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Carbon-supported single-atom catalysts were found to suffer reversible deactivation in catalytic hydrogenation, but the mechanism is still unclear. Herein, nitro compounds hydrogenation catalyzed by N-doped carbon-supported Co single atom (Co1/NC) was taken as a model to uncover the mechanism of the reversible deactivation phenomenon. Co1/NC exhibited moderate adsorption towards the substrate molecules (i.e., nitro compounds or related intermediates), which could be strengthened by the confinement effect from the porous structure. Consequently, substrate molecules tend to accumulate within the pore channel, especially micropores that host Co1, making it difficult for the reactants to access the active sites and finally leading to their deactivation. The situation could be even worse when the substrate molecules possess a large size. Nevertheless, the catalytic activity of Co1/NC could be restored via a simple thermal treatment, which could remove the adsorbates within the pore channel, hence releasing active sites that were originally inaccessible to reactants. [ABSTRACT FROM AUTHOR]

The electrochemical conversion of CO2 into value-added chemicals is a promising approach for addressing environmental and energy supply problems. In this study, electrochemical CO2 catalysis to ethanol is achieved using incorporated Cu/CuxO nanoparticles into nitrogenous porous carbon cuboids. Pyrolysis of the coordinated Cu cations with nitrogen heterocycles allowed Cu nanoparticles to detach from the coordination complex but remain dispersed throughout the porous carbon cuboids. The heterogeneous composite Cu/CuxO-PCC-0h electrocatalyst reduced CO2 to ethanol at low overpotential in 0.5 M KHCO3, exhibiting maximum ethanol faradaic efficiency of 50% at −0.5 V vs. reversible hydrogen electrode. Such electrochemical performance can be ascribed to the synergy between pyridinic nitrogen species, Cu/CuxO nanoparticles, and porous carbon morphology, together providing efficient CO2 diffusion, activation, and intermediates stabilization. This was supported by the notably high electrochemically active surface area, rich porosity, and efficient charge transfer properties. [ABSTRACT FROM AUTHOR]

The electrochemical conversion of CO2 into value-added chemicals is a promising approach for addressing environmental and energy supply problems. In this study, electrochemical CO2 catalysis to ethanol is achieved using incorporated Cu/CuxO nanoparticles into nitrogenous porous carbon cuboids. Pyrolysis of the coordinated Cu cations with nitrogen heterocycles allowed Cu nanoparticles to detach from the coordination complex but remain dispersed throughout the porous carbon cuboids. The heterogeneous composite Cu/CuxO-PCC-0h electrocatalyst reduced CO2 to ethanol at low overpotential in 0.5 M KHCO3, exhibiting maximum ethanol faradaic efficiency of 50% at −0.5 V vs. reversible hydrogen electrode. Such electrochemical performance can be ascribed to the synergy between pyridinic nitrogen species, Cu/CuxO nanoparticles, and porous carbon morphology, together providing efficient CO2 diffusion, activation, and intermediates stabilization. This was supported by the notably high electrochemically active surface area, rich porosity, and efficient charge transfer properties.

Carbon material has widely been utilized in the synthesis of efficient carbon-supported Pt (Pt/C) catalysts, in which the structural properties greatly influence the electrocatalytic performances of Pt/C catalysts. However, the effects of intrinsic defects in carbon supports on the performance of the alkaline hydrogen evolution reaction (HER) have not been systematically investigated. Herein, porous carbon supports with different degrees of intrinsic defects were prepared by a simple template-assisted strategy, and the resulting samples were systematically studied by various analytical methods. The results suggested that the presence of abundant intrinsic defects (vacancy and topological defects) in the carbon support was advantageous in terms of favoring the dispersion and anchoring of Pt species, promoting electron transfer between Pt atoms and the carbon support, and tuning the electronic states of Pt species. These features improved the HER performance of Pt/C catalysts. Compared to the nontemplate-assisted carbon-supported Pt catalyst (Pt/NTC) with an overpotential of 178 mV, the optimized template-assisted carbon-supported Pt catalyst (Pt/TC) exhibited a lower overpotential of 58 mV at 10 mA cm -2 . Besides, the Pt/TC catalyst displayed better HER durability than the Pt/NTC catalyst owing to its strong metal-support interaction. The DFT calculations confirmed the important role played by intrinsic defects (vacancy and topological defects) in stabilizing Pt atoms, with Pt-C3 coordination identified as the most favorable structure for improving the HER performance of Pt. Overall, novel insights on the significant contribution of intrinsic defects in porous carbon supports on the HER performances of Pt/C catalysts were provided, useful for future design and fabrication of advanced carbon-supported catalysts or other carbon-based electrode materials.

Porous nitrogen-doped and nitrogen-free carbon materials possessing high specific surface areas (400−1000 m2 g−1) were used for deposition of Ni by impregnation with nickel acetate followed by reduction. The nitrogen-doped materials synthesized by decomposition of acetonitrile at 973, 1073, and 1173 K did not differ much in the total content of incorporated nitrogen (4−5 at%), but differed in the ratio of the chemical forms of nitrogen. An X-ray photoelectron spectroscopy study showed that the rise in the synthesis temperature led to a strong growth of the content of graphitic nitrogen on the support accompanied by a reduction of the content of pyrrolic nitrogen. The content of pyridinic nitrogen did not change significantly. The prepared nickel catalysts supported on nitrogen-doped carbons showed by a factor of up to two higher conversion of formic acid as compared to that of the nickel catalyst supported on the nitrogen-free carbon. This was related to stabilization of Ni in the state of single Ni2+ cations or a few atoms clusters by the pyridinic nitrogen sites. The nitrogen-doped nickel catalysts possessed a high stability in the reaction at least within 5 h and a high selectivity to hydrogen (97%).

• A unified agglomerate model suitable for cold-start and nominal-working conditions. • Effects of ice/liquid water on transport and reaction outside/inside carbon particle considered. • Structure-performance relations revealed for different carbon microstructures. • Porous carbon boosts both nominal working and cold start performance. • Greater carbon radius and interior Pt fractions deteriorate cell performance. Replacing the conventional catalyst support of Pt/C for proton exchange membrane fuel cells (PEMFC) by meso-porous carbon is considered highly promising in improving the catalyst usage and the cell performance. However, ambiguity on the mechanism of such performance enhancement hinders further optimization and implementation of the porous carbon supports. Herein, we propose a unified agglomerate model for PEMFC catalyst layers with different carbon supports, valid for both normal-working and cold-start conditions, and utilizing minimal phenomenological parameters. Parametric study regarding key material properties reveals that typical porous carbon supports such as Ketjenblack enables easier cold start but slightly deteriorates the nominal working cell performance. Using sensitivity analysis, five carbon property variables have been identified as most significantly affecting the overall cell performance. Fine-tuning the carbon radius and the platinum fraction inside the micropores of Ketjenblack is found pivotal for maximizing the catalyst layer effectiveness. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mo doped carbon aerogels are active catalysts in hydroconversion of acetic acid. [•] The mechanism of the hydrogenation depends on Mo concentration. [•] Post-catalysis analysis reveals severe changes in morphology and chemistry. [•] Highest selectivity for ethanol is 16% when 85% of the acetic acid is converted. [Copyright &y& Elsevier]

Precise adjustment of the metal site structure in single-atom catalysts (SACs) plays a key role in addressing the oxygen evolution reaction (OER). Herein, we report the synthesis of O-doped Ni SACs anchored on porous graphene-like carbon (Ni-O-G) using molten salts (ZnCl 2 and NaCl) as templates, in which the unique Ni-O 4 structure serves as the active sites. Ni-O-G, with an overpotential of only 238 mV (@ 10 mA cm -2 ), is one of the more advanced catalysts. An array of characterizations and density functional theory calculations show that the Ni-O 4 coordination enables Ni to be closer to the Fermi level compared to traditional Ni-N 4 , enhancing the electronic metal-support interaction to facilitate OER kinetics. Thus, this work offers an alternative strategy for the structural modulation of Ni SACs and the effect of different coordination elements with the same atomic coordination structure on the intrinsic OER activity.

Porous nitrogen-doped and nitrogen-free carbon materials possessing high specific surface areas (400–1000 m2 g−1) were used for deposition of Ni by impregnation with nickel acetate followed by reduction. The nitrogen-doped materials synthesized by decomposition of acetonitrile at 973, 1073, and 1173 K did not differ much in the total content of incorporated nitrogen (4–5 at%), but differed in the ratio of the chemical forms of nitrogen. An X-ray photoelectron spectroscopy study showed that the rise in the synthesis temperature led to a strong growth of the content of graphitic nitrogen on the support accompanied by a reduction of the content of pyrrolic nitrogen. The content of pyridinic nitrogen did not change significantly. The prepared nickel catalysts supported on nitrogen-doped carbons showed by a factor of up to two higher conversion of formic acid as compared to that of the nickel catalyst supported on the nitrogen-free carbon. This was related to stabilization of Ni in the state of single Ni2+ cations or a few atoms clusters by the pyridinic nitrogen sites. The nitrogen-doped nickel catalysts possessed a high stability in the reaction at least within 5 h and a high selectivity to hydrogen (97%). [ABSTRACT FROM AUTHOR]