In Situ Analysis of the Facets of Cu-Based Electrocatalysts in Alkaline Media Using Pb Underpotential Deposition.

Establishing relationships between the surface atomic structure and activity of Cu-based electrocatalysts for CO2 and CO reduction is hindered by probable surface restructuring under working conditions. Insights into these structural evolutions are scarce as techniques for monitoring the surface facets in conventional experimental designs are lacking. To directly correlate surface reconstructions to changes in selectivity or activity, the development of surface-sensitive, electrochemical probes is highly desirable. Here, we report the underpotential deposition of lead over three low index Cu single crystals in alkaline media, the preferred electrolyte for CO reduction studies. We find that underpotential deposition of Pb onto these facets occurs at distinct potentials, and we use these benchmarks to probe the predominant facet of polycrystalline Cu electrodes in situ. Finally, we demonstrate that Cu and Pb form an irreversible surface alloy during underpotential deposition, which limits this method to investigating the surface atomic structure after reaction.

Fingerprint Voltammograms of Copper Single Crystals under Alkaline Conditions: A Fundamental Mechanistic Analysis.

A critical step toward the systematic development of electrocatalysts is the determination of the microscopic structure and processes at the electrified solid/electrolyte interface. The major challenges toward this end for experiment and computations are achieving sufficient cleanliness and modeling the complexity of electrochemical systems, respectively. In this sense, benchmarks of well-defined model systems are sparse. This work presents a rigorous joint experimental-theoretical study on the single-crystal (SC) Cu/aqueous interface. Within typical computational uncertainties, we find quantitative agreement between simulated and experimentally measured voltammograms, which allows us to unequivocally identify the *OH adsorption feature in the fingerprint region of Cu(110), Cu(100), and Cu(111) SCs under alkaline conditions. We find the inclusion of hydrogen evolution reaction kinetics in the theoretical model to be crucial for an accurate steady-state description that gives rise to a negligible H* coverage. A purely thermodynamic description of the H* coverage through a Pourbaix analysis would incorrectly lead to a H* adsorption peak. The presented results establish a fundamental benchmark for all electrochemical applications of Cu.

On the Possibilities and Considerations of Interfacing Ultra-High Vacuum Equipment with an Electrochemical Setup.

Efficient electrocatalysts are required in order for electrocatalysis to play a large role in a future largely based on renewable energy sources. To rationally design these catalysts we need to understand the fundamental origin of their activities. In order to elucidate the relationship between catalyst structure and electrochemical behaviour, we investigate well-defined single-crystal catalysts in a UHV chamber interfaced with an electrochemical setup. Using the capabilities of UHV based methods, we can prepare more complex surface structures than it is possible with traditional EC methods and investigate their electrochemical behaviour. We exemplify this by showing results from both clean and intentionally structured Pt(111), Cu(111) and Pt/Cu(111).

Polycrystalline and Single-Crystal Cu Electrodes: Influence of Experimental Conditions on the Electrochemical Properties in Alkaline Media.

Single and polycrystalline Cu electrodes serve as model systems for the study of the electroreduction of CO2 , CO and nitrate, or for corrosion studies; even so, there are very few reports combining electrochemical measurements with structural characterization. Herein both the electrochemical properties of polycrystalline Cu and single crystal Cu(1 0 0) electrodes in alkaline solutions (0.1 m KOH and 0.1 m NaOH) are investigated. It is demonstrated that the pre-treatment of the electrodes plays a crucial role in determining their electrochemical properties. Scanning tunneling microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry are performed on Cu(1 0 0) electrodes prepared under UHV conditions; it is shown that the electrochemical properties of these atomically well-defined electrodes are distinct from electrodes prepared by other methods. Also highlighted is the significant role of residual oxygen and electrolyte convection in influencing the electrochemical properties.