Enhanced Stabilities of Ag Electrocatalyst as Self-Standing and Multiwalled Carbon Nanotube Supported Nanostructures for Oxygen Reduction in Alkaline Medium

Abstract

Self-supported silver nanoflowers (AgNFs) and unmodified multi-walled carbon nanotube (MWCNT) supported silver nanostructures (Ag/MWCNT) were synthesized by an environmentally amicable slow chemical reduction method using ascorbic acid at room temperature. Structural morphologies were analyzed by scanning and transmission electron microscopic techniques and crystallinities were determined by X-ray diffraction method. Electrocatalytic activities for oxygen reduction reaction (ORR) were investigated for both Ag NF and Ag/MWCNT catalysts using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). From CV profiles the electrochemically active surface areas of Ag NF and Ag/MWCNT were estimated to be 87.7 m2/g and 19.8 m2/g respectively. The LSV showed the maximum limiting current densities of 4.7 and 3.76 mA/cm2 at the electrode rotation rate of 2400 rpm with specific activities of 1.26 and 1.06 mA/cm2 measured at −0.1 V for Ag NF and Ag/MWCNT, respectively, confirmed their high ORR activities in 0.5 M KOH medium. Accelerated durability tests revealed that Ag/MWCNT possessed an excellent stability, that is, it has retained nearly 83% of its initial activity after 3000 potential cycles, which is much higher than modified MWCNT supported Ag catalyst reported in literature.