hydrogen production from water using solar cells powered nafion ...

Ioroi et al. examined the effects of several additives, such as Nafion, PTFE, iridium,
on the oxygen electrode of a regenerative fuel cell. They found out that as the PTFE content
increased from 0 wt. % to 12 wt. %, the electrolysis cell voltage increased from 1900mV to
1950mV at 500mA/cm 2 current density. As it is expected hydrophobic effect of PTFE
increases the cell voltage and also causes to decrease the voltage efficiency of the cell.
However, Nafion as an additive to the anode electrode was found to have a favorable effect
and in fact, 14 wt. % Nafion additive decreased the cell voltage up to 200mV at
500mA/cm 2 which equaled to an 8% increase in voltage efficiency. In addition, they
reported that iridium content had the most significant effect for the electrolysis voltage. For
example, even 1 wt% iridium additive was able to decrease the cell potential of 100mV and
also 50 wt. % Ir loading decreased the cell potential up to 500mV at 500mA/cm 2 . (Ioroi et
al. 2002)
Grigoriev and coworkers showed that the activity of the electrode with 50% RuO2
was better than that with pure IrO2. They investigated four anode electrocatalysts which are
summarized in Table 2.1.
Table 2.1. Electrode types versus Cell Potential
(Source: Grigoriev et al. 2006)
Catalysts Anode Cathode Potential at 1A/cm 2
1 2.4 mg/cm 2 Ir (100 wt %) Pt30/C 2.0 mg/cm 2
2
2.0 mg/cm 2 RuO2-IrO2-
SnO2 (30-32-38 wt %)
Pt30/C 2.0 mg/cm 2
3 2.4 mg/cm 2 Ir (100 wt %) Pd40/C 2.4 mg/cm 2
4
2.0 mg/cm 2 RuO2-IrO2
(50:50 wt %)
Pt30/C 2.0 mg/cm 2
(Pt30/C: 30 wt% pf Pt on carbon carrier electrolysis temp:90 o C)
1750 mV
1700mV
1660mV
1650mV
It is seen that RuO2-IrO2 loaded anode electrode shows the smallest cell potential
with respect to others. Grigoriev and coworkers reported that electrolyzers were operated
up to 10000 hour but they did not mention about the degradation of anode loadings (thus
voltage increments) with respect to time which is another important parameter.
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