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- Günther, Tyran, et al.
(author)
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Redox-site accessibility of composites containing a 2D redox-active covalent organic framework : from optimization to application
- 2023
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 11:26, s. 13923-13931
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Journal article (peer-reviewed)abstract
- Redox-active covalent organic frameworks (RACOFs) can be employed in various functional materials and enesrgy applications. A crucial performance or efficiency indicator is the percentage of redox centres that can be utilised. Herein, the term redox-site accessibility (RSA) is defined and shown to be an effective metric for developing and optimising a 2D RACOF (viz., TpOMe-DAQ made from 2,4,6-trimethoxy-1,3,5-benzenetricarbaldehyde [TpOMe] and 2,6-diaminoanthraquinone [DAQ]) as an anode material for potential organic-battery applications. Pristine TpOMe-DAQ utilises only 0.76% of its redox sites, necessitating the use of conductivity-enhancement strategies such as blending it with different conductive carbons, or performing in situ polymerisation with EDOT (3,4-ethylenedioxythiophene) to form a conductive polymer. While conductive carbon-RACOF composites showed a modest RSA improvement of 4.0%, conductive polymer-RACOF composites boosted the redox-site usage (RSA) to 90% at low mass loadings. The material and electrochemical characteristics of the conductive polymer-RACOF composite containing more-than-necessary conductive polymer showed a reduced surface area but almost identical electrochemical behaviour, compared to the optimal ratio. The high RSA of the optimally loaded composite was replicated in a RACOF-air battery with over 90% active redox sites. We believe that the reported approach and methods, which can be employed on a milligram scale, could serve as a general guide for the electrification and characterisation of RACOFs, as well as for other redox-active porous polymers.
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| 3. |
- Oka, Kouki, et al.
(author)
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Conducting Redox Polymer as Organic Anode Material for Polymer-Manganese Secondary Batteries
- 2020
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In: ChemElectroChem. - : Wiley. - 2196-0216. ; 7:15, s. 3336-3340
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Journal article (peer-reviewed)abstract
- Manganese-based aqueous batteries have attracted significant attention due to their earth-abundant components and low environmental burden. However, state-of-the-art manganese-zinc batteries are poorly rechargeable, owing to dendrite formation on the zinc anode. Organic materials could provide a safe and sustainable replacement. In the present work, a conducting redox polymer (CRP) based on a trimer of EPE (E=3,4-ethylenedioxythiophene; P=3,4-propylenedioxythiophene) and a naphthoquinone (NQ) pendant group is used as anode in polymer-manganese secondary batteries. The polymer shows stable redox conversion around+0.05 V vs. Ag/AgCl, and fast kinetics that involves proton cycling during pendant group redox conversion. For the first time, a CRP-manganese secondary battery was fabricated with pEP(NQ)E as the anode, manganese oxide as the cathode, and manganese-containing acidic aqueous solution as the electrolyte. This battery yielded a discharge voltage of 1.0 V and a discharging capacity of 76 mAh/ganode over >50 cycles and high rate capabilities (up to 10C).
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| 6. |
- Zaar, Felicia, et al.
(author)
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Characterization and catalytic prospects of metalloporphyrin-functionalized conducting polymers
- 2023
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In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 467
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Journal article (peer-reviewed)abstract
- Molecular catalysts are attracting interest as drivers of redox reactions for sustainable applications. Through systematic molecular design, they could be engineered to have high selectivity and activity towards a multitude of catalytic reactions. However, as long as they are used in homogeneous setups, they will suffer from inconvenient energy supply, inefficient charge transport and difficulty in separation from reaction products. To be relevant for industrial applications, molecular catalysts must be bound to solid materials in direct contact with the energy source. In this regard, conducting polymers are particularly interesting, as they provide a straightforward means of both surface immobilization and charge transport. In this work, we synthesize and characterize three different metalloporphyrin-functionalized conducting polymers and apply them to catalysis of the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR). We show that incorporation of porphyrins into conducting polymers is a reliable immobilization method, that the properties of both the porphyrin units and the polymer backbone are preserved in all systems, and that the polymers provide efficient charge transport to and from the catalytic centers. Nevertheless, we also find that the polymers are negatively affected by intermediates formed during the HER and the ORR. We conclude that the choice of immobilization method has a large impact on the quality of the molecular catalyst, and that the effect of the catalytic cycle on the immobilization matrix must be considered in the molecular design process.
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| 9. |
- Zaar, Felicia, et al.
(author)
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Tetraphenylporphyrin electrocatalysts for the hydrogen evolution reaction : applicability of molecular volcano plots to experimental operating conditions
- 2023
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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 52:30, s. 10348-10362
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Journal article (peer-reviewed)abstract
- Recent years have seen an increasing interest in molecular electrocatalysts for the hydrogen evolution reaction (HER). Efficient hydrogen evolution would play an important role in a sustainable fuel economy, and molecular systems could serve as highly specific and tunable alternatives to traditional noble metal surface catalysts. However, molecular catalysts are currently mostly used in homogeneous setups, where quantitative evaluation of catalytic activity is non-standardized and cumbersome, in particular for multistep, multielectron processes. The molecular design community would therefore be well served by a straightforward model for prediction and comparison of the efficiency of molecular catalysts. Recent developments in this area include attempts at applying the Sabatier principle and the volcano plot concept - popular tools for comparing metal surface catalysts - to molecular catalysis. In this work, we evaluate the predictive power of these tools in the context of experimental operating conditions, by applying them to a series of tetraphenylporphyrins employed as molecular electrocatalysts of the HER. We show that the binding energy of H and the redox chemistry of the porphyrins depend solely on the electron withdrawing ability of the central metal ion, and that the thermodynamics of the catalytic cycle follow a simple linear free energy relation. We also find that the catalytic efficiency of the porphyrins is almost exclusively determined by reaction kinetics and therefore cannot be explained by thermodynamics alone. We conclude that the Sabatier principle, linear free energy relations and molecular volcano plots are insufficient tools for predicting and comparing activity of molecular catalysts, and that experimentally useful information of catalytic performance can still only be obtained through detailed knowledge of the catalytic pathway for each individual system.
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