The electrolyte is another pivotal factor that determines the fundamental electrochemistry of Zn electrodes. Therefore, modifying the electrolyte would effectively alter the corrosion behavior of Zn electrodes. In a few early studies, the influence of electrolyte conditions on Zn electrode corrosion has been investigated, especially in concentrated alkaline solutions. The HER rate would be increased if impurities introduce metal cations such as Cu²⁺, Ni²⁺, As³⁺, and Sb³⁺ into the electrolyte. On the contrary, the presence of Pb²⁺ can decrease the HER rate (Era et al., 1968). Adding some metal oxide or hydroxide (e.g., In₂O₃) into Zn powder gel is also beneficial to the corrosion resistance of anode material (Sato et al., 1992). Apart from inorganic inhibitors, many organic additives such as α-diphenylglyoxime, polyethylene glycol (600), tartrate, and dinonylphenol phosphate ester are also explored by investigators (Nartey et al., 1994; Moon et al., 2005; Lee et al., 2006b; Qu, 2006). The inhibition mechanism of these organic species is generally considered to be adsorption onto Zn surface. Qu et al. proposed that an effective inhibitor should cover the surface of Zn electrode when the battery was at rest and had fast desorption kinetics after applying anodic potential. In this case the negative effect on discharge performance of the Zn electrode could be minimized (Qu, 2006).

In recent years, there are some new inhibitors in traditional alkaline electrolytes for different Zn batteries reported by investigators. Xiao et al. (2018) compared benzotriazole, thiourea and sodium dodecyl benzene sulfonate and found that benzotriazole is the most effective to decrease Zn corrosion in Zn-air battery. Huang et al. (2018) studied the influence of ethylenediaminetetraacetic acid (EDTA), polysorbate 20, and tartaric acid on Zn electrode behavior in a Zn-air battery. It was found that EDTA was superior to the other two in preventing not only corrosion but also dendrite formation.

In addition to traditional alkaline electrolytes, novel aqueous or non-aqueous liquid electrolytes and solid-state electrolytes are continuously developed (Chen et al., 2019; Fan et al., 2019a). Due to the different electrochemical environment, the corrosion behavior of Zn electrode should be re-estimated. For example, Han et al. manufactured a type of salt reinforced gelatin-based solid-state electrolyte, which contained less free water compared to traditional aqueous electrolytes and showed lower corrosion tendency (Han et al., 2019). In addition, inhibitors that can be compatible to new electrolytes have also been studied. Chen and coworkers developed a mildly acidic electrolyte containing 5% fumed silica (FS) for Zn-LiMn₂O₄ battery (Hoang et al., 2017; Xiong et al., 2018; Mitha et al., 2019). This electrolyte reduced the dendrite growth of Zn electrode but would increase the corrosion rate. They explored several inhibitors including pyrazole, lignin and poly(ethylene glycol) in this system and optimized the corresponding concentrations. For example, the liner polarization curves of Zn electrodes revealed that the FS electrolyte increased the corrosion of Zn electrode and the addition of pyrazole largely mitigated the corrosion tendency.

Modifying the composition of Zn electrode is a commonly adopted method to control anode corrosion. A lot of heavy metal elements including Cd, In, Sn, Ti, Pb, and Bi (or their oxides) have been investigated as additives into Zn electrodes (McBreen and Gannon, 1981, 1983, 1985; Biegler et al., 1983; Sato et al., 1983; Bonnick and Dahn, 2012). Due to high HER overpotential, these elements could reduce Zn corrosion. In more recent studies, Bi is the most widely used alloying element which is also reported to be beneficial to controlling dendrite growth and shape change of Zn electrodes (Kim et al., 2015; Jo et al., 2017; Chotipanich et al., 2018; Park et al., 2018).

To reduce the cost of additives, some investigators also explored some inexpensive alloying elements. In primary Zn-air battery, Durmus et al. (2019) studied Zn alloy electrode that contained 10 wt. % Al and found it more corrosion resistant than pure Zn electrode. Lee and Ryu (2018) added different amount of Al and Si (1–3 wt.%) into Zn gel electrodes for secondary Zn-air batteries and found that 2 wt.% Al-mixed anodes were the least prone to corrosion compared to bare Zn and Si-mixed Zn electrodes.

In some investigations, multiple additives were simultaneously utilized. Aremu et al. (2019) added K₂S and PbO into Zn-BiO electrodes. The results of electrochemical tests showed that the coexistence BiO, K₂S, and PbO would restrain corrosion to the maximum level. Besides, the capacity of Zn-BiO-K₂S-PbO electrode was superior to Zn-BiO, Zn-BiO-K₂S, and Zn-BiO-PbO electrodes (Aremu et al., 2019). In Ni-Zn batteries, Wang et al. (2017) fabricated Zn electrodes with different amount of Al and Sb. The electrode structure was layered double hydroxides. The enhanced corrosion resistance of Zn-Al-Sb electrode was also attributed by the authors to the high HER overpotential of Sb (Wang et al., 2017). Similarly, they introduced graphic carbon nitride into Zn-Al layered double oxide electrode and also found the increased corrosion resistance (Cui et al., 2019).

As mentioned, the electrode morphology (e.g., porosity) affects the corrosion kinetics on Zn anodes. A larger specific surface area leads to a higher HER exchange current. The HER rate on Zn powder with small particle size is faster than that on Zn powder with large particle size (Zhang, 2008). However, the corrosion in a real system should consider more complex factors. In a recent study, Liu et al. prepared a series of porous Zn electrodes with different pore sizes (average values ranging from 300 μm to 8 μm as shown in Figures 2a–h). According to the polarization curves (Figure 2i), the Zn electrode with pore size of 300 μm had larger corrosion current than pure Zn electrode, which was corresponding to the phenomenon described above. But when the pore size further decreased, the corrosion potential altered to negative values and the corrosion current reduced. This opposite phenomenon was possibly attributed to the accumulation of zincate as the corrosion product in the smaller pore structure (Liu P. et al., 2019). In some earlier studies (Gregory et al., 1972; Vorkapić et al., 1974), it was also reported that the presence of Zn(OH)42- in alkaline electrolytes can restrain the HER rate.

Another strategy to mitigate Zn electrode corrosion is introducing coating on the Zn surface. For example, Lee et al. (2013) fabricated aluminum oxide coated Zn electrode and found it had enhanced corrosion resistance. Hu et al. (2019) rolled and tore Zn foil and Sn foil and then coated a Pb film via surface chemical reaction to prepare Zn electrode with artificial solid electrolyte interface (ASEI) in a Zn-Ni battery. The HER overpotential was enhanced on this type of Zn electrode. Besides, the dendrite growth behavior of the Zn electrode was also changed (Hu et al., 2019). Polyaniline coating (Jo et al., 2019) and carbon shell (Wei et al., 2019) were also reported to be beneficial to reduce self-discharge of Zn electrode.