Selective CO₂ Capture by Activated Carbons: Evaluation of the Effects of Precursors and Pyrolysis Process

Activated carbons are produced from different Canadian waste biomasses including agricultural waste (wheat straw and flax straw), forest residue (sawdust and willow ring), and animal manure (poultry litter). The precursors are carbonized through the fast and slow pyrolysis processes and then activated with potassium hydroxide. A fixed-bed reactor is used for temperature swing adsorption of CO₂ in a gas mixture of N₂, O₂, and CO₂ to study the cyclic CO₂ adsorption capacity and selectivity of the produced activated carbons. The breakthrough adsorption capacity of the produced activated carbon is measured under a flue gas condition of 15 mol % of CO₂, 5 mol % of O₂, and 80% of N₂ at 25 °C and atmospheric pressure. Slow pyrolysis based activated carbon has a lower surface area and total pore volume but higher adsorption capacity in the presence of N₂. Sawdust based activated carbon synthesized using the slow pyrolysis process creates the highest ultra-micropore volume of 0.36 cm³/g, and the highest adsorption capacity in N₂ (78.1 mg/g) but low selectivity (2.8) over O₂ because of the oxygen functional groups on the surface. Ultra-micropores and surface chemistry of adsorbents are far more important than particle size, total pore volume, and internal surface area of the adsorbents. All the samples fully recovered their initial adsorption capacity in each cycle (for up to 10 cycles). This work also demonstrates that adsorption capacity and selectivity of activated carbon can be controlled and optimized through the choice of starting material and carbonization conditions

Electrochemical Changes in Lithium-Battery Electrodes Studied Using ⁷Li NMR and Enhanced ¹³C NMR of Graphene and Graphitic Carbons

An anode composed of tin-core, graphitic-carbon-shell nanoparticles distributed on graphene nanosheets, Sn@C-GNs, is studied during the lithiation process. ⁷Li NMR provides an accurate measure of the stepwise reduction of metallic Sn to lithium–tin alloys and reduction of the graphitic carbon. The metallic nanoparticle cores are observed to form ordered, crystalline phases at each step of the lithiation process. The ⁷Li 2D experiments presented provide insight into the proximity of the various phases, reflecting the mechanism of the electrochemical reaction. In particular, a sequential model of nanoparticle lithiation, rather than a simultaneous process, is suggested. Movement of lithium ions between two elements of the nanostructured Sn@C-GNs material, the metallic core and carbon shell, is also observed. Conventional ¹³C solid-state NMR, SSNMR, experiments on <5 mg of active material from electrochemical cells were found to be impossible, but signal enhancements (up to 18-fold) via the use of extended echo trains in conjunction with magic-angle spinning enabled NMR characterization of the carbon. We demonstrate that the ¹³C data is extremely sensitive to the added electron density when the graphitic carbon is reduced. We also investigate ex situ carbon electrodes from cycled Li–O₂ cells, where we find no evidence of charge sharing between the electrochemically active species and the graphitic carbon in the ¹³C NMR spectroscopy

<i>In Situ</i> X‑ray Absorption Near-Edge Structure Study of Advanced NiFe(OH)_<i>x</i> Electrocatalyst on Carbon Paper for Water Oxidation

A promising NiFe­(OH)_<i>x</i> catalyst for oxygen evolution reaction (OER) has been successfully fabricated and studied in detail using <i>in situ</i> X-ray absorption near-edge structure (XANES) spectroscopy. The chemical nature of elements (Ni, Fe) in electrocatalysts has been elucidated from Fe and Ni K- and L-edge XANES. The increase of oxidation states of Ni from Ni­(III) to Ni(3.6) together with a highly covalent Fe­(IV)–O bond under OER process is observed. Charge transfer between Ni and Fe through a “Ni–O–Fe” bond is proposed, accounting for the high catalytic activities of NiFe­(OH)_<i>x</i>

Observation of Surface/Defect States of SnO₂ Nanowires on Different Substrates from X-ray Excited Optical Luminescence

SnO₂ nanowires (NWs) have been successfully synthesized on two different substrates (stainless steel (SS) and copper) via a facile hydrothermal process. SnO₂ NWs with varying degrees of crystallinity are obtained on different substrates. The growth mechanisms are also deducted by observing the morphology revolution at various reaction times. Furthermore, the electronic structures and optical properties have been investigated by X-ray absorption near edge structure (XANES) and X-ray excited optical luminescence (XEOL) measurements. The yellow-green luminescence from SnO₂ NWs is originated from the intrinsic surface states. Compared with SnO₂ NWs on copper, a near infrared (NIR) luminescence is observed for SnO₂ NWs on SS, which resulted from poor crystallinity and an abundance of defect/surface states

Defect-Rich Crystalline SnO₂ Immobilized on Graphene Nanosheets with Enhanced Cycle Performance for Li Ion Batteries

A one-step microwave-assisted hydrothermal method (MAHM) has been developed to synthesize SnO₂/graphene composites. It is shown that fine SnO₂ nanoparticles with an average size of 3.5 nm can be homogeneously deposited on graphene nanosheets (GNSs) using this technique. The electronic structure as revealed from X-ray absorption near edge structure (XANES) shows that the SnO₂ nanoparticles are abundant in surface defects with oxygen vacancies, which facilitate the immobilization of SnO₂ onto GNSs by electronic interaction. Carbon K edge XANES provide direct evidence of strong interaction between SnO₂ and GNSs. The SnO₂/graphene nanocomposites deliver a superior reversible capacity of 635 mAh g^–1 after 100 cycles and display excellent rate performance. All these desirable features strongly indicate that SnO₂/graphene composite is a promising anode material in high-performance lithium ion batteries

Probing the Functionality of LiFSI Structural Derivatives as Additives for Li Metal Anodes

Lithium (Li) metal is a compelling replacement for graphite anodes in Li-ion batteries to increase gravimetric energy if the cyclability can be improved. Motivated by high Li Coulombic efficiency (CE) achieved with electrolytes featuring the bis(fluorosulfonyl)imide (FSI–) anion, this work examined chemically related sulfonyl/sulfamoyl fluoride additives to correlate FSI–-relevant structural features with CE. Across three exemplary carbonate- and glyme-based electrolytes, extended solid, liquid, and gas phase characterizations reveal that Li+ coordination is necessary yet insufficient for FSI– derivatives to affect cycling. Beyond coordination, the reactivity of the baseline solvent and the key structural features of the additives are shown to strongly regulate CE, with possession of an N centercommon to sulfamoylfluorides and FSI–consistently leading to higher CE. Some derivatives outperform FSI– in short-term cycling; however, they have difficulty competing with the longevity of FSI–. These results provide insights for developing improved additives in the future through careful consideration of reactant structure and solvent codesign