Wednesday, October 29, 2014

One ALD layer can increase the efficiency of photoelectrodes for water splitting

Here is a new paper from Massimo Tallarida and co-workers group in Cottbus at Brandenburg University of Technology in collaboration with Helsinki, Tartu and Alicante. The published paper below in Journal of Physical Chemistry Letters, gives for the first time a reasonable explanation of why 1 ALD layer can increase the efficiency of photoelectrodes for water splitting, just using the chemistry of ALD (in particular, only TMA).

Modification of Hematite Electronic Properties with Trimethyl Aluminum to Enhance the Efficiency of Photoelectrodes

Massimo Tallarida, Chittaranjan Das, Dejan Cibrev, Kaupo Kukli, Aile Tamm, Mikko Ritala, Teresa Lana-Villarreal, Roberto Gómez, Markku Leskelä, and Dieter Schmeisser

J. Phys. Chem. Lett., 2014, 5 (20), pp 3582–3587
The electronic properties of hematite were investigated by means of synchrotron radiation photoemission (SR-PES) and X-ray absorption spectroscopy (XAS). Hematite samples were exposed to trimethyl aluminum (TMA) pulses, a widely used Al-precursor for the atomic layer deposition (ALD) of Al2O3. SR-PES and XAS showed that the electronic properties of hematite were modified by the interaction with TMA. In particular, the hybridization of O 2p states with Fe 3d and Fe 4s4p changed upon TMA pulses due to electron inclusion as polarons. The change of hybridization correlates with an enhancement of the photocurrent density due to water oxidation for the hematite electrodes. Such an enhancement has been associated with an improvement in charge carrier transport. Our findings open new perspectives for the understanding and utilization of electrode modifications by very thin ALD films and show that the interactions between metal precursors and substrates seem to be important factors in defining their electronic and photoelectrocatalytic properties.
The building Panta Rhei, home for the Chair of Applied Physics and Sensors (Prof. Dr. Dieter Schmeißer) at Brandenburg Universitxy of Technology. The main research area of the department is spectroscopic and micro spectroscopic investigation of layers and layer structures in order to get information about the electronic properties and the geometrical structures of several materials, such as high-k oxides, metal and mixed oxides, inter metallic interfaces, semiconductors, conducting and semiconducting polymers, and with recent focus graphene. In addition, the department is very active in the research area of atomic layer deposition (ALD). In particular the initial layer growth is in the focus of interest. The layer deposition as well as the characterization are done in situ = "(in situ)2", where the characterization can be performed "cycle by cycle". (further information)

The authors conclude that the ALD of Al2O3 based on TMA produces modifications in the electronic properties of α-Fe2O3 favoring the improvement of its photoelectrochemical behavior. Reactions between TMA and α-Fe2O3 induce electron donation to the substrate in the form of small polarons and modify the covalent character of the Fe−O bonds. These Fe2O3 surface modifications probably allow for an enhanced charge carrier transport next to the interface and explain the photoelectrochemical enhancement observed in hematite photoanodes. We believe that this work contributes to the understanding of some of the mechanisms underlying the enhancement of hematite photoanodes by means of surface modification and that it may open new avenues for further improving their performance in the context of water splitting.


A vision of a sustainable hydrogen fuel community based on Artificial photosynthesis (APS) has been described in man yplaces and in particular in a relatively recent review in Nature Photonics (here).


Vision of a sustainable hydrogen fuel community based on Artificial photosynthesis (APS) - Hydrogen is produced from an APS solar water-splitting power plant using seawater on floating ports, tankers and seashore plants. Electricity needed to operate such an infrastructure is provided by renewable energy sources such as photovoltaic, wind and tidal power. (Nature Photonics, 6 (2012) 511)