Initial Stages of Sodium Deposition onto Au(111) from [MPPip][TFSI]: An In‐Situ STM Study for Sodium‐Ion Battery Electrolytes

Sodium-ion batteries are promising candidates for post-lithium-ion batteries. While sodium has a less negative standard electrode potential compared to lithium, it is still a strong reducing agent. Ionic liquids are suitable solvents for sodium metal batteries, since metallic sodium is very reactive, particularly with water and molecules containing acidic hydrogen atoms. In this study, the initial stages of electrodeposition of sodium on Au(111) from N-methyl-N-propylpiperidinium [MPPip] bis(trifluoromethanesulfonyl)imide [TFSI] were studied using voltammetry and in-situ scanning tunnelling microscopy. Four subsequent underpotential deposition stages were observed: (i) nucleation at the Au(111) reconstruction elbows, followed by (ii) growth of small monoatomically high islands that form (iii) a smooth layer via coalescence, and (iv) further island growth on top of the existing layers. The electrocrystallisation mode changed from smooth layer formation to 3D growth, resulting in cauliflower-like structures. The deposition process was accompanied by simultaneous alloy formation

Oxoanion adlayers on Au(111) : an in-situ scanning tunneling microscopy study

The aim of this work is to investigate the adsorption of formate at a molecular level under electrochemical conditions. Before doing so however, high-resolution in-situ STM images of the well-established Au(111) in 0.1 M H2SO4 system should first be acquired to ensure the possibility of studying a more complicated system. Interestingly, during those measurements, new findings into the potential dependence on the kinetics of surface reconstruction and into the adsorbed sulfate structure were observed. Next, since acetate compared to formate, is not active on the Au(111) surface, the adsorption of acetate will first be studied to help gain more insight on formate adsorption. Both findings will later be compared to one another. Finally, the adsorption of phosphate anions will be investigated as an example of a four-oxygen oxoanion which strongly blocks formic acid oxidation at higher pH values. In the course of phosphate adsorption study, insight into the impact of the coadsorption of additional spectator species like alkali metal cations (K+, Na+, Li+), which are widely used components of supporting electrolytes, will be given. Cyclic voltammetry is preliminarily used to characterize an electrochemical system. With the help of this method, it is possible to acquire information about electrochemical processes and to determine the potentials at which they occur. Cyclic voltammetry and in-situ STM are used to characterize the configuration and bonding of sulfate, phosphate, acetate and formate anions to a Au(111) substrate

Hydrogen Peroxide Oxidation Reaction on a 4-Mercaptopyridine Self-Assembled Monolayer on Au(111) Metallized by Platinum Nanoislands

A systematic investigation of the hydrogen peroxide oxidation reaction (HPOR) in phosphate buffer (pH = 7.3) on an Au(111) single crystal modified with a 4-mercaptopyridine self-assembled monolayer (SAM) has been conducted before and after metallization with Pt. While bare Au(111) shows considerable electrocatalytic activity towards the HPOR, the inhibition of the oxidation reaction after modification with the SAM implies that adsorbed 4-mercaptopyridine molecules do not catalyze the HPOR. However, SAM-modified Au(111) recovers catalytic activity for the HPOR already after a single metallization step fabricating Pt islands on-top. Hydrogen peroxide (HP) may then either react at the (non-metallic) Pt nanoislands or on reactivated Au sites, made accessible by structural changes of the SAM induced by the metallization. The shape of the voltammetric profiles for the HPOR on repeatedly metallized SAMs suggests that the contribution of Au to the total current density gradually diminishes with increasing Pt coverage while the contribution of the Pt islands increases. The electrochemical behavior is dominated by the Pt islands at a coverage of 0.5 ML obtained by three subsequent metallization steps