Shape-tunable Pt–Ag nanocatalysts with excellent performance for oxygen reduction reaction

Shape-tunable PtAg nanocatalysts including PtAg nanoflowers (NFs) and PtAg nanowires (NWs) are prepared by a facile hydrothermal reduction method, via adjusting the precursor ratio of Pt/Ag and subsequent UV-irradiation. Physicochemical characterizations reveal that the as-prepared catalysts have a porous structure, which forms from the conversion of AgCl to Ag nanoparticles. These features favor both oxygen mass transfer and accessibility of active sites. The as-prepared Pt₁Ag₄ NWs exhibit superior catalytic performances for ORR. The mass activity of Pt₁Ag₄ NWs is 11.4 times higher than that of 20% Pt/C. More important, the electrochemically active surface area (ECSA) of Pt₁Ag₄ NWs is 2.5 times larger than that of commercial Pt/C.     

Exploration of unalloyed bimetallic Au–Pt/C nanoparticles for oxygen reduction reaction

The synthesis of carbon-supported unalloyed Au–Pt bimetallic nanoparticles using polyol method at a temperature as low as 85 °C is reported. Various compositions of Au–Pt/C bimetallic nanoparticles are characterized using transmission electron microscopy (TEM), X-ray florescence (XRF), X-ray diffraction and cyclic voltammetry. Electron microscopy shows that the particles have a near-narrow size distribution that peaks at an average size of ∼5 to 6 nm. The electrocatalytic activity of Au–Pt/C nanoparticles towards the oxygen reduction reaction (ORR) is studied by linear sweep polarization measurements obtained using a rotating disc electrode (RDE). The results reveal that a four-electron transfer pathway is mainly operative for ORR and the half-wave potential for ORR on bimetallic Au–Pt/C (20%:20%) is ∼100 mV less negative when compared with that of Pt/C (home-made and E-Tek). Studies of the methanol oxidation reaction (MOR) on these catalysts show that the MOR activity is significantly lowered with increasing content of Au in Au–Pt/C.     

Highly efficient PtCo nanoparticles on Co–N–C nanorods with hierarchical pore structure for oxygen reduction reaction

Developing platinum-based nanoparticles on carbon catalysts with high activity and stability for oxygen reduction reaction (ORR) is of great significance for the practical application of fuel cells. Herein, a synchronous strategy of preparing nano-sized PtCo supported on atomic Co and N co-doped carbon nanorods (PtCo/Co–N–C NR) was developed to replace the conventional method of impregnating Pt sources into ready-made carbon materials, in which metal-organic frameworks (MOFs) with Co and Zn ions of rhombic dodecahedron were first prepared using 2-methylimidazole as building block and then their morphology was transformed into porous nanorods via the reduction of Co ions to Co–B–O complex in the MOFs by NaBH₄; subsequently, Pt was deposited on the Co–Zn MOF nanorods through the displacement reaction of PtCl₆^2- and metallic Co and coordination between MOF and PtCl₆^2-; after pyrolysis and acid-leaching process, highly dispersed PtCo/Co–N–C NR was obtained. Attributed to its unique characteristics of hierarchical pore structure, uniform PtCo alloy nanoparticles with the average size of 7.0 nm and strong supporting interaction effect, the catalyst exhibits high ORR activity and stability with the mass activity of 577.0 mA mg^?1_Pt and specific activity of 1.4 mA cm^?2 at 0.9 V vs RHE in 0.1 M HClO₄, which is about 3.6 times and 3.5 times high than that of commercial Pt/C catalyst respectively. This strategy would provide a flexible route to develop highly active and stable ORR electrocatalysts with various morphologies for optimizing the exposure of active sites.     

Pulse-reverse electrodeposition of Pt–Co bimetallic catalysts for oxygen reduction reaction in acidic medium

Pt–Co electrodeposited by pulse reverse current on carbon cloth (CC) and glassy carbon (GC) are studied. On both substrates, applying a higher reverse current or a longer reverse-time increases the Pt content due to higher Co dissolution from Pt–Co structures, but does not affect the morphology. Despite similar morphologies and compositions deposited on CC or GC, the electrochemical behaviors of Pt–Co on both substrates are significantly different. Distinct hydrogen under-potential deposition (HUPD) adsorption/desorption peaks are not observed on CC, while well-defined peaks are established on GC. Oxygen reduction reaction (ORR) of Pt–Co on CC is significantly higher than on GC due to its highly porous structure. The ORR on GC changes with the Pt content controlled by varying the reverse pulse during electrodeposition, where Pt–Co with 58 at.% Pt or higher provides a better activity than Pt, with 77 at.% Pt having the highest ORR activity.     

Effect of pretreatment on Pt–Co/C cathode catalysts for the oxygen reduction reaction

Carbon supported Pt and Pt–Co electrocatalysts for the oxygen reduction reaction in low temperature fuel cells were prepared by the reduction of the metal salts with sodium borohydride and sodium formate. The effect of surface treatment with nitric acid on the carbon surface and Co on the surface of carbon prior to the deposition of Pt was studied. The catalysts where Pt was deposited on treated carbon the ORR reaction preceded more through the two electron pathway and favored peroxide production, while the fresh carbon catalysts proceeded more through the four electron pathway to complete the oxygen reduction reaction. NaCOOH reduced Pt/C catalysts showed higher activity that NaBH₄ reduced Pt/C catalysts. It was determined that the Co addition has a higher impact on catalyst activity and active surface area when used with NaBH₄ as reducing agent as compared to NaCOOH.     

Mechanically activated Pt–Ni and Pt–Co alloys as electrocatalysts in the oxygen reduction reaction

Mixtures of powders of platinum with nickel or cobalt to obtain Ni_0.75Pt_0.25 or Co_0.75Pt_0.25 were mechanical alloyed by high energy ball milling. The results of crystal structure, morphology and electrocatalytic performance are presented for mechanically activated powders after 3 and 9 h of ball milling. Total solid solutions of Ni and Co with platinum were analyzed by X-ray diffraction after 3 h of ball milling. After 9 h of ball milling, in both cases, the total solid solution was accompanied by the appearance of NiO or CoO and ZrO associated with a redox reaction with the milling media. The presence of zirconium monoxide was confirmed by energy dispersive spectroscopy analysis. In both cases, an amorphization was detected. X ray absorption spectroscopy measurements showed changes in atomic and electronic environment of platinum, a reduction of the distance to the first coordination sphere and increased d-band vacancy vs pure Pt and Pt nanoparticles were observed for both studied systems. The electrocatalytic activity was determined using cyclic and linear voltammetry. The Co_0.75Pt_0.25 alloy milled for 9 h showed a higher electrochemical activity for the oxygen reduction reaction (ORR) compared with the other samples, including Pt-Etek. The degree of the ORR electrochemical activity was correlated with the presence of ZrO, which could affect the oxygen adsorption and improve the catalytic activity for the oxygen reduction reaction.     

Pt and Pt–Ag nanoparticles supported on carbon nanotubes (CNT) for oxygen reduction reaction in alkaline medium

In this work, we investigated the effect of the carbon nanotubes (CNT) as alternative support of cathodes for oxygen reduction reaction (ORR) in alkaline medium. The Pt and Pt–Ag nanomaterials supported on CNT were synthesized by sonochemical method. The crystalline structure, morphology, particle size, dispersion, specific surface area, and composition were investigated by XRD, SEM-EDS, TEM, HR-TEM, N₂ adsorption-desorption and XPS characterization. The electrochemical activity for ORR was evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) in alkaline medium. The electrochemical stability was researched by an accelerated degradation test (ADT). Pt/CNT showed the better electrocatalytic activity towards ORR compared with Pt–Ag/CNT and Pt/C. Pt/CNT exhibited higher specific activity (1.12 mA cm^?2 _Pt) than Pt/C (0.25 mA cm^?2 _Pt) which can be attributed to smaller particle size, Pt-CNT interaction, and Pt load (5 wt%). The Pt monometallic samples supported on CNT and Vulcan showed higher electrochemical stability after ADT than Pt–Ag bimetallic. The ORR activity of all materials synthesized proceeded through a four-electron pathway. Furthermore, the EIS results showed that Pt/CNT exhibited the lower resistance to the transfer electron compared with conventional Pt/C and Pt–Ag/CNT.     

Well-dispersed Co–Co3O4 hybrid nanoparticles on N-doped carbon nanosheets as a bifunctional electrocatalyst for oxygen evolution and reduction reactions

Bifunctional catalysts are vital for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in metal-air batteries. In this work, Co–Co₃O₄/N-doped carbon nanosheets (NCNs) were developed as highly efficient bifunctional oxygen catalysts via the pyrolysis of a hybrid ZIF-67/CNs precursor. It is found that the introduced CNs play important roles. On one hand, the introduced CNs can tune the surface contents of Co, N and/or O species that are closely correlated with OER and ORR activity. On the other hand, they also facilitate to achieve high specific surface areas for the catalysts. In addition, the introduced CNs helps the formed Co–Co₃O₄ hybrid nanoparticles with uniform and small sizes to be well-distributed on the NCNs substrates. Despite such important roles, it should be noted that a moderate content of the introduced CNs is required to achieve optimal oxygen catalytic activity. As a result, the optimized ZIF-67/CNs(1)-600 exhibits a low value of η₁₀ (~350 mV) for OER and a high value of E_1/2 (~0.85 V) for ORR. Its overall bifunctional activity (ΔE) is as low as ~0.73 V, which is comparable to the recent reported Co-based catalysts.     

Cr2O3 nanoparticles boosting Cr–N–C for highly efficient electrocatalysis in acidic oxygen reduction reaction

Transition metal–nitrogen–carbon (M–N–C) catalysts have attracted significant attention for catalyzing oxygen reduction reactions (ORR). In this study, a porous Cr₂O₃@Cr–N–C catalyst with a small amount of Cr₂O₃ nanoparticles loaded on the surface of Cr–N₄–C nanomaterials was prepared using synergistic heat treatment (SHT) method with zeolite imidazole frameworks (ZIFs) as precursors. TEM and spherical aberration-corrected TEM results demonstrated the presence of hollow morphologies, Cr₂O₃ nanoparticles and atomic-level Cr distribution in Cr₂O₃@Cr–N–C. XPS, XRD and XAFS analysis indicated the coexistence of Cr₂O₃ nanoparticles and Cr–N₄ sites which were believed to act as active centers for ORR. In 0.1 M HClO₄, this material showed outstanding ORR catalytic activity with a half-wave potential of 0.78 V that was 40 mV higher than the traditional heat treatment derived Cr–N–C. It also revealed relatively low Tafel slope of 52.2 mV dec^?1; 4-electron pathway; remarkable stability and long-term durability. The improved ORR performance is mainly attributed to the synergy between Cr–N₄ active center and Cr₂O₃ nanoparticle. The SHT strategy reported here provides a new route to prepare highly efficient non-precious metal M?N–C catalysts with greater ORR activity and stability in acidic environments.     

Pt–Co nanoparticles anchored by ZrO2 for highly efficient and durable oxygen reduction reaction in H2-air fuel cells

Synthesis of Pt-based catalysts with high activity and durability for oxygen reduction reaction (ORR) remains a very challenging task in the field of fuel cells. Here, Co-doped Pt nanoparticles (NP) with surface-defect ZrO₂ are supported on the multi-walled carbon nanotubes (MWCNTs) (denoted as Pt–Co + ZrO₂/MWCNTs). The Pt–Co + ZrO₂/MWCNTs displays an ORR mass activity of 0.98 A mg_Pt^?1 at 0.9 V, which is 4.1-fold higher than that of the commercial Pt/C (0.238 A mg_Pt^?1). Further durability test shows that the Pt–Co + ZrO₂/MWCNTs remains nearly unchanged ORR mass activity after 50000 accelerated durability testings (ADTs). Based on the mass performance and surface performance, the fuel cell with Pt–Co + ZrO₂/MWCNTs cathode has far better power performance than that with commercial Pt/C. Moreover, the fuel cell with Pt–Co + ZrO₂/MWCNTs cathode undergo only a 6.1% maximum power loss after 50000 ADTs. However, that with commercial Pt/C cathode after 30000 ADTs has 39.6% maxinum power loss. More impressively, compared to the 220 mV loss of Pt/C after 30000 ADTs, the Pt–Co + ZrO₂/MWCNTs cathode also displays only 20 mV loss at 0.8 A/cm² after 50000 ADTs. The enhanced intrinsic activity of Pt–Co + ZrO₂/MWCNTs may be attributed to the Co-doped Pt NPs and interface effect of Co-doped Pt NPs and surface defect-rich ZrO₂.     

Sponge tofu-like graphene-carbon hybrid supporting Pt–Co nanocrystals for efficient oxygen reduction reaction and Zn-Air battery

Developing highly efficient electro-catalysts for oxygen reduction reaction (ORR) by an economic and green manner is vital for the practical application of fuel cells and metal-air batteries. Herein, inspired by the manufacturing process of sponge tofu (Chinese Food), we develop a sponge tofu-like graphene-carbon hybrid supporting Pt–Co nanoparticles catalyst (denoted as Pt–Co/CB + RGO-3D) by a cheap and environment-friendly freeze-drying technology using ice as the template. The electrochemical tests show that Pt–Co/CB + RGO-3D exhibits approximately 16-fold higher ORR activity and better stability compared with Pt/C. Its excellent performance could be attributed to the high mass transfer efficiency and enhanced electron transfer capacity, which roots in its unique structure. Furthermore, the Pt–Co/CB + RGO-3D-based Zn-air battery exhibits superior performance, corroborating its commercial application potential. This work not only provides a prospective method to fabricate catalysts with porous structure but also offers an effective strategy to design highly efficient electrocatalysts with special structure.     

Co–Co3O4 nanostructure with nitrogen-doped carbon as bifunctional catalyst for oxygen electrocatalysis

In view of the development of advanced bi-functional oxygen electrodes for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), herein, we report the synthesis of Co–Co₃O₄ nanostructure encased in N-doped carbon (Co–Co₃O₄/NC) by carbothermal reduction followed by controlled oxidative treatment. The formation of a protective-active oxide layer on the metallic-Co not only facilitated the effective charge separation and transport but also displayed improved stability of Co–Co₃O₄/NC in an alkaline operating condition. The Co–Co₃O₄/NC catalyst afforded 0.810 V overvoltage between ORR and OER in 0.1 M KOH solution, consequently, this lower reversible overvoltage would result in energy saving of around 0.246 V if Co–Co₃O₄/NC is used as an oxygen electrode instead of commercially available 40 wt % Pt/C. Furthermore, in comparison with the use of Pt/C + IrO₂ as an ORR and OER catalyst, respectively the single bi-functional electrocatalyst i.e., Co–Co₃O₄/NC would result in energy saving of around 0.13 V.     

Effect of surface composition of Pt–Fe nanoparticles for oxygen reduction reactions

The aim of this work is primarily to rationalize the effect of surface composition on electrocatalytic activity. To investigate this point, we compared two types of nanoparticles with a different surface composition, namely Fe-rich and Pt–Fe mixed surfaces. We synthesized highly dispersed carbon-supported Pt₁Fe_x (x = 1, 2, and 3) nanoparticles with the Fe-rich surface (∼2 nm), through a preferential interaction of a capping agent and the metal, i.e., Fe-OOC. The electronic structure and electrocatalytic properties of Pt₁Fe_x nanoparticles with the Fe-rich surface were found to be virtually independent from the Pt/Fe ratio. In contrast, nanoparticles with the Pt–Fe mixed surface, prepared by utilizing the difference of segregation energy, showed a clear dependence of the electronic and electrochemical characteristics on the amount of Pt and Fe, possibly because of the interaction between these two metals on the surface of the electrocatalysts. Compared to Pt, the Pt₁Fe₂ nanoparticles with the Pt–Fe mixed surface showed the highest enhancement in the activity of the oxygen reduction reaction. This resulted from the development of a more electrochemically stable structure of the Pt–Fe mixed surface. This study demonstrated that the electrocatalytic properties of the Pt–Fe nanoparticles can be tuned using the surface composition rather than the bulk composition.     

Carbon supported Palladium–Iron nanoparticles with uniform alloy structure as methanol-tolerant electrocatalyst for oxygen reduction reaction

Carbon supported Palladium–Iron bimetallic nanoparticles (Pd–Fe/C) electrocatalyst is synthesized by the direct thermal decomposition method of nontoxic metallic acetate salt. During the preparation of the Pd–Fe/C electrocatalyst, the tedious wash post-treatment of electrocatalyst is effectively avoided due to non-existence of inorganic anion. The physico-chemical properties of the Pd–Fe/C electrocatalyst are characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). These structural analyses reveal that the Pd–Fe/C electrocatalyst possesses the high alloying degree and the small particle size. Electrochemical data indicate that the eletrocatalytic activity of the Pd–Fe/C electrocatalyst for oxygen reduction reaction (ORR) is much higher than that of Pd/C electrocatalyst, which originates from the synergistic effect between Pd atom and Fe atom.     

Two step synthesis of TiO2–Co3O4 composite for efficient oxygen evolution reaction

For an active hydrogen gas generation through water dissociation, the sluggish oxygen evolution reaction (OER) kinetics due to large overpotential is a main hindrance. Herein, a simple approach is used to produce composite material based on TiO₂/Co₃O₄ for efficient OER and overpotential is linearly reduced with increasing amount of TiO₂. The scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) investigations reveal the wire like morphology of composite materials, formed by the self-assembly of nanoparticles. The titania nanoparticles were homogenously distributed on the larger Co₃O₄ nanoparticles. The powder x-ray diffraction revealed a tetragonal phase of TiO₂ and the cubic phase of Co₃O₄ in the composite materials. Composite samples with increasing TiO₂ content were obtained (18%, 33%, 41% and 65% wt.). Among the composites, cobalt oxide-titanium oxide with the highest TiO₂ content (CT-20) possesses the lowest overpotential for OER with a Tafel slope of 60 mV dec^?1 and an exchange current density of 2.98 × 10^?3A/cm². The CT-20 is highly durable for 45 h at different current densities of 10, 20 and 30 mA/cm². Electrochemical impedance spectroscopy (EIS) confirmed the fast charge transport for the CT-20 sample, which potentially accelerated the OER kinetics. These results based on a two-step methodology for the synthesis of TiO₂/Co₃O₄ material can be useful and interesting for various energy storage and energy conversion systems.     

Pd–Co nanoparticles decorated on different carbon based substrates as electrocatalyst for O2 reduction reaction

In this study, a facile process for the synthesis of bimetallic Pd–Co nanotubes on multi-walled carbon nanotubes (MWCNTs) and chemically reduced graphene oxide (rGO) is reported. The synthesized nanocatalysts are characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). Catalysts are evaluated for the oxygen reduction reaction (ORR) in basic media. The electrocatalytic performance of Pd–Co supported on rGO and MWCNTs toward ORR is compared with bimetallic and single Pd nanoparticles decorated on Vulcan carbon (XC-72R) by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and rotating disk electrode (RDE) in 0.1 M NaOH solution. The specific electrochemical surface areas of Pd–Co supported on rGO is higher than the corresponding carbon-supported Pd nanoparticles (222.09 vs. 41.57 m² g⁻¹, respectively). The RDE results confirm that the final product of the oxygen reduction is water and the proposed main path is direct 4 electron transfer process with smooth transfer kinetic rate on the Pd–Co/rGO in comparison to Pd–Co/C. Furthermore, the lower charge transfer resistance of the particles in ORR process for the Pd–Co/rGO compared to single Pd/C catalyst, indicating it could be excellent candidate for ORR in alkaline media.     

The structure-activity relationship of Pd–Co/C electrocatalysts for oxygen reduction reaction

The Pd–Co/C alloy catalysts with an atomic ratio of 3:1 were deposited at various pH values and reduced at different temperatures for oxygen reduction reaction (ORR). The structure-activity relationship of the prepared catalysts has been elucidated. The pH values and reduction temperatures during the preparation process affect the deposition and reduction rates of Pd and Co ions significantly, and thus the degrees of alloying, surface species, and ORR activities of the Pd–Co/C catalysts are also influenced. Due to the enhancement of Co surface segregation and the formation of Co oxide on the surface, a deterioration of ORR activity for the catalysts reduced at high temperatures and high pH values is observed. The catalysts deposited at pH value of 9 and reduced at a very low temperature of 390 K have well-formed Pd–Co alloy structure, Pd-rich surface, and excellent ORR activity.     

Eu2O3–Cu/NC nanocomposite catalyst with improved oxygen reduction reaction activity for Zn-air batteries

Rare earth oxide promoted transition metal composite catalyst Eu₂O₃–Cu/NC with outstanding oxygen reduction reaction (ORR) performance, is constructed by hydrothermal and subsequent high-temperature calcination, considering replacing Pt/C. This synthesis method yields Eu₂O₃–Cu nanoparticles with uniform distribution, improved oxygen vacancies and increased content of N-doping. And the strong synergistic effect was created between promoter Eu₂O₃ and chief Cu. In addition, the accommodate adsorption and transfer of O species endow Eu₂O₃–Cu/NC the improved ORR activity than Eu₂O₃/NC and Cu/NC. Meanwhile, the stability of Eu₂O₃–Cu/NC is also strengthened compared to Cu/NC on account of the interaction of active sites, and the H₂O₂ yield of Eu₂O₃–Cu/NC is very low. For practical application, a rechargeable Zn-air battery with an air cathode of Eu₂O₃–Cu/NC displays a larger power density, excellent charge-discharge cycle stability and good rate capability. The designed composite shows potential application prospects in the fields of energy conversion.     

Efficient electrocatalyst of Pt–Fe/CNFs for oxygen reduction reaction in alkaline media

Transition metal iron-based catalysts are promising electrocatalysts for oxygen reduction reaction (ORR), and they have the potential to replace noble metal catalysts. The one-dimensional of carbon nanofibers with tubular structure can effectively promote the electrocatalytic activity, which facilitates electron transport. Herein, the Pt–Fe/CNFs were synthesized by electrospinning and subsequent calcination. Benefiting from the advantages of one-dimensional structure, Pt–Fe/CNFs-900 with fast electrochemical kinetics and excellent stability for ORR with excellent onset of 0.99 V, a low Tafel slope of 62 mV dec⁻¹ and high limiting current density of 6.00 mA cm⁻². Long-term ORR testing indicated that the durability of this catalyst was superior to that of commercial Pt/C in alkaline electrolyte. According to RRDE test, the ORR reaction process of Pt–Fe/CNFs-900 was close to four-electron transfer routes.     

Ni–Fe nanocubes embedded with Pt nanoparticles for hydrogen and oxygen evolution reactions

Electrochemical water-splitting is widely regarded as one of the essential strategies to produce hydrogen energy, while Metal-organic frameworks (MOFs) materials are used to prepare electrochemical catalysts because of its controllable morphology and low cost. Herein, a series of trimetallic porous Pt-inlaid Ni–Fe nanocubes (NCs) are developed with bifunctions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In the process of prepare the electrochemical catalysts, Pt nanoparticles are uniformly embedded in the Fe–Ni PBA cube structure, and ascorbic acid is employed as a reducing agent to reduce Pt²⁺ to Pt nanoparticles. In this work, the cubic structure of Fe–Ni PBA is maintained and the noble metal Pt nanoparticles are embedded. Remarkably, the formation of PBA cubes, Pt inlay and reduction are completed in one step, and Pt nanoparticles are embedded by a simple method for the first time. By employing acid etching method, a porous structure is formed on the PBA cube, which increases the exposed area of the catalyst and provides more active sites for HER and OER. Due to the porous structure, highly electrochemical active surface area and the embedded of highly dispersed Pt nanoparticles, the porous 0.6 Ni–Fe–Pt nanocubes (NCs) exhibits excellently electrocatalytic performance and durable stability to HER and OER. In this work, for HER and OER, the Tafel slopes are 81 and 65 mV dec⁻¹, the overpotential η at the current density of 10 mA cm⁻² are 463 and 333 mV, and the onset potential are 0.444 and 1.548 V, respectively. And after a 12-h i-t test and 1000 cycles of cyclic voltammetry (CV), it maintained high stability and durability. This work opens up a new preparation method for noble metal embedded MOF materials and provided a new idea for the preparation of carbon nanocomposites based on MOF.