Nanocast nitrogen-containing ordered mesoporous carbons from glucosamine for selective CO2 capture

D-glucosamine is investigated as a non-toxic and sustainable carbon/nitrogen (C/N) source for the templated synthesis of nitrogen-containing CMK-8 ordered mesoporous carbons (NOMCs) conceived for selective CO2 uptake. Pyrolysis temperature is varied during nanocasting using the KIT-6 silica hard template to tailor microporosity and nitrogen inclusions. NOMCs exhibit large surface area (600–1000 m2 g-1) and excellent pore ordering. The CO2/adsorbent interaction energy is estimated by the isosteric enthalpy of adsorption (∼33–40 kJ mol-1) and Henry's constants. The role of nitrogen content (∼7–12 at.%) and of each type of N-species on CO2 adsorption is studied by X-ray photoelectron spectroscopy, and CO2/N2 selectivity is attributed, being pyridinic functionalities the most effective ones. NOMCs are tested at different temperatures, gas flow compositions, reversibility, and so on; in all tested conditions, they outperform a homologous bare sucrose-derived carbon. Enhancing micropore volume allows achieving maximum adsorption capacity in pure CO2 (1.47 mmol g−1 at 30 °C/0.9 bar), whereas increasing surface N-content accounts for the highest selectivity in CO2/N2 mixtures (20/80 v/v) at 35 °C/1 bar (maximum CO2 uptake 0.82 mmol g−1). The combination of a suitable C/N precursor and the hard templating synthetic route is effective for obtaining high-performing, sustainable, and reusable selective CO2 sorbents, without any activation steps or N-doping post-treatments

Effects of Iron Species on Low Temperature CO2 Electrolyzers

Electrochemical energy conversion devices are considered key in reducing CO2 emissions and significant efforts are being applied to accelerate device development. Unlike other technologies, low temperature electrolyzers have the ability to directly convert CO2 into a range of value‐added chemicals. To make them commercially viable, however, device efficiency and durability must be increased. Although their design is similar to more mature water electrolyzers and fuel cells, new cell concepts and components are needed. Due to the complexity of the system, singular component optimization is common. As a result, the component interplay is often overlooked. The influence of Fe‐species clearly shows that the cell must be considered holistically during optimization, to avoid future issues due to component interference or cross‐contamination. Fe‐impurities are ubiquitous, and their influence on single components is well‐researched. The activity of non‐noble anodes has been increased through the deliberate addition of iron. At the same time, however, Fe‐species accelerate cathode and membrane degradation. Here, we interpret literature on single components to gain an understanding of how Fe‐species influence low temperature CO2 electrolyzers holistically. The role of Fe‐species serves to highlight the need for considerations regarding component interplay in general

Investigating the platinum electrode surface during Kolbe electrolysis of acetic acid

Platinum is commonly applied as the anode material for Kolbe electrolysis of carboxylic acids thanks to its superior performance. Literature claims that the formation of a barrier layer on the Pt anode in carboxylic acid electrolyte suppresses the competing oxygen evolution and promotes anodic decarboxylation. In this work, we show by using a combination of complementary in situ and ex situ surface sensitive techniques, that the presence of acetate ions also prevents the formation of a passive oxide layer on the platinum surface at high anodic potentials even in aqueous electrolyte. Furthermore, Pt dissolves actively under these conditions, challenging the technical implementation of Kolbe electrolysis. Future studies exploring the activity-structure-stability relation of Pt are required to increase the economic viability of Kolbe electrolysis

Enhancing OER Activity of Ni/Co Oxides via Fe/Mn Substitution within Tailored Mesoporous Frameworks

Non-noble mixed metal oxides are promising electrocatalysts for water splitting reactions in alkaline media. The synthesis of complex mixed metal oxides with the desired composition is challenging due to the formation of phase impurities when synthesis is performed via classical approaches. In this work, we applied the nanocasting technique combined with low-temperature calcination (200 degrees C) in a quasi-sealed container to obtain highly ordered mesoporous mixed metal (Mn/Fe/Ni/Co) oxides. This procedure provides electrocatalysts with distinctive physicochemical characteristics and improved electrocatalytic properties. Partial Ni substitution in Ni0.5Co2.5O4 by Fe and Mn in combination with the highly ordered mesostructure offers a large number of active sites and enhances the performance of the catalyst toward the oxygen evolution reaction (OER) in the alkaline electrolyte. The Mn/Fe/Ni/Co oxide calcined at 200 degrees C outperforms all other synthesized oxides (current density of 262 mA cm-2 at 1.7 V versus RHE and overpotential of 363 mV at 10 mA cm-2) due to synergistic effects. Moreover, this catalyst exhibits significantly higher activity compared to the oxide of identical composition calcined at higher temperature. The results presented in this work show that tuning the synthesis conditions and composition of mixed metal oxides is a simple way to tailor their surface chemistry, mesoporous structure, and catalytic performance for the OER.11Nsciescopu

Design of nitrogen-containing carbonaceous adsorbents for CO2 capture and energy storage applications

The increase of global CO2 concentration, mainly due to anthropogenic emissions from combustion of fossil fuels, is responsible for severe environmental issues, in particular global warming. Limitations in the use of polluting energy sources and the development of strategies for the reduction of CO2 emissions are therefore strictly urgent. Activated carbons can be employed for several applications: separation processes, as catalyst supports as well as electrode/electrolyte components in electrochemical energy storage/conversion devices. Among these, nitrogen-containing ordered mesoporous carbons (NOMCs) are proposed for CO2 up-take. Ordered mesoporous carbons (OMCs) can be synthesized with different pore architectures as nano-replications of a silica hard template, using a three-step procedure: i) infiltration of the carbon source inside the pore channels of silica, ii) pyrolysis of the hybrid system and iii) template removal. For example, this approach has been used to prepare the well-known CMK-type materials: CMK-1, CMK3, CMK-6 and CMK-8 are synthesized using MCM-48, SBA-15, SBA-16 and KIT-6 silica templates, respectively. NOMCs are here proposed as CO2 adsorbents in the context of the carbon capture and storage technologies. In this work, the aforementioned approach, known for the reparation of the so-called CMK-type materials, is exploited for tuning the textural features of the carbonaceous adsorbents and therefore optimizing their capture performances and the kinetics of gas diffusion. Moreover, a nitrogen-containing carbon source was chosen as a precursor, in order to introduce basic sites useful to promote the interaction with the acidic CO2 molecule, fostering in this way also a selective adsorption in a gas mixture. Therefore, the regular, ordered mesoporous architecture and the superficial chemical properties have been investigated in order to study their effect on the CO2 capture performances. The described NOMCs can be applied not only for CO2 up-take, but also in energy storage and conversion devices (lithium or sodium based batteries for instance), photocatalysis or electrocatalytic reduction of CO2. For these applications, they can be used as-synthesized or eventually decorated with specifically selected metal oxides

Nitrogen-containing ordered mesoporous carbons applied as CO2 adsorbents and anode materials in energy storage devices

Porous carbons, thanks to their easily tunable features (porosity, surface chemical properties, etc.), can be employed for several applications: separation processes, as catalyst supports as well as electrode components in electrochemical energy storage/conversion devices. Among these, in the framework of strategies for the mitigation of global warming and climate changes, nitrogen-containing ordered mesoporous carbons (NOMCs) are proposed as CO2 adsorbents, thanks to their outstanding adsorption ability and selectivity. NOMCs can be synthesized with different pore architectures as nano-replications of a silica hard template, using a three-step procedure: i) infiltration of the carbon/nitrogen source inside the pore channels of silica, ii) pyrolysis of the hybrid system, and iii) template removal. This method is particularly useful for achieving the optimal textural properties, i.e. a hierarchical pore architecture composed of both micro- and mesopores able to promote at the same time improved capture performances and fast kinetics of gas diffusion, respectively. In this work, the aforementioned approach, known for the preparation of the so-called CMK-type materials, is exploited for tuning the textural features of the carbonaceous adsorbents. Moreover, a natural occurring nitrogen/carbon source was chosen as a precursor, in order to introduce basic sites useful to promote the interaction of the carbon framework with the acidic CO2 molecule, thus also fostering a selective adsorption in a gas mixture. Therefore, the regular, ordered mesoporous architecture and the chemical surface properties were investigated to unveil their effect on the CO2 capture performances. In addition, the described NOMCs can be applied not only for CO2 up-take, but also in energy storage and conversion devices (e.g., lithium or sodium-based batteries), photocatalysis or electrocatalytic reduction of CO2. For these applications, they can be used as-synthesized or eventually decorated with specifically selected metal oxides, and related results are here shown

Nitrogen-containing mesoporous carbons via nanocasting for CO2 capture and energy storage applications

In this work, nitrogen-containing ordered mesoporous carbons (NOMCs) are proposed as CO2 adsorbents. The nanocasting approach, using ordered mesoporous silica hard templates, was exploited for tuning the textural features of the carbonaceous adsorbents and therefore optimizing their capture performances and the kinetics of gas diffusion. Moreover, an eco-friendly nitrogen-containing carbon source was chosen as a precursor, in order to introduce basic sites useful to promote the interaction with the acidic CO2 molecule, thus fostering a selective adsorption in a gas mixture. CMK-8 materials were prepared using KIT-6 templates, varying the pyrolysis temperature in order to evaluate the role of microporosity and nitrogen species (amount and type of N inclusions, i.e. pyridinic, pyrrolic and graphitic) in CO2 adsorption. An extensive characterization of the ordered mesoporous architecture (low-angle XRD, FESEM, TEM and N2 physisorption at 77K), microporosity (CO2 isotherms at 273K) and surface chemical properties by XPS was carried out. CO2 capture tests were performed in different conditions of temperature and pressure. An adsorption of 1.05 mmol/g (4.6% weight increase) was achieved at 30 °C and 90 kPa in a pure CO2 flow. Also selectivity in a mixture with N2 and reusability upon cycling was investigated. The described NOMCs can be applied not only for CO2 up-take, but also in energy storage and conversion devices (e.g., lithium or sodium based batteries), photocatalysis or electrocatalytic reduction of CO2. For these applications, they can be used as-synthesized or decorated with specifically selected metal oxides and testing is now in progress in our laboratories

Data from: Cu+ transient species mediate Cu catalyst reconstruction during CO2 electroreduction

<p>Understanding metal surface reconstruction is of the uttermost importance in heterogeneous<br> catalysis as this phenomenon directly affects the nature of available active sites. However,<br> surface reconstruction is notoriously difficult to study because of the dynamic nature of the<br> phenomena behind it, particularly when solid/liquid interfaces are involved. Here, we report<br> on the intermediates which drive the rearrangement of copper catalysts for the electrochemical<br> CO2 reduction reaction (CO2RR). Online mass spectrometry and UV-Vis absorption<br> spectroscopy data are consistent with a dissolution–redeposition process, previously<br> demonstrated by in-situ electron microscopy. The data indicate that the soluble transient<br> species contain copper in +1 oxidation state. Density functional theory identifies copper adsorbate<br> complexes which can exist in solution under operating conditions. Copper carbonyls and oxalates are suggested as the major reaction-specific species driving copper reconstruction during CO2RR. This work motivates future methodological studies to enable the direct detection of these compounds and strategies which specifically target them to improve the catalyst operational stability.</p&gt