Pressurized PEM water electrolysis: Efficiency and gas crossover

Schalenbach, Maximilian; Carmo, Marcelo; Fritz, David; Mergel, Jürgen; Stolten, Detlef

doi:10.1016/j.ijhydene.2013.09.013

Cited by 269 publications

(171 citation statements)

References 44 publications

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“…31 In contrast, the gas diffusivities in the solid phase of the Zirfon separator were estimated to be negligible. In addition, the hydrogen and oxygen diffusivity and solubility in aqueous alkaline solutions are lower than those in acidic solutions.…”

Section: Ionic Conductivity-inmentioning

confidence: 99%

“…On the basis of these two different cases, the voltage efficiency including the power consumption of the heat balance (denoted asη U ) is described by:η [16] The overall cell efficiency including the heating of the cell is calculated byη cell =η U η c [17] In the following,η cell normalized to U ref = Gas crossover.-The permeation of cathodic hydrogen to the anode leads to a direct loss of the produced hydrogen and thus reduces the efficiency. Anodic hydrogen is typically not oxidized at the oxidecovered anodic catalyst 31,32 and thus mixes with the oxygen produced…”

Section: Voltagementioning

confidence: 99%

“…In the case of the acidic cells with the Nafion N117 and NR212 membranes, Equation 24 was fitted to the measured anodic hydrogen contents (measurement procedure described in the SI). These fits were conducted with the hydrogen diffusivity in Nafion reported in the literature 31 (stated in Table II) as fixed parameter, while the cathodic partial pressure increase factor ϒ H 2 was used as the only free parameter. Within the measurement precision of approximately 0.2% of the anodic hydrogen content, the modeled data in the form of the fits and the measured data agree.…”

Section: 31mentioning

confidence: 99%

See 2 more Smart Citations

Acidic or Alkaline? Towards a New Perspective on the Efficiency of Water Electrolysis

Schalenbach

Tjarks

Carmo

et al. 2016

J. Electrochem. Soc.

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275

182

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Water electrolysis is a promising technology for enabling the storage of surplus electricity produced by intermittent renewable power sources in the form of hydrogen. At the core of this technology is the electrolyte, and whether this is acidic or alkaline affects the reaction mechanisms, gas purities and is of significant importance for the stability and activity of the electrocatalysts. This article presents a simple but precise physical model to describe the voltage-current characteristic, heat balance, gas crossover and cell efficiency of water electrolyzers. State-of-the-art water electrolysis cells with acidic and alkaline electrolyte are experimentally characterized in order to parameterize the model. A rigorous comparison shows that alkaline water electrolyzers with Ni-based catalysts but thinner separators than those typically used is expected be more efficient than acidic water electrolysis with Ir and Pt based catalysts. This performance difference was attributed mainly to a similar conductivity but approximately 38-fold higher diffusivities of hydrogen and oxygen in the acidic polymer electrolyte membrane (Nafion) than those in the alkaline separator (Zirfon filled with a 30 wt% KOH solution In the endeavor to realize an environmentally-benign power supply infrastructure, water electrolysis for the production of hydrogen may prove a key technology for enabling energy conversion on a large scale.1,2 By applying a voltage to two electrodes immersed in an aqueous electrolyte, water can be electrochemically decomposed, evolving hydrogen at the negative pole, the cathode, and oxygen at the positive pole, the anode. During this process, protons or hydroxide ions must pass through the electrolyte to enable the electrochemical reactions at the electrodes. In order to achieve low extents of charge transport losses in electrolyzers, electrolytes with high conductivities are typically used. Such highly conductive electrolytes provide large quantities of ionic charge carriers (protons or hydroxide ions) and are thus either strong bases or acids. The reaction equations in acidic and alkaline aqueous regimes are displayed in Table I.Besides liquid aqueous electrolytes in combination with porous separators, polymer electrolyte membranes (PEMs) are typically used as electrolytes for water electrolysis and to separate the hydrogen and oxygen produced during operation.3 In PEMs, ionizable functional groups are embedded within a polymer matrix providing either mobile protons or hydroxide ions. 4 In an aqueous phase that is separated from the solid polymeric phase 5,6 the protons or hydroxide ions are dissolved but attracted to the oppositely charged ions of the functional group which are covalently bonded to the polymer matrix. As a result, the dissolved ions are captured inside the aqueous phase of the PEM. Hence, an advantage of solid PEMs is that pure water can supplied to the cell, which means that only the components that are in direct contact with the PEM are exposed to its corrosive alkaline or acidic aqueous ph...

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Section: Ionic Conductivity-inmentioning

confidence: 99%

Section: Voltagementioning

confidence: 99%

Section: 31mentioning

confidence: 99%

See 1 more Smart Citation

Acidic or Alkaline? Towards a New Perspective on the Efficiency of Water Electrolysis

Schalenbach

Tjarks

Carmo

et al. 2016

J. Electrochem. Soc.

Self Cite

275

182

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“…Consequently, for small current densities, the H 2 flux to the anode is in the range of the O 2 production. Since H 2 does not react with O 2 at the anode but accumulates, 50 its presence effectively lowers the O 2 partial pressure at the anode, which leads to a reduction of E rev according to Eq. 4.…”

Section: Journal Of the Electrochemical Society 163 (11) F3179-f3189mentioning

confidence: 99%

Influence of Ionomer Content in IrO₂/TiO₂Electrodes on PEM Water Electrolyzer Performance

Bernt

Gasteiger

2016

J. Electrochem. Soc.

297

267

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In this study, the influence of ionomer content in IrO 2 /TiO 2 anode electrodes for a proton exchange membrane (PEM) electrolyzer is investigated (Nafion 212 membrane; 2.0 mg Ir cm −2 / 0.35 mg Pt cm −2 (anode/cathode)) and the contributions of ohmic losses, kinetic losses, proton transport losses in the electrodes, and mass transport losses to the overall cell voltage are analyzed. Electrolysis tests are performed with an in-house designed high pressure electrolyzer cell at differential pressure up to 30 bar. The best performance is obtained for an ionomer content of 11.6 wt% and a cell voltage of 1.57 V at 1 A cm −2 and less than 2 V at 6 A cm −2 (ambient pressure, 80 • C). Performance losses at lower ionomer contents are the result of a higher proton conduction resistance. For higher ionomer contents, on the other hand, performance losses can be related to a filling of the electrode void volume by ionomer, leading to a higher O 2 mass transport resistance, an increased electronic contact resistance, and the electronic insulation of parts of the catalyst by ionomer. At high pressure operation, the performance corrected by the shift of the Nernst voltage increases with H 2 pressure and we propose a new explanation for this effect. In the course of the transition from fossil-based to renewable energy sources, hydrogen technology has gained considerable attention during the past decades. Proton exchange membrane (PEM) electrolyzers are well suited to be coupled with intermittent energy sources such as wind and solar and could provide electrolytic hydrogen for long-term energy storage or fuel cell mobility. At the moment, the large-scale application of PEM electrolyzers is still hindered by their high capital costs.1,2 One attempt to overcome this challenge is to increase the H 2 output by operating an electrolyzer at current densities much higher than the values typically reported in the literature (1-2 A cm −2 ). 2 Recent publications have shown that current densities of 5 A cm −2 and higher are possible. 3,4 Another factor that can be economically beneficial is the operation at high pressure because it allows direct storage of H 2 without subsequent mechanical compression. However, high-pressure operation leads to more demanding materials requirements, imposes additional safety precautions, and reduces the faradaic efficiency due to a higher gas permeation through the membrane. 5,6 It was reported that an operating pressure of 30-45 bar could be a good compromise, 7 with differential pressure operation ( p O 2 ≈ ambient pressure) being more efficient than balanced pressure operation ( p O 2 ≈ p H 2 ).8 However, increasing the current density and the operating pressure of an electrolyzer will increase the cell voltage, leading to a lower overall voltage efficiency and thus higher operating costs. Since the latter are, along with the capital costs, one of the main cost drivers for large-scale applications, 9 minimizing cell voltage at high current densities and pressures is essential for economic competitiveness...

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“…Replacing anodic oxygen evolution with the oxidation of much more readily oxidizable species leads to a significant reduction of the potential required to produce hydrogen. Following this strategy, compounds such as ammonia 7,8 , methanol 9 , ethanol [10][11][12][13] , glycerol 14,15 and urea 16 have been recently tested. These electrolytic processes that lead to the concomitant generation of chemicals at the anode and hydrogen at the cathode are often indicated as 'electrochemical reforming'.…”

mentioning

confidence: 99%

Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis

et al. 2014

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The energetic convenience of electrolytic water splitting is limited by thermodynamics. Consequently, significant levels of hydrogen production can only be obtained with an electrical energy consumption exceeding 45 kWh kg À 1 H 2 . Electrochemical reforming allows the overcoming of such thermodynamic limitations by replacing oxygen evolution with the oxidation of biomass-derived alcohols. Here we show that the use of an original anode material consisting of palladium nanoparticles deposited on to a three-dimensional architecture of titania nanotubes allows electrical energy savings up to 26.5 kWh kg À 1 H 2 as compared with proton electrolyte membrane water electrolysis. A net energy analysis shows that for bio-ethanol with energy return of the invested energy larger than 5.1 (for example, cellulose), the electrochemical reforming energy balance is advantageous over proton electrolyte membrane water electrolysis.

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Pressurized PEM water electrolysis: Efficiency and gas crossover

Cited by 269 publications

References 44 publications

Acidic or Alkaline? Towards a New Perspective on the Efficiency of Water Electrolysis

Acidic or Alkaline? Towards a New Perspective on the Efficiency of Water Electrolysis

Influence of Ionomer Content in IrO₂/TiO₂Electrodes on PEM Water Electrolyzer Performance

Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis

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Pressurized PEM water electrolysis: Efficiency and gas crossover

Cited by 269 publications

References 44 publications

Acidic or Alkaline? Towards a New Perspective on the Efficiency of Water Electrolysis

Acidic or Alkaline? Towards a New Perspective on the Efficiency of Water Electrolysis

Influence of Ionomer Content in IrO2/TiO2Electrodes on PEM Water Electrolyzer Performance

Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis

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Product

Resources

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Influence of Ionomer Content in IrO₂/TiO₂Electrodes on PEM Water Electrolyzer Performance