Construction, characterization, and DFT analysis of Li, P co-doped g-C₃N₄ multifunctional materials with boosted performance as photocatalyst and supercapacitor electrode

The present work demonstrates the synthesis and optimization of Li doped g-C₃N₄ (LCN), P doped g-C₃N₄ (PCN), and Li, P co-doped g-C₃N₄ (LPCN) with varied concentrations of Li and P for photocatalysis and energy applications. Characterization results confirmed that P substitutes C and Li-coordinated bonds with the N of the g-C₃N₄ framework, which improves their light-harvesting capacity, charge separation, and photocatalytic performance. Additionally, this increases conductivity, which leads to better charge storage capacity. The photocatalysis performance was evaluated to photodegrade the cationic dye, Rhodamine B (RhB). The co-doped material LPCN (10 mmol Li and 1 mmol P) achieved the highest photodegradation efficiency of 99.07 % RhB removal in 100 min, and the degradation rate is 22 times that of undoped g-C₃N₄. The scavenger study reveals that holes were prominent active species during the degradation process. Further, Li and P co-doped g-C₃N₄ samples were evaluated for electrochemical performance, which shows that co-doped g-C₃N₄ gives a specific capacitance of 367.40 F/g at 2 A/g, which is 17 times more than undoped g-C₃N₄ (21.08 F/g at 2 A/g). The EIS analysis shows that the electrochemically active surface area of LPCN (795 m²/g) was 3 times than g-C₃N₄ (285 m²/g) and minimal ion diffusion resistance of LPCN and more efficient charge transfer kinetics, indicating that doping in LPCN provides more active sites and improved ion diffusion pathways, thereby enhancing charge storage capacity. DFT study also supports that doping in g-C₃N₄ reduces band gap and binding energy, which explains LPCN as an efficient photocatalyst and supercapacitor electrode.