The values of standard electrode potentials are given in the table below in volts relative to the standard hydrogen electrode and are for the following conditions:
Legend: (s) – solid; (l) – liquid; (g) – gas; (aq) – aqueous (default for all charged species); (Hg) – amalgam.
Half-reaction | E° (V)[note 1] | Ref. |
---|---|---|
N2(g) + H+ + e− HN3(aq) | 3⁄2−3.09 | [1] |
Li+ + e− Li(s) | −3.0401 | [2] |
N2(g) + 4 H2O + 2 e− 2 NH2OH(aq) + 2 OH− | −3.04 | [1] |
Cs+ + e− Cs(s) | −3.026 | [2] |
Rb+ + e− Rb(s) | −2.98 | [2] |
K+ + e− K(s) | −2.931 | [2] |
Ba2+ + 2 e− Ba(s) | −2.912 | [2] |
La(OH)3(s) + 3 e− La(s) + 3 OH− | −2.90 | [2] |
Sr2+ + 2 e− Sr(s) | −2.899 | [2] |
Ca2+ + 2 e− Ca(s) | −2.868 | [2] |
Eu2+ + 2 e− Eu(s) | −2.812 | [2] |
Ra2+ + 2 e− Ra(s) | −2.8 | [2] |
Na+ + e− Na(s) | −2.71 | [2][3] |
La3+ + 3 e− La(s) | −2.379 | [2] |
Y3+ + 3 e− Y(s) | −2.372 | [2] |
Mg2+ + 2 e− Mg(s) | −2.372 | [2] |
ZrO(OH)2(s) + H2O + 4 e− Zr(s) + 4 OH− | −2.36 | [2] |
Al(OH)4− + 3 e− Al(s) + 4 OH− | −2.33 | |
Al(OH)3(s) + 3 e− Al(s) + 3 OH− | −2.31 | |
H2(g) + 2 e− 2 H− | −2.25 | |
Ac3+ + 3 e− Ac(s) | −2.20 | |
Be2+ + 2 e− Be(s) | −1.85 | |
U3+ + 3 e− U(s) | −1.66 | [4] |
Al3+ + 3 e− Al(s) | −1.66 | [3] |
Ti2+ + 2 e− Ti(s) | −1.63 | [3] |
ZrO2(s) + 4 H+ + 4 e− Zr(s) + 2 H2O | −1.553 | [2] |
Zr4+ + 4 e− Zr(s) | −1.45 | [2] |
Ti3+ + 3 e− Ti(s) | −1.37 | [5] |
TiO(s) + 2 H+ + 2 e− Ti(s) + H2O | −1.31 | |
Ti2O3(s) + 2 H+ + 2 e− 2 TiO(s) + H2O | −1.23 | |
Zn(OH)42− + 2 e− Zn(s) + 4 OH− | −1.199 | [2] |
Mn2+ + 2 e− Mn(s) | −1.185 | [2] |
Fe(CN)64− + 6 H+ + 2 e− Fe(s) + 4HCN(aq) | −1.16 | [6] |
Te(s) + 2 e− Te2− | −1.143 | [7] |
V2+ + 2 e− V(s) | −1.13 | [7] |
Nb3+ + 3 e− Nb(s) | −1.099 | |
Sn(s) + 4 H+ + 4 e− SnH4(g) | −1.07 | |
SiO2(s) + 4 H+ + 4 e− Si(s) + 2 H2O | −0.91 | |
B(OH)3(aq) + 3 H+ + 3 e− B(s) + 3 H2O | −0.89 | |
Fe(OH)2(s) + 2 e− Fe(s) + 2 OH− | −0.89 | [6] |
Fe2O3(s) + 3 H2O + 2 e− 2Fe(OH)2(s) + 2 OH− | −0.86 | [6] |
TiO2+ + 2 H+ + 4 e− Ti(s) + H2O | −0.86 | |
H2O + 2 e− H2(g) + 2 OH− | 2−0.8277 | [2] |
Bi(s) + 3 H+ + 3 e− BiH3 | −0.8 | [2] |
Zn2+ + 2 e− Zn(Hg) | −0.7628 | [2] |
Zn2+ + 2 e− Zn(s) | −0.7618 | [2] |
Ta2O5(s) + 10 H+ + 10 e− 2 Ta(s) + 5 H2O | −0.75 | |
Cr3+ + 3 e− Cr(s) | −0.74 | |
e− Au(s) + 2 CN− | [Au(CN)2]− +−0.60 | |
Ta3+ + 3 e− Ta(s) | −0.6 | |
PbO(s) + H2O + 2 e− Pb(s) + 2 OH− | −0.58 | |
TiO2(s) + 2 H+ + 2 e− Ti2O3(s) + H2O | 2−0.56 | |
Ga3+ + 3 e− Ga(s) | −0.53 | |
U4+ + e− U3+ | −0.52 | [4] |
H3PO2(aq) + H+ + e− P(white)[note 2] + 2 H2O | −0.508 | [2] |
H+ + 2 e− H3PO2(aq) + H2O | H3PO3(aq) + 2−0.499 | [2] |
H3PO3(aq) + 3 H+ + 3 e− P(red)[note 2] + 3 H2O | −0.454 | [2] |
Fe2+ + 2 e− Fe(s) | −0.44 | [3] |
CO2(g) + 2 H+ + 2 e− HOOCCOOH(aq) | 2−0.43 | |
Cr3+ + e− Cr2+ | −0.42 | |
Cd2+ + 2 e− Cd(s) | −0.40 | [3] |
GeO2(s) + 2 H+ + 2 e− GeO(s) + H2O | −0.37 | |
Cu2O(s) + H2O + 2 e− 2 Cu(s) + 2 OH− | −0.360 | [2] |
PbSO4(s) + 2 e− Pb(s) + SO42− | −0.3588 | [2] |
PbSO4(s) + 2 e− Pb(Hg) + SO42− | −0.3505 | [2] |
Eu3+ + e− Eu2+ | −0.35 | [4] |
In3+ + 3 e− In(s) | −0.34 | [7] |
Tl+ + e− Tl(s) | −0.34 | [7] |
Ge(s) + 4 H+ + 4 e− GeH4(g) | −0.29 | |
Co2+ + 2 e− Co(s) | −0.28 | [2] |
H3PO4(aq) + 2 H+ + 2 e− H3PO3(aq) + H2O | −0.276 | [2] |
V3+ + e− V2+ | −0.26 | [3] |
Ni2+ + 2 e− Ni(s) | −0.25 | |
As(s) + 3 H+ + 3 e− AsH3(g) | −0.23 | [7] |
AgI(s) + e− Ag(s) + I− | −0.15224 | [2] |
MoO2(s) + 4 H+ + 4 e− Mo(s) + 2 H2O | −0.15 | |
Si(s) + 4 H+ + 4 e− SiH4(g) | −0.14 | |
Sn2+ + 2 e− Sn(s) | −0.13 | |
O2(g) + H+ + e− HO2•(aq) | −0.13 | |
Pb2+ + 2 e− Pb(s) | −0.13 | [3] |
WO2(s) + 4 H+ + 4 e− W(s) + 2 H2O | −0.12 | |
P(red) + 3 H+ + 3 e− PH3(g) | −0.111 | [2] |
H+ + 2 e− HCOOH(aq) | CO2(g) + 2−0.11 | |
Se(s) + 2 H+ + 2 e− H2Se(g) | −0.11 | |
H+ + 2 e− CO(g) + H2O | CO2(g) + 2−0.11 | |
SnO(s) + 2 H+ + 2 e− Sn(s) + H2O | −0.10 | |
SnO2(s) + 2 H+ + 2 e− SnO(s) + H2O | −0.09 | |
WO3(aq) + 6 H+ + 6 e− W(s) + 3 H2O | −0.09 | [7] |
P(white) + 3 H+ + 3 e− PH3(g) | −0.063 | [2] |
Fe3+ + 3 e− Fe(s) | −0.04 | [6] |
HCOOH(aq) + 2 H+ + 2 e− HCHO(aq) + H2O | −0.03 | |
H+ + 2 e− H2(g) | 20.0000 | ≡ 0 |
AgBr(s) + e− Ag(s) + Br− | +0.07133 | [2] |
S4O62− + 2 e− 2 S2O32− | +0.08 | |
Fe3O4(s) + 8 H+ + 8 e− 3 Fe(s) + 4 H2O | +0.085 | [8] |
N2(g) + 2 H2O + 6 H+ + 6 e− 2 NH4OH(aq) | +0.092 | |
HgO(s) + H2O + 2 e− Hg(l) + 2 OH− | +0.0977 | |
Cu(NH3)42+ + e− Cu(NH3)2+ + 2 NH3 | +0.10 | [7] |
Ru(NH3)63+ + e− Ru(NH3)62+ | +0.10 | [4] |
N2H4(aq) + 4 H2O + 2 e− 2 NH4+ + 4 OH− | +0.11 | [1] |
H2MoO4(aq) + 6 H+ + 6 e− Mo(s) + 4 H2O | +0.11 | |
Ge4+ + 4 e− Ge(s) | +0.12 | |
C(s) + 4 H+ + 4 e− CH4(g) | +0.13 | [7] |
HCHO(aq) + 2 H+ + 2 e− CH3OH(aq) | +0.13 | |
S(s) + 2 H+ + 2 e− H2S(g) | +0.14 | |
Sn4+ + 2 e− Sn2+ | +0.15 | |
Cu2+ + e− Cu+ | +0.159 | [7] |
H+ + 2 e− SO2(aq) + 2 H2O | HSO4− + 3+0.16 | |
UO22+ + e− UO2+ | +0.163 | [4] |
H+ + 2 e− SO2(aq) + 2 H2O | SO42− + 4+0.17 | |
TiO2+ + 2 H+ + e− Ti3+ + H2O | +0.19 | |
SbO+ + 2 H+ + 3 e− Sb(s) + H2O | +0.20 | |
AgCl(s) + e− Ag(s) + Cl− | +0.22233 | [2] |
H+ + 3 e− As(s) + 3 H2O | H3AsO3(aq) + 3+0.24 | |
GeO(s) + 2 H+ + 2 e− Ge(s) + H2O | +0.26 | |
UO2+ + 4 H+ + e− U4+ + 2 H2O | +0.273 | [4] |
Re3+ + 3 e− Re(s) | +0.300 | |
Bi3+ + 3 e− Bi(s) | +0.308 | [2] |
VO2+ + 2 H+ + e− V3+ + H2O | +0.34 | |
Cu2+ + 2 e− Cu(s) | +0.340 | [7] |
e− [Fe(CN)6]4− | [Fe(CN)6]3− ++0.36 | |
O2(g) + 2 H2O + 4 e− 4 OH−(aq) | +0.40 | [3] |
H+ + 3 e− Mo3+ + 2 H2O | H2MoO4 + 6+0.43 | |
H+ + 2 e− CH4(g) + H2O | CH3OH(aq) + 2+0.50 | |
H+ + 4 e− S(s) + 2 H2O | SO2(aq) + 4+0.50 | |
Cu+ + e− Cu(s) | +0.520 | [7] |
CO(g) + 2 H+ + 2 e− C(s) + H2O | +0.52 | |
I3− + 2 e− 3 I− | +0.53 | [3] |
I2(s) + 2 e− 2 I− | +0.54 | [3] |
e− Au(s) + 4 I− | [AuI4]− + 3+0.56 | |
H+ + 2 e− H3AsO3(aq) + H2O | H3AsO4(aq) + 2+0.56 | |
e− Au(s) + 2 I− | [AuI2]− ++0.58 | |
MnO4− + 2 H2O + 3 e− MnO2(s) + 4 OH− | +0.59 | |
S2O32 − + 6 H+ + 4 e− 2 S(s) + 3 H2O | +0.60 | |
Fc+ + e− Fc(s) | +0.641 | [9] |
H+ + 2 e− MoO2(s) + 2 H2O | H2MoO4(aq) + 2+0.65 | |
H+ + 2 e− | + 2+0.6992 | [2] |
O2(g) + 2 H+ + 2 e− H2O2(aq) | +0.70 | |
Tl3+ + 3 e− Tl(s) | +0.72 | |
PtCl62− + 2 e− PtCl42− + 2 Cl− | +0.726 | [4] |
H+ + 4 e− Se(s) + 3 H2O | H2SeO3(aq) + 4+0.74 | |
PtCl42− + 2 e− Pt(s) + 4 Cl− | +0.758 | [4] |
Fe3+ + e− Fe2+ | +0.77 | |
Ag+ + e− Ag(s) | +0.7996 | [2] |
Hg22+ + 2 e− 2 Hg(l) | +0.80 | |
NO3−(aq) + 2 H+ + e− NO2(g) + H2O | +0.80 | |
FeO42− + 5 H2O + 6 e− Fe2O3(s) + 10 OH− | +0.81 | [6] |
e− Au(s) + 4 Br− | [AuBr4]− + 3+0.85 | |
Hg2+ + 2 e− Hg(l) | +0.85 | |
MnO4− + H+ + e− HMnO4− | +0.90 | |
Hg2+ + 2 e− Hg22+ | 2+0.91 | [7] |
Pd2+ + 2 e− Pd(s) | +0.915 | [4] |
e− Au(s) + 4 Cl− | [AuCl4]− + 3+0.93 | |
MnO2(s) + 4 H+ + e− Mn3+ + 2 H2O | +0.95 | |
e− Au(s) + 2 Br− | [AuBr2]− ++0.96 | |
H2O + 2 e− + [HXeO4]− + 4 OH− | [HXeO6]3− + 2+0.99 | [10] |
H6TeO6(aq) + 2 H+ + 2 e− TeO2(s) + 4 H2O | +1.02 | [11] |
Br2(l) + 2 e− 2 Br− | +1.066 | [2] |
Br2(aq) + 2 e− 2 Br− | +1.0873 | [2] |
H+ + 4 e− HIO(aq) + 2 H2O | IO3− + 5+1.13 | |
e− Au(s) + 2 Cl− | [AuCl2]− ++1.15 | |
H+ + 2 e− H2SeO3(aq) + H2O | HSeO4− + 3+1.15 | |
Ag2O(s) + 2 H+ + 2 e− 2 Ag(s) + H2O | +1.17 | |
ClO3− + 2 H+ + e− ClO2(g) + H2O | +1.18 | |
H2O + 8 e− Xe(g) + 11 OH− | [HXeO6]3− + 5+1.18 | [10] |
Pt2+ + 2 e− Pt(s) | +1.188 | [4] |
ClO2(g) + H+ + e− HClO2(aq) | +1.19 | |
IO3− + 12 H+ + 10 e− I2(s) + 6 H2O | 2+1.20 | |
ClO4− + 2 H+ + 2 e− ClO3− + H2O | +1.20 | |
O2(g) + 4 H+ + 4 e− 2 H2O | +1.229 | [3] |
MnO2(s) + 4 H+ + 2 e− Mn2+ + 2 H2O | +1.23 | |
H2O + 6 e− Xe(g) + 7 OH− | [HXeO4]− + 3+1.24 | [10] |
Tl3+ + 2 e− Tl+ | +1.25 | |
Cr2O72− + 14 H+ + 6 e− 2 Cr3+ + 7 H2O | +1.33 | |
Cl2(g) + 2 e− 2 Cl− | +1.36 | [3] |
CoO2(s) + 4 H+ + e− Co3+ + 2 H2O | +1.42 | |
NH3O H+ + H+ + 2 e− N2H5+ + 2 H2O | 2+1.42 | [1] |
HIO(aq) + 2 H+ + 2 e− I2(s) + 2 H2O | 2+1.44 | |
Ce4+ + e− Ce3+ | +1.44 | |
BrO3− + 5 H+ + 4 e− HBrO(aq) + 2 H2O | +1.45 | |
β-PbO2(s) + 4 H+ + 2 e− Pb2+ + 2 H2O | +1.460 | [7] |
H+ + 2 e− Pb2+ + 2 H2O | α-PbO2(s) + 4+1.468 | [7] |
BrO3− + 12 H+ + 10 e− Br2(l) + 6 H2O | 2+1.48 | |
H+ + 10 e− Cl2(g) + 6 H2O | 2ClO3− + 12+1.49 | |
MnO4− + 8 H+ + 5 e− Mn2+ + 4 H2O | +1.51 | |
H+ + e− H2O2(aq) | HO2• ++1.51 | |
Au3+ + 3 e− Au(s) | +1.52 | |
NiO2(s) + 4 H+ + 2 e− Ni2+ + 2 OH− | +1.59 | |
HClO(aq) + 2 H+ + 2 e− Cl2(g) + 2 H2O | 2+1.63 | |
Ag2O3(s) + 6 H+ + 4 e− 2 Ag+ + 3 H2O | +1.67 | |
H+ + 2 e− HClO(aq) + H2O | HClO2(aq) + 2+1.67 | |
Pb4+ + 2 e− Pb2+ | +1.69 | [7] |
MnO4− + 4 H+ + 3 e− MnO2(s) + 2 H2O | +1.70 | |
AgO(s) + 2 H+ + e− Ag+ + H2O | +1.77 | |
H2O2(aq) + 2 H+ + 2 e− 2 H2O | +1.78 | |
Co3+ + e− Co2+ | +1.82 | |
Au+ + e− Au(s) | +1.83 | [7] |
BrO4− + 2 H+ + 2 e− BrO3− + H2O | +1.85 | |
Ag2+ + e− Ag+ | +1.98 | [7] |
S2O82− + 2 e− 2 SO42− | +2.010 | [2] |
O3(g) + 2 H+ + 2 e− O2(g) + H2O | +2.075 | [4] |
H+ + 2 e− MnO2(s) + 2 H2O | HMnO4− + 3+2.09 | |
XeO3(aq) + 6 H+ + 6 e− Xe(g) + 3 H2O | +2.12 | [10] |
H+ + 8 e− Xe(g) + 6 H2O | H4XeO6(aq) + 8+2.18 | [10] |
FeO42− + 3 e− + 8 H+ Fe3+ + 4 H2O | +2.20 | [12] |
XeF2(aq) + 2 H+ + 2 e− Xe(g) + 2HF(aq) | +2.32 | [10] |
H+ + 2 e− XeO3(aq) + H2O | H4XeO6(aq) + 2+2.42 | [10] |
F2(g) + 2 e− 2 F− | +2.87 | [7][3] |
F2(g) + 2 H+ + 2 e− 2 HF(aq) | +3.05 | [7] |
Oxidative phosphorylation is the means by which organism generate energy, and is driven by differences in electrode potential between intermediaries in a chain of reactions.
The following values are calculated for pH 7, which is more biologically realistic, but makes the values incompatible with the values in the table above with standard criteria.
Respiratory enzyme | Redox pair | Midpoint potential
(Volts) |
---|---|---|
NADH dehydrogenase | NAD+ / NADH | −0.32[13] |
Succinate dehydrogenase | FMN or FAD / FMNH2 or FADH2 | −0.20[13] |
Cytochrome bc1 complex | Coenzyme Q10ox / Coenzyme Q10red | +0.06[13] |
Cytochrome bc1 complex | Cytochrome box / Cytochrome bred | +0.12[13] |
Complex IV | Cytochrome cox / Cytochrome cred | +0.22[13] |
Complex IV | Cytochrome aox / Cytochrome ared | +0.29[13] |
Complex IV | O2 / HO− | +0.82[13] |