The first product to be detected upon photoelectrochemical CO2
reduction was CH3OH (47.5 ppm at 15 min), but its concentration
decreased rapidly (16.5 ppm at 30 min) and became almost negligible
after longer times. Scheme 1 depicts the mechanism of product
formation during photoelectrolysis. Although the scheme also
represents formic acid (HCOOH) formation, we did not detect this
product in the experimental conditions adopted here. According to
a previous author [4], the HCOOH generated during photoelectrochemical
CO2 reduction is readily reduced to form CH2O and CH3-
OH, as demonstrated in reactions 2 and 3 of the mechanism
proposed in Scheme 1