Cobalt-Based Incorporated Metals in Metal-Organic Framework-Derived Nitrogen-Doped Carbon as a Robust Catalyst for Triiodide Reduction in Photovoltaics

The development of cost-effective electrocatalysts is a key challenge for facilitating advanced electrochemical energy-conversion technologies. In this study, transition metals (niobium, bismuth, and molybdenum)-/cobalt-assisted nitrogen-doped carbon electrocatalysts with a unique rhombic dodecahedron structure were fabricated via pyrolysis of the Co-metal organic framework. Solar cells fabricated using the Mo/Co-N-C counter electrode (CE) exhibited a significantly higher power conversion efficiency (PCE) of 7.98%, while the cells with Nb/Co-N-C and Bi/Co-N-C CE catalysts attained PCEs of 7.46 and 7.65%, respectively, much enhanced than that of the Pt-based photovoltaic cell (7.10%). This robust behavior was mainly attributed to the synergistic effect between the bimetallic active sites (Nb/Co, Bi/Co, and Mo/Co) and the nitrogen-doped carbon network, which resulted in a pronounced decrease in the charge-transfer resistance and superior device stability. Furthermore, the catalytic mechanism of these catalysts was investigated by the general strategy based on the surface adsorption of iodine atoms with the CE, work function, and electronic structure of the as-prepared nanohybrids, using first-principles density functional theory. The calculated adsorption energy and bond lengths were -0.82 eV and 3.05 angstrom for Co-N-C, -0.91 eV and 3.22 angstrom for Nb/Co-N-C, -1.00 eV and 3.28 angstrom for Bi/ Co-N-C, and -1.20 eV and 3.46 angstrom for Mo/Co-N-C, respectively. The density-of-states calculation predicted the metallic behavior of the as-prepared samples, and Bader charge analysis revealed that the development of uneven potential on the material surfaces with the addition of transition metals increases their polarities and the ability to adsorb I-3(-) ions on the CE surface, which enhances the credibility of these catalysts. In addition, the enhanced value of the calculated work function also indicates their superior catalytic behavior and fast electron transfer mechanism for the triiodide reduction reaction. This work opens an era for the rational design of incorporated transition-metal/Co electrocatalysts with nitrogen-doped carbon networks for advanced energy devices in catalytic fields.

Automated summary

This study synthesized transition metals/cobalt-assisted nitrogen-doped carbon electrocatalysts with a unique structure, leading to significantly higher efficiency and stability in solar cells. The synergistic effect between bimetallic active sites and nitrogen-doped carbon network, as well as investigations into the catalytic mechanisms using density functional theory, were key factors in enhancing the credibility of these catalysts.