[H + ] b spans across more than two orders of magnitude in the different starting electrolyte concentrations, and the CO 2 available in a 2 M KHCO 3 solution is less than half of that available in pure water as a result of the increased ionic strength of the solution. These bulk variations also impact the local conditions at OHP (Figure (a)): at less negative At less negative potentials, even though the P CO 2 ,OHP is lower for high buffer concentrations, [K + ] OHP is higher, which is sufficient to increase the availability of microenvironments on the electrocatalyst, resulting in higher current densities for higher buffer concentrations (Figure (a)). However, at strongly negative potentials, as the cations approach the steric limit, the effect of the decrease in P CO 2 ,OHP becomes more relevant and the system transitions from a kinetic-dominated regime to a transport-dominated one (Figure (b)) reducing the availability of CO 2 in concentrated buffers.