(1) In artificial photosynthesis, energy required to drive water electrolysis is
ID: 1005347 • Letter: #
Question
(1) In artificial photosynthesis, energy required to drive water electrolysis is provided
from light energy in the presence of photocatalyst. What is the longest wavelength of
light for successful water-splitting. Is it possible to do water-splitting with infrared light?
If necessary, use the following values: Planck constant (h) = 6.626x10-34 J•s; speed of
light (c) = 2.99x108 m s-1; elementary charge (e) = 1.6x10-19 C.
(2) In reality, however, we have to use light with shorter wavelength than we calculated
in (1). Explain why we have to use shorter-wavelength light.
Explanation / Answer
2 H2O<---> 2H2+O2
Minimum voltage required for water spitting photolytically =1.23 V at 0 pH
Minimmum energy or band gap for the same=1.23 eV=1.23*1.60218*10^-19Joules
E=hv=h*c/y=6.626x10-34 J•s *2.99*10^8 m/s/y=1.23*1.60218*10^-19Joules
Y=6.626x10-34 J•s *2.99*10^8 m/s / 1.23*1.60218*10^-19Joules=10.0532 * 10^-7 m=1005.32nm
As for infrared the wvelength>700-1mm nm ,it is possible to spit water into H2 AND O2
In reality a shorter wavelength is recommended as at high wavelength low efficiency of photocatalytic splitting of water is reported.380 nm or less is a good parameter for the purpose at higher voltages around 3.0 Volt a.At high wavelength ,the reaction is very slow due to reduced catalytic effect.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.