热电集成助力光电化学分解水

An integrated thermoelectric-assisted photoelectrochemical system to boost water splitting

光电催化水分解电池的核心吸光部件是半导体光电极.为实现太阳光下自发水分解,对于单光电极系统要求半导体光电极的带隙要不小于1.8 eV,以满足水分解反应的热力学(理论电压1.23 V)和动力学要求(热损耗与过电势~0.6 eV),而即便对于通过引入梯度带隙的双光电极构建串联型系统,背面的窄带隙光电极材料的带隙也通常需要大于1.0 eV.因此,传统的光电催化水分解电池难以有效利用太阳光谱中波长大于1250 nm的红外光,一定程度上限制了能量转化效率的提升.为实现太阳光谱的全谱有效利用,本文设计了一种热电器件集成的光电催化水分解系统,利用被太阳光谱中红外光加热的电解液作为热端、环境温度的水作为冷端,通过集成热电器件将二者温差转化为电压施加于光电催化水分解电池上以辅助分解水.对比传统串联型光电催化水分解电池,该热电器件集成的串联型光电催化电池的太阳能转化效率可提高近60%.本研究工作为构建可全光谱有效利用的光电催化水分解系统提供了具有普适性的策略.

Common solar-driven photoelectrochemical(PEC) cells for water splitting were designed by using semiconducting photoactive materials as working photoelectrodes to capture sunlight. Due to the thermodynamic requirement of 1.23 eV and kinetic energy loss of about 0.6 eV, a photo-voltage of 1.8 V produced by PEC cells is generally required for spontaneous water splitting. Therefore, the minimum bandgap of1.8 eV is demanded for photoactive materials in single-photoelectrode PEC cells, and the bandgap of about 1 eV for back photoactive materials is appropriate in tandem PEC cells. All these PEC cells cannot effectively utilize the infrared light from 1250 to 2500 nm. In order to realize the full spectrum utilization of solar light, here, we develop a solar-driven PEC water splitting system integrated with a thermoelectric device. The key feature of this system is that the thermoelectric device produces a voltage as an additional bias for the PEC system by using the temperature difference between the incident infrared-light heated aqueous electrolyte in the PEC cell as the hot source and unirradiated external water as the cold source. Compared to a reference PEC system without the thermoelectric device, this system has a significantly improved overall water splitting activity of 1.6 times and may provide a strategy for accelerating the application of full spectrum solar light-driven PEC cells for hydrogen production.