| Summary: | Oxygen reduction reaction (ORR) can be efficiently catalyzed by noble metals. Amongst all these catalysts, Ag has a better performance to cost ratio due to its low price and abundant reserve. Surface energy is known to play an important role in the catalytic reaction and straining of electrocatalysts is an effective method to increase their surface energy that weakens the binding towards adsorbates and inhibits the formation of passivation films.
In this research, sonication becomes an efficient and simple method to induce strain into Ag nanowires (NWs) via plastic deformation. The ORR performance of Ag NWs before and after the straining is evaluated in an alkaline medium using linear sweep voltammetry (LSV) through electrochemical cathodic polarization test. The measured diffusion limiting current density produced from Ag NWs increases by more than 20% (from -4.98 mA/cm2 to -6.00 mA/cm2) after sonication straining with the onset potential that remains almost constant (i.e. 0.95 V vs RHE). The enhanced electrocatalytic performance on ORR is a result of strain induction which contribute to more active sites on the surface and higher reaction kinetics.
Besides, high-index facets are generated on Ag NWs through laser irradiation. The original (1 1 1) facets in many surface areas are transformed into (1 1 5) and (1 1 6) high-index facets via the rearrangement of atoms operated by laser irradiation. High-index facets have been proved to possess higher surface free energy than low-index facets which can promote the ORR activity. Moreover, the ORR performance including the onset potential and diffusion limiting current is evaluated to depend on the power of laser irradiation from 2 W to 8 W. Ag NWs subject to 4 W laser irradiation reach the highest onset potential with a decrease of 0.034 V vs RHE of overpotential and most negative diffusion limiting current with a 26% improvement comparing with the original silver nanowires. Hence, it indicates that the generation of high-index facets could be the reason that significantly enhances the ORR activity of Ag NWs
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