The integration of the glycerol oxidation reaction (GOR) with the hydrogen evolution reaction in photoelectrochemical (PEC) cells is a desirable alternative to PEC water splitting since a large quantity of glycerol is easily accessible as the byproduct from the biodiesel industry. However, the PEC valorization of glycerol to the value-added products suffers from low Faradaic efficiency and selectivity, especially in acidic conditions, which is beneficial for hydrogen production. Herein, by loading bismuth vanadate (BVO) with a robust catalyst composed of phenolic ligands (tannic acid) coordinated with Ni and Fe ions (TANF), we demonstrate a modified BVO/TANF photoanode for the GOR with a remarkable Faradaic efficiency of over 94% to value-added molecules in a 0.1 M Na 2 SO 4 /H 2 SO 4 (pH = 2) electrolyte. The BVO/TANF photoanode achieved a high photocurrent of 5.26 mA•cm −2 at 1.23 V versus reversible hydrogen electrode under 100 mW/cm 2 white light irradiation for formic acid production with 85% selectivity, equivalent to 573 mmol/(m 2 • h). Transient photocurrent and transient photovoltage techniques and electrochemical impedance spectroscopy along with intensitymodulated photocurrent spectroscopy indicated that the TANF catalyst could accelerate hole transfer kinetics and suppress charge recombination. Comprehensive mechanistic investigations reveal that the GOR is initiated by the photogenerated holes of BVO, while the high selectivity to formic acid is attributed to the selective adsorption of primary hydroxyl groups in glycerol on TANF. This study provides a promising avenue for highly efficient and selective formic acid generation from biomass in acid media via PEC cells.

Photon energy loss to interfacial charge recombination is one of the key challenges to achieving high efficiencies for solar water splitting in photoelectrochemical cells (PECs). Herein, BiVO4-based photoanodes are constructed, where BiVO4, cadmium sulfide nanosheets (CdS NSs), hole transport molecules (HTs), and oxygen evolution cocatalysts (OECs) assemble sequentially in a cascade band alignment for efficient photogenerated hole extraction and accumulation to OECs. In the photoanode assemblies, CdS NSs act as energetic barriers to suppress surface recombination. Thiolate-functionalized aryl amine HTs that anchor to CdS NSs are interfacial-charge-transfer mediators that efficiently extract the photogenerated holes. The oxidized HT (HT+) hops isoenergetically among adjacent HTs and finally accumulates oxidative equivalents to OEC. Transient absorption spectroscopy along with intensity-modulated photocurrent spectroscopy proves that HTs and CdS NSs accelerate hole-transfer kinetics and suppress recombination of surface-accumulated holes and electrons. Among the three HTs, triphenylamine shows the best performance. The best-performing photoanode assembly exhibits increased photocurrent density from 0.87 to 5.2 mA/cm2. The molecular approach to hole extraction from BiVO4 photoanodes provides a promising avenue for efficient photogenerated charge separation and collection to optimize the performance of PEC for water splitting.