Fig 1.
Synthetic route of Mn-modified phosphomolybdates.
Fig 2.
SEM images: Product-1 at scaling (a) 50 μm, (b) 10 μm and histogram according to the particles (c) length and (d) wide; Product-2 at scaling (e) 10 μm, (f) 5 μm, and corresponding histogram; Product-3 at scaling (g) 10 μm, (h) 5 μm; (j) EDS of all Products.
Fig 3.
XRDs of prepared products.
Fig 4.
XPS spectrum of Product-1; (a) survey scan; Narrow spectrum of (b) Mn 2p, (c) Mn 3s, (d) Mo 3s, (e) Mo 3p, (f) Mo 3d, (g) C 1s, (h) N 1s, (i) O 1s, and (j) P 2p.
Fig 5.
XPS spectrum of Product-2; (a) survey scan; Narrow spectrum of (b) Mn 2p, (c) Mn 3s, (d) Mo 3s, (e) Mo 3p, (f) Mo 3d, (g) C 1s, (h) N 1s, (i) O 1s, and (j) P 2p.
Fig 6.
XPS spectrum of Product-3; (a) survey scan; Narrow spectrum of (b) Mn 2p, (c) Mn 3s, (d) Mo 3s, (e) Mo 3p, (f) Mo 3d, (g) C 1s, (h) N 1s, (i) O 1s, and (j) P 2p.
Fig 7.
FTIR spectra of prepared products.
Fig 8.
TGA of prepared products.
Fig 9.
CV of Product-1@GCE (a) at different scan rates, (b) scan rate vs. peak current density, (c) Log (scan rate) vs. Log (peak current density), (d) SQRT (scan rate) vs. Ip/SQRT (scan rate), (e) contribution ratio at different scan rates, and (f) capacitive contribution coverage at 60 mVs-1.
Fig 10.
CV of Product-2@GCE (a) at different scan rates, (b) scan rate vs. peak current density, (c) Log (scan rate) vs. Log (peak current density), (d) SQRT (scan rate) vs. Ip/SQRT(scan rate), (e) contribution ratio at different scan rates, and (f) capacitive contribution coverage at 5 mVs-1.
Fig 11.
CV of Product-3@GCE (a) at different scan rates, (b) scan rate vs. peak current density, (c) Log (scan rate) vs. Log (peak current density), (d) SQRT (scan rate) vs. Ip/SQRT (scan rate), (e) contribution ratio at different scan rates, and (f) capacitive contribution coverage at 6 mVs-1.
Fig 12.
GCD of Product-1@GCE (a) at different current densities and their (b) rate capabilities, (c) cycling over 200 cycles at current density 0.4 Ag-1.
Fig 13.
GCD of Product-2@GCE (a) at different current densities and their (b) rate capabilities, (c) cycling over 200 cycles at current density 2.0 Ag-1.
Fig 14.
GCD of Product-3@GCE (a) at different current densities and their (b) rate capabilities, (c) cycling over 200 cycles at current density 2.0 Ag-1.
Table 1.
List of POM-based electrode materials and their specific discharge capacitances with respect to applied current densities.
Fig 15.
Combined (a) CVs and (b) GCD curves of all electrodes at scan rate 5 mVs-1 and current density 2.0 Ag-1, respectively.
Fig 16.
EIS of Modified Product-1, 2 and 3@GCE during GCD testing; (a) Nyquist plot and (b) its close view at high frequency range; (c, d, e) fitting circuits; Bode plots of frequency dependent (f) impedance and (g) phase angle.
Fig 17.
Error analysis of Nyquist plot; (a) Frequency vs. Zreal (b) Frequency vs. Zim of Product-1, 2, and 3@GCE for before and after GCD, and (c) the relationship of corresponding Zreal and the reciprocal root square of angular frequency (ω-1/2).
Fig 18.
(a) Kegging cluster, (b) Bonding of Mn with imidazolium unit, and (c) Possible structure of Product-1.
Fig 19.
(a) Unit cell cluster, and (b) Possible structure of Product-2.
Fig 20.
Possible structure for the major constituent of Product-3.