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Capturing the surface-structural dynamics of metal electrocatalysts under certain electrochemical environments is intriguingly desired for understanding the behavior of various metal-based electrocatalysts. However, in situ monitoring of the evolution of a polycrystalline metal surface at the interface of electrode-electrolyte solutions at negative/positive potentials with high-resolution scanning tunneling microscopy (STM) is seldom. Here, we use electrochemical STM (EC-STM) for in situ monitoring of the surface evolution process of a silver electrode in both an aqueous sodium hydroxide solution and an ionic liquid of 1-methyl-1-octylpyrrolidinium bis(trifluoromethylsulfonyl) amide driven by negative potentials. We found silver underwent a surface change from a polycrystalline structure to a well-defined surface arrangement in both electrolytes. In NaOH aqueous solution, the silver surface transferred in several minutes at a turning-point potential where hydrogen adsorbed and formed mainly (111) and (100) pits. Controversially, the surface evolution in the ionic liquid was much slower than that in the aqueous solution, and cation adsorption was observed in a wide potential range. The surface evolution of silver is proposed to be linked to the surface adsorbates as well as the formation of their complexes with undercoordinated silver atoms. The results also show that cathodic annealing of polycrystalline silver is a cheap, easy, and reliable way to obtain quasi-ordered crystal surfaces.

Polyoxometalates (POMs) have emerged as potential anode materials for lithium-ion batteries (LIBs) owing to their ability to transfer multiple electrons. Although POM anode materials exhibit notable results in LIBs, their energy-storage mechanisms have not been well-investigated. Here, we utilize various in operando and ex situ techniques to verify the charge-storage mechanisms of a Keplerate-type POM Na2K23{[(MoVI)MoVI5O21(H2O)3(KSO4)]12 [(VIVO)30(H2O)20(SO4)0.5]}·ca200H2O ({Mo72V30}) anode in LIBs. The {Mo72V30} anode provides a high reversible capacity of up to ∼1300 mA h g-1 without capacity fading for up to 100 cycles. The lithium-ion storage mechanism was studied systematically through in operando synchrotron X-ray absorption near-edge structure, ex situ X-ray diffraction, ex situ extended X-ray absorption fine structure, ex situ transmission electron microscopy, in operando synchrotron transmission X-ray microscopy, and in operando Raman spectroscopy. Based on the abovementioned results, we propose that the open hollow-ball structure of the {Mo72V30} molecular cluster serves as an electron/ion sponge that can store a large number of lithium ions and electrons reversibly via multiple and reversible redox reactions (Mo6+ ↔ Mo1+ and V5+/V4+↔ V1+) with fast lithium diffusion kinetics (DLi+: 10-9-10-10 cm2 s-1). No obvious volumetric expansion of the microsized {Mo72V30} particle is observed during the lithiation/delithiation process, which leads to high cycling stability. This study provides comprehensive analytical methods for understanding the lithium-ion storage mechanism of such complicated POMs, which is important for further studies of POM electrodes in energy-storage applications.

Accurate forecasting of lithium-ion battery performance is important for easing consumer concerns about the safety and reliability of electric vehicles. Most research on battery health prognostics focuses on the R&D setting where cells are subjected to the same usage patterns, yet in practice there is great variability in use across cells and cycles, making forecasting much more challenging. Here, we address this challenge by combining electrochemical impedance spectroscopy (EIS), a non-invasive measurement of battery state, with probabilistic machine learning. We generated a dataset of 40 commercial lithium-ion coin cells cycled under multistage constant current charging/discharging, with currents randomly changed between cycles to emulate realistic use patterns. We show that future discharge capacities can be predicted with calibrated uncertainties, given the future cycling protocol and a single EIS measurement made just before charging, and without any knowledge of usage history. Our method is data-efficient, requiring just eight cells to achieve a test error of less than 10%, and robust to dataset shifts. Our model can forecast well into the future, attaining a test error of less than 10% when projecting 32 cycles ahead. Further, we find that model performance can be boosted by 25% by augmenting EIS with additional features derived from historical capacity-voltage curves. Our results suggest that battery health is better quantified by a multidimensional vector rather than a scalar State of Health, thus deriving informative electrochemical `biomarkers' in tandem with machine learning is key to predictive battery management and control.

Accurate forecasting of lithium-ion battery performance is essential for easing consumer concerns about the safety and reliability of electric vehicles. Most research on battery health prognostics focuses on the research and development setting where cells are subjected to the same usage patterns. However, in practical operation, there is great variability in use across cells and cycles, thus making forecasting challenging. To address this challenge, here we propose a combination of electrochemical impedance spectroscopy measurements with probabilistic machine learning methods. Making use of a dataset of 88 commercial lithium-ion coin cells generated via multistage charging and discharging (with currents randomly changed between cycles), we show that future discharge capacities can be predicted with calibrated uncertainties, given the future cycling protocol and a single electrochemical impedance spectroscopy measurement made immediately before charging, and without any knowledge of usage history. The results are robust to cell manufacturer, the distribution of cycling protocols, and temperature. The research outcome also suggests that battery health is better quantified by a multidimensional vector rather than a scalar state of health.

The competition between the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) on a polycrystalline Pt (pc-Pt) electrode in weakly acidic solutions (pH ≈ 3) under the condition w...

While redox flow batteries carry a large potential for electricity storage, specifically for regenerative energies, the current technology-prone system—the all-vanadium redox flow battery—exhibits two major disadvantages: low energy and low power densities. Polyoxometalates have the potential to mitigate both effects. In this publication, the operation of a polyoxometalate redox flow battery was demonstrated for the polyoxoanions [SiW12O40]4– (SiW12) in the anolyte and [PV14O42]9– (PV14) in the catholyte. Emphasis was laid on comparing to which extent an upscale from 25 to 1400 cm2 membrane area may impede efficiency and operational parameters. Results demonstrated that the operation of the large cell for close to 3 months did not diminish operation and the stability of polyoxometalates was unaltered.

Accurate forecasting of Li-ion battery performance is important for easing consumer concerns about the safety and reliability of electric vehicles. Most research on battery health prognostics focuses on the R&D setting where cells are subjected to the same usage patterns, yet in practice there is great variability in use across cells and cycles, making forecasting much more challenging. In my talk, I will show that a combination of battery `biomarkers’ derived from electrochemical impedance signals with probabilistic machine learning enables us to accurately forecast future battery performance amid uneven usage, even when cell history is completely unknown. More broadly, our results bring into question the concept of a scalar State of Health, and instead suggest that battery state is better quantified by a multidimensional vector. I will discuss how this insight lays the foundations for novel algorithms for battery prognostics and control. I will further outline our application of such algorithms in optimal protocol design for intelligent battery charging, and low-data inference via transfer learning across cell chemistries and usage patterns.

Forecasting the state of health and remaining useful life of Li-ion batteries is an unsolved challenge that limits technologies such as consumer electronics and electric vehicles. Here, we build an accurate battery forecasting system by combining electrochemical impedance spectroscopy (EIS)—a real-time, non-invasive and information-rich measurement that is hitherto underused in battery diagnosis—with Gaussian process machine learning. Over 20,000 EIS spectra of commercial Li-ion batteries are collected at different states of health, states of charge and temperatures—the largest dataset to our knowledge of its kind. Our Gaussian process model takes the entire spectrum as input, without further feature engineering, and automatically determines which spectral features predict degradation. Our model accurately predicts the remaining useful life, even without complete knowledge of past operating conditions of the battery. Our results demonstrate the value of EIS signals in battery management systems., Forecasting the state of health and remaining useful life of batteries is a challenge that limits technologies such as electric vehicles. Here, the authors build an accurate battery performance forecasting system using machine learning.

The VO2 +/VO2+ redox reaction takes place in the catholyte solution of the all-vanadium redox flow battery (VRFB), one of the few options to electrochemically store energy from intermittent renewable sources on a large scale. However, the sluggish redox kinetics of the VO2 +/VO2+ couple limit the power density of the VRFB, which increases the footprint of the power converters and increases capital costs. Therefore, catalysis of the redox reaction and a deeper understanding of its intricate reaction pathways is desirable. The kinetics of the VO2 +/VO2+ redox reaction have been investigated in 1 M sulfuric and 1 M phosphoric acid by cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy and flow battery tests. It was found that in 1 M phosphoric acid the electron transfer constant k0 is up to 67 times higher than in 1 M sulfuric acid. At higher over-potentials the determined currents match for the two electrolytes. This over-potential dependent difference in electron transfer constant is explained by variable contributions from three reaction mechanisms for the oxidation of VO2 + to VO2+, and by the presence of adsorbed intermediates for the reduction of VO2+. This study shows that the redox kinetics of the VO2 +/VO2+ can be considerably accelerated by altering the chemical environment of the vanadium ions, and that this effect can also be transferred into a flow battery.

Electrochemical energy storage is one of the few options to store the energy from intermittent renewable energy sources like wind and solar. Redox flow batteries (RFBs) are such an energy storage system, which has favorable features over other battery technologies, e.g. solid state batteries, due to their inherent safety and the independent scaling of energy and power content. However, because of their low energy-density, low power-density, and the cost of components such as redox species and membranes, commercialised RFB systems like the all-vanadium chemistry cannot make full use of the inherent advantages over other systems. In principle, there are three pathways to improve RFBs and to make them viable for large scale application: First, to employ electrolytes with higher energy density. This goal can be achieved by increasing the concentration of redox species, employing redox species that store more than one electron or by increasing the cell voltage. Second, to enhance the power output of the battery cells by using high kinetic redox species, increasing the cell voltage, implementing novel cell designs or membranes with lower resistance. The first two means reduce the electrode surface area needed to supply a certain power output, thereby bringing down costs for expensive components such as membranes. Third, to reduce the costs of single or multiple components such as redox species or membranes. To achieve these objectives it is necessary to develop new battery chemistries and cell configurations. In this review, a comparison of promising cell chemistries is focused on, be they all-liquid, slurries or hybrids combining liquid, gas and solid phases. The aim is to elucidate which redox-system is most favorable in terms of energy-density, power-density and capital cost. Besides, the choice of solvent and the selection of an inorganic or organic redox couples with the entailing consequences are discussed.

Lithium-ion batteries are prevalent in everyday usage and ensuring they are used efficiently is of paramount concern. The degradation of lithium-ion batteries under cycling can affect various components in the cells. Understanding the degradation characteristics of the cell can aid in ensuring longer lifetime through optimized usage. Long-term automated EIS data collection has been used as a non-destructive tool to track the impedance changes within the cells over time due to repeated cycling. Separating the different degradation factors contributed by the graphite and NMC electrodes in a non-invasive way is still a challenge. In this work, EIS measurements of half-cells dissembled from full cells are shown to provide further insight into cell degradation characteristics. By using this methodology to differentiate the degradation at different electrodes, new materials can be easily screened for their viability in next generation batteries. The methodology also helps estimate the degradation changes with cycling and provides useful information for further understanding the degradation mechanism.

Electrochemical storage of energy is a necessary asset for the integration of intermittent renewable energy sources such as wind and solar power into a complete energy scenario. Redox flow batteries (RFBs) are the only type of battery in which the energy content and the power output can be scaled independently, offering flexibility for applications such as load levelling. However, the prevailing technology, the all Vanadium system, comprises low energy and low power densities. In this study we investigate two polyoxometalates (POMs), [SiW12O40]4− and [PV14O42]9−, as nano-sized electron shuttles. We show that these POMs exhibit fast redox kinetics (electron transfer constant k0 ≈ 10−2 cm s−1 for [SiW12O40]4−), thereby enabling high power densities; in addition, they feature multi-electron transfer, realizing a high capacity per molecule; they do not cross cation exchange membranes, eliminating self-discharge through the separator; and they are chemically and electrochemically stable as shown by in situ NMR. In flow battery studies the theoretical capacity (10.7 A h L−1) could be achieved under operating conditions. The cell was cycled for 14 days with current densities in the range of 30 to 60 mA cm−2 (155 cycles). The Coulombic efficiency was 94% during cycling. Very small losses occurred due to residual oxygen in the system. The voltage efficiency (∼65% at 30 mA cm−2) was mainly affected by ohmic rather than kinetic losses. Pathways for further improvement are discussed.

Scanning electrochemical potential microscopy (SECPM) is a type of probe microscopy, in which a sharp tip similar to those employed in electrochemical tunnelling microscopy is connected to a high impedance amplifier, but the tip potential instead of tip current is used as the signal in the feedback loop. SECPM has been found to provide much higher spatial resolution than would be expected on the basis of a mechanism in which the tip responds to the local electrochemical potential of the solution; in fact, it can obtain atomic resolution similar to STM, but is a superior technique for imaging electronically insulating objects such as proteins on a metal surface. We suggest a mechanism for these high-resolution images based on electron exchange between tip and substrate coupled to faradaic processes at the tip/solution interface. This mechanism operates alongside the conventional mechanism in which the tip responds to the local potential in the diffuse layer of the substrate and allows a simple description of the sigmoidal tip potential−distance curves that have been reported.

Replacing a part of energy derived from fossil fuels with bioenergy derived from solid waste streams may be a promising method to tackle the dual crisis of increasing waste pile-up and global climate change. In this study we propose a decentralised sewage sludge and woody biomass co-gasification system for Singapore. We evaluate the greenhouse gas emission of the proposed system and compare it to the existing system through life cycle assessment. The proposed system is expected to provide a net annual emission reduction of 137.0–164.1 kilotonnes of CO 2 eq. Increase in electricity recovery, carbon sequestration in the biochar produced and the avoidance of the use of supplementary fuel for sewage sludge incineration are the major contributors for the emission reduction. The proposed system is able to increase the net electricity production from sewage sludge and woody biomass by 3–24%. This could lead to an annual increase in electricity recovery of 12.1–74.8 GWh. It is estimated that the proposed system can produce 34 kilotonnes of biochar annually. It is found that decentralisation helps to reduce the annual tonne-km driven by 4.23 million tonne-km which could decrease the number of on-road vehicles required for waste handling.

Power generation from biomass residues is an attractive option for supplying the rapidly increasing power demand of the Association of South East Asian Nations (ASEAN) in a sustainable and a cost-effective manner. In this paper, we assess the total quantity and location of biomass residues from agriculture, livestock and forestry activities in ASEAN, evaluate their technical power generation potential and estimate the cost of electricity production from these residues. A cost optimization model is developed to identify cost-effective options of power generation from biomass residues using various conversion technologies. We estimate the total available thermal energy from biomass residues in ASEAN to be approximately 1076 TWh. About 86% of the total energy potential is provided by agricultural residues, with rice, sugarcane and palm oil residues being the major contributors. We find the highest energy potentials to be located in Indonesia (407 TWh), Thailand (194 TWh) and Vietnam (153 TWh). The estimated maximum technical potential for electricity generation from biomass residues in ASEAN amounts to 360 TWh. Power generation costs vary within a wide range from less than 40 USD/MWh to more than 200 USD/MWh.

Porous carbon materials are of tremendous importance for electrochemical energy storage. Their low cost, wide potential window and high surface area make them ideal electrodes for many applications. The activity of the electrode towards a certain reaction is given by both the available wetted surface area and the electron transfer constant k0. The present study investigates which electrochemical methods are suitable to determine k0 on porous carbon electrodes. For this purpose, we investigate the ferric/ferrous redox couple on a porous carbon nanotube electrode as model system. We show that results from cyclic voltammetry (CV) can yield an apparent catalytic effect and elucidate its origin. Chronoamperometry and electrochemical impedance spectroscopy are shown to produce consistent values for the exchange current density I0, which can then be normalized to k0. Limitations of both methods in terms of k0 and diffusion constants are discussed. The gathered insights in terms of validity of methods on porous electrodes are harnessed to review the recent literature on the vanadium redox reactions. Reported k0 values spread over four orders of magnitude and there is no consensus on the influence of heat- or acid-treatment on the kinetics. Taking into account the difficulties of CVs on porous electrodes we conclude that reasonable values for the vanadium reactions are k 0 1.2 10 − 4 c m s − 1 and that oxidation of the samples increases surface area, catalyzes the V2+/V3+ redox reaction but impedes the VO2+/VO2+ redox reaction.

Catalytic effects of surface groups on porous carbon electrodes are claimed in literature for the redox reactions V(II)/V(III) and V(IV)/V(V). The literature is critically analysed also in relation to work of this group. A method how to overcome the problem of assessing the electrochemically active surface area on porous electrodes is presented. Applying this method, no catalytic effects for above reactions can be substantiated. It is further pointed out that the parameters electrochemical potential and temperature need to be used to assess electrocatalysis.

The reversible intercalation of solvated Na-ions into graphite and the concomitant formation of ternary Na–graphite intercalation compounds (GICs) are studied using several in operando techniques, such as X-ray-diffraction (XRD), electrochemical scanning tunnelling microscopy (EC-STM) and electrochemical quartz crystal microbalance techniques (EQCM). Linear ethylene glycol dimethyl ether homologues (“glymes”) Gx with x + 1 O-atoms were used as solvents, where x is 1–4. The intercalation mechanism of Na+(Gx)y-complexes was investigated with a focus on the phase transitions and diffusion rates of the Na+(Gx)y-complexes inside the graphite lattice. For the four shortest glymes (G1 to G4), it is found using XRD that an intermediate stage 2 Na–GIC (NaC48) is formed upon the partial sodiation of the graphite electrode. At full sodiation stage 1 Na–GIC (NaC18, 112 mA h g−1) is obtained for G1, G2 and G4, while the G3 system also forms a stage 1 Na–GIC but with less Na incorporated (NaC30, 70 mA h g−1). The phase transitions of a battery electrode upon ion-intercalation are visualised using STM on the atomic scale for the first time. In addition, the local diffusion rates of the intercalated species inside the electrode were determined, a unique approach for determining kinetic effects in batteries on the atomic scale. The formation of a solid electrolyte interphase (SEI) is observed with STM as well as with an EQCM, while the latter technique is used for novel in situ hydrodynamic spectroscopy, giving further insight into the intercalation mechanism.

Polyoxometalates (POMs) have been reported as promising electrode materials for energy storage applications due to their ability to undergo fast redox reactions with multiple transferred electrons per polyanion. Here we employ a polyoxovanadate salt, Na6[V10O28], as an electrode material in a lithium-ion containing electrolyte and investigate the electron transfer properties of Na6[V10O28] on long and short timescales. Looking at equilibrated systems, in situ V K-edge X-ray absorption near edge structure (XANES) studies show that all 10 V5+ ions in Na6[V10O28] can be reversibly reduced to V4+ in a potential range of 4–1.75 V vs. Li/Li+. Focusing on the dynamic response of the electrode to potential pulses, the kinetics of Na6[V10O28] electrodes and the dependence of the fundamental electron transfer rate k0 on temperature are investigated. From these measurements we calculate the reorganization energy and compare it with theoretical predictions. The experimentally determined reorganization energy of λ = 184 meV is in line with the theoretical estimate and confirms the hypothesis of small values of λ for POMs due to electrostatic shielding of the redox center from the solvent.

The presence of water in room temperature ionic liquids (RTILs) can have a strong effect on their properties. In particular, water adsorption at electrodes can reduce the electrochemical potential window of the system. It is thus important to understand where water will be present depending on the electrode potential, the type of ionic liquid and the electrode material. We investigate the influence of water on RTILs by measuring the potential dependent double layer capacitance of various water-RTIL mixtures. The resulting capacitance versus potential curves are reproduced employing mean-field theory calculations. From the parameters used to obtain the best agreement between experimental and theoretical curves some properties of the RTILs can be deducted, such as a stronger interaction of water with RTIL anions than cations and an agglomeration of water at potentials positive or negative of the potential of zero charge.

We report that an ultrafast kinetics of reversible metal-ion insertion can be realized in anatase titanium dioxide (TiO2). Niobium ions (Nb5+) were carefully chosen to dope and drive anatase TiO2 into very thin nanosheets standing perpendicularly onto transparent conductive electrode (TCE) and simultaneously construct TiO2 with an ion-conducting surface together with expanded ion diffusion channels, which enabled ultrafast metal ions to diffuse across the electrolyte/solid interface and into the bulk of TiO2. To demonstrate the superior metal-ion insertion rate, the electrochromic features induced by ion intercalation were examined, which exhibited the best color switching speed of 4.82 s for coloration and 0.91 s for bleaching among all reported nanosized TiO2 devices. When performed as the anode for the secondary battery, the modified TiO2 was capable to deliver a highly reversible capacity of 61.2 mAh/g at an ultrahigh specific current rate of 60 C (10.2 A/g). This fast metal-ion insertion behavior was...

Vanadium flow batteries are a promising system for stationary energy storage. One of their shortcomings is a low power density caused by slow kinetics of the redox reactions. To alleviate this drawback, many studies tried to catalyze the redox reactions. However, up to now, there is no consensus in the literature on which of the two half-cell reactions, the V2+/V3+ or the VO2+/VO2+reaction, features the slower electron transfer. The present study is the first showing that reaction rates for the half-cells are of the same order of magnitude with their respective rate constants depending on the composition of the electrode material. The surface functional groups hydroxyl, carbonyl, and carboxyl on carbon increase the wetted surface area, catalyze the V2+/V3+ redox reaction, but impede the VO2+/VO2+ redox reaction. This complex situation was unraveled by using a newly developed procedure based on electrochemical impedance spectroscopy. Reaction mechanisms based on these results are discussed.

The two 16-manganese-containing, Keggin-based 36-tungsto-4-silicates [Mn(III)10Mn(II)6O6(OH)6(PO4)4(A-α-SiW9O34)4](28-) (1) and [Mn(III)4Mn(II)12(OH)12(PO4)4(A-α-SiW9O34)4](28-) (2) have been prepared by reaction of the trilacunary Keggin precursor [A-α-SiW9O34](10-) with either Mn(OOCCH3)3·2H2O (for 1) or MnCl2·4H2O (for 2), in aqueous phosphate solution at pH 9. Polyanions 1 and 2 comprise mixed-valent, cationic {Mn(III)10Mn(II)6O6(OH)6}(24+) and {Mn(III)4Mn(II)12(OH)12}(24+) cores, respectively, encapsulated by four phosphate groups and four {SiW9} units in a tetrahedral fashion. Both polyanions were structurally and compositionally characterized by single-crystal XRD, IR, thermogravimetric analysis, and X-ray absorption spectroscopy. Furthermore, studies were performed probing the magnetic, electrochemical, oxidation catalytic, and Li-ion battery performance of 1 and 2.

Electrochemical scanning tunneling microscopy (EC-STM) has been successfully applied to study the electron-transfer (ET) reactions of biomolecules at solid-liquid interfaces.1–4 However, there are still limitations, including requirement of sample conductivity and potential damage to the biomolecules from strong tunneling current, to be overcome. A different type of probe microscopy, scanning electrochemical potential microscopy (SECPM), can be used as a promising alternative. SECPM shares the similar hardware setup with EC-STM, except for the current amplifier being substituted by a potentiometer to measure the local electrochemical potential as feedback signal. This feature enables SECPM to work on less conductive biomolecular samples. It has been shown that SECPM is capable of imaging horseradish peroxidase (HRP) at single molecular level under in situ conditions, with image resolution comparable or even better than EC-STM (Figure 1). 5 The electrochemical double layer (EDL) existing at the solid-liquid interface in an electrochemical cell can be investigated by SECPM using tip-distance curves. Preliminary results will be shown. In this work, we use SECPM to image HRP molecules adsorbed on HOPG under in situ conditions, with varying electrochemical potentials applied to the substrate. HRP redox reactions were controlled by varying the substrate potential, and the corresponding change of the potential distribution in the EDL covering the adsorbed HRP surface was recorded by SECPM. The experimental results could offer a novel perspective to understand how the ET reactions influences the EDL, and then help the further research on biosensors and EDL capacitors. This work is supported in part by the North-East Centre for Energy Materials (EP/R021503/1) funded by EPSRC. References: 1. E. P. Friis et al., Proc. Natl. Acad. Sci., 96, 1379–1384 (1999) 2. Q. Chi, O. Farver, and J. Ulstrup, Proc. Natl. Acad. Sci., 102, 16203–16208 (2005) 3. M. Wang, S. Bugarski, and U. Stimming, Small, 4, 1110–1114 (2008) 4. M. Wang, S. Bugarski, and U. Stimming, J. Phys. Chem. C, 112, 5165–5173 (2008) 5. C. Baier and U. Stimming, Angew. Chemie - Int. Ed., 48, 5542–5544 (2009) Figure 1

Catalytic effects of surface groups on porous carbon electrodes are claimed in literature for the redox reactions V(II)/V(III) and V(IV)/V(V). The literature is critically analysed also in relation to work of this group. A method on how to overcome the problem of assessing the electrochemically active surface area on porous electrodes is presented [1]. Applying this method, no catalytic effects for above reactions can be substantiated. It is further pointed out that the parameters electrochemical potential and temperature need to be used to assess electrocatalysis. The main control parameter determining the rate of an electrochemical reaction is the Gibbs free enthalpy of activation, ΔG≠ , in contrast to ΔH≠ for e.g. a heterogeneous surface reaction. This would suggest to clearly define electrocatalysis as the “lowering the activation barrier, ΔG≠ , in an electrochemical reaction” where, in fact, the lowering of ΔG≠ can result from a change in ΔH≠ and/or ΔS≠ (∂ ΔG≠ /∂η=∂ ΔH≠ /∂η−T∂ΔS≠/∂η , as in Figure1). Such a treatment of data of temperature dependent electrochemical reactions has been described in literatures [2,3]. An analysis according to the above-discussed procedures would pin down which quantity is responsible for the lowering of ΔG ≠ that may allow for a better interpretation of the electrocatalytic effect. Using the example of the redox reactions V(II)/V(III) and V(IV)/V(V) the literature was analysed regarding possible catalytic effects of functional groups on carbon electrodes, as in Figure2. The conclusion was that no electrocatalysis of either of these reactions can be confirmed. Observed enhancements of currents can rather be attributed to a change in the effective surface area of the, usually, porous electrode. A method is suggested how such effects can be distinguished from electrocatalysis by using electrochemical impedance spectroscopy (EIS). Figure2 gives an example how EIS data are used for evaluation. In more general terms, the criteria for electrocatalysis were described. Experimentally, an investigation should contain both, measurements of the potential dependence and the temperature dependence since the main parameter in electrocatalysis is the lowering of ΔG≠ . Only then, the respective influence of ΔH≠ and ΔS≠ can be assessed. Acknowledgments This work was supported in part by Siemens AG through a research grant and by EPSRC through funding for the North East Centre of Energy Materials (NECEM) (EP/R021503/10). References: [1] U. Stimming, J. Wang, and A. Bund, ChemPhysChem, 2019, 20, 1-7. [2] B. E. Conway, In Modern Electrochemistry, Vol. 16. New York: Plenum Press, 1987. [3] Z. Borkowska, M. Cappadonia, and U. Stimming, Electrochim. Acta, 1992, 37(3), 565-568. [4] J. Friedl, C. M. Bauer, A. Rinaldi, and U. Stimming, Carbon, 2013, 63, 228-239. Figure 1

Electrochemical impedance spectroscopy (EIS) is a powerful tool for the non-destructive diagnosis of lithium ion batteries (LIBs). Thanks to the measurement over a wide frequency range, electrochemical processes of different kinetics are reflected in EIS, which contains rich information on battery aging and degradation. Distribution of relaxation times (DRT) method has been increasingly utilised to interpret EIS data. Compared to conventional EIS presentations such as Nyquist plot and Bode plot, DRT isolates the processes with different time constants and gives an explicit showcase of timescales in the battery [1]. Another advantage of DRT is the possibility to separate contributions from cathode and anode without the meticulous work to make three-electrode cells, given that relaxation time peaks can be identified with half cells [2]. The information acquired through DRT can provide insight into battery degradation paths and help improve data-driven methods for battery diagnosis/prediction. This work looks into the DRT evolution of commercial NMC/graphite cylindrical cells (Sony US14500VR2 with a nominal capacity of 715mAh) under various cycling conditions. Before the experiment starts, the cells are in shipping status i.e. undergone pre-aging and kept at approximately 70% state of charge (SoC). All cells then go through one 0.1C/0.1C cycle and 99 continuous cycles under various C-rates and temperatures (see table 1). The lower C-rates under 25ºC and 35ºC are scaled against 45ºC by Arrhenius relation. All charges are constant-current constant-voltage and all discharges are constant-current, between 3V and 4.2V. Impedance spectra are measured over 10kHz~0.1Hz range after being fully charged and fully discharged in each cycle. The impedance spectra measured after every full charge of cells 1~5 are shown in Figure 1(a) ~ (e). The decrease of semicircle size as temperature increases can be seen. During continuous cycling, internal resistance and semicircle size grow monotonically as cycle number increases. While the semicircles in each EIS curve are overlapping, the impedance components with different relaxation times are clearly separated in the DRT plotted in Figure 2. In Figure 2(a) and (b), there are constantly four relaxation time peaks as cycle number increases in 25ºC. The feature time constant in lies tightly within 25ms~50ms range, corresponding to 20Hz~40Hz frequencies, regardless of C-rates. In Figure 2(c) and (d), relaxation time peaks differ with C-rates right after 35ºC cycling starts. With 0.5C/1C rate, the evolution trend of relaxation time is similar to 25ºC cases. With 1C/2C rate however, there are initially only three relaxation time peaks and the mid-frequency (between 0.1s and 1s) peak “splits” into two as cycle number approaches 100. This could be related to joule heating resulting from higher C-rate or kinetic factors, and is more similar to the 45ºC case as shown in Figure 2(e). In 45ºC with 1C/2C rate, the relaxation time peaks start with three and “split” into four around the 60th cycle. While the evolution of DRT needs further interpretation and more long-term experiments, we can see the effective of time scale separation for EIS under various cycling conditions. The time scale features can be incorporated into data-driven methods e.g. machine learning to aim at accurate battery diagnosis/prediction. Also, the fact that feature relaxation times (may be battery-type specific) are distributed in a relatively narrow range suggests the EIS measurement can be done with reduced frequency points to save on-board resources for future system-level application. This work is supported by Faraday Institution (EP/S003053/1) and North-East Centre of Energy Materials (EP/R021503/1) funded by EPSRC. [1] Ciucci, F., & Chen, C. (2015). Analysis of electrochemical impedance spectroscopy data using the distribution of relaxation times: A Bayesian and hierarchical Bayesian approach. Electrochimica Acta, 167, 439-454. [2] Sabet, P. S., Stahl, G., & Sauer, D. U. (2018). Non-invasive investigation of predominant processes in the impedance spectra of high energy lithium-ion batteries with Nickel-Cobalt-Aluminum cathodes. Journal of Power Sources, 406, 185-193. Figure 1

Lithium-Ion Batteries (LIBs) are widely discussed and investigated as versatile energy storage systems. However, LIBs may pose safety risks, such as flammability of the electrodes and the electrolytes, which is a problem that may be amplified when transitioning from small-scale to medium- or large-scale energy storage. Yet, large-scale low-cost energy storage is crucial for the transition from a fossil fuel-based energy economy to renewable energy sources and in order to utilise the already existing energy sources like wind and solar power more efficiently. A promising technology for this task are Redox-Flow-Batteries (RFBs). The RFB is the only type of battery where power output and energy capacity can be scaled independently, allowing it to be specifically tailored to a variety of applications. However, the most mature RFB so far, the All-Vanadium RFB, suffers from low energy density and low power density. In order to overcome these challenges while maintaining the advantages of an aqueous RFB, like non-flammability and minimal self-discharge, we are investigating new redox chemistries. As redox systems, polyoxometalates (POMs) and specifically [SiW12O40]4- and [PV14O42]9- as nano-sized electron shuttles were investigated.1 These POMs exhibit fast redox kinetics (electron transfer constant k 0 ≈ 10-2 cm s-1 for [SiW12O40]4-) which together with their high solubility in water and multiple redox-centres per molecule provides the potential for for high power densities and high energy densities. The POMs that were used also exhibit high electrochemical and chemical stability, thus providing long cycle lifetimes. Other POMs were investigated as well. The system was scaled up from a lab-sized cell of 25 cm2 membrane area to a cell of 1400 cm2 in order to assess the implications on efficiency and operational parameters.2 The cell was operated for 1400 cycles over a time of nearly three months, providing some very promising results; the Coulombic efficiency was nearly 100% with the energy efficiency dropping only from 86.1% to 85.1% during the whole period, indicating a highly stable system. The observed capacity loss of 0.011% per cycle could be attributed to ambient air leakage leading to oxidation of SiW12. Post-cycling analysis showed no sign of degradation of the electrolytes. Acknowledgement We acknowledge funding and the fruitful cooperation with SIEMENS AG. Also, funding from NECEM, the North East Centre for Energy Materials (EP/R021503/10) is thankfully acknowledged.

Lithium ion battery usage has grown significantly in recent years. To obtain the best from the li-ion battery technology, it is important to understand both advantages and the limitations from the fundamental point of view. In lithium-ion batteries, layer structured graphite is the most commonly used anode material and NMC is one of the modern choices of cathode materials for high capacity Li-ion batteries in the electric vehicle applications [1,2,3]. During the first charging process, the electrochemical reduction of electrolyte components gets deposited on the surface of anode resulting solid electrolyte interface (SEI) layer formation [4,5,6]. It is widely accepted that the batteries benefit from a proper SEI formation, as it can improve their lifetime, cycle life, power capability and safety [7]. Morphological structure of SEI layer formed on HOPG and cathode electrolyte interface (CEI) layer formed on NMC plays an important role in lithium-ion battery (LIB), particularly for its cyclability and safety. For the development of high-performance LIB’s, it is crucial to understand the SEI layer formation on anode side [8] and the less studied corresponding layer formed on cathode side termed as CEI, whose composition and role are debated [9]. Microscopic techniques, which include scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are the most powerful tools to measure the electric current and surface topography [10,11]. Within this work, we present in-situ electrochemical atomic force microscopic (EC-AFM) studies of surface reaction and topographic evolution of SEI and CEI layers formed on HOPG and NMC811 substrates. EC-AFM morphological analysis is also complemented with XPS (X-ray Photoemission Spectroscopy) characterisation for elemental composition, which brings a new insight in the comparison of SEI/CEI decomposition products. Acknowledgements: This work is partially supported by Faraday Institution (EP/S003053/1) and North-East Centre of Energy Materials-NECEM (EP/R021503/1) funded by EPSRC. References: [1] H. Sun and K. Zhao, J Physical Chem C, 2017, 121, 6002-6010. [2] S. Bak, E. Hu, Y.Zhou, X.Yu, S.D. Senanayake, S. Cho, K. Kim, K.Y. Chung, X. Q. Yang and K. W. Nam, ACS Applied Materials &Interfaces, 2014, 6, 22594-22601. [3] P. Rozier and J. M. Tarascon, J Electrochem. Soc, 2015, 162, A2490-A2499. [4] L.Seidl, S.Martens, J. Ma, U.Stimming and O.Schneider, Nanoscale,2016, 8, 14004. [5] D.Xin, L.XingRui, Y. Huijuan,W.Dong and W.Lijun, Chem. Methodol,2014,57,178-183. [6] M.Steinhauer, M.Stich, M. Kurniawan, B.K. Seidlhofer, M.Trapp, A. Bund, N.wagner and K.A.Friedrich, ACS Appl.Mater.Interfaces, 2017,9,35794-35801. [7] P.B. Balbuena and Y.Wang, Lithium-ion batteries solid-electrolyte interface, imperial college press,2004. [8] V. A. Agubra, J. W. Fergus, J. Power Sources, 2014, 268, 153−162. [9] L. Yao-min, G.N. Bruno, L. E. Jennifer, A.G. Andrew, J. Anal.Chem,2016,88,7171-7177. [10] C. Shen, M. Buck, Beilstein J. Nanotechnol, 2014, 5, 258−267. [11] C. Shen, I. Cebula, C. Brown, J. L. Zhao, M. Zharnikov, M. Buck, Chem. Sci, 2012, 3, 1858−1865. Figure 1

The actual energy demand and consumption issues make it necessary to critically discuss and compare different energy conversion and storage systems. At present, only one third of the primary energy is converted into end energy, for example, electrical energy. Losses are associated with a high consumption of fossil fuels and large CO2 emissions. They can be avoided by considering important electrochemical processes for energy conversion, using batteries, fuel cells, supercapacitors and electrochemical photovoltaics and by incorporating energy storage, employing rechargeable batteries, supercapacitors, generation of hydrogen via electrolysis, and generation of methanol.

Scanning probe microscopy (SPM) techniques have had a great impact on research fields of surface science and nanotechnology during the last decades. They are used to investigate surfaces with scanning ranges between several 100 mm down to atomic resolution. Depending on experimental conditions, and the interaction forces between probe and sample, different SPM techniques allow mapping of different surface properties. In this work, scanning tunneling microscopy (STM) in air and under electrochemical conditions (EC-STM), atomic force microscopy (AFM) in air and scanning electrochemical potential microscopy (SECPM) under electrochemical conditions, were used to study different single crystalline surfaces in electrochemistry. Especially SECPM offers potentially new insights into the solid-liquid interface by providing the possibility to image the potential distribution of the surface, with a resolution that is comparable to STM. In electrocatalysis, nanostructured catalysts supported on different electrode materials often show behavior different from their bulk electrodes. This was experimentally and theoretically shown for several combinations and recently on Pt on Au(111) towards fuel cell relevant reactions. For these investigations single crystals often provide accurate and well defined reference and support systems. We will show heteroepitaxially grown Ru, Ir and Rh single crystalline surface films and bulk Au single crystals with different orientations under electrochemical conditions. Image studies from all three different SPM methods will be presented and compared to electrochemical data obtained by cyclic voltammetry in acidic media. The quality of the single crystalline supports will be verified by the SPM images and the cyclic voltammograms. Furthermore, an outlook will be presented on how such supports can be used in electrocatalytic studies.

The SEI-formation on graphitic electrodes operated as an Li(+)-ion battery anode in a standard 1 M LiPF6 EC/DMC (1 : 1) electrolyte has been studied in situ by EC-STM. Two different modes of in situ study were applied, one, which allowed to follow topographic and crystallographic changes (solvent cointercalation, graphite exfoliation, SEI precipitation on the HOPG basal plane) of the graphite electrode during SEI-formation, and the second, which gave an insight into the SEI precipitation on the HOPG basal plane in real time. From the in situ EC-STM studies, not only conclusions about the SEI-topography could be drawn, but also about the formation mechanism and the chemical composition, which strongly depend on the electrode potential. It was shown that above 1.0 V vs. Li/Li(+) the SEI-formation is still reversible, since the molecular structure of the solvent molecules remains intact during an initial reduction step. During further reduction, the molecular structures of the solvents are destructed, which causes the irreversible charge loss. The STM studies were completed by electrochemical methods, like cyclic voltammetry, the potentiostatic intermittent titration technique and charge/discharge tests of MCMB electrodes.

We demonstrate that (NH

We demonstrate that (NH4)2Si0.5Ti0.5P4O13 is an excellent proton conductor. The crystallographic information concerning the hydrogen positions is unraveled from neutron-powder-diffraction (NPD) data for the first time. This study shows that all the hydrogen atoms are connected though H bonds, establishing a two-dimensional path between the [(Si0.5Ti0.5)P4O132-]n layers for proton diffusion across the crystal structure by breaking and reconstructing intermediate H-O=P bonds. This transient species probably reduces the potential energy of the H jump from an ammonium unit to the next neighboring NH4+ unit. Both theoretical and experimental results support an interstitial-proton-conduction mechanism. The proton conductivities of (NH4)2Si0.5Ti0.5P4O13 reach 0.0061 and 0.024 S cm-1 in humid air at 125 and 250 °C, respectively. This finding demonstrates that (NH4)2Si0.5Ti0.5P4O13 is a promising electrolyte material operating at 150-250 °C. This work opens up a new avenue for designing and fabricating high-performance inorganic electrolytes. Fil: Sun, Chunwen. Chinese Academy Of Sciences; China. Chinese Academy of Sciences; República de China Fil: Chen, Lanli. Shanghai University; China Fil: Shi, Siqi. Shanghai University; China Fil: Reeb, Berthold. Bavarian Center for Applied Energy Research; Alemania Fil: Lopez, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentina Fil: Alonso, José Antonio. Instituto de Ciencia de Materiales de Madrid; España. Consejo Superior de Investigaciones Científicas; España Fil: Stimming, Ulrich. Bavarian Center for Applied Energy Research; Alemania. University of Newcastle; Reino Unido

The influence of a high defect density on an Au(111) surface on electrocatalytic properties of electrochemically deposited Pt nanoislands was evaluated. Therefore, the electrocatalytic activities of Pt nanoislands on a defect-poor and on a defect-rich Au(111) surface were compared for the hydrogen reactions (HER and HOR). These investigations were expected to yield higher activities of defect-rich surfaces since the spillover effect should be promoted. In fact, our expectations were met: The electrocatalytic activity of Pt nanoislands on defect-rich Au(111) was found to be more than twice as high as on defect-poor Au(111). This was thought to originate from a higher reactivity of the defect-rich Au surface, which plays a fundamental role for the spillover process. Another factor, which has to be taken into account, is the influence of differences in the hydrogen adsorption energies of Pt nanoislands, which are supported on Au(111) terraces and on Au(111)-defect sites. Hence, different electrocatalytic activities can also be due to different hydrogen adsorption energies.

Several alternative fuel–vehicle combinations are being considered for replacement of the internal combustion engine (ICE) vehicles to reduce greenhouse gas (GHG) emissions and the dependence on fossil fuels. The International Energy Agency has proposed the inclusion of low carbon alternatives such as electricity, hydrogen and biofuels in the transport sector for reducing the GHG emissions and providing a sustainable future. This paper compares the use of these alternative fuels, viz. electricity, hydrogen and bio-ethanol in combination with battery electric vehicle (BEV) and fuel cell electric vehicle (FCEV) technologies on the basis of their overall efficiency and GHG emissions involved in the conversion of the primary energy source to the actual energy required at wheels through a well-to-wheel analysis. The source of energy for electricity production plays a major role in determining the overall efficiency and the GHG emissions of a BEV. Hence electricity production mix of Germany (60% fossil fuel energy), France (76% nuclear energy), Sweden and Austria (60 and 76% renewable energy, respectively), the European Union mix (48% fossil fuel energy) and the United States of America (68% fossil fuel energy) are considered for the BEV analysis. In addition to the standard hydrogen based FCEVs, CNG and bio-ethanol based FCEVs are analysed. The influence of a direct ethanol fuel cell (DEFC) on GHG emissions and overall chain efficiency is discussed. In addition to the standard sources of bio-ethanol (like sugarcane, corn, etc.), sources like wood waste and wheat straw are included in the analysis. The results of this study suggest that a BEV powered by an electricity production mix dominated by renewable energy and bio-ethanol based DEFC electric vehicles offer the best solution in terms of GHG emissions, efficiency and fossil fuel dependency. Bio-ethanol as a fuel has the additional advantage to be implemented readily in ICE vehicles followed by advancements through reformer based FCEVs and DEFC electric vehicles. Although important, this analysis does not include the health effects of the alternative vehicles. Bio-ethanol used in an ICE may lead to increased emission of acetaldehydes which however might not be the case if it is used in fuel cells.

A novel nanohybrid material that combines single-walled carbon nanotubes (SWCNTs) with a polyoxometalate (TBA)5[PVV2MoVI10O40] (TBA-PV2Mo10, TBA: [(CH3(CH2)3)4N]+, tetra-n-butyl ammonium) is investigated for the first time as an electrode material for supercapacitors (SCs) in this study. The SWCNT-TBA-PV2Mo10 material has been prepared by a simple solution method which electrostatically attaches anionic [PV2Mo10O40]5− anions with organic TBA cations on the SWCNTs. The electrochemical performance of SWCNT-TBA-PV2Mo10 electrodes is studied in an acidic aqueous electrolyte (1 M H2SO4) by galvanostatic charge/discharge and cyclic voltammetry. In this SWCNT-TBA-PV2Mo10 nanohybrid material, TBA-PV2Mo10 provides redox activity while benefiting from the high electrical conductivity and high double-layer capacitance of the SWCNTs that improve both energy and power density. An assembled SWCNT-TBA-PV2Mo10 symmetric SC exhibits a 39% higher specific capacitance as compared to a symmetric SC employing only SWCNTs as electrode materials. Furthermore, the SWCNT-TBA-PV2Mo10 SC exhibits excellent cycling stability, retaining 95% of its specific capacitance after 6500 cycles.

Nanotechnology and synthetic biology are rapidly converging, with DNA origami being one of the leading bridging technologies. DNA origami was shown to work well in a wide array of biotic environments. However, the large majority of extant DNA origami scaffolds utilize bacteriophages or plasmid sequences thus severely limiting its future applicability as a bio-orthogonal nanotechnology platform. In this paper we present the design of biologically inert (i.e., "bio-orthogonal") origami scaffolds. The synthetic scaffolds have the additional advantage of being uniquely addressable (unlike biologically derived ones) and hence are better optimized for high-yield folding. We demonstrate our fully synthetic scaffold design with both DNA and RNA origamis and describe a protocol to produce these bio-orthogonal and uniquely addressable origami scaffolds.

Electrochemical properties of two tri-manganese substituted Keggin-based tungstosilicates [MnII3(OH)3(H2O)3(A-α-SiW9O34)]7− (MnII3SiW9) and[MnIII3(OH)3(H2O)3(A-α-SiW9O34)]4− (MnIII3SiW9) were investigated. The two polyanions are isostructural, the only difference being the oxidation state of the Mn-ions. Despite their structural similarity the electrochemical behaviour is not identical. While it is well established that polyoxometalate (POM) electrochemistry is influenced by interplay between the pH of the electrolyte, the present ions and the pKa values of the complex, this is the first report that the initial oxidation state of the POM has a major influence on the electrochemistry of the transition metal within the molecule. In order to understand the influence of the initial oxidation state extensive electrochemical investigations were performed and the potential dependent adsorption behavior of the molecules on graphite was observed with atomic force microscopy. The reaction mechanism of the two POMs was determined and it was asserted that the divergent redox behavior is caused by a ligand exchange which takes place during the measurement. This influences the adsorption of the molecules on graphite which can be explained by the Born solvation model. Performing controlled potential electrolysis, a stable tri-manganese substituted Keggin ion containing MnIV3 was obtained electrochemically.

The combination of surface science and electrochemistry is an effective method to approach a fundamental understanding of electrocatalytic systems, especially of the catalyst/support assemblies. Extrinsic chemical defects in the support can affect the performances and this topic is much investigated in recent electrocatalyst research. In this work, nitrogen functional groups are introduced into the outermost layers of highly oriented pyrolytic graphite (HOPG) by ion implantation with a beam energy of 100 eV. Palladium nanoparticles (Pd NPs) are then electrochemically deposited onto both pure and nitrogen doped HOPG (N-HOPG). Pd2+ species located at the interface between the NPs and the nitrogen-rich surface were observed in the latter case. The supported Pd NPs on N-HOPG show the same electrocatalytic activity for oxygen reduction reaction (ORR) as compared with those supported on pure HOPG. However, the stability of Pd NPs on N-HOPG towards potential cycling decreases strongly due to the existence of Pd2+ at the interface, which can accelerate the dissolution of Pd atoms. This result is contradictory to results on supported Pt NPs from the literature where the merit of the N-doping was outlined.

Ionic liquids have found widespread applications in electrochemistry, and are increasingly used in the field of electrochemical energy conversion and storage. In battery technology, the use of ionic liquids can increase the device safety significantly and help in enabling alternative technologies like Mg ion batteries. In fuel cell technology, new, water-free proton conducting membranes and new options for synthesis and improvement of catalysts are in the focus of research. In this paper some applications, advantages and drawbacks of ionic liquids in electrochemical energy technology are reviewed. Some examples from the authors’ own work in batteries and electrocatalysis using standard electrolytes are presented, and the potential improvements by using ionic liquids in these studies are discussed.

This paper demonstrates a novel polymer electrolyte membrane (PEM) based methanol electrolyzer stack with a catalyzed membrane for hydrogen production. The physical and electrochemical properties of the catalyzed membrane, single cell and stack are examined using various characterization techniques, such as X-ray diffraction, scanning electron microscopy with EDX and polarization studies. The results demonstrate that the with Pt-catalyzed membrane electrode assembly (MEA) exhibits significantly better performance than a normal MEA. The developed electrolyzer stack produces 102 L h−1 of 99% pure hydrogen without CO and CO2. The excellent stability of the PEM methanol electrolyzer system is demonstrated by running the stack for 2500 h of intermittent operation with constant current density.

In order to utilise intermittent renewable energy sources like wind and solar power more efficiently, flexible and inexpensive electricity storage capabilities are required. One particularly well-suited option for this task are Redox-Flow-Batteries (RFBs). RFBs are the only type of battery where power and capacity can be scaled independently, thus providing high flexibility and versatile applications. However, the prevailing technology, the all vanadium system, comprises low energy and low power densities. We investigate two polyoxometalates (POMs), [SiW12O40]4- and [PV14O42]9-, as nano-sized electron shuttles.1 We show that these POMs exhibit fast redox kinetics (electron transfer constant k 0 ≈ 10-2 cm s-1 for [SiW12O40]4-), thereby enabling high power densities. Furthermore, we could show that these POMs exhibit some more favourable properties for their use in a battery, like high solubility, multiple redox-centres per molecule and a high (electro)chemical stability, which lead to high energy densities and long cycle lifetimes. Water as a solvent provides inherent safety to the system, as no flammable electrodes or electrolytes are used. In collaboration with Siemens AG, we were also able to scale up the presented system from a 25 cm2 lab cell to a cell with 1400 cm2.2 Cycling over a period of nearly three months provided some very promising results, including a coulombic efficiency of nearly 100%. Post-cycling analysis of the electrolytes indicated no sign of degradation and the observed capacity loss of 0.011% per cycle could be attributed to air oxidation. The energy efficiency dropped from 86.1% to 85.1% over the course of 1400 cycles, again showing a highly stable performance. References 1 J. Friedl,M. V. Holland-Cunz, F. Cording, F. L. Pfanschilling, C. Wills, W. McFarlane, B. Schricker, R. Fleck, H. Wolfschmidt, U. Stimming, Energy Environ. Sci., 2018, 11 (10), 3010–3018. https://doi.org/10.1039/C8EE00422F 2 J. Friedl, M. V. Holland-Cunz, F. L. Pfanschilling, R. Fleck, B. Schricker, H. Wolfschmidt, U. Stimming, submitted.