In situ controllably self-assembled amorphous Co–TDPAT MOFs as superior cocatalysts of α-Fe2O3 nanosheet arrays for highly efficient and ultrastable photoelectrochemical oxygen evolution

Abstract

Amorphous MOFs (a-MOFs) could be highly promising cocatalysts of 3-D α-Fe₂O₃ to greatly improve its photoelectrochemical oxygen evolution performance, but their effective synthesis and assembly on 3-D α-Fe₂O₃ presents formidable challenges. A conformal and ultrathin layer of amorphous Co–TDPAT (a-Co–TDPAT) MOF cocatalyst has been in situ self-assembled on an α-Fe₂O₃ nanosheet array (NSA) by employing 5,5′,5″-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalic acid (H₆TDPAT) as the organic ligand. The obtained α-Fe₂O₃ NSA@a-Co–TDPAT core–shell NSA exhibits a photocurrent density of 1.54 mA cm⁻² (1.23 V), onset potential of ∼0.48 V, and photoconversion efficiency of 0.25%, 6.2 times higher, 290 mV lower, and 12.5 times higher, respectively, than those of the α-Fe₂O₃ NSA. The photocurrent density and the photoconversion efficiency are among the highest reported for photoanodes based on the FTO-supported α-Fe₂O₃ NSA without addition of noble metals, and the onset potential is the lowest among those of FTO-supported α-Fe₂O₃-based photoanodes reported. It is discovered that a-Co–TDPAT significantly enhances charge separation and accelerates charge transport and transfer for a fast oxygen evolution reaction, thus greatly boosting PEC oxygen evolution. This work not only provides a novel strategy to produce highly efficient, highly stable, low-cost, and earth-abundant core–shell water splitting photoanodes via in situ self-assembly of conformal, ultrathin a-MOFs on an α-Fe₂O₃ NSA, but sheds light on the mechanisms for controlled self-assembly of MOFs and PEC performance enhancement of α-Fe₂O₃-based photoelectrodes.