However, one obstacle for the wide application of the KPFM on electrochemical systems is the interpretation of the measured CPD on mixed ionic-electronic conductors (MIECs). These conductors play a major role for all solid electrolytes in batteries and for light-absorbing active layers in perovskite solar cells. In contrast to MIECs, the CPD is well defined for electron and hole conducting samples, which are either metals or semiconductors. In this case, the CPD signal results from the difference of the electronic work function between tip and sample. However, a clear attribution of the measured CPD value to electrochemical parameters in the case of MIECs is missing.
Therefore, we investigate a possible influence of the ions’ electrochemical potential on the measured KPFM signal. For this purpose, KPFM is performed on Wagner-Hebb cells. They comprise one reversible electrode, a solid electrolyte and an ion-blocking electrode. Typically, such cells are used for determining the electronic conductivity [3]. After initial polarization, the ionic contribution of the current vanishes in the steady-state and only the electronic current is present. Thus Wagner-Hebb cells allow to separate electronic and ionic influences on the KPFM signal. In this context, CPD maps obtained on Wagner-Hebb cells and their indications on the origin of the CPD on MIECs are discussed.
References:
[1] H. Masuda, K. Matsushita, D. Ito, D. Fujita and N. Ishida, Commun Chem, 2(1) (2019).
[2] S. A. L. Weber, I. M. Hermes, S.-H. Turren-Cruz, C. Gort, V. W. Bergmann, L. Gilson, A. Hagfeldt, M. Graetzel, W. Tress and R. Berger, Energy Environ. Sci., 11(9), 2404–2413 (2018).
[3] I. Riess, Solid State Ionics, 157(1-4), 1–17 (2003).