Showing posts with label Water splitting. Show all posts
Showing posts with label Water splitting. Show all posts

Thursday, November 10, 2016

Researchers at Lawrence Berkeley National Laboratory integrate water-splitting catalyst with a solar cell by PEALD

Meanwhile, a team of international researchers at Lawrence Berkeley National Laboratory have been very busy taking a major steps towards artificial photosystems employing PEALD processes performed at the Molecular Foundry at Berkeley Lab.

The CoOx catalyst films were deposited in a Oxford Instruments FlexAL PEALD reactor using CoCp2 (98% Strem Chemicals) and oxygen plasma was the oxidant.

Schematic of the multi-functional water splitting catalyst layer engineered using atomic layer deposition for integration with a high-efficiency silicon cell. (Credit: Ian Sharp/Berkeley Lab)


A multifunctional biphasic water splitting catalyst tailored for integration with high-performance semiconductor photoanodes [OPEN ACCESS]
Jinhui Yang, Jason K. Cooper, Francesca M. Toma,  Karl A. Walczak, Marco Favaro, Jeffrey W. Beeman, Lucas H. Hess,  Cheng Wang, Chenhui Zhu, Sheraz Gul, Junko Yano, Christian Kisielowski, Adam Schwartzberg & Ian D. Sharp
Nature Materials doi:10.1038/nmat4794
 
Artificial photosystems are advanced by the development of conformal catalytic materials that promote desired chemical transformations, while also maintaining stability and minimizing parasitic light absorption for integration on surfaces of semiconductor light absorbers. Here, we demonstrate that multifunctional, nanoscale catalysts that enable high-performance photoelectrochemical energy conversion can be engineered by plasma-enhanced atomic layer deposition. The collective properties of tailored Co3O4/Co(OH)2 thin films simultaneously provide high activity for water splitting, permit efficient interfacial charge transport from semiconductor substrates, and enhance durability of chemically sensitive interfaces. These films comprise compact and continuous nanocrystalline Co3O4 spinel that is impervious to phase transformation and impermeable to ions, thereby providing effective protection of the underlying substrate. Moreover, a secondary phase of structurally disordered and chemically labile Co(OH)2 is introduced to ensure a high concentration of catalytically active sites. Application of this coating to photovoltaic p+n-Si junctions yields best reported performance characteristics for crystalline Si photoanodes.


Sunday, May 31, 2015

Photoelectrochemical (PEC) water splitting technology using active ALD layers for enhanced performance

Researchers from Japan, including Fujifilm Corporation, has investigated how thin ALD NiO enhance the performance of  photoelectrochemical (PEC) devices that can be used in future water splitting plants scalable production of renewable hydrogen fuels. To do so they used a BENEQ TSF reactor for deposition of the NiOx layer. There findings were published in Journal of American Chemical Society recently online (abstract below). The conclusion was that depositing NiO on the surfaces of CoOx/BiVO4 electrodes by ALD using the Beneq TFS 200 system enhanced the performance (higher current density at lower potential) for the PEC devices.


A look inside a Beneq TFS 200 reactor (www.beneq.com)

Surface Modification of CoOx Loaded BiVO4 Photoanodes with Ultrathin p-Type NiO Layers for Improved Solar Water Oxidation

Miao Zhong, Takashi Hisatomi, Yongbo Kuang, Jiao Zhao, Min Liu, Akihide Iwase, Qingxin Jia, Hiroshi Nishiyama, Tsutomu Minegishi, Mamiko Nakabayashi, Naoya Shibata, Ryo Niishiro, Chisato Katayama, Hidetaka Shibano, Masao Katayama, Akihiko Kudo, Taro Yamada, and Kazunari Domen

J. Am. Chem. Soc., 2015, 137 (15), pp 5053–5060 DOI: 10.1021/jacs.5b00256 Publication Date (Web): March 24, 2015






Depositing NiO on the surfaces of CoOx/BiVO4electrodes by atomic layer deposition (ALD) using the Beneq TFS 200 system enhanced the performance (higher current density at lower potential) for the PEC devices.

Photoelectrochemical (PEC) devices that use semiconductors to absorb solar light for water splitting offer a promising way toward the future scalable production of renewable hydrogen fuels. However, the charge recombination in the photoanode/electrolyte (solid/liquid) junction is a major energy loss and hampers the PEC performance from being efficient. Here, we show that this problem is addressed by the conformal deposition of an ultrathin p-type NiO layer on the photoanode to create a buried p/n junction as well as to reduce the charge recombination at the surface trapping states for the enlarged surface band bending. Further, the in situ formed hydroxyl-rich and hydroxyl-ion-permeable NiOOH enables the dual catalysts of CoOx and NiOOH for the improved water oxidation activity. Compared to the CoOx loaded BiVO4(CoOx/BiVO4) photoanode, the ∼6 nm NiO deposited NiO/CoOx/BiVO4 photoanode triples the photocurrent density at 0.6 VRHE under AM 1.5G illumination and enables a 1.5% half-cell solar-to-hydrogen efficiency. Stoichiometric oxygen and hydrogen are generated with Faraday efficiency of unity over 12 h. This strategy could be applied to other narrow band gap semiconducting photoanodes toward the low-cost solar fuel generation devices.

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)