Near-unity charge transfer efficiency on bare semiconductor photoanodes induced by polyols and ammonia co-oxidation

Inefficient charge separation and poor interfacial reaction selectivity constitute major barriers to semiconductor-driven photoelectrocatalytic synthesis of high-value-added chemicals. Herein, we find that the co-oxidation of polyols and NH3 on four typical and unprotected photoanodes [i.e., BiVO4, α-Fe2O3, TiO2 and WO3] generates even higher photocurrent densities than those commonly used hole scavengers. Detailed research on BiVO4 photoanodes shows that the co-oxidation process induces the in situ formation of Bi/V-rich surfaces and enables the interfacial charge transfer efficiency approaching 100%. The achieved photocurrent density of 7.3 mA cm−2 at 1.23 VRHE approaches the theoretical limit of BiVO4 on the unprotected photoanodes, which delivers formamide production of 171.5 μmol cm−2 h−1. By using an amplified flow photoelectrochemical cell, the photocurrent reaches 1.2A, producing formamide at the rate of 17.5 mmol h−1 and achieving the gram-scale synthesis. The co-oxidation method illustrates an efficient strategy for designing photoelectrochemical systems at ampere-level photocurrents. Poor charge separation and reaction selectivity limit photoelectrochemical synthesis efficiency. This study demonstrates that co-oxidation of polyols and NH3 on BiVO4 photoanodes achieves near-unity interfacial charge transfer efficiency.