Niobium- and cobalt-modified dual-source-derived porous carbon with a honeycomb-like stable structure for supercapacitor and hydrogen evolution reaction.

Designing porous carbon materials with tailored architecture and appropriate compositions is essential for supercapacitor (SC) and hydrogen evolution reaction (HER). Herein, Nb/Co-modified dual-source porous carbon (Nb/Co-DSPC) with a honeycomb structure was obtained by introducing a secondary carbon source (Co/Zn-ZIF) and transition metal Nb into activated Typha carbon (ATC). The addition of a secondary carbon source and Nb resulted in superior specific surface area (1272.38 m2/g), excellent hydrophilicity (34.73°) and abundant bimetallic active sites (Nb/Co-Nx) in Nb/Co-DSPC, providing excellent charge storage capacity and electrocatalytic activity. The Nb/Co-DSPC electrode displayed an outstanding capacitance of 337 F/g at 0.5 A/g and showed excellent stability after 15,000 charge-discharge cycles. In addition, Nb/Co-DSPC shows an overpotential of 114 mV at 10 mA cm-2, better than those of Co-DSPC (139 mV) and ATC (162 mV) alone. This study offers a reliable strategy for advanced multifunctional porous carbon electrode materials preparations.

Designing nitrogen-enriched heterogeneous NiS@CoNi2S4 embedded in nitrogen-doped carbon with hierarchical 2D/3D nanocage structure for efficient alkaline hydrogen evolution and triiodide reduction.

Fabrication of efficient non-precious electrocatalysts with hierarchical nanostructures and the desired compositions is highly desirable to enhance the catalytic activity and stability for hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR). This work proposes a zeolitic imidazolate framework (ZIF) template-based strategy to generate sulfide embedded in nitrogen-doped carbon with a hierarchical 2D/3D nanocage structure. ZIF-67, as a sacrificial template, is first etched to form 2D/3D NiCo layered double hydroxide/2-Methylimidazole (NiCo LDH/MeIm) and then converted to CoNi2S4 nanoparticles embedded in nitrogen-doped carbon (CoNi2S4/NC) through one-step sulfurization and pyrolysis. When a core-shell ZIF-8@ZIF-67 is designed as a template for the generation of Ni@NiCo LDH/MeIm, the obtained NiS@CoNi2S4/NC not only retains the unique 2D/3D nanostructure but also has a high N content, abundant active sites, larger specific surface area, and hierarchical pore distribution. NiS@CoNi2S4/NC mediates an overpotential of 126 mV at 10 mA cm-2 and a Tafel slope of 47.2 mV dec-1 in the alkaline HER. The solar cell equipped with NiS@CoNi2S4/NC as the IRR catalyst achieves a high cell efficiency of 7.96 %. NiS@CoNi2S4/NC shows durably high HER and IRR activity. This controllable synthetic strategy provides a valuable support for developing efficient catalysts in electrocatalytic energy conversion systems.

A multi-dimensional hierarchical strategy building melamine sponge-derived tetrapod carbon supported cobalt-nickel tellurides 0D/3D nanohybrids for boosting hydrogen evolution and triiodide reduction reaction.

Designing efficient nanohybrid electrocatalysts with advanced structure is of great essential for energy conversion devices. Herein, a multi-dimensional hierarchical strategy is proposed to design melamine sponge-derived sulfur and nitrogen co-doped tetrapod carbon (SNTC) supported cobalt-nickel telluride (CoTe2/SNTC, NiTe2/SNTC, and CoNiTe2/SNTC) 1D/3D and 0D/3D nanohybrids for boosting hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR). Among these, the CoNiTe2/SNTC 0D/3D hybrid exhibited superior catalytic activities and excellent electrochemical stability. In alkaline HER, the CoNiTe2/SNTC catalyst had a low Tafel slope of 72 mV dec-1, which was comparable to that of Pt/C (49 mV dec-1). CoNiTe2/SNTC served as counter electrode catalyst in photovoltaics and obtained a power conversion efficiency (PCE) of 8.11%, which is higher than that of Pt (7.25%). This investigation provides a novel approach for designing highly efficient nanohybrid catalysts in advanced energy devices.

Defect engineering tuning electron structure of biphasic tungsten-based chalcogenide heterostructure improves its catalytic activity for hydrogen evolution and triiodide reduction.

The design and exploration of high-efficiency and low-cost electrode catalysts are of great significance to the development of novel energy conversion technologies. In this work, metal and nonmetal heteroatoms co-doped biphasic tungsten-based chalcogenide heterostructured catalyst (Co-WS2/P-WO2.9) with rich defects is successfully synthesized by a vulcanization technique. The electrocatalytic performance of WS2/WO3 in the hydrogen evolution reaction (HER) and triiodide reduction reaction is significantly enhanced by modifying and optimizing its electronic structure through a defect engineering strategy. As an electrocatalyst for HER, the optimized Co-WS2/P-WO2.9 exhibits a low overpotential at 10 mA cm-2 of 146 and 120 mV with small Tafel slopes of 86 and 74 mV dec-1 in alkaline and acidic electrolyte, respectively. In addition, a Co-WS2/P-WO2.9 assembled solar cell yields a short circuit current density of 15.85 mA cm-2, an open-circuit voltage of 0.74 V, a fill factor of 0.66, and a competitive power conversion efficiency (7.83%), which is comparable or higher than conventional Pt-based solar cell (16.02 mA cm-2, 0.70 V, 0.63, 7.14%). The formation of a heterostructure in Co-WS2/P-WO2.9 leads to the presence of a built-in electric field in the interfacial region between Co-WS2 and P-WO2.9, which leads to an increased open-circuit voltage from 0.70 V for Pt to 0.74 V for Co-WS2/P-WO2.9. This work can provide a technical support for developing high-performance heterostructured catalysts, which open up a way for improving catalytic performance of heterostructured catalysts in the field of electrocatalysis.

Designing and Understanding the Outstanding Tri-Iodide Reduction of N-Coordinated Magnetic Metal Modified Defect-Rich Carbon Dodecahedrons in Photovoltaics.

Nitrogen-coordinated metal-modified carbon is regarded as a novel frontier electrocatalyst in energy conversion devices. However, the construction of intrinsic defects in a carbon matrix remains a great challenge. Herein, N-coordinated magnetic metal (Fe, Co) modified porous carbon dodecahedrons (Fe/Co-NPCD) with a large surface area, rich intrinsic defects, and evenly distributed metal-Nx species are successfully synthesized via the rational design of iron precursor and the bimetallic-organic frameworks. Because of a synergistic effect between N-coordinated dual magnetic metal active sites, the Fe/Co-NPCD exhibits exceptional electrocatalytic activity and electrochemical stability. A solar cell fabricates with the Fe/Co-NPCD yields an impressive power conversion efficiency of 8.35% in dye-sensitized solar cells, superior to that of mono-metal-doped carbon-based cells and conventional Pt-based cells. Furthermore, density functional theory calculations illustrate that Fe, Co, and N doping are in favor of improving the adsorption capacity of the catalyst for I3 - species by optimizing the magnetic momentum between the magnetic metal atoms, thereby upgrading its catalytic activity. This work develops a general strategy for synthesizing a high-performance defect-rich carbon-based catalyst, and offers valuable insight into the role of magnetic metals in catalysis, which can be used to guide the design of high-performance catalysts in the energy field.

Implanted metal-nitrogen active sites enhance the electrocatalytic activity of zeolitic imidazolate zinc framework-derived porous carbon for the hydrogen evolution reaction in acidic and alkaline media.

Developing electrocatalysts with excellent catalytic performance and superior durability for hydrogen evolution reaction (HER) remains a challenge. Herein, metal-nitrogen sites (M-Nx, M = Ni and Cu) are successfully implanted into zeolitic imidazolate zinc framework (ZIF-8)-derived nitrogen-doped porous carbon (ZIF/NC) to prepare Ni-ZIF/NC and Cu-ZIF/NC electrocatalysts for the HER. These M-Nx active sites significantly enhanced the electrocatalytic activities of Ni-ZIF/NC and Cu-ZIF/NC. Metal Ni acted as a catalyst for catalysis of Ni-ZIF/NC to form carbon nanotubes-like structures, which provided convenient ion transmission pathways. Owing to its special morphology and an increased number of defects, Ni-ZIF/NC displayed superior electrocatalytic activity in the HER compared to those of Cu-ZIF/NC and ZIF/NC. In an alkaline environment, Ni-ZIF/NC exhibited an overpotential at the current density of 10 mA cm-2 (η10) of 163.0 mV and Tafel slope of 85.0 mV dec-1, demonstrating an electrocatalytic property equivalent to that of Pt/C. In an acidic environment, Ni-ZIF/NC yielded a η10 of 177.4 mV and Tafel slope of 83.9 mV dec-1, which were comparable to those of 20 wt.% Pt/C. Moreover, Ni-ZIF/NC and Cu-ZIF/NC also exhibited superior stabilities in alkaline environments. This work offers a valuable strategy for controlling the morphology and implanting M-Nx active sites into carbon for designing novel catalysts for use in alternative new energy applications.

Boosting catalytic activity of niobium/tantalum-nitrogen active-sites for triiodide reduction in photovoltaics.

To fabricate high-quality catalysts with abundant active sites, a series of transition-metal-modified nitrogenous carbon catalysts (Ta-NOC, Nb-NOC, and Nb/Ta-NOC) was successfully fabricated via pyrolysis and ion exchange. Owing to the high conductivity and ion transport capacity of its unique nitrogen-carbon structure, and synergistic effect of dual-metal active sites on modulating electronic structure, Nb/Ta-NOC catalyst exhibited an excellent catalytic performance and a remarkable electrochemical stability in triiodide reduction reaction (IRR) and hydrogen evolution reaction (HER). Nb/Ta-NOC catalyst achieved an ideal conversion efficiency of 8.45% for IRR in solar cells, which was higher than that of Pt electrode (7.63%). Furthermore, Nb/Ta-NOC catalyst exhibited a small overpotential of 145 mV at a current density of 10 mA·cm-2 and a Tafel slope of 77 mV dec-1 for HER. This work provided a new approach for the rational design of the active-sites-rich electrocatalysts for energy conversion applications.