Ce-Modified MnCo2O4 Flower-like Nanosheet Electrodes via PVP-Assisted Assembly for MnCo2O4//Carbon-Supported Iron Oxide Asymmetric Supercapacitors

Ce-modified MnCo2O4 flower-like nanosheet electrodes were prepared on nickel foam by a hydrothermal-calcination route and sequentially optimized with respect to reaction time, nominal Ce content, and PVP addition. Comparative SEM, XRD, XPS, and N2-sorption analyses identify MnCo2O4-9 h-3%Ce-PVP as the optimized electrode, with an open hierarchical nanosheet network and a BET surface area of 210.0 m2 g−1. The direct XRD/XPS control comparison distinguishes Ce-associated lattice and surface-state changes from PVP-associated synthesis effects without treating either trend as proof of substitutional Ce occupancy or quantitatively established oxygen vacancies. Likewise, PVP is treated as a morphology-directing additive whose transient adsorption or bridging role remains a synthesis hypothesis rather than a directly verified molecular mechanism. The optimized positive electrode delivers 2008 F g−1 at 1 A g−1, retains 1227 F g−1 at 20 A g−1, and shows 99.0% capacitance retention after 10,000 cycles at 5 A g−1. A carbon-supported iron oxide negative electrode, designated C/Fe2O3 only as a sample label because its exact oxide phase was not independently resolved by XRD or Raman spectroscopy, provides 443 F g−1 at 1 A g−1. The resulting charge-balanced asymmetric device operates over 0–1.6 V and delivers 34.6 F g−1 at 1 A g−1, corresponding to 12.30 Wh kg−1 at 0.8 kW kg−1. At 10 A g−1, it retains 29.8 F g−1 and delivers 10.60 Wh kg−1 at 8.0 kW kg−1, equivalent to 86.1% capacitance retention over a tenfold increase in current density. All device-level gravimetric values are calculated using the total active mass of both electrodes.