Water splitting technology is characterized by a process that uses a chemical reaction to separate water (H2O) into oxygen and hydrogen. Effective water splitting can be achieved using a number of different techniques including electrolysis, photosynthesis, photoeclectrochemical, photocatalytic, radiolysis, photobiological, and thermolysis. Highly conformal ALD has proven critical to optimize cell efficiencies as latest achievements have focused on the use of nanoparticles and thin film catalysts to split water at lower reaction temperatures. Economical and efficient water splitting is a critical component for hydrogen generation as an alternative energy source. Research in this field will investigate and test the feasibility of transitioning to a hydrogen economy.
Photo-oxidation of water
Atomic layer deposition techniques can be used to create high surface area structures for wafer splitting applications. The fabrication of high surface area conducting and transparent frameworks were developed for the photo-oxidation of water (water splitting).
Atomic Layer Deposition (ALD) films using the Savannah S200 were deposited using the Exposure mode technique for ITO and Fe2O3 on inverse opal structures, to generate a high surface area nanostructure.
ALD Benefits for Water Splitting
Excellent conformality over 3D nanostructures
High quality pinhole-free films
Nanolaminate and doped films available
Wide range of functional materials including TCOs, iron oxide, insulators
High specific surface area transparent and conducting frameworks for
photo-oxidation of water. Iron oxide Fe2O3, ITO and SiO2 are deposited by ALD on
an inverse scaffold structure.
Ref: Riha, S. C, et al.. Acs Appl Mater Inter5, 360–367 (2013).
Indium-tin oxide (ITO) using InCp, TDMASn, and O3
Ferrocene (Fe2O3) using FeCp2 and O3
Highly transparent, large surface area nanolaminate stacks were created for water
splitting using ALD techniques.
The onset of water oxidation was shifted by -200 mV and the photocurrent at
1.53 V vs. the reversible hydrogen electrode was tripled. (compared with
Greenlight water oxidation via Ti substitution in Fe2O3
Ti alloying was used to improve ultrathin (6 nm thick) hematite conversion
efficiencies, in particular the hole collection efficiency generated by green
photons ( 500 – 600 nm). The Savannah S200 was used to deposit films of both
TiO2 and Fe2O3 in this study.
Titanium alloying of Fe2O3 is used to increase to improve catalytic utilization for photoelectrochemical oxidation of water
Ref: Kim, D. W. et al. Greenlighting Photoelectrochemical Oxidation of Water by Iron Oxide. ACS Nano 141203161851003 (2014).
Ti substitution in ultrathin Fe2O3 increases the lifetime of surface-localized holes.
Increased photocurrent performance was observed with the Ti-substituted films.
Enhanced absorbed photon-to-current efficiency (APCE) was observed,
particularly in the 500 - 600 nm range.
No change was observed in optical absorption.
REFERENCES – Recent publications done on Ultratech CNT ALD platforms
Dias, P. et al. Transparent Cuprous Oxide Photocathode Enabling a Stacked Tandem Cell for Unbiased Water Splitting. Adv. Energy Mater. n/a–n/a (2015). doi:10.1002/aenm.201501537
Luo, J. et al. Targeting Ideal Dual‐Absorber Tandem Water Splitting Using Perovskite Photovoltaics and CuInxGa1‐xSe2 Photocathodes. Adv. Energy Mater. (2015). doi:10.1002/aenm.201501520
Landsmann, S. et al. Design Guidelines for High-Performance Particle-Based Photoanodes for Water Splitting: Lanthanum Titanium Oxynitride as a Model. ChemSusChem n/a–n/a (2015). doi:10.1002/cssc.201500830
Barreca, D. et al. Fe2O3–TiO2 Nano‐heterostructure Photoanodes for Highly Efficient Solar Water Oxidation. Advanced Materials Interfaces n/a–n/a (2015). doi:10.1002/admi.201500313
Michaux, K. E. et al. Visible Photoelectrochemical Water Splitting Based on a Ru(II) Polypyridyl Chromophore and Iridium Oxide Nanoparticle Catalyst. The Journal of … (2015). doi:10.1021/acs.jpcc.5b05711
Luo, J. et al. Solution Transformation of Cu2O into CuInS2 for Solar Water Splitting. Nano Lett15, 1395–1402 (2015).
Schoen, D. T., Atre, A. C., García-Etxarri, A., Dionne, J. A. & Brongersma, M. L. Probing Complex Reflection Coefficients in One-Dimensional Surface Plasmon Polariton Waveguides and Cavities Using STEM EELS. Nano Lett15, 1–8 (2014).
Kim, D. W. et al. Greenlighting Photoelectrochemical Oxidation of Water by Iron Oxide. ACS Nano 141203161851003 (2014). doi:10.1021/nn503869n
Azevedo, J. et al. On the stability enhancement of cuprous oxide water splitting photocathodes by low temperature steam annealing. Energy Environ. Sci.7, 4044–4052 (2014).
Yang, X. et al. Improving Hematite-based Photoelectrochemical Water Splitting with Ultrathin TiO 2by Atomic Layer Deposition. Acs Appl Mater Inter 140804065734002 (2014). doi:10.1021/am500948t
Klahr, B. & Hamann, T. Water Oxidation on Hematite Photoelectrodes: Insight into the Nature of Surface States through In Situ Spectroelectrochemistry. J. Phys. Chem. C118, 10393–10399 (2014).
Zandi, O., Beardslee, J. A. & Hamann, T. Substrate Dependent Water Splitting with Ultrathin α-Fe 2O 3Electrodes. J. Phys. Chem. C 140501145249004 (2014). doi:10.1021/jp4116657
Tilley, D. S. & Grätzel, M. Ruthenium Oxide Hydrogen Evolution Catalysis on Composite Cuprous Oxide Water-Splitting Photocathodes. Advanced Functional … 1–9 (2014). doi:10.1002/adfm201301106
Yang, X., Du, C., Liu, R., Xie, J. & Wang, D. Balancing photovoltage generation and charge-transfer enhancement for catalyst-decorated photoelectrochemical water splitting: A case study of the hematite/MnOx combination. Journal of Catalysis304, 86–91 (2013).
Liu, M., Nam, C.-Y., Black, C. T., Kamcev, J. & Zhang, L. Enhancing Water Splitting Activity and Chemical Stability of Zinc Oxide Nanowire Photoanodes with Ultrathin Titania Shells. J. Phys. Chem. C 130610143036005 (2013). doi:10.1021/jp404032p
Riha, S. C. et al. Atomic Layer Deposition of a Sub-Monolayer Catalyst for the Enhanced Photoelectrochemical Performance of Water Oxidation with Hematite. ACS Nano 130212010712000 (2013). doi:10.1021/nn305639z
Riha, S. C., DeVries Vermeer, M. J., Pellin, M. J., Hupp, J. T. & Martinson, A. B. F. Hematite-based Photo-oxidation of Water Using Transparent Distributed Current Collectors. Acs Appl Mater Inter5, 360–367 (2013).
Klug, J. A. et al. Low temperature atomic layer deposition of highly photoactive hematite using iron(iii) chloride and water. J. Mater. Chem. A1, 11607 (2013).
Maijenburg, A. W. et al. Electrochemical synthesis of coaxial TiO2-Ag nanowires and their application in photocatalytic water splitting. J. Mater. Chem. A (2013). doi:10.1039/c3ta14551d
Klahr, B., Gimenez, S., Fabregat-Santiago, F., Bisquert, J. & Hamann, T. W. Photoelectrochemical and Impedance Spectroscopic Investigation of Water Oxidation with ‘Co–Pi’-Coated Hematite Electrodes. J Am Chem Soc134, 16693–16700 (2012).
Paracchino, A. et al. Ultrathin films on copper(I) oxide water splitting photocathodes: a study on performance and stability. Energy & Environmental Science5, 8673–8681 (2012).
Klahr, B., Gimenez, S., Fabregat-Santiago, F., Bisquert, J. & Hamann, T. W. Electrochemical and photoelectrochemical investigation of water oxidation with hematite electrodes. Energy & Environmental Science5, 7626–7636 (2012).
Klahr, B. M., Martinson, A. B. F. & Hamann, T. W. Photoelectrochemical Investigation of Ultrathin Film Iron Oxide Solar Cells Prepared by Atomic Layer Deposition. Langmuir27, 461–468 (2011).
Liu, R. et al. Water Splitting by Tungsten Oxide Prepared by Atomic Layer Deposition and Decorated with an Oxygen-Evolving Catalyst. Angew. Chem. Int. Ed.50, 499–502 (2010).