More Like this

1. Heterogeneous Nature of Electrocatalytic CO/CO ₂ Reduction by Cobalt Phthalocyanines

   https://doi.org/10.1002/cssc.202001396  

   Wu, Yueshen; Hu, Gongfang; Rooney, Conor_L; Brudvig, Gary_W; Wang, Hailiang (July 2020, ChemSusChem)

   Abstract Molecular catalysts for electrochemical CO₂reduction have traditionally been studied in their dissolved states. However, the heterogenization of molecular catalysts has the potential to deliver much higher reaction rates and enable the reduction of CO₂by more than two electrons. In light of the recently discovered reactivity of heterogenized cobalt phthalocyanine molecules to catalyze CO₂reduction into methanol, direct comparison is needed to uncover the distinct catalytic activity and selectivity in homogeneous catalysis versus heterogeneous catalysis. Herein, soluble cobalt phthalocyanine derivatives were synthesized, and their catalytic activities in the homogeneous solutions were evaluated. The results show that the observed catalytic activities for both CO₂‐to‐CO and CO‐to‐methanol conversions in aqueous solutions of the cobalt phthalocyanines are predominantly heterogeneous in nature through the adsorbed species on the electrode. 

   more » « less
2. Aqueous Photoelectrochemical CO ₂ Reduction to CO and Methanol over a Silicon Photocathode Functionalized with a Cobalt Phthalocyanine Molecular Catalyst

   https://doi.org/10.1002/anie.202215213  

   Shang, Bo; Rooney, Conor L.; Gallagher, David J.; Wang, Bernie T.; Krayev, Andrey; Shema, Hadar; Leitner, Oliver; Harmon, Nia J.; Xiao, Langqiu; Sheehan, Colton; et al (January 2023, Angewandte Chemie International Edition)

   Abstract We report a precious‐metal‐free molecular catalyst‐based photocathode that is active for aqueous CO 2 reduction to CO and methanol. The photoelectrode is composed of cobalt phthalocyanine molecules anchored on graphene oxide which is integrated via a (3‐aminopropyl)triethoxysilane linker to p‐type silicon protected by a thin film of titanium dioxide. The photocathode reduces CO 2 to CO with high selectivity at potentials as mild as 0 V versus the reversible hydrogen electrode (vs RHE). Methanol production is observed at an onset potential of −0.36 V vs RHE, and reaches a peak turnover frequency of 0.18 s −1 . To date, this is the only molecular catalyst‐based photoelectrode that is active for the six‐electron reduction of CO 2 to methanol. This work puts forth a strategy for interfacing molecular catalysts to p‐type semiconductors and demonstrates state‐of‐the‐art performance for photoelectrochemical CO 2 reduction to CO and methanol. 

   more » « less
3. Phosphine‐Ligated Cobalt(II) Acetylacetonate Complexes

   https://doi.org/10.1002/ejic.202500157  

   Jayawardhena, J_P_I_Dulmini; Krause, Jeanette_A; Guan, Hairong (June 2025, European Journal of Inorganic Chemistry)

   Cobalt(II) acetylacetonate complexes bearing a phosphine ligand can be key intermediates or precursors to cobalt‐based catalysts; however, they have been rarely studied, especially from a molecular structure point of view. This work is focused on the understanding of how different phosphines react with Co(acac)₂(acac = acetylacetonate). To do so, a variety of analytical tools, including NMR and IR spectroscopy, X‐ray crystallography, mass spectrometry, and elemental analysis, have been used to study the reactions and characterize the isolated products. These results have shown that the monodentate ligand, HPPh₂, binds to Co(acac)₂weakly and reversibly to produce Co₂(acac)₄(HPPh₂), whereas the bidentate ligand, 1,2‐bis(diphenylphosphino)ethane (dppe), interacts with Co(acac)₂more strongly to yield a 1D coordination polymer of Co(acac)₂(dppe). 2‐(Dicyclohexylphosphino)methyl‐1 H‐pyrrole (^CyPN^H), which is a pyrrole‐tethered phosphine, forms an unusual 5‐coordinate cobalt complex, Co(acac)₂(^CyPN^H), in which the pyrrole moiety participates in a bifurcated hydrogen–bonding interaction with the [acac]^–ligands. In contrast, another bidentate ligand, 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene (xantphos), fails to react with Co(acac)₂, presumably due to its wide bite angle and difficulty in bridging two metals. 

   more » « less
4. Electronic structure of cobalt valence tautomeric molecules in different environments

   https://doi.org/10.1039/d2nr06834f  

   Mishra, Esha; Ekanayaka, Thilini K.; Panagiotakopoulos, Theodoros; Le, Duy; Rahman, Talat S.; Wang, Ping; McElveen, Kayleigh A.; Phillips, Jared P.; Zaid Zaz, M.; Yazdani, Saeed; et al (January 2022, Nanoscale)

   Future molecular microelectronics require the electronic conductivity of the device to be tunable without impairing the voltage control of the molecular electronic properties. This work reports the influence of an interface between a semiconducting polyaniline polymer or a polar poly-D-lysine molecular film and one of two valence tautomeric complexes, i.e. , [Co III (SQ)(Cat)(4-CN-py) 2 ] ↔ [Co II (SQ) 2 (4-CN-py) 2 ] and [Co III (SQ)(Cat)(3-tpp) 2 ] ↔ [Co II (SQ) 2 (3-tpp) 2 ]. The electronic transitions and orbitals are identified using X-ray photoemission, X-ray absorption, inverse photoemission, and optical absorption spectroscopy measurements that are guided by density functional theory. Except for slightly modified binding energies and shifted orbital levels, the choice of the underlying substrate layer has little effect on the electronic structure. A prominent unoccupied ligand-to-metal charge transfer state exists in [Co III (SQ)(Cat)(3-tpp) 2 ] ↔ [Co II (SQ) 2 (3-tpp) 2 ] that is virtually insensitive to the interface between the polymer and tautomeric complexes in the Co II high-spin state. 

   more » « less
5. Enhancing CO ₂ Reduction Efficiency on Cobalt Phthalocyanine via Axial Ligation

   https://doi.org/10.1002/cctc.202300576  

   Kang, Hongxing; Staples‐West, Aaliyah; Washington, Audrey; Turchiano, Chris; Cooksy, Andrew; Huang, Jier; Gu, Jing (June 2023, ChemCatChem)

   Abstract Electrochemical reduction of carbon dioxide (CO₂RR) to value‐added products is a promising strategy to alleviate the greenhouse gas effect. Molecular catalysts, such as cobalt (II) phthalocyanine (CoPc), are known to be efficient electrocatalysts that are capable of converting CO₂into carbon monoxide (CO). Herein, we report an axial modification strategy to enhance CoPc's CO₂RR performance. After coordinating with axial ligands, the electron density of Co was depleted via π‐backbonding. This π‐backbonding weakened the Co‐CO bond, resulting in rapid desorption of CO. Also, the presence axial ligands elevated the Co dz²orbital energy, resulting in a significantly enhanced CO selectivity, evidenced by an increased faradaic efficiency (FE) from 82 % (CoPc) to 91 % and 94 % with the presence of pyridine (CoPc‐py) and imidizal ligands (CoPc‐im), respectively, at −0.82 V vs. RHE. Density functional theory calculations reveal that axial ligation of CoPc can reduce the energy barrier for CO₂activation and facilitate the formation of^*COOH. 

   more » « less