VO(2) as a Highly Efficient Electrocatalyst for the Oxygen Evolution Reaction

Herein, we report high electrocatalytic activity of monoclinic VO(2) (M1 phase) for the oxygen evolution reaction (OER) for the first time. The single-phase VO(2) (M1) nanoparticles are prepared in the form of uniformly covering the surface of individual carbon fibers constituting a carbon fiber paper (CFP). The VO(2) nanoparticles reveal the metal-insulator phase transition at ca. 65 °C (heating) and 62 °C (cooling) with low thermal hysteresis, indicating a high concentration of structural defect which is considered a grain boundary among VO(2) nanoparticles with some particle coalescence. Consequently, the VO(2)/CFP shows a high electrocatalytic OER activity with the lowest η(10) (350 mV) and Tafel slope (46 mV/dec) values in a 1 M aqueous solution of KOH as compared to those of the vacuum annealed V(2)O(5) and the hydrothermally grown VO(2) (M1), α-V(2)O(5), and γ′-V(2)O(5). The catalytically active site is considered V(4+) components and V(4+/5+) redox couples in VO(2). The oxidation state of V(4+) is revealed to be more favorable to the OER catalysis compared to that of V(5+) in vanadium oxide through comparative studies. Furthermore, the amount of V(5+) component is found to be increased on the surface of VO(2) catalyst during the OER, giving rise to the performance degradation. This work suggests V(4+) and its redox couple as a novel active component for the OER in metal-oxide electrocatalysts.