Nanoporous BiVO4 Decorated with Carbon Quantum Dots for Efficient Photoelectrochemical Water Splitting

The sluggish kinetics of oxygen evolution is widely recognized as one of the major challenges in developing a BiVO₄-based photoanode. To address this intrinsic limitation, we present an integrated photoanode composed of nanoporous BiVO₄ decorated with 5 nm carbon quantum dots (CQDs). The CQDs function as an efficient hole transfer layer due to their lower surface potential, creating an outward interfacial built-in electric field with the higher surface potential of bulk BiVO₄. This electric field is capable of driving photogenerated holes to the CQDs’ surface for efficient water oxidation. The CQDs-BiVO₄ demonstrates an improved photocurrent of 2.7 mA cm^–2 at 1.23 V vs RHE under simulated sunlight, which is approximately 3.0 times higher than that of pristine BiVO₄. The nanoporous CQDs-BiVO₄ also achieves an enhanced surface charge transfer efficiency of 45.8% and a shorter electron transport time of 0.23 ms at a flow rate of 300 W m^–2. Time-resolved photoluminescence analysis reveals that a longer lifetime is achieved (τ₁ = 3.7 ns and τ₂ = 49.0 ns) for CQDs-BiVO₄, confirming that the reduced electron–hole recombination is beneficial for bulk charge transfer.