基于氮化钽光阳极的自发光解水电池的改性与机理研究

Photoelectrochemical(PEC) water splitting represents a promising method to utilize solar energy. The purported high efficiency of PEC water splitting, however, has remained elusive, and systems based on photoelectrode/H2O junctions typically feature low efficiencies. The research goal of this proposal is to construct an unassisted water splitting cell by understanding a promising photoelectrode material, Ta3N5. It has the potential to enable water splitting of theoretical efficiencies up to 15% in a tandem configuration. As a photoanode, the key problems presented by Ta3N5 are the high turn on potential and poor stabilities. We hypothesize that presently the performance of Ta3N5 is limited by Fermi level pinning on its surface and plan to eliminate the negative influence based on the understanding of it poor stability. we will systematically follow the structural, chemical and energetic evolution of the Ta3N5 surface as a function of photo water oxidation. A strong correlation between the Ta3N5 surface oxidation and its PEC performance degradation, as well as the change of turn on potential, is expected. It helps validate our hypothesis that the Fermi level pinning due to direct OER on the surface of Ta3N5 is the key to the issues faced by this otherwise promising photoanode material. Guided by our new insight, we will apply an ultrathin layer of passivation to improve surface photovoltage for more negative turn on potential and co-catalysts for better stabilities. In the end, the outcome will likely build a basis for future development of high efficiency and highly stable photoelectrodes that can split water without the need for externally applied potentials. The proposed project is designed to understand what limits the performance of one otherwise promising photoelectrode material, Ta3N5. The knowledge generated will be transferrable to other materials. The approach proposed to address the issues of Ta3N5 will likely find applications on other photoelectrode materials, as well. More importantly, the research efforts present us with an opportunity to broaden the impact by teaching the general public on the importance of sustainable development.

光电化学池分解水反应是一种高效利用太阳能的途径，但是现有体系通常面临着低光生电压和低转换效率的问题，难以实现自发反应。理论计算表明，氮化钽(Ta3N5)的理论转换效率高达15%，是最具潜力的光阳极材料之一。然而在实际应用中，它着与其能带位置不匹配的低光生电压，且其光解水电流随时间衰减迅速。为了明确这一现象的根本原因，已有实验结果支持着如下假设：氮化钽的低光生电压和高衰减速率缘于其表面形成的无定型层，该结构的费米能级钉扎效应影响了光阳极材料的表面能级。本项目拟基于该假设提出解决方案：通过表面保护层和助催化剂的协同作用，抑制光阳极表面无定型层的形成，从而制备出具有低起始电位且能稳定工作的氮化钽阳极，最终设计和构建出基于氮化钽纳米棒光阳极的自发光解水电池设备。本项目从探究氮化钽性能衰减的根本原因出发，有望彻底解决光电池阳极问题，为发展人工光合作用技术和扩大其应用范围提供理论基础和技术路线。

在我国低碳发展和环境污染治理力度不断加大的背景下，人类对绿色新能源的需求推动着非化石能源的探索与创新。光电化学分解水制氢是一种高效且价格低廉的太阳能转换途径。氮化钽是一种在带隙宽度、能带位置和光吸收特性等方面均较为理想的光阳极材料。现阶段，氮化钽光阳极材料面临着三个问题：由不良电子特性导致的载流子复合、光解水反应中性能的迅速衰减以及低光生电压导致的过正光解水起始电位。本项目聚焦于发展高活性氮化钽材料的制备与改性，探究其光生电压和电流密度不理想的根本原因，并设计了可自发光解水的串联电池。首先，针对氮化钽光生载流子扩散距离和光吸收深度不匹配的问题，我们采用了Zr元素掺杂的方法，促进体相材料中载流子传输行为，并抑制了氮化钽表面光生空穴和电子的复合，实现对其光解水反应中起始电位和光电流密度的提升。其次，利用原子层沉积方法在氮化钽表面制备氧化物保护层，将氮化钽和电解液在物理上隔离开，结合表面Co基析氧催化剂的修饰，促进光生空穴向电解液中的转移，提升氮化钽在光解水中的服役稳定性。为了测量氮化钽光阳极在光解水器件中的效率，我们发展了与之匹配的能在碱性溶液中稳定工作的CuBi2O4光阴极材料。通过限制退火条件中的氧气含量，在CuBi2O4薄膜中引入更多的氧空位，并探究了氧空位提升光解水效率的作用机制。通过磁控溅射法在CuBi2O4薄膜表面沉积了TiO2保护层，提升其在碱性溶液中的长时间稳定性。最终，基于优化后的光阳极和光阴极材料，我们设计并构建了在碱性溶液中可以自发光解水的串联电池，并且总结了该器件存在的不足。本项目的顺利完成，解决了氮化钽光电池阳极材料面临的问题，为发展人工光合作用技术和扩大其应用范围提供了理论基础和技术路线。