Abstract: Photoelectrocatalytic (PEC) water splitting can directly convert solar energy into hydrogen energy, which is a highly promising green hydrogen production technology. However, traditional PEC systems mostly rely on an applied external bias, and single photoelectrode systems are limited by the thermodynamic requirements of the water-splitting reaction, which can only utilize ultraviolet light and part of visible light. Infrared light, which accounts for more than 50% of the energy in the solar spectrum, is mostly wasted in the form of heat loss, limiting solar energy utilization efficiency. To break through this bottleneck and achieve efficient full-spectrum utilization of solar energy, this paper designs a bias-free PEC water splitting system based on the coupling of bismuth vanadate photoanode materials and thermoelectric devices, which recovers waste heat generated during the operation of the PEC reactor and converts it into electrical energy by integrating a thermoelectric module to provide an auxiliary bias for the water-splitting reaction. Experimental results show that the integrated photoelectric/photothermal device can achieve stable unbiased water splitting for hydrogen production under one-sun illumination; when further concentrated irradiation is applied, the voltage supply and heat dissipation effects of the thermoelectric module become more significant due to the increased light intensity and enhanced heat generation of the system, and the unbiased hydrogen production performance of the system is significantly enhanced (when the light intensity is increased to 7.3 suns, the steady-state unbiased photocurrent of the device increases from 0.35 mA to 5 mA). Notably, the integrated thermoelectric module can not only provide an auxiliary bias for the photoelectrode but also maintain the coupled system at an appropriate operating temperature through efficient heat dissipation. This strategy of spectral-splitting utilization of solar energy based on waste heat recovery (infrared light is converted into thermal energy and then recovered to generate electricity, while visible light is used for photoelectrocatalysis) provides a feasible idea for realizing bias-free PEC water splitting with a single photoelectrode and the development and application of high-concentration-ratio PEC devices.