Andres F Badel’s scientific contributions

Cement production is currently the largest single industrial emitter of CO 2 , accounting for 8% (2.8 Gtons/year) of global CO 2 emissions in 2015. Deep decarbonization of cement manufacturing will require remediation of both the CO 2 emissions due to the decomposition of CaCO 3 to CaO, and that due to combustion of fossil fuels (primarily coal) in the calcining (~900°C) and sintering (~1,450°C) processes. Here, we demonstrate an electrochemical process that uses neutral water electrolysis to produce a pH gradient in which CaCO 3 is decarbonated at low pH and Ca(OH) 2 is precipitated at neutral to high pH, concurrently producing a high purity O 2 /CO 2 gas mixture (1:2 molar ratio at demonstrated stoichiometric operation) at the anode and H 2 at the cathode, as shown in Figure 1. We show that the solid Ca(OH) 2 product readily decomposes and reacts with SiO 2 to form alite, the majority cementitious phase in Portland cement. Our electrochemical calcination approach produces concentrated gas streams from which the CO 2 may be readily separated and sequestered, the H 2 and/or O 2 may be used to generate electric power via fuel cells or combustors, the O 2 may be used as a component of oxyfuel in the cement kiln to further lower CO 2 and NO x emissions, or the output gases may be used for other value-added processes including liquid fuel production. Analysis shows that in a scenario where the hydrogen produced by the reactor is combusted to heat the high temperature kiln, the electrochemical cement process can be powered solely by renewable electricity. Figure 1. Schematic of the electrolyzer-based decarbonation cell. Reactions 1a and 1b are the O 2 evolution and H 2 evolution half-cell reactions respectively, under near-neutral pH. Reactions 2a and 2b represent the decomposition of CaCO 3 and release of CO 2 . Reaction 3 is the normal formation of water from its component ions. In Reaction 4, the hydroxide ions in Reaction 3 instead go towards the formation of Ca(OH) 2 , and the protons protonate carbonate ions (Reaction 2b). The overall reaction in which CaCO 3 is converted to Ca(OH) 2 with the attendant release of H 2 , O 2 and CO 2 is shown at the bottom. Figure 1

Sulfur is an attractive reactant for such concepts due to its exceptionally low cost, high natural abundance, and high specific and volumetric capacity owing to its two-electron reaction. Taking the cost-per-capacity (e.g., in US$/Ah) as a metric, sulfur has the lowest cost of any known electrode-active compound with the exception of water and air. However, in order to take advantage of sulfur’s low-cost potential, all other components must also have low cost. Towards enabling ultralow cost grid storage, we demonstrate an ambient-temperature aqueous rechargeable flow battery that uses low-cost polysulfide chemistry in conjunction with lithium or sodium as the working ion, and an air-breathing cathode. Four different laboratory cell constructions are used to test the half-cell and full-cell reactions, including a pumped air-breathing cell that exhibits stable room-temperature cycling over 960h with a lithium polysulfide anolyte and dissolved lithium sulfate catholyte. In this approach the solution energy density is 30-150 Wh/L, which exceeds current solution-based flow batteries, and the chemical cost of stored energy is exceptionally low, especially when using sodium polysulfide (~1 US$/kWh). Results of techno-economic modeling are also presented, which show that when projected to full system-level, this new approach has energy and power costs that are comparable to those of pumped hydroelectric storage (PHS) and underground compressed air energy storage (CAES), but without their geographical and environmental constraints. This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

Organic redox active compounds offer a new pathway towards affordable aqueous redox flow batteries (RFBs) due to their electrochemical performance, low cost, and design flexibility. Proposed organic active material candidates for aqueous RFBs have been limited to quinones 1–3 , a class of cyclic organic molecules distinguished by an even number of ketone (R–C(=O)–R’) groups ⁴ . Our experimental study widens the search for organic active material candidates to quinoxaline, a bicyclic organic molecule consisting of fused benzene and pyrazine rings. Quinoxaline electrochemical behavior has previously been characterized in non-aqueous electrolytes 5–9 , and several derivatives have been tested in a non-aqueous redox flow battery ¹⁰ . Aqueous quinoxaline was also recently applied as a redox active compound in a solar-rechargeable RFB device ¹¹ , but the exploration of quinoxaline electrochemical behavior was not the focus of that study. To the best of our knowledge, the work presented here is the first comprehensive study to consider the electrochemical behavior of aqueous quinoxaline. The electrochemical behavior of quinoxaline in aqueous electrolytes spanning a wide range of cations (Li ⁺ , Na ⁺ , K ⁺ ), anions (Cl ⁻ , NO 3 ⁻ , OH ⁻ , SO 4 ²⁻ , HCO 3 ⁻ , C 2 H 3 O 2 ⁻ ), and pH were investigated to determine the best conditions for the (electro)chemical reversibility and mass-transfer properties of quinoxaline. Specifically, this work focuses on interpreting results from cyclic voltammetry (CV) and rotating disk voltammetry (RDV) to analyze quinoxaline electrochemical performance. Several key trends were identified. First, solution pH has the strongest impact on quinoxaline electrochemical performance, reducing peak separation (Figure 1) and improving cycle stability (Figure 2). When stable, quinoxaline was found to have a redox potential of E ᵒ = -0.5 V vs. RHE. Second, certain anions were found to reduce peak separation (Cl ⁻ , SO 4 ²⁻ ) but to a lesser degree than increased alkalinity. Third, cations were found to have a negligible effect on CV behavior. Quantitative analyses, performed on select electrolytes, indicated that aqueous quinoxaline redox behavior was characterized by a single wave, two-electron transfer process, resulting in a theoretical capacity of 410 mAh g ⁻¹ . Further, quinoxaline solubility in KCl-based electrolytes was found to be as high as 4 M. This combination of high gravimetric capacity, high solubility, and low redox potential makes quinoxaline a promising material for application in an aqueous RFB. Acknowledgments We gratefully acknowledge the financial support of the Massachusetts Institute of Technology Energy Initiative and the National Science Foundation Graduate Research Fellowship Program. The assistance of Dr. Kyler Carroll, Dr. Emily Carino, Mr. Jeffry Kowalski, and Mr. Steven Brown is also much appreciated. References 1. B. Huskinson et al., Nature , 505 , 195–198 (2014). 2. Y. Xu, Y.H. Wen, J. Cheng, G.-P. Cao, and Y.-S. Yang, Electrochimica Acta , 55 , 715–720 (2010). 3. B. Yang, L. Hoober-Burkhardt, F. Wang, G. S. Prakash, and S. R. Narayanan, J. Electrochem. Soc. , 161 , A1371–A1380 (2014). 4. G. P. Moss, P. A. S. Smith, and D. Tavernier, Pure Appl. Chem. , 67 , 1307–1375 (1995). 5. D. van der Meer and D. Feil, Recl. Trav. Chim. Pays-Bas , 87 , 746–754 (1968). 6. D. van der Meer, Recl. Trav. Chim. Pays-Bas , 88 , 1361–1372 (1969). 7. D. van der Meer, Recl. Trav. Chim. Pays-Bas , 89 , 51–67 (1970). 8. J. R. Ames, M. A. Houghtaling, and D. L. Terrain, Electrochimica Acta , 37 , 1433–1436 (1992). 9. K. R. Barqawi and M. A. Atfah, Electrochimica Acta , 32 , 597–599 (1987). 10. F. R. Brushett, J. T. Vaughey, and A. N. Jansen, Adv. Energy Mater. , 2 , 1390–1396 (2012). 11. N. F. Yan, G. R. Li, and X. P. Gao, J. Electrochem. Soc. , 161 , A736–A741 (2014). Figures Figure 1