High-voltage symmetric supercapacitors developed by engineering DyFeO3 electrodes and aqueous electrolytes

Abstract

Aqueous supercapacitors (SCs) are often constrained by low operational voltage and energy density due to the low decomposition voltage of water. In this work, we address these limitations by fabricating symmetric SCs using nanoporous dysprosium orthoferrite (DyFeO₃) electrodes in dilute, neutral aqueous electrolytes. The nanoporous architecture of the DyFeO₃ electrode material, with an average pore size of 3.41 nm, was confirmed using Brunauer–Emmett–Teller analysis and comprehensively characterized through XRD, FESEM, TEM, XPS, Raman spectroscopy, EPR, and zeta potential measurements. The fabricated SC, operating in a 0.5 M Na₂SO₄ aqueous electrolyte, exhibited a high working voltage of 2.5 V, delivering an energy density of 41.81 W h kg⁻¹ at a power density of 1250 W kg⁻¹, with 90% capacitance retention after 10 000 cycles. Furthermore, the addition of 20% acetonitrile (AN) to the 0.5 M Na₂SO₄ electrolyte extended the potential window to 3.1 V, increasing the energy density to 84.43 W h kg⁻¹ at a power density of 1550 W kg⁻¹. The fabricated symmetric SC demonstrated excellent long-term stability, retaining approximately 99% capacitance and Coulombic efficiency after a 600 hours float voltage test. These findings, for the first time, reveal the potential of nanoporous DyFeO₃ as electrode material in a 0.5 M Na₂SO₄(aq.)/20%AN electrolyte for advancing symmetric SCs, featuring an unprecedented ultra-wide electrochemical stability window along with significantly enhanced energy and power densities.