Question

Artificial photosynthesis is an emerging technology to produce chemical fuels from abundant renewable resources by using sunlight, based on principles learned from Nature. For example, huge efforts have been made to develop photoelectrochemical system to produce hydrogen gas by electrolysis of water. In principle, it is a very clean and sustainable process because it uses water and sunlight as a raw material and unlimited energy source, respectively, and produces only oxygen gas as a byproduct. Answer to the following questions.

(a) Calculate a cell potential required for electrolysis of water. If necessary, use the information given in the right table

(b) In artificial photosynthesis, energy required to drive water electrolysis is provided from light energy. The energy of a photon or single pulse of light energy (E) can be calculated using the Planck energy relation: E = hv = hc/λ where h is the Planck constant (6.62610 J⋅s), v is the frequency of light, c is the speed of light in vacuum (2.9910 m⋅s), and λ is the wavelength of the light. In reality, however, we have to use light with a wavelength shorter than the theoretically calculated one. Explain the possible causes for this discrepancy.

(c) Find the mathematical expression for the relationship between pH and a half cell potential (vs. Ag/AgCl) for both cathodic and anodic reactions.

Answer 1

a) Artificial photosynthesis is a process that uses sunlight and water to produce hydrogen ,oxygen,carbon.

electrosis of water is the decomposition of water into oxygen,hydrogen gas due to the passage of an electric current.

ideal requires a potential different of 1.23 volts to split water.

2H2o ----->2 H2 +o2

reduction of cathode: 2H+ 2e ------> H2

oxidative at anode : 2H2O -----> O2 + 4H +4e

cathode : 2H2O + H2 + 2 OH

anode : : 2OH -------> 1/2 o2 + H2O + 2e

overall reaction : 2 H2O ----> 2H2 + O2.