Modification of the Electronic Structure and Surface State of LaFeO3 for Improved Visible Light Photoelectrochemical Water Oxidation

Abstract

Photocatalytic hydrogen generation by solar energy is a promising approach to clean energy resource and has attracted great attention over the past decades. [1] Perovskites ABO3 structures provide the basic stable framework to both crystal and electronic structures modification, which have found extensive applications in photocatalysis, solar cells and photoelectrochemical (PEC) water splitting. [2] LaFeO3 has a suitable band gap of 2.07eV [3, 4] and exhibits excellent visible light photocatalytic performance. However, the poor charge transport and slow reaction kinetics at the surface [3, 4] are the main factors limiting its further improvement on photocatalytic application. To overcome these obstacles, transition metals (Mn, Co, Cu) are introduced into LaFeO3 and the photocurrent of 10% Cu doped sample is improved by three times than that of LaFeO3. The reduced charge transport resistance owing to the Fe3+ discharge is identified to benefit the PEC performance improvement after TM doping. On the other hand, the surface state of LaFeO3 is modified by electrodepositing of amorphous cobalt-phosphate (Co-Pi). It shows that the presence of Co-Pi down-shifts the onset potential by ~ 560 mV for anodic photocurrent and the improvement can be attributed to the enhanced water oxidation due to the CoII/CoIII-OH discharge on Co-Pi decorated layers. The transition anodic photocurrent is improved by about six times after Co-Pi coating under visible light at 0.50 V vs. Ag/AgCl and the electrochemical impedance spectroscopy certifies the enhanced charge transfer, which contributes to the meliorative anodic photocurrent. The incident photon-to-current conversion efficiencies of LaFeO3 can be promoted from 1.37% to 2.14% at 400 nm after Co-Pi coating. Our results demonstrate that modification of the electronic structure (TM doping) and surface state (Co-Pi coating) are the promising way to promote the photoconversion efficiency of LaFeO3-based PEC cells under visible light.