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Molecular catalysts for water oxidation and other electrochemical transformations have been a focus of significant research over recent decades. Among these, α-[Fe(mcp)L2] complexes stand out as one of the most active non-heme iron-based molecular catalyst for water oxidation. This study investigates how the Fe(II)/Fe(III) redox potential of these catalysts varies with the identity of their labile ligands (L). Using cyclic voltammetry and complementary spectroscopic techniques (UV/Vis, 1H-NMR), we examined how ligands bind to the metal centre. Systematic variation of the labile ligand (L) demonstrated that the catalyst's redox potential in acetonitrile solution strongly depends on ligand identity. By introducing stoichiometric amounts of different anions to the electrolyte, the redox potential was tuned across a 1.5 V potential window.In aqueous solutions, the redox potential depended on both pH and electrolyte anion identity. These dependencies were successfully fitted to a thermodynamic model that was obtained by extending the typical proton-coupled electron transfer square scheme into a cube scheme that incorporates anion binding. The equation derived from this model provides valuable insights into the ligand-binding dynamics at the iron centre under diverse conditions.

Organic redox-active quinones are promising candidates for future energy storage. While aqueous electrolytes offer advantages such as safety, sustainability, and low cost compared to organic electrolytes, the oxidized states of quinones are typically electron-deficient and prone to nucleophilic attack by water, hindering the development of high-potential quinone-based cathodes. Acidic electrolytes can shift the formal potential of quinones to higher values, but they introduce challenges such as corrosion of battery components (e.g., current collector, anode, separator) and increased risk for end-users. These issues highlight the need for high-potential quinone cathodes in neutral aqueous electrolytes. In this study, we employed proton-trap technology to increase the formal potential of 1,4-benzoquinone (Q) by 0.21 V in a neutral aqueous medium. The proton-trap mechanism involves integrating pyridine/pyridinium into the cathode as a proton acceptor/donor for H2Q/Q redox transfer, enabling internal proton transfer. This effectively decouples the Q redox chemistry from the electrolyte pH. Using proton-trap technology, the H2Q/Q redox couple maintained a constant formal potential of 0.42 V (vs. SHE) in aqueous electrolytes across a pH range of 3-9. The proton-trap poly(1Q-2pyridine-EDOT) copolymer exhibited an initial capacity of 65.5 mAh/g at 10 C, with 83 % capacity retention after 100 cycles. When paired with an anthraquinone (AQ) anode, the all-quinone organic battery delivered a voltage output of 0.9 V in a 17 M NaClO4 pH-neutral aqueous electrolyte. This approach offers a promising pathway for stable, high-potential quinonebased energy storage in safe and sustainable aqueous systems

Quinones exhibit considerable promise as active components in energy storage applications, owing to their high theoretical storage capacity, well-defined redox potentials, rapid reaction kinetics, structural diversity, and proficiency in cycling both protons and metal ions. In this study, six quinone derivatives underwent comprehensive electrochemical and computational analyses using TBA+, H+, Li+, K+, Na+, Ca2+, and Mg2+-based electrolytes, aiming to uncover novel cycling chemistries with organic materials. Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV) elucidated the widely recognized 2H+/2e- redox process during proton cycling, as well as the two-step 1e- redox process in the presence of other cycling ions. Additionally, it was established that the quinone formal redox potential for different cycling chemistries followed the sequence TBA+ < K+ < Na+ < Li+ < H+, and cycling of the divalent cations resulted in potentials within the same range as those observed for proton cycling. DFT calculations provided insights into how cycling ions influenced the quinone formal redox potential, attributing it to the cation’s ability to accommodate a portion of the bisolate anion charge upon reduction. Cations inducing a higher quinone formal redox potential and accommodating a larger fraction of the negative charge demonstrated a greater stabilizing effect on the reduced state. This stabilizing effect exhibited a strong correlation with the ionization energies of the respective cations.

The high surface area, open pore-structure and atomic-level organization inherent in many covalent organic frameworks (COFs) make them an attractive polymer platform for developing functional materials. Herein, a chemically robust 2D COF (TpOMe-DAPQ COF) containing phenanthraquinone moieties was prepared by condensing 2,4,6-trimethoxy-1,3,5-benzenetricarbaldehyde (TpOMe) and 2,7-diamino-9,10-phenanthraquinone (DAPQ) using the convenient mechanochemical method. The poor charge-storage capacity of the pristine TpOMe-DAPQ COF was substantially improved by first investigating its redox-site accessibility (RSA) using different conductivity-enhancement methods, and then optimizing the amount of EDOT needed to perform an in-situ polymerization. The resulting composite (0.4EDOT@TpOMe-DAPQ) was characterized and its enhanced charge-storage capabilities enabled it to be used as an anode material in an aqueous Mn beaker-cell battery capable of delivering 0.76 V. This work outlines the rational design approach used to develop a functional charge-storage material utilizing a COF-based polymerization platform.

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.

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.