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Modifying pristine graphite felt (GF) active electrode, highly active platinum/multiwalled carbon nanotubes (Pt/MWNTs) electrocatalyst, helps in developing new V(III)/V(V) vanadium redox flow battery (VRFB) and the improving the performance of the V(II)/V(V) battery. Cyclic voltammetry analyzes demonstrated that Pt/MWNT electrocatalyst has an excellent capacity for enhancing V3+/VO2+ and VO2+/VO2 + redox reactions, and both reactions are quasireversible. The V3+/VO2+ redox couple provides the V(III)/V(V) battery redox reaction. The VO2+/VO2 + and V3+/VO2+ redox reactions occurred in the pristine GF of the positive active electrode and in the Pt/MWNT + GF of the negative active electrode, respectively, using the same electrolyte (1 M VO2+ –1 M H2SO4). At the operating current densities of 12 and 20 mA cm−2, the cell coulombic efficiency reached 93.75% and 83.88%, respectively. A test V(II)/V(V) battery was assembled with the positive active electrode of Pt/MWNT + GF and the negative active electrode of the GF. The charge–discharge curves showed a slight IR drop in the active electrode, which was likely caused by the Pt/MWNT electrocatalyst. At an operating current density of 20 mA cm−2, the cell energy efficiency was 11.58% higher than that without an electrocatalyst. The results show the potential of Pt/MWNT catalysts in VRFB applications

The oxygen reduction reaction was investigated at platinum electrodes in phosphoric acid in the concentration range 0.7M (6.6%) to 17.5M (95%) at 25°C using the rotating ring‐disk electrode technique. As a complement, cyclic voltammograms on platinum and potentials of zero charge of mercury were obtained as a function of phosphoric acid concentration. The mechanism of the oxygen electrode reaction is discussed in terms of the direct four‐electron transfer reduction to water and the formation of hydrogen peroxide as an intermediate in a parallel two‐electron transfer reaction. The rate constants of the intermediate reaction steps were calculated from the ring‐disk data for various potentials and electrolyte concentrations. The characteristics of the reaction were found to be markedly dependent on the concentration of phosphoric acid. These results are interpreted in terms of changes in oxygen solubility, proton activity, and double layer characteristics when passing over from a water to a phosphoric acid solvent structure.

This study investigates the effects of platinum/carbon (Pt/C) catalysts on the performance of a vanadium redox flow battery. The Pt/C catalysts were synthesized using the impregnation-reduction method. The activity of these catalysts on the V(IV)/V(V) redox reaction was investigated using cyclic voltammetry, linear sweep voltammetry, and the rotating disk electrode (RDE) technique. The reaction rate constant K0 and exchange current density i0 were calculated from the RDE data. The Ko increased from 3.37 × 10−6 cm·s−1 to 6.86 × 10−6 cm·s−1, and i0 increased from 13.79 μA to 72.96 μA as the Pt loading increased. Single-cell charge-discharge tests were performed with Pt/C on carbon felt as the positive electrode and raw carbon felt as the negative electrode. The energy efficiency of cells increased from 51.8% to 72.3% as the electrode material changed from carbon felt to Pt/C on carbon felt at a constant current density of 10 mA·cm−2. The best Cell-D energy efficiency was 20.5% higher than that without an electrocatalyst (Cell-A). The Pt/C catalyst can also effectively reduce the cell internal resistance. The charge/discharge efficiency of a single cell with different anode catalyst is increased in the following order: Pt/C 15 wt% > Pt/C 10 wt% > Pt/C 5 wt% >carbon felt

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