Phosphomolybdate@Carbon-Based Nanocomposites as Electrocatalysts for Oxygen Reduction Reaction

Functional materials as electrocatalysts for the oxygen reduction reaction (ORR) are crucial for several renewable energy applications. Herein, we report the application of several nanocomposites, prepared by the incorporation of a vanadium-substituted phosphomolybdate [PMo11VO40](4-) (PMo11V) into some carbon-based materials (carbon black (CBV), single-walled carbon nanotubes (SWCNT) and graphene (GF)), as ORR electrocatalysts. All nanocomposites, denominated as PMo11V@CBV, PMo11V@SWCNT and PMo11V@GF, show electrocatalytic activity for the ORR in acidic medium (pH 2.5 H2SO4/Li2SO4 buffer solution), with a strong dependency between the electrocatalytic ORR performance and the carbon- based material employed. Among the materials studied, the PMo11V@GF nano-composite exhibits the most promising performance, having the less negative onset potential (Eonset=-0.16 V vs. Ag/AgCl (0.18 V vs. RHE)), which is explained by the excellent electronic properties of GF. An ORR process based in a 2-electron mechanism is assumed for all modified electrodes. The PMo(11)Vand the nanocomposite-modified electrodes are also effective for the reduction of hydrogen peroxide, with PMo11V@GF displaying the most promising electrocatalytic performance. The successful preparation of the nanocomposites is confirmed by X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy techniques. The electrochemical characterization of all modified electrodes is also reported.