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

Abstract

Layered perovskites such as La2–xSrxCuO4 are active electrocatalysts for CO2 reduction, but they suffer from structural instability under catalytic conditions. This structural instability is found to arise from the reaction of CO2 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 CO2. Electrochemical impedance spectroscopy identifies a redox active surface state at this voltage, whose concentration is increased by electrochemical reduction in the presence of CO2. In situ spectroelectrochemical FTIR identifies surface bound carbonates as being involved in the formation of these surface sites. The orthorhombic lattice for La2CuO4 is found to uniquely enable binding bidentate binding of carbonate ions to the surface through reaction with CO2. 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.