Different methanol oxidation behaviors on defectively nanoporous hematite photoanode modified with platinum via photoreduction versus electrodeposition

Abstract

The present study involved the fabrication of a novel photoanode which was comprised with porously hematite nanorods (Vo-α-Fe2O3 PNRs); the electrode was subsequently employed as a support for anchoring Pt and used as a catalyst for the methanol oxidation reaction (MOR). Depending upon Pt decorations (electrodeposition versus photoreduction), the proposed photoanodes towards MOR displayed notable disparities. The electrode after Pt decoration by photoreduction (Vo-α-Fe2O3 PNRs/PtPR) demonstrated a hysteresis pattern in the cyclic voltammetry which was a typically catalytic oxidation of methanol. In the forward scan, the density of peak current reached 2.46 mA/cm2 at 0.71 VRHE. In contrast, the electrode after Pt decoration by electrodeposition (Vo-α-Fe2O3 PNRs/PtED) showed a robust lift in photocurrent as the voltage was increased in the voltammogram, reaching 2.5 mA/cm2 at 0.7 VRHE. The product generated at the latter electrode was identified to be formaldehyde with an impressive Faradaic efficiency of 95%. This finding was innovative and attractive. The detailed characterizations and DFT calculation revealed that the platinum’s different valence state and the charge transfer resistance variation on the electrode were the main factors for their disparate catalytic functions. Those two factors were closely related to the different Pt decoration methods. The disparate catalytic functions and their associated reaction mechanisms were proposed in this work.