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Durability testing of photoelectrochemical hydrogen production under day/night light cycled conditions
| Content Provider | Semantic Scholar |
|---|---|
| Author | Bae, Dowon Seger, Brian Hansen, Ole Vesborg, Peter Christian Kjærgaard Chorkendorff, Ib |
| Copyright Year | 2019 |
| Abstract | This work investigates long-term photoelectrochemical hydrogen evolution (82 days) in 1M HClO4 using a TiO2:H protected crystalline Si-based photocathode with metal-oxide-semiconductor (MOS) junctions. It is shown that day/night cycling leads to relatively rapid performance degradation while photocurrent under the continuous light condition is relatively stable. We observed that the performance loss is mainly due to contamination of catalytic surface with carbonaceous material. By ultraviolet (UV) light exposure, we also observed that the activity can be restored likely owing to the photocatalytic degradation of organics on the TiO2 protection layer. A photoelectrochemical (PEC) approach to convert solar energy to useful fuels or chemicals is highly appealing due to the fact that two processes can be integrated into a single device, thus potentially lowering capital costs. While a wide variety of PEC reactions have recently seen great interest, direct water splitting into H2 and O2 remains a good benchmarking reaction because of the facile H2 catalysis and the lack of any issues related to product selectivity. A dual absorber (tandem) approach, which uses a high band gap and low band gap photoelectrode in series, has been widely accepted to give the optimum efficiency in AM1.5 sunlight as previous modelling has shown. This field has primarily focused on optimizing the photovoltage and current needed to split water efficiently, and these efforts have borne fruit with multiple works showing greater than 10% efficient devices. Recently, attention has turned towards stability with most publications about devices having stabilities for at least 24 hours. On the other hand, long-term durability tests (> 1 month) have been much more limited. Maier et al. demonstrated relatively low, but stable photocurrent under the HER conditions for 60 days in 1M HCl using a Pt-coated crystalline silicon (c-Si), while a recent study by the Jaramillo group used a thin MoS2 protected c-Si to show durability for up to 62 days. While these long-term tests demonstrate steady state operational stability of these devices, practical devices will be subjected to daily day/night cycling, which will vary the potential at the semiconductor/protection layer/catalyst-electrolyte interface. Thus there is a need to understand how this cycling will affect stability. When an electrode is continually photoirradiated the interface between the photocathode and the electrolyte is held at a constant potential, thus stability is only measured at that potential. However, when the cell is in the dark the interface potential switches to that of the liquid. If the surface potential reaches sufficiently anodic conditions in the dark, it could potentially oxidize the semiconductor or catalyst. If this oxidized state is water soluble, this will lead to corrosion. Pourbaix diagram analysis can give an indication of where corrosion would be expected, but Pourbaix diagrams are based on thermodynamics and do not consider kinetic effects. Viz. a real system could be kinetically stable even if thermodynamics indicate instability. Thus experimental work is needed to accurately determine corrosion rates. Works by Young and Bae et al., have shown that GaAs and Si, respectively, can be effectively protected at open circuit potential in the dark. However, cycling between two potentials can sometimes cause serious corrosion as exemplified by catalyst corrosion in the PEM fuel cells. In a previous study, we presented a long-term photocathodic H2 evolution experiment in 1M HClO4 under continuous light at a fixed potential (Fig. 1a) for 41 days using a TiO2 protected MOSbased Si photocathode with Pt nanoparticles (Fig. 1b, more details are shown in the ESI†). This study is a continuation of that previous study where we continue to analyse the same electrode by starting to cycle the electrode between light and dark conditions (with frequency of 12 hours light on/off, see Fig. 1a). The advantage of using this approach is that the steady-state stability of the device under continuous light is well characterized, thus allowing us to accurately isolate the effects due purely to cycling. In other words, we have taken the electrode from ref [15] that has already operated for 41 days, and then start to cycle it between illuminated and dark conditions. The results of this experiment are shown in Fig. 2a. It shows the long-term stability (AM 1.5G with 635 nm long-pass filter, see Fig. S1) of the TiO2 protected photocathode sample measured at a [a] Dr. D. Bae, Prof. B. Seger, Prof. O. Hansen, Prof. P.C.K. Vesborg, Prof. I. Chorkendorff * Surface Physics & Catalysis (SurfCat) Department of Physics Technical University of Denmark Fysikvej B311, 2800 Kongens Lyngby (Denmark) E-mail: ibchork@fysik.dtu.dk [b] Prof. O. Hansen Department of Microand Nanotechnology Technical University of Denmark Ø rsteds Plads B344, 2800 Kongens Lyngby (Denmark) † Current address: Materials for Energy Conversion and Storage (MECS), Department of Chemical Engineering, Delft University of Technology * Corresponding author Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate)) Figure 1. Light illumination conditions (a) and schematic (b) of the TiO2 protected MOS-based c-Si photocathode (p nc-Si/SiOX/p-Si/SiOX/n nc-Si) with Pt nanoparticles used for the stability experiments. 10.1002/celc.201800918 A cc ep te d M an us cr ip t ChemElectroChem This article is protected by copyright. All rights reserved. |
| Starting Page | 106 |
| Ending Page | 109 |
| Page Count | 4 |
| File Format | PDF HTM / HTML |
| DOI | 10.1002/celc.201800918 |
| Volume Number | 6 |
| Alternate Webpage(s) | https://backend.orbit.dtu.dk/ws/portalfiles/portal/152808102/Bae_et_al_2018_ChemElectroChem.pdf |
| Alternate Webpage(s) | https://backend.orbit.dtu.dk/ws/files/152808102/Bae_et_al_2018_ChemElectroChem.pdf |
| Alternate Webpage(s) | https://orbit.dtu.dk/files/152808102/Bae_et_al_2018_ChemElectroChem.pdf |
| Alternate Webpage(s) | https://orbit.dtu.dk/ws/files/152808102/Bae_et_al_2018_ChemElectroChem.pdf |
| Alternate Webpage(s) | https://doi.org/10.1002/celc.201800918 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
