Photoelectrochemical Selective Oxidation of Glycerol to Glyceraldehyde with Bi-Based Metal-Organic-Framework-Decorated WO3 Photoanode.

The conversion of glycerol to high-value-added products via photoelectrochemical (PEC) oxidation has emerged as a promising approach for utilizing a sustainable and clean energy source with environmental and economic benefits. Moreover, the energy requirement for glycerol to produce hydrogen is lower than that for pure water splitting. In this study, we propose the use of WO3 nanostructures decorated with Bi-based metal-organic frameworks (Bi-MOFs) as the photoanode for glycerol oxidation with simultaneous hydrogen production. The WO3-based electrodes selectively converted glycerol to glyceraldehyde, a high-value-added product, with remarkable selectivity. The Bi-MOF-decorated WO3 nanorods enhanced the surface charge transfer and adsorption properties, thereby improving the photocurrent density and production rate (1.53 mA/cm2 and 257 mmol/m2·h at 0.8 VRHE). The photocurrent was maintained for 10 h, ensuring stable glycerol conversion. Furthermore, at 1.2 VRHE, the average production rate of glyceraldehyde reached 420 mmol/m2·h, with a selectivity of 93.6% between beneficial oxidized products over the photoelectrode. This study provides a practical approach for the conversion of glycerol to glyceraldehyde via the selective oxidation of WO3 nanostructures and demonstrates the potential of Bi-MOFs as a promising cocatalyst for PEC biomass valorization.

Lowering the onset potential of Zr-doped hematite nanocoral photoanodes by Al co-doping and surface modification with electrodeposited Co-Pi.

Herein, in situ zirconium-doped hematite nanocoral (Zr-Fe2O3 (I) NC) photoanode was prepared via a specially designed diluted hydrothermal approach and modified with Al3+ co-doping and electrodeposited cobalt-phosphate ("Co-Pi") cocatalyst. Firstly, an unintentional in situ Zr-Fe2O3 (I)) NC photoanode was synthesized, which achieved an optimum photocurrent density of 0.27 mA/cm2 at 1.0 V vs. RHE but possessed a more positively shifted onset potential than conventionally prepared hematite nanorod photoelectrodes. An optimized amount of aluminum co-doping suppresses the bulk as well as surface defects, which causes a negative shift in the onset potential from 0.85 V to 0.8 V vs. RHE and enhances the photocurrent density of Zr-Fe2O3(I) NC from 0.27 mA/cm2 to 0.7 mA/cm2 at 1.0 V vs. RHE. The electrodeposited Co-Pi modification further reduce the onset potential of Al co-doped Zr-Fe2O3(I) NC to 0.58 V vs. RHE and yield a maximum photocurrent of 1.1 mA/cm2 at 1.0 V vs. RHE (1.8 mA/cm2 at 1.23 V vs RHE). The improved photocurrent at low onset potential can be attributed to synergistic effect of Al co-doping and Co-Pi surface modification. Further, during photoelectrochemical water-splitting, a 137 and 67 µmol of hydrogen (H2) and oxygen (O2) evolution was achieved over the optimum Co-Pi-modified Al-co-doped Zr-Fe2O3(I) NC photoanode within 6 h. The proposed charge transfer mechanism in optimum Co-Pi-modified Alco-doped Zr-Fe2O3(I) NC photoanodes during the photoelectrochemical water splitting was also studied.