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1. Roundtrip Energy Efficiency Optimization of an Energy Storage System Using Products of Iron Combustion

   https://doi.org/10.1115/1.4071808  

   You, Dongchuan; Metghalchi, Hameed; Levendis, Yiannis (January 2026, ASME Open Journal of Engineering)

   Hamidzedeh, Hamid (Ed.)

   Iron has attracted increasing attention as a cyclic energy carrier for large-scale, long-duration, and transportable energy storage. In this study, an integrated iron-based energy storage system is presented and thermodynamically analyzed by coupling an iron reduction cycle with a power generation cycle. The reduction cycle is designed as an energy-recovery process to convert Fe2O3 into iron fuel for power generation, where hydrogen serves as the reducing agent and thermal energy is recovered through a series of energy exchangers. The power generation cycle is configured as a combined cycle consisting of a closed air Brayton topping cycle and a reheat steam Rankine bottoming cycle, where the chemical energy stored in iron is released through combustion for electricity generation. Since hydrogen is used as the reducing agent and iron is combusted with oxygen rather than air, NOx formation in the main reactive processes is avoided. The reduction and combustion processes are modeled using Reaktoro/NASA-CEA thermodynamic data, while the air and steam properties in the power cycle are obtained from REFPROP. A comprehensive parametric study and optimization were performed to evaluate the effects of reactor hydrogen inlet temperature, air cycle pressure, steam cycle pressure, and air turbine inlet temperature on system performance. The results show that the minimum fresh hydrogen requirement is achieved at a reactor hydrogen inlet temperature of 1233 K, corresponding to approximately 4.36 mol H2 per mol Fe2O3. In the power cycle, parametric studies have been made to determine the air cycle high pressure and steam cycle high pressure. The results indicate that when air turbine inlet temperature is either 1500 K or 1600 K, the higher the steam cycle pressure and air cycle pressure, the higher the power cycle efficiency. However, when air turbine inlet temperature is 1400 K, while the power cycle efficiency still increases when steam cycle pressure increases, the air cycle pressure reaches the maximum efficiency at about 1750 kPa. The maximum power cycle efficiency reaches about 61–64% when air turbine inlet temperature ranges from 1400 K to 1600 K. For hydrogen production electricity consumption ranging from 42 kWh/kg-H2 to 55 kWh/kg-H2, the overall roundtrip energy efficiency of the integrated system ranges from about 26% to 34%, with the best performance obtained at the optimized reduction condition, higher turbine inlet temperatures, air cycle pressure, and steam cycle pressure. These results demonstrate the thermodynamic potential of iron-based energy storage systems with hydrogen and combined-cycle power generation. 

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2. (Invited Talk): Designing smart materials for efficient energy conversion: The story of transition metal chalcogenides

   Nath, Manashi; Masud, Jahangir; Swesi, Abdurazag; De Silva, Umanga; Amin, Bahar; Umapathi, Siddesh; Liyanage, Wipula (March 2018, 255th ACS National Meeting & Exposition, New Orleans, LA, United States, March 18-22, 2018 (2018), ENFL-330)

   Energy harvesting from solar and water has created ripples in materials energy research for the last several decades, complemented by the rise of Hydrogen as a clean fuel. Among these, water electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage, with applications ranging from metal-​air batteries, fuel cells, to solar-​to-​fuel energy conversion systems. In fact, solar water splitting is one of the most promising method to produce Hydrogen without depleting fossil-​fuel based natural resources. However, the efficiency and practical feasibility of water electrolysis is limited by the anodic oxygen evolution reaction (OER)​, which is a kinetically sluggish, electron-​intensive uphill reaction. A slow OER process also slows the other half- cell reaction, i.e. the hydrogen evolution reaction (HER) at the cathode. Hence, designing efficient catalysts for OER process from earth-​abundant resources has been one of the primary concerns for advancing solar water splitting. In the Nath group we have focused on transition metal chalcogenides as efficient OER electrocatalysts. We have proposed the idea that these chalcogenides, specifically, selenides and tellurides will show much better OER catalytic activity due to increasing covalency around the catalytically active transition metal site, compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chem. potential around the transition metal center, [e.g. lowering the Ni 2+ -​-​> Ni 3+ oxidn. potential in Ni-​based catalysts where Ni 3+ is the actually catalytically active species]​. Based on such hypothesis, we have synthesized a plethora of transition metal selenides including those based on Ni, Ni-​Fe, Co, and Ni-​Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA​/cm 2 [Ni 3 Se 2 - 200 - 290 mV; Co 7 Se 8 - 260 mV; FeNi 2 Se 4 -​NrGO - 170 mV (NrGO - N-​doped reduced graphene oxide)​; NiFe 2 Se 4 - 210 mV; CoNi 2 Se 4 - 190 mV; Ni 3 Te 2 - 180 mV]​. 

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3. A robust solid oxide electrolyzer for highly efficient electrochemical reforming of methane and steam

   https://doi.org/10.1039/c9ta00467j  

   Liu, Tong; Liu, Hao; Zhang, Xiaoyu; Lei, Libin; Zhang, Yanxiang; Yuan, Zhihao; Chen, Fanglin; Wang, Yao (June 2019, Journal of Materials Chemistry A)

   In this work, a robust solid oxide electrolysis cell with Sr 2 Fe 1.5 Mo 0.5 O 6−δ –Ce 0.8 Sm 0.2 O 1.9 (SFM–SDC) based electrodes has been utilized to verify the conceptual process of partial oxidation of methane (POM) assisted steam electrolysis, which can produce syngas and hydrogen simultaneously. When the cathode is fed with 74%H 2 –26%H 2 O and operated at 850 °C, the open circuit voltage (OCV), the minimum energy barrier required to overcome the oxygen partial gradient, is remarkably reduced from 0.940 to −0.012 V after changing the feed gas in the anode chamber from air to methane, indicating that the electricity consumption of the steam electrolysis process could be significantly reduced and compensated by the use of low grade thermal energy from external heat sources. It is found that after ruthenium (Ru) impregnation, the electrolysis current density of the electrolyzer is effectively enhanced from −0.54 to −1.06 A cm −2 at 0.6 V and 850 °C, while the electrode polarization resistance under OCV conditions and 850 °C is significantly decreased from 0.516 to 0.367 Ω cm 2 . Long-term durability testing demonstrates that no obvious degradation but a slight improvement is observed for the electrolyzer, which is possibly due to the activation of the SFM–SDC electrode during operation. These results indicate that the robust Ru infiltrated solid oxide electrolyzer is a very promising candidate for POM assisted steam electrolysis applications. Our result will provide insight to improve the electrode catalysts used in POM assisted steam electrolysis. 

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4. Ultra-Low Voltage Bipolar Hydrogen Production from Biomass-Derived Aldehydes and Water in Membrane-Less Electrolyzers

   https://doi.org/10.1039/D2EE01427K  

   Liu, Hengzhou; Agrawal, Naveen; Ganguly, Arna; Chen, Yifu; Lee, Jungkuk; Yu, Jiaqi; Huang, Wenyu; Mba-Wright, Mark; Janik, Michael J.; Li, Wenzhen (August 2022, Energy environmental science)

   Water electrolysis using renewable energy inputs is being actively pursued as a green route for hydrogen production. However, it is limited by the high energy consumption due to the sluggish anodic oxygen evolution reaction (OER) and safety issues associated with H2 and O2 mixing. Here, we replaced OER with an electrocatalytic oxidative dehydrogenation (EOD) of aldehydes for bipolar H2 production and achieved industrial-level current densities at cell voltages much lower than during water electrolysis. Experimental and computational studies suggest a reasonable barrier for C-H dissociation on Cu surfaces, mainly through a diol intermediate, with a potential-dependent competition with the solution-phase Cannizzaro reaction. The kinetics of EOD reaction was further enhanced by a porous CuAg catalyst prepared from a galvanic replacement method. Through Ag incorporation and its modification of the Cu surface, the geometric current density and electrocatalyst durability were significantly improved. Finally, we engineered a bipolar H2 production system in membrane-electrode assembly-based flow cells to facilitate mass transport, achieving a maximum current density of 248 and 390 mA cm−2 at cell voltages of 0.4 V and 0.6 V, respectively. The faradaic efficiency of H2 from both cathode and anode reactions both attained ~100%. Taking advantage of the bipolar H2 production without the issues associated with H2/O2 mixing, an inexpensive, easy-to-manufacture dialysis porous membrane was demonstrated to substitute the costly anion exchange membrane, achieving an energy-efficient and cost-effective process in a simple reactor for H2 production. The estimated H2 price of $2.51/kg from an initial technoeconomic assessment is competitive with US DoE’s “Green H2” targets. 

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5. Temperature-induced changes in the synthesis gas composition in a high-temperature H2O and CO2 co-electrolysis system

   https://doi.org/10.1016/j.apcata.2020.117697  

   Deka, D.J.; Kim, J.; Gunduz, S.; Ferree, M.; Co, A.C.; Ozkan, U.S. (January 2020, Applied catalysis)

   Solid oxide electrolysis cell (SOEC) is an attractive renewable technology capable of producing synthesis gas (H2+CO) from H2O and CO2. An SOEC consists of a solid oxide electrolyte and two ceramic or metal-ceramic electrodes. H2O and CO2 are electrolyzed at the cathode producing H2 and CO, releasing O2− ions, which travel through the electrolyte to the anode side and recombine to produce pure oxygen gas as the byproduct. In the present study, a La0.7Sr0.2Ni0.2Fe0.8O3 cathode was used to co-electrolyze H2O and CO2 at three different op- erating temperatures- 700 °C, 750 °C and 800 °C. Synthesis gas was produced at all three operating temperatures with 100 % Faradaic efficiency. The composition of the syngas, however, was found to be a function of the operating temperature. In general, the H2/CO ratio in the syngas decreased with increased temperature. This was partially due to CO2 electrolysis becoming more favorable compared to H2O electrolysis at higher temperatures. 

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