The Role of Composition of Uniform and Highly Dispersed Cobalt Vanadium Iron Spinel Nanocrystals for Oxygen Electrocatalysis

Abstract

Cation substitution in transition metal oxides is an important approach to improve electrocatalysts by the optimization of their composition. Herein, we report on phase-pure spinel-type CoV2-xFexO4 nanoparticles with 0 ≤ x ≤ 2 as a new class of bi-functional catalysts for the oxygen evolution (OER) and oxygen reduction reactions (ORR). The mixed-metal oxide catalysts exhibit high catalytic activity for both OER and ORR that strongly depends on the V and Fe content. CoV2O4 is known to exhibit a high conductivity, while in CoFe2O4 the cobalt cation distribution is expected to change due to the inversion of the spinel structure. The optimised catalyst, CoV1.5Fe0.5O4, shows an overpotential for OER of ~300 mV for 10 mA cm-2 with a Tafel slope of 38 mV dec-1 in alkaline electrolyte. DFT+U+SOC calculations on cation ordering confirm the tendency towards the inverse spinel structure with increasing Fe concentration in CoV2-xFexO4 that starts to dominate already at low Fe contents. The theoretical results also show that the variation of oxidation states are related to the surface region, where the redox activity was found experimentally to be manifested in the transformation of V3+ → V2+. The high catalytic activity, facile synthesis, and low cost of the CoV2-xFexO4 nanoparticles render them very promising for application in bifunctional electrocatalysis

Rational Design of Spinel Cobalt Vanadate Oxide Co2VO4 for Superior Electrocatalysis

“…Goodenough hypothesized that when the V–V distance is less than the critical separation of 2.97 Å, d electrons can be shared by the V atoms along the V atomic chains, resulting in metallic behavior. The marrying of vanadium with electroactive transition metal cations in oxides appears, therefore, to offer a means to address poor conductivity of oxide materials. However, there are very few reports on these materials for highly active electrocatalysis.…”

Synergistic Effects of Mo2C‐NC@CoxFey Core–Shell Nanoparticles in Electrocatalytic Overall Water Splitting Reaction

“…Monodispersed Co‐substituted Fe 3 O 4 spinel NPs prepared by solvothermal methods were used as metal sources (E1, Supporting Information) . Typically, spinel nanoparticles prepared with 1.5 mmol Co and 1.5 mmol Fe precursor were dispersed in 18 mL ethanol and 2 mL deionized water followed by the addition of 0.5 mmol molybdenum acid and 1.5 molar citrate acid, which improved the solubility of molybdic acid .…”

Molecular discovery of half-metallic one-dimensional metal-organic framework

“…The U-J values were selected from the work of Carter et al, who adopted an ab initio approach to generate these values. [34][35][36][37][38][39][40]…”