# Zinc Plating on Inkjet-Printed Ti3C2 Tx MXene: Effect of Electrolyte and PEG Additive
## 3 Results  
Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXenes were successfully obtained by the well-known procedure of mixed acid (HF-HCI) etching and subsequent delamination in LiCl solution. Successful etching was confirmed by SEM analyses (Figure S1a), which clearly showed the \"open-book\" morphology of the particles as a result of the Al selective etching [33]. EDX analyses (Figure S1b,c) also reported a very low average Al-to-Ti atomic ratio (0.041), confirming successful Al removal. On the other hand, XRD (Figure S2) assessed the successful delamination into individual Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXenes sheets because of the left shift of the intense [002] peak to a very low diffraction angle (6\({}^{\circ}\)) as well as the progressive disappearance of the higher-order peaks [44; 45]. According to the average hydrodynamic diameter measured by DLS analysis (Figure S3), the average lateral size of the 2D MXene sheets was estimated to be 302 nm [41]. Inkjet printing is a well-known technique capable of quickly producing thin coatings on any substrate by the jetting of small droplets of a colloidal nanoparticle suspension through the nozzles of the printhead. Despite its wide industrial employment and suitability for the interfacial engineering regulation of the electrodes, poor attention was devoted to inkjet printing, and the usual slurry electrode coating is usually preferred. The Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXene ink we formulated was easily printable, and Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\)-coated electrodes could be quickly produced. The consistency and repeatability of the printing process were checked by weighting the samples. Figure S4 shows that even after more than 1 month of ink storage, the printed Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) mass was highly reproducible, meaning that the as-prepared ink was stable and no agglomeration or nozzle clogging occurred. Samples were prepared by printing 20 consecutive overlayers, resulting in a Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) mass load of 0.452 mg cm\({}^{-2}\). The EDX mapping (Figure S5) of the bright bluish Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\)-coated electrodes revealed a very smooth surface and uniform elemental distribution. The thickness of the dried Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) 20-layer coating was estimated to be \(\sim\)2 \(\upmu\)m by the SEM analysis of the cross-section (Figure S6). The CVs of the Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\)-coated electrodes in chloride or sulfate-based zinc electrolytes, with and without 10% wt. PEG400 as additive, are reported in Figure 1a. At a low scan rate (2 mV s\({}^{-1}\)), the typical Zn plating and stripping behavior was clearly visible for each of the investigated electrolytes, with a sloped cathodic curve and a broad anodic peak corresponding to the Zn reduction (plating) and oxidation (stripping), respectively. As reported in Table 1, in terms of charges and current density peaks, the chloride-based electrolyte generally resulted in the highest values when compared to the sulfate-based one. For instance, the charge related to Zn plating (Q\({}_{\rm plat}\)) in the PEG-free 2M ZnCl\({}_{2}\) electrolyte was 3.34 higher than the PEG-free 2M ZnSO\({}_{4}\). Evidently, PEG addition induced a reduction of the electrochemical activity, suggesting that the kinetics of the Zn plating were partially hindered by the PEG400 macromolecules. In fact, when the Q\({}_{\rm plat}\) is considered, a 10% wt. PEG400 addition resulted in a 36.8% reduction in ZnCl\({}_{2}\)-based electrolytes and 55.4% in the ZnSO\({}_{4}\)-based one. The higher extent of the zinc ion reduction and consecutive zinc metal oxidation, with respect to the electrolyte composition, can be related to faster nucleation and growth rate.