A thermodynamic analysis of the SO2/H2SO4 system in SO2-depolarized electrolysis

Gorensek, Maximilian B.; Staser, John A.; Stanford, Thomas G.; Weidner, John W.

doi:10.1016/j.ijhydene.2009.06.020

Cited by 85 publications

(76 citation statements)

References 26 publications

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“…In addition, accurate concentrations enables us to predict the equilibrium potential (U eq ) at different temperatures, pressures, currents, and reactant flow rates as described previously. 25 Using the predicted values for U eq from OLI and i R A from the data in Fig. 3 (i.e., R A = 0.050 Ohm · cm 2 ), the anodic overpotential was obtained from the measured cell voltage and Eqn.…”

Section: Resultsmentioning

confidence: 99%

“…6, and 7, and the equilibrium potentials were predicted using the OLI software in conjunction with thermodynamics examined in previous works. 25 At 0.5 A/cm 2 , the cell voltage is approximately 660 mV, which consists of 290 mV from the equilibrium potential, 345 mV of anodic overpotential, and 25 mV iR A drop due to membrane resistance. The largest contribution toward the total cell voltage at desired current densities is due to the anodic overpotential.…”

Section: Resultsmentioning

confidence: 99%

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Characterizing Voltage Losses in an SO₂Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

Garrick

Wilkins

Pingitore

et al. 2017

J. Electrochem. Soc.

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The hybrid sulfur cycle has been investigated as a means to produce CO 2 -free hydrogen efficiently on a large scale through the decomposition of H 2 SO 4 to SO 2 , O 2 , and H 2 O, and then electrochemically oxidizing SO 2 back to H 2 SO 4 with the cogeneration of H 2 . The net effect is the production of hydrogen and oxygen from water. Recently, sulfonated polybenzimidazoles (s-PBI) have been investigated as a replacement for Nafion due to the ability to offer increased process efficiency through the generation of higher acid concentrations at lower potentials. Here, we measure the acid concentrations and individual potential contributions toward the overall operating voltage seen in the SO 2 -depolarized-electrolyzer. We then determine model parameters necessary to predict voltage losses in a cell over a wide range of operating temperatures, pressures, currents and reactant flow rates. The hydrogen production program at the U. S. Department of Energy is examining an array of distributed and centralized hydrogen facilities that could contribute to the hydrogen generation infrastructure.1 Thermochemical cycles are being considered for large scale, centralized facilities due to their potential for high efficiencies at low costs. These cycles involve a series of chemical reactions that result in the splitting of water at much lower temperatures (∼500-1000• C) than direct thermal dissociation (>2500 • C) and at much higher efficiencies than direct water electrolysis.2 Chemical species in these reactions are recycled resulting in the consumption of only energy and water to produce hydrogen and oxygen. Although there are hundreds of possible thermochemical cycles, the hybrid-sulfur (HyS) process is the only all-fluid, two step thermochemical cycle. 3-6The high temperature step (850-950• C) involves the decomposition of H 2 SO 4 to produce oxygen and sulfur dioxide via the following reaction:The SO 2 is separated, cooled, and sent to the SO 2 -depolarized electrolyzer (SDE). The resulting reactions at the anode and cathode, respectively, are:Thus, the overall reaction in the electrolyzer is represented as:Considerable progress was made in the last decade in lowering the operating voltage and increasing the current density of the SDE by moving from a microporous rubber diaphragm separator used by Westinghouse 7 to a perfluorinated sulfonic acid membrane (e.g., DuPont's Nafion). [8][9][10][11][12] For example, Westinghouse was only able to get the cell voltage down to 1.0 V at 400 mA/cm 2 , where we achieved 500 mA/cm 2 at 0.71 V and 1.2 A/cm 2 at 1.0 V using Nafion 212 (N212). However, to achieve overall process efficiency, concentrated sulfuric acid as well as low cell voltage at high current densities are * Electrochemical Society Member.* * Electrochemical Society Student Member. * * * Electrochemical Society Fellow.z E-mail: taylor.garrick@gm.com; weidner@cec.sc.edu necessary. The key issue when using membranes like Nafion that rely on water for their proton conductivity is that high acid concentrations dehydrate ...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Characterizing Voltage Losses in an SO₂Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

Garrick

Wilkins

Pingitore

et al. 2017

J. Electrochem. Soc.

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“…7,9,18 Lower acid concentrations would allow more efficient electrolyzer operation in the hybrid sulfur cycle due to lower reversible potential, 19 so concentrations as low as 30 wt% (expressed as 0.068 mole fraction SO 3 , where 1 mole H 2 SO 4 is equivalent to 1 mole H 2 O + 1 mole SO 3 ) were considered. A value of 90 wt% (0.384 mole fraction SO 3 ) was used for the upper limit.…”

Section: Operating Variable Domainmentioning

confidence: 99%

Energy Efficiency Limits for a Recuperative Bayonet Sulfuric Acid Decomposition Reactor for Sulfur Cycle Thermochemical Hydrogen Production

Gorensek

Edwards

2009

Ind. Eng. Chem. Res.

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A recuperative bayonet reactor design for the high-temperature sulfuric acid decomposition step in sulfur-based thermochemical hydrogen cycles was evaluated using pinch analysis in conjunction with statistical methods. The objective was to establish the minimum energy requirement. Taking hydrogen production via alkaline electrolysis with nuclear power as the benchmark, the acid decomposition step can consume no more than 450 kJ/mol SO 2 for sulfur cycles to be competitive. The lowest value of the minimum heating target, 320.9 kJ/mol SO 2 , was found at the highest pressure (90 bar) and peak process temperature (900°C) considered, and at a feed concentration of 42.5 mol% H 2 SO 4 . This should be low enough for a practical watersplitting process, even including the additional energy required to concentrate the acid feed.Lower temperatures consistently gave higher minimum heating targets. The lowest peak process temperature that could meet the 450-kJ/mol SO 2 benchmark was 750°C. If the decomposition reactor were to be heated indirectly by an advanced gas-cooled reactor heat source (50°C temperature difference between primary and secondary coolants, 25°C minimum temperature difference between the secondary coolant and the process), then sulfur cycles using this concept could be competitive with alkaline electrolysis provided the primary heat source temperature is at least 825°C. The bayonet design will not be practical if the (primary heat source) reactor outlet temperature is below 825°C.

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“…In this process sulfuric acid is thermally decomposed at high temperature (> 800 °C) producing SO 2 [3], while low temperature water electrolysis has a reversible half cell potential of -1.23 V (SHE). Thus the HyS process requires much less electrical energy input than water electrolysis.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of proton-conducting membranes for use in a sulfur dioxide depolarized electrolyzer

Elvington

Colón-Mercado

McCatty

et al. 2010

Journal of Power Sources

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The chemical stability, sulfur dioxide transport, ionic conductivity, and electrolyzer performance have been measured for several commercially available and experimental proton exchange membranes (PEMs) for use in a sulfur dioxide depolarized electrolyzer (SDE). The SDE's function is to produce hydrogen by using the Hybrid Sulfur (HyS) Process, a sulfur based electrochemical/thermochemical hybrid cycle. Membrane stability was evaluated using a screening process where each candidate PEM was heated at 80 °C in 60 wt. % H 2 SO 4 for 24 hours. Following acid exposure, chemical stability for each membrane was evaluated by FTIR using the ATR sampling technique. Membrane SO 2 transport was evaluated using a two-chamber permeation cell. SO 2 was introduced into one chamber whereupon SO 2 transported across the membrane into the other chamber and oxidized to H 2 SO 4 at an anode positioned immediately adjacent to the membrane. The resulting current was used to determine the SO 2 flux and SO 2 transport.Additionally, membrane electrode assemblies (MEAs) were prepared from candidate membranes to evaluate ionic conductivity and selectivity (ionic conductivity vs. SO 2 transport) which can serve as a tool for selecting membranes. MEAs were also performance tested in a HyS electrolyzer measuring current density versus a constant cell voltage (1V, 80 °C in SO 2 saturated 30 wt% H 2 SO 4 ). Finally, candidate membranes were evaluated considering all measured parameters including SO 2 flux, SO 2 transport, ionic conductivity, HyS electrolyzer performance, and membrane stability. Candidate membranes included both PFSA and non-PFSA polymers and polymer blends of which the non-PFSA polymers, BPVE-6F and PBI, showed the best selectivity.

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A thermodynamic analysis of the SO2/H2SO4 system in SO2-depolarized electrolysis

Cited by 85 publications

References 26 publications

Characterizing Voltage Losses in an SO₂Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

Characterizing Voltage Losses in an SO₂Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

Energy Efficiency Limits for a Recuperative Bayonet Sulfuric Acid Decomposition Reactor for Sulfur Cycle Thermochemical Hydrogen Production

Evaluation of proton-conducting membranes for use in a sulfur dioxide depolarized electrolyzer

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A thermodynamic analysis of the SO2/H2SO4 system in SO2-depolarized electrolysis

Cited by 85 publications

References 26 publications

Characterizing Voltage Losses in an SO2Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

Characterizing Voltage Losses in an SO2Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

Energy Efficiency Limits for a Recuperative Bayonet Sulfuric Acid Decomposition Reactor for Sulfur Cycle Thermochemical Hydrogen Production

Evaluation of proton-conducting membranes for use in a sulfur dioxide depolarized electrolyzer

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Characterizing Voltage Losses in an SO₂Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

Characterizing Voltage Losses in an SO₂Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes