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

Abstract

The development of cost-effective electrocatalysts is a key challenge for facilitating advanced electrochemical energyconversion 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 Å for Co−N−C, −0.91 eV and 3.22 Å for Nb/Co−N−C, −1.00 eV and 3.28 Å for Bi/ Co−N−C, and −1.20 eV and 3.46 Å 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.

In-Situ Grafting of Single-Atomic Titanium–Nitrogen Moiety onto Carbon Nanostructures for Efficient Photovoltaic Devices

“…Triiodide tends to adsorb on the Ti metal center in Ti 1 /NC-SAC, and the calculated adsorption free energy was −1.93 eV, indicating an energetically preferred adsorption. , Upon triiodide adsorption, the Ti center undergoes axial displacement (moving toward the carbon matrix plane) and establishes a strong bonding interaction with triiodide species (Ti–I bond length: 2.66 Å, the atop configuration). As a result, the original bond length 2.83 Å of I–I in the triiodide significantly increases to 3.33 Å (Figure a), far exceeding those (3.06 Å, 3.22 Å) in representative studies of Co– and Fe–N–C catalysts. , The elongated bond length demonstrates a favored dissociation of triiodide on the Ti center. Specifically, from the DOS and PDOS diagram, pronounced orbital overlapping and hybridization between the I p orbital and Ti d orbital can be observed in Ti 1 /NC-SAC, which rationalizes the enhanced adsorption of I 3 – on Ti 1 /NC-SAC (Figure b,c).…”

“…As a result, the original bond length 2.83 Å of I−I in the triiodide significantly increases to 3.33 Å (Figure 5a), far exceeding those (3.06 Å, 3.22 Å) in representative studies of Co− and Fe−N−C catalysts. 16,34 The elongated bond length demonstrates a favored dissociation of triiodide on the Ti center. Specifically, from the DOS and PDOS diagram, pronounced orbital overlapping and hybridization between the I p orbital and Ti d orbital can be observed in Ti 1 / NC-SAC, which rationalizes the enhanced adsorption of I 3 − on Ti 1 /NC-SAC (Figure 5b,c).…”

Nickel Single-Atom Catalyst-Mediated Efficient Redox Cycle Enables Self-Checking Photoelectrochemical Biosensing with Dual Photocurrent Readouts

“…To further evaluate their catalytic performance for the iodide/tri-iodide redox activity, cyclic voltammetry (CV) was performed to test the electrochemical reactivity of electrodes (Figure d and Figure S3). Both CV curves of Ni SACs and N-C show redox peaks compared to the bare ITO electrode, and the Red 1 /Ox 1 peaks indicate redox reactions of iodide/tri-iodide ions ( I 3 – + 2 e – ↔ 3 I – ) . Usually, there are two important factors of peak-to-peak gap (termed as E pp ) and peak current density, which represents the reaction rate and reversibility, respectively. , The Ni SACs possess a smaller E pp value of 563 mV than the bare matrix of N-C (741 mV).…”

“…Therefore, to circumvent the plague of the related hole- or electron-trapping agents, the introduction of recyclable redox couples and corresponding efficient cocatalysts is a potential and practical approach for an efficient interfacial reaction. Atomically dispersed metal–nitrogen–carbon materials as one of the most promising single-atom catalysts (SACs) have aroused considerable concern as effective cocatalysts, which display excellent catalytic performance due to their unique electronic structures and fully exposed active sites. − Hence, it is greatly expected to slightly adjust the voltage for achieving photocurrent polarity switching in the presence of redox couples and advanced SACs.…”

Electrochemical quantification of sulfamethoxazole antibiotic in environmental water using zeolitic imidazolate framework (ZIF)-derived single-atom cobalt catalyst in nitrogen-doped carbon nanostructures

“…ZIF-8 was synthesized following previously reported procedures. 38,39 Briefly, 1.848 g of 2-mIm was dissolved in 45 mL of methanol. Then, 1.674 g of Zn(NO 3 ) 2 •6H 2 O (in 45 mL of methanol) was added under continuous vigorous stirring for 8 h at room temperature (23 ± 2 °C).…”