Photoelectrochemical (PEC) water splitting is a promising method for converting solar energy into hydrogen fuel, offering a sustainable solution for future energy needs. However, traditional PEC systems face challenges such as low efficiency and the need for additional voltage bias. To address these limitations, researchers have explored integrating PEC systems with PV cells to create hybrid systems that can achieve higher overall energy conversion efficiencies. One key challenge in these hybrid systems is the efficient utilization of the solar spectrum, as most photoelectrodes are not fully transparent and can block light from reaching the PV cells.

The research team led by Professor Jinzhan Su at Xi’an Jiaotong University proposed a novel self-biased hybrid system that incorporates spectral beam splitters (BSs) to direct specific parts of the solar spectrum to different components of the system. The hybrid system includes TiO₂ and BiVO₄ photoelectrodes, which are optimized for different spectral ranges, and a PV cell that converts solar energy into electricity to power the PEC process. The BSs are designed to reflect shorter wavelengths of light to the photoelectrodes while transmitting longer wavelengths to the PV cell, ensuring that both components operate at their maximum efficiency.

The results of the study demonstrate that the integration of spectral BSs significantly enhances the performance of the hybrid system. The current density of the self-biased water splitting system with BSs exceeds that of conventional tandem systems, with the intersection point of the I–V curves for the photoanodes and solar cell being closer to the maximum power output of the solar cell. The power output of the hybrid system with BSs is 18.8 times higher than that of the conventional TiO₂ + BiVO₄–PV system. The hydrogen production rate of the system with BSs reaches 12.1 µmol/(h∙cm²), while the solar-to-hydrogen (STH) efficiency is enhanced by factors of 12.38 and 19.87 compared to conventional TiO₂ + BiVO₄–PV and TiO₂/BiVO₄–PV tandem systems, respectively.

This study provides an innovative approach to achieving self-biased water splitting by coupling spectral beam splitting with a PV-PEC system, resulting in improved solar energy harvesting efficiency. The findings highlight the potential of spectral BSs to enhance the efficiency of solar-driven water splitting systems, paving the way for more sustainable and efficient hydrogen production technologies. The results also suggest that further optimization of photoelectrode materials and the configuration of PV cells could lead to even higher efficiencies, making this hybrid system a promising candidate for large-scale solar-to-hydrogen conversion applications.