Tuning the surface states by in-situ Zr/Hf co-doping and MoO3 hole transport layer modification for boosting photoelectrochemical performance of hematite photoanode

Abstract

Hematite (α-Fe2O3) is a potential photoanode material for photoelectrochemical (PEC) water splitting; nevertheless, its PEC performance is constrained by substantial bulk and surface charge recombination rates. Herein, the effect of in-situ Zr/Hf dual-ion doping and the MoO3 hole transport layer (HTL) on regulating the surface states of α-Fe2O3 photoanodes for effective water oxidation is investigated. The co-doping improves bulk properties by enhancing the electrical conductivity, thereby facilitating hole transfer via intermediate surface states (i-SS). Furthermore, the MoO3 HTL passivates the recombination surface states (r-SS), thus alleviating the Fermi level pinning, resulting in an improved open-circuit photovoltage. As a result, a novel Zr/Hf-HT:MoO3 photoanode attains a photocurrent density of 2.34 mA cm−2 at 1.23 V vs. RHE (1.23 VRHE), which is 123% higher than that of Bare-HT. The Zr/Hf-HT:MoO3 photoanode achieves 86 and 61.3% of surface charge separation and charge transfer efficiencies at 1.23 VRHE, respectively, representing 26 and 100% enhancements over those of Bare-HT. Lastly, the FeNi(OH)x cocatalyst coated Zr/Hf-HT:MoO3 photoanode reaches a photocurrent density of 2.62 mA cm−2 at 1.23 VRHE with 98% stability and generates 47.8 and 22 μmol h−1 of H2 and O2 gases, respectively.