半导体异质结提高气敏和光电催化裂解水的性能与机制

Solar driven catalysis on semiconductors to produce clean chemical fuels, such as hydrogen, is widely considered as a promising route to mitigate environmental issues caused by the combustion of fossil fuels and to meet increasing worldwide demands for energy. The wide-band gap semiconducting metal oxides (SnO2, ZnO and In2O3 etc.) based sensors can been used to detect environmental toxic gases due to their interior non-stoichiometry. For water splitting, these narrow gap semiconductors of Fe2O3, WO3 and BiVO4 have attracted increasing attention because they not only possess appropriate band gap positions with the valence band more positive than the potential of water oxidation (1.23 V) but also exhibit appropriate surface reaction kinetics and reasonable stability in aqueous solution under prolonged irradiation. However, for a single semiconductor, the high operating temperature leads to high power consumption, safety hazards and low stability, limiting their practical application in gas detection. While the conducting polymers such as polyaniline (PANI), polypyrrole (PPy) and polythiophene (PTh) are sensitive to VOCs at room temperature and have advantages of environmental stability, low cost and facile synthesis. It is a feasible strategy to combine the characters of semiconducting metal oxides and conducting polymers, the sensing performance of the new gas sensing material will over the constituent counterparts due to their synergistic and complementary effects. One of the key limiting factors affecting efficiency in artificial photosynthesis is recombination of charge carriers. Therefore, substantial efforts have been put into solving these problems, in particular, the coupling secondary semiconductors that can act as either electrons or holes acceptors to suppress charge carriers recombination. The loading double transition metal–LDH can act as an efficient oxygen evolution co-catalyst to accelerate the water oxidation kinetics that is the rate determining step during water splitting. The theoretical modelling of semiconductor electronic structures at interfaces, and how these explain the functionality of the junction structures are provided in the project according to the first principle calculation. This strategy in the project provides opportunities for much improved solar energy effective utilization and high solar-to-chemical fuel conversion efficiency.

单一宽禁带半导体如SnO2和ZnO，由于其本征化学非计量性对一些有毒气体具有敏感响应，但选择性差和操作温度高导致耗能和不安全。通过与导电高分子杂化的异质结能构成室温传感器，并进一步提高其气敏性能。而窄禁带半导体，如α-Fe2O3，WO3和BiVO4，不仅具有合适的禁带宽度,价带最高低于水氧化热力学电位而且持续光照下在含水溶液中稳定，可吸收可见光作裂解水的光催化剂。但往往会遭遇光生电子与空穴的重结合和受阳极水氧化缓慢动力学的限制。本项目选择第二种半导体作为电子或空穴的接受体，按费米能级差和能带位置相匹配原则构建p-n异质结能有效抑制电子-空穴的再结合；同时负载层状双金属氢氧化物或碳酸盐作为水氧化催化剂，缓解电极表面空穴的积累，不仅加速水氧化动力学并能抑制电荷载流子的重结合。借助于密度泛函理论的第一性原理计算揭示提高气敏和光电化学转换的作用机制。该项目对缓解能源短缺和环境污染具有重要意义。

开发和研究实时检测环境污染的高灵敏度、高选择性、快速响应和低温操作的气体传感器和高效的太阳能制氢光电化学水裂解系统是解决我们面临的日益增长能源需求和环境污染问题的有效途径。实质性工作是研制高效、低成本的气敏和光电极材料。半导体金属氧化物由于其结构稳定、制备方法简单、成本低和效率高等优点，是开发气体传感器和光电化学水裂解光电极的核心并具有很大的发展潜力。本项目采用设备简单、条件温和的低温水热、化学沉淀、浸渍、热分解、静电纺丝法等方法制备大长径比、大比表面的一维纳米丝、纳米棒，二维纳米片和由低维纳米材料自组装的分级纳米结构金属氧化物半导体，包括 n-型和p-型，宽带隙（SnO2、ZnO、Co3O4、NiO）和窄带隙半导体（α-Fe2O3、BiVO4和BiFeO4等），表征它们的结构和形貌，并测试它们的气敏和光电化学性能。结果表明，单一金属氧化物不能满足当前气敏和光电化学水裂解的需求。因此，我们研究了各种策略改善其性能，如形貌和结构调控、金属元素掺杂、催化剂负载、rGO修饰和构建异质结复合物。实验证明构建异质结是提高单一金属氧化物气敏和光电化学性能的有效方法。我们依据两种金属氧化物能带匹配原则，采用低温水热法、电化学沉积法、简单滴烧法，模板诱导水热阴离子交换法和光辅助电沉积方法制备了各种异质结复合物，如WO3/α-Fe2O3、α-Fe2O3/BiVO4、ZnO/BiVO4、SnO2/BiVO4、ZnO/CdO、MoO3/BiVO4和BiVO4/Cu2O等。提高了复合物的气敏和光电化学性能，并从热力学能带结构和表面反应动力学详细讨论了提高机理。为进一步提高材料性能，在异质结上修饰了rGO和助催化剂，如各种2D层状氢氧化物（LDHs），如Ni-Fe LDH、Ni-Co LDH、Co-Al LDH 或普鲁士蓝，以抑制电子空穴的复合和加速水氧化反应动力学。在此基础上，我们还引进了三元双金属氧化物半导体作为气敏和光电极材料，如ZnSnO3、BiVO4、BiFeO4、ZnWO4、BiWO4、和ZnFe2O4，因为在过去几十年中，几乎所有可能的二元金属氧化物都被研究，然而，令人满意的气体传感器和光电极仍然存在很大的竞争，而且开发新材料永远是各个领域的前沿课题，这也促进我们的研究工作。