纳米α-Fe2O3半导体光阳极的界面改性、电化学行为及机理研究

Photoelectrochemical (PEC) water splitting for converting solar to hydrogen is one of the promising and attractive strategies to achieve sustainable and renewable energy in an environment friendly way. Hematite (α-Fe2O3), with suitable optical band gap, as a promising candidate of photoelectrode in photoelectrochemical water splitting, has been widely investigated for solar-to-fuel conversion. However, the transportation limitation of photogenerated charge carriers in the semiconductor, between the interface of the semiconductor and liquid junction (SCLJ) is the reason why α-Fe2O3 could not achieve the theoretical solar conversion efficiency (12.9%). Herein, the PEC catalysts based on hematite semiconductor with controllable structure are constructed in nano level. Then, the molecular groups will be decorated and moderated on the hematite photoanode to fabricate favorable SCLJ interface with optical band gap and favorable photoexcited charge carriers’ separation and transportation. The physical and chemical, electrochemical characterization and PEC performance of the PEC catalyst are researched by the modern spectroscopy, electrochemical technology and PEC cell test to study the electrochemical behavior during the photoelectrochemical water splitting. Moreover, combined with calculation and simulation based on the density functional theory (DFT), the mechanism of charge carriers’ separation and transportation is investigated. Meanwhile, the structure-activity relationship inside the PEC catalyst and electrolyte is also studied. Based on this project, theoretical guidance and experimental support will be developed for solar water splitting catalyst with high PEC performance.

光电解水直接将太阳能转换成化学能，是一种理想的制氢途径，实现太阳能产氢的关键是开发具有优良微观界面结构及性能的光电催化材料。赤铁矿（α-Fe2O3）半导体具有窄的禁带宽度、强的可见光响应等优点，引起广泛关注；但纳米α-Fe2O3光阳极用于光电解水时内部光生载流子在半导体颗粒间的界面、半导体与基底、溶液(SCLJ)界面传递是限制其太阳能-氢气转化效率达到计算值12.9%的重要因素。本项目拟设计构筑微观界面结构可控的纳米α-Fe2O3半导体；进一步通过界面修饰改性，形成纳米α-Fe2O3半导体光阳极提高半导体界面的吸光特性、能带弯曲及载流子的分离传输；最后，扩展电化学表征方法结合在线的光电性能测试和理论计算模拟，研究该光阳极在光电解水中的电化学行为和内部反应机理，阐明纳米α-Fe2O3半导体光阳极微观形貌、界面特性与光电解性能的构效关系，为开发高性能的光电解催化剂提供理论指导和实验依据。

光电催化分解水制氢，是一种利用太阳能生产清洁能源的方法。α-Fe2O3作为窄带隙半导体，广泛应用于光电解水产氢过程。但α-Fe2O3导电性差，光生载流子传输距离短、易复合，析氧反应较慢等因素使其效率远未达到理论值（12.9%）。本项目在不同导电基底上制备和修饰多维α-Fe2O3，将所得样品应用于光电解水。利用物理化学及电化学表征结合计算结果，分析其在析氧过程中的界面载流子注入分离、析氧反应机理，为高效光电解阳极催化剂的设计合成及未来应用提供了理论指导和实验依据。主要结果如下：.1）合成了Co修饰的α-Fe2O3-H@CoO/TF，样品呈纳米麦穗状，表面存在氧空位。α-Fe2O3-H@CoO/TF的光电流密度为1.6 mA/cm2@1.23V vs. RHE，起始电位为-0.385 V。此外，物理化学和电化学表征结果证明PEC性能提高主要是由于氧空位缺陷位点促进光吸收、水氧化过程以及空穴/电子对的分离，暴露更多活性面积。.2）采用水热原位共掺杂在泡沫镍上合成了CoOx修饰的纳米花状Fe2O3/CoOx，并在其表面电沉积等离子体Au。Fe2O3/CoOx/Au光阳极在1.23 VRHE下的光电流密度达到3.88 mA/cm2，是α-Fe2O3的9.24倍。其1.18 VRHE下的ABPE效率为0.10％，电荷注入和分离效率分别是α-Fe2O3的3.96和2.3倍。分析表明CoOx和Au协同作用促进了光吸收，降低了界面处的电荷转移电阻，从而提高光电性能。.3）采用水热法在FTO导电基底上制备蠕虫状的α-Fe2O3纳米棒，通过两部浸渍法在其表面沉积助催化剂Co-Pi。结果表明Co-Pi修饰提高了偏置光子-电流效率，电荷分离效率和电荷注入分离，Co-Pi中Co2+与Co3+的相互转化降低了界面处的电荷转移电阻，同时有效降低析氧反应能垒，加速了光阳极和电解质之间界面处的水氧化动力学从而有效的提高了氧化铁的光电性能。.4）采用电化学法及N2中退火得到α-Fe2O3纳米颗粒，在其表面沉积双金属羟基氧化物NiFeOOH，在1.23 VRHE下的光电流密度达到1.39 mA/cm2，起始电位为0.65 VRHE，比α-Fe2O3降低了140 mV。结果表明NiFeOOH协同作用明显提高了电荷分离效率，加速了光阳极和电解质之间表面反应的水氧化动力学从而有效的提高了氧化铁的光电性能。