# Zinc Plating on Inkjet-Printed Ti3C2 Tx MXene: Effect of Electrolyte and PEG Additive
## 3 Results
In general, the I\({}_{002}\)/I\({}_{101}\) increased when moving from a chloride-based to a sulfate-based electrolyte, i.e., 0.49 vs. 1.5, respectively, indicating how the [002] orientation growth was favored, which was compatible with the results obtained by SEM images, where apparently hexagonal-like Zn crystals were obtained with the 2M ZnSO\({}_{4}\) electrolyte. Moreover, PEG400 addition induced a slight increase in the I\({}_{002}\)/I\({}_{101}\) ratio in both chloride and sulfate-based solutions, i.e., 0.87 and 2.3, respectively. This result suggested that the increased surface overpotential produced by PEG400 effectively improved preferential [002] direction growth, which, however, was not evidently clear from the SEM results. However, as predicted from the SEM analyses, 2M ZnSO\({}_{4}\) + 10 wt.% PEG400 electrolyte XRD patterns (Figure 3d) confirmed the presence of small peaks located at \(\sim\)12\({}^{\circ}\), associated with the formation of Zn hydroxide sulfate structures (CPDS #39-0690). In terms of crystallite dimensions, ZnCl\({}_{2}\) with and without PEG400 and 2M ZnSO\({}_{4}\) gave similar results, corresponding to average crystallite sizes of 48.8 nm, 57 nm, and 48.8 nm, respectively. Only in the case of 2M ZnSO\({}_{4}\) + 10 wt.% PEG400 was the calculated crystallite size sensibly lower, counting to 37.92 nm coherently with the low efficiency of Zn deposition and lower grain growth rate. In general, SEM and XRD results suggest that the inkjet-printed Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) coating seemed to not play any role in the preferential orientation alignment by epitaxial growth  
Figure 3: XRD diffractograms of Zn deposits obtained by Hull cell sample preparation in different electrolytes: (**a**) 2M ZnCl\({}_{2}\), (**b**) 2M ZnCl\({}_{2}\) + 10 wt.% PEG400, (**c**) 2M ZnSO\({}_{4}\), (**d**) 2M ZnSO\({}_{4}\) + 10 wt.% PEG400, varying the applied current density. Insets: magnified portion of each XRD diffraction patterns in the range 35–45\({}^{\circ}\). of the zinc crystals, and the surface texture was solution-controlled rather than substrate-controlled. In fact, previous work demonstrated that the substrate zincompilicity could effectively regulate the Zn growth up to very narrow Zn thickness, and above a 1 nm-thick layer, the Zn electrolrystallization was kinetically controlled rather than thermodynamically, so that the substrate affinity became negligible [56]. However, it is also likely that the very limited average lateral size of the Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) 2D sheets used in our work (required for inkjet printing) negatively affected the epitaxial growth of the first Zn nuclei. In fact, the restacking of the small Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) 2D sheets produced a huge density of Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) edges and boundaries. As a consequence, this work may suggest that inkjet printing is not a convenient technique to prepare Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) zicmophilic coatings for [002]-textured Zn deposition in Zn-ion battery applications. Future works may finally address this question and will be devoted to the investigation of the effect of Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXene sheet size on the texturing of plated Zn and its reversibility by multiple plating-stripping cycles.