Acknowledgements

semiconductor itself [85]. Recently, the hybrid system which consists of a semiconductor light harvester and a complex of metal co-catalyst has received a huge attention. In this system, the water is considered the main source of electron donors and protons for the reduction of CO2 at the surface of cathode. An example of hybrid system has been discussed by Zhao et al. [86]. They studied the full cell of photocathode with InP/Ru-complexes that was coupled with a TiO2/Pt based photoanode, as shown in Figure 12. In this full cell, in order to avoid the formate re-oxidation at the surface of photoanode, the proton exchange membrane was used as a separator. However, Arai et al. constructed a wireless full cell for photoelectrochemical CO2 reduction in which the system consists of the InP/Ru-complex as a hybrid photocathode and a photoanode of SrTiO3 (Figure 13). In this system, the redox reactions of CO2 and H2O will occur via sunlight irradiation without applying any bias. The obtained results showed that the conversion efficiency from solar to chemical energy in these two full cells was 0.03% and 0.14% for TiO2–InP/[RuCP] and SrTiO3–InP/[RuCP], respectively. Barton et al. [61] successfully reduced CO2 to methanol by using catalyzed p-GaP-based photoelectrochemical (PEC) cell in a process called chemical carbon mitigation. Chemical carbon mitigation term describes the photoinduced CO2 conversion to methanol without the use of additional CO2 generating power source. The obtained results showed that the methanol selectivity and CO2 conversion

Figure 13. The one-compartment photoelectrochemical cell for CO2 reduction [87].

54 Carbon Dioxide Chemistry, Capture and Oil Recovery

Carbon dioxide conversion is presenting both an opportunity and a challenge worldwide for the sustainability of environment and energy. The main strategies of CO2 reduction should focus on the utilization of CO2, the CO2 recycling combined with the renewable energy to save carbon sources, and the useful chemicals production from CO2. Therefore, the conversion of CO2 into energy product such as methanol will consume large amount of captured CO2 in which the market scale of methanol is potentially extensive. Furthermore, the generated

were found to be 100 and 95%, respectively.

3. Future prospective and conclusions

The authors would like to acknowledge the support of Center for Advanced Materials, Qatar University (QU) for this work. Ms. Sajeda Alsaydeh also acknowledges QU for Graduate Assistantship awarded to her.
