Mn₃O₄ anchored on carbon nanotubes as an electrode reaction catalyst of V(IV)/V(V) couple for vanadium redox flow batteries

Highlights: • Mn₃O₄/MWCNTs (multi-walled carbon nanotubes) composite fabricated by a simple solvothermal method was developed as electrochemical catalyst of V(IV)/V(V) redox couple for vanadium redox flow batteries for the first time. • The electrocatalytic kinetics of the redox reactions of three electrocatalysts (pure Mn₃O₄, pure MWCNTs, Mn₃O₄/MWCNTs) were compared, and were in the order of Mn₃O₄/MWCNTs > MWCNTs > Mn₃O₄. • The cell using Mn₃O₄/MWCNTs has lower electrochemical polarization, with larger discharge capacity and energy efficiency. The average energy efficiency of the cell using Mn₃O₄/MWCNTs is 84.65%, 3.73% higher than that of the pristine cell. - Abstract: Mn₃O₄/MWCNTs (multi-walled carbon nanotubes) composite fabricated by a simple solvothermal method was developed as electrochemical catalyst of V(IV)/V(V) redox couple for vanadium redox flow batteries. The electrochemical activity of V(IV)/V(V) redox couple can be enhanced by the electrochemical catalysts (Mn₃O₄, MWCNTs, Mn₃O₄/MWCNTs), and the electrocatalytic kinetics of the redox reactions were in the order of Mn₃O₄/MWCNTs > MWCNTs > Mn₃O₄. The cell using Mn₃O₄/MWCNTs composite as electrochemical catalyst was assembled and the charge-discharge performance was evaluated. Compared with the pristine cell, the cell using positive graphite felt modified by Mn₃O₄/MWCNTs had lower electrochemical polarization, larger discharge capacity and energy efficiency. The average energy efficiency of the cell using modified positive electrode for 50 cycles was 84.65%, 3.73% higher than that of the pristine cell. The superior electrocatalytic performance of Mn₃O₄/MWCNTs composite was mainly due to the effective mixed conducting network, facilitating the electron transport and ion diffusion in the electrode/electrolyte interface