Boric acid assisted engineering of CeO2@kaolin hybrid electrodes for advanced electrochemical energy storage

Abstract

A novel boric acid-functionalized cerium oxide/kaolin hybrid composite (B@CeO2@kaolin) was successfully synthesized through a two-step strategy involving calcination-assisted immobilization of CeO2 nanoparticles onto kaolin followed by boric acid modification under hydrothermal conditions. The synergistic integration of redoxactive CeO2, porous kaolin support, and boron-induced electronic modulation was designed to enhance the electrochemical energy storage performance of the resulting electrode material. Structural, morphological, surface, and electrochemical properties of the synthesized composites were systematically investigated using XRD, BET, SEM, XPS, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) analyses. Electrochemical investigations revealed that the B@CeO2@kaolin electrode exhibited superior charge storage behavior compared to pristine kaolin and CeO2@kaolin electrodes. Dunn and b-value analyses demonstrated that the charge storage mechanism was predominantly diffusion-controlled at low scan rates, while surface-controlled capacitive contributions became increasingly dominant at higher scan rates. The calculated b-value of 0.59 confirmed the hybrid pseudocapacitive/battery-type behavior of the ternary composite. EIS analyses revealed significantly reduced charge transfer resistance and enhanced ion diffusion kinetics after boron functionalization. The B@CeO2@kaolin electrode delivered a remarkably high specific capacitance of 424.24 F g(-1) at 0.7 A g(-1) in a three-electrode configuration. In addition, the symmetric B@CeO2@kaolin//B@CeO2@kaolin supercapacitor achieved an energy density of 40.50 Wh kg(-1) at a power density of 1166.42 W kg(-1) and retained 78.27% of its initial capacitance after 10,000 charge-discharge cycles. The enhanced electrochemical performance was attributed to the synergistic effect of CeO2 redox activity, boron-induced conductivity improvement, optimized porous morphology, and accelerated ion transport pathways. These findings demonstrate that the B@CeO2@kaolin hybrid composite is a promising electrode material for high-performance and long-life symmetric supercapacitor applications operating in acidic electrolytes.