Direct evidence for the key role of protons in the protonic p-n junction using L-band EPR and polyaniline as a proton-sensitive spin probe

Due to the dependence of electrical conductivity and spin density from proton concentration (affecting the protonation degree of polyaniline molecules), polyaniline in the emeraldine base form (PANI EB) is an effective proton-sensitive spin probe, which has been used in studying of the protonic p-n junction with a L-band EPR. The method leads to the direct insight into the protonic p-n junction, including changes in proton density with bias voltage: the concentration of protons in the p-n junction area increases with forward polarization (positive at the proton-donor doped site) and decreases with the blocking polarization (in the reverse direction). The results make the first direct evidence for the key role of protons in the protonic p-n junction.