Electrochemical studies on NH4MnPO4.H2O–rGO Hybrid Composite Synthesized via Microwave Route for High Energy Supercapacitors

In the present study, as-synthesized pure ammonium manganese phosphate hydrate (AMP) is infused with rGOx variate (Xmg = 25, 50, 75, 100) and four different hybrid composites (AMPG1, AMPG2, AMPG3 and AMPG4) have been synthesized by facile microwave route. The XRD results show two prominent peaks, one at 2θ = 10.04° (010) and other at 2θ = 31.3° (200) in all AMPGs. The Debye–Scherrer’s calculations show minimum crystallite size only for AMPG2 (80.9 nm). The Raman study confirms the rGO presence in AMPG2. The XPS confirms the existence of Mn as Mn2+ in AMPG2. The SEM/HR-TEM shows a cluster of uniform rectangular flake slabs only for AMPG2. The CV reveals that pure AMP and AMPGs exhibit pseudocapacitance. The GCD shows higher specific capacitance of 705 F g−1 at a current density of 1 A g−1 for AMPG2. The AMPG2//rGO hybrid device at 3 M aqueous H2SO4 shows higher specific capacitance of 336 F g−1 at 1 A g−1 in the potential window 0–1.8 volts, and even after 5000 cycles, the device retained 80% of its specific capacitance. The reason may be due to mapping of optimal concentration of rGO (50 mg) with $${\text{PO}}₄^{3 -} $$ and $${\text{NH}}₄ ⁺ $$ of AMP by forming strong coordination for better activation sites for ion mobility. The energy and power densities of AMPG2//rGO device are 151 Wh kg−1 and 448 W kg−1 at 1 A g−1, which are reported for the first time for high-energy supercapacitor applications.