# Zinc Plating on Inkjet-Printed Ti3C2 Tx MXene: Effect of Electrolyte and PEG Additive
## 4 Conclusions  
This work focused on the Zn nucleation and growth behavior of inkjet-printed Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXene substrates. Different electrolytes were investigated, namely zinc chloride- and sulfate-based solutions with and without PEG400 as an organic additive to improve the surface texture. We showed that, in chloride-based electrolytes, the fastest reaction rates were achieved. On the contrary, SO\({}_{4}\)\({}^{2-}\) solutions were characterized by the highest nucleation overpotentials and charge transfer resistance as a consequence of the slower ion mobility in sulfate-based solutions or the adsorption of different anions at the Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) surface. In agreement with recent literature, SEM and XRD analyses demonstrated that to achieve more [002]-textured Zn plating, excessively high reaction rates are unfavorable. In this regard, PEG400 effectively improved the preferential [002] orientation in both the Cl\({}^{-}\) and SO\({}_{4}\)\({}^{2-}\) electrolytes, but, in the latter one, the excessive surface overpotential induced poor Zn deposition, favoring zinc hydroxide sulfate precipitation. This work also suggests that inkjet-printed Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXene coatings are not effective in promoting the epitaxial growth of a Zn layer that is electrolyte-controlled. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14020682/s1](https://www.mdpi.com/article/10.3390/app14020682/s1)]([https://www.mdpi.com/article/10.3390/app14020682/s1](https://www.mdpi.com/article/10.3390/app14020682/s1)), Figure S1: (a) SEM image of the multi-layered Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) flakes after etching step and (b,c) the corresponding EDX quantiative analysis results; Figure S2: XRD pattern of the delaminated Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXenes. For the analysis, a diluted delaminated Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) aqueous suspension was vacuum filtered and dried to obtain a free-standing Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) film; Figure S3: DLS of the Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) ink employed for electrode MXene-coated electrode preparation; Figure S4: Deposited areal (dry) Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) mass loaded as function of overprinting layers with (a) the fresh ink and (b) aged ink after 50 days of storage; Figure S5: EDX mapping of the 20 layer printed Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) on SS316 disk substrate; Figure S6: (a) Picture of the SS316 disk coated with 20 layer of Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) by inkjet printing. The typical bright bluish colour the Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXene is visible. In (b) is reported the SEM of the cross section of the Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) coating, showing a thickness of roughly 2 \(\mu\)m; Figure S7: CVs of Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) electrode in different electrolytes, i.e., 2M ZnCl\({}_{2}\) (a), 2M ZnCl\({}_{2}\) + 10 wt.% PEG (b), 2M ZnSO\({}_{4}\) (c) and 2M ZnSO\({}_{4}\) + 10 wt.% PEG (d), recorded varying scan rate, i.e., 2, 5, 10, 25, 50, 100 mV s\({}^{-1}\); Figure S8: (a) picture of the Hull-cell employed in this work. The Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) coated SS316 plate is placed on the oblique side of the trapezoidal cell while a Pt plate on the short side of the cell; (b) card for the local current density estimation with the cathode coupon underneath; Figure S9: SEM image of the pristine Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) coated electrode. Conceptualization, E.G. and P.V. ; methodology, P.V., V.M. and E.G. ; software, P.V. and V.M. ; validation, P.V. and V.M. ; formal analysis, P.V., V.M. and E.G. ; investigation, P.V. and V.M. ; resources, V.M. and E.G. ; data curation, V.M., P.V. and E.G. ; writing--original draft preparation, P.V. and E.G. ; writing--review and editing, P.V., L.M. and E.G. ; supervision, L.M. and E.G. All authors have read and agreed to the published version of the manuscript.