Structural transformation between rutile and spinel crystal lattices in Ru–Co binary oxide nanotubes: enhanced electron transfer kinetics for the oxygen evolution reaction

Abstract

A variety of binary Ru–Co mixed oxide nanotubes (Ru_xCo_1−xO_y with x = 0.19, 0.33, 0.47, 0.64 and 0.77) were readily synthesized via electrospinning and subsequent calcination. Ru_xCo_1−xO_y nanotubes (0 < x < 0.77) were composed of both rutile (Ru in RuO₂ is replaced with Co) and spinel (Co in Co₃O₄ is replaced with Ru) structures. This elemental substitution created oxygen vacancies in the rutile structure and also resulted in the incorporation of Ru³⁺ in the octahedral sites of the spinel structure. The as-prepared Ru_xCo_1−xO_y nanotubes were investigated for oxygen evolution reaction (OER) electrocatalytic activity in 1.0 M HClO₄ aqueous solution. Ru_xCo_1−xO_y nanotubes with x ≥ 0.47 presented an excellent OER activity comparable to pure RuO₂, known to be the best OER catalyst. Even after more than half of the noble/active Ru content was replaced with cheap/less-active Co, Ru_0.47Co_0.53O_y showed a good OER activity and a greatly improved stability compared to RuO₂ under the continuous OER. These attractive catalytic properties of Ru_xCo_1−xO_y can be attributed to the relatively large surface area of the tubular morphology and the substituted structures, presenting feasibility as a practical and economical OER catalyst.