梯度掺杂的石墨型氮化碳纳米棒阵列光阳极制备及产氧性能研究

Using photoelectrochemical (PEC) water splitting to prepare clean energy is considered as one of the effective ways to solve the energy crisis and environmental pollution. Graphitic carbon nitride (g-CN) is a low cost, good stability of the n-type non-metallic organic semiconductor photocatalyst, but so far only the planar film structure of the photoanode have been adopted for its PEC applications, which has the key issues of small specific surface area and serious recombination of photogenerated charges. In order to solve the above problems, the applicant proposes a novel gradient doped g-CN nanorod array photoanode structure by in-situ thermal polymerization. Compared to the planar film, the nanostructures have larger specific surface area and ratio of depletion region, which can promote the exciton dissociation and enhance the hole injection efficiency. The one-dimensional rod-like structure facilitates the transfer of electrons to the substrate, and decreases electron-hole recombination in the bulk. The long axis of the rod-shaped nanostructures can absorb light sufficiently, while the short radial length shortens the hole collection distance, which can well solve the contradiction that the material needs to have a large absorption thickness and a small charge collection distance. In addition, the excellent resistance to light reflection of the nanoarray structure helps to further increase the light absorption. The gradient doping along the longitudinal (transverse) direction of the nanorod will also further enhance the charge separation and transfer. This work will greatly enhance the g-CN PEC oxygen production performance, and this strategy will shed light on the design of future photoelectrode structures in the solar energy conversion field.

光电催化分解水被认为是解决能源危机和环境污染问题的有效途径之一。石墨型氮化碳（g-CN）是一种成本较低、稳定性良好的ｎ型非金属有机半导体光催化剂，但目前在光阳极的应用中都采用平面膜结构，存在光生电荷复合严重和产氧动力学较慢的问题。为解决以上问题，申请人提出通过原位热聚合的方法制备新颖的梯度掺杂的g-CN纳米棒阵列光阳极结构。同平面膜相比，该纳米结构具有较大的比表面积和耗尽区比例，能够促进激子解离和提升空穴的界面注入效率；一维结构有利于电子向基底的传输，减少体相中的电荷复合；棒状纳米结构的长轴方向可充分吸收光，较短的径向长度会缩短空穴收集距离，能够很好的解决需要材料光吸收厚度大与电荷收集距离小之间的矛盾。另外，纳米阵列结构优异的抗光反射的能力有助于增加光吸收。沿纳米棒纵（横）向梯度掺杂会进一步提高电荷的分离和传输效率。该设计思想可极大提升g-CN光阳极性能，并对其它材料的开发有借鉴意义。

由于有机聚合物局域的π-电子共轭和较大的激子结合能导致的光生电荷利用效率低，其光电化学催化分解水的效率受到严重限制。以石墨型氮化碳（g-CN）聚合物为例，我们制备了一种新型光阳极，该纳米棒（PNR）阵列以阳极氧化铝为模板采用热缩聚方法制备。g-CN PNR阵列表现出了优越的性能，在一个标准强度太阳光照和1.23 VRHE电压下，其光电流密度可达120.5 μA cm−2；在360 nm光照射下，最高的入射光-电流转化效率是现有报道最高的，可达∼15%；在0.1 M浓度的硫酸钠水溶液中实现了很高的产氧性能，且我们的实验没有添加任何牺牲试剂。与平面结构相比，PNR阵列的性能增强主要是因为其独特的结构，芳香环π-电子偶联使其具有更高的载流子迁移率，为选择性设计性能更好的催化剂提供了新的途径。