Voltage–concentration relations with enhanced slopes in electrochemical cells based on Nafion®

Jak, M.J.G.; Raz, S.; Rij, L.N van; Schoonman, J.; Riess, I.

doi:10.1016/s0167-2738(01)00841-4

Cited by 18 publications

(10 citation statements)

References 20 publications

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“…By inserting various protonic species for x in eq , and using the equilibrium between water and oxygen (eq ) expressions for the emf in each case can be obtained. For H + , OH – , H 3 O + , and generally hydrated protons H 2 m +1 O m + these are , …”

Section: Transport Number Measurementsmentioning

confidence: 99%

“…Polymers are able to swell and keep the water inside, while porous nanocrystalline oxides on the contrary need high RH and small pore sizes, allowing pore condensation, to keep the water in the material. By transport number measurements, the average number of water molecules the proton is carrying in the vehicle ( n in eq ) is determined to be 2.65 H 2 O in Nafion at full hydration. ,, We may therefore expect that the drag coefficient also increases to values larger than unity for porous oxides at high relative humidity and thick water layers.…”

Section: Low Temperature Proton Conduction Mechanism Of Porous Oxidesmentioning

confidence: 99%

“…A more direct way to distinguish the protonic transport mechanism is through transport number determination by measuring the electro-motive force (emf) under a water vapor gradient. 36 There are no reports on transport number measurements for porous oxides, but the technique has been used as direct evidence of vehicle-type transport of protons in polymeric membranes, 37,38 which is generally accepted as the predominant protonic transport mechanism in these materials at high RH. The present contribution is part of a dedicated effort to investigate the protonic charge carrier mechanism in porous nanocrystalline oxides as a function of temperature and relative humidity.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms of Protonic Surface Transport in Porous Oxides: Example of YSZ

2017

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The electrical properties and the charge carrier mechanism of porous 8 mol% yttria-stabilized zirconia (8YSZ) ceramic samples have been investigated over wide ranges of relative humidity (RH) and temperature (25-400 ºC). The presence of humidity introduces protonic surface conduction, and porous YSZ shows pure protonic conduction below ~150 ºC. H/D isotope effect studies combined with transport number measurements reveal a change in transport mechanism from structural diffusion (Grotthuss type) to vehicular transport when the relative humidity exceeds ~60% RH, coinciding with a change in the adsorbed water layer from an "ice-like" to a "water-like" structure. Similarly, the activation energy for proton transport decreases from 0.43 eV to 0.28 eV when the relative humidity increases from 20% RH to 84% RH, reflecting changes in the enthalpies of formation and migration of charged species with increasing water layer thickness.

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Section: Transport Number Measurementsmentioning

confidence: 99%

Section: Low Temperature Proton Conduction Mechanism Of Porous Oxidesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mechanisms of Protonic Surface Transport in Porous Oxides: Example of YSZ

2017

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“…Similar observations have been reported on Nafion and were attributed to mixed potentials. [18,19] To provide further confirmation for the electrochemical reaction, i.e., water dissociation and association, we shortcircuited the cell (water, Pt|electrolyte|Pt, P H 2 O = 6.6 x 10 -3 bar) and measured the current using an electrometer.…”

mentioning

confidence: 99%

Unprecedented Room‐Temperature Electrical Power Generation Using Nanoscale Fluorite‐Structured Oxide Electrolytes

et al. 2008

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The conversion of chemical energy to electrical energy through the use of fuel cells is an important step in the transition to a hydrogen-based economy. [1,2] Of the many types of fuel cells, solid oxide fuel cells (SOFCs), employing either oxygen ions or protons as charge carriers, provide an efficient, environmentally benign, and fuel-flexible power generation system that can be adapted for small power units (including mobile applications) and for large scale power plants. [3,4] However, SOFCs require high temperatures (800-1000°C), a condition that presents material degradation problems, [5,6] as well as other technological complications and economic obstacles. [7] Numerous attempts have been made to find alternative systems that can be operated at lower temperatures. [8,9] We report here unprecedented observations of power generation at temperatures as low as room temperature using dense bulk nanostructured yttria-stabilized zirconia (YSZ) and samaria-doped ceria (SDC) as electrolytes. This behavior is observed only when the material is nanostructured (grain size ∼ 15 nm). Open circuit electromotive force (emf) (up to 180 mV for YSZ and 400 mV for SDC) and closed circuit currents (∼ 6 nA for YSZ and 30 nA for SDC) were measured from water concentration cells, indicating proton conduction within the nanostructured oxides. These results show that with optimization, viable power generation using water concentration cells at room temperature is a possible goal. Low-temperature protonic conduction has been reported before for polymeric electrolytes and for structurally hydrated (i.e., hydrous) oxides. However, these materials have limitations that have largely restricted their further considerations for practical utilization. Polymeric electrolytes (e.g., Nafion) have limitations with respect to thermal stability, so that they are mostly limited to temperatures below 100°C. [10,11] In addition, polymeric systems require a catalyst whose optimal operation temperature is inconsistent with the thermal stability of the polymer. Another factor for these systems is the cost. In the case of hydrous oxides (e.g., SnO 2 · nH 2 O, ZrO 2 · nH 2 O, WO 3 · nH 2 O [11][12][13][14] ), the loss of structural water (at low temperatures, < 100°C) changes the protonic conductivity irreversibly, [12] with a concomitant degradation of mechanical properties. We were successful in making dense, bulk nanostructured YSZ (8 mol % yttria) and SDC (20 mol % samaria) with a grain size of ∼ 15 nm through the use of field-activated sintering of nanopowders.[15] We found ionic conductivity at low temperatures in structurally unhydrated YSZ only when the grain size of the material is in the nanoscale. [16] In the present work, we use these materials as electrolytes and demonstrate electrical power generation at room temperature using water concentration cells. We constructed concentration cells, using the nanostructured YSZ and SDC as electrolytes, as shown schematically in Figure 1. We measured the emf of both the YSZ and the SDC cells at room t...

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“…In processes on Nafion, an electrochemical reaction is preferred to a chemical one. 8 In the non-faradaic electrochemical modification of catalytic activity -"NEMCA" effect, the chemical reaction is preferred to the electrochemical one. 9,10 In another example, both an electrochemical and chemical reaction take place resulting in different products (CO and CO 2 ) of the same reactants (oxygen and CH 4 ).…”

Section: Generalmentioning

confidence: 99%

Catalytic Requirements for Mixed Reactant Fuel Cells

Riess

2008

Funct. Mater. Lett.

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Significant advantage could be achieved if mixed reactant fuel cells, MR-FC, were functioning. These cells are intended to operate on a mixture of air and fuel introduced into both the cathode and anode compartment. Symmetry is broken by using different electrode materials exhibiting special and different catalytic properties. No high temperature fuel cell was reported to date to function as a true MR-FC and only one, low temperature type, did function properly. We discuss the required catalytic properties which are unique in that they promote electrochemical reactions and suppress chemical ones as well as possible ways to search for them. The chemical reaction which has to be suppressed is the direct reaction of fuel and oxygen as the two components are premixed and the mixture is then introduced into the fuel cell at both electrode compartments. The electrochemical reactions that should be promoted are the reduction of oxygen at the cathode and the oxidation of fuel at the anode only by oxygen ions that emerge from the solid electrolyte. Conditions to promote this selectivity are discussed. These are derived from the theory of chemisorption as applied to heterogeneous catalysis.

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Voltage–concentration relations with enhanced slopes in electrochemical cells based on Nafion®

Cited by 18 publications

References 20 publications

Mechanisms of Protonic Surface Transport in Porous Oxides: Example of YSZ

Mechanisms of Protonic Surface Transport in Porous Oxides: Example of YSZ

Unprecedented Room‐Temperature Electrical Power Generation Using Nanoscale Fluorite‐Structured Oxide Electrolytes

Catalytic Requirements for Mixed Reactant Fuel Cells

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