Project 5

Development of catalysts, namely manganese oxides and molybdenum sulphides, for an implementation in a light-driven water-splitting device using a multi-junction solar cell

  • Prof. Dr. Holger Dau, Freie Universität Berlin, Fachbereich Physik, Institut für Experimentalphysik
  • Prof. Dr. Sebastian Fiechter, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
  • Prof. Dr. Philipp Kurz, Albert-Ludwigs-Universität Freiburg, Institut für Anorganische und Analytische Chemie

This project aims at precious-metal-free catalysts suitable for implementation in a light-driven device for producing H2, as a 'solar fuel', from water. The envisioned device comprises:

a) amorphous Mn oxides for water oxidation catalysis,

b) Mo sulphides for catalysis of proton reduction, and

c) a multi-junction semiconductor system for light-induced generation of an electrical potential difference.

Structural and functional investigations will facilitate a knowledge-guided optimisation of the catalysts, which are functional mimics of metalloenzymes and of high interest also for employment in other water-splitting systems. We are aiming at bio-inspired and thus precious-metal-free catalysts, which could facilitate large-scale application unhindered by raw-material scarcity. The anodic and cathodic catalysts are investigated separately by combining electrochemistry with spectroscopy. Atomic structures and oxidation states of the mostly amorphous catalysts are investigated X-ray absorption spectroscopy (XAS). As a proof-of-principle, a complete hybrid cell will be assembled and studied in detail.

Our main focus of the first funding period has been basic insights in structure-activity relations of Mn-based OER (oxygen evolution reaction) and MoSx-based HER (hydrogen evolution reaction) electrocatalysts deposited on inert electrodes. In the second funding period, we plan to go ahead using the now established combination of

(i) catalyst synthesis,

(ii) functional characterisation,

(iii) investigation of the atomic structure, and

(iv) catalyst operation in a photovoltaic test system.

We will continue with a research strategy that aims at basic insights rather than merely empirical catalyst and device optimisation, but will shift focus towards matching the requirements of the catalyst materials with those of the solar-cell. Our central objectives for the second funding period are:

(1) knowledge-guided catalyst modification of Mn-based OER and MoSx-based HER catalysts for improved compatibility with the current-voltage properties of an irradiated multi-junction solar cell; (2) improved methods for the stable immobilisation (deposition) of the electrocatalysts on the contact layers of the solar cell assembly;

(3) insights into the electrolyte requirements for efficient OER and HER electrocatalysis with focus on the role of pH regime, proton-accepting ions, and compatibility with the photovoltaic system;

(4) operation of test systems for light-driven H2-formation comprising triple-junction PV cells and earth-abundant catalyst materials based on manganese and molybdenum.