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.
Hydrogen production from solar water splitting, especially via photovoltaic-electrocatalysis, has been regarded as a promising approach for the conversion of abundant but intermittent solar energy into storable chemical fuels. Despite much progress, conventional combined photoelectrochemical devices usually suffer from severe instability issues, which largely inhibit them for practical applications and may also lead to the uncertain efficiency value for true overall water splitting. Here, we report an unassisted solar water splitting device with concurrent high efficiency and stability, which is constructed by spatial coupling of tandem III-V-based GaInP/GaAs/Ge light absorber and robust earth-abundant Ni foil-based MoNi 4 /MoO 2 bifunctional electrocatalysts . Remarkably, apart from the outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance, bifunctional MoNi 4 /MoO 2 electrocatalysts also largely avoid electrode contamination issues, while the robust Ni substrate protects III-Vs from conventional corrosion problems . Consequently, this integrated photovoltaic-electrolysis system device exhibits a high solar-to-hydrogen (STH) conversion efficiency of 17.6 % in alkaline electrolytes with long-term stability of up to 845 h. Further construction into a wireless unassisted monolithic device could lead to an artificial leaf with an STH efficiency of 4.28 %, holding great promise in future solar fuel production with concurrent high efficiency, good stability as well as low cost.
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