# Zinc Plating on Inkjet-Printed Ti3C2 Tx MXene: Effect of Electrolyte and PEG Additive
## 2 Materials and Methods  
_Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) MXene Synthesis_--Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) MXene was synthesized through the mixed-acid approach [31; 42]. A mass of 10 g of Ti\({}_{3}\)AlC\({}_{2}\) MAX phase (Luoyang Advanced Material Co., Ltd., Luoyang, China) was added to an etchant solution composed of 30 mL of HF, 120 mL of HCl, and 60 mL of H\({}_{2}\)O. The solution was left to stir at 300 rpm for 24 h at 35 \({}^{\circ}\)C. The obtained multilayered Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) was washed multiple times by centrifugation at 3500 rpm for 5 min until a pH of 5-6 was obtained. A final delamination step of the multilayered Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) phase was performed, adding 2 g of Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) to a solution of 40 mL of water and 2 g of LiCl. The solution was placed in a vial and agitated with a mixer homogenizer for 30 min at 2400 rpm. Then the solution was subjected to this series of centrifuges: 3 cycles at 3500 rpm for 10 min, 1 cycle at 5000 rpm for 1 h, and 1 cycle at 8000 rpm for 20 min, discarding the transparent supernatant and redesigning the sediment between each cycle. _Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) MXene In Preparation and Printing_--The Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) ink preparation was re-adapted from a previously reported protocol [43] and prepared according to the following procedure: 40 mL of the delaminated suspension were placed in a beaker, and 0.1 g of Na-asc was added. The solution was stirred for 10 min, transferred to a bath sonicator (2 W/L) for 30 min, and then to a probe sonicator (2 s on, 2 s off, 180 W, 30 min of total time). The Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) dispersion was finally centrifuged for 10 min at 1000 rpm, and ultimately, 3 mM of LDS (lithium dodecyl sulfate) were added to obtain the final ink. A flat-bed thermal inkjet printer (Breva, Jlet2L, San Vittore Olona, Italy) equipped with a Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) ink-filled HP45 cartridge was employed for inkjet printing operations. The native printer resolution was 600 dpi. Typically, the substrates were placed on the flat bed and heated at 40 \({}^{\circ}\)C, and 20 layers of the Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) ink were consecutively overprinted to achieve a consistent MXene load. After printing, the Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\)-coated samples were dried in an oven at 70 \({}^{\circ}\)C for 1 h.  
_Characterization_--electrolytes were prepared by dissolving 2M ZnCl\({}_{2}\) or 2M ZnSO\({}_{4}\) in water solution with and without 10% wt. PEG400 (Sigma-Aldrich, Saint Louis, MO, USA). Electrolyte conductivity was investigated through a portable multi-range conductometer (Hanna Instruments, Villafranca Padovana, Italy). For electrochemical analyses, 20 layers of the Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) ink were printed on an SS316 disk of 15 mm diameter. Cyclic voltammetries were performed through a Squidstat Plus potentiostat (Admiral Instruments, Tempe, AZ, USA) using a pure Zn wire (diameter 1.5 mm) as the counter electrode and Ag/AgCl (3M KCl) as the reference electrode. All the electrochemical tests were performed without stirring the solution. Tafel plots were built on the cathodic scan only of the 2 mV s\({}^{-1}\) cyclic voltammetries. Electrochemical impedance spectroscopy (EIS) measurements were performed with the same three-electrode configuration described above using a Biologic VSP-300 potentiostat equipped with an EIS channel in the frequency range 100 kHz-100 mHz using 10 mV as pulse amplitude at open circuit potential. All measurements were performed at room temperature. Hull cell tests were carried out using a small 3D-printed (polypropylene) trapezoidal-shape Hull cell (33 mL volume, long side of 65 mm, short side of 25 mm, height of 32 mm). A 20-printed layer of Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) on a steel plate (34 mm \(\times\) 50 mm \(\times\) 1 mm) and a Pt plate (32 mm \(\times\) 32 mm \(\times\) 2 mm) were used as the cathode and anode panels, respectively, fixing the current at 100 mA for 20 min.