Thermodynamics and Efficiency of a CuCl(aq)/HCl(aq) Electrolyzer

Hall, Derek M.; Akinfiev, N. N.; LaRow, Eric G.; Schatz, Rich S.; Lvov, Serguei N.

doi:10.1016/j.electacta.2014.08.018

Cited by 37 publications

(49 citation statements)

References 35 publications

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“…An in depth analysis of the values and equations needed to describe the equilibrium potentials were published previously. 17 As can be seen from the LSV data collected, the small overpotentials needed to reach the limiting current densities suggested that the Cu II /Cu I reaction was very fast and required a very small overpotential on both Pt and GC. Furthermore, the increase in the limiting current as the rotation rate increased supported the assumption that diffusion of the active species was the source of the limiting current.…”

Section: Resultsmentioning

confidence: 95%

“…In solutions with high concentrations of Cl − (aq), CuCl 3 2− (aq) species had the largest concentration among Cu I complexes by about 3 orders of magnitude. 17 For this kinetic study, the next closest Cu I complex was CuCl 2 − (aq) with a bulk concentration of 10 −6 mol/kg, whereas CuCl 3 2− (aq) had a bulk concentration that was effectively 10 −3 mol/kg. The large difference in Cu I bulk concentrations in combination with the observed high current densities and limiting currents suggested that this species was a likely candidate as an electrochemically active species.…”

Section: Resultsmentioning

confidence: 99%

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Electrochemical Kinetics of CuCl(aq)/HCl(aq) Electrolyzer for Hydrogen Production via a Cu-Cl Thermochemical Cycle

Hall

LaRow

Schatz

et al. 2014

J. Electrochem. Soc.

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An electrochemical kinetics investigation of the CuCl(aq)/HCl(aq) electrolyzer identified methods to significantly reduce the platinum loadings required to achieve a high cell current density of 0.5 A/cm 2 at 0.7 V. As the CuCl(aq)/HCl(aq) electrolyzer is a key component of the Cu-Cl thermochemical cycle, the economic viability of the Cu-Cl thermochemical cycle was significantly improved by reducing the loading required to achieve 0.5 A/cm 2 . Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) with a rotating disc electrode were employed to investigate the kinetics of the aqueous Cu II /Cu I chloride complexes reaction on platinum and glassy carbon using a three-electrode cell. It was found that the standard exchange current density of the anodic Cu II /Cu I electrochemical reaction on platinum, 4-12 A/cm 2 , was significantly larger than the values reported for the HER cathodic reaction thus far. In addition, SEM was used to observe the effectiveness of different catalyst application techniques. Through SEM observations, and electrochemical data analysis, the amount of platinum used in a laboratory scale CuCl(aq)/HCl(aq) electrolyzer was reduced from 0.8 mg/cm 2 applied to both electrodes to 0.4 mg/cm 2 on the cathode and zero at the anode while still maintaining a current density of 0.5 A/cm 2 at 0.7 V of applied potential difference. As interest in an energy storage option capable of storing both thermal and electrical energy produced via solar resources increases, low temperature hybrid thermochemical cycles are becoming an attractive candidate to fill this role. In particular, the Cu-Cl hybrid thermochemical cycle's high efficiency and moderate temperature requirements have established itself as a promising option for inexpensive hydrogen generation through harnessing excess thermal and electrical energy from solar resources.1 In addition to utilizing excess energy, the Cu-Cl thermochemical cycle provides a means of efficiently producing hydrogen gas not reliant on fossil fuels.The Cu-Cl hybrid thermochemical cycle uses a number of intermediate compounds, heat, and a small amount of electrical energy, within a series of physical and chemical reactions to split water into hydrogen and oxygen.2-10 One of the most important components in the hybrid cycle is the CuCl(aq)/HCl(aq) electrolytic cell. 11 In the electrolytic step of this cycle, the general electrochemical reaction consists of an anode reaction in which aqueous Cu I chloride complex species are oxidized to aqueous Cu II chloride complex species, and a cathode reaction in which HCl(aq) is reduced to H 2 (aq) with transfer of H + (aq) through a cation conductive membrane. This process is usually simplified as follows:To increase the solubility of CuCl(s) in the anolyte, a high concentration of HCl(aq) is typically used. Similarly, the catholyte comprises of highly concentrated HCl(aq) to avoid copper deposition at the cathode. 9Previous research established an electrolytic cell design that employed membrane electrode assemb...

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Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

Electrochemical Kinetics of CuCl(aq)/HCl(aq) Electrolyzer for Hydrogen Production via a Cu-Cl Thermochemical Cycle

Hall

LaRow

Schatz

et al. 2014

J. Electrochem. Soc.

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“…13 The nonohmic impedance contribution decreased from 4.8 to 0.27 . While it is difficult to correctly interpret the faradaic impedances as the cell reaction mechanism has not been well-established yet, 11 we have previously shown 8 that R 1 is dependent on the applied potential and related to the charge-transfer kinetics. As the anodic reaction in the cell is significantly faster than the cathode, 7 it is fair to assume that the anode kinetics are faster at 80…”

Section: Resultsmentioning

confidence: 96%

“…11 Two 85 cm 2 graphite blocks having serpentine flow channels were obtained from Electrochem Inc. and used as the end plates. 2 mol CuCl(s) dissolved in 7 mol L −1 HCl (aq), and 7 mol L −1 HCl(aq), were, respectively, fed into the anode and the cathode electrodes with a flow rate of 130 ml min −1 .…”

Section: 33mentioning

confidence: 99%

Effect of Clamping Pressure and Temperature on the Performance of a CuCl(aq)/HCl(aq) Electrolyzer

Khurana

Hall

Schatz

et al. 2015

ECS Electrochemistry Letters

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Changes in the performance of a CuCl(aq)/HCl(aq) electrolytic cell are reported as a function of temperature and the compression pressure applied at the end plates during cell assembly. The pressure applied on the end plates effected the contact resistance, and an optimum compression pressure of 6.3 psi (bolt torque: 20 Nm) showed the best performance. Polarization curves and EIS data were taken at 40, 60, and 80 • C to observe the changes in ohmic and nonohmic impedance contributions. A significant increase in the cell performance was observed as the temperature was increased from 40 to 80 • The Cu-Cl thermochemical cycle is among the most attractive technologies proposed for hydrogen production, 1-4 and significant improvements in the current and voltage efficiencies of the CuCl(aq)/HCl(aq) electrolytic cell -a key component in the cycle -have recently been reported. [5][6][7] In our previous work, 7 kinetic properties of the CuCl electrolyzer were investigated to successfully reduce the catalyst loading by 68% without causing any adverse effect on the cell performance and durability of the cell was reported for 168 h of operation. 8A significance performance limitation for a CuCl(aq)/HCl(aq) electrolytic cell is the ohmic losses associated with the contact resistance. The contact resistance between the flow field channels of the end plate and the carbon cloth electrodes plays a significant part in ensuring good electrical connection. The contact resistance is heavily dependent on the clamping pressure, and despite the link between compression and electrochemical performance, there are no published results related to optimum amount of pressure needed to assemble a CuCl(aq)/HCl(aq) electrolytic cell. While insufficient clamping pressure may result in high electrical resistance at the electrodes/flow-field channel interface, a high clamping pressure could lead to mechanical deformation of the MEA and uneven pressure distribution. An excessive compression pressure also increases the mass transport problems with a reduction in cell performance at high current densities. 9,10 In this study, an optimum value of the compression pressure resulting from torque on the bolts that clamp the cell was observed to be 20 Nm. Also, this study highlights the increase in performance of a CuCl(aq)/HCl(aq) electrolyzer by increasing the temperature from 40 to 80• C. ExperimentalPreparation of MEA.-The experimental setup consisting of Nafion 117 polymer membrane, which was used to fabricate the MEA, and the pretreatment method was same as discussed previously.6 The membrane was pretreated by the following steps to remove the organic and inorganic contaminants before being used in the electrolyzer. First, the membrane was soaked in 3 wt% H 2 O 2 solution at 80• C, followed by soaking in 80• C DI-water to remove traces of H 2 O 2 . Then, the membrane was soaked in 1 mol L −1 H 2 SO 4 (aq). Finally, the membrane was soaked in in DI-water at 80• C to remove any residual H 2 SO 4 (aq). The membrane was placed in each solution for 1 h. ...

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“…Canada Nuclear Laboratories (formerly Atomic Energy of Canada Limited) demonstrated hydrogen production by a CuCl electrolyzer continuously for several days and reported that electrolysis is feasible at low potentials (0.6‐0.7 V) at a current density of 0.1 A cm −2 using inexpensive materials . The Pennsylvania State University has carried out comprehensive experiments and theoretical developments on the cycle . Balashov et al performed an experimental study on a CuCl/HCl electrolyzer and reported a voltage efficiency of 80% and a current efficiency of 98%, which is with a good agreement with Faraday law.…”

Section: Introductionmentioning

confidence: 83%

Kinetic and electrochemical analyses of a CuCI/HCl electrolyzer

2019

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Summary An electrochemical analysis is carried out from a kinetic electrochemistry perspective of a CuCl/HCl electrolysis cell, within the CuCl thermochemical water splitting process for hydrogen production. The anolyte is a solution of 2 mol L−1 CuCl(aq) and 10 mol L−1 HCl(aq) while the catholyte solution is 11 mol L−1 HCl(aq). The cell current density of 0.5 A cm−2 and voltage of 0.7 V are the desired working conditions for a CuCl/HCl electrolyzer. The current density of 0.5 A cm−2 is assumed to occur at a 5% anolyte conversion degree. At 25°C, the activation overpotential of the anode half‐reaction is found to be 53 mV for a current density of 0.5 A cm−2 while the activation overpotential of the cathode half‐reaction for the same condition is 87 mV. An increase in working temperature decreases the overpotential of the anode half‐reaction and increases the cathode half‐reaction activation overpotential. The ohmic overpotential of the cell membrane is almost 1000 times smaller than that of the activation overpotentials of the electrode half‐reactions for the same temperature and current density. A higher working temperature results in a lower membrane ohmic overpotential. The required voltage to trigger electrolysis for a current density of 0.5 A cm−2 is found to be 0.53 V at 25°C and 0.59 V at 80°C and a higher temperature results in a higher electrochemical efficiency. The cell electrochemical efficiency increases linearly with working temperature while the voltage efficiency peaks at 75% at 60°C.

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Thermodynamics and Efficiency of a CuCl(aq)/HCl(aq) Electrolyzer

Cited by 37 publications

References 35 publications

Electrochemical Kinetics of CuCl(aq)/HCl(aq) Electrolyzer for Hydrogen Production via a Cu-Cl Thermochemical Cycle

Electrochemical Kinetics of CuCl(aq)/HCl(aq) Electrolyzer for Hydrogen Production via a Cu-Cl Thermochemical Cycle

Effect of Clamping Pressure and Temperature on the Performance of a CuCl(aq)/HCl(aq) Electrolyzer

Kinetic and electrochemical analyses of a CuCI/HCl electrolyzer

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