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Developing an efficient and low-cost synthetic approach to controllably synthesize non-precious-metal counter electrode (CE) electrocatalysts with superior catalytic activity and electrochemical stability is critically important for the mass production of dye-sensitized solar cells (DSSCs). Herein, we proposed a simple, economical, and easily scalable synthetic route for copyrolysis of melamine and nickel acetate precursors to access the well-defined Ni-encapsulated and nitrogen-doped carbon nanotubes (Ni-NCNTs). The synthetic mechanism was comprehensively investigated by creatively analyzing the phase structure evolution and dynamical decomposition behaviors, and revealed the construction of Ni-NCNTs based on the Ni-catalyzed tip-growth mechanism. Furthermore, the meticulous structural design of Ni nanoparticles intercalated in N-doped CNTs endows Ni-NCNTs with homogeneously distributed Ni–C interfaces, abundant structural defects, and a porous architecture, as well as good electrical conductivity and corrosion-resistance properties. When used as counter electrode for DSSCs, the device delivers a high power conversion efficiency of 8.94% under simulated sunlight (AM 1.5, 100 mW cm–2) and long-term stability with a remnant efficiency of 8.34% after 100 h of illumination, superior to those of conventional Pt. The outstanding catalytic performance of Ni-NCNTs was mainly attributed to the synergetic effect of intercalated Ni with N-doped CNTs at the unique Ni–C interfaces, and the concomitant electronic interaction of Ni and N with C atoms in the interfacial nanoregime. The systematic studies on the synthetic mechanism and structure–activity relationship provide a new insight into the rational design of structural and electronic properties for high-performance Ni-NCNT CEs, as well as into the fundamental understanding of their catalytic mechanism for triiodide reduction.

Ultralight benzoxazine-derived porous nitrogen self-doped carbon aerogels with good yield can be prepared by direct polymerization of trifunctional benzoxazine monomers under acid catalysis using concentrated hydrochloric acid. This allows for a significantly widened density range (0.8-4.5 mg cm-3) and avoids any sacrificial etching. When serving as electrode materials for supercapacitors, the resulting hierarchical porous carbon aerogels show ultrahigh specific capacitance, excellent rate performance and good cycling stability (retention of 97.3% even after 10 000 continuous charge-discharge cycles). Besides energy storage devices, the interconnected nanoporous carbon aerogels can also find applications in oil/water separation, heavy metal removal, catalyst supports, and so forth.

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Hydrothermal treatment of nickel acetate and phosphoric acid aqueous solution followed with a carbothermal reduction assisted phosphorization process using sucrose as the carbon source for the controlled synthesis of NiP/C was successfully realized for the first time. The critical synthesis factors, including reduction temperature, phosphorus/nickel ratio, pH, and sucrose amount were systematically investigated. Remarkably, the carbon serves as a reducer and plays a determinative role in the transformation of NiPO into NiP/C. The synthesis strategy is divided into four distinguishable stages: (1) hydrothermal preparation of Ni(PO)·8HO precursor for stabilizing P sources; (2) dimerization of Ni(PO)·8HO into more thermal stable NiPO amorphous phase along with the generation of NiO; (3) carbothermal reduction and phosphidation of NiO into NiP (0 ≤ y/x ≤ 0.5); and (4) further phosphidation of mixed-phase NiP and carbothermal reduction of NiPO into single-phase NiP. The resultant NiP, the highly active phase in electrocatalysis, was applied as counter electrode in a dye-sensitized solar cell (DSSC). The DSSC based on NiP with 10.4 wt.% carbon delivers a power conversion efficiency of 9.57%, superior to that of state-of-the-art Pt-based cell (8.12%). The abundant Ni and P active sites and the metal-like conductivity account for its outstanding catalytic performance.

A new class of hybrids with the unique electrocatalytic nanoarchitecture of FeS anchored on FeC-encapsulated and N-doped carbon nanotubes (FeS/FeC-NCNTs) is innovatively synthesized through a facile one-step carbonization-sulfurization strategy. The efficient synthetic protocols on phase structure evolution and dynamic decomposition behavior enable the production of the FeS/FeC-NCNT hybrid with advanced structural and electronic properties, in which the Fe vacancy-contained FeS showed the 3d metallic state electrons and an electroactive Fe in +2/+3 valence, and the electronic structure of the CNT was effectively modulated by the incorporated FeC and N, with the work function decreased from 4.85 to 4.63 eV. The meticulous structural, electronic, and compositional control unveils the unusual synergetic catalytic properties for the FeS/FeC-NCNT hybrid when developed as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), in which the FeC- and N-incorporated CNTs with reduced work function and increased charge density provide a highway for electron transport and facilitate the electron migration from FeC-NCNTs to ultrahigh active FeS with the electron-donating effect, and the Fe vacancy-enriched FeS nanoparticles exhibit ultrahigh I adsorption and charge-transfer ability. As a consequence, the DSSC based on the FeS/FeC-NCNT CE delivers a high power conversion efficiency of 8.67% and good long-term stability with a remnant efficiency of 8.00% after 168 h of illumination, superior to those of traditional Pt. Furthermore, the possible catalytic mechanism toward I reduction is creatively proposed based on the structure-activity correlation. In this work, the structure engineering, electronic modulation, and composition control opens up new possibilities in constructing the novel electrocatalytic nanoarchitecture for highly efficient CEs in DSSCs.