Engineering the Structural Defects of Spinel Oxide Nanoneedles by Doping of V for a Highly Efficient Oxygen Evolution...

Rational design of multi-structural defects in the transition-metal oxides is a very alluring and challenging strategy to significantly improve its oxygen evolution reaction (OER) performance. Herein, a simple and promising element doping approach is demonstrated to fabricate a poor-crystalline V-doping CuCo₂O₄ (V-CuCo₂O₄) nanoneedle with rich oxygen vacancies (V_o), partially amorphous phase, and Co²⁺ defects on the carbon fiber (CF) (V-CuCo₂O₄/CF). The results indicate that the V doping could further weaken the crystallinity of V-CuCo₂O₄, providing the thoroughfares for the convenience of electrolyte penetration and the exposure of active sites. Meanwhile, [CoO₆] octahedron in the V-CuCo₂O₄ lattice is gravely distorted due to a strong electronic interaction between the doped V and Co atoms, creating more Co²⁺ active species. With the merits of these multiple structural defects, V-CuCo₂O₄/CF exhibits rich active sites, and its intrinsically electrocatalytic activity is significantly enhanced. The optimized V-CuCo₂O₄/CF electrocatalyst has a significantly enhanced OER activity with a required low overpotential of ∼204 and ∼246 mV at a current density of 100 and 300 mA cm^-2, respectively, a small Tafel slope of 40.7 mV dec^-1, and excellent stability in an alkaline medium. Furthermore, the results from the projected partial density of states calculation not only demonstrate that the 3-fol-coordinated Co near V_o bonded with Cu and V sites (Cu-Co_(surf-Vo)-V) exhibits an enhanced electronic transfer activity but also reveal that the doped V could protect the Co sites from the deactivation by intermediates overbinding on the V sites. This work provides new insights into structure engineering of spinel phase copper cobaltite, resulting in significantly boosting electrocatalytic OER activity.