Anode/solid electrolyte

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

SOFC. Thus, it is desirable to have a thermal expansion compatible ceramic phase in intimate contact with both the solid electrolyte and the metallic electrode at the anode/solid electrolyte interface of an SOFC for wetting purposes. 

Fig. 34 SEM SE image of the anode/solid electrolyte interfacial region. (A) Substrate (ytterbia and yttria stabilized zirconia) (B) Pt metailic electrode (C) PEVD product (yttria stabilized zirconia).

Finally, the rate performance of the all-solid-state lithium-ion batteries before and after interfacial modification was examined. Figure 12.13 shows the discharge profiles of the all-solid-state lithium-ion battery with the modified interface. Anode, solid electrolyte and cathode were graphite, Li7P3Sn and LiNbOs-coated UC0O2, respectively. Applied... 

XPS and Fourier transform infrared spectroscopy (FTIR) measurements of the electrodes indicated the presence of poly(meth-ylene ethylene carbonate) on the anode siuface. The modification of the anode solid electrolyte interphase correlates with significant improvements in the cycling performance at 60°C (53). 

Sodium-Sulfur Batteries. The sodium-sulfur battery consists of molten sodium at the anode, molten sulfur at the cathode, and a solid electrolyte of a material that allows for the passage of sodium only. For the solid electrolyte to be sufficiently conductive and to keep the sodium and sulfur in a liquid state, sodium-sulfur cells must operate at 300°C to 350°C (570°F to 660°F). There has been great interest in this technology because sodium and sulfur are widely available and inexpensive, and each cell can deliver up to 2.3 volts. 

Electrocatalysis Again by definition, an electrocatalyst is a solid, in fact an electrode, which can accelerate a process involving a net charge transfer, such as e.g. the anodic oxidation of H2 or the cathodic reduction of 02 in solid electrolyte cells utilizing YSZ ... 

In recent years it was shown that solid electrolyte fuel cells with appropriate electrocatalytic anodes can be used for chemical cogeneration i.e. for the simultaneous production of electrical power and useful chemicals. 

Strictly speaking I0 is a measure of the electrocatalytic activity of the tpb for a given electrocatalytic reaction. It expresses the rates of the forward (anodic) and reverse (cathodic) electrocatalytic reaction under consideration, e.g. reaction (4.1), when there is no net current crossing the metal-solid electrolyte or, equivalently, the tpb. In this case the rates of the forward and the reverse reactions are obviously equal. It has been recently shown that, in most cases, as one would intuitively expect, I0 is proportional to the length, tpb, of the tpb.8... 

The obvious question then arises as to whether the effective double layer exists before current or potential application. Both XPS and STM have shown that this is indeed the case due to thermal diffusion during electrode deposition at elevated temperatures. It is important to remember that most solid electrolytes, including YSZ and (3"-Al2C)3, are non-stoichiometric compounds. The non-stoichiometry, 8, is usually small (< 10 4)85 and temperature dependent, but nevertheless sufficiently large to provide enough ions to form an effective double-layer on both electrodes without any significant change in the solid electrolyte non-stoichiometry. This open-circuit effective double layer must, however, be relatively sparse in most circumstances. The effective double layer on the catalyst-electrode becomes dense only upon anodic potential application in the case of anionic conductors and cathodic potential application in the case of cationic conductors. 

A fuel cell is a layered structure consisting of an anode, a cathode, and a solid electrolyte (Fig. 8.31). Hydrogen reacts on the anode, typically Pt or Pt/Ru nano-particles deposited on a conducting graphite support, where it is oxidized into protons and electrons ... 

An overview about more than 10 years of R D activities on solid electrolyte interphase (SEI) film forming electrolyte additives and solvents at Graz University of Technology is presented. The different requirements on the electrolyte and on the SEI formation process in the presence of various anode materials (metallic lithium, graphitic carbons, and lithium storage metals/alloys are particularly highlighted. 

Kim SD, Lee JJ, Moon H, Hyun SH, Moon J, Kim J et al. Effects of anode and electrolyte microstructures on performance of solid oxide fuel cells. J. Power Sources 2007 169 265-270. 

Fig. 11.7 Schematic diagram of an all-solid state lithium-air battery using lithium anode, an inorganic solid electrolyte, and an air electrode composed of carbon nanotubes and solid electrolyte particles. Reprinted with permission from Hirokazu Kitaura etai, Energy Environ. Sci., 2012, 5,...

Mixed conducting (i.e., electronic and ionic) materials for anodes may be advantageous if H2 oxidation can occur over the entire surface of the electrode to enhance current production, instead of only in the region of the three-phase interface (gas/solid electrolyte/electrode). Similarly, mixed conductors also may be advantageous for cathodes. 

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