Abstract
In spite of high mean transfer number and catalytic ability of the oxygen reduction reaction (ORR), α-MnO 2 is lack of electric conductivity and specific surface area to fully exert the performance of rechargeable Zn-air battery. Here, carbons in various forms are chosen as substrates for uniform dispersion of α-MnO 2 to form air electrode catalysts to evaluate the influences of carbon types on the catalytic activities of the ORR and OER (oxygen evolution reaction). The morphology and physicochemical properties of various α−MnO 2 /carbon composites are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Electrochemical studies include rotating ring-disk electrode (RRDE) voltammetry of catalysts, linear sweep voltammetry (LSV) of air electrodes, and the charge-discharge-cycling test of full cells. The discharge peak power density of Zn-air batteries varies from 66.3 (α−MnO 2 /carbon nanotubes with diameter ≈10 nm, denoted as α−MnO 2 /CNT10) to 40.5 mW cm −2 (α−MnO 2 /super fine mesophase graphite powder) in 6 M KOH under ambient condition. The rechargeable Zn-air battery with the air electrode containing α−MnO 2 /CNT10 is stably operated for 100 cycles at 10 mA cm −2 , which shows that an increase in 0.09 V between charge (decayed ca. 0.05 V) and discharge (decayed ca. 0.04 V) cell voltages.