Al3+-doped 3d-transitional metal (Mn/Cu) ferrite impregnated rGO for PEC water-splitting/supercapacitor electrode with oxygen vacancies and surface intercalation aspects

Aluminum (Al3+) doped manganese (Mn)/copper (Cu) ferrite impregnated rGO hybrids are verified for photoelectrocatalytic water-splitting and super-capacitor electrode applications. Energy band gaps of 2.17 eV (Mn) and 2.25 eV (Cu) confirm photocatalytic activity in the visible-band. High anodic photo-currents around 18-40 and 2-9 mA/cm(2) (1 V vs. Ag/AgCl) are observed for Mn and Cu systems. Formation of oxygen vacancies due to aluminum doping assisted in efficient charge transfer behavior both at surface and lattice orders due to the structural adjustments. 2-D rGO surface disorders (I-D/I-2D) emphasized the retardation of the charge recombination at the metal-oxide and rGO junction. During visible-light irradiation current densities are increased by 0.7-9.2 mA/cm(2) with a better redox behavior. The difference in transient currents are observed around 0.01-0.02 mA/cm(2) at 0 V vs. Ag/AgCl [0.7 mA/cm(2) at 0.5 V]. Intrinsic photo-current at zero voltage infers builtin potentials at the hybrid and electrolyte interface (Schottky- junction). Impedance study implicates better electron-transfer/ion diffusion characteristics during photon irradiation with a semi-infinite diffusion ratelimiting step. Specific-capacities (Three-electrode) are observed around 216 F g(-1) (Mn), 142 F g(-1) (Cu) with combined pseudo-capacitance and EDLC characteristics. Li+-intercalation results in ultrahigh stability up to 100,000 cycles (t similar to 69.4 h) at 0.8 V s(-1) with a capacity retention of 127%. Two-Electrode performance shows 99.1% capacity retention after 5000 cycles with decrease in the impedance (1.38 Omega to 1.06 Omega), and a maximum areal energy density of 0.54 mu Wh cm(-2) at power density of 50 mu W cm(2).