Abstract
The oxidation of water to form oxygen gas provides charge balance for the cathodic deposition of metals, such as zinc, in the electrorefining industry. This is a corrosive, four-electron electrochemical reaction that causes deterioration of lead-silver alloy anodes employed in these processes. A sacrificial manganese oxide layer on the anode surface, formed in-situ from manganese sulfate, is used in industry to reduce the corrosion rate of these anodes by preferentially enabling water oxidation rather than lead dissolution. Still, it is poorly understood how the activity of manganese oxide as a water oxidation catalyst relates to its anticorrosive properties. Here, we show how the presence of water oxidation catalysts both formed in-situ (including the industry standard manganese oxide) and heterogenized prior to electrolysis on lead anodes affect the corrosion potential of these anodes. We find that corrosion potential under dynamic polarization conditions is the parameter most affected by the coatings formed in-situ and applied ex-situ prior to electrolysis.
Highlights
Research on water oxidation catalysts to provide protons and electrons for solar fuel production is pursued around the globe, with thousands of studies published on the topic [1]
We explore the effect of Mn2+ and Co2+ separately in solution, which form catalytic metal oxide species in-situ, and a cobalt oxide-based heterogeneous water oxidation catalyst (as a model system, we use Co-dppe (cobalt 1,2-bis(diphenylphosphino)ethane)) [11,12], which is applied as an electrode coating ex-situ prior to electrolysis, on the electrode potential of PbAg anodes
We investigate the properties of a pre-applied cobalt oxide-based catalyst, Co-dppe, to investigate how the surface electrochemistry of the Pb anodes is changed compared to the Co- and Mn-based solution phase additives that form catalytic layers in-situ
Summary
Research on water oxidation catalysts to provide protons and electrons for solar fuel production is pursued around the globe, with thousands of studies published on the topic [1]. The gap between research investment and commercial use continues to widen as solar fuel integrated systems published today face challenges producing a positive economic return. The electrochemical industry uses water oxidation and similar oxidative electrochemical half-reactions to produce metals, chlorine, and other feedstock independent of fuel. Reversible water oxidation and oxygen reduction are used in batteries, such as zinc-air batteries where reversible water oxidation catalysts improve energy efficiency [4]. Electrochemical coating processes, such as cathodic electrodeposition, where positively-charged metal ions are reduced on the surface of a substrate forming a conformal metal coating, use water oxidation to balance overall charges of the system [5]
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