Rational Design and Convenient Synthesis of Carbazole-Modified A-D-Type Phenazine-Conjugated PAHs as Electrocatalyst Carriers toward Ethanol Oxidation

Phenazine-based small molecules with well-defined structures and adjustable potentials may accurately disperse and support Pd nanoparticles, making them suitable as anode carrier materials for direct alcohol fuel cells. Herein, a series of carbazole-modified A-D-type phenazine-conjugated polycyclic aromatic hydrocarbons (PAHs) were conveniently obtained via the tandem cross-oxidative coupling/aromatization of readily available polyaromatic amines (PAAs) with <i>p</i>-phenylenediamine and subsequent coupling with diiodobiphenyl. These nitrogen-rich and insoluble organic small molecules with tunable properties can efficiently disperse and load Pd nanoparticles and can be used as anode carrier materials for ethanol oxidation. By adjustment of the electronic structure, stacking mode, and strength of the interaction between Pd and active sites of the carrier, the catalytic activity of the electrocatalysts can be regulated. Comparative studies unveil that there exist moderate Pd-N-C interactions in loosely stacked rod-shaped Pd/PPACz, resulting in the minimum Pd particle size of 2.6 ± 0.9 nm. The as-prepared electrochemical stable electrode exhibits good durability and the highest mass-specific current density of 3058 mA mg^-1. Through the analysis of carrier morphology and Pd-N-C interactions, we attributed the high catalytic activity of Pd/PPACz to the effective dispersion of Pd on the carrier surface and the synergistic effect of the Pd and PPACz carriers. The results indicate that different PAH blocks have a direct effect on the morphology and electronic structure of the carrier material film. The coplanarity between the strong electron donor carbazole and the phenazine nucleus electron acceptor can directly change the electronic state of Pd, thereby affecting the adsorption behavior of Pd toward the intermediate products. Moreover, the nanoscale and effectively dispersed morphology of the carriers provide additional active centers. This study provides a new strategy for the rational design and rapid construction of organic small-molecule electrode materials for energy storage and conversion.