Outstanding stability and photoelectrochemical catalytic performance of (Fe,Ni) co-doped Co3O4 photoelectrodes for solar hydrogen production

In this work, pure and (Fe, Ni) co-doped Co₃O₄ nanostructured photoelectrodes of different doping levels and thicknesses were manufactured at constant substrate temperature (450 °C) using the spray pyrolysis technique. In addition to the chemical compositions; the structural, optical, electrical, and photoelectrochemical (PEC) properties were investigated through the use of various analysis techniques. By increasing the codpoing ratio to 6%, the low energy band gap is decreased from 1.43 to 1.3 eV and the high energy bandgap is increased from 2.63 to 2.87 eV, in addition to the reduction in particle size from 30.2 to 12.0 nm. The high energy gap vanishes by increasing the codoped film's spread volume to 60 ml. X-ray photoelectron spectroscopy of 6%(Fe, Ni)-60ml Co₃O₄ confirms the existence of Ni^2+,3+ and Fe^2+,3+. Among the studied photoelectrodes, the 6%(Fe, Ni)-60ml Co₃O₄ photoelectrode displays a photocatalytic hydrogen output rate of 150 mmol/h.cm² @-1V in 0.3M Na₂SO₄ electrolyte. The photocurrent density of 6%(Fe, Ni)-60ml photoelectrode reached up to 13.6 mA/cm²@-1V with an IPCE (incident photon to current conversion efficiency) of ～42%@405 nm and STH (solar to hydrogen conversion efficiency) of ～11.37%, which are the highest values yet for Co₃O₄-based photocatalysts. The value of ABPE(applied bias photon-to-current efficiency) is 0.34%@(-0.28V and 636 nm). Interestingly, this photoelectrode shows a photogenerated current density of ?0.14 mAcm^?2 at 0 V and a PEC current onset over 0.266V. The thermodynamic parameters, corrosion parameters, PEC surface areas, Tafel slopes, and impedance spectroscopies are also being studied to confirm and classify the PEC H₂ production mechanism. The 6%(Fe, Ni)-60ml Co₃O₄ photoelectrode stability/reusability shows only a 6.6% reduction in PEC performance after ten successive runs at -1V with a corrosion rate of 1.2 nm/year. This work offered a new codoping strategy for the design of a highly active Co₃O₄ based photocatalyst for the generation of solar light-driven hydrogen.