The in-depth understanding of the reported photoelectrochemical properties of the layered carbon nitride, poly(triazine imide)/LiCl (PTI/LiCl), has been limited by the apparent disorder of the Li/H atoms within its framework....
We report the development of a hybrid catalyst consisting of carbon nitride (CN x ) and cobalt phthalocyanine tetracarboxylic acid (CoPc-COOH), which converts CO 2 to CO with high reaction rate (1067 μmol/g•h) and high selectivity (over 98%), under simulated solar irradiation. The carboxylic acid substituents on the phthalocyanine ligands play a critical role as they bind to the amine groups of CN x to enable nearly ideal monolayer coverage of the molecular cocatalyst on the semiconductor surface and promote catalytic activity from the molecular complex. Specifically, the CN x / CoPc-COOH hybrid material achieves a reaction rate 16 times higher than a CN x material containing unsubstituted CoPc molecules. We further show that activation and deactivation of the CN x / CoPc-COOH composite, which are associated with the reduction and decomposition of CoPc-COOH, respectively, both proceed at a nearly constant rate regardless of the CO 2 reduction reaction rate. The decoupling of charge carrier injection and CO 2 reduction catalysis has important mechanistic implications for future performance optimization and materials design of photocatalysts for CO 2 reduction.
Inherently disordered structures of carbon nitrides have hindered an atomic level tunability and understanding of their catalytic reactivity. Herein, coordination of copper cations within a crystalline carbon nitride, i.e., poly(triazine imide) or CNx, was found to yield two ordered structures for Cu-CNx wherein one or two Cu(I) cations coordinate to its intralayer N-triazine groups. The crystallites electrophoretically deposit from aqueous particle suspensions and yield current densities of ~10 to 50 mA/cm2 with a concomitant and increasing reduction of CO2 and H2O. Reduction of CO2 increases for smaller particles as mechanistic calculations reveal its catalysis mediated by two intralayer Cu atoms.
The in-depth understanding of the reported photoelectrochemical properties of the layered carbon nitride, poly(triazine imide)/LiCl (PTI/LiCl), has been limited by the apparent disorder of the Li/H atoms within its framework. To understand and resolve the current structural ambiguities, an optimized one-step flux synthesis (470 oC, 36 h, LiCl/KCl flux) was used to prepare PTI/LiCl and deuterated-PTI/LiCl in high purity. Its structure was characterized by a combination of neutron/X-ray diffraction and transmission electron microscopy. The range of possible Li/H atomic configurations were enumerated for the first time and, combined with total energy calculations, reveals a more complex energetic landscape than previously considered. Experimental data were fitted against all possible structural models, exhibiting the most consistency with a new orthorhombic model (Sp. Grp. Ama2) that also has the lowest total energy. In addition, a new Cu(I)-containing PTI (PTI/CuCl) was prepared with the more strongly scattering Cu(I) cations in place of Li, and which also most closely matched with the partially-disorded structure in Cmc21. Thus, a complex configurational landscape of PTI is revealed to consist of a number of ordered crystalline structures that are new potential synthetic targets, such as with the use of metal-exchange reactions.
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