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In this study, we developed a novel confinement-synthesis approach to layered double hydroxide nanodots (LDH-NDs) anchored on carbon nanoparticles, which formed a three-dimensional (3D) interconnected network within a porous carbon support derived from pyrolysis of metal-organic frameworks (C-MOF). The resultant LDH-NDs@C-MOF nonprecious metal catalysts were demonstrated to exhibit super-high catalytic performance for oxygen evolution reaction (OER) with excellent operation stability and low overpotential (∼230 mV) at an exchange current density of 10 mAcm−2. The observed overpotential for the LDH-NDs@C-MOF is much lower than that of large-sized LDH nanosheets (321 mV), pure carbonized MOF (411 mV), and even commercial RuO2 (281 mV). X-ray absorption measurements and density functional theory (DFT) calculations revealed partial charge transfer from Fe3+ through an O bridge to Ni2+ at the edge of LDH-NDs supported by C-MOF to produce the optimal binding energies for OER intermediates. This, coupled with a large number of exposed active sides and efficient charge and electrolyte/reactant/product transports associated with the porous 3D C-MOF support, significantly boosted the OER performance of the LDH-ND catalyst with respect to its nanosheet counterpart. Apart from the fact that this is the first active side identification for LDH-ND OER catalysts, this work provides a general strategy to enhance activities of nanosheet catalysts by converting them into edge-rich nanodots to be supported by 3D porous carbon architectures.

The development of catalysts with high activity and selectivity for electrochemical reduction of CO2 could provide renewable energy sources and improved environmental remediation. However, most current electrocatalysts have large energy barriers that lower their activity and selectivity. Here, we designed a class of electrocatalysts with 3d transition bimetallic active sites embedded into covalent organic frameworks (COFs) and discovered that they were more efficient than noble metals and single-atom electrocatalysts in CO2 reduction reaction to CO. To facilitate rational design and quick screening of desired catalysts, an intrinsic descriptor was identified for the catalysts, which correlates the catalytic activity with the topological, bonding, and electronic structures. Among the catalysts, Fe/Cu-, Ni/Zn-COFs could be excellent electrocatalysts, with the low overpotential (~0.25 V) while suppressing side reactions. The excellent activity and selectivity of the catalysts stems from their unique bimetallic sites that break the constraint of scaling relations, leading to much more adsorption modes and facilitating intermediates to achieve the ideal states.

Proton exchange fuel cells (PEFCs) are one of the most popular and promising energy conversion devices because of their highly stable and efficient membranes in acidic media, but there is a lack of durable non-noble metal electrocatalysts suitable for acidic environments. Herein, we designed a new type of electrocatalysts consisting of transition metal halide molecules covered by graphene sheets, which is supported by experiments. To rapidly screen the best catalysts from numerous candidate materials, the electronic structures, reaction free energies and overpotentials of those graphene-covered halide catalysts were studied by the first-principles calculations to predict the catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). An intrinsic descriptor, the electrostatic force induced by the metallic ions, was found to well describe the catalytic activities and provide a better understanding of the local electrical field effects on catalytic activities. The spin-down d-band center was also introduced to describe catalytic activities of the catalysts. The results demonstrate that the graphene-covered CrBr2 shows the best bifunctional catalytic activities for fuel cells while graphene-covered CoF2 could well facilitate H2O2 production. These catalysts are better than the best commercial noble metal catalysts (e.g., Pt and RuO2) in terms of overpotentials and activities. This work provides a theoretical base for rationally designing durable electrocatalysts with excellent catalytic activities.

In 3+ co-doped YVO 4 :5%Eu 3+ red phosphors were synthesized via a facile hydrothermal method. The impacts of In 3+ co-doping concentration onto the crystal structure, morphology, and photoluminescence properties were elucidated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectra, and the luminescence intensity change. The results indicated that with increasing the In 3+ co-doping concentration, the intensity of excitation and emission spectra was continuously increased, reached maximum at In 3+ concentration of 5 mol%, and then was diminished for higher In 3+ content which indicated concentration quenching. The distinct enhancement of the photoluminescence of YVO 4 :Eu 3+ , In 3+ phosphors at lower In 3+ co-doping concentration can be attributed to the incorporation of In 3+ improving the host lattice absorption of YVO 4 . Thereafter, with the increase of In 3+ concentration exceeding 5 mol%, the emission intensity was decreased which is mainly due to the fact that the electronegativity of indium is greater than yttrium, and it is not beneficial to the charge transfer process of O 2− → V 5+ inside the VO 4 3− ions, thus further weakening the energy transfer from VO 4 3− groups to Eu 3+ ions.

Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) both have sluggish kinetics, which normally requires the use of noble metal-based catalysts (e.g. RuO2, IrOx and Pt). Unfortunately, the high cost of these noble metals has severely restricted their large-scale applications. Herein, we report the fabrication of a cost-effective OER/ORR bifunctional catalyst by embedding atomic Fe–Ni dual metal pairs into nitrogen-doped carbon hollow spheres (Fe–NiNC-50). The resultant catalyst shows exceptional catalytic performance towards both OER and ORR, which is even comparable to the noble metal-based benchmarks. By virtue of its bi-functionality, a rechargeable zinc-air battery is constructed and presents high power density (~220 mW cm−2), stable discharge voltage and large specific energy density (~932.66 Wh kgZn−1). Moreover, the rechargeable Zn-air battery exhibits long-term durability in a charge-discharge cycling test (100 h) with negligible performance degradation. The outstanding bifunctional catalytic performance can be ascribed to the formation of Fe–Ni atomic pairs, which imposes mutual effects for tuning electronic structures of both Fe and Ni sites. Experiments and theoretical calculations further unravel that the electronically modified Ni and Fe atoms are the active sites for OER and ORR, respectively, facilitating both OER and ORR by tuning the binding energy of the reaction intermediates.

Carbon nanomaterials are promising metal-free catalysts for energy conversion and storage, but the catalysts are usually developed via traditional trial-and-error methods. To rationally design and accelerate the search for the highly efficient catalysts, it is necessary to establish design principles for the carbon-based catalysts. Here, theoretical analysis and material design of metal-free carbon nanomaterials as efficient photo-/electrocatalysts to facilitate the critical chemical reactions in clean and sustainable energy technologies are reviewed. These reactions include the oxygen reduction reaction in fuel cells, the oxygen evolution reaction in metal-air batteries, the iodine reduction reaction in dye-sensitized solar cells, the hydrogen evolution reaction in water splitting, and the carbon dioxide reduction in artificial photosynthesis. Basic catalytic principles, computationally guided design approaches and intrinsic descriptors, catalytic material design strategies, and future directions are discussed for the rational design and synthesis of highly efficient carbon-based catalysts for clean energy technologies.

Covalent organic frameworks (COFs) are promising for catalysis, sensing, gas storage, adsorption, optoelectricity, etc. owning to the unprecedented combination of large surface area, high crystallinity, tunable pore size, and unique molecular architecture. Although COFs are in their initial research stage, progress has been made in the design and synthesis of COF-based electrocatalysis for the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and CO2 reduction in energy conversion and fuel generation. Design principles are also established for some of the COF materials toward rational design and rapid screening of the best electrocatalysts for a specific application. Herein, the recent advances in the design and synthesis of COF-based catalysts for clean energy conversion and storage are presented. Future research directions and perspectives are also being discussed for the development of efficient COF-based electrocatalysts.

Solar fuels produced from sunlight via photocatalytic water splitting and artificial photosynthesis represent one of the most promising clean energy sources. Various semiconductors, including graphitic carbon nitride (g-C3N4) and transition metal oxides, have been considered as photocatalysts for the fuel production, but there lacks of the design principles for rapid screening of the best photocatalysts from numerous candidate materials. Here, we demonstrate, for the first time, a universal guiding principle that governs the photocatalytic activities of p-orbital element-doped C3N4-based photocatalysts for photocatalytic water splitting, which is also applicable to other doped semiconductors including ZnO and TiO2 for water splitting and carbon dioxide reduction. An activity indictor is introduced to determine the efficiency of non-metal-doped semiconductor photocatalysts for the solar fuel production. These predictions are supported by experimental results. This generalized principle could guide a broad photochemical production of solar fuels including hydrogen, hydrocarbon, and other green chemicals.