High-efficiency oxygen evolution on γ-FeO catalysts with BiVO photoabsorbers and TpAQ hole transport layers for photoelectrochemical water splitting.

The interfacial energy levels between oxygen-excavating co-catalysts (OECs) and BiVO often lead to carrier recombination. Modulating the interface using a hole transport layer (HTL) can effectively inhibit interfacial recombination, realizing efficient photoelectrochemical (PEC) water splitting. Herein, we design BiVO@γ-FeO/TpAQ photoanodes by one-step solvothermal insertion of TpAQ COF between BiVO and γ-FeO co-catalysts as HTL layer. The positive transient surface photovoltage signals indicate that the introduction of TpAQ COF provides an additional driving force for photogenerated hole transfer, which effectively improves the carrier transfer efficiency of BiVO. Meanwhile, the fastest transfer rate of BiVO@γ-FeO/TpAQ in the intensity-modulated photocurrent spectroscopy (IMPS) test confirms the excellent charge transfer kinetics of TpAQ COF HTL. In addition, a combination of photoluminescence and energy band calculations showed that a type II heterojunction was constructed between the TpAQ COF and BiVO, thus avoiding photogenerated electron-hole pair recombination. BiVO@γ-FeO/TpAQ exhibited the highest PEC water oxidation capability, achieving a photocurrent density of 6.3 mA cm at 1.23 V under the optimized photoanode. Attributed to the TpAQ COF HTL, the BiVO@γ-FeO/TpAQ photoanode exhibits excellent incident monochromatic photon-electron conversion efficiencies (up to 95.23% at 420 nm) and charge injection efficiencies (up to 94.6% at 1.23 V).