Unveiling the potential of gadolinium-doped nitrogen-enriched Co/CoS as an efficient electrode for dye-sensitized solar cell and supercapacitor applications

Abstract

Cobalt sulfide (CoS) has emerged as a promising electrode material for various energy-related applications, including dye-sensitized solar cells (DSSCs) and supercapacitors (SCs). Nevertheless, poor electrical conductivity, suboptimal microstructural features, and limited long-term stability often hinder its practical performance. These drawbacks can be effectively mitigated by gadolinium (Gd) doping, which induces lattice distortion and defect formation, thereby improving charge transport and enhancing structural stability. In this work, nitrogen-enriched gadolinium-doped Co/CoS (Gd–N–Co/CoS) materials with different gadolinium contents were prepared, coated onto fluorine-doped tin oxide (FTO) glass substrates, and employed as counter electrodes in dye-sensitized solar cells (DSSCs). The 4% Gd-doped-N–Co/CoS electrode exhibited the lowest charge-transfer resistance. It achieved a notable power conversion efficiency (PCE) of 7.3%, outperforming the conventional platinum (Pt) electrode (6.6%) under simulated solar irradiation (100 mW cm⁻²). When employed in a symmetric supercapacitor configuration, the same 4% Gd-doped-N–Co/CoS electrode delivered a wide operating potential window of 1.6 V, a specific capacitance of 92.1 F g⁻¹ at 1 A g⁻¹, a specific energy of 32.74 Wh kg⁻¹, and a specific power of 1687 W kg⁻¹. Moreover, it retained 94.6% of its initial capacitance and maintained a coulombic efficiency of 92.05% after 2000 charge–discharge cycles. Overall, this work demonstrates the potential of Gd–N–Co/CoS as a high-performance electrode material for next-generation energy-harvesting and storage devices.