Structural Evolution of Pt, Au and Cu Anodes by Electrolysis up to Contact Glow Discharge Electrolysis in Alkaline Electrolytes**

Abstract

Applying a voltage to metal electrodes in contact with aqueous electrolytes results in the electrolysis of water at voltages above the decomposition voltage and plasma formation in the electrolyte at much higher voltages referred to as contact glow discharge electrolysis (CGDE). While several studies explore parameters that lead to changes in the I-U characteristics in this voltage range, little is known about the evolution of the structural properties of the electrodes. Here we study this aspect on materials essential to electrocatalysis, namely Pt, Au, and Cu. The stationary I-U characteristics are almost identical for all electrodes. Detailed structural characterization by optical microscopy, scanning electron microscopy, and electrochemical approaches reveal that Pt is stable during electrolysis and CGDE, while Au and Cu exhibit a voltage-dependent oxide formation. More importantly, oxides are reduced when the Au and Cu electrodes are kept in the electrolysis solution after electrolysis. We suspect that H 2 O 2 (formed during electrolysis) is responsible for the oxide reduction. The reduced oxides (which are also accessible via electrochemical reduction) form a porous film, representing a possible new class of materials in energy storage and conversion studies.

Electric Potential Distribution Inside the Electrolyte During High Voltage Electrolysis

“…To illustrate this aspect more clearly, we studied the formation of a Au oxide layer on a Au wire anode during normal electrolysis (see Ref. 29) as a function of the electrolyte resistance. The latter has been varied by step-wise increasing the distance between the WE and the CE (WE-CE distance) from 2 to 8 cm.…”

“…The amount of Au oxide formed during electrolysis can be inferred from the charge passed during the electrochemical reduction of the electrodes (see experimental section and Ref. 29). The corresponding charges are depicted in Fig.…”

“…Electrochemical Measurements: The electrochemical characterization follows a procedure similar to the one reported in Ref. 29. The electrochemical measurements were performed in a round glass cell (diameter 6 cm) containing 60 mL of 0.01 M KOH.…”

In‐Liquid Plasma for Surface Engineering of Cu Electrodes with Incorporated SiO2 Nanoparticles: From Micro to Nano

“…Furthermore, plasma electrolysis at these extreme voltages is accompanied by the formation of reducing species (e.g., H 2 O 2 ) and massive hydrogen evolution that could chemically reduce CuO. [65,66] In comparison, after polarization of Cu electrodes solely in 0.01 M KOH electrolyte at voltages in the range of 50 V ≤ U < 500 V, a thick oxide layer forms on their surfaces as indicated by 50% of O (Figure S1b, Supporting Information). Moreover, for the plasma regime (500-600 V), the thickness of the surface oxide layer decreases drastically, and the surface becomes smoother, as indicated by the SEM and EDS results in Figures S1a,b, Supporting Information.…”

Cathodic corrosion of Au in aqueous methanolic alkali metal hydroxide electrolytes: Notable role of water

“…The EASA factors are obtained by matching the double-layer capacity of the corroded and as-polished Au electrodes at -0.60 V versus MSE where neither Faraday reactions nor adsorption processes occur. [1,5,19,20] Correction for the IR-drop is considered to determine the actual potentials. Electrochemical impedance spectroscopy measurements were carried out to determine the solution resistance R of the KOH and NaOH electrolytes.…”