Silicon nanowires' based photoanode for hydrogen evolution
Introduction
Energy and environmental issues at a global level belong to the most important topics. It is indispensable to construct clean energy systems in order to solve the issues. Hydrogen will play an important role in such systems due to the fact that it is the ultimate clean energy and it can be used in fuel cells. The use of solar energy for electricity generation and the use of this electricity for hydrogen production by alkaline water electrolysis promises to be a truly sustainable scheme for hydrogen economy [1], [2], [3].
There are several ways of solar hydrogen production and storage [4], [5], [6], [7]. One of them is the photocatalytic water splitting process, in which the photon energy is converted into chemical energy accompanied with a largely positive change in the Gibbs free energy through water splitting [8], [9], [10]. This reaction is similar to photosynthesis used by green plants because these are uphill reactions. Therefore, photocatalytic water splitting is regarded as an artificial photosynthesis and is an attractive and challenging theme in chemistry.
During the past 40 years, various photocatalyst materials have been developed to split water into H2 and O2 under UV and visible light illumination. However, efficient materials for water splitting under visible light irradiation have not been found yet. Nevertheless, new photocatalyst materials for water splitting have recently been discovered one after another. One of the perspective material is the nanocrystalline silicon, which is a surface-nanostructured Si with an extremely efficient light absorption capability [11], [12] and, regrettably, with intense charge recombination and low electrochemical stability. Nevertheless, the photocatalytic water splitting is still a challenging reaction even though the research history is long. Moreover, hydrogen produced by this process can be either stored in metal hydride or carbon nanotubes, polymers and chemical complexes for subsequent utilization [13], [14], [15].
For that reason, this work was focused on evolution of hydrogen in a newly designed (photo)electrochemical cell in which two photovoltaic panels served as the source of electric energy for long-term experiments. Specially prepared Si nanowires on molybdenum were employed as one of electrodes [16]. Subsequently, utilization of evolving hydrogen for preparation of nanoparticle catalysts together with its storage in Palladium were also tested. This method is unique since the preparation of nanoparticles can be carried out continuously without an addition of further reducing agents.
Section snippets
Preparation of Si nanowires
Si nanowires were grown on molybdenum (0.5 mm, 99.9 w/w%, Aldrich) and iron substrates (0.5 mm, 99.9w/w%, Aldrich) in a quartz tube placed in an oven. Prior to the deposition, 2 nm thick gold layers were sputtered on the substrate. First of all, the tube was evacuated using a turbo station unit (TC110 Pfeiffer Vacuum) to reach pressure lower than 5.0 10−4 Pa. Subsequently, the temperature in the oven was increased up to 500 °C and after reaching that value, silane SiH4 was allowed to enter the
Layers preparation
The deposition of silane on molybdenum, which yielded thick brown films, was applied for the electrode preparation based on Si nanowires on Mo substrate with 2 nm thick gold layers. The used preparation system provided the growth of Si nanowires with a uniform thickness profile. EDX analysis (not shown) revealed that nanowires are composed of silicon. According to the Scanning Electron Microscopy (SEM) photographs (Fig. 2a), a large part of prepared nanowires possessed the length of more than
Conclusion
The system for evolution of hydrogen by a photo-electrochemical reaction and its utilisation in preparation of nanoparticles was successfully tested. The hydrogen evolution took place at the surface of specially designed photoanode based on silicon-nanowires deposited on Mo. The photovoltaic cell was employed as the only source of electrical energy for the electrochemical cell. The electrochemical results verified the photo-electrochemical stability of the system up to 0.6 V bias against the
Acknowledgment
The support of Grant Agency of the Czech Republic (grant No. 15-14228S) and the Operational Programme Research, Development and Education of the Ministry of Education, Youth and Sports of the Czech Republic (listed as “ÚCHP Mobilita”), reg. number – CZ.02.2.69/0.0/0.0/16_027/0007931 is gratefully acknowledged.
References (24)
- et al.
Thermodynamic analysis and experimental investigation of a unique photoelectrochemical hydrogen production system
Int J Hydrogen Energy
(2018) - et al.
Investigation of hydrogen production performance of a reactor assisted by a solar pond via photoelectrochemical process
Int J Hydrogen Energy
(2018) - et al.
Solar-hydrogen: environmentally safe fuel for the future
Int J Hydrogen Energy
(2005) - et al.
Energy and exergy analyses of a novel photoelectrochemical hydrogen production system
Int J Hydrogen Energy
(2017) - et al.
Electrochemical hydrogen storage: opportunities for fuel storage, batteries, fuel cells, and supercapacitors
Int J Hydrogen Energy
(2017) - et al.
Si/ZnO core–shell nanowire arrays for photoelectrochemical water splitting
Int J Hydrogen Energy
(2011) - et al.
Nanomaterials for photoelectrochemical water splitting – review
Int J Hydrogen Energy
(2018) - et al.
Photoelectrode nanomaterials for photoelectrochemical water splitting
Int J Hydrogen Energy
(2017) - et al.
Facile fabrication of silicon nanowires as photocathode for visible-light induced photoelectrochemical water splitting
Int J Hydrogen Energy
(2017) - et al.
Silicon/TiO2 core-shell nanopillar photoanodes for enhanced photoelectrochemical water oxidation
Int J Hydrogen Energy
(2017)
Ambient temperature hydrogen storage in porous materials with exposed metal sites
Int J Hydrogen Energy
Kinetically stabilized hydrogen storage materials
Scripta Mater
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