Mechanistic insights into the spontaneous reaction between CO2 and La2–xSrxCuO4

Layered perovskites such as La 2–x Sr x CuO 4 are active electrocatalysts for CO 2 reduction, but they suffer from structural instability under catalytic conditions. This structural instability is found to arise from the reaction of CO 2 with surface sites. Variable scan rate voltammetry shows the growth of a Cu-based redox couple when potentials cathodic of 0.6 V vs. RHE are applied in the presence of CO 2 . Electrochemical impedance spectroscopy identifies a redox active surface state at this voltage, whose concentration is increased by electrochemical reduction in the presence of CO 2 . In situ spectroelectrochemical FTIR identifies surface bound carbonates as being involved in the formation of these surface sites. The orthorhombic lattice for La 2 CuO 4 is found to uniquely enable binding bidentate binding of carbonate ions to the surface through reaction with CO 2 . The incorporation of Sr(II) induces a transition to a tetragonal lattice, for which only monodentate carbonate ions are observed. It is proposed that the binding of carbonate ions in a bidentate fashion generates sufficient strain at the surface to result in amorphization at the surface, yielding the observed Cu(II)/Cu(I) redox couple.