Photocurrent Density Increase and Charge-Transfer Resistance Reduction of GaAs Induced by Double-Frequency Excitation during Photocatalytic Hydrogen Evolution Reaction

The effective generation and migration of photogenerated carriers are crucial challenges for maximizing solar-to-hydrogen conversion in semiconductor-based water splitting. Herein, we report an enhancement effect of double-frequency dual-wavelength excitation in GaAs under simultaneous irradiation with 375 and 740 nm. Compared to single-wavelength excitation at 740 nm, dual-wavelength excitation at 375 and 740 nm increases the photocurrent density from 0.3 to 4.7 mA·cm–2 (∼15.7-fold enhancement), reduces the charge-transfer resistance (Rct) from 10.9 to 1.4 kΩ (87% reduction), enhances the hydrogen evolution rate from 3.33 to 11.01 μmol·g–1·h–1 (3.3-fold improvement), and boosts the apparent quantum efficiency (AQE) from 0.42% to 0.80% (∼90% relative enhancement). The 370 nm excitation notably extends the decay times of both ground-state bleaching (GSB) and excited-state absorption (ESA), with average GSB at 580 nm and ESA at 740 nm lifetimes reaching 49.4 and 110.9 ps in the femtosecond transient absorption spectra (fs-TAS) measurement, respectively, significantly longer than those under 480 and 565 nm excitation. This double-frequency excitation effect follows a modified Rydberg formula and represents the natural property of GaAs. This work could help us to better understand the double-frequency excitation and offer a strategic approach to boost the photoelectrochemical reaction performance over semiconductors.