Redox Capacitors Research Articles

Preparation of B/N co-doped carbon nanosheets and their electrochemical performance in Zn-ion redox capacitors

The low energy density for conventional supercapacitors has limited their further application in a large scale. To enhance the energy density of supercapacitor, a novel redox Zn-ion supercapacitor is fabricated by using B, N codoped carbon nanosheets as cathode material and hydroquinone as redox electrolyte. The B, N co-doping is found to be beneficial for the enhanced electrochemical performance, and the introduced redox electrolyte has increased the capacitance of supercapacitor greatly. The B, N codoped carbon nanosheets shows a capacity of 168 mAhg−1 in the hydroquinone based redox electrolyte at 2 Ag−1, nearly 2 times as that (83 mAhg−1) in conventional Zn-ion electrolyte. Density functional calculation shows B, N- dual doping can increase the adsorption capability of carbon toward hydroquinone. This work shows that the combination of cathode material modification and redox electrolyte can enhance Zn-ion hybrid supercapacitor.

Redox-Active Ferrocene Polymer for Electrode-Active Materials: Step-by-Step Synthesis on Gold Electrode Using Automatic Sequential Polymerization Equipment.

Redox-active polymers have garnered significant attention as promising materials for redox capacitors, which are energy-storage devices that rely on reversible redox reactions to store and deliver electrical energy. Our focus was on optimizing the electrochemical performance in the design and synthesis of redox-active polymer electrodes. In this study, a redox-active polymer was prepared through step-by-step synthesis on a gold electrode. To achieve this, we designed an automatic sequential polymerization equipment that minimizes human intervention and enables a stepwise polymerization reaction. The electrochemical properties of the polymer gold electrodes were investigated. The degree of polymerization of the polymer grown on the gold electrode can be controlled by adjusting the cycle of the sequential operation. As the number of cycles increases, the amount of accumulated charge increases proportionally, indicating the potential for enhanced electrochemical performance.

Influence of surface groups on the properties of disperse systems

Published data on the influence of surface groups on various properties of disperse systems are integrated and analyzed. The preparation of these systems is considered in relation to activated carbon. The discussion addresses the effect of redox reactions of surface groups on the energy efficiency of electrochemical supercapacitors, operation of capacitive deionization units for water desalination, and functioning of redox capacitors based on organic monomers. It is shown that very high energy and power characteristics of lithium ion capacitors are based on the redox reactions of lithium-containing surface groups of highly dispersed graphene electrodes. The effect of surface groups on the self-discharge of electrochemical supercapacitors with activated carbon-based electrodes is demonstrated. The prospects for the production of drinking water by capacitive deionization using mosaic cation/anion exchange membranes are evaluated. The practically important inversion of sulfo groups relative to the polymer chain in the catalyst layers of fuel cells with proton exchange membranes is noted.<br> The bibliography includes 181 references.

Ion-Conducting Robust Cross-Linked Organic/Inorganic Polymer Composite as Effective Binder for Electrode of Electrochemical Capacitor

Poly(ionic liquid)s (PILs) are used in many electrochemical energy storage/conversion devices owing to their favorable physical properties. Therefore, PIL binders have been examined as polymeric binders for electrodes in energy storage systems (ESSs) and have shown superior performance. Several innovative technologies have been developed to improve the properties of polymers, with cross-linking being the most effective and easy strategy to achieve this. In this study, we designed a breakthrough complex cross-linking and composite technique that could successfully develop the physical properties of a polymer in a simple one-step process. Additionally, the technique could improve the thermal stability and mechanical properties of the polymer. The proposed polymeric binder showed better adhesion, higher capacitance, and good energy density with improved cyclic stability compared to that shown by conventional polyvinylidene fluoride (PVDF). This study revealed that cross-linked networks in polymeric binders are long-cycle-life features for electrochemical redox capacitors.

Nanocomposite films as electrochemical sensors for detection of catalase activity.

Cross-linked hydrogel substrates have garnered attention as they simultaneously enable oxidoreductase reactions in a control volume extended to adsorption of redox capacitors for amplification of electrochemical signals. In this study, the effect of catalase immobilization in mold-casted alginate-based thin films (1 mm × 6 mm × 10 mm) containing multi walled carbon nanotubes (MWCNT) coated with chitosan has been studied via amperometry. The amperometric response was measured as a function of peroxide concentration, at a fixed potential of −0.4 V vs. SPCE in phosphate-buffered saline (pH = 7.4). Results indicate substrate detection is not diffusion-limited by the 100 μm thick chitosan layer, if the cationic polyelectrolyte is in contact with the sensing carbon electrode, and the linear detection of the enzyme absent in solution is enabled by immobilization (R 2 = 0.9615). The ferricyanide-mediated biosensor exhibited a sensitivity of 4.55 μA/mM for the optimal formulation at room temperature comparable to other nanomaterial hybrid sensing solution namely amine-functionalized graphene with an average response time of 5 s for the optimal formulation. The suitability of the optimized chitosan-coated alginate slabs nano-environment for co-encapsulation of catalase and carbon nanotubes was confirmed by cyclic voltammetry.

Realization of room temperature exchange bias effect in Co/NiO bilayer via all-solid-state Li-ion redox capacitor

The electric field-controlled exchange bias effect has drawn considerable attention of researchers as it shows great application scope in the development of modern low power consuming spintronic devices. In this research work, we have realized a reversible controlled exchange bias effect in Co/NiO heterostructures by utilizing all-solid-state Li-ion redox capacitors having antiferromagnetic electrodes, at room temperature. The nonvolatile and reversible control of exchange bias is obtained at room temperature, resulting from controlled intercalation and deintercalation of Li-ion in antiferromagnetic NiO via galvanostatic charge and discharge process. The ion migration-controlled exchange bias mechanism in Co/NiO heterostructures is studied by using various structural, electrochemical and magnetic characterizations. This work designs an approach to control the exchange bias phenomena in all-solid state magnetoionics at room temperature, which has potential importance in establishing modern spintronic devices such as magnetic random-access memories.

Capacitor properties of 3D hierarchical structured electrodes prepared by one-step electrodeposition of cobalt nanowires on stainless steel fiber sheets

Redox or pseudo-capacitors using a cobalt (II) hydroxide (Co(OH)2) material have been regarded as promising options for renewable energy storage. In this study, we deposited cobalt nanowires with a Co(OH)2 surface layer on a newly developed stainless steel fiber sheet by a one-step electrodeposition method, without any templates, to form a 3D hierarchical structured electrode. This electrode achieved a specific capacitance of 880 F g−1 at a current density of 1.8 A g−1, which is much higher than the values attained with cobalt-nanowire-deposited stainless steel (200 F g−1) and indium-tin-oxide-coated glass (455 F g−1) plates. Moreover, the cobalt nanowire electrode coupled with a nickel-plated stainless steel fiber sheet exhibited increasing capacitance performance with repeated charge–discharge cycles, eventually developing approximately twice the capacity of the above electrode. These results demonstrate the potential of stainless steel fiber sheets for developing high-performance redox capacitors using a very facile method.

Specific and ultrasensitive detection of Staphylococcus aureus with a catechol-chitosan redox capacitor based electrochemical aptasensor

• To construct an ultrasensitive electrochemical aptasensor for S. aureus analysis. • Preparation of a redox capacitor amplification system to improve sensitivity. • The aptasensor shows an LOD of 2 CFU/mL and a detection time of 25 mins. • The aptasensor shows good adaptability to real blood samples. The effective and accurate detection of Staphylococcus aureus ( S. aureus ) is of great importance for quickly treating infected patients, preventing the spread of infection and reducing the formation of resistant strains. This paper describes an electrochemical aptasensor for specific and ultrasensitive detection of S. aureus by combining a redox capacitor amplification system and a specific aptamer. The redox capacitor amplification system was constructed using catechol-chitosan film and 1,1′-ferrocene dimethanol (Fc)-hexaammineruthenium (III) chloride (Ru 3+ ) mediators. The aldehyde-modified aptamer was immobilized on the electrode surface by the Schiff base reaction with the amino groups of chitosan and served as a specific biological recognition element for S. aureus . The proposed electrochemical aptasensor presented great performance in terms of detection time (25 min), linear range (10 ∼ 10 8 cfu/mL) and detection limit (2 cfu/mL). The proposed biosensor also displayed good reproducibility and selectivity. The electrochemical apatsensor can quantitatively and directly detect S. aureus in whole blood samples (the spiked recovery rate was 90.5–100.1%), laying the foundation for its clinical application.

Facile synthesis of rGO@ CoO nanocomposites electrode material for photocatalytic hydrogen generation and supercapacitor applications

Herein this work, a simple one-step hydrothermal method for decorating CoO nanostructures uniformly on rGO surfaces. The produced CoO/rGO electrode material was uniformly characterised physiochemical techniques to determine its structure and its morphological behaviour. The CoO nanostructures deposited on rGO surfaces could act effectively as a highly conductive material that aids in uniform redox reactions. Electrochemical measurements indicate that the CoO/rGO nancomposite modified electrode has a specific capacitance value of 592 F g−1 at 2 A g−1 in 1 M aqueous KOH with a good stability of 90% capacitance stability even after 3000 charge-discharged cycles, making it an attractive material for use in electrochemical energy storage devices. Furthermore, the RGO has mainly double role as electron mediator to improve the charge transportation and improving the light absorption behaviour in the visible light region. The constructed CoO/rGO nanocomposite applied as photocatalyst for water splitting exhibits improved H2 production (830 μmol h−1 g−1) under the visible light. The major findings of this work offer a unique opportunity for constructing visible light response photoactive material, and electrochemical redox capacitors for energy needs.

Performance of an ionic liquid based gel polymer electrolyte and its application in a redox capacitor

In the modern technology based society, attraction towards the redox capacitors is increasing rapidly as one of the best energy storage devices. Capacitors fabricated by using the Ionic liquid (IL) based Gel polymer electrolytes (GPEs) have been attracted tremendously as eco-friendly energy sources based on their unique features such as satisfactory specific capacitance, good cycle ability, and good stability. The present study reports about a redox capacitor fabricated with the IL, 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl) imide (1E3Mbis(TF)I) and sodium trifluoromethanesulfonate (CF 3 NaO 3 S - NaTF). Reported highest room temperature conductivity was 7.7 × 10 −4 S cm −1 with the composition of 1 Polyvinyl chloride (PVC):1 1E3MIbis(TF)I:2 NaTF. The conductivity mechanism of GPEs follows free volume theory. The redox capacitor with the configuration, polypyrrole (PPy):NaTF/1 PVC:1 1E3MIbis(TF)I:2 NaTF/PPy:NaTF showed a single electrode specific capacitance (C SC ) of 31.5 F g −1 based on Nyquist plot. Its relaxation time was 13.6 s and this confirms fairly fast charge storage process. Initial C SC of the redox capacitor was about 126.3 F g −1 for the potential window from −1.2 V to 1.2 V. Initial single electrode discharge capacitance (C sd ) observed by Galvanostatic charge discharge (GCD) test under a constant current of 240 μA was 24.1 F g −1 . It was gradually decreased to 9.57 F g −1 with cycling due to the formation of a passivation layer on the electrode and the degradation of electrolyte/electrode interface.

Improvement of Electrochemical Properties of Poly(3,4-ethylene dioxythiophene) (PEDOT) Thin Film by UV Irradiation.

Electrochemical redox supercapcitor is one of promising rechargeable power sources for portable electronic, display or telecommunication devices since it has a large energy density, very fast charge/discharge time and long life cycle. In this study, poly(3,4-ethylene dioxythiophene) (PEDOT) thin film as the electrode of electrochemical supercapacitor was deposited on a metal current collector by in-situ polymerization method. Symmetrical electrochemical capacitor was then assembled using PEDOT films as working and counter electrodes, where 0.1 M lithium perchlorate (LiClO₄) solution in acetonitrile was used as the electrolyte solution. Typical specific discharge capacitance of the capacitor was about 70 F/g and showed little decrease after 1,000 charge/discharge cycles. We also found that UV irradiation improved the electrochemical properties of redox capacitor by formation of hydrophilic polar groups on PEDOT film surface. After UV irradiation on the surface of PEDOT film for 2 hours with the intensity of 30 mW/cm², the specific discharge capacitance increased by about 10% compared to capacitance of pristine PEDOT film.

Nanoconfined 3D redox capacitor-based electrochemical sensor for ultrasensitive monitoring of metabolites in bacterial communication

The ability to monitor metabolites related to cell communication is important for understanding bacterial physiology, identifying bacterial species in a cellular community, and providing insights into the stage of infection. Here, we developed a nanostructured electrochemical sensor comprising a 3D-redox-capacitor-coated electrode, which was prepared by grafting a redox capacitor molecule, catechol/o-quinone, at high density to a chitosan layer. It provided high sensitivity in detecting redox-active bacterial metabolites through a redox cycling reaction in the nanoconfined structures of the electrode. We used it to monitor the secretion of signalling-related metabolites at different growth phases of Pseudomonas aeruginosa. We also used the electrode to detect signalling-related metabolites in diverse simulated body fluids mixed with P. aeruginosa culture. It was able to provide information on bacterial communication and help in sensitive diagnostic monitoring of bacterial infection.

Preliminary study on the performance of a redox capacitor with the use of ionic liquid-based gel polymer electrolyte and polypyrrole electrodes

Redox capacitor, which is one type of supercapacitor, has been attracted tremendously as it shows a satisfactory specific capacitance, good cycle ability, and good stability. The present study reveals a redox capacitor fabricated with an ionic liquid (IL)-based gel polymer electrolyte (GPE). Electrodes of the redox capacitor were fabricated with the conducting polymer, polypyrrole (PPy). The composition of the GPE was polyvinylidenefluoride–co-hexafluoropropylene (PVdF–co-HFP): 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF): ZnTF. Characterization of redox capacitor was done by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) tests. The relaxation time constant (τ0) of the redox capacitor is about 31.57 s implying somewhat fast redox reactions. Initial single electrode specific capacitance (CSC) was 150.2 Fg−1, and at the 500th cycle, it was 40.03 Fg−1. The decrease of the CSC may be due to the formation of the passivation layer at the GPE/electrode interface, resulting in degradation upon cycling. The GCD test resulted 48.4 Fg−1 of initial single-electrode specific discharge capacitance (Csd) value. Upon 1000 cycles, it was reached 22.3 Fg−1. The decrease of Csd may be due to the degradation of the electrode and the IL-based GPE upon prolonged cycling.

High-performance TEMPO-oxidised cellulose nanofibre/PEDOT:PSS/ionic liquid gel actuators

In a previous study that the authors have conducted, actuators based on cellulose nanofibre/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/ionic liquid (CNF/PEDOT:PSS/IL) gel electrodes and CNF/IL gel electrolytes could not be fabricated due to poor adhesion between the electrode and electrolyte layers. However, in this study, a series of novel actuators were developed using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidised cellulose nanofibre (TOCN)/PEDOT:PSS/IL gel electrode with a TOCN/IL or poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF(HFP)/IL) gel electrolyte due to good adhesion between the electrode and electrolyte layers. The TOCN/PEDOT:PSS/IL gel electrode actuators exhibited high strain performance. These actuators mainly operated via an electrostatic double-layer capacitor mechanism, with a redox capacitor mechanism making a relatively small contribution. The TOCN/PEDOT:PSS/IL gel electrode actuators showed frequency-dependent displacement responses, and a model of double-layer charging kinetics considering the combined resistance of the gel electrode/electrolyte successfully simulated the experimental results. The development of electrodes with excellent electrical conductivity (PVdF(HFP)/IL electrolytes) and electrodes/electrolytes with excellent electrical and ionic conductivities (TOCN/IL gel electrolytes) will facilitate the optimisation of the performance of TOCN/PEDOT:PSS/IL-based polymer actuators. These flexible films will be applicable for the development of actuator materials for use in wearable and transparent electronic and energy conversion devices.

Mechanism of electron transfers mediated by cytochromes c and b 5 in mitochondria and endoplasmic reticulum: classical and murburn perspectives

We explore the mechanism of electron transfers mediated by cytochrome c, a soluble protein involved in mitochondrial oxidative phosphorylation and cytochrome b 5, a microsomal membrane protein acting as a redox aide in xenobiotic metabolism. We found minimal conservation in the sequence and surface amino acid residues of cytochrome c/b 5 proteins among divergent species. Therefore, we question the evolutionary logic for electron transfer (ET) occurring through affinity binding via recognition of specific surface residues/topography. Also, analysis of putative protein-protein interactions in the crystal structures of these proteins and their redox partners did not point to any specific interaction logic. A comparison of the kinetic and thermodynamic constants of wildtype vs. mutants did not provide strong evidence to support the binding-based ET paradigm, but indicated support for diffusible reactive species (DRS)-mediated process. Topographically divergent cytochromes from one species have been substituted for reaction with proteins from other species, implying the involvement of non-specific interactions. We provide a viable alternative (murburn concept) to classical protein-protein binding-based long range ET mechanism. To account for the promiscuity of interactions and solvent-accessible hemes, we propose that the two proteins act as non- specific redox capacitors, mediating one-electron redox equilibriums involving DRS and unbound ions. Communicated by Ramaswamy H. Sarma

A novel redox capacitor with a natural rubber-based solid polymer electrolyte for energy applications

The development of high-performance power sources such as super capacitors (EDLCs and redox capacitors) has become an urgent requirement in recent years due to the unprecedented growth of portable technology. The present study was carried out to fabricate a redox capacitor using a natural rubber-based solid polymer electrolyte (SPE). Zinc trifluoromethanesulfonate (ZnTf), propylene carbonate (PC), and pyrrole were used as electrode materials whereas ZnTf and methyl-grafted natural rubber (MGNR) were used to prepare the SPE. Warburg type diffusion as well as capacitive behavior was observed from the EIS test. Single electrode specific capacitance (Csc) from cyclic voltammetry (CV) was 27.5 Fg−1 at the scan rate of 10 mVs−1. Retention of the Csc value was 92% over 500 cycles. Single electrode specific discharge capacitance (Csd) found from galvanostatic charge discharge test was 6 Fg−1.

Fabrication of an Organic Redox Capacitor with a Neutral Aqueous Electrolyte Solution

Fabrication of an Organic Redox Capacitor with a Neutral Aqueous Electrolyte Solution

Performance of a Na Based Ionic Liquid Based Gel Polymer Electrolyte in a Redox Capacitor

In the modern technology based society, attraction towards the redox capacitors is increasing rapidly as one of the best energy storage devices. Capacitors fabricated by using the ionic liquid (IL) based gel polymer electrolytes (GPEs) have been attracted tremendously as eco-friendly energy sources based on their unique features such as satisfactory specific capacitance, good cycle ability, and good stability. The present study reports about a redox capacitor fabricated with the IL, 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl) imide (1E3Mbis(TF)I) and sodium trifluoromethanesulfonate (CF 3 NaO 3 S - NaTF). Reported highest room temperature conductivity was 7.7 x 10 -4 S cm -1 with the composition of 1 polyvinyl chloride (PVC): 1 1E3MIbis(TF)I: 2 NaTF. The conductivity mechanism of GPEs follows free volume theory. The redox capacitor with the configuration, polypyrrole (PPy): NaTF / 1 PVC: 1 1E3MIbis(TF)I: 2 NaTF / PPy: NaTF showed a single electrode specific capacitance (C SC ) of 31.5 F g -1 based on Nyquist plot. Its relaxation time was 13.6 s and this confirms fairly fast charge storage process. Initial C SC of the redox capacitor was about 126.3 F g -1 for the potential window from -1.2 V to 1.2 V. Initial single electrode discharge capacitance (C sd ) observed by Full words Galvanostatic charge discharge (GCD) test under a constant current of 240 μA was 24.1 F g -1 . It was gradually decreased to 9.57 F g -1 with cycling due to the formation of a passivation layer on the electrode and the degradation of electrolyte/electrode interface.

Supercapacitive Characteristics and Charge-Discharge Mechanism of Mn-Ni Oxide Solid Solution Electrodes

In recent years, electrochemical capacitors, also called supercapacitors, have attracted attention because of their high power density and long cycle life compared with secondary batteries. Manganese oxide having a high theoretical capacity has been actively studied as a typical electrode material for redox capacitors. Zuo et al. reported that an aqueous asymmetric capacitor combining a divalent Mn-Ni oxide solid solution (Mn-Ni-O) electrode and an activated carbon electrode exhibited an operating voltage up to 2.4 V.1 However, in the paper, essential parameters such as specific capacitance and energy density based on mass of electrode materials are not shown, and it is also unclear whether the synthesis condition and microstructure of Mn-Ni-O are optimal. For further improvement of supercapacitive performance of the Mn-based oxide electrodes, these issues need to be clarified. In this study, the synthesis conditions of Mn-Ni-O were examined, and the potential window was successfully expanded to an upper limit of 1.5 V vs. Ag/AgCl in LiCl aqueous solution. This led to achievement of the cell voltage of 2.5 V in an asymmetric capacitor with an activated carbon (AC) electrode. Moreover, relationship between the oxidation number and potential of divalent Mn-Ni-O electrode was estimated and discussed to clarify the charge-discharge mechanism. Mn-Ni-O was synthesized by hydrothermal method and subsequent heat treatment similar to those described in the literature.1 Carbon was introduced to the active material to improve the conductivity. These were deposited on a Ti mesh substrate to prepare an Mn-Ni-O/C electrode. The synthesis conditions such as temperature and concentration of constituents in precursor solution were optimized. The resultant electrodes were characterized by SEM, EDX, XRD, and ICP. The electrochemical characteristics were evaluated by cyclic voltammetry (CV) in a 1 M LiCl aqueous solution at room temperature, using an AC electrode as a counter electrode and an Ag/AgCl/saturated KCl electrode as a reference electrode. An aqueous asymmetric capacitor was assembled using an Mn-Ni-O/C electrode as the cathode and an AC electrode as the anode. Its capacitive performance was investigated by galvanostatic charge-discharge (GCD) tests. In order to obtain an insight for charge-discharge mechanism of the electrode, average oxidation numbers of Mn were estimated by XPS after holding the electrode at various potentials of -0.2, 0, 0.5, 1.0, and 1.5 V. For an optimized Mn-Ni-O/C electrode, it was found that oxide solid solution with composition of Mn0.75Ni0.25O was deposited relatively uniformly on the Ti mesh substrate. Fig. 1 shows CV curves of the Mn-Ni-O/C electrodes. It was found that the optimized electrode had a potential window up to 1.5 V vs. Ag/AgCl and a specific capacitance of 363 F g-1 (based on mass of Mn-Ni-O). This electrode was synthesized with decreasing the conventional concentration of NH4F in precursor solution from 0.2 M as described in the literature1 to 0.1 M, resulting in significant improvement in the specific capacitance. This can be ascribed to an increase in the utilization ratio of the active material by forming further uniform, dense and thin layer on the Ti mesh substrate. As shown in Fig. 2, an aqueous asymmetric capacitor cell with the optimized Mn-Ni-O/C and AC electrodes exhibited an upper limit voltage of 2.5 V in GCD tests. The energy density and average power density (based on total mass of Mn-Ni-O and AC) can be calculated as 23.3 Wh kg-1 and 12.7 kW kg-1, respectively. The average oxidation numbers of Mn at different electrode potentials were shown in Fig. 3. It was indicated for the first time that the oxidation number of Mn in the electrode changed nearly from divalent to tetravalent during charge and discharge. Considering such a large available range of the oxidation number compared with conventional MnO2-based electrodes, divalent MnO-based electrode materials can be very important candidates for further increasing the capacitance and energy density of supercapacitors. Acknowledgement This work was supported by JSPS Grants-in Aid for Scientific Research (C) JP19K05596. References 1) W. Zuo et al., Adv. Mater., 29, 1703463 (2017). Figure 1

Are plastocyanin and ferredoxin specific electron carriers or generic redox capacitors? Classical and murburn perspectives on two photosynthetic proteins

In the light reaction of oxygenic photosynthesis, plastocyanin (PC) and ferredoxins (Fd) are small/diffusible redox-active proteins playing key roles in electron transfer/transport phenomena. In the Z-scheme mechanistic purview, they are considered as specific affinity binding-based electron-relay agents, linking the functions of Cytochrome b 6 f (Cyt. b6f), Photosystem I (PS I) and Fd:NADPH oxidoreductase (FNR). The murburn explanation for photolytic photophosphorylation deems PC/Fd as generic ‘redox capacitors’, temporally accepting and releasing one-electron equivalents in reaction milieu. Herein, we explore the two theories with respect to structural, distributional and functional aspects of PC/Fd. Amino acid residues located on the surface loci of key patches of PC/Fd vary in electrostatic/contour (topography) signatures. Crystal structures of four different complexes each of Cyt.f-PC and Fd-FNR show little conservation in the contact-surfaces, thereby discrediting ‘affinity binding-based electron transfers (ET)’ as an evolutionary logic. Further, thermodynamic and kinetic data of wildtype and mutant proteins interactions do not align with Z-scheme. Furthermore, micromolar physiological concentrations of PC and the non-conducive architecture of chloroplasts render the classical model untenable. In the murburn model, as PC is optional, the observation that plants lacking PC survive and grow is justified. Further, the low physiological concentration/distribution of PC in chloroplast lumen/stroma is supported by murburn equilibriums, as higher concentrations would limit electron transfers. Thus, structural evidence, interactive dynamics with redox partners and physiological distribution/role of PC/Fd support the murburn perspective that these proteins serve as generic redox-capacitors in chloroplasts. Communicated by Ramaswamy H. Sarma