Materials Engineering

The effect of polyaniline (PANI) nanofibers content on the electrochemical properties of composites based on SnO 2 nanoflakes was studied. PANI nanofibers and SnO 2 nanoflakes were synthesized and characterized (SEM, BET, FTIR, XPS, and XRD) and mixed in solution at different proportions. The resulting composites were characterized electrochemically (CV, EIS, and GCD) to determine their specific capacitance, electric resistance, and cyclic stability to be used as electrochemical capacitor electrodes (ECs). It was found that the SnO 2 -PANI-(80/20) composite at 5 mVs −1 exhibited higher specific capacitance (C AS  = 1.1 Fg −1 ) than SnO 2 (C AS  = 0.99 Fg −1 ); meanwhile, SnO 2 -PANI-(95/5) at 100 mVs −1 exhibited higher capacitance (C AS  = 0.66 Fg −1 ) than PANI (C AS  = 0.42 Fg −1 ). The GCD results indicate that SnO 2 , PANI, and their composites presented coulombic efficiencies higher than 90% after 5000 cycles. Also, the highest initial capacitance (C = 0.4 Fg −1 , at 2 mAcm −2 ) was found for SnO 2 -PANI-(80/20), and the highest final capacitance (C = 0.28 Fg −1 , 5000 cycles at 2 mAcm −2 ) was for SnO 2 -PANI-(95/5). Finally, PEIS behavior was studied, and the equivalent circuits were proposed, resulting that the contact resistance to charge transfer (R CT ) of composites (R CT  = 1.61–2.28 Ω) were lower than precursors (SnO 2 , R CT  = 3.66 Ω; PANI, R CT  = 4.47 Ω). In addition, it was observed that the capacitance of composites increased, and resistance to charge transfer decreased with the PANI content. Electrode material presents a synergetic effect promoted by the appropriate mixing in solution along with the nanoscale morphologies of the components showing improved specific capacitance, and low both contact and charge transfer resistances, with high coulombic efficiencies (> 90% after 5 k cycles).