Improving the cycling stability and rate performance of an aqueous sodium-ion supercapattery via mitigating metal dissolution and boosting conductivity by anchoring FePBA on rGO

Abstract

To fulfill the research goal of deriving high energy and high specific power in a sustainable, safe, and cost-effective manner, Prussian Blue Analogue (PBA)-based Na⁺ ion hybrid capacitors have drawn great interest. However, inherent poor conductivity and metal dissolution problems limit their full-scale exploration as a cathode material. This work attempts to address the above two challenges by compositing a Fe-PBA (Na_xFe[Fe(CN)₆]·nH₂O) (FPBA) with reduced graphene oxide (rGO). The highly conductive nature of rGO boosts the overall conductivity of the FPBA/rGO composite, rendering improved rate performance. At the same time, the surface and edge functional groups (epoxy, hydroxy and carboxylate) on rGO provide firm anchorage to surface Fe ions of FPBA through coordination and thus suppress the metal dissolution, eventually leading to longer cyclability. Due to the synergistic effect of rGO and FPBA, the FPBA/rGO composite also shows significantly enhanced charge storage capacity (437 C g⁻¹ at 1 A g⁻¹) compared to FPBA (204 C g⁻¹ at 1 A g⁻¹). The detailed mechanistic and kinetic studies reveal that, besides faradaic-type charge storage, FPBA/rGO also involves a significant portion of electrical double layer charging due to the presence of rGO. The hybrid charge storage mechanism in FPBA/rGO enables the fabricated symmetric supercapacitor device (FPBA/rGO//FPBA/rGO) to exhibit high specific energy as well as specific power (^maxE = 62.32 W h kg⁻¹ @ 0.9 kW kg⁻¹; ^maxP = 9.0 kW kg⁻¹ @ 31.92 W h kg⁻¹). Moreover, owing to suppressed metal dissolution, the symmetrical device having the FPBA/rGO composite electrodes shows excellent capacitive retention of 91% after 10 000 cycles compared to that with the FPBA-based device (75%).