Fuel cells are electrochemical devices that convert the chemical energy of a fuel, such as hydrogen, into electrical energy through an oxidation-reduction (redox) reaction.
Catalysts are used to facilitate the redox reactions occurring at the electrodes of the fuel cell. Platinum and palladium are commonly used as catalysts in fuel cells due to their high catalytic activity, stability, and resistance to corrosion.
Therefore, the correct answer is (B) Platinum - Palladium.
Platinum (Pt) and Palladium (Pd) are used as catalysts in fuel cells because of their high efficiency in facilitating the redox reactions. Platinum, especially, acts as a catalyst for both the hydrogen oxidation at the anode and the oxygen reduction at the cathode.
These metals provide an active surface for the electrochemical reaction, improving the performance and efficiency of the fuel cell.
Correct Answer: Platinum - Palladium
Standard electrode potential for \( \text{Sn}^{4+}/\text{Sn}^{2+} \) couple is +0.15 V and that for the \( \text{Cr}^{3+}/\text{Cr} \) couple is -0.74 V. The two couples in their standard states are connected to make a cell. The cell potential will be:
To calculate the cell potential (\( E^\circ_{\text{cell}} \)), we use the standard electrode potentials of the given redox couples.
Given data:
\( E^\circ_{\text{Sn}^{4+}/\text{Sn}^{2+}} = +0.15V \)
\( E^\circ_{\text{Cr}^{3+}/\text{Cr}} = -0.74V \)
The circuit shown in the figure contains two ideal diodes \( D_1 \) and \( D_2 \). If a cell of emf 3V and negligible internal resistance is connected as shown, then the current through \( 70 \, \Omega \) resistance (in amperes) is: 