Nucleotide(s)-mediated simultaneous N, P co-doped reduced graphene oxide (N, P-rGO) porous nanohybrids as high-performance electrode materials for designing sustainable binder-free high-voltage (2.8 V) aqueous symmetric supercapacitors and electrochemical sensors

Abstract

Nucleotide(s) have provided environmentally benign natural innovative molecules for performing the simultaneous reduction and functionalization of GO to yield binary heteroatom(s), i.e., N, P co-doped reduced porous graphene oxide nanohybrids. The incorporation of N and P into the rGO microstructure was revealed by the HR-TEM analysis of the fringes observed along the edges of the nanohybrids, depicting differing interlayer spacings of 0.38 and 0.42 nm, respectively, with the formation of the new bonds, C–N, P–C and P–O–C in N, P-rGO and the creation of more defects in the rGO lattice, as shown by IR and XPS, and Raman spectroscopy, respectively. The electrochemical performance of the binder-free aqueous symmetric supercapacitor (SSC), designed by employing 5′-adenosine monophosphate (5′-AMP)-mediated N, P co-doped rGO as an electrode material, demonstrated excellent electrochemical performance in K₂SO₄ (0.5 m) and NaClO₄ (17 m) referred to as salt-in-water (SIW) and water-in-salt (WIS) electrolytes, respectively. In these electrolytes, the cell voltages and energy density (W h kg⁻¹) at power density (W kg⁻¹) were observed to be 2.6 V, 37.7 @ 521.7 and 2.8 V, 59.2 @ 489.6 respectively. Interestingly, SO₄²⁻ anions exhibited a better chaotropic nature as compared to NO₃⁻ anions reversing the previous findings. Further, K⁺ ions containing electrolytes were found to be more effective in improving the electrochemical performance as compared to those of Na⁺ ions containing electrolytes. The high energy storage capability of SSC in the WIS electrolyte was also demonstrated by forming a tandem device by joining three such cells in series, which exhibited an increased output voltage of 8.4 V with long-term cyclic stability as well as by the illumination of 114 white LEDs lasting for more than 5 min and the driving of an electric motor for running an electric fan for about 20 s upon charging a single SSC for 30 s in each case. The creation of active centers and defects on the porous microstructure of N, P-rGO also rendered the effective separation of biogenic neurotransmitters, dopamine and serotonin with an LOD of 20.0 and 10.0 nM, respectively.