For all cations, the shift to a transport-limited regime happens when P Furthermore the higher PCET barriers for K + than Cs + (Figure (e)) lead to a shift in peak potentials towards more negative values. Li + current densities are still within an order of magnitude of K + at less negative potentials (Figure (a)) due to its PCET barriers for CO 2 to COOH being lower by 0.15 eV with respect to K + (Figure (e)).