Boosting the performance of aqueous zinc-ion battery by regulating the electrolyte solvation structure

Abstract

The practical implementation of aqueous Zn-ion batteries (ZIBs) for large-scale energy storage is impeded by the challenges of water-induced parasitic reactions and uncontrolled dendrite growth. Herein, we propose a strategy to regulate both anions and cations of electrolyte solvation structures to address above challenges, by introducing an electrolyte additive of 3-hydroxy-4-(trimethylammonio)butyrate (HTMAB) into ZnSO₄ electrolyte. Consequently, the deposition of Zn is significantly improved leading to a highly reversible Zn anode with paralleled texture. The Zn/Zn cells with ZnSO₄/HTMAB exhibit outstanding cycling performance, showcasing a lifespan exceeding 7500 h and an exceptionally high accumulative capacity of 16.47 Ah cm⁻². Zn/NaV₃O₈·1.5H₂O full cell displays a specific capacity of ~130 mAh g⁻¹ at 5 A g⁻¹ maintaining a capacity retention of 93% after 2000 cycles. This work highlights the regulation on both cations and anions of electrolyte solvation structures in optimizing interfacial stability during Zn plating/stripping for high performance ZIBs.

INTRODUCTION

The aqueous batteries are considered as a viable candidate for large-scale energy and devices due to their intrinsic safety, cost-effectiveness and environmental compatibility.^1,2 Among these aqueous batteries, Zinc-ion batteries (ZIBs) have been featured for the high capacity (820 mAh g⁻¹ and 5854 mAh cm⁻³) of zinc metal anode and abundant resource.^3,4 Nevertheless, the instability of Zn anode-electrolyte interface during (dis)charge substantially hinders the commercialization of ZIBs.⁵ In the common ZnSO₄ electrolyte, zinc cations are typically solvated by water molecules and sulfate anions in both inner and outer layers, forming solvent-separated ion pairs (SIP, [Zn²⁺-(H₂O)₆∙${\mathrm{SO}}_4^{2-}$]) and contact ion pairs (CIP, [Zn²⁺-(H₂O)₅∙O${\mathrm{SO}}_3^{2-}$]). During Zn plating process, a large amount of de-solvated water molecules and sulfate ions were brought into the electric double layer (EDL), causing severe parasitic hydrogen evolution reaction (HER) and the formation of passivated Zn₄(OH)₆SO₄·xH₂O (ZHS) by-products on the zinc anode.^6–8 The cluttered by-products as well as the intrinsic imperfections on Zn metal surface further deteriorate the uniformity of interfacial electric field/ion flow and exacerbate rampant dendrite growth.^9,10 The above issues result in not only the diminished reversibility and shortened life span of the zinc anode, but also a constrained Zn utilization (known as depth of discharge, DOD_Zn) and inferior energy density.^11,12

Great efforts have been devoted to suppressing the dendrite growth and HER, through approaches such as Zn alloy anode,¹³ artificial interfacial layer,^14,15 polymer electrolyte,¹⁶ deep eutectic electrolyte,¹⁷ etc. The incorporation of additives into electrolytes is regarded as a more promising strategy in terms of its cost-effectiveness and facile preparation process.¹⁸ Regulating the electrolyte solvation structure by additives can effectively inhibit side reactions and modulate the Zn electro-deposition behavior.^4,19,20 However, the current researches primarily focus on investigating the interaction between solvated water molecules and Zn²⁺. Some researchers revealed that electrolyte additives with higher affinity toward Zn²⁺ can participate the solvation structure by replacing a certain amount of active water molecules, thereby inhibiting HER to some extent.^21–23 However, numerous water and sulfate ions remain on the EDL during plating process, triggering the HER and by-products under large current densities and long-term cycling. Notably, anions which are the important source of by-products, has been ignored in terms of its impact on side reactions and Zn anode deposition behavior.

In this work, we present an approach to regulate both anions and cations of electrolyte solvation structures by adding 3-hydroxy-4-(trimethylammonio)butyrate (HTMAB) with both nucleophilic (COO⁻) and electrophilic ((CH₃)₃N⁺) groups into ZnSO₄ solution. In the obtained hybrid electrolyte (a.k.a ZS/HTMAB), the functional groups can regulate both cations and anions of the solvation structure, thus effectively inhibiting side reactions and inducing parallel textured Zn anode. With the addition of HTMAB, Zn anode exhibits significantly improved cycling life in Zn/Zn symmetric cell with a lifetime over 7300 h, which is about 33-fold than that of the cell in ZS. When being assembled in a full cell setting with NaV₃O₈·1.5H₂O (NVO) cathode, it achieves the stable capacity of ~110 mA h g⁻¹ at 5 A g⁻¹ after 2000 cycles with 93% capacity retention, which flag great potentials in future scaling up application.

RESULTS AND DISCUSSION Regulation on electrolyte solvation structure and interfacial properties

In the conventional ZnSO₄ electrolyte, the self-ionization of water (2H₂O ↔ H₃O⁺ + OH⁻) occurs as result of the electron transfer from the coordinated water to the empty orbital of Zn²⁺, which leads to a lower pH value of ZnSO₄ solution than that of pure water (Figure S1).^24,25 Notably, the pH values of electrolytes increase substantially from 4.21 for ZS to 4.88 for ZS/HTMAB upon the addition of HTMAB, which may be ascribed to the stronger coordination of the nucleophilic group in HTMAB with Zn²⁺, thus alleviating the self-ionization of water. From the nuclear magnetic resonance (NMR) results in Figure 1A, the ¹H peak shifts toward larger chemical shift of ZS (4.713 ppm) compared to that of pure H₂O (4.703 ppm), ascribing to the strong coordination between Zn²⁺ and water molecules.²¹ The ¹H peak of ZS comes back to a smaller chemical shift with the addition of HTMAB (4.708 ppm) suggesting the attenuated interaction of Zn²⁺ with water, which is consistent with the increased pH values of ZS/HTMAB. The Fourier transform infrared spectra (FTIR) in Figure 1B demonstrate that the symmetric stretching vibrations of COO⁻ group at around 1400 cm⁻¹ for 0.1 M HTMAB moves to higher wavenumbers for ZS/HTMAB,²⁶ verifying the affinity of COO⁻ nucleophilic group to Zn²⁺. Furthermore, the binding energy of Zn²⁺ with HTMAB (−290.38 kcal mol⁻¹) is much lower than that with H₂O (−95.47 kcal mol⁻¹), revealing that Zn²⁺ preferentially coordinates with the COO⁻ group of HTMAB than H₂O molecule (Figure 1E). Therefore, HTMAB with nucleophilic group can substitute for H₂O to interact with Zn²⁺, thus effectively decreasing the active water content.

It is worth noting that electrophilic group of (CH₃)₃N⁺ in HTMAB also contributes to the regulation of electrolyte solvation structure, which is manifested by Raman. In Figure 1C, the peak of (CH₃)₃N⁺ locating at 762 cm⁻¹ for 0.1 M HTMAB moves to higher wavenumber of 764 cm⁻¹ for ZS/HTMAB, implying the interaction of HTMAB with ${\mathrm{SO}}_4^{2-}$.²⁷ Accordingly, the evident blueshift of ${\mathrm{SO}}_4^{2-}$ band from 980 cm⁻² in ZS to 982 cm⁻² in ZS/HTMAB, further confirms the enhanced constraint of ${\mathrm{SO}}_4^{2-}$ with the addition of HTMAB (Figure 1D). Besides, the lower binding energy between (CH₃)₃N⁺– and ${\mathrm{SO}}_4^{2-}$ (−84.76 kcal mol⁻¹) further confirms the attraction of electrophilic (CH₃)₃N⁺– group with ${\mathrm{SO}}_4^{2-}$ (Figure 1F). Figure 1G illustrates the molecular electrostatic potential mapping of HTMAB and ${\mathrm{SO}}_4^{2-}$. After complexing with ${\mathrm{SO}}_4^{2-}$, the electrostatic potential of HTMAB decreased significantly with a crossed potential energy surface, which further verifies the electron transfer between electrophilic (CH₃)₃N⁺– group and ${\mathrm{SO}}_4^{2-}$. The combination of HTMAB with sulfate anions is conducive to the suppression of Zn₄(OH)₆SO₄·xH₂O by-product.

We next analyze the adsorption of HTMAB by calculating the EDL differential capacitance (C_dl) of Zn electrode, according to Cdl = dQ/dE = i/(dE/dt).^28,29 In Figure 2A, the evaluated C_dl of Zn anode decreased significantly from 0.292 mF cm⁻² in ZS to 0.137 mF cm⁻² in ZS/HTMAB, indicating that electrochemical active surface area of Zn anode decreased due to the adsorption of additive.²⁸ To assess the adsorption ability of HTMAB on Zn anode, a Zn sheet is firstly soaked into 0.1 M HTMAB aqueous solution for 4 h and then carefully rinsed with deionized water to remove the residual solution on the surface. FTIR results of Zn plates before and after immersion are shown in Figure S2. The peaks at 1397 and 1586 cm⁻¹ (representing peaks for the vibration of carboxylate group) emerge for the Zn plate after being immersed in HTMAB solution while no peak can be detected for bare Zn.^26,30 Besides, the first-principle calculations for adsorption energies of H₂O and HTMAB on Zn (002) slab are shown in Figure 2B. The more negative adsorption energy of HTMAB compared to H₂O on Zn (002) facet demonstrates the preferential adsorption of HTMAB on the Zn anode over water. The charge density difference of HTMAB adsorbed on the Zn (002) slab is illustrated in Figure 2C. The presence of distinct charge transfer between HTMAB (both nucleophilic and electrophilic groups) and Zn slab, further confirms the robust interaction between HTMAB and Zn metal.

The anti-corrosion performance is analyzed on the electrode-electrolyte interface. After immersing a Zn plate into ZS for 7 days, a coarse surface morphology (Figure 2D) with numerous lamellate products occurs due to the severe corrosion, which have been identified as Zn₄SO₄(OH)₆·xH₂O (ZHS) by XRD results (Figure S3). In contrast, the Zn plate treated with HTMAB-containing electrolyte exhibits a smooth surface (Figure 2E) with no new XRD peaks appeared (Figure S3), indicating an enhanced anti-corrosion effect. The linear sweep voltammetry (LSV) is performed to assess the HER on Zn electrode (Figure 2F), with the ZnSO₄ replaced by Na₂SO₄ (NS) to avoid the influence of Zn deposition. The onset potential of NS/HTMAB moved negatively (−1.98 V vs. Ag/AgCl) compared to that of NS (−1.82 V vs. Ag/AgCl), accompanied by a significant decrease in current responses, revealing that the HER on Zn anode has been dramatically suppressed by HTMAB additive. The Tafel plots (Figure 2G) confirm the anti-corrosion effect of HTMAB, as ZS/HTMAB exhibits a smaller corrosion current density (i_corr) of 0.45 mAcm⁻² and a more positive corrosion potential (E_corr) of −0.968 V versus Ag/AgCl compared to ZS with i_corr = 1.09 mAcm⁻² and E_corr = −0.972 V versus Ag/AgCl.^31,32

Modulation on Zn Deposition Behavior

The in-situ optical microscope images in Figure 3A,B provide intuitive evidence for the Zn deposition behavior in the electrolytes with and without HTMAB. The rough surface with irregular deposits can be observed on the Zn electrode in ZS (Figure 3A) while a uniform surface with dense deposits is maintained in ZS/HTMAB (Figure 3B) during the deposition process at 10 mA cm⁻². The morphologies are further characterized on Cu substrates by SEM and the corresponding 3D optical images. In Figure 3C, the electrodeposits in ZS are disheveled threadlike dendrites with the average roughness (Ra) of 4.8 μm. On the contrary, homogeneous electrodeposits with parallel texture (Figure S4) are unveiled in ZS/HTMAB with a smaller Ra of 1.1 μm (Figure 3D). After stripping for 5 mAh cm⁻² at 5 mA cm⁻², some parts of electrode collapse inwards with the percentage of pits area reaching to 5.2% in ZS, while much flat surface can be maintained (with only 0.1% pits area) in ZS/HTMAB. The above morphological evidence claims that the electrochemical behavior of Zn anode is regulated by HTMAB additive, resulting in the even Zn plating/stripping process and horizontally textured Zn anode.

The effect of HTMAB on crystallographic orientation modulation and side reaction inhibition during cycling is further evaluated with the Zn/Zn symmetrical cells. In Figure 3E and S5a, shaggy deposits, randomly lamellar by-products and some caves covered on the Zn electrode after 50 cycles in ZS under 5 mA cm⁻² and 5 mAh cm⁻². Contrarily, the electrode presents compact and uniform morphology with horizontal oriented texture after cycled in ZS/HTMAB (Figures 3F and S5b). The XRD patterns for Zn anodes after cycling are shown in Figure 3G. The electrode after cycled in ZS exhibits a distinct new peak at 8° attributed to the presence of ZHS, while showing little change in Zn crystal orientation compared to its pristine state. By adding HTMAB, the by-products are greatly suppressed and the intensity of peak belonging to Zn (002) seems be significantly enhanced. To investigate the evolution in crystallographic orientation of Zn surface during cycling, the XRD results of Zn anodes after cycling are shown in Figure S6. The peak intensity ratios of Zn (002) to Zn (101), denoted as I₍₀₀₂₎/I₍₁₀₁₎, are exhibited in Figure S7. The intensity of Zn (002) increased gradually as cycling, and the I₍₀₀₂₎/I₍₁₀₁₎ ratio of Zn anode increases from 0.51 (pristine Zn) to 0.71 and 0.92 after 10 and 20 cycles, respectively. After 50 cycles, Zn (002) peak becomes the strongest diffraction peak with the ratio of I₍₀₀₂₎/I₍₁₀₁₎ reaching to 1.58. However, I₍₀₀₂₎/I₍₁₀₁₎ ratio of Zn after cycling in ZS is similar to that of pristine Zn (Figure 3G and S7). The increased I₍₀₀₂₎/I₍₁₀₁₎ ratio of Zn in Zn/HTMAB indicates that the additive can successfully induce the anode texture by regulating the deposition behavior.

During the Zn deposition, it has been well known that the ion transportation in the bulk electrolyte, the de-solvation process and Zn²⁺/adatom self-diffusion of the deposited metal, can remarkably influence the deposition morphology.^33,34 Little difference in ionic conductivity has been detected before (59.63 mS cm⁻²) and after (58.36 mS cm⁻²) adding HTMAB, indicating the negligible influence of HTMAB on ion transportation. The similar contact angles of ZS and ZS/HTMAB on bare Zn demonstrates the comparable wettability of these two electrolytes (Figure S8). The de-solvation ability is assessed by the charge transfer resistance (R_ct) of symmetrical Zn/Zn cells (Figure S9). According to Arrhenius equation, the activation energy (Ea) of ZS/HTMAB (56.85 kJ mol⁻¹) decrease significantly compared to ZS (64.54 kJ mol⁻¹), indicating the better de-solvation ability of Zn²⁺ with addition of HTMAB.³⁵

The Zn²⁺/adatom self-diffusion is another crucial process for dendrites formation.^36,37 The rapid 2D diffusion of Zn²⁺ results in its preferential deposition on protrusions, commonly known as ‘tip effect’, thereby accelerating the growth of dendrites.³⁶ In Figure 3I, the continuous increasing current density of ZS implying the 2D diffusion of Zn²⁺. The stable polarization current is retained in ZS/HTMAB suggesting a restricted 2D diffusion, due to the adsorption of HTMAB on the interface. In Figure S10, the increased nucleation overpotential of ZS/HTMAB than that of ZS is conducive to obtaining the smaller crystal nucleus for uniform deposition.^38,39 Therefore, the modulation of HTMAB on electrolyte solvation structure and interfacial properties results in the regulation on Zn deposition behavior, thereby suppressing by-products and realizing densely packed Zn anode with parallel texture.

Performance of Zn anode and full cells

We then assess the long-term cycling performance of Zn anode in Zn/Zn symmetric cells. Figure S11 shows the ionic conductivities of electrolytes with various amount of HTMAB. Despite the decrease in ionic conductivities with the increasing content of HTMAB, the adverse impact becomes negligible at lower concentrations (0.05 and 0.1 M). In Figure S12, the Zn/Zn batteries exhibit the longest cycling life with the addition of 0.1 M HTMAB, while batteries with other electrolytes displayed undesirable performance. Therefore, 0.1 M HTMAB in ZS (ZS/HTMAB) is considered as the optimal electrolyte. The cycling performance of Zn/Zn cell at regular condition of 1 mA cm⁻² and 1 mAh cm⁻² is shown in Figure 4A. HTMAB based cell possesses ultra-long cycling lifetime of 7300 h with a very stable polarization hysteresis (∼23 mV), which is around 33 times of ZS electrolyte (216 h). The cell cycled with HTMAB remain stable for 1000 h at 5 mA cm⁻² with the capacity of 5 mAh cm⁻², whereas the battery without additive is short-circuited after 50 h (Figure 4B). Interestingly, the lifespan of Zn/Zn cell with HTMAB reaches 1600 h at 20 mA cm⁻² with 1 mAh cm⁻² leading to an extremely high accumulative capacity of 16.47 Ah cm⁻², which surpasses most reported work (Figure 4C,F). Zn utilization rate (DOD_Zn) is also investigated with thin Zn plates of 30 μm. As shown in Figure S13, the cell with ZS/HTMAB remain stable for 150 h even at a high DOD_Zn of 85.4%.

The reversibility of Zn anode is explored within Zn/Cu asymmetric batteries. In Figure 4D, the ZS based cell appears inferior stability and fails at 74th cycle under 1 mA cm⁻² and 1mAh cm⁻². Zn/Cu cell with ZS/HTMAB displays extended lifespan for over 1600 cycles (Figure 4D) with gradually increasing Coulombic efficiencies (Figure 4E). The high average Coulombic efficiency of 99.74% and large accumulative capacity of 16.47 Ah cm⁻² demonstrate the excellent Zn anode performance, which distinguish itself among existing works^{21,22,24,36,37,40–46} (Figure 4F).

The ZS/HTMAB electrolyte is further assessed in full cell settings by using NaV₃O₈·1.5H₂O (NaVO) as cathodes and zinc foils as anodes. The morphology and crystal structure characterizations of NaVO in Figure S14, show a good consistency with the previous report.⁴⁷ From the LSV curve in Figure S15, no current response can be observed before the water splitting, demonstrating the excellent electrochemical stability of HTMAB. Figure 5A shows the cyclic voltammetry (CV) curves of Zn/NaVO cell with ZS/HTMAB electrolyte. Two couples of redox peaks can be observed due to Zn²⁺ intercalation/extraction, which can be attribute to the valent changes of vanadium from V⁵⁺ to V⁴⁺ and then V³⁺.⁴⁷ In Figure 5B,C, the rate performance plots suggest that ZS/HTMAB based battery exhibits a high discharge capacity of around 300 mAh g⁻¹ at a current density of 0.1 A g⁻¹, retaining the specific capacities of around 268, 221, 188, 158 and 109 mAh g⁻¹ at 0.2, 0.5, 1, 2 and 5 A g⁻¹, respectively.

The galvanostatic charge/discharge curves in Figure 5D summarize the performance for Zn/NaVO cells at 1st, 100th and 500th cycles under 5 A g⁻¹. The battery with ZS shows increased polarization and decreased capacity with cycling, whereas battery with ZS/HTMAB presents relatively stable potential and capacity. The long-term cycling data of Zn/NaVO cells at a high current density of 5 A g⁻¹, indicate that the capacity of cell with ZS decays rapidly to ~62 mAh g⁻¹ in the first 600 cycles and then gradual deteriorate till fail. Benefiting from the HTMAB, the Zn/NaVO cell displays a stable cycle capacity of ~130 mAh g⁻¹ under 5 A g⁻¹, leading to a capacity retention rate up to 93% after 2000 cycles. In addition, a pouch cell (4 cm × 4 cm) with a thin Zn foil (10 μm) and NaVO cathode (3.86 mg cm⁻²) at a N/P ratio of ~4 was assembled. The galvanostatic discharge–charge measurements at 0.5 A g⁻¹ (Figure S16) suggests an excellent cycling stability for 200 cycles of the Zn/NaVO pouch cell with ZS/HTMAB, delivering a capacity of ~60 mAh g⁻¹.

CONCLUSION

In this work, we describe an approach to regulate the electrolyte solvation structure by adding the HTMAB with both nucleophilic (COO⁻) and electrophilic (N⁺(CH₃)₃) groups in ZS. The strong coordination of the COO⁻ nucleophilic group with Zn²⁺, as well as the combination between N⁺(CH₃)₃ electrophilic group and ${\mathrm{SO}}_4^{2-}$ significantly inhibits HER and the by-products. As such, it significantly affects the Zn electrochemical deposition behavior, leading to the reconstruction of Zn texture with more exposed Zn (002) crystal plane after cycling. Consequently, the Zn/Zn cell with ZS/HTMAB displays excellent cycling performance with the cycling life of 7300 h and the accumulative capacity up to 16.47 Ah cm⁻². Meanwhile, the Zn/NaVO full cell shows a specific capacity of around 130 mAh g⁻¹ with a remarkable capacity retention of 93% after 2000 cycles at 5 A g⁻¹. This study sheds light on the effect of regulation on both cations and anions of the electrolyte solvation structure to boost the high-performance aqueous zinc-ion batteries.

EXPERIMENTAL SECTION Electrolytes and electrodes preparation

All reagents and materials were commercially available without further purification. ZnSO₄·7H₂O was dissolved into deionized water to obtain 2 M ZnSO₄ solution (denoted as ZS). Different amounts of 3-hydroxy-4-(trimethylammonio)butyrate (HTMAB) additive were added into ZS and the electrolyte with optimized concentration of 0.1 M is labeled as ZS/HTMAB.

Zn foils (100/30 μm thickness) and Cu foil (20 μm) with the diameter of 16 mm were used for symmetric Zn/Zn cells and asymmetric Zn/Cu cells. The NaV₃O₈·1.5H₂O (NaVO) cathode material was synthesized according to the literature.⁴⁷ Typical, 1 g commercial V₂O₅ powder was dispersed into 15 mL 2 M NaCl aqueous solution. After stirring for 96 h at 30°C, the mixture was washed with water thoroughly. Finally, the black red product was obtained by freeze-drying. The NaVO cathode was prepared by mixing NVO powder, super P and PVDF in a weight ratio of 7:2:1 in NMP, then casting the slurry on Ti foils with the mass loading around 5 mg cm⁻².

Material characterizations

The electrode morphology was characterized by the field emission scanning electron microscope (SEM, ZEISS Ultra 55). The crystal structure of electrode was determined with X-ray diffractometer (XRD, Empyrean). The electrolyte structure was characterized by Fourier transform infrared spectra (FTIR, Thermo Scientific Nicolet iS20), Raman spectra (Horiba LabRAM HR Evolution) with an excitation wavelength of 532 nm and nuclear magnetic resonance (NMR, Bruker 400 MHz).

Electrochemical tests

Chronopotentiometry (CP) in different electrolytes were conducted in Zn/Zn symmetric cells. Linear sweep voltammetry (LSV) was tested to evaluate hydrogen evolution reaction by three-electrode system with Zn plate as the working electrode, Ti foil as the counter electrode and Ag/AgCl as the reference electrode. The Tafel plots was conducted by a three-electrode system with Zn plate as the working electrode, Pt as the counter electrode and Ag/AgCl as the reference electrode. The ionic conductivity (ơ) was tested by using two blocking electrodes (Pt foil) and evaluated according to the following equation:[Image Omitted. See PDF]where S represents the area of the blocking electrode, L is the distance between the two electrodes, and R represents the resistance from EIS measurements. The electrochemical performance of Zn/Zn, Zn/Cu and Zn-NaVO cells was tested by CR2025 coin-type cells with Neware BTS-5 test system.

Quantum chemistry (QC) calculations

QC calculations were performed using the Gaussian 16 software package.⁴⁸ The M06-2X⁴⁹ hybrid exchange-correlation functional (including 54% of Hartree-Fock exchange) in combination with the def2-TZVP basis set⁵⁰ was used for the geometry optimization and frequency calculations. Then a single-point energy calculation of each optimized structure was performed at the same functional and basis set. The D3 empirical dispersion correction⁵¹ was included to account for the van der Waals interactions. The solvation effects were simulated using the SMD model⁵² for the aqueous environment and binding energy $\left(E_{\mathrm{BE}}\right)$ is calculated using the formula:[Image Omitted. See PDF]where $E_{\mathrm{AB}}$, $E_{\mathrm{A}}$, and $E_{\mathrm{B}}$ denote the total energies of the AB complexes, bare A, and bare B, respectively. $E_{\text{BSSE}}$ is the basis set superposition error (BSSE)⁵³ correction energy, which is applied using the counterpoise method.

First-principle calculations

First-principle calculations were conducted using the Vienna Ab initio Simulation Package (VASP)^54,55 employing the projector-augmented wave (PAW) method⁵⁶ with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional.⁵⁷ A plane-wave basis set with a kinetic energy cutoff of 450 eV was employed for electronic wavefunctions. Adsorption calculations utilized a 2 × 2 × 1 Γ-centered k-point mesh. Convergence criteria for forces and energy were set at 0.03 eV/Å and 10⁻⁵ eV, respectively. The adsorption model involved a 7 × 7 supercell with a four-layer Zn (002) slab, where the bottom two layers were constrained to simulate bulk properties. A 15 Å vacuum layer was introduced to prevent artificial interactions between periodic images. Crystal structures were visualized using VESTA,⁵⁸ and post-processing of data was conducted using the VASPKIT code.⁵⁹ The adsorption energy $\left(E_{\mathrm{ads}.}\right)$ between Zn (002) slab and different adsorbate molecules (water and HTMAB) was defined as following equation:[Image Omitted. See PDF]where $E_{\mathrm{Zn}\left(002\right)+\text{Molecules}}$, $E_{\mathrm{Zn}\left(002\right)}$ and $E_{\text{Molecules}}$ represent the total energies of the Zn (002) slab with adsorbed molecules, Zn (002) slab, and adsorbate molecules, respectively.

AUTHOR CONTRIBUTIONS

Xingxing Wu, Yinzhu Jiang: Conceptualization. Xingxing Wu, Yufan Xia, Ben Bin Xu, Muhammad Wakil Shahzad: Methodology; data collection, and analysis. Yufan Xia: Formal analysis. Shuang Chen, Zhen Luo: Validation and visualization. Zhang Xuan, Hongge Pan, Mi Yan: Resource. Xingxing Wu, Ben Bin Xu, Yinzhu Jiang: Writing original draft; editing and review. Yinzhu Jiang: Project administration and funding acquisition.

ACKNOWLEDGMENTS

This work was supported by the National Key R&D Program (2022YFB2502000), Zhejiang Provincial Natural Science Foundation of China (LZ23B030003), and the Fundamental Research Funds for the Central Universities (2021FZZX001-09). BBX is grateful for the support from the Engineering and Physical Sciences Research Council (EPSRC, UK) RiR grant—RIR18221018-1. Xingxing Wu and Yufan Xia contributed equally to this work.

CONFLICT OF INTEREST STATEMENT

The author team wants to declare a conflict of interest that one of the authors, Professor Ben Bin Xu, who is an associate editor of EcoMat. Therefore, he should be excluded from any stages in assessing this submission.