Kinetic study of the enhanced photoelectrochemical properties of microwave-assisted Al and Si co-doped Zr-Fe₂O₃ photoanodes

Unintended metal oxide layer development during co-doping has been suggested as being highly effective in intensifying the oxygen evolution reaction. Herein, we studied the influence of microwave-assisted co-doping of trivalent Al³⁺ and tetravalent Si⁴⁺ into Zr-Fe₂O₃ photoanode for effective photoelectrochemical (PEC) performance. The Si co-doping showed effective diffusion into the hematite bulk during high-temperature quenching. Relative to SiO_x, an Al₂O₃ layer notably passivated the surface defects, whilst Si⁴⁺ co-doping markedly improved the bulk charge transfer features, compared to Al³⁺ co-doping. Because of the active passivation effect of the Al₂O₃ layer, the photocurrent density of Al/Zr-Fe₂O₃ photoanode was considerably increased at lower potentials. In specific, the Al/Zr-Fe₂O₃ photoanode displayed an almost 100% enhancement in surface charge transfer rate constant than that of the bare Zr-Fe₂O₃ at 1.23 V_RHE. The comprehensive experimental results provided evidence of the consequence of tri/tetravalent co-dopants on charge transfer in the bulk of the hematite and at the photoanode-electrolyte interface. A probable charge transfer mechanism was proposed under illumination to demonstrate how the Si and Al microwave-assisted attachment impacted the photogenerated charge recombination reduction in the photoanode and subsequently advanced its PEC water splitting performance.