({}_{5}\)NSO\({}_{3}\) to refine grain structure, reduce cracking, and improve the morphology and adhesion of the coating, while sodium lauryl sulfate C\({}_{12}\)H\({}_{25}\)SO\({}_{4}\)Na is commonly used as a surfactant to prevent pitting defects. Due to variations in bath composition and the diversity of codeposited metals, it is not possible to clearly determine the influence of individual components on the quality and properties of the resulting alloys. Nevertheless, NiFeCoMoW alloys obtained from acidic solutions under galvanostatic conditions can serve as illustrative examples. [PERSON] et al. [22] obtained compact, crack-free amorphous deposits of Fe38 NiGeO31 Mo14W11 composition with a cauliflower-like morphology from a sulfate-citrate-oxyanion bath (pH 5, 75 mA/cm\({}^{2}\)). In contrast, [PERSON] et al. [28] reported cracked deposits with a nearly similar composition Fe36 Ni8 Co23 Mo13W20 obtained from a sulfate-chloride-citrate-oxyanion bath (pH 4.5, 80 mA/cm\({}^{2}\)). Despite the use of similar metal ion concentrations, bath pH, and current densities, the observed differences in deposit morphology can be attributed to the presence of different organic additives with anti-stress properties, namely saccharin [22] and sulfanilic acid [28]. The role of saccharin is particularly noteworthy, as it is widely employed in nickel plating both as a brightener and as an effective internal stress reducer [2]. Its effectiveness appears to exceed that of sulfanilic acid, as reflected in the improved structural integrity and reduced cracking of the resulting deposits.