Research On The Effect Of Electrodes And Electrolyte On H₂O₂ Open Circuit Potential

H2O2 has an higher standard reduction potential than O2, so H2O2 serves as oxidant in fuel cells has advantage than O2. However, the open circuit potential of H2O2 is usually smaller than its theoretical equilibrium potential, which leads to the lower open circuit voltage of H2O2 fuel cell.Therefore, examination of the reasons that cause H2O2 open circuit potential smaller than its theoretical equilibrium potential is of great significance for the study of H2O2 fuel cell. In this work, the effect of electrode material, pH of the electrolyte, H2O2 concentration, electrolyte anion and temperature on H2O2 open circuit potential was investigated. Also, electrode reactions occurred on the electrode surface were studied, and summarize reasons that cause open circuit potential less than the theoretical value.In acid electrolytes, the open circuit potential of H2O2 and the logarithm of acid concentration has a linear relation for Pt, Pd, Au and GC electrode. In the sulfuric acid solution, the relationship between the open circuit potential of H2O2 and the concentration of sulfuric acid was E= 0.8+0.051g(c(H2SO4)) for Pt, E= 0.797+ 0.0491g(c(H2SO4)) for Pd, E= 0.805+0.051g(c(H2SO4)) for Au, and E= 0.813+ 0.051g(c(H2SO4)) for glass carbon (GC). H2O2 open circuit potential does not vary with H2O2 concenteration. Electrolyte anions slightly influence H2O2 open circuit potential on Pt, Pd, Au and GC electrode. The increase of temperature results in a decrease of H2O2 open circuit potential. For Au and Pt electrode, the average rate of open circuit potential change with temperature was between-1.0 mV/K and-0.1 mV /K.In alkline electrolytes, relation between the open circuit potential and NaOH concentration on Pt, Pd and Au electrode obys the Nernst relationship. The slope between open circuit potential and the logarithm of NaOH concentration was 0.04～0.06. For GC electrode, the slope was -0.099, so the open circuit potential and the logarithm of NaOH concentration did not follow the Nernst relationship. The relationship between the open circuit potential of H2O2 and the concentration of NaOH was:E= 0.056-0.0591g(c(NaOH)) for Pt, E= 0.063-0.0551g(c(NaOH)) for Pd, E= 0.027-0.041g(c(NaOH)) for Au, and E=-0.008-0.0991g(c(NaOH)) for GC. In 0.1mol·-1H2O2+0.1mol·L-1 NaOH electrolyte, the rate of open circuit potential change with temperature was-1.34 mV/K on Pt electrode.Changes of H2O2 open circuit potential with the variation of the pH and H2O2 concentration were consistent with mixed potential conclutions. The results of CV, Tafel polarization curve and linear potential sweep showed that real open circuit potential of H2O2 on noble metal electrode (Pt, Pd and Au) was a mixed potential of H2O2 electro-oxidation and H2O2 electrochemical reduction. However, H2O2 real open circuit potential on GC electrode was not mixed potential. It is H2O2 electro-oxidation reaction that causes open circuit potential lower than H2O2 standard reduction potential.