Noble metal-free catalysts supported on carbon for CO2 electrochemical reduction

- Non-noble metal catalysts supported on carbon were tested for CO2 electroreduction.
- The activity of metal oxide-based electrocatalysts for CO2 reduction was studied.
- CO2 reduction species were adsorbed on the catalysts inhibiting the H2 formation.
- The formation of adsorbates seems to be promoted by the use of the carbon support.
- A strong H2 evolution inhibition was observed on Cu oxide-based catalysts.

In the present work, a wide variety of electrocatalysts, involving different metals, synthesis routes and oxidation states, have been prepared and the response towards the CO2 reduction on carbon-supported established. In particular, catalysts based on non-noble metals (Cu, Co, Fe and Ni) supported on carbon black (Vulcan XC-72R) were tested in the electrochemical reduction of CO2. Amorphous oxides of magnetite/maghemite and crystalline CuO and Cu2O oxides obtained by different methodologies were also studied. Previously, the efficiency of the catalysts for the hydrogen formation was evaluated in 0.1 M NaHCO3 since it takes place as a competitive reaction during CO2 reduction in aqueous electrolytes. By comparison of the voltammograms in the absence and presence of CO2, an inhibition of the hydrogen evolution was showed for all (metal and oxide-based) catalysts due to the adsorption of species from CO2 reduction (CO2,red). Interestingly, the CO2,red formation on Co and Fe-surfaces operating under these conditions has not been stated before. A strong current decrease, and consequently, a higher adsorbate amount, was observed on copper-oxides (75-85%) vs. the metal catalyst (45%).