Mesoporous Carbon Support Research Articles

Oxygen Reduction Catalyzed by Pt Nanoparticles Confined in Mesoporous Carbon Supports Doped with Single Fe Atoms

Oxygen Reduction Catalyzed by Pt Nanoparticles Confined in Mesoporous Carbon Supports Doped with Single Fe Atoms

Improving Carbonate-Promoted C–H Carboxylation Using Mesoporous Carbon Supports

C–H carboxylation is an attractive way to utilize CO2 for chemical production provided that it does not consume resource-intensive reagents. Alkali carbonates dispersed into the pores of mesoporous supports display strongly basic reactivity under CO2, allowing them to be used as base promoters for C–H carboxylation of (hetero)arenes in the absence of other reagents or catalysts. Mesoporous oxides are convenient support materials, but only a relatively small fraction of the dispersed carbonate (ca. 10–20%) is converted to carboxylate products when metal oxide supports are used. Here, we compare mesoporous oxide and carbon supports and investigate the dependence of carbonate reactivity on the pore structure. We show that using mesoporous carbon supports can increase the carbonate conversion by 2–4× when compared to oxide supports. This improved carbonate reactivity is maintained across a variety of mesoporous carbons with different pore structures (ordered vs disordered) and pore diameters, indicating that the dispersed carbonate is intrinsically more reactive on the surface of a carbon material compared to an oxide surface. Reaction of the carboxylate products with dimethyl carbonate yields isolable methyl esters as the final product and regenerates the dispersed carbonate. We show that mesoporous carbon supports are robust to at least five cycles of successive C–H carboxylation and methylation. Understanding how the support structure affects dispersed carbonate reactivity is valuable for advancing C–H carboxylation toward practical application and utilizing these materials in other CO2 transformations.

Engineering of the N-doped carbon support for improved performance of supported Pd catalysts in hydrogen production from gas-phase formic acid

Development of N-doped Pd/C catalysts for hydrogen production from gas-phase formic acid is a challenge. To elucidate the efficient routes of nitrogen insertion on the surface of a mesoporous carbon support, the latter was treated with melamine (Mel), dicyandiamide or NH3 at 673 and 823 K. Pyrolysis of the melamine/carbon mixture taken in a 1:2 ratio provides an increase in the reaction rate by a factor of 5. The inserted N-sites strongly interact with Pd leading to the formation of highly dispersed Pd nanoparticles (∼1.6 nm) and active atomically dispersed Pd2+ species. With a further increase of the Mel/C ratio, the number of surface N-sites decreases due to occupation of carbon support pores with a g–C3N4–type residue. This provides a decrease in the Pd dispersion leading to lower reaction rates. Therefore, melamine is an efficient N precursor. The considered synthesis of N-doped catalysts could be scaled.

Translating insights from experimental analyses with single-crystal electrodes to practically-applicable material development strategies for controlling the Pt/ionomer interface in polymer electrolyte fuel cells

Ionomers are used in polymer electrolyte fuel cells (PEFCs) catalyst layers to improve proton conduction. Recent analytical studies have clarified that the adsorption of the ionomer on the surface of a Pt catalyst deteriorates the catalytic activity for the oxygen reduction reaction and oxygen transport properties near the catalyst surface. These findings have led to the development of new materials, such as mesoporous carbon support and highly oxygen-permeable ionomer, which are now commercially used. In this review article, we summarize recent analytical studies of the Pt/ionomer interface focusing on half-cell experiments with single-crystal electrodes. We also present promising approaches for mitigating ionomer adsorption, as well as the remaining challenges in the application of these approaches to PEFCs.

Study on the Roles of Water in Solid Amine-Based Direct Air Capture of CO2

Climate change triggered by the increasing amount of CO2 released into the atmosphere has become a global priority. Direct Air Capture (DAC) of CO2 has been regarded as one of the disruptive technologies to realize negative emission. Among the multiple strategies employed, adsorption on solid amines is a promising choice owing to its low energy requirements. Since the water vapor ubiquitously exists in ambient air, understanding the role it plays in DAC by the amine-functionalized solid sorbents is of vital importance. Due to the diversity in amine and support features, both promotion and deterioration of water impact on CO2 adsorption were revealed. Herein we present a multifaceted review of the trends and innovations in DAC by solid amines under humid conditions. The effect of water was discussed over four groups of materials, based on the support categories, i.e., (a) mesoporous silica, (b) mesoporous alumina, (c) mesoporous carbon and other inorganic supports, and (d) cellulose and other organic supports.

Ag nanoparticles on mesoporous carbon support as cathode catalyst for anion exchange membrane fuel cell

Silver nanocatalyst (40 wt%) is deposited on commercial mesoporous carbon support material (Ag/C) using two different wet chemical methods, to obtain high electrochemically active surface area. The catalyst materials are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis and are evaluated toward the oxygen reduction reaction (ORR) in alkaline media employing the rotating disk electrode method. It is worth noting that the Ag/C leads to oxygen reduction through a direct four-electron pathway in alkaline medium. The silver catalyst on mesoporous carbon exhibits relatively higher mass activity for ORR (38 A g−1) compared to that with Vulcan carbon (32 A g−1) at −0.2 V vs SCE at room temperature. Anion exchange membrane fuel cell shows maximum power density of 310 mW cm−2 with Ag/C cathode catalyst using H2 and O2 gases at 65% RH conditions at 65 °C.

Engineering the Electronic Structure of Single-Atom Iron Sites with Boosted Oxygen Bifunctional Activity for Zinc-Air Batteries.

Rechargeable zinc-air batteries typically require efficient, durable, and inexpensive bifunctional electrocatalysts to support oxygen reduction/evolution reactions (ORR/OER). However, sluggish kinetics and mass transportation challenges must be addressed if the performance of these catalysts is to be enhanced. Herein, a strategy to fabricate a catalyst comprising atomically dispersed iron atoms supported on a mesoporous nitrogen-doped carbon support (Fe SAs/NC) with accessible metal sites and optimized electronic metal-support interactions is developed. Both the experimental results and theoretical calculations reveal that the engineered electronic structures of the metal active sites can regulate the charge distribution of Fe centers to optimize the adsorption/desorption of oxygenated intermediates. The Fe SAs/NC containing Fe1 N4 O1 sites achieves remarkable ORR activity over the entire pH range, with half-wave potentials of 0.93, 0.83, and 0.75V (vs reversible hydrogen electrode) in alkaline, acidic, and neutral electrolytes, respectively. In addition, it demonstrates a promising low overpotential of 320mV at 10mA cm-2 for OER in alkaline conditions. The zinc-air battery assembled with Fe SAs/NC exhibits superior performance than that of Pt/C+RuO2 counterpart in terms of peak power density, specific capacity, and cycling stability. These findings demonstrate the importance of the electronic structure engineering of metal sites in directing catalytic activity.

(PEFC&E 2022 Student Poster Award Winner - 2nd Place) Investigation of a Correlation Between IV Performance and Cathode Structure for MEAs Using Mesoporous Carbon Supports

Introduction Polymer Electrolyte Fuel Cell (PEFC) is a promising energy technology for a future decarbonized society. PEFC is composed of porous electrode catalyst layers, which largely determines current-voltage (IV) performance. However, the optimal structure of porous catalyst layers is still unknown. Carbon supports are the main component to build up such porous structure. Mesoporous carbon (MC) supports are recently paid more attention to since they are used in Toyota’s fuel cell vehicles, MIRAI. We are also studying MC whose diameter is about 10 nm. Therefore, we are interested in a correlation between IV performance and the structure of catalyst layers based on MC supports. The aim of this study is to clarify the optimal structure of cathode catalyst layers for high IV performance. In this study, we synthesized two types of MC, MC bulk and fibers, and evaluated the IV performance and cathode structure of MC based cathode catalyst layers. Experimental MC bulk was prepared based on self-organization of Pluronic F127 and carbon precursors (resorcinol, formaldehyde, and triethyl orthoacetate). They were mixed in the acid solution, and then the supernatant was removed after centrifugation. The remaining portion was heated in the oven for polymerization of carbon precursors. The resulting material was heated by stepwise in the oven under the nitrogen atmosphere in order to decompose Pluronic F127 and carbonized precursors. MC fibers were made by electrospinning of the similar precursor solution mentioned in the above, but for electrospinning phloroglucinol instead of resorcinol was in use, and PVA was added. Then, after MC bulk and fibers were milled by hands or zirconia balls, Pt nanoparticles were deposited on MC supports by using Pt(acac)2 as a precursor. MEAs with 1cm2 electrodes were fabricated by spray-printing of catalyst dispersions on the Nafion film. Prepared MC based catalysts were used for the cathode, and 46.5% Pt/KB (TEC10E50E) was used for the anode. Results and discussion IV performance of MEAs using MC based cathodes was evaluated and compared to that of a standard MEA. MEA with MC bulk support showed slightly lower IV performance than that of standard MEA. By analyzing each overvoltage separately, ohmic overvoltage was found to be a biggest problem, and low concentration overvoltage was realized as an advantage. In order to find out the reason of low concentration overvoltage, the structure of cathode layers was evaluated using FIB-SEM. The 300 cross-sectional SEM images were obtained by slicing cathodes every 10 nm, and the cathode was reconstructed into a three dimensional image. As a result, the size of MC support was found to be much larger than that of KB. When pore diameter distribution was evaluated based on the reconstructed image, as shown in Figure 1, rather large pores expressed in red in the figure was observed for MC bulk based cathode probably owing to large MC particles. The low concentration most likely comes from the existence of such large pores. In this structural analysis, the analysis of mesopores is not included, and so in reality mesopores might have contributed to lowering concentration overvoltage. Similar analyses were done for MC fiber based cathodes. We have found that the IV performance and structure of cathodes is rather influenced by the milling processes, which will be discussed in detail. Figure 1

(Invited) Effects of Support Mesoporosity on Pt Dissolution in PEM Fuel Cells

Interest in hydrogen as an energy carrier continues to grow due to the high demand for clean and sustainable, energy sources in the global energy market. Polymer exchange membrane fuel cells (PEMFCs) convert the chemical energy of hydrogen to electricity and have great potential as power sources for automotive applications. A key challenge in the development of cost-efficient and reliable PEMFC electrodes is catalyst layer durability. Typically, PEMFC cathodes comprise Pt-based electrocatalysts supported on high-surface-area carbons. It has been previously shown that the morphology and surface chemistry of carbon supports play significant roles in modulating both the activity and stability of Pt-based catalysts.Here, we will present our recent efforts to investigate the effects of the porous structures and surface properties of different mesoporous carbon powders on Pt dissolution in PEMFC cathodes. Using atomic layer deposition (ALD), we fabricate cathodes by depositing Pt nanoparticles of uniform sizes and mass loadings onto mesoporous carbon supports with varying pore sizes and surface areas. We then evaluate the beginning-of-life and end-of-life performance of these cathodes after accelerated Pt dissolution tests under single cell conditions, while comparing them to a microporous Ketjenblack-based cathode as a benchmark. Based on our findings, we discuss new insights into the underlying mechanisms for Pt dissolution within the porous structures of mesoporous carbon supports.

Improvements in Oxygen Diffusivity, ORR Activity and Durability of Pt-Based Catalysts By Mesoporous Carbon Support and Melamine Decoration

1. Introduction In Japan, an extremely high I-V performance is required for polymer electrolyte fuel cells (PEFCs) used in fuel cell electric vehicles after 2030 (red line in Figure 1) [1]. Therefore, we have to design Pt-based catalysts that have a high ORR activity and a durability as well as a high oxygen diffusivity [2]. In this study, the Pt-based catalysts were supported on a mesoporous carbon to increase oxygen diffusivity and the catalysts were decorated with melamine to improve ORR activity and durability [3, 4]. 2. Experimental Ketjen Black EC-300J (KB-300J: SBET: 922 m2/g, LION), Ketjen Black EC-600JD (KB-600JD: SBET: 1,345 m2/g, LION) and a mesoporous carbon (CNovel MH-18, SBET 1,334 m2/g, TOYO TANSO [5]) were used as carbon supports in the synthesis of PtCo alloy and Pd@Pt core-shell catalysts. A commercially available Pt/KB-300J catalyst (TEC10E50E, Pt size: 2.5 nm, Pt metal loading: 46.3 wt.%, TKK) was used as a reference catalyst. The PtCo alloy catalyst was synthesized by an oleylamine reduction method [6] and the Pd@Pt core-shell catalyst was synthesized by a direct displacement reaction method [7]. The metal loadings of Pt and Co in the alloy catalysts were 41 wt.% and 3 wt.%, respectively, and those of Pt and Pd in the Pd@Pt core-shell catalyst were 20 wt.% and 30 wt.%, respectively. The particle sizes of the PtCo alloy and the Pd@Pt core-shell catalyst NPs were 3.0 nm and 5.5 nm, respectively. CV of the catalyst was recorded at 25oC in Ar-saturated 0.1 M HClO4 with a potential scan rate of 50 mV/s and LSV was measured by RDE method at 25oC in O2-saturated 0.1 M HClO4 with a potential scan rate of 10 mV/s at a rotation speed of 1,600 rpm. An accelerated durability test (ADT) of the catalysts was conducted by a square wave potential cycling of 0.6 V (3 s)-1.0 V (3 s) vs. RHE performed in Ar-saturated 0.1 M HClO4 at 80oC for 10,000 cycles with and without melamine addition (10 µM to the electrolyte). MEA was fabricated by a decal method using a reinforced membrane (12 µm in thickness, Gore) and a GDL (TORAY). Nafion® DE2020 was used as an ionomer for the catalyst ink preparation (I/C: 0.83). I-V performance of a single cell was evaluated at 80oC, 75% RH by using the MEA with an active area of 1 cm2 in which the Pt loading in the cathode catalyst layer was set to 0.1 mg-PGM/cm2. H2 gas (418 NmL) and air (998 NmL) were supplied to the anode and the cathode, respectively, and the H2 gas was pressurized to 150 kPa at the gas-outlet (H2 utilization: 5% at a current density of 3.0 A/cm2). 3. Results and Discussion Pore size distribution of the carbon supports is summarized in Figure 2. KB-300J has no clear mesopores, while KB-600JD and CNovel MH-18 have the mesopores. Figure 1 shows I-V performance of Pd@Pt core-shell catalysts, indicating that Pt/Pd/CNovel MH-18 catalyst exhibits a superior cell performance to that of Pt/Pd/KB-600JD catalyst. Connectivity of mesopores in KB-600JD and CNovel MH-18 supports analyzed by 3D-TEM is shown in Figure 3. It is clear that the connectivity in CNovel MH-18 support is much higher than that in KB-600JD support, which is considered to contribute to the superior I-V performance of Pt/Pd/CNovel MH-18 catalyst observed in Figure 1.Figures 4 depicts morphological change of PtCo/CNovel MH-18 alloy catalyst by ADT performed at 80oC for 10,000 cycles. A very small amount of melamine addition to the electrolyte (10 µM) notably suppressed the catalyst NPs agglomeration in ADT, which significantly mitigated ECSA decay of the catalysts. More importantly, Co dealloying of the PtCo alloy catalyst in ADT was remarkably suppressed by the melamine addition, and thus the alloy catalyst retained a high ORR mass activity even after ADT. Therefore, we believe that the target cell performance as well as the high durability of the Pt-based catalysts can be realized by combination of the mesoporous carbon support and the decoration with melamine or melamine derivatives.This study was partly supported by NEDO, Japan.

Selective oxidation of benzyl alcohol over sulphated zirconia incorporated ordered mesoporous carbon by a hard template method

An ordered mesoporous carbon (OMC) support was prepared by a hard template method using cellulose (C source) and SBA-16 (silica source) as templates. The silica-carbon composite was treated with 10 % HF to completely remove silica from the composite to create a mesoporous nature. Afterwards, Zr (10–30 wt%) and 4 % of SO42- were incorporated over OMC by a hydrolysis method. The prepared catalysts were characterized by various techniques such as XRD, Raman, BET, Py-FT-IR, TGA, SEM, Elemental mapping, and TEM. The detailed investigation of selective oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH). This study exhibited the SO42-/Zr-OMC (30) catalyst showed its superior activity in the oxidation of benzyl alcohol (about>97 % of the conversion and BzH selectivity of>98 %) under the optimized reaction conditions. Furthermore, the reusability of the SO42-/Zr-OMC (30) catalyst up to the 5th run. This result revealed the stability of the prepared SO42-/Zr-OMC (30) catalyst, which was associated with its physicochemical properties.

Investigation of a Correlation Between IV Performance and Cathode Structure for MEAs Using Mesoporous Carbon Supports

The cathode catalyst layer in PEFC plays an important role for further improvement of performance and durability toward heavy–duty vehicles. Since carbon is the main component to define the porous cathode structure, realization of optimal structure of carbon is desired. Therefore, in this study, using lab-made Pt/mesoporous carbon and Pt/mesoporous carbon fiber, and commercially available Pt/Ketjen Black as cathode materials, membrane electrode assemblies were made, and evaluated electrochemically and structurally. Then, a correlation between IV performance and three dimensional structure was investigated. From the three dimensionally reconstructed images, we found that large carbon particles most likely lead to higher ohmic resistance owing to interparticle resistance between the particles. Homogeneous distribution of large pores was found to lower concentration overvoltage.

PEFC Electrocatalysts Using Sn-Based Materials Dispersed on Mesoporous Carbon

Significant improvement in the durability of polymer electrolyte fuel cell (PEFC) electrocatalysts is essential for heavy-duty applications. Carbon-based supports suffer from carbon corrosion during start-stop potential cycles, leading to Pt detachment. Load cycles can also cause degradation mainly associated with Pt dissolution/re-deposition. Here, nanocomposite electrocatalysts with Pt and SnO2 decorated on mesoporous carbon (MC) are prepared for improvement of start-stop and load-cycle durability. These nanocomposite electrocatalysts are found to be deposited within the mesopores of the MC support. It is demonstrated by half-cell tests that such electrocatalysts exhibit a high durability for potential changes simulating start-stop and load-cycles.

Synthesis and Characterization of Mesoporous Carbon Supported Ni-Ga Catalyst for Low-Pressure CO2 Hydrogenation

In this study, the atmospheric-pressure hydrogenation of CO2 was carried over bimetallic Ni-Ga catalyst supported on mesoporous carbon (MC). MC was successfully prepared using the soft-template method as proven by Fourier Transform Infra Red (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy - Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Brunauer–Emmett–Teller Surface Area Analyzer (BET SAA), and Transmission Electron Microscopy (TEM) characterizations. The Ni-Ga/MC catalyst was synthesized using the impregnation method, and based on the XRD characterization, the formation of bimetallic Ni-Ga on the MC support is confirmed. The EDS mapping image shows the uniform distribution of the bimetallic Ni-Ga on the MC surface, especially for the Ni5Ga3/MC and NiGa3/MC catalysts. Moreover, the TEM images show an excellent pore size distribution. The formation of Ni-Ga alloy was identified as an active site in the CO2 hydrogenation. Ni5Ga3/MC catalyst exhibited a 10.80% conversion of CO2 with 588 μmol/g formaldehyde at 1 atm, 200 °C, and H2/CO2 ratio of 3/1. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Green synthesis of cyclohexanone to adipic acid over Fe–W oxides incorporated mesoporous carbon support

We have prepared iron and tungsten oxides incorporated mesoporous carbon (MC) catalysts using a simple hydrothermal methodology with different carbon sources, and the catalytic performance was investigated for cyclohexanone oxidation. An adequate amount of metal oxide loading has displayed a key role in the selective catalyst for adipic acid (AA) synthesis. The MC catalyst has shown its prime activity under the influence of redox properties of W5+/W6+ and Fe2+/Fe3+ as promoters. The 10%Fe 90%W-MC fructose as a carbon source catalyst has provided its best selectivity of 87% for AA at 120 °C.

Ultrafine PdZn bimetallic nanoparticles anchored on sulfur-doped mesoporous carbon for the partial hydrogenation of alkynols

The catalytic partial hydrogenation of alkynols is a key approach for the synthesis of enols, which are crucial chemical intermediates for pharmaceuticals and essences. Low selectivity is the main challenge of the partial hydrogenation of alkynols due to the easy over-hydrogenation of alkynyl groups. Herein, ultrafine PdZn bimetallic nanoparticles (NPs) were anchored on a S-doped mesoporous carbon catalyst (PdZn/Meso_S-C) and used for the partial hydrogenation of alkynols. Zn metal with a high electron density was used to modify the active metal Pd to change the electronic and geometric configuration of the Pd active sites, which improve the selectivity of enols during the partial hydrogenation of alkynols. Furthermore, the use of a S-doped mesoporous carbon support dispersed and stabilized the ultrafine PdZn NPs due to strong interactions between the metal atoms and S sites. This also prevented PdZn ultrafine NPs from aggregating and increased the partial hydrogenation selectivity. The partial hydrogenation of propynol ethoxylate (PME) catalyzed by PdZn/Meso_S-C reached 96.0% enol selectivity, while the alkynol conversion reached 97.5%. The general applicability of PdZn/Meso_S-C for the partial hydrogenation of various alkynols has also been demonstrated. Thus, this work has great application prospects for the high-efficiency catalytic partial hydrogenation of alkynols.

Nanoarchitectured superparamagnetic iron oxide-doped mesoporous carbon nanozymes for glucose sensing

The incorporation of nanoarchitectonics into the development of nanozymes to achieve target-specific geometry, dense active sites, and cascade catalysis is highly demanded for developing ultrasensitive bioassays. The improved dispersion and uniform distribution of metal active sites onto a three-dimensional (3D) mesoporous carbon support (MC) with a high surface area can lead to enhanced substrate binding, mobility, and collision probability and therefore, increased peroxidase mimetic activity. Herein, we report the fabrication of well-dispersed superparamagnetic iron oxide (IO) nanoparticles (NPs) on mesoporous carbon (IO-MC) support with high Fe3+ active sites, high surface area, and ordered mesoporous pore channels that show promising catalytic activity at room temperature. The as-prepared IO-MC shows good nanozyme activity at room temperature with highly favorable Michaelis-Menten constant, Km (0.242 mM) and fast reaction rate (0.193 × 10−7 MS−1). Finally, we demonstrate the functionality and pre-eminence of IO-MC nanozyme for bioassay. As a proof-of-concept, we develop a superior glucose assay that provides a LOD (limit of detection) of 2 µM in the spiked sample. These findings suggest that homogeneously dispersed iron oxide NPs on MC show promising potential as next-generation nanozyme for developing sensitive bioassays.

Nickel sulphide decorated nitrogen rich ordered mesoporous carbon (NOMC) as an efficient catalyst for the electrocatalytic oxidation of urea in alkaline medium

The urea oxidation reaction (UOR), as a feasible alternative for the slow oxygen evolution reaction (OER), is recognized as an encouraging puissant approach for hydrogen generation through water splitting. The route also offers excellent potential for hydrogen production through wastewater remediation. Here, a simple synthetic strategy has been adopted to embed NiS in a nitrogen-rich stable and activated mesoporous carbon matrix (NOMC) that has been successfully exploited for UOR. The NOMC supported nickel sulfide catalyst with high electrochemically active surface area (ECSA) exhibits a very good response towards the electro-catalytic oxidation of urea in an alkaline medium with a low working oxidation potential (potential corresponding to the current density value of 10 mA/cm2 taken as a standard) of 1.34 V (vs. RHE). The introduction of heteroatom (N) to the mesoporous carbon support and subsequent incorporation of metal sulfide rather than metal oxide or metal hydroxide, as reported previously, is done purposefully to increase the electrocatalytic activity of the catalyst through the synergistic effects of charge density with carbon support. The synergism is further supported by the comparative response in urea oxidation reaction (UOR) for NiS/NOMC catalyst compared to other Ni-based catalysts like Ni(OH)2, NiS, and NiS/CMK-3, which indicates that the activity is highest for NiS/NOMC. The catalyst attains good stability in an alkaline medium. The mesoporous carbon framework (NOMC) with considerably high BET surface area, large pore volume, and interconnected ion diffusion channels accelerate the transport of electrons through the porous surface, which makes NiS/NOMC highly efficient and stable as an electrocatalyst for the oxidation of urea in comparison to its other composite catalysts in alkaline medium.

Peroxidase-mimetic activity of a nanozyme with uniformly dispersed Fe3O4 NPs supported by mesoporous graphitized carbon for determination of glucose.

A Fe3O4/mesoporous graphitized carbon (Fe3O4/m-GC) composite was prepared through a facile calcination method with iron-based metal-organic frameworks (Fe-MOFs) as a sacrificial template. After carbonization, the Fe3O4 nanoparticles were uniformly dispersed in the mesoporous carbon support, resulting in spatial structural stability. The mesoporous carbon support obtained was highly graphitized and exhibited eminent electrical conductivity, which accelerated the electron transfer between the Fe3O4 nanoparticles by Fe(II)/Fe(III) redox cycles and m-GC by C = Csp2/C-Csp3 redox cycles, leading to the excellent peroxidase-mimetic activity of Fe3O4/m-GC. Km values for tetramethylbenzidine (TMB) and H2O2 were 26.8 and 15.8 times lower than that of natural horseradish peroxidase, respectively. Taking advantage of the peroxidase-mimetic activity of Fe3O4/m-GC, a colorimetric assay was fabricated for detecting glucose in the range 0.5 ~ 200μM, with a limit of detection of 0.24μM. Fig 1 A Schematic illustration of the preparation process of Fe3O4/m-GC, B schematic illustration of a proposed synergistic catalytic mechanism of TMB oxidation by Fe3O4/m-GC.

Boosting formate production from CO2 electroreduction over gas diffusion electrode with accessible carbon mesopores

Electroreduction of CO2 to formate (ERCF) over a gas diffusion electrode with a Nafion-bonded carbon-supported Sn-based catalyst layer provides a promising approach for formate production. The ERCF performance is largely dependent on the carbon supports. However, the key influencing factors of the carbon supports for the ERCF performance have not yet been elucidated. We employed a variety of carbon supports with different pore structure features (activated carbon, acetylene black, and ordered mesoporous carbon) to explore the main factors influencing ERCF performance. The results showed that the pore size distribution was crucial for the ERCF performance. The ideal pore size was 5–20 nm. As it had the highest specific surface area within this pore size range among all the carbon supports examined, the ordered mesoporous carbon support obtained the highest ERCF performance (Faraday efficiency and current density for formate were 97.45 ± 2.97% and 80.12 ± 5.91 mA cm−2, respectively). Further analyses revealed that the increased ERCF performance was likely due to the large electroactive surface area, enhanced surface adsorption and activation capability of CO2, mesopore-induced proton transfer limitations for the hydrogen evolution reaction, and excellent charge transfer. This work is of significance for the further design of high-performance gas diffusion electrodes for the ERCF process.