Extended Data Figure 5: Electrode potentials of H2O and O2 redox couples in pH 7 water, plotted on the vacuum scale.
From: Doped polymer semiconductors with ultrahigh and ultralow work functions for ohmic contacts
Conditions: neutral H2O; pressure, 1 bar (O2, H2); concentration, 1 M (H2O2, O2•−, HO•, HO2•). The reference voltage (0.00 V) on the standard hydrogen electrode (SHE) scale corresponds to 4.46 eV on the vacuum scale. Electrode potentials of O2/O2•− were computed from ref. 31; other electrode potentials were computed from ref. 32. p-doped films with ultrahigh work functions (UHWF) of greater than about 5.3 eV and n-doped films with low work functions (LWF) of less than about 5.3 eV can oxidize neutral H2O to O2, and reduce O2 to neutral H2O, respectively, and so cannot remain indefinitely stable in the presence of these species. If the oxygen reduction reaction proceeds through one-electron steps, then the relevant first one-electron couple (O2/O2•−) lies in the range 4.15–3.65 eV, depending on the dielectric medium, which opens up a stability window for films with ultralow work functions (ULWF). The stability of the films with ultralow work functions is ultimately limited by the electrode potential at the minimum practical O2 concentration during film preparation (p.p.m. range). To overcome this limitation, precursor n-dopants can be incorporated into the self-compensated platform (see main text). Conversely, the relevant first one-electron couple for water oxidation ((H+ + HO•)/H2O) lies at 6.75 eV, which opens up a stability window for films with ultrahigh work functions. DMSO, dimethyl sulfoxide; BMIM BF4, 1-butyl-3-methylimidazolium tetrafluoroborate.
