One-pot electrodeposition of cobalt flower-decorated silver nanotrees for oxygen reduction reaction

In this paper, we demonstrate a simple fabrication of bimetallic silver (Ag) and cobalt (Co) nanostructures (AgCo) with various Ag to Co relative contents via electrochemical co-deposition. A series of AgCo catalysts was electrodeposited on glassy carbon (GC) electrodes at −0.57 V vs. SCE in the deposition solutions, containing Ag precursor, Co precursor, Triton X-100, and 0.3 M KNO ₃ aqueous solution, with various Ag to Co precursor concentration ratios (1:x, x was varied from 3 to 11). The films, deposited with the total deposition charge of 0.042C, were denoted as Ag ₁ Co _x . SEM and TEM analyses showed that Ag ₁ Co _x formed a structure consisted of flower-like Co grown on tree-like Ag backbones while it had more Co flowers with a greater x. The ORR activities were examined in 0.1 M NaOH solution with rotating disk electrode (RDE) voltammetry and Ag ₁ Co ₇ showed the best catalytic activity. The co-deposition mechanism was further investigated by varying the deposition time of Ag ₁ Co ₇ . At the early stage of deposition, Ag-tree branches were formed predominantly, followed by the growth of flower-like Co nanostructures on the Ag nanotrees: More Co flowers were produced on Ag backbones with longer deposition time, being attributed to both a less negative reduction potential of Ag ⁺ to Ag than Co ²⁺ to Co and promoted Co ²⁺ reduction on the initially formed Ag surface. Ag ₁ Co ₇ electrodeposited for 200 s, consisted of ∼14% Co, showed the greatest ORR catalytic activity which was better or comparable to noble metal Pt.