We investigated the chemistry of Hg(II) during exposure of exponentially growing bacteria (Escherichia coli, Bacillus subtilis, and Geobacter sulfurreducens) to 50 nM, 500 nM, and 5 μM total Hg(II) with and without added cysteine. With X-ray absorption spectroscopy, we provide direct evidence of the formation of cell-associated HgS for all tested bacteria. The addition of cysteine (100–1000 μM) promotes HgS formation (>70% of total cell-associated Hg(II)) as a result of the biodegradation of added cysteine to sulfide. Cell-associated HgS species are also detected when cysteine is not added as a sulfide source. Two phases of HgS, cinnabar (α-HgS) and metacinnabar (β-HgS), form depending on the total concentration of Hg(II) and sulfide in the exposure medium. However, α-HgS exclusively forms in assays that contain an excess of cysteine. Scanning transmission electron microscopy images reveal that nanoparticulate HgS(s) is primarily located at the cell surface/extracellular matrix of Gram-negative E. coli and G. sulfurreducens and in the cytoplasm/cell membrane of Gram-positive B. subtilis. Intracellular Hg(II) was detected even when the predominant cell-associated species was HgS. This study shows that HgS species can form from exogenous thiol-containing ligands and endogenous sulfide in Hg(II) biouptake assays under nondissimilatory sulfate reducing conditions, providing new considerations for the interpretation of Hg(II) biouptake results.
The redox flow battery (RFB) is a promising electrochemical energy storage solution that has seen limited deployment due, in part, to the high capital costs of current offerings. While the search for lower-cost chemistries has led to exciting expansions in available material sets, recent advances in RFB science and engineering may revivify older chemistries with suitable property profiles. One such system is the iron-chromium (Fe-Cr) RFB, which utilizes a low-cost, high-abundance chemistry, but the poor Cr redox reaction kinetics and high hydrogen evolution reaction (HER) rates challenge efficient, long-term operation. Of late, renewed efforts have focused on HER mitigation through materials innovation including electrocatalysts and electrolyte additives. Here, we show electrochemical purification, where soluble contaminants are deposited onto a sacrificial electrode prior to cell operation, can lead to a ca. 5× reduction in capacity fade rates. Leveraging data harvested from prior literature, we identify an association between coulombic efficiency and discharge capacity decay rate, finding that electrochemical purification can enable cell performance equivalent to that with new and potentially-expensive materials. We anticipate this method of mitigating HER may reduce capacity maintenance needs and, in combination with other advances, further durational Fe-Cr RFBs.
Redox flow batteries (RFBs) are a promising electrochemical storage solution for power sector decarbonization, particularly emerging long-duration needs. While the battery architecture can host many different redox chemistries, the vanadium RFB (VRFB) represents the current state-of-the-art due to its favorable combination of performance and longevity. However, the relatively high and volatile price of vanadium has hindered VRFB financing and deployment opportunities. Here we evaluate the vanadium supply chain to understand how it enables or constrains VRFB advancement and assess opportunities for accelerated growth. We find that – while vanadium may not be scarce – its abundance is confounded by highly concentrated production coupled with the disperse nature of sources suitable for potential supply increase. These factors challenge rapid growth, limiting deployment rate and magnitude. We estimate gigawatt-hour deployment scales are feasible over the next decade, which would represent marked expansion of the RFB industry and drive down system costs substantially, though this would require growth rates above historical averages. Accordingly, we review opportunities to accelerate supply chain growth and economic strategies to stabilize the market. Finally, we posit terawatt-hour deployment scales will be challenged by vanadium market conditions and, even, resource availability, motivating the continued efforts developing next-generation RFB chemistries.
<p>Redox flow batteries, a promising grid-scale energy storage solution, have an open architecture that can facilitate a broad range of redox electrolytes. Vanadium is the most mature chemistry, which is largely due to its symmetry, where all active species are based on a single parent compound, that allows for inexpensive crossover remediation via rebalancing; however, the industry has increasingly sought chemistries with lower-cost and higher-abundance redox couples. Most chemistries cannot be configured symmetrically, though, necessitating research into capacity-recovery methods for asymmetric chemistries. In this work, we adapt our previously developed levelized cost of storage model, which tracks capacity fade and recovery and evaluates the costs across the battery’s lifetime, to analyze two classes of asymmetric chemistries, those with active species of finite or infinite lifetimes, and their respective remediation options. For finite-lifetime chemistries, we explore active-species replacement to counter decay. For infinite-lifetime chemistries, we consider two methods for addressing crossover: imposition of pseudo-symmetry via the spectator strategy and elimination of crossover via membranes with perfect selectivity. We anticipate this framework will help guide the evaluation and design of new redox chemistries, balancing the desire for low capital costs with the need to remediate capacity repeatedly and inexpensively.</p>
Energy storage is expected to play an important role in enabling deep decarbonization of the electric sector by addressing the intermittencies of renewable power generation 1 . The redox flow battery (RFB) is a potential energy storage solution whose unique decoupling of energy and power make it increasingly competitive, on a capital cost basis, at longer discharge durations 2 . While the capital cost benefits to RFBs are well-described in the literature 3 , there are additional economic benefits associated with operation and maintenance of open systems (e.g., tune-ups, sparing strategies) 4 as compared to closed systems like lithium-ion batteries. For example, crossover, undesirable species transport through the semi-permeable membrane that separates the positive and negative electrolytes, leads to comparatively rapid capacity fade in RFBs 5 but can be remediated via electrolyte rebalancing, replacement, or other servicing, all of which can be performed without sacrificing or altering the reactor components. The costs necessary to maintain battery performance over time impact its economic viability, but are not captured in the conventional capital cost estimations 6 . This motivates the development of techno-economic models that consider the variable operating principles of different battery formats and chemistries. In this presentation, we describe a simple levelized cost of storage (LCOS) model for RFBs that captures long-term performance changes and maintenance costs by including capacity fade and recovery 7 . We use this model to assess the impact of different design and operational decisions on RFB cost. Specifically, we contemplate different chemistries (symmetric vs. asymmetric, finite lifetime vs. infinite lifetime), operating strategies (e.g., rebalancing schedule), performance improvements (e.g., reducing fade rates), design decisions (e.g., battery sizing), and investment approaches (e.g., electrolyte leasing). We find that there are tradeoffs in capital and operating expenses, and in many cases upfront investments pay off in long-term savings. We anticipate this analysis will provide new insights into the cost-drivers for RFBs and motivate further research efforts in the evaluation and development of new chemistries, component materials, and reactor configurations. Acknowledgements We gratefully acknowledge funding from the MIT Energy Initiative. References Intergovernmental Panel on Climate Change. Global Warming of 1.5 C . https://www.ipcc.ch/sr15/ (2018). Darling, R. M., Gallagher, K. G., Kowalski, J. A., Seungbum, H. & Brushett, F. R. Pathways to low-cost electrochemical energy storage: a comparison of aqueous and nonaqueous flow batteries. Energy Environ. Sci. 7 , 3459–3477 (2014). Viswanathan, V. et al. Cost and performance model for redox flow batteries. J. Power Sources 247 , 1040–1051 (2014). Yuan, X.-Z. et al. A review of all-vanadium redox flow battery durability: Degradation mechanisms and mitigation strategies. Int. J. Energy Res. 1–40 (2019) doi:10.1002/er.4607. Prifti, H., Parasuraman, A., Winardi, S., Lim, T. M. & Skyllas-Kazacos, M. Membranes for redox flow battery applications. Membranes vol. 2 275–306 (2012). US Department of Energy. Grid Energy Storage . https://www.energy.gov/sites/prod/files/2014/09/f18/Grid Energy Storage December 2013.pdf (2013). Rodby, K. E. et al. Assessing the levelized cost of vanadium redox flow batteries with capacity fade and rebalancing. J. Power Sources 460 , 227958 (2020).
This paper elaborates on the characterization of vanadium redox flow battery (VRFB) performance for energy arbitrage optimization based on the experimental data obtained in-house. Typical figures-of-merit used for evaluating VRFBs include coulombic, voltaic, and energy efficiencies. However, these metrics along with the deliverable power vary as a function of discharge/charge current during cycling. Thus, using a basic energy storage model with constant efficiency and fixed maximum power is not a rigorous approach for predicting the performance of VRFBs in applications with variable supply/demand of electricity. Moreover, optimization based on such an oversimplified treatment may result in inaccurate battery dispatch signal and may overestimate arbitrage profit. Here, we propose a more detailed VRFB model with dynamic efficiency and maximum power limits as a function of state of charge (SOC). These data were obtained using lab-scale VRFB cells over a range of operating conditions. The dynamic model's performance is compared to the basic model for various day-ahead electricity price profiles. Substantial difference between the predictions of two modeling approaches on the battery dispatch and profits was observed. The results indicate that the dynamic model provides more accurate predictions on the battery performance for applications with intermittent energy profile.
Abstract Creating diverse, inclusive, and respectful environments is the #1 recommendation of the 2018 National Academies of Sciences, Engineering, and Medicine report on “Sexual Harassment of Women” [1]. To accomplish this goal, the report suggests that academic institutions cater their training to specific populations, use qualified, in-person trainers, and instruct participants how to intervene. These recommendations motivated a chemical engineering department at a technical institute to develop a custom in-person training program in collaboration with the Title IX and Bias Response (T9BR) and the Violence Prevention and Response (VPR) offices. The in-person trainings, entitled “Promoting a Professional and Inclusive Lab Culture,” were mandatory for all laboratory groups in the department, including faculty, staff, and trainees. To promote discussion and interaction within the context of individual lab cultures, training sessions were small (~20 participants) and grouped lab members together. The trainings were facilitated by members of the T9BR and VPR offices and covered aspects of a culture (including values and beliefs, verbal expressions, and behaviors), contexts of power, methods of intervening, and resources/support. The 120-minute sessions included presentation, interactive activities, and realistic example scenarios customized to the department with the goal of promoting respectful work behavior. Approximately 480 individuals participated in the training, representing 33 lab groups in a total of 28 sessions held over the course of 8 months. Exit survey results indicate that 95% of participants felt there was a good mix of presentation and interactivity and 93% felt that the content was neither too basic nor too advanced. In the follow-up survey, greater than 85% of respondents “strongly agreed” or “agreed” that these trainings sent a positive message about departmental values and would recommend the trainings in other departments. We believe that custom in-person trainings such as the one described here have the potential to positively impact the culture of an engineering department. [1] National Academies of Sciences, Engineering, and Medicine, Sexual Harassment of Women: Climate, Culture, and Consequences in Academic Sciences, Engineering, and Medicine. National Academies Press: 2018.
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