Recombination (surface) D C B Recombination (bulk)

Table 1 Reduction potential values for carbon dioxide (the value for hydrogen production from water is included for comparative purpose and its relevance in CO2 reduction) Reaction E0redox in eV CO2 + e → CO2- >-1.9 CO2 + 2H+ + 2e → HCOOH CO2 + 2H2O +2e → HCOOH_ + OH- -0.61 -1.491 CO2 + 2H+ + 2e → CO + H2O CO2 + 2H2O + 2e → CO + 2OH_ 2CO2 + 2H+ + 2e → H2C2O4 2CO2 + 2e → C2O42- -0.53 -1.347 -0.913 -1.003 CO2 + 4H+ + 4e → C + 2H2O -0.20 CO2 + 4H+ + 4e → HCHO +H2O CO2 + 3H2O + 4e →HCHO + 4OH- CO2 + 2H2O + 4e → C + 4OH__ -0.48 -1.311 -1.040 CO2 + 6H+ + 6e → CH3OH + H2O CO2 + 5H2O + 4e →CH3OH +6H2O -0.38 -1.225 CO2 + 8H+ + 8e → CH4 + 2H2O CO2 + 6H2O + 8e → CH4 +8OH-- -0.24 -1.072 2CO2 + 12H+ + 12e→ C2H4 + 4H2O 2 CO2 + 8H2O + 12e→ C2H4 + 12 OH— 2CO2 + 12H+ + 12e→ C2H5 OH + 3H2O 2CO2 + 9H2O +12e→ C2H5 OH + 12 OH-- -0.349 -1.177 -0.329 -1.157 2CO2 + 14H+ + 14e → C2H6 +4H2O -0.270 3CO2 +18H+ + 18e → C3H7 OH +H2O -0.310 2H+ + 2e → H2 -0.42

Molecular orbital diagram of dinitrogen The bond order for dinitrogen (1σg21σu22σg22σu21πu43σg2) is three because two electrons are now also added in the 3σ MO. The MO diagram correlates with the experimental photoelectron spectrum for nitrogen.[ The 1σ electrons can be matched to a peak at 410 eV (broad), the 2σg electrons at 37 eV (broad), the 2σu electrons at 19 eV (doublet), the 1πu4 electrons at 17 eV (multiplets), and finally the 3σg2 at 15.5 eV (sharp)

on-demand, and easy for scale-up applications the process is controllable by electrode potentials and reaction temperature; (2) the supporting electrolytes can be fully recycled so that the overall chemical consumption can be minimized to simply water or wastewater; (3) the electricity used to drive the process can be obtained without generating any new CO2 —sources include solar, wind, hydro- electric, geothermal, tidal, and thermoelectric processes; and (4) the electrochemical reaction systems are compact, modular, on-demand, and easy for scale-up applications

1) Biological systems, including mainly algae; (2) Inorganic photocatalysts, mostly transition metal oxides (or semiconductors), in particular TiO2 -based catalysts; (3) Organic photocatalysts, including mainly metal- organic complexes; and (4) inorganic and organic/biological hybrid, or the so-called biomimetic systems, consisting of enzyme-activated or dye-se nsitized semiconductors.

Elimination or reduction of CO2 in the atmosphere is a serious problem faced by humankind, and it has become imperative for chemists to find ways of transforming undesirable CO 2 to useful chemicals. One of the best means is the use of solar energy for the photochemical reduction of CO2. In spite of considerable efforts discovery of stable photocatalysts which work in the absence of scavengers has remained a challenge although encouraging results have been obtained in the photocatalytic reduction of CO2 in both gas and liquid phases. Semi-conductor-based catalysts, multicomponent semiconductors, metal−organic frameworks (MOFs), and dyes as well as composites involving novel composite materials containing C3N4 and MoS2 have been employed for the photoreduction process. Semiconductor heterostructures, especially those containing bimetallic alloys as well as chemical modification of oxides and other materials with aliovalent anion substitution (N 3− and F − in place of O2−), remain worthwhile efforts.

To date, photocatalytic reduction of CO2 is still in progress by leaps and bounds and a number of questions remain to be solved by researchers: enhancement of photocatalysts by utilizing visible light instead of UV light and also improvement in the photocatalytic efficiency by considering all reaction parameters (temperature, H2O/CO2 molar ratio, illumination duration and light intensity) in order to comercialize this photocatalysis process for large scale applications.

The Steady Rise of Kesterite Solar Cells

Photo-catalytic Reduction of Carbon dioxide Current Status – Nothing Encouraging! Solution does not appear? What or Where shall this area will go?