The importance of a charge transfer descriptor for the screening of electrocatalysts at the example of CO2 reduction.

It has been over twenty years, since the linear scaling of reaction intermediate adsorption energies has started to coin the fields of heterogeneous and electrocatalysis 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 maximal catalytic conversion rate. 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). The PZC-dependence arises from the interaction of the electric double layer with reaction intermediates which does not scale with adsorption energies. At the example of the electrochemical reduction of CO2, we show that the PZC descriptor breaks the scaling relations, opening up a huge chemical space which is readily accessible via PZC-based material design. The PZC dependence also reveals intriguing material trends in close agreement with reported experimental data highlighting the importance of the PZC for electrocatalyst design.