Molecular-Level Synthesis of Cobalt Phosphide Nanocrystals Confined in Highly Nitrogen-Doped Mesoporous Carbon Electrocatalyst for Highly Efficient Dye-Sensitized Solar Cells

Abstract

Developing an efficient synthetic approach for the accurate synthesis of nonprecious metal counter electrode (CE) electrocatalysts with superior catalytic activity and electrochemical stability is critically important for the commercial application of dye-sensitized solar cells (DSSCs). In this study, a new molecular-level synthetic strategy was innovatively developed by copolymerization of melamine and resorcinol with formaldehyde under specific pH conditions and their hydrothermal cooperative assembly with organic–inorganic cobalt phosphate and F127 to construct the high-molecular-weight EDTMPA-Co/melamine-formaldehyde-resorcinol resin/F127 copolymer with good thermal stability and compositional homogeneity. The subsequent carbothermal reduction of EDTMPA-Co using melamine-formaldehyde-resorcinol resin as carbon–nitrogen cosources and F127 as a soft template contributed to the accurate synthesis of uniformly dispersed cobalt phosphide nanoparticles incorporated in a highly nitrogen-doped mesoporous carbon (CoP/NMC) catalyst for the first time. It was found that the abundant mesopores, high-nitrogen-content conductive carbon walls (12.8 atom %), and numerous exposed CoP nanoparticles were creatively formed in the resultant CoP/NMC hybrid, which greatly accelerated the electrolyte/electron transportation and supplied sufficient ion-accessible electrocatalytic nanoactive sites for catalysis. When applied as a CE catalyst, the CoP/NMC hybrid revealed a strong synergistic effect in adsorption and catalytic reduction of triiodide ions, and the CoP/NMC reached a low charge transfer resistance (R ct) of 1.35 Ω. As a consequence, the CoP/NMC CE assembled DSSC delivered a high photo-to-electricity conversion efficiency (η) of 8.53% and exceptional long-term electrochemical stability with a remnant efficiency of 7.80% after 200 h of illumination, outperforming the state-of-the-art Pt. The catalytic mechanism of CoP/NMC CE toward triiodide reduction was studied by density functional theory calculations, which revealed that the relative energy for breaking the I–I bond was significantly improved by chemisorption-induced formation of Co–I covalent bonds between the triiodide intermediate and Coσ+ atoms in the exposed CoP nanoactive sites, and the electrocatalytic reduction of I2* to I–* was substantially facilitated.

Porous organic–inorganic hybrid materials for catalysis, energy and environmental applications

“…Chen et al developed another organic-inorganic hybrid system, where cobalt phosphide nanoparticles were uniformly distributed in N-doped carbon, and the resulting CoP/NMC 20 material showed high efficiency in a dye sensitized solar cell. Here, melamine and resorcinol condensed with formaldehyde in the presence of triblock copolymer F127 under hydrothermal conditions together with cobalt phosphate, resulting in the formation of the CoP/NMC nanocomposite under carbothermal reduction.…”

Efficient Iron Phosphide Catalyst as a Counter Electrode in Dye-Sensitized Solar Cells

“…Metallic Pt possesses excellent catalytic performance, but the high cost limits its widespread application. A variety of alternative materials has been studied as CE materials for DSSCs, such as carbon-based materials, − transition metals, metal chalcogenides, − metal nitrides, metal carbides, polymers, and few compounds made of transition metal phosphides (TMPs). − Among these materials, TMPs are attractive because they offer good electrical conductivity, catalytic activity, and long-term stability . TMPs with a general formula M x P y represent an important class of binary metal/nonmetal catalytic materials with compositions usually being rich in metal or phosphorus.…”

Cost effective dye sensitized solar cell based on novel Cu polypyrrole multiwall carbon nanotubes nanocomposites counter electrode

“…The DSSC assembled with composite CoP / CoMoP 2 CE delivered a high photovoltaic efficiency of 8.69% 38 . The nitrogen doped mesopours carbon and cobalt phosphide nanoparticles composite COP/NMC CE based DSSC exhibit an impressive power conversion efficiency of 8.53% 39 .…”