Amine and amide functionalized mesoporous carbons: a strategy improving sulfide/host interactions in Li‐S batteries

Lithium-sulfur (Li-S) batteries are of great interest due to their potentially high energy density, but the low electronic conductivity of both the sulfur (S-8) cathode active material and the final discharge product lithium sulfide (Li2S) require the use of a conductive host. Usually made of relatively hydrophobic carbon, such hosts are typically ill-suited to retain polar discharge products such as the intermediate lithium polysulfides (LiPs) and the final Li2S. Herein, we propose a route to increase the sulfur utilization by functionalizing the surface of ordered mesoporous carbon CMK3 with polar groups. These derivatized CMK3 materials are made using a simple two-step procedure of bromomethylation and subsequent nucleophilic substitution with amine or amide nucleophiles. We demonstrate that, compared to the unfunctionalized control, these modified CMK3 surfaces have considerably larger binding energies with LiPs and Li2S, which are proposed to aid the electrochemical conversion between S-8 and Li2S by keeping the LiPs species in close proximity to the carbon surface during Li-S battery cycling. As a result, the functionalized cathodes exhibit significantly improved specific capacities relative to their unmodified precursor

Amine‐ and Amide‐Functionalized Mesoporous Carbons: A Strategy for Improving Sulfur/Host Interactions in Li–S Batteries

Lithium-sulfur (Li-S) batteries are of great interest due to their potentially high energy density, but the low electronic conductivity of both the sulfur (S-8) cathode active material and the final discharge product lithium sulfide (Li2S) require the use of a conductive host. Usually made of relatively hydrophobic carbon, such hosts are typically ill-suited to retain polar discharge products such as the intermediate lithium polysulfides (LiPs) and the final Li2S. Herein, we propose a route to increase the sulfur utilization by functionalizing the surface of ordered mesoporous carbon CMK3 with polar groups. These derivatized CMK3 materials are made using a simple two-step procedure of bromomethylation and subsequent nucleophilic substitution with amine or amide nucleophiles. We demonstrate that, compared to the unfunctionalized control, these modified CMK3 surfaces have considerably larger binding energies with LiPs and Li2S, which are proposed to aid the electrochemical conversion between S-8 and Li2S by keeping the LiPs species in close proximity to the carbon surface during Li-S battery cycling. As a result, the functionalized cathodes exhibit significantly improved specific capacities relative to their unmodified precursor

Sequential "click'' functionalization of mesoporous titania for energy-relay dye enhanced dye-sensitized solar cells

Energy relay dyes (ERDs) have been investigated previously as a mean to achieve panchromatic spectral response in dye-sensitized solar cells via energy transfer. To reduced the distance between the ERDs and energy-accepting injection dyes (IDs) on the surface of a mesoporous titanium dioxide electrode, the ERDs were immobilized adjacent to the IDs via a sequential functionalization approach. In the first step, azidobenzoic acid molecules were co-adsorbed on the mesoporous titanium dioxide surface with the ID. In the second step, the highly selective copper(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition "click'' reaction was employed to couple an alkyne-functionalized ERD to the azidobenzoic acid monolayer. The cycloaddition step in the mesoporous electrode was slowed dramatically due to reactants and catalysts forming agglomerates. In solar cell devices, the close proximity between the surface-immobilized ERD and energy-accepting squaraine sensitizer dyes results in energy transfer efficiencies of up to 91%. The relative improvement in device performance due to the additional ERD spectral response was 124%, which is among the highest reported. The sequential functionalization approach described herein is transferrable to other applications requiring the functionalization of electrodes with complex molecules

Birch Reductive Alkylation of Methyl <i>m</i>‑(Hydroxymethyl)benzoate Derivatives and the Behavior of <i>o</i>- and <i>p</i>‑(Hydroxymethyl)benzoates under Reductive Alkylation Conditions

Birch reductive alkylation of methyl <i>m</i>-(hydroxymethyl)­benzoate derivatives, using lithium in ammonia–tetrahydrofuran in the presence of <i>tert</i>-butyl alcohol, can be achieved without significant loss of benzylic oxygen substituents. Similar treatment of <i>o</i>- and <i>p</i>-(hydroxymethyl)­benzoate derivatives results largely in loss of benzylic oxygen substituents. The results are rationalized by computations describing electron density patterns in the putative radical anion intermediate involved in these reactions

Birch Reductive Alkylation of Methyl <i>m</i>‑(Hydroxymethyl)benzoate Derivatives and the Behavior of <i>o</i>- and <i>p</i>‑(Hydroxymethyl)benzoates under Reductive Alkylation Conditions

Birch reductive alkylation of methyl <i>m</i>-(hydroxymethyl)­benzoate derivatives, using lithium in ammonia–tetrahydrofuran in the presence of <i>tert</i>-butyl alcohol, can be achieved without significant loss of benzylic oxygen substituents. Similar treatment of <i>o</i>- and <i>p</i>-(hydroxymethyl)­benzoate derivatives results largely in loss of benzylic oxygen substituents. The results are rationalized by computations describing electron density patterns in the putative radical anion intermediate involved in these reactions

Birch Reductive Alkylation of Methyl <i>m</i>‑(Hydroxymethyl)benzoate Derivatives and the Behavior of <i>o</i>- and <i>p</i>‑(Hydroxymethyl)benzoates under Reductive Alkylation Conditions

Birch reductive alkylation of methyl <i>m</i>-(hydroxymethyl)­benzoate derivatives, using lithium in ammonia–tetrahydrofuran in the presence of <i>tert</i>-butyl alcohol, can be achieved without significant loss of benzylic oxygen substituents. Similar treatment of <i>o</i>- and <i>p</i>-(hydroxymethyl)­benzoate derivatives results largely in loss of benzylic oxygen substituents. The results are rationalized by computations describing electron density patterns in the putative radical anion intermediate involved in these reactions