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I am using silver oxide as a cathode because it's common. I was reading that " some solid metal oxides (e.g., silver oxide, lead dioxide, and manganese dioxide) possess high redox potentials. Manganese dioxide and lead dioxide are usually not employed as electron acceptors but as catalysts for oxygen reduction "

Silver oxide/silver (Ag2O/Ag) couple has been used for decades in alkaline batteries. The standard reduction potential of Ag2O/Ag is 0.342 V vs the standard hydrogen electrode (SHE).

What is an example of another electron acceptor metal oxide I can use that might have a higher voltage than silver oxide?

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  • $\begingroup$ There was used silver(I,III) oxide // Silver(I,III) oxide or tetrasilver tetroxide is the inorganic compound with the formula Ag4O4. It is a component of silver zinc batteries. $\endgroup$
    – Poutnik
    Apr 19, 2023 at 10:51

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A few oxides do beat silver oxide (or at least the silver(I) oxide reported in the question) in terms of reduction potential. Here, examples are given for basic solutions and for acid solutions. Reduction potential data are taken from https://wisc.pb.unizin.org/chem103and104/chapter/appendix-k-standard-electrode-potentials-in-acidic-or-basic-solutions/.

Basic solution

Nickel dioxide, $\ce{NiO2}$, is reduced to nickel(II) hydroxide at +0.49 V versus the standard hydrogen electrode with the latter at pH 0. For basic cells it would ge more appropriate to correct the hydrogen electrode voltage for a pH of 14, which the Nernst Equation renders as 0.83 V. Thus $\ce{NiO2}$ comes in at +1.32 V over the pH-14 hydrogen reduction, versus +1.17 V against tge same reference for $\ce{Ag2O}$ reduction. Note that in actual silver-zinc batteries may the silver oxide there is silver(I,III) oxide, $\ce{Ag^+(AgO2^-)}$, so the silver oxide reduction potential may be different from that given in the question.

Acidic solution

Lead dioxide should nit ge so easily dismissed. It is the electron acceptor in lead-acid batteries commonly seen in cars. Helped along by precipitating lead sulfate from the sulfuric acid solution electrolyte, $\ce{PbO2}$ reduction in that acid weighs in at +1.69 V over the hydrogen electrode in acid. $\ce{NiO2}$ reduction to nickel(II) ion in acid solution is close behind at +1.68 V, although $\ce{NiO2}$ is usually used with basic electrolytes.

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