From a catalytic viewpoint, the selectivity of CO2 reduction on
the Cu/Cu2O photoelectrode might depends on pH, once the ratedetermining
step involves CO2 adsorption and/or stabilization of
intermediates to improve electron transfer and subsequent reactions
involving the hydroxyl radical. Hence, the pH of the electrolyte
solution strongly affects the equilibrium and the relative
concentrations of CO2, H2CO3, and the deprotonated forms HCO3
(bicarbonate) and CO3
2 (carbonate), as well as the adsorption of
CO2 and/or unstable intermediates [52]. According to Zeebe and
Wolf-Gladrow [53], in pH 8 the CO2 is dissolved as HCO3
; in pH
9 exists an equilibrium between the species HCO3
and CO3 2 with
a predominance of HCO3
; in pH 10 the concentration of HCO3
and CO32 are practically equal in the middle; and, in pH 11 CO3 2
species are predominant..