Electrolyte Engineering for Oxygen Evolution Reaction Over Non‐Noble Metal Electrodes Achieving High Current Density in the Presence of Chloride Ion

Abstract

Direct seawater electrolysis potentially simplifies the electrolysis process and leads to a decrease in the cost of green hydrogen production. However, impurities present in the seawater, especially chloride ions (Cl À ), cause corrosion of the electrode material, and its oxidation competes with the anodic oxygen evolution reaction (OER). By carefully tuning electrode substrate and electrolyte solutions, the CoFeO x H y /Ti electrode with high double-layer capacitance actively and stably electro-catalyzed the OER in potassium borate solutions at pH 9.2 in the presence of 0.5 mol kg À 1 Cl À . The electrode possesses an active site motif composed of either a Co-or Fe-domain and benefits from an enlarged surface area. Selective OER was demonstrated in Cl Àcontaining electrolyte solutions at an elevated reaction temperature, stably achieving 500 mA cm À 2 at a mere potential of 1.67 V vs. reversible hydrogen electrode (RHE) at 353 K for multiple on-off and long-term testing processes with a faradaic efficiency of unity toward the OER.

Electrolyte Engineering Applying Concentrated Chloride Ions with Mixed Buffer Solutions for a Versatile High-Productivity Water-Splitting System

“…By employing the mixed buffer electrolyte solution, the OER half-reaction performance was investigated using the previously reported CoFeO x H y /TF anode Figure b shows the Tafel slope as a function of mixed buffer electrolyte pH (between 9.2 and 10.5) as obtained from the Tafel plots analysis, as shown in Figure S5.…”

“…The peaks at 455 and 590 cm –1 were ascribable to the O–Co–O vibration. , The XRD patterns reveal that the major peak at 18.2° was significantly reduced in some conditions compared with the one from the as-made sample; however, the peaks were not diminished completely, indicating that the crystalline structure was retained (Figure S20). Fe-derived peaks were not detected in the Raman spectrum because the amount of Fe was so small that Fe was distributed within the cobalt hydroxide structure . The SEM images show the different trends of surface features in the presence of Cl – (Figure S21).…”

“…Here, we suggest a new concept of electrolyte engineering for efficient overall water splitting in the presence of Cl − . We first discuss the electrolyte properties of mixed buffer electrolytes from the perspective of conductivity, pK a , buffer capacity, and corresponding half-reaction performances over a reported CoFeO x H y /Ti felt (TF) anode 26 and in a RuNiO x H y / Ni felt (NF) cathode. We then show that a varying pK a and the molality of the mixed buffer electrolyte�as well as introducing a third additive of Na/K−Cl�boosted the conductivity and affected both half-reactions.…”

Quantitative Description of Bubble Formation in Response to Electrolyte Engineering

“…In addition to a conventional approach to tune hydrophilicity at the electrode surface, adjusting electrolyte ions, namely, electrolyte engineering, would introduce changes in the reaction mechanism, 24 the electrode kinetics, 25 and the mass transport. 26 These concepts are further expanded in the bubble management in this study. Quantitative descriptions of the relationship between bubbles and electrolyte properties in electrochemical reactions would help to develop efficient water-splitting devices.…”

“…There are still a lack of detailed investigations into the relationship between the electrolyte physical properties and bubble departure diameters. In addition to a conventional approach to tune hydrophilicity at the electrode surface, adjusting electrolyte ions, namely, electrolyte engineering, would introduce changes in the reaction mechanism, the electrode kinetics, and the mass transport . These concepts are further expanded in the bubble management in this study.…”