Investigation of N-rGO/NH4MnPO4·H2O as battery-type electrode material for high-performance supercapatteries

Heteroatom-rich materials have emerged as promising electrode materials for the development of high-performance electrochemical energy storage devices. This study investigated the electrochemical synergy of the N- and P-rich ammonium manganese phosphate hydrate (NH₄MnPO₄·H₂O, Mn-AMP) decorated on N-doped reduced graphene oxide (N-rGO) as a potential hybrid battery-type electrode material for high energy and power supercapatteries. The half-cell analysis of the N-rGO/Mn-AMP nanohybrid demonstrated a high areal capacity of 147.4 µAh cm⁻² (1061.6 mF cm⁻²) compared to 110.3 µAh cm⁻² (794. mF cm⁻²) of Mn-AMP and 100.1 µAh cm⁻² (720.4 mF cm⁻²) obtained from the N-rGO. A hybrid supercapacitor (HSC) was constructed using the N-rGO/Mn-AMP nanohybrid and activated carbon as the positive and negative electrodes, respectively. The AC//N-rGO/Mn-AMP nanohybrid HSC demonstrated a high specific capacity of 85.4 µAh cm⁻² (205 mF cm⁻²)*, high areal energy of 50.6 µWh cm^-2 with a corresponding areal power of 0.36 mW cm^-2 at an areal current of 0.6 mA cm⁻², as well as a maximum areal power of 5.15 mW cm^-2 with areal energy of 19.1 µWh cm^-2 at 10.0 mA cm⁻². The HSC was able to demonstrate excellent electrochemical stability with ∼92 % retention of the initial capacity, as well as 98.8 % Coulombic efficiency after 10 000 GCD cycles at 3.0 mA cm⁻². Computational studies of the N-rGO/Mn-AMP nanohybrid showed capacitance in the nanohybrid that could be attributed to the increase in conductivity due to the charge transfer between the Mn-AMP and N-rGO as a result of the strong hybridisation between the C 2p and O 2p states of N-rGO with O 2p and Mn 3d orbitals of Mn-AMP at both valance and conduction band. The experimental and molecular modelling studies have shown the synergy achieved by integrating Mn-AMP nanoplatelets with N-rGO nanosheets. This combination highlights the potential of the N-rGO/Mn-AMP nanohybrid as an electrode material for high-performance supercapacitors.