Improving the Sustainability of Electrochemical Direct Air Capture in a 3D Printed Redox Flow Cell

To enable the scale-up of electrochemical direct air capture (DAC), it is critical to enhance the sustainability of the process by maximizing efficiency and optimizing for targeted durability. Currently, many of the organic molecules reportedly used for electrochemical CO2 capture suffer from degradation upon extended redox cycling in the presence of oxygen, which generates chemical waste. Furthermore, off-the-shelf electrochemical flow cellsan integral piece of equipment for redox flow processescost thousands of dollars to procure. In this work, we addressed these challenges by exploring the DAC cyclability of five organic molecules. The highest performing molecule was phenazine, which maintained an average Coulombic efficiency of 100% over 9.5 h of testing with a theoretical minimum energy of 77.2 kJ/mol of CO2 captured. Additionally, we report the design and development of an economical 3D printed redox flow cell and its demonstration for electrochemical DAC

Microwave-Assisted Solvothermal Synthesis and Optical Properties of Tagged MIL-140A Metal–Organic Frameworks

A series of tagged MIL-140A-R frameworks have been synthesized using a microwave-assisted solvothermal method. Compared with their UiO-66-R polymorphs, the absorption energies in the MIL-140A-R series (R = NH₂, NO₂, Br, Cl, and F) are extended toward the visible region because of the spatial arrangement of the linkers

In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn²⁺ Coordination Framework

An investigation of the redox-active tris­[4-(pyridin-4-yl)­phenyl]­amine (NPy₃) ligand in the solution state and upon its incorporation into the solid-state metal–organic framework (MOF) [Zn­(NPy₃)­(NO₂)₂·<i>x</i>MeOH·<i>x</i>DMF]_<i>n</i> (MeOH = methanol and DMF = <i>N</i>,<i>N</i>-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs

In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn²⁺ Coordination Framework

An investigation of the redox-active tris­[4-(pyridin-4-yl)­phenyl]­amine (NPy₃) ligand in the solution state and upon its incorporation into the solid-state metal–organic framework (MOF) [Zn­(NPy₃)­(NO₂)₂·<i>x</i>MeOH·<i>x</i>DMF]_<i>n</i> (MeOH = methanol and DMF = <i>N</i>,<i>N</i>-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs

In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn²⁺ Coordination Framework

An investigation of the redox-active tris­[4-(pyridin-4-yl)­phenyl]­amine (NPy₃) ligand in the solution state and upon its incorporation into the solid-state metal–organic framework (MOF) [Zn­(NPy₃)­(NO₂)₂·<i>x</i>MeOH·<i>x</i>DMF]_<i>n</i> (MeOH = methanol and DMF = <i>N</i>,<i>N</i>-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs

Electronic, Optical, and Computational Studies of a Redox-Active Napthalenediimide-Based Coordination Polymer

The new one-dimensional coordination framework (Zn­(DMF)­NO₃)₂(NDC)­(DPMNI), where NDC = 2,6-naphthalenedicarboxylate and DPMNI = <i>N</i>,<i>N</i>′-bis­(4-pyridylmethyl)-1,4,5,8-naphthalenetetracarboxydiimide, which has been crystallographically characterized, exhibits two redox-accessible states due to the successive reduction of the naphthalenediimide (NDI) ligand core. Solid-state electrochemical and vis–near-IR spectroelectrochemical measurements coupled with density functional theory (DFT) calculations enabled the origins of the optical transitions in the spectra of the monoradical anion and dianion states of the material to be assigned. Electron paramagnetic resonance (EPR) spectroscopy revealed that the paramagnetic radical anion state of the DPMNI core could be accessed upon broad-spectrum white light irradiation of the material, revealing a long-lived excited state, possibly stabilized by charge delocalization which arises from extensive π<i>–</i>π* stacking interactions between alternating NDC and NDI aromatic cores which are separated by a distance of 3.580(2) Å

Untangling Complex Redox Chemistry in Zeolitic Imidazolate Frameworks Using Fourier Transformed Alternating Current Voltammetry

Two zeolitic imidazolate frameworks, ZIF-67 and ZIF-8, were interrogated for their redox properties using Fourier transformed alternating current voltammetry, which revealed that the 2-methylimidazolate ligand is responsible for multiple redox transformations. Further insight was gained by employing discrete tetrahedral complexes, [M­(DMIM)₄]²⁺ (DMIM = 1,2-dimethylimidazole, M = Co^II or Zn^II) which have similar structural motifs to ZIFs. In this work we demonstrate a multidirectional approach that enables the complex electrochemical behavior of ZIFs to be unraveled

Electronic, Optical, and Computational Studies of a Redox-Active Napthalenediimide-Based Coordination Polymer

The new one-dimensional coordination framework (Zn­(DMF)­NO₃)₂(NDC)­(DPMNI), where NDC = 2,6-naphthalenedicarboxylate and DPMNI = <i>N</i>,<i>N</i>′-bis­(4-pyridylmethyl)-1,4,5,8-naphthalenetetracarboxydiimide, which has been crystallographically characterized, exhibits two redox-accessible states due to the successive reduction of the naphthalenediimide (NDI) ligand core. Solid-state electrochemical and vis–near-IR spectroelectrochemical measurements coupled with density functional theory (DFT) calculations enabled the origins of the optical transitions in the spectra of the monoradical anion and dianion states of the material to be assigned. Electron paramagnetic resonance (EPR) spectroscopy revealed that the paramagnetic radical anion state of the DPMNI core could be accessed upon broad-spectrum white light irradiation of the material, revealing a long-lived excited state, possibly stabilized by charge delocalization which arises from extensive π<i>–</i>π* stacking interactions between alternating NDC and NDI aromatic cores which are separated by a distance of 3.580(2) Å

Crystal Structures, Magnetic Properties, and Electrochemical Properties of Coordination Polymers Based on the Tetra(4-pyridyl)-tetrathiafulvalene Ligand

Seven new coordination polymers based on the redox-active tetra­(4-pyridyl)-tetrathiafulvalene ligand (TTF­(py)₄) and different transition-metal ions, namely, {[Cu­(hfac)₂]­[TTF­(py)₄]·2­(CH₂Cl₂)}_<i>n</i> (<b>1</b>), {[Co­(acac)₂]­[TTF­(py)₄]_0.5·(CHCl₃)}<i>_n</i> (<b>2</b>), {[Mn­(hfac)₂]­[TTF­(py)₄]_0.5}<i>_n</i> (<b>3</b>), {[Cu₂(OAc)₄]­[TTF­(py)₄]_0.5·1.5­(CHCl₃)·0.5­(H₂O)·(CH₃CN)}<i>_n</i> (<b>4</b>), {[Mn­(SCN)₂]­[TTF­(py)₄]·6­(CH₂Cl₂)}_<i>n</i> (<b>5</b>), {[Mn­(SeCN)­Cl]­[TTF­(py)₄]}_<i>n</i> (<b>6</b>), and {Cu₂[TTF­(py)₄]₂·(ClO₄)₂·2.5­(CH₂Cl₂)·1.5­(CH₃CN)}<i>_n</i> (<b>7</b>), were synthesized and characterized. The tetrapyridyl ligand coordinates to metal ions in a bidentate or tetradentate fashion, forming complexes <b>1</b>–<b>7</b> with different structures. Complex <b>1</b> exhibits a one-dimensional chain structure. Complexes <b>2</b>, <b>3</b>, and <b>4</b> possess similar (4,2)-connected binodal two-dimensional networks, while complexes <b>5</b> and <b>6</b> have similar (4,4)-connected binodal two-dimensional networks with two different rings. Complex <b>7</b> shows a 2-fold interpenetrated (4,4)-connected binodal PtS-type three-dimensional framework. Meanwhile, these complexes feature diverse nonclassical hydrogen bonding interactions. In addition, magnetic and solid-state electrochemical properties for typical complexes have been studied

Crystal Structures, Magnetic Properties, and Electrochemical Properties of Coordination Polymers Based on the Tetra(4-pyridyl)-tetrathiafulvalene Ligand

Seven new coordination polymers based on the redox-active tetra­(4-pyridyl)-tetrathiafulvalene ligand (TTF­(py)₄) and different transition-metal ions, namely, {[Cu­(hfac)₂]­[TTF­(py)₄]·2­(CH₂Cl₂)}_<i>n</i> (<b>1</b>), {[Co­(acac)₂]­[TTF­(py)₄]_0.5·(CHCl₃)}<i>_n</i> (<b>2</b>), {[Mn­(hfac)₂]­[TTF­(py)₄]_0.5}<i>_n</i> (<b>3</b>), {[Cu₂(OAc)₄]­[TTF­(py)₄]_0.5·1.5­(CHCl₃)·0.5­(H₂O)·(CH₃CN)}<i>_n</i> (<b>4</b>), {[Mn­(SCN)₂]­[TTF­(py)₄]·6­(CH₂Cl₂)}_<i>n</i> (<b>5</b>), {[Mn­(SeCN)­Cl]­[TTF­(py)₄]}_<i>n</i> (<b>6</b>), and {Cu₂[TTF­(py)₄]₂·(ClO₄)₂·2.5­(CH₂Cl₂)·1.5­(CH₃CN)}<i>_n</i> (<b>7</b>), were synthesized and characterized. The tetrapyridyl ligand coordinates to metal ions in a bidentate or tetradentate fashion, forming complexes <b>1</b>–<b>7</b> with different structures. Complex <b>1</b> exhibits a one-dimensional chain structure. Complexes <b>2</b>, <b>3</b>, and <b>4</b> possess similar (4,2)-connected binodal two-dimensional networks, while complexes <b>5</b> and <b>6</b> have similar (4,4)-connected binodal two-dimensional networks with two different rings. Complex <b>7</b> shows a 2-fold interpenetrated (4,4)-connected binodal PtS-type three-dimensional framework. Meanwhile, these complexes feature diverse nonclassical hydrogen bonding interactions. In addition, magnetic and solid-state electrochemical properties for typical complexes have been studied