Direct formic acid electro-oxidation on pt doped and undoped La_1-xSr_xCoO₃: Activity suppression due to proton reduction reaction

Combustion synthesized Pt-doped and undoped La_1-xSr_xCoO₃ are utilized for formic acid electro-oxidation. Cyclic-voltammetry (CV) during formic acid electro-oxidation demonstrates that the oxidation current initially increases and then decays to zero on both the catalysts. This implies that the HCOOH possibly has some poisoning effect on the catalysts. Both materials show a unique reduction peak in the oxidation scan right after the addition of HCOOH in the electrolyte, demonstrating a reduction process in the oxidation cycle. When HCOOH is replaced by potassium formate, the reduction peak is found absent. Further, significant increase in the current is observed in the case of La_1-xSr_xCoO₃. This confirms that the protons which are generated during the electro-oxidation of HCOOH are reduced on the catalyst’s surface generating the reduction peak in the CV. This process suppresses the counter-reaction to diminish the current. Instead of protons, K⁺ ions are generated with potassium formate which greatly prevents the proton reduction reaction and leads to the formate ion oxidation. Only CO₂ was evolved during the electro-oxidation which was confirmed through gas chromatography. Further investigations reveal that apart from proton reduction reaction, Pt-doped La_1-xSr_xCoO₃ gets poisoned in presence of CO₂ also; the main oxidation product of both HCOOH and KCOOH.