Photoassisted Control of Pt Electrodeposition on p-Type Si

Abstract

A new method to control the size and distribution of electrodeposited metal on a semiconductor was investigated, using a system of Pt deposition on p-type Si. Pt is a noble metal, and electrodeposition is possible on p-type Si through hole injection to the valence band. When the Si surface is illuminated, an additional charge-transfer path becomes possible utilizing electrons photoexcited to the conduction band. The two pathways give different morphologies for the deposits. Fine and dispersed particles were electrodeposited under illumination, indicating the nucleation process was prevailing; in the dark, grown deposits were observed and the dominant process was crystal growth. We used the different deposition behavior to control the size and distribution of electrodeposits by the illumination-modulated method. Initial illumination gives nuclei of electrodeposits, and the adjustment of the duration can control the number of electrodeposits. The following electrolysis in the dark grows the deposits and can control the size. The method showed the possibility of controlling the size and distribution of Pt electrodeposits on p-type Si without changing applied potential.Recently, the hydrogen energy system is attracting a great deal of attention due to its small environmental burden, compared with the system using conventional fossil fuels. Photoelectrochemical hydrogen evolution from water on a semiconductor can play an important role in realizing a clean hydrogen society. 1,2 Many kinds of semiconductors, such as titanium dioxide or tantalum oxynitride, have been proposed as the material for solar-hydrogen evolution. These semiconductors need enhancement of electrocatalysis in some way, like the deposition of fine metal particles. 3-6 Heller has reported the use of n-GaAs, CdS, p-InP, etc. modified with particles of a noble metal ͑Pt, Ru, Rh͒ for the application to photoelectrochemical cells. 7 Si is also a possible photocathode for hydrogen evolution from water. Si has a bandgap suitable for the effective utilization of solar energy, and the position of the conduction band is suitable for hydrogen evolution in photoelectrochemical cells. However, Si has some problems in its actual use as an electrode for photoelectrochemical hydrogen evolution. First, it is corrosive in aqueous solution under illumination. Some proposals to overcome the problem have been made, for example, stabilization of the semiconductor with surface alkylation. 8,9 Second, the charge-transfer rate at a semiconductor is quite slow. 10 The size and distribution of metal particles on a semiconductor affect the electrocatalysis greatly in photoelectrochemical hydrogen evolution. 11 Nakato et al. investigated hydrogen evolution on p-Si with Pt particles. 12,13 Metal particles on a semiconductor behave as reaction centers on the semiconductor electrode. However, they also work as carrier recombination centers and reduce the energy conversion efficiency. To suppress the recombination, the size of the metal particles needs to be very fine. 14 Additiona...

Spatioselective Electrochemical and Photoelectrochemical Functionalization of Silicon Microwires with Axial p/n Junctions

“…The applied potential of −0.7 V versus Ag/AgCl (3 m NaCl) is sufficiently negative to overcompensate the provided potential of the n + /p junction under illumination (Figure S9, Supporting Information) and thus deposition occurred on both top n + ‐Si and bottom p‐Si segments simultaneously (Figure S10, Supporting Information). The particles deposited under illumination were much finer than in the dark, which is in agreement with literature . Two deposition boundaries were observed, at 2.3 and 3.4 μm from the top, with an unmodified band of 1.1 μm in between (Figure S10, Supporting Information).…”

Mesoporous Pt and Pt/Ru alloy electrocatalysts for methanol oxidation

“…The current increases observed in Fig. 1 around 100-150 s is characteristic of a growing step, as a consequence of the restriction in the diffusion of the catalysts precursors that originate the formation of a large number of embryos from which the structure will growth increasing its area [28][29][30]. The current peak decreases as the applied overpotential increases, and disappears completely at overpotentials of −300 mV for Pt and −400 mV for Pt/Ru alloys, as a consequence of the formation of smaller particles.…”

Synthesis of Bi2WO6 photoanode on transparent conducting oxide substrate with low onset potential for solar water splitting

“…p-Si photocathode was prepared from Si (111) substrate (boron doped, 0.1-0.3 U cm resistivity), and Pt was deposited on the Si electrode by electrochemical deposition under illumination with 0.04 M H 2 PtCl 6 $5.6H 2 O (Kojima Chemicals Co. Ltd., 98%) precursor solution. 27 To shi the onset potential of Si photocathode toward anodic direction, p-Si/n-Si junction was formed by doping with phosphorous on the surface of the p-Si substrate as Boettcher et al reported. 28 Spin on phosphorous dopant (Filmtronics, P509) solution was coated on the HF cleaned p-Si substrate by spin coating at 2000 rpm followed by baking at 150 C, and annealing at 950 C for 1 h. Aer the annealing, spin on dopant was removed by etching in buffered HF solution (Aldrich) before Pt electrodeposition.…”