Active Site Engineering in CoP@NC/Graphene Heterostructures Enabling Enhanced Hydrogen Evolution.
TL;DR: In this article, porous N-doped carbon-encapsulated CoP nanoparticles on both sides of graphene (CoP@NC/GR) are derived from a bimetallic metal-organic framework (MOF)@graphene oxide composite.
Abstract: As the core of an electrocatalyst, the active site is critical to determine its catalytic performance in the hydrogen evolution reaction (HER). In this work, porous N-doped carbon-encapsulated CoP nanoparticles on both sides of graphene (CoP@NC/GR) are derived from a bimetallic metal-organic framework (MOF)@graphene oxide composite. Through active site engineering by tailoring the environment around CoP and engineering the structure, the HER activity of CoP@NC/GR heterostructures is significantly enhanced. Both X-ray photoelectron spectroscopy (XPS) results and density functional theory (DFT) calculations manifest that the electronic structure of CoP can be modulated by the carbon matrix of NC/GR, resulting in electron redistribution and a reduction in the adsorption energy of hydrogen (ΔGH*) from -0.53 to 0.04 eV. By engineering the sandwich-like structure, active sites in CoP@NC/GR are further increased by optimizing the Zn/Co ratio in the bimetallic MOF. Benefiting from this active site engineering, the CoP@NC/GR electrocatalyst exhibits small overpotentials of 105 mV in 0.5 M H2SO4 (or 125 mV in 1 M KOH) to 10 mA cm-2, accelerated HER kinetics with a low Tafel slope of 47.5 mV dec-1, and remarkable structural and HER stability.
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TL;DR: In this article , an efficient in-plane heterostructured CoOOH/Co(OH)2 catalyst was developed via in-situ electrochemical dehydrogenation method, in which the dehydrogenated co-products at the surface synergistically boost the hydrogen evolution reaction (HER) kinetics in base.
15 citations
TL;DR: In this article , the synergistic effect of metal-organic frameworks (MOFs) and carbon-based hybrid materials (Co/CHMs) in the field of overall water splitting is discussed.
Abstract: Ranging from structure to property, the design of reasonable structures leading to high-performance electrochemical properties has enabled metal–organic frameworks (MOFs) to have great achievement in energy conversion. Since Co(II) has multiple valence states and is especially abundant, CoMOFs have emerged as latent materials of electrocatalysts in overall water splitting. In fact, CoMOFs/carbon-based hybrid materials (Co/CHMs) exhibit all kinds of architectures, marvelous electrochemical capabilities, and synergistic effects, overcoming the relative insulation of CoMOFs and single structure carbon materials. The synergistic effect of CoMOFs-based materials and carbon materials forming a unique interface can increase the specific surface area and accelerate electron transfer rates, resulting in enhanced overall water splitting. In terms of this review, the various Co/CHMs (carbon = GO/RGO, CNT, and carbon black) are summarized. The relationship between the synergistic effect of Co/CHMs and the activity of overall water splitting is discussed. Finally, this review can supply a certain degree of reference for Co/CHMs as electrocatalysts in the field of overall water splitting and a number of helpful comments for prospective energy materials.
10 citations
TL;DR: In this article , metal-organic framework (MOF)-derived composites have emerged as a promising class of materials for energy conversion systems due to their tunable pore size, large surface area, and high catalytic performance.
2 citations
TL;DR: In this paper , the authors reviewed the applications and challenges of metal-organic frameworks (MOFs) in electrocatalytic water splitting and highlighted typical development strategies (e.g., construction of multi-metallic site of MOF-based materials, structural morphology designing and controlling, engineering of doping, defect, vacancy, coupling with conductive carrier or constructing heterostructures).
1 citations
TL;DR: In this paper , a metal-organic framework derived from carbon is used as a precursor to increase hydrogen evolution reaction (HER) and water splitting with its advanced features of large surface area and exposed active sites.
Abstract: Metal-organic frameworks (MOFs) are highly porous structures that are made up of metal ions/cluster and organic ligands. Its large surface area and tuneable pore size make it efficient for the storage of clean energy, particularly hydrogen gas. Synthetic methods of MOF have been developed over the years by either doping with nanoparticles or noble metals. They are also employed in polymers, carbons, ionic liquids as well as solid inorganic compounds to increase the efficiency of MOFs as an energy storage unit. However, its poor conductivity and low stability are one of the limitations that can hinder potential applications. This is why hybrid MOFs-carbon are proposed to overcome such limitations. Carbon with its extensive and conductive matrix can act as a template for MOF to further enhance hydrogen and other gas storage capacities, electrocatalysis, and energy storage and conversion. This review mainly focuses on a metal-organic framework derived from carbon as a precursor to increase hydrogen evolution reaction (HER) and water splitting with its advanced features of large surface area and exposed active sites. We briefly discuss the relationship between the designs and the HER activity, morphology, characterization, and synthetic methods. Last but not least, the challenges and limitations are also mentioned in this article. One of the major problems for electrochemical water splitting is that it requires a high overpotential and is constricted by oxygen evolution reaction (OER) and HER occurring at the same time. It is difficult to obtain a highly functioning catalyst that is low in cost and stable. In spite of many achievements, metal-organic framework-derived carbon composites are seen as an excellent bifunctional catalyst for overall water splitting when doped with other inexpensive metals or nanoparticles in harsh alkaline/acid conditions.
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TL;DR: A novel hybrid nanostructure with CoP nanoparticles embedded in a N-doped carbon nanotube hollow polyhedron (NCNHP) through a pyrolysis-oxidation-phosphidation strategy derived from core-shell ZIF-8@ZIF-67 is reported, benefiting from the synergistic effects between highly active CoP NPs and NCNHP.
Abstract: The construction of highly active and stable non-noble-metal electrocatalysts for hydrogen and oxygen evolution reactions is a major challenge for overall water splitting. Herein, we report a novel hybrid nanostructure with CoP nanoparticles (NPs) embedded in a N-doped carbon nanotube hollow polyhedron (NCNHP) through a pyrolysis–oxidation–phosphidation strategy derived from core–shell ZIF-8@ZIF-67. Benefiting from the synergistic effects between highly active CoP NPs and NCNHP, the CoP/NCNHP hybrid exhibited outstanding bifunctional electrocatalytic performances. When the CoP/NCNHP was employed as both the anode and cathode for overall water splitting, a potential as low as 1.64 V was needed to achieve the current density of 10 mA·cm–2, and it still exhibited superior activity after continuously working for 36 h with nearly negligible decay in potential. Density functional theory calculations indicated that the electron transfer from NCNHP to CoP could increase the electronic states of the Co d-orbital a...
1,411 citations
TL;DR: A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low-temperature phosphidation of a Co3O4/C NT precursor and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm(-2), respectively.
Abstract: The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. The strongly acidic conditions in proton exchange membranes create a need for acid-stable HER catalysts. A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low-temperature phosphidation of a Co3O4/CNT precursor. As a novel non-noble-metal HER catalyst operating in acidic electrolytes, the nanohybrid exhibits an onset overpotential of as low as 40 mV, a Tafel slope of 54 mV dec−1, an exchange current density of 0.13 mA cm−2, and a Faradaic efficiency of nearly 100 %. This catalyst maintains its catalytic activity for at least 18 hours and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm−2, respectively.
1,007 citations
TL;DR: Density functional theory (DFT) calculations indicate that the ultrathin graphene shells strongly promote electron penetration from the CoNi nanoalloy to the graphene surface, which results in superior HER activity on the graphene shells.
Abstract: Major challenges encountered when trying to replace precious-metal-based electrocatalysts of the hydrogen evolution reaction (HER) in acidic media are related to the low efficiency and stability of non-precious-metal compounds. Therefore, new concepts and strategies have to be devised to develop electrocatalysts that are based on earth-abundant materials. Herein, we report a hierarchical architecture that consists of ultrathin graphene shells (only 1-3 layers) that encapsulate a uniform CoNi nanoalloy to enhance its HER performance in acidic media. The optimized catalyst exhibits high stability and activity with an onset overpotential of almost zero versus the reversible hydrogen electrode (RHE) and an overpotential of only 142 mV at 10 mAcm(-2), which is quite close to that of commercial 40% Pt/C catalysts. Density functional theory (DFT) calculations indicate that the ultrathin graphene shells strongly promote electron penetration from the CoNi nanoalloy to the graphene surface. With nitrogen dopants, they synergistically increase the electron density on the graphene surface, which results in superior HER activity on the graphene shells.
984 citations
TL;DR: New 2D sandwich-like zeolitic imidazolate framework (ZIF) derived graphene-based nitrogen-doped porous carbon sheets (GNPCSs) obtained by in situ growing ZIF on graphene oxide (GO) show comparable onset potential, higher current density, and especially an excellent tolerance to methanol and superior durability in the ORR.
Abstract: Nitrogen-doped carbon (NC) materials have been proposed as next-generation oxygen reduction reaction (ORR) catalysts to significantly improve scalability and reduce costs, but these alternatives usually exhibit low activity and/or gradual deactivation during use. Here, we develop new 2D sandwich-like zeolitic imidazolate framework (ZIF) derived graphene-based nitrogen-doped porous carbon sheets (GNPCSs) obtained by in situ growing ZIF on graphene oxide (GO). Compared to commercial Pt/C catalyst, the GNPCSs show comparable onset potential, higher current density, and especially an excellent tolerance to methanol and superior durability in the ORR. Those properties might be attributed to a synergistic effect between NC and graphene with regard to structure and composition. Furthermore, higher open-circuit voltage and power density are obtained in direct methanol fuel cells.
807 citations
761 citations