Electrochemical CO2 Reduction to Fuels Using Pt/CNT Catalysts Synthesized in Supercritical Medium

The electrochemical reduction of CO2 in the gas phase has been carried out in a solid polymer electrolyte type cell (25 cm(2) geometric area) in continuous operation mode using carbon nanotube-supported platinum catalysts (Pt/CNT). The main novelty of this work relies on the use of supercritical media (supercritical CO2) for Pt deposition on CNT. Supercritical synthesis has allowed obtaining small Pt nanoparticles divided into two modal distributions (for 3-4 nm and 8-9 nm, respectively) with a high deposition efficiency (about 80%). The main reaction products of the electrocatalytic conversion of CO2 have been formic acid (59-89%), methane (2-33%), CO (3-11%), methanol (0-1.9%), and small amounts of acetone, isopropanol, and methyl acetate. The CO2 conversion rate multiplies almost by four when increasing current density, although selectivity barely changes. Lower temperature promotes further reduction of CO2 to methane (33% of selectivity) to the detriment of formic acid and CO. However, increases of temperature favor mainly formic acid production (up to 89%) as well as methanol formation (1.9%) at the expense of methane. In addition, low CO2 flow rate favors production of methane and methanol (in a lesser extent) to the detriment of CO and formic acid. The maximum CO2 conversion rate attained has been 2.8 x 10(-2) mmol h(-1) for the highest current density studied. Attending to the selectivity, a low CO2 flow rate favored the production of fuels such as methane (5.2 X 10(-3) mmol h(-1)) and methanol (3.6 X 10(-4) mmol h(-1)). These results indicate that the supercritical synthesis of the Pt/CNT electrocatalyst improves the results reported in the literature up to now.