Theory and experiments join forces to characterize the electrocatalytic interface

Electrocatalysis is gaining impetus as a key technology in fuel cells and for the medium-term energy storage in the context of intermittent, renewable energy sources such as wind and solar power. Furthermore, electrocatalysis promises to convert rather inert molecules such as CO2 and N2 into reduced products such as CO and ammonia under relatively mild conditions (1, 2). Harnessing the full power of electrocatalysis is, however, hampered by a lack of understanding of the governing physical and chemical processes at the metal–electrolyte interface. In PNAS, Cheng et al. (3) bring key insight to the characterization of reaction intermediates during CO2 electroreduction via first-principles molecular dynamics modeling. This reaction is timely and has, over the last few years, served as the playground for advanced atomistic modeling of electrocatalysis (4⇓⇓⇓⇓–9). The general lack of understanding is due to the inherent complexity of the electrified interface and its characterization. The characterization is difficult since most metal–liquid interfaces are amorphous. Therefore, no long-range ordering can be detected. Experimentally, the characterizations heavily rely on spectroscopy that provides average molecular orientations [infrared (IR) and Raman] or elemental composition and oxidation states (X-ray photoelectron, X-ray absorption near-edge, etc.) (10⇓–12). Atomically resolved structures can be obtained only for rare, crystalline interfaces such as pyridine on gold single-crystal surfaces via scanning tunneling microscopy imaging (13, 14). Theoretically, the simulations of electrochemical interfaces are challenging for two reasons. The first challenge originates from the structure and dynamics of the interface; that is, its size and the relevant timescales. Just like for experiments, the amorphous nature of the interface means that, when working with periodic boundary conditions to well describe the metallic nature of the electrode and the liquid nature of the electrolyte, large systems need … [↵][1]1To whom correspondence should be addressed. Email: sautet{at}ucla.edu. [1]: #xref-corresp-1-1