Interfacially Coupled and Synergistic Effect of Ag/Co3O4-C Nanocomposites for Enhanced Oxygen Reduction (ORR) and Evolution (OER) Reaction

초록

Overpotentials associated with the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remain key challenges hindering the practical deployment of advanced electrochemical energy conversion technologies such as alkaline fuel cells. While Pt/C demonstrates excellent ORR activity, its sluggish OER kinetics and poor durability in alkaline environments significantly limit its applicability. Herein, we report the design of an Ag/ Co3O4-C nanocomposite, synthesized via a two-step approach involving hydrothermal growth of ultrafine Co3O4 nanoparticles having a particle size of 5 nm, followed by uniform deposition of Ag nanoparticles having a particle size of 20-30 nm. TEM/EDS shows Co3O4 nanoparticles (similar to 5 nm) uniformly anchored on the carbon matrix with finely dispersed Ag (similar to 28 nm), producing a homogeneous Ag- Co3O4 distribution. XPS indicates no substantial charge transfer, with performance arising from ensemble/heterointerface effects. The resulting hybrid exhibits superior ORR activity with an onset potential of 0.10 V vs. Hg/HgO and a half-wave potential of -0.186 V vs. Hg/HgO, while simultaneously delivering enhanced OER activity by reaching 10 mA cm- 2 at a substantially lower overpotential compared to Ag/C and Co3O4-C. In addition, when integrated into Zn-air batteries, the Ag/ Co3O4-C cathode demonstrates a high discharge capacity of 730 mAh g- 1, a peak power density of 67 mW cm- 2, and stable cycling for 200 cycles, validating its strong bifunctional electrocatalytic performance. The synergistic coupling of Ag and Co3O4 nanoparticles, anchored on a conductive carbon framework, enables efficient interfacial charge transfer and optimizes the adsorption of oxygenated intermediates, thereby accelerating reaction kinetics in alkaline media. Owing to these complementary features, the Ag/Co3O4-C catalyst demonstrates excellent bifunctional activity, highlighting its promise for next-generation oxygen electrocatalysis.

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