The electrochemical engineering aspects of high aspect ratio cells, such as those used in in situ electrochemical scanning transmission microscopy (ec-S/TEM) were examined, focusing on aspects that could cause non-uniform current distribution. Having a uniform current distribution across the working electrode is important for any spectroelectrochemical technique in order to provide accurate electrochemical information as well as structural electrolyte-electrode interface information. An analytical model was developed to determine current density distribution and a Wagner number was derived for a small cell height with coplanar electrodes. The main assumptions of this analysis are: 1) mass transport effects are negligible, 2) a uniform potential distribution in the direction of the cell height due to their small size, and 3) the working electrode potential is constant across its length. With our analysis, the assumptions were found to be reasonable. In addition, the effect of the conductivity and thickness of the thin film electrode and its potential effect on current density distribution have been analyzed. Now, with this work, high aspect ratio cells with a small cell heights and coplanar thin electrodes can be analyzed to determine their current density distribution.

This work investigates a bromide supported electrolyte for use in an all-copper flow battery (CuFB). In this battery, halide ions stabilize the cuprous ion. During charge, the cuprous halide complex is reduced to copper metal at the negative electrode and the complex is oxidized to a cupric halide complex at the positive electrode. Our measurements indicated that the CuFB utilizing a bromide electrolyte can achieve a higher open circuit potential (OCP) as compared to using a chloride electrolyte. The CuFB has negligible hydrogen and bromine evolution indicating that high coulombic efficiencies are achievable. A bromide supported all-CuFB with graphitic porous felt electrodes was demonstrated and the OCP after the initial charge was observed to be 0.81 V. The cell was cycled with a geometric current density of 150 mA cm −2 for 50 cycles with state of charge swings of 0 to 60%, and had a voltaicof 64%, however, copper electrodeposits were nodular and non-adherent to the substrate. We conclude that further understanding of plating morphology and the effect of substrates are necessary to take advantage of this chemistry in a conventional hybrid battery configuration, and that this system could benefit from a slurry electrode.

This study examines the diffusion coefficients of cuprous and cupric ions in aqueous solutions containing 4–6 mol·dm–3 bromide ion. Under these conditions, the majority of the Cu2+ species is the complex CuBr4 –2, and the majority of Cu+ species is the complex CuBr3 –2. Diffusion coefficients were obtained for temperatures ranging from 298 to 334 K via a rotating disk electrode and the Levich relationship. Diffusion coefficients for the cuprous bromide complex were found to be between 11.9 and 19.1 × 10–6 cm2·s–1. Diffusion coefficients for the cupric bromide complex ranged between 4.5 and 12.0 × 10–6 cm2·s–1. Confidence intervals were calculated with reasonable uncertainties. The diffusion coefficients were found to be in good agreement with literature values of cuprous and cupric chloride complexes.

One major issue limiting the implementation of renewable energy sources is the lack of efficient, cost-effective, and reliable energy storage technologies. Recently, vanadium redox flow batteries (VRFBs) have gained a significant interest as a promising electrochemical technology for large-scale energy storage due to their ability to decouple energy and power ratings and to store energy efficiently [1]. However, the high capital cost of vanadium-based electrolyte represents a major bottleneck for the commercialization of these systems [2]. By this motivation, in this study, a novel all-copper flow battery (CFB) using flowable slurry electrode is introduced.  CFBs have a great potential for commercialization, as copper is a less toxic, widely abundant, and less expensive element than vanadium [3]. Moreover, its relatively smaller cell potential eliminates hydrogen evolution as a side reaction. However, electrochemical-plating of copper within the negative electrode during charging recouples energy and power ratings, which limits the widespread implementation of these systems. In order to mitigate this issue, a flowable slurry electrode strategy is implemented for the negative half-cell instead of using a conventional, stationary electrode [4-5]. A schematic of an all-copper flow battery using a flowable slurry electrode for the negative half-cell is shown in Fig. 1. The slurry electrode carries the deposited metal out of the stack to the reservoir, allowing the energy and power capabilities of the battery to be scaled independently. This study is investigating the performance of a CFB using a flowable slurry electrode with a novel copper-bromide chemistry by conducting polarization curve (Fig. 2), battery cycling and efficiency analyses. As seen in Fig. 2, with the copper-bromide electrolyte and flowable slurry electrode strategy, much higher operating current densities (maximum power density of ~85 mW/cm2 obtained at 200 mA/cm2) have been reached compared to literature values for an all-copper flow battery. This indicates that the slurry electrode cannot only de-couple the energy and power ratings, but can also provide an acceptable level of polarization losses. References: [1] A. Z. Weber, M. M. Mench, J. P. Meyers, P. N. Ross, J. T. Gostick, Q. Liu, J. Appl. Electrochem., 41, 1137-1164 (2011). [2] R. M. Darling, K. G. Galagher, J. A. Kowalsky, S. Ha, F. R. Brushett, Energy Environ. Sci., 7, 3459-3477 (2014). [3] L. Sanz, D. Lloyd, E. Magdalena, J. Palma, K. Kontturi, J. Power Sources, 268, 121-128 (2014). [4] T. Petek, N. C. Hoyt, J. S Wainright, R. F. Savinell, Submitted to J. Power Sources, March (2015). [5] T. Petek, N. C. Hoyt, J. S Wainright, R. F. Savinell, Submitted to J. Electrochem. Soc., March (2015). [5] T. Petek, N. C. Hoyt, J. S Wainright, R. F. Savinell, Submitted to J. Electrochem. Soc., March (2015). Figure 1

Electrochemical nucleation of metals have long been investigated using chronoamperometry1, cyclic voltammetry2, and electrochemical impedance spectroscopy3 . The current/potential time transients from these methods are used as basis for models for various proposed nucleation mechanisms such as instantaneous and progressive nucleation4. Physical insight has been primarily inferred from the current/potential time transient models and ex situ analysis of the deposit thereafter. However, surface restructuring is known to occur ex situ. In situ methods, such as in situ STM5 and in situ AFM6, minimize ambiguous understanding due to surface restructuring; however, the time resolution of these methods are lacking7. Thus direct correlation between the nucleation processes and electrochemical measurements have not been studied in great detail due to the present lack of in situ characterization methods that permit the simultaneous acquisition of electrochemical measurements with high spatial resolution imaging and high time resolution processing within the electrolyte. Recent advances in liquid cell in situ electrochemical scanning/transmitting electron microscopy (ec-STEM), mitigates ambiguity due to surface restructuring following nucleation7, 8. In situ ec-STEM can acquire and analyze time-resolved images of the nucleation and growth process at the nanometer-scaled spatial resolution while quantitative electrochemical measurements are concurrently performed. Therefore, this technique can also provide clarity between nucleation growth and classical electrochemical nucleation models such as the Scharifker and Hills4 model and the Sluyter-Rehbach9 model. Recent advances in an all-copper flow battery has created a renewed interest in copper electrodeposition from a high halide electrolyte10. The high halide electrolyte is unique compared to traditional damascene plating in that the copper (I) oxidation state is stabilized. Here, we apply the in situ ec-STEM approach to investigate the electrochemical nucleation of copper in order to understand the negative electrode reaction in these all-copper batteries. This presentation compares the electrochemical nucleation of copper of high bromide ion electrolyte on a carbon versus copper electrode and discusses the nuances of in situ liquid cell ec-S/TEM. 1. Heerman, L.; Tarallo, A. Journal of Electroanalytical Chemistry 1999, 470, (1), 70-76. 2. Williams, D. E.; Wright, G. A. Electrochimica Acta 1976, 21, (11), 1009-1019. 3. Cachet, C.; Saïdani, B.; Wiart, R. Electrochimica Acta 1989, 34, (8), 1249-1250. 4. Scharifker, B.; Hills, G. Electrochimica Acta 1983, 28, (7), 879-889. 5. Itaya, K.; Tomita, E. Surface Science 1988, 201, (3), L507-L512. 6. Rynders, R. M.; Alkire, R. C. Journal of The Electrochemical Society 1994, 141, (5), 1166-1173. 7. Williamson, M. J.; Tromp, R. M.; Vereecken, P. M.; Hull, R.; Ross, F. M. Nat Mater 2003, 2, (8), 532-536. 8. Unocic, R. R.; Sacci, R. L.; Brown, G. M.; Veith, G. M.; Dudney, N. J.; More, K. L.; Walden, F. S., II; Gardiner, D. S.; Damiano, J.; Nackashi, D. P. Microscopy and Microanalysis 2014, 20, (02), 452-461. 9. Sluyters-Rehbach, M.; Wijenberg, J. H. O. J.; Bosco, E.; Sluyters, J. H. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1987, 236, (1–2), 1-20. 10. Lloyd, D.; Magdalena, E.; Sanz, L.; Murtomäki, L.; Kontturi, K. Journal of Power Sources 2015, 292, (0), 87-94.