Cobalt@Ruthenium Core@Shell nanoparticles embedded within nitrogen-doped carbon nanosheets as reversible oxygen electrocatalysts

Rational design and engineering of cost-effective, high-performance reversible oxygen electrocatalysts for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is imperative in advancing the progress of rechargeable metal-air batteries (r-MABs). Herein, nanocomposites based on Co@Ru core@shell nanoparticles embedded within N-doped carbon nanosheets (Co@Ru/CS) are prepared via facile galvanic exchange reactions of RuCl₃ with Co/NC and used as an effective oxygen electrocatalyst for rechargeable zinc-air battery (r-ZAB). Electrochemical studies demonstrate a remarkable bifunctional catalytic performance of Co@Ru/CS towards both ORR and OER, featuring a low potential gap (ΔE) of only 0.69 V between the OER potential (E_10,OER) at 10 mA cm⁻² and half-wave potential (E_1/2,ORR) of ORR, which is much lower than that of commercial Pt/C + RuO₂ catalysts (0.76 V). Combined studies of experimental characterizations and density functional theory calculations show that the ORR activity arises primarily from the N-doped carbon and CoN_x moieties in the composites, whereas RuO₂/CoOOH produced at high electrode potentials is responsible for the OER activity. Co@Ru/CS based r-ZAB exhibits an open circuit voltage of 1.447 V, specific capacity of 781 mAh g_Zn⁻¹, and maximum power density of 115 mW cm⁻² at 0.83 V, a performance better than that with commercial Pt/C + RuO₂ (1.412 V, 760.56 mAh g_Zn⁻¹, and 91 mW cm⁻²). Results from this research underline the substantial impact of structural engineering on optimizing the electrocatalytic activity of nanocomposites for r-MABs.