Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University; Collaborative Innovation Center of Chemical Science and Engineering , Tianjin 300072, China.
Acc Chem Res. 2016 May 17;49(5):911-21. doi: 10.1021/acs.accounts.6b00036. Epub 2016 Apr 14.
Continuous efforts have been devoted to searching for sustainable energy resources to alleviate the upcoming energy crises. Among various types of new energy resources, solar energy has been considered as one of the most promising choices, since it is clean, sustainable, and safe. Moreover, solar energy is the most abundant renewable energy, with a total power of 173 000 terawatts striking Earth continuously. Conversion of solar energy into chemical energy, which could potentially provide continuous and flexible energy supplies, has been investigated extensively. However, the conversion efficiency is still relatively low since complicated physical, electrical, and chemical processes are involved. Therefore, carefully designed photocatalysts with a wide absorption range of solar illumination, a high conductivity for charge carriers, a small number of recombination centers, and fast surface reaction kinetics are required to achieve a high activity. This Account describes our recent efforts to enhance the utilization of charge carriers for semiconductor photocatalysts toward efficient solar-to-chemical energy conversion. During photocatalytic reactions, photogenerated electrons and holes are involved in complex processes to convert solar energy into chemical energy. The initial step is the generation of charge carriers in semiconductor photocatalysts, which could be enhanced by extending the light absorption range. Integration of plasmonic materials and introduction of self-dopants have been proved to be effective methods to improve the light absorption ability of photocatalysts to produce larger amounts of photogenerated charge carriers. Subsequently, the photogenerated electrons and holes migrate to the surface. Therefore, acceleration of the transport process can result in enhanced solar energy conversion efficiency. Different strategies such as morphology control and conductivity improvement have been demonstrated to achieve this goal. Fine-tuning of the morphology of nanostructured photocatalysts can reduce the migration distance of charge carriers. Improving the conductivity of photocatalysts by using graphitic materials can also improve the transport of charge carriers. Upon charge carrier migration, electrons and holes also tend to recombine. The suppression of recombination can be achieved by constructing heterojunctions that enhance charge separation in the photocatalysts. Surface states acting as recombination centers should also be removed to improve the photocatalytic efficiency. Moreover, surface reactions, which are the core chemical processes during the solar energy conversion, can be enhanced by applying cocatalysts as well as suppressing side reactions. All of these strategies have been proved to be essential for enhancing the activities of semiconductor photocatalysts. It is hoped that delicate manipulation of photogenerated charge carriers in semiconductor photocatalysts will hold the key to effective solar-to-chemical energy conversion.
人们一直在努力寻找可持续的能源资源，以缓解即将到来的能源危机。在各种新能源中，太阳能被认为是最有前途的选择之一，因为它清洁、可持续、安全。此外，太阳能是最丰富的可再生能源，地球连续不断地接收着总功率为 173000 太瓦特的太阳能。人们广泛研究了将太阳能转化为化学能，这可能提供连续和灵活的能源供应。然而，由于涉及复杂的物理、电气和化学过程，转换效率仍然相对较低。因此，需要精心设计具有宽太阳能照明吸收范围、高载流子导电性、少复合中心和快速表面反应动力学的光催化剂，以实现高活性。本综述描述了我们最近为提高半导体光催化剂中载流子的利用效率以实现高效太阳能到化学能转换而做出的努力。在光催化反应中，光生电子和空穴参与复杂过程，将太阳能转化为化学能。初始步骤是在半导体光催化剂中产生载流子，这可以通过扩展光吸收范围来增强。已证明等离子体材料的集成和自掺杂的引入是提高光催化剂光吸收能力以产生更多光生载流子的有效方法。随后，光生电子和空穴迁移到表面。因此，加速传输过程可以提高太阳能转换效率。已经证明了不同的策略，例如形态控制和导电性改善，可以实现这一目标。精细调节纳米结构光催化剂的形态可以减少载流子的迁移距离。通过使用石墨材料提高光催化剂的导电性也可以改善载流子的传输。在载流子迁移过程中，电子和空穴也容易复合。通过构建异质结可以增强光催化剂中的电荷分离，从而抑制复合。表面状态作为复合中心也应去除，以提高光催化效率。此外，表面反应是太阳能转换过程中的核心化学过程，也可以通过应用助催化剂以及抑制副反应来增强。所有这些策略都被证明是增强半导体光催化剂活性的关键。希望在半导体光催化剂中精细操纵光生载流子将是实现有效太阳能到化学能转换的关键。
