Efficient Photon-to-Current and Hydrogen Conversion by Decomposition of Formic Acid on TiO2 Photoanode

Presently, the development of a technology to stably produce hydrogen (H2) from hydrogen carriers at high speed and with high efficiency is highly required. Biomass-derived formic acid (HCOOH) can be a promising hydrogen carrier for the realization of a carbon-neutral H2 production process. Here, we show that ultraviolet (UV)-light irradiation (λex = 365 nm, light intensity = 200 mW cm–2) of mesoporous anatase TiO2 nanocrystalline film-coated fluorine-doped tin oxide (mp-TiO2/FTO) electrode generates anodic photocurrent of 22.8 mA cm–2 at electrode potential (E) = 1.4 V vs standard hydrogen electrode (SHE) in an HCOOH aqueous electrolyte solution, while the photocurrent is saturated at 1 mA cm–2 at E > 0.3 V without HCOOH. Also, the addition of HCOOH increases the incident photon-to-current conversion efficiency from 30% to 100% at λex = 340 nm and E = 1.4 V. Further, the HCOOH-photoelectrochemical cell yields equimolar H2 and CO2 with a rate of 116 μmol h–1 cm–2 and ∼100% Faradaic efficiency. These remarkable cell performances can stem from the oxidation of HCOOH by valence band holes followed by the efficient current doubling and the direct photoinduced electron injection from the chemisorbed HCOOH to the conduction band of TiO2.