Investigating the platinum electrode surface during Kolbe electrolysis of acetic acid

The Influence of Alkali Cations on the Performance of Pt Electrodes in Kolbe Electrolysis of Acetic Acid

“…We demonstrated that the precise surface coverage is highly dependent on the cation composition, affecting the local pH and surface coverage of acetate. Though the experimental observations agree well with the theory of cation induced non-covalent interactions (Scheme 1), it is important to note that also the oxidation of the Pt surface [12,48,58] is affected by monovalent cations of smaller radii. These summarized phenomena are also affected by a factor we have not discussed previously, which is the applied current density.…”

“…OER was found to be negligible for K + , while minor quantities of O 2 were detected for the other cations (Cs + < Na + < Li + as shown in Figure S12)consequently lowering the FE of ethane in the inverse order following Li + < Na + < Cs + < K + ( Figure 2b). Based on the above assessment, it is clear that Li + and Na + cations may induce significant dissolution of Pt at pH 3, and favourable oxygen evolution at pH 5 (minor quantities, see Figure S12), both assigned to similar surface and interfacial phenomena associated with the extent of the formation of Pt oxides [48] and the coverage of the surface with acetate, respectively (see for an illustration Scheme 1).…”

“…[22] Thus, the local conditions at the electrode surface are also found to be determining factors for OER as evidenced by mechanistic calculations. [34] Based on the above, it can be hypothesized that cations should influence the electronic or structural properties of Pt oxides, the phase present under reaction conditions, [47,48] affecting the kinetics (current density, FE, and selectivity) of acid decarboxylation, similar to observations made in the context of the OER. Moreover, prior research has shown that adsorption of alkali metal cations on the Pt surface affects the formation of its oxides.…”

“…[25] Platinum oxide formation is considered a prerequisite for Kolbe electrolysis allowing for stronger acetate radical binding further supporting the hypothesis that monovalent cations are indeed modulating Kolbe electrolysis. [12,48] In this study, we conducted a comprehensive experimental investigation to reveal the impact of cation composition on the OER, Kolbe, and Hofer Moest processes, across a wide range of (bulk) electrolyte pH (3)(4)(5)(6)(7)(8)(9)(10)(11)(12) and applied current densities (10-50 mA/cm 2 ). We employed online product detection and rotating ring-disk electrode (RRDE) measurements to reveal the product selectivity, and to measure the transition between oxygen evolution and Kolbe oxidation or Hofer Moest reaction, i. e., the inflection zone.…”