## 4 Discussion
### Explanations in Other Literature  
As there is a lack of prior research on the use of these novel electrode materials in hydrogen peroxide fuel cells and the unavailability of advanced instrumentation, it is difficult to further investigate and precisely theorize the reasons for the newly investigated electrode behaviors. Some indirect references strengthen the hypothesis. Rare earth metals have been indirectly investigated in their reaction with hydrogen peroxide. Cerium dioxide (CeO\({}_{2}\)) and other oxides of lanthanum (La) have been used as the active catalysts in fuel cells to oxidize low molecular weight alcohol [22]. In these electrochemical reactions, the rate of oxidation reactions to the molecules adsorbed onto their surface is enhanced by these rare metal oxides, providing a localized oxygen storage capacity. This publication describes CeO\({}_{2}\)'s reaction with hydrogen peroxide using chemical Equations (6) and (7). The equations show that the oxide of Ce at lower oxidation states transform into an oxide with a high oxidation state, carrying more oxygen as an oxygen storage source. The higher oxidation state CeO\({}_{2}\) catalytically reacts with the hydrogen peroxide to return to its lower oxidation state, converting the hydrogen peroxide to water. \[2\,\mathrm{CeO}_{2}+2\,\mathrm{H}^{+}\,2\,\mathrm{e}\longrightarrow\mathrm{ Ce}_{2}\mathrm{O}_{3}+\mathrm{H}_{2}\mathrm{O} \tag{6}\]  
\[\mathrm{Ce}_{2}\mathrm{O}_{3}+\mathrm{H}_{2}\mathrm{O}\longrightarrow 2\, \mathrm{Ce}_{2}+\mathrm{H}_{2}\mathrm{O} \tag{7}\]  
Figure 12: Proposed mechanism of hydrogen peroxide redox catalysis over electrode metal oxide surfaces in acidic pH. Metals include those tested in this chapter: Dy, Tb, Er, Ho, Gd, Ta, and Sb. MeXOA and MeYOB represent different oxides of the same metal at different oxidation states. Note that the novel electrode metals introduced in this chapter favor one of oxidation or reduction over the other, and not both simultaneously to then result in disproportionation. A different report demonstrated that rare earth metals such as Ce can act similarly to the infamous Fenton reaction, catalytically reacting and decomposing hydrogen peroxide [23]. Another study examined the reaction mechanisms involved in using CeO\({}_{2}\) and gadolinium oxide to decompose hydrogen peroxide [24]. The reactions involves the adsorption of hydrogen peroxide molecules onto the metal oxide surfaces, which proceeds to its catalytic decomposition to form water and oxygen. A thin layer of the respective oxides may be forming on the electrode surfaces when inserted into the alkaline peroxide electrolyte, which then acts as a catalytic surface for the peroxide oxidation to occur. Salts of La and lanthanum-doped zinc hydroxycarbonates also catalytically induce disproportionation of hydrogen peroxide [25; 26]. Gadolinium-doped cerium oxide is reported to oxidize hydrogen peroxide to form hydroxyl radicals [27]. Therefore, existing publications indicate that the electrocatalytic activities of some rare earth metals occur from their oxides instead of the metals in their pure unreacted forms. Fewer publications investigate the electrocatalytic ability of Sb and Ta in hydrogen peroxide, as demonstrated by this experiment. One experiment observed that Sb has a higher order reaction order to form SB(OH)\({}_{4-}\) as a hydroxide byproduct [27], explaining Sb's susceptibility to corrode in alkaline peroxide solution. However, this does not explain the same corrosion without the presence of hydrogen peroxide. Sb is commonly used in simple pH meter electrodes [28; 29]. It provides a good degree of robustness to test the pH of highly alkaline and acidic solutions, where the pH function is related to the natural layer of antimony oxide formed on the electrode surface. In terms of catalytic activity, antimony oxide films have been used to produce hydrogen peroxide when an electric potential of 3.08 V is applied [30].