Alleviating Charge Recombination Caused by Unfavorable interaction of P and Sn in Hematite for Photoelectrochemical Water Oxidation

Abstract

Hematite (Fe₂O₃) is a promising photoanode for photoelectrochemical (PEC) water splitting, yet its performance is hindered by low electrical conductivity and charge recombination. Phosphorus (P) doping into hematite has been highlighted for its potential to enhance conductivity and minimize recombination by preventing electron trapping through P⁵⁺ states. Despite the interest in P doping to improve hematite photoanodes, establishing an effective P-doping synthesis remains challenging, often resulting in suboptimal PEC outcomes. In this study, we identify that unintentional tin (Sn) diffusion from the fluorine-doped tin oxide (FTO) substrate significantly impacts P-doped Fe₂O₃ performance. Addressing the detrimental interaction between unintentional Sn⁴⁺ and intentional P⁵⁺ dopants, we introduce titanium (Ti) as a guest dopant to mitigate dopant repulsion. The resulting P:Sn:Ti–Fe₂O₃ exhibits a 4-fold increase in photocurrent density to 3.44 mA cm^–2 at 1.23 V_RHE, marking a significant advancement in P-doped hematite research. With a NiFeO_x cocatalyst, the NiFeO_x/P:Sn:Ti–Fe₂O₃ photoanode further reaches a peak photocurrent density of 4.30 mA cm^–2 at 1.23 V_RHE. Our findings, both experimental and computational, demonstrate that overcoming negative dopant interactions is crucial for enhancing PEC performance and ensuring the photoanode’s thermodynamic stability.