The effect of URT additive on the solvation structure of Zn
2+ was studied by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy (Figs. S6 and S7 in Supporting information). There is no obvious deviation for the URT/ZnSO
4 electrolyte on the ATR-FTIR and Raman spectra, which is probably due to the trace amount of URT comparing to Zn
2+ and the additive primarily functioning through interface adsorption. Thus, we calculated the adsorption energies of the additive URT molecule and H
2O with Zn, respectively. The binding energy of URT-Zn is −1.2 eV, which is much higher than the −0.61 eV of H
2O-Zn (
Fig. 2a), indicating that the URT molecule is before adsorption onto the Zn surface. The URT additive will preferentially adsorb on the Zn metal anode and accumulate in an electric double layer (EDL) through strong electrostatic adsorption between negatively charged N atoms and positively charged site surfaces [
31]. Consequently, the electric double layer capacitance (EDLC) for Zn anodes in ZnSO
4 electrolytes is measured to confirm it (
Fig. 2b). Obviously, the EDLC of URT/ZnSO
4 electrolyte is 2.46 µF/cm
2, lower than pure ZnSO
4 electrolyte of 3.69 µF/cm
2. These results illustrate that the introduction of the URT additive positively influences the diffusion of Zn
2+. The EDS maps show a uniform distribution of Zn, S, O, and N elements (Fig. S8 in Supporting information), which are consistent with the composition of SEI. At the same time, the zeta potential test can also prove the adsorption of additive molecules. The Zeta potential in ZnSO
4 electrolytes is −0.86 mV, and the Zeta potential moves negatively to −6.47 mV after adding URT additive to it, but the potential is corrected compared with ZnSO
4 electrolytes, indicating that URT molecules are electronegative and can adsorb zinc ions (Fig. S9 in Supporting information). In addition, the TAFEL curves are tested to further demonstrate the corrosion inhibition effects of URT additives. As exhibited in
Fig. 2c, the corrosion potential of Zn metal is increased from −0.013 V to 0.002 V (
vs. Ag/AgCl) after introducing URT, and the corrosion current (
icorr) is reduced from 0.97 mA/cm
2 to 0.28 mA/cm
2, indicating that URT molecules significantly inhibit the corrosion reaction [
32]. Besides, the overpotential of hydrogen evolution of URT/ZnSO
4 electrolyte is shifted to more negative (
Fig. 2d) from the linear sweep voltammetry (LSV) test, manifesting that the URT additive greatly inhibits the hydrogen evolution. The by-products of alkaline zinc sulfate are further confirmed by X-ray diffraction (XRD) patterns at different current densities (Figs. S10 and S11 in Supporting information). It is observed that the URT additive dramatically inhibits the formation of by-products. Additionally, the
Rct (Fig. S12 in Supporting information) in EIS of URT/ZnSO
4 electrolyte is much smaller than pure ZnSO
4 electrolyte, which indicates that the URT additives greatly promote the charge transfer, in the consistency of the results of
Ea. The nucleation overpotential of URT/ZnSO
4 electrolyte is 40 mV (|AB| = 40 mV) from the cyclic voltammetry (CV) curves with the scan rate of 10 mV/s in
Fig. 2e, which promotes the nucleation kinetics of Zn [
33]. The nucleation/growth behavior of URT/ZnSO
4 electrolyte is also detected by chronoamperometry (CA). As shown in
Fig. 2f, the current density of the URT/ZnSO
4 electrolyte quickly increased in the first tens of seconds and then tended towards stability, implying rapidly realized a stable 3D diffusion utilizing the URT additives. In contrast, the current density of pure ZnSO
4 electrolytes is enlarged all the time, indicating a longer 2D diffusion process with a localized Zn deposition.