The original fundamental concepts at solid-electrolyte interfaces are reviewed including the traditional microcapacitor model of the Helmholtz layer¹. Theoretical approaches that expand beyond the classical dielectric model for water and solvation shells are accounted for and recent advanced experiments will be presented that enable a direct profiling of the energetics at this junction by tender x-ray synchrotron radiation photoelectron spectroscopy (TSRPES) ^2,3. Combined (photo)electrochemical and surface analytical investigations are presented. For the rectifying semiconductor - solution junction, the space charge behavior of semiconductors in concentrated electrolytes is examined and in dilute solutions, the Galvani potential profiles at metal - electrolyte junctions are followed by TSRPES. The role of truncated profiles for thinner water layers and dilute electrolytes on charge equilibration and build-up of contact potential differences is analyzed. Fig.1 shows an example of the resulting photoelectron spectroscopy tomography.

Fig.1: (left): scheme for tomographic peak sampling; (right): influence of electrostaic potential on peak width

Implications regarding charge transfer and the development of efficient devices for light - induced fuel generation are outlined and optimized structures which show unassisted water splitting are presented, obtained upon modifying the surfaces of III-V tandem absorbers. Application of (photo)electrochemically induced surface transformations ^4,5 and of re-directed (photo)corrosion reactions allows passivation of surface and interface states and increased robustness. Details of these procedures will be given. The achieved efficiencies are compared to theoretically achievable limits of solar hydrogen evolution for the respective material combinations⁶. The influence of the optical properties of the combined catalyst - electrode - solution composite structures is described and routes to more advanced multi-electron and proton transfer reactions are outlined.

 References

1. D.C. Grahame, Chem. Rev. 41 (1947) 441-501

2. M.F. Lichtermann, M.H. Richter et al., Energy Environm. Sci. 8 (2015) 2409-2416

3. M.F. Lichtermann, M.H. Richter et al., J. Electrochem. Soc. 163 (2016) H 139-146

4. H.J. Lewerenz, C. Heine et al., Energy Environm. Sci. 3 (2010) 748-760

5. M.M. May, H.J. Lewerenz et al., Nature Comm. 6 (2015) 8286

6. K.T. Fountaine, H.J. Lewerenz, H.A. Atwater, Nature Comm. 7 (2016) 13706