Boosting electrochemical energy storage properties of SrGd<inf>2</inf>O<inf>4</inf> through Yb³⁺ and Tm³⁺ rare earth ion doping

Abstract

Electrochemical supercapacitors represent advanced energy storage devices that excel in the swift storage and delivery of electrical energy, effectively bridging the gap between conventional capacitors and batteries. The present work, aimed to investigate charge storage properties of SrGd2O4 and rare earth ions Yb3+ and Tm3+ doped in SrGd2O4. Both materials were prepared via simple sol-gel synthesis and characterized by XRD, XPS, and FE-SEM with EDS. Characterization confirmed the presence of Tm3+ and Yb3+ in the SrGd2O4 matrix with a uniform distribution of elements. The charge storage behavior of pure SrGd2O4 and SrGd2O4:Yb4Tm1 in various electrolytes was thoroughly explored. Large electrochemical potential windows were shown by both electrode materials in aqueous 6 M KOH (1.7 V), which is essential for supercapacitors to achieve high specific energy. Furthermore, SrGd2O4:Yb4Tm1 demonstrated a substantially more pronounced charge storage effect in 6 M KOH electrolyte, with almost double times higher specific capacitance values compared with an un-doped SrGd2O4 sample. The main impact on the electrochemical window had matrix SrGd2O4, while the main impact on specific capacitance had rear earth dopants (Yb3+ and Tm3+). Improved charge storage characteristics of SrGd2O4:Yb4Tm1 were also evident through a notable reduction in overall resistance observed in electrochemical impedance spectroscopy experiments. Concerning the two-electrode GCD measurements, the SrGd2O4:Yb4Tm1 electrode in 6 M KOH showed a specific capacitance of 143 F g−1, with the specific energy of 12.5 Wh kg−1 at 0.6 A g−1. These findings demonstrate the potential of rare earth ion doping in enhancing the energy storage properties of SrGd2O4, offering promising avenues for the development of high-performance supercapacitors.