Metal–Organic Frameworks Derived Cobalt Phosphide Architecture Encapsulated into B/N Co-Doped Graphene Nanotubes for All pH Value Electrochemical Hydrogen Evolution
TL;DR: In this paper, a bottom-up strategy for synthesis of transition metal phosphide (TMP) architecture encapsulated into BCN nanotubes (CoP@BCN) through pyrolysis and phosphidation is introduced.
Abstract: DOI: 10.1002/aenm.201601671 easy for the agglomeration under high current and long-term testing for HER, which showed poor stability and exhibited low HER activity irrespective of pH value.[7] Recently, researchers employed carbon shell to protect the metal or their compounds NPs from acidic atmospheric degradation and agglomeration with neighboring NPs.[8] These new metal/carbon composites not only enabled the catalytic applications of metal NPs which are also not stable as the naked in ambient atmosphere, but also improved their electron transport to certain extent. However, if the carbon layers on active species are too thick or with low porosity, it could hinder the desired access of mass transport, and as a result catalytic activity of metal is significantly decreased.[9] In this regard, recently developed in situ technology to prepare metal@carbon by using metal–organic frameworks (MOFs) as precursors has highlighted new functionality for such application.[10] MOFs are crystalline regular porous materials prepared by the coupling of metal ions with organic linkers,[11] and their derived composites, like nitrogendoped porous carbon, exhibit large surface area and hierarchical pore structures, which play important roles to ample the various catalytic reactions, such as HER, oxygen reduction, and evolution reaction.[12] However, such kind of materials consisted of some low degree of graphitization and poor bonding interactions between active metal NPs and derived carbon.[13] To improve the electron transport and valid mass diffusion path for HER, we apply this concept by using B/N co-doped graphene (BCN) nanotubes to confine MOF-derived CoP NPs. Furthermore, it is well documented that chemical replacement of carbon atom by nitrogen (N) and boron (B) can modulate the charge polarization of carbon nanotubes.[14] In particular, the two elements are reverse in electronegativity to that of carbon as B and N co-doping could activate the electron spin density between heteroatom and adjacent carbon atom. Thus, synergistic effect of ternary system of BCN nanotubes greatly enlarges the catalytic surface area.[14a,15] Meanwhile, it is anticipated that co-doping of B and N in graphene nanotubes encapsulated metal phosphide NPs will not only prevent the agglomeration of metal but also produce the additional active sites to enhance the HER performance. To the best of our knowledge, encapsulation of metal phosphide NPs in heteroatom graphitic nanotubes is a challenging task and has rarely been reported. Herein, we introduce a bottom-up strategy for synthesis of CoP architecture encapsulated into BCN nanotubes (CoP@BCN) through pyrolysis and phosphidation as shown in Owing to the increasing worldwide concern over energy crisis and environmental issues, great attention has been triggered for the development of clean and highly efficient energy conversion and storage techniques by electrocatalytic reaction in recent years.[1] As a promising candidate for the future energy supply, molecular hydrogen (H2) possess the highest gravimetric energy density and produced from electrocatalytic water splitting. The highly efficient electrocatalysts are crucial for lower overpotential to improve the energy transfer efficiency in hydrogen evolution reaction (HER).[2] Traditionally, rare earth metal Pt has been regarded as the best electrocatalyst to accelerate the kinetics in HER which is a prerequisite.[3] Unfortunately, their commercial applications are impeded by high cost and scarcity.[4] A key strategy to replace the precious Pt catalyst with earth abundant metals would promote global scalability of such potential clean energy applications.[5] Thus motivated by these several challenges, the search for a cost-effective, large earth abundant, highly efficient, and long stability has been made of immense significance toward earth-enriched metal for HER electrocatalysts. Recently, transition metal phosphide (TMP) based electrocatalysts have been broadly applied for HER activity.[5] Among the existing myriad of TMP, cobalt phosphide (CoP) has been identified as a promising candidate for HER as compared to iron, copper, nickel, and tungsten phosphides.[6] It has been identified that phosphorus (P) atom insertion into cobalt crystal lattice plays a crucial role for HER performance, because P atoms with more electronegativity can grab electron from metal atoms and act as a proton carrier.[2c] Nevertheless, the higher concentration of P in TMP restricts the delocalization of the metal atoms and impede the electron transportation which discards the HER activity.[6f ] Besides this, these electrocatalysts with certain morphologies of nanoparticles (NPs) or nanowires (NWs) are
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TL;DR: A wide range of applications based on these materials for ORR, OER, HER and multifunctional electrocatalysis are discussed, with an emphasis on the required features of MOF-derived carbon-based materials for the Electrocatalysis of corresponding reactions.
Abstract: Oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are three key reactions for the development of green and sustainable energy systems. Efficient electrocatalysts for these reactions are highly desired to lower their overpotentials and promote practical applications of related energy devices. Metal–organic frameworks (MOFs) have recently emerged as precursors to fabricate carbon-based electrocatalysts with high electrical conductivity and uniformly distributed active sites. In this review, the current progress of MOF-derived carbon-based materials for ORR/OER/HER electrocatalysis is presented. Materials design strategies of MOF-derived carbon-based materials are firstly summarized to show the rich possibilities of the morphology and composition of MOF-derived carbon-based materials. A wide range of applications based on these materials for ORR, OER, HER and multifunctional electrocatalysis are discussed, with an emphasis on the required features of MOF-derived carbon-based materials for the electrocatalysis of corresponding reactions. Finally, perspectives on the development of MOF-derived carbon-based materials for ORR, OER and HER electrocatalysis are provided.
970 citations
TL;DR: This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER.
Abstract: Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.
923 citations
TL;DR: In this paper, the authors systematically summarize the versatile synthetic strategies to fabricate MOF-derived porous materials and give an overview on their recent progress on organic heterogeneous catalysis, photocatalysis and electrocatalysis.
672 citations
TL;DR: In this article, a rational design of hollow Mo-doped CoP (Mo-CoP) nanoarrays, which simultaneously combine electronic structure modification through doping with a high density of reaction sites through nanostructuring, is reported.
558 citations
TL;DR: This strategy of using a diverse MOF as a structural and compositional material to create a new multifunctional composite/hybrid may expand the opportunities to explore highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.
Abstract: Metal-organic frameworks (MOFs) have recently emerged as a type of uniformly and periodically atom-distributed precursor and efficient self-sacrificial template to fabricate hierarchical porous-carbon-related nanostructured functional materials. For the first time, a Cu-based MOF, i.e., Cu-NPMOF is used, whose linkers contain nitrogen and phosphorus heteroatoms, as a single precursor and template to prepare novel Cu3 P nanoparticles (NPs) coated by a N,P-codoped carbon shell that is extended to a hierarchical porous carbon matrix with identical uniform N and P doping (termed Cu3 P@NPPC) as an electrocatalyst. Cu3 P@NPPC demonstrates outstanding activity for both the hydrogen evolution and oxygen reduction reaction, representing the first example of a Cu3 P-based bifunctional catalyst for energy-conversion reactions. The high performances are ascribed to the high specific surface area, the synergistic effects of the Cu3 P NPs with intrinsic activity, the protection of the carbon shell, and the hierarchical porous carbon matrix doped by multiheteroatoms. This strategy of using a diverse MOF as a structural and compositional material to create a new multifunctional composite/hybrid may expand the opportunities to explore highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.
499 citations
References
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TL;DR: The Co₃O₄/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER.
Abstract: Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co₃O₄ nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co₃O₄ or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co₃O₄/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co₃O₄ and graphene.
4,898 citations
TL;DR: This work engineer the surface structure of MoS(2) to preferentially expose edge sites to effect improved catalysis by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS (2) bicontinuous network with nanoscaled pores.
Abstract: Controlling surface structure at the atomic scale is paramount to developing effective catalysts. For example, the edge sites of MoS(2) are highly catalytically active and are thus preferred at the catalyst surface over MoS(2) basal planes, which are inert. However, thermodynamics favours the presence of the basal plane, limiting the number of active sites at the surface. Herein, we engineer the surface structure of MoS(2) to preferentially expose edge sites to effect improved catalysis by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS(2) bicontinuous network with nanoscaled pores. The high surface curvature of this catalyst mesostructure exposes a large fraction of edge sites, which, along with its high surface area, leads to excellent activity for electrocatalytic hydrogen evolution. This work elucidates how morphological control of materials at the nanoscale can significantly impact the surface structure at the atomic scale, enabling new opportunities for enhancing surface properties for catalysis and other important technological applications.
2,792 citations
TL;DR: The catalytically active Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.
Abstract: Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solutions, under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high density of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.
2,441 citations
TL;DR: A highly active and durable class of electrocatalysts is synthesized by exploiting the structural evolution of platinum-nickel (Pt-Ni) bimetallic nanocrystals by exploitingThe starting material, crystalline PtNi3 polyhedra, transforms in solution by interior erosion into Pt3Ni nanoframes with surfaces that offer three-dimensional molecular accessibility.
Abstract: Control of structure at the atomic level can precisely and effectively tune catalytic properties of materials, enabling enhancement in both activity and durability. We synthesized a highly active and durable class of electrocatalysts by exploiting the structural evolution of platinum-nickel (Pt-Ni) bimetallic nanocrystals. The starting material, crystalline PtNi3 polyhedra, transforms in solution by interior erosion into Pt3Ni nanoframes with surfaces that offer three-dimensional molecular accessibility. The edges of the Pt-rich PtNi3 polyhedra are maintained in the final Pt3Ni nanoframes. Both the interior and exterior catalytic surfaces of this open-framework structure are composed of the nanosegregated Pt-skin structure, which exhibits enhanced oxygen reduction reaction (ORR) activity. The Pt3Ni nanoframe catalysts achieved a factor of 36 enhancement in mass activity and a factor of 22 enhancement in specific activity, respectively, for this reaction (relative to state-of-the-art platinum-carbon catalysts) during prolonged exposure to reaction conditions.
2,252 citations
TL;DR: Fe-N-C materials quasi-free of crystallographic iron structures after argon or ammonia pyrolysis are synthesized, demonstrating that the turnover frequency of Fe-centred moieties depends on the physico-chemical properties of the support.
Abstract: While platinum has hitherto been the element of choice for catalysing oxygen electroreduction in acidic polymer fuel cells, tremendous progress has been reported for pyrolysed Fe-N-C materials. However, the structure of their active sites has remained elusive, delaying further advance. Here, we synthesized Fe-N-C materials quasi-free of crystallographic iron structures after argon or ammonia pyrolysis. These materials exhibit nearly identical Mossbauer spectra and identical X-ray absorption near-edge spectroscopy (XANES) spectra, revealing the same Fe-centred moieties. However, the much higher activity and basicity of NH3-pyrolysed Fe-N-C materials demonstrates that the turnover frequency of Fe-centred moieties depends on the physico-chemical properties of the support. Following a thorough XANES analysis, the detailed structures of two FeN4 porphyrinic architectures with different O2 adsorption modes were then identified. These porphyrinic moieties are not easily integrated in graphene sheets, in contrast with Fe-centred moieties assumed hitherto for pyrolysed Fe-N-C materials. These new insights open the path to bottom-up synthesis approaches and studies on site-support interactions.
1,561 citations