Photoelectrochemical Driving and Simultaneous Synthesis of 3-pyridinecarboxylic Acid and Hydrogen in WO3 Photoanode-Based Cell

Abstract

In conventional photoelectrochemical (PEC) cell for solar water splitting, its solar-to-hydrogen efficiency is limited by the sluggish oxygen evolution on its photoanode. 3-pyridinecarboxylic acid (3-PA) is an important organic in industry, but there are several disadvantages in its conventional synthesis approaches. Here, we reported that the oxidation of 3-methylpyridine (3-MP) into 3-PA as an alternative to the oxygen evolution on WO3 photoanode for improving the hydrogen-evolution efficiency and the product added-value of PEC cell. In a WO3 film photoanode-based dual-chamber PEC cell, 3-PA and hydrogen were simultaneously synthetized. Since the oxidation of 3-MP into 3-PA is more thermodynamically and kinetically favorable than water oxidation, higher efficiency of hydrogen evolution was achieved in the PEC cell with function of 3-PA synthesis relative to the conventional PEC cell for water splitting. Our investigations indicated that the oxidation of 3-MP into 3-PA on WO3 photoanode is co-initiated by the photogenerated holes and the H2O2 intermediate that originated from two-holes pathway of solar water oxidation on WO3. Additionally, the Cr2O72−/Cr3+ redox pair could mediate and promote the oxidation of 3-MP into 3-PA on WO3 photoanode, and thus the PEC efficiency of 3-PA synthesis can be improved by adding Cr3+ into the H2SO4-3-MP electrolyte.