**5. Intermediate and low temperature electrochemical reactors with multilayer functional electrode**

In 2006 *K.Hamamoto et.al.* (Hamamoto et.al., 2006, 2007) proposed to use an electrochemical rector with multilayer functional electrode for intermediate temperature operation. The cell performance represented on (5b) was used for intermediate temperature operation.

8YSZ (8 mol % Y2O3-doped ZrO2), 10YSZ (10 mol % Y2O3-doped ZrO2) and ScCeSZ (10 mol % Sc2O3 and 1 mol % CeO2-doped ZrO2) were selected as solid electrolytes. The electrocatalytic electrodes with compositions NiO–8YSZ, NiO–10YSZ and NiO–ScCeSZ (with 55 mol % of NiO) were deposited on the surface of 8YSZ, 10YSZ and ScCeSZ solid electrolyte disks, respectively. Figure 18 shows the values of current efficiency () plotted as a function of applied voltage for such electrochemical reactors operated at 475C. The value of selectivity (sel) of such reactors for NO gas molecules decomposition is also displayed in Fig. 18 (Hamamoto et.al., 2006). From Fig.18 it is seen that in electrochemical reactors with electro-catalytic electrodes the probability for NO gas molecules to be adsorbed and decomposed is at least 5 times higher than for oxygen gas molecules.

Electrochemical Cells with Multilayer Functional Electrodes for NO Decomposition 199

electrochemical reactors effectively decompose NOx even at low temperature range

deNOx (%) deNOx (%) deNOx (%) deNOx (%)

without adsorbent K-Pt-Al2O-Pt-Al2O3 Na-Pt-Al2O3 Cs-Pt-Al2O3

0 2 4 6 8 10

Fig. 19. Dependence of NO decomposition and of the value of current efficiency on the O2 concentrations for the YSZ based electrochemical reactor with and without a NOx adsorbent

> without adsorbent K-Pt-Al2O-Pt-Al2O3 Na-Pt-Al2O3 Cs-Pt-Al2O3

Oxygen concentration (%)

0 2 4 6 8 10

Fig. 20. Dependence of NO/O2 selectivity on the O2 concentrations for the YSZ based

electrochemical reactor with and without a NOx adsorbent at 500°C.

Oxygen concentration (%)

0

5

10

Current efficiency (%)

15

20

(<300C).

at 500°C.

0

0

5

10

NO/O2 selectivity

15

20

25

20

40

NO decomposition (%)

60

80

100

η/η y

Fig. 18. Dependence of current efficiency for NO decomposition and NO/O2 selectivity on operating voltage at 475°C.

In 2008 *K.Hamamoto et.al.* (Hamamoto et al., 2008) proposed to use an electrochemical reactor with additional NOx adsorption layer deposited on the top of the multilayer electrocatalytic electrode. Such type of cell can be represented by following cell arrangement:

NOx adsorbent | (Covering layer |Cathode |Electro-catalytic electrode) **|**YSZ**|** (Anode) (18)

The authors (Hamamoto et al., 2008) tested three systems which are generally used as NOx adsorber catalyst. The Pt/K/Al2O3, Pt/Na/Al2O3 and Pt/Cs/ Al2O3 adsorbents were prepared from a Al2O3 (Merck, p.a., specific surface area = 10 m2 g−1) support suspension in water, to which a solution containing KNO3 (NaNO3, CsNO3) and with aqueous solutions of platinum nitrate (Pt(NO3)2) was added, in order to obtain a load of 10 wt% of K (Na, Cs) and 3 wt% of Pt. The mixture was heated while being vigorously stirred until a paste was achieved, which was dried in an oven for 24 h at 200C and crushed and calcined at 600C for 2 h.

To clarify the capability of a NOx adsorption layer on the multilayer cathode, *K.Hamamoto et.al.* (Hamamoto et al., 2008) carried out the NOx decomposition measurements of the YSZ based cells with and without a NOx adsorbent at a fixed operating voltage, *U*=2.5 V, on the cells under various O2 concentrations at 500°C by passing a mixed gas with 1000 ppm of NO in He through the cell at a gas flow rate of 200 ml/min (Fig. 19). As a result, NOx adsorption layers have improved the NOX decomposition properties though the current values of each cell were almost the same.

From Fig.19 it is seen that the values of current efficiency () for electrochemical reactor with the Pt/K/Al2O3 adsorbent are four - five times higher compared with the reactor without adsorbent. The values of current efficiency in such reactors increase up to 20% and the values of the NO/O2 selectivity up to 25 (Fig.20). Additionally we should mention that such

η/η y η/ηtheory

1.75 2 2.25 2.5

Fig. 18. Dependence of current efficiency for NO decomposition and NO/O2 selectivity on

Voltage ( V )

In 2008 *K.Hamamoto et.al.* (Hamamoto et al., 2008) proposed to use an electrochemical reactor with additional NOx adsorption layer deposited on the top of the multilayer electrocatalytic electrode. Such type of cell can be represented by following cell arrangement:

The authors (Hamamoto et al., 2008) tested three systems which are generally used as NOx adsorber catalyst. The Pt/K/Al2O3, Pt/Na/Al2O3 and Pt/Cs/ Al2O3 adsorbents were prepared from a Al2O3 (Merck, p.a., specific surface area = 10 m2 g−1) support suspension in water, to which a solution containing KNO3 (NaNO3, CsNO3) and with aqueous solutions of platinum nitrate (Pt(NO3)2) was added, in order to obtain a load of 10 wt% of K (Na, Cs) and 3 wt% of Pt. The mixture was heated while being vigorously stirred until a paste was achieved, which was dried in an oven for 24 h at 200C and crushed and calcined

To clarify the capability of a NOx adsorption layer on the multilayer cathode, *K.Hamamoto et.al.* (Hamamoto et al., 2008) carried out the NOx decomposition measurements of the YSZ based cells with and without a NOx adsorbent at a fixed operating voltage, *U*=2.5 V, on the cells under various O2 concentrations at 500°C by passing a mixed gas with 1000 ppm of NO in He through the cell at a gas flow rate of 200 ml/min (Fig. 19). As a result, NOx adsorption layers have improved the NOX decomposition properties though the current

From Fig.19 it is seen that the values of current efficiency () for electrochemical reactor with the Pt/K/Al2O3 adsorbent are four - five times higher compared with the reactor without adsorbent. The values of current efficiency in such reactors increase up to 20% and the values of the NO/O2 selectivity up to 25 (Fig.20). Additionally we should mention that such

NOx adsorbent | (Covering layer |Cathode |Electro-catalytic electrode) **|**YSZ**|** (Anode) (18)

8YSZ 10YSZ ScCeSZ

2

3

NO / O2 Selectivity

4

5

4

6

8

Current efficiency (

operating voltage at 475°C.

at 600C for 2 h.

values of each cell were almost the same.

) ()

10

12

electrochemical reactors effectively decompose NOx even at low temperature range (<300C).

Fig. 19. Dependence of NO decomposition and of the value of current efficiency on the O2 concentrations for the YSZ based electrochemical reactor with and without a NOx adsorbent at 500°C.

Fig. 20. Dependence of NO/O2 selectivity on the O2 concentrations for the YSZ based electrochemical reactor with and without a NOx adsorbent at 500°C.

Electrochemical Cells with Multilayer Functional Electrodes for NO Decomposition 201

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