Morphology-dependent Photoelectric Properties and Photocatalytic CO<sub>2</sub> Reduction of Zinc Porphyrin Nanocrystals
Ying He, Renfu Li, Amin Cao, Xiao Xu, Weifeng Huang, Miao Sun, Junqiang Li, Xueyuan Chen, Longtian Kang
Abstract
Morphology-dependent photoelectric properties and photocatalytic hydrogen evolution performance of organic nanostructures have been found; however, the corresponding photocatalytic activity for the CO2 reduction reaction (CO2RR) and its relationship with photocurrent are hardly studied. In this work, zinc porphyrin (ZnP) nanocrystals, including ZnP nanosheets (ZnP NSs), ZnP roughened octahedrons (ZnP ROhs), and ZnP octahedrons (ZnP Ohs), are synthesized and systematically evaluated. The experimental results show that the photocurrent order is ZnP ROhs > ZnP Ohs > ZnP NSs, while the photocatalytic activity for the CO2RR follows the following order: ZnP NSs > ZnP ROhs > ZnP Ohs. A series of characterizations and analyses reveal that they are closely related to the growth ratio along the [020] and [200] directions (R[020]/[200]). Higher R[020]/[200] results in a higher photocurrent due to more efficient generation and transportation of intermolecular charge transfer excitons with a longer lifetime along the [020] direction. Unfortunately, higher R[020]/[200] also means less exposure of {020} facets containing more Zn–N4 active sites for the photocatalytic CO2RR. Therefore, the inconformity between the photoelectric conversion and interfacial reaction can confirm that it is not enough to only expose more active sites for higher photocatalytic activity as reported. This work provides an important idea of morphology-dependent photocatalysis on the basis of conjugated metal–organic molecules.