Preparation and characterization of agar as a binder for the Porous zinc anode in a Zinc-air battery

Numerous studies have been conducted to improve the performance of Zn-air battery. Other than its low cost and abundant availability, the Zn-air battery has received much attention because of its chemical reactions that are initiated by extracting oxygen from ambient air instead of by storing heavy materials. In the anode part, the binder plays an important role to produce compact Zn powder, which is chosen for its high ionic mobility. The mass manufacturing of Zn-air batteries has resulted in high demand for binders. However, the use of synthetic binders has led to chemical releases that pollute the environment. Therefore, this study introduces a non-toxic binder to address the concerns of a greener environment. Two types of agar were chosen as a binder: Bacto-agar and commercial agar. Both agars were subjected to conductivity and stability window measurements. Then, the agar was fabricated as part of a porous Zn anode to function as a binder. Then, the chemical bonding, structural, morphological, thermal, and corrosion resistance properties of the binders were characterized. Conductivity tests reveals that the commercial agar in 0.2 M KOH has the highest conductivity, 2.51 x 10-2 Scm-1, followed by Bacto agar (1.73 x 10-2 Scm-1) in the same concentration of KOH. Conductivity increased with an increase in KOH concentration. The stability potential window also shows that commercial agar in 0.2 M KOH has higher stability than Bacto-agar, i.e. 2.219 V versus 1.900 V. A wider electrochemical stability window indicates the agar with better properties in anodic and cathodic reactions. The FTIR spectra shows both agar producing similar patterns because both have agar-like galactan properties. The addition of Zn and KOH altered the chemical bonding of the agar spectrum. The changes in the agar spectrum proves the successful incorporation of Zn and KOH ions into the structure of the agar. In the XRD test, the agar gives broad peaks, indicating it as an amorphous material. In contrast, Zn can be categorized as crystalline in structure since its XRD presented a sharp peak. Morphological studies present the function of the agar as a bridge due to its continuous bonding between Zn particles; thus improving ionic conductivity since ions can penetrate the agar binder. In a thermal analysis, the porous Zn anode shows the ability of both agars to survive in high temperatures of up to 600 °C. In conclusion, Bacto-agar and commercial agar can be used as binders. However, commercial agar proves to be a better binder than Bacto-agar based on the characterization and electrochemical measurements conducted in this study.