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

A variety of binary Ru-Co mixed oxide nanotubes (RuCoO with x = 0.19, 0.33, 0.47, 0.64 and 0.77) were readily synthesized via electrospinning and subsequent calcination. RuCoO nanotubes (0 < x < 0.77) were composed of both rutile (Ru in RuO is replaced with Co) and spinel (Co in CoO is replaced with Ru) structures. This elemental substitution created oxygen vacancies in the rutile structure and also resulted in the incorporation of Ru in the octahedral sites of the spinel structure. The as-prepared RuCoO nanotubes were investigated for oxygen evolution reaction (OER) electrocatalytic activity in 1.0 M HClO aqueous solution. RuCoO nanotubes with x≥ 0.47 presented an excellent OER activity comparable to pure RuO, 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, RuCoO showed a good OER activity and a greatly improved stability compared to RuO under the continuous OER. These attractive catalytic properties of RuCoO 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.