KCS

It has been almost twenty years, that the linear scaling of adsorption energies of reaction intermediates in heterogeneous catalysis has started to coin the field as a blessing and a curse at the same time. It has established the possibility to construct activity volcano plots as a function of a single or two readily accessible adsorption energies as descriptors, but also limited the minimal theoretical overpotential that a catalyst can reach. In this work, we find that these established adsorption energy-based descriptor spaces are not applicable to electrochemistry, because they are lacking an important additional dimension, the Potential of Zero Charge (PZC). To reach this conclusion, we performed surface-charge dependent DFT calculations on the electrochemical CO₂ reduction to CO on various metallic surfaces, for which commonly the CO adsorption energy has been identified as descriptor. From this, we found that material trends of charge stabilization of reaction intermediates cannot be well depicted by the CO adsorption energy alone. Instead, one has to also consider the Fermi level or PZC as an additional charge-transfer descriptor, which is almost uncorrelated with the CO adsorption energy and thus effectively breaking the scaling relations. By careful comparison with published experimental data, we find the new descriptor space to rationalize experimental trends, such as the higher activity of Gold for CO production compared to Silver, but also the product selectivity for CO₂RR across various metallic and bimetallic systems. We believe that the discovery of the PZC as a critical design parameter could hold the key towards a new era of electrocatalyst design.