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The electrocatalytic reduction of CO2 (CO2RR) on carbon-supported palladium-based (Pd/C, Pd-Cu2O/C, Pd-SnO2/C) and non-precious metal oxides (Cu2O/C and SnOX/C) was investigated through physicochemical and electrochemical measurements. The formation of a solid solution in the bimetallic Pd-based compounds was confirmed by a contraction of the Pd unit cell volume, measurements of the TEM interplanar distance, and cyclic voltammetry characterization. Pd-based electrocatalysts presented smaller crystallite sizes (9 nm–18 nm) than Cu2O/C and SnOX/C (62 nm and 82 nm, respectively). Pd/C, Pd-Cu2O/C, and Pd-SnO2/C showed the highest electrochemical activity to perform the CO2RR due to a lower overpotential value compared to Cu2O/C and SnOX/C. The Tafel plots during CO2RR revealed a small slope in the region of lower overpotentials for the Pd-based electrocatalysts (less than 52 mV dec-1), which indicates a better kinetic compared to Cu2O/C and SnOX/C (165 and 193 mV dec-1, respectively). SnOX presented the highest selectivity toward HER instead of CO2 reduction. DEMS measurements allowed the determination of the selectivity for the electrocatalysts to produce specific CO2 reaction products. Pd-based materials are suitable to perform the CO2RR since bimetallic electrocatalyst (Pd-Cu2O/C and Pd-SnO2/C) generates CO, formic acid, and CH4 as reaction products. At the same time, Pd/C produced CO and H2. On the other hand, Cu2O presented lower electrochemical activity than Pd-based materials, with CO as the main reaction product. The low overpotential and the faradic vs. ionic current profiles showed that SnOX/C could be classified as a promising material for hydrogen production in the presence of CO2.

It is accepted that the mechanism of electro-generated active chlorine (i.e. chloride oxidation on DSAs) involves water oxidation and hydroxyl radical co-electrosorption to initially form HOClads on the anode surface in a single pathway, and subsequent production of Cl2 and OCl− ions. The present study comprehensively evaluates the chloride oxidation on Ti/RuO2-IrO2 in solutions containing different NaCl concentrations and pH values. Differential Electrochemical Mass Spectroscopy (DEMS) is used to account for the in-situ surface reactions simultaneously occurring during chloride and water oxidations. It is found that HOCl does not lead the chlorine mechanism since OCl⦁ is detected in considerably larger amounts under some experimental conditions, and its onset overpotential is ~150 mV more negative than HOCl appearance at 0.2 mol L−1 NaCl. Additionally, the mass signals of OCl⦁ and HOCl are virtually similar at pH = 2 and slightly different at pH = 10, where these species should not respectively exist according to thermodynamic information. Under this premise, an extension of the reaction mechanism is proposed to consider an independent pathway producing adsorbed hypochlorite radical (OCl•ads) for electro-generated active chlorine, which could be the preferential one since RuO2 and IrO2 belong to the category of “active” anodes towards the Oxygen Evolution Reaction (OER), thus allowing the formation of the so-called higher oxide MOx(⦁O)ads (chemisorbed oxygen). Although the mechanisms involving the productions of HOClads and OCl•ads can simultaneously occur on two type of non-identified active sites, promoting the generation of both MOx(⦁OH)ads and MOx(⦁O)ads species, both strongly depend on surface pH.