# Zinc Plating on Inkjet-Printed Ti3C2 Tx MXene: Effect of Electrolyte and PEG Additive
## 1 Introduction  
Environmentally responsible, reliable, and long-lasting energy power sources are nowadays highly demanded and are at the core of research and industry attention. In this frame, electrochemical energy storage systems represent valid solutions as they reliably store energy in case of necessity, being able to compensate for the limitations of renewable energies linked to intermittency and instability. Lithium-ion batteries (LIBs) are nowadays the dominant technology in electric vehicles and portable electronics applications because of their high power and energy densities [1, 2]. However, LIB alternatives are currently under study because of the limited availability of lithium and the general high costs associated with the production of these devices. Moreover, safety concerns associated with the use of organic, poisonous electrolytes pose severe limitations on the large-scale adoption of LIBs [3, 4, 5]. Among such alternatives, zinc-ion batteries (ZIBs) have attracted interest because of their high element earth-abundance, high Zn specific capacity (820 mAh g\({}^{-1}\)) and lower estimated costs (US $65 kW h\({}^{-1}\) for ZIBs vs. over US $300 kW h\({}^{-1}\) for LIBs) [6]. In particular, the low Zn redox potential, i.e., \(-\)0.763 V vs. SHE, allows ZIBs with aqueous electrolyte chemistry that are intrinsically safer with respect to the organic one used in LIBs [7, 8]. However, ZIBs are usually plagued by zinc mossy growth, resulting in poor coulombic efficiency of charge and discharge cycles as a result of the poor electrification ofthe loosely bounded Zn mossy structures, eventually leading to battery failures [9; 10; 11; 12]. Such phenomenon, which is worsened in alkaline electrolytes, is usually associated with a low surface potential and/or uneven Zn ion diffusion toward the anode electrode surface. In this case, Zn ions are preferentially reduced on Zn protuberances rather than on the flat Zn surface, according to the well-known \"tip effect\" [13; 14; 15]. Considering this, researchers are applying considerable effort toward finding solutions able to erase or mitigate Zn dendritic growth, favoring a homogeneous Zn-plating process. These include the development of novel structural designs of Zn anodes, electrode-electrolyte interface optimization by the formation of in-situ or ex-situ interfacial coatings and protective layers, and electrolyte additives as well as functionalized separators [11; 16; 17; 18]. Organic and inorganic electrolyte additives can efficiently inhibit Zn dendrite formation, favoring the growth of a smooth and bright surface, usually achieved thanks to the preferential [002] orientation of Zn crystals [19; 20]. More specifically, such additives are able to create a blocking barrier for the reactants, i.e., zincates, at the electrode surface, favoring a more even deposition and suppressing preferential Zn growth on dendrites [21]. In particular, among the various organic additives, polyethylene glycols (PEGs) were extensively investigated, whose inhibiting effects derive from the oxygen radicals used for adsorption [22], in which it was shown how their addition to an electrolyte can influence the morphology of the zinc deposit. Specifically, grain sizes were reduced, producing smooth deposits [22; 23]. In terms of interfacial engineering, \"zincophilic\" coatings such as Ti\({}_{3}\)C\({}_{2}\)T\({}_{\mathrm{x}}\) MXene (MX) were recently demonstrated to be particularly effective as an interfacial layer to achieve smooth deposition on metal anodes such as Li, Na, K, and Zn [24; 25; 26; 27]. Ti\({}_{3}\)C\({}_{2}\)T\({}_{\mathrm{x}}\) MXene can unlock fast electrochemical kinetics in the plating/stripping process due to its high electronic conductivity and rapid Zn-ion diffusion. In fact, Ti\({}_{3}\)C\({}_{2}\)T\({}_{\mathrm{x}}\) MXene has also been employed in Zn-ion supercapacitors owing to their outstanding Zn-ion adsorption capability [28; 29].