Synthesis of V-doped urchin-like NiCo2O4 with rich oxygen vacancies for electrocatalytic oxygen evolution reactions

In this paper, 3D urchin-like V-doped NiCo2O4 was synthesized as an efficient electrocatalyst for electrocatalytic oxygen evolution reaction (OER). NH4VO3 and VCl3 act as various dopants to provide V5+ and V3+ ions, and the valence effects of V dopants on the structural modulation of NiCo2O4 are examined systematically. XPS results show that the doping of V3+ to NiCo2O4 provides an extra 16.40% percentage of oxygen vacancies (Ov) than that of V5+ doping, which can significantly modulate the OH− adsorption on NiCo2O4. EPR tests further confirm that the content of Ov in V3+ doped NiCo2O4 (V(Ⅲ)-NiCo2O4) is 2.81 times higher than that in V5+ doped NiCo2O4 (V(V)-NiCo2O4). Besides, V(Ⅲ)-NiCo2O4 shows higher molar content of Co2+ comparing to V(V)-NiCo2O4, resulting in an increased probability of forming CoOOH catalytic active sites. Electrochemical investigations show that V(Ⅲ)-NiCo2O4 electrocatalyst achieves excellent OER catalytic activity with a low overpotential of 344 mV at 10 mA cm−2, and it holds superior OER stability of electrocatalysis at 100 mA cm−2 for 50 h without significant change in electrode potential. Thus, this paper shows the importance of the valence of dopant precursor to the doped structures, and these findings pave a new sight of designing heteroatom doped electrocatalysts for OER.