The importance of a charge transfer descriptor for screening potential CO2 reduction electrocatalysts

Abstract

It has been over twenty years since the linear scaling of reaction intermediate adsorption energies 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, it is found 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. This extra dimension 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 it is shown that the addition of this descriptor breaks the scaling relations, opening up a huge chemical space that is readily accessible via potential of zero charge-based material design. The potential of zero charge also explains product selectivity trends of electrochemical CO2 reduction in close agreement with reported experimental data highlighting its importance for electrocatalyst design.

Trace-Level Cobalt Dopants Enhance CO2 Electroreduction and Ethylene Formation on Copper

“…This effectively poisons these sites, however, as well. Decreasing the adsorption strength of CO on Cu would, however, in turn increase the barrier for *COOH formation according to the *CO-*COOH scaling relations. , There is thus an optimal *CO adsorption energy which we found to lie at a bit stronger binding strength compared to Cu from free energy diagrams and microkinetic modeling presented in Figure a,b …”

“…43,44 There is thus an optimal *CO adsorption energy which we found to lie at a bit stronger binding strength compared to Cu from free energy diagrams and microkinetic modeling presented in Figure 4a,b. 45 Since CO-bound Co sites will most likely be a common surface feature under CO 2 RR conditions, we thus investigated the CO 2 to CO free energy diagram on Cu sites neighboring such sites (CO@Co 1L , where a single CO is bound to the Co site, and we test the adsorption of further molecules at surrounding sites). Indeed, we found a balanced stabilization of both *CO and *COOH for only a single Cu site at a close distance to the CO@Co 1L , which resulted in lower barriers to form *COOH while still enabling *CO desorption (Figure 4a).…”

Theoretical understanding of the effect of specifically adsorbed halide anions on Cu-catalyzed CO2 electroreduction activity and product selectivity

“…The most recent theoretical study from Ringe indicated that the potential of zero charge (PZC) in electric double-layer interfaces is an important charge-transfer descriptor during CO 2 electroreduction. 45 Furthermore, the PZC is well known to be proportional to the work function. 46,47 Thus, the enhanced electron-accepting ability of CO 2 in the order of I À 4 Br À 4 Cl À 4 F À can be also explained by the work functions or the PZCs of the F À -, Cl À -, Br À -, and I À -modified Cu(111)/H 2 O interfaces, in which smaller work functions will result in more electron transfer into the adsorbed CO 2 .…”

Potential Effects on the Catalytic Mechanisms of OER and ORR

“…Under the actual potential condition, how do the physical quantities such as Gibbs free energy and charge state of a catalytic intermediate evolve with potential during a reaction? Besides, the scaling relations, i.e., a linear correlation of intermediate’s adsorption energies, are one of the breakthroughs in heterogeneous catalysis and computational electrochemistry, which can reduce the spatial dimension of catalytic activity. , Then, do the previous proposed scaling relations still work under the actual potential condition? These questions remain to be further understood.…”