Highly Ordered Pore Structures in Photoelectrodes: Impact on the Solar Water Splitting Process

• Applicant: Dr. Marcus Einert
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 469377211

Hydrogen - produced by solar water splitting - is considered as a renewable energy source substituting fossil fuels in order to reduce CO2 emission, and thus, the worldwide climate change.The goal of the research proposal of the Walter-Benjamin program is to identify the impact of an increased surface area of copper-based photoelectrodes on the photoelectrochemical hydrogen production.This research will be addressing the question on how the ordering of nanopores in a semiconductor will affect the charge carrier mobility at the electrode-electrolyte interface. Previous research has shown that an increase in the surface area results in an enhanced contact area between the electrode and the electrolyte, which in turn could potentially lead to an improved charge carrier exchange rate and thus to a higher solar-to-hydrogen efficiency. Furthermore, it is taken into account that the “travelling distances” for the charge carriers from the point of excitation to the electrode-electrolyte interface, where the hydrogen evolution takes place, are also remarkably decreased due to the nanoporous morphology of the electrode.In contrast to the (potentially) positive impact of nanopores, increasing the surface area may also result in negative properties. A larger electrode surface area gives rise to several so-called defect states on its surface, which act as electron traps for the migrating charge carriers. As soon as the charge carriers are trapped, they are no longer capable of contributing to the hydrogen production.The objective of the proposal is therefore to synthesis porous materials by wet chemical processes via the well-known dip-coating technique, and to evaluate the influence of defect states on the photoelectrochemical hydrogen production by means of X-Ray Photoelectron Spectroscopy and Surface Photovoltage Spectroscopy. Both methods are highly suitable for the detailed determination of the presence of surface defect states and could answer the question, to what extent they influence the overall photoelectrochemical performance by electron trapping of migrating charge carriers. The materials will be prepared with distinct polymer-templates, which show up various degrees of pore ordering. Hence, the impact of pore ordering will be investigated systematically and correlated with the determined surface defect states.Finally, the obtained results will provide important structure-property relationships, which should give insight to the charge carrier transfer processes both within the bulk and on the surface of the material. The study will also assess how photoelectrodes could be further improved towards efficient solar water splitting.

• DFG Programme: WBP Position