Question

The p-GaP semiconductor has a bandgap of 2.3 eV with a conduction band redox potential located at -1.2 V vs SHE. Would this material be suitable for direct photoelectrochemical water splitting? Why or why not?

Short answer

The p-GaP semiconductor has not suitable for direct photoelectrochemical water splitting.

Step-by-step solution

The given data;

The band gap of the p-GaP semiconductor = 2.3 eV.

Redox potential energy of conduction band = -1.2 eV vs. SHE.

The Semiconductors

The semiconductors are metals with a large band gap between the highest occupied molecular orbital in the valance band and the lowest unoccupied molecular orbital in the conduction band.

The mathematical formula of the band gap is shown below;

${\text{ε=ε}}_{\text{CB}}{\text{-ε}}_{\text{VB}}$ --- (a)

Here,

${\text{ε}}_{\text{CB}}$- is the conduction band energy.

${\text{ε}}_{\text{VB}}$- is the valance band energy

Photoelectrochemical splitting is a process involving a chemical reaction of splitting hydrogen and oxygen atom.

The energy of the valance band.

We know the p-GaP semiconductor has a band gap of 2.3 eV, and the energy of the conduction band with redox potential -1.2 eV vs. SHE is 1.2 eV.

Now, the band gap is;

${\text{ε=ε}}_{\text{CB}}{\text{-ε}}_{\text{VB}}$

Rearranging the formula;

${\text{ε}}_{\text{VB}}{\text{=ε}}_{\text{CB}}\text{-ε}$

role="math" localid="1663501856110" $\begin{array}{c}\text{=1.2eV-2.3eV}\\ {\text{ε}}_{\text{VB}}\text{=-1.1eV}\end{array}$

Therefore, the energy of the valance band is -1.1 eV for a potential of 1.1 V.

The p-GaP semiconductor is not suitable for photoelectrochemical water splitting.

The reduction potential for this ${\text{H}}_{\text{2}}|{\text{H}}^{\text{+}}$is0.0 V and${\text{O}}_{\text{2}}|{\text{H}}_{\text{2}}\text{O}$is 1.229 V.

The potential of the conduction band has a greater negative value than 0.0 V to reduce${\text{H}}^{\text{+}}$.

Similarly, the potential of the valance band has a greater positive value than 1.229 V to oxidize${\text{H}}_{\text{2}}\text{O}$.

We know the value of the conduction band is -1.2 eV; the value is sufficient to reduce${\text{H}}^{\text{+}}$to${\text{H}}_{\text{2}}$.

The potential of the valance band is 1.1 V; the value is insufficient to oxidize${\text{H}}_{\text{2}}\text{O}$to${\text{O}}_{\text{2}}$.

Hence, the p-GaP would not be a suitable semiconductor for direct photoelectrochemical water splitting.