Does the presence of only specific active sites control the switch of selectivity from C1 to C2+ products in CO2RR?

There is an extensive but not conclusive debate about the factors determining selectivity in the competitive path to C1 vs. C2+ products in the electrocatalytic reduction of CO2 (CO2RR). While the predominant indication is that C2+ products require specific active sites and/or surface features of the electrocatalyst, we prove here that selectivity can be entirely switched from C2+ to C1 products by controlling H+ accessibility. This indicates that the electrocatalytic path is determined by proton availability rather than the intrinsic presence of specific active sites. To validate this, we investigated CO2RR on CuO nanoplates with identical structural and morphological features (confirmed by XRD, SEM-EDX, TEM, HRTEM analyses) but varying wettability characteristics using different precursors (Li or Na), thereby modulating the surface H+ accessibility. The applied potential also controls this accessibility. By analysing Faradaic selectivity as a function of applied potential across CuO nanoplate samples with different wettability, we observe a transition from 100 % C2+ selectivity to 100 % C1 selectivity, with the potential threshold for this switch dependent on wettability. Our findings demonstrate that the C2+ vs. C1 product pathway in CO2RR is not an intrinsic property of the electrocatalyst but is governed by the availability of surface protons, which is a function of the operating conditions and electrode/electrocatalyst characteristics that regulate proton access to the catalyst surface.