The Potential of Zero Charge and the Electrochemical Interface Structure of Cu(111) in Alkaline Solutions

Abstract

Copper (Cu) is a unique electrocatalyst, which is able to efficiently oxidize CO at very low overpotentials and reduce CO 2 to valuable fuels with reasonable Faradaic efficiencies. Yet, knowledge of its electrochemical properties at the solid/liquid interface is still scarce. Here, we present the first two-stranded correlation of the potential of zero free charge (pzfc) of Cu(111) in alkaline electrolyte at different pH values through application of nanosecond laser pulses and the corresponding interfacial structure changes by in situ electrochemical scanning tunneling microscopy imaging. The pzfc of Cu(111) at pH 13 is identified at −0.73 V SHE in the apparent double layer region, prior to the onset of hydroxide adsorption. It shifts by (88 ± 4) mV to more positive potentials per decreasing pH unit. At the pzfc, Cu(111) shows structural dynamics at both pH 13 and pH 11, which can be understood as the onset of surface restructuring. At higher potentials, full reconstruction and electric field dependent OH adsorption occurs, which causes a remarkable decrease in the atomic density of the first Cu layer. The expansion of the Cu–Cu distance to 0.3 nm generates a hexagonal Moiré pattern, on which the adsorbed OH forms a commensurate (1 × 2) adlayer structure with a steady state coverage of 0.5 monolayers at pH 13. Our experimental findings shed light on the true charge distribution and its interrelation with the atomic structure of the electrochemical interface of Cu.

Interfacial Water Structure as a Descriptor for Its Electro-Reduction on Ni(OH)2-Modified Cu(111)

“…Cu as a coinage metal has been repeatedly found to dynamically restructure upon anion adsorption, 20 − 24 under reaction conditions (e.g., hydrogen evolution, 25 , 26 CO (2) reduction, 27 − 29 or CO oxidation 30 ), and even at its pzfc. 14 This gives rise to an inherently much lower stability of Cu surfaces compared to, e.g., Pt. While decorating Pt(111) with Ni(OH) 2 was found to result in well-separated, randomly distributed Ni(OH) 2 clusters, 5 , 6 it is doubtful that the Cu surface stays intact upon Ni(OH) 2 deposition due to its much lower cohesive energy (3.5 eV vs 5.84 eV for Pt).…”

“…At around 0.07–0.09 V RHE , coinciding with the onset of the OH adsorption peak, the transients change their sign to negative, as was previously shown for bare Cu(111) electrodes, which suggest that below this potential, a negative free charge resides at the surface. 14 , 35 This change of sign is generally attributed to the position of the pme and a turn-over of the water ad-layer. At the pme, water molecules at the interface distribute randomly, and there is no net dipolar contribution to the electrode potential.…”

“…At more negative potentials, where the transients turn negative again, a decrease in the potential dependence of the thermal coefficient is recorded ( Figure 5 d). Since it has been recently found that Cu(111) reconstructs as a consequence of the change in free charge on the surface, 14 we performed further in situ EC-STM imaging for Cu(111)/0.2 ML of Ni(OH) 2 to examine possible further structural changes below the second pme.…”

Versatile 3D‐Printed Micro‐Reference Electrodes for Aqueous and Non‐Aqueous Solutions

“…[ 21 , 22 ] It has been shown that these electrodes are stable in certain electrolytes (including ionic liquids). [ 23 , 24 ] Nevertheless, their potential strongly depends on the particular electrolyte and is often only stable in a certain potential range. This is different from ideal non‐polarizable electrodes where the electrode potential does not change upon charging the electrode via faradaic or, capacitive contributions, or both.…”

Versatile 3D‐Printed Micro‐Reference Electrodes for Aqueous and Non‐Aqueous Solutions

“…[21,22] It has been shown that these electrodes are stable in certain electrolytes (including ionic liquids). [23,24] Nevertheless,t heir potential strongly depends on the particular electrolyte and is often only stable in acertain potential range.T his is different from ideal non-polarizable electrodes where the electrode potential does not change upon charging the electrode via faradaic or, capacitive contributions,o r both. [12,20] Overall, the task of finding au niversal reference electrode,especially for ILs,isvery complicated due to the unique chemical and physical properties of each system.…”