1/8CO2+H + +e =1/8CH4+1/4 H2O
pE= pE0 +lg [(PCO2/P CH4) 1/8 × aH+ ]
= pE0 – pH +1/8 lg (PCO2/P CH4)
= 2.87 –7.00 + 1/8 lg (0.35/0.65)
= -4.16
Eh = 2.303/F *（RT pE）= 2.303 ×8.314 ×298 ×
（-4.16）/96484.5
= -0.246V