The Role of Silicate Enrichment on the Discharge Duration of Silicon-Air Batteries.

Silicon-air batteries are candidates for next generation batteries from non-critical raw materials. However, current silicon-air batteries with alkaline electrolytes suffer from premature termination of the discharge process. To understand this process, we investigated the correlation of dissolved silicon in the electrolyte and the discharge duration until passivation. The air- and Si-electrode could be excluded as the source of the voltage drop, while the concentration of silicates in the electrolyte was identified as the decisive factor. A low silicate concentration in the electrolyte was found to be crucial for a sustained discharge of silicon-air batteries with alkaline electrolytes and full consumption of the silicon electrode used in these conditions was shown.

Atomic Layer Deposition of Cobalt Phosphide for Efficient Water Splitting.

Transition-metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co-P films were deposited by using PH3 plasma as the phosphorus source and an extra H2 plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self-limited layer-by-layer growth, and the deposited Co-P films were highly pure and smooth. The Co-P films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar Co-P films prepared by the traditional post-phosphorization method. Moreover, the deposition of ultrathin Co-P films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex three-dimensional (3D) architectures.

Photoelectrochemical hydrogen evolution of tapered silicon nanowires.

The origin of the photocurrent enhancement and the overpotential reduction in solar water splitting employing nanostructured silicon is still a matter of debate. A set of tapered Si nanowires (SiNWs) has been designed for clarifying the impact of nanostructured Si on the hydrogen evolution reaction (HER) while precisely tailoring several interference factors such as surface area, light absorption and surface defect density. We find that defect passivation by KOH achieved by tapering is much more beneficial than the optical gain. Surfactant-mediated modification of SiNWs is capable of engineering the band structure. As a result, we suggest a guideline for nanostructured Si photoelectrodes optimized for the HER.

CMOS-compatible metal-stabilized nanostructured Si as anodes for lithium-ion microbatteries.

The properties of fully complementary metal-oxide semiconductor (CMOS)-compatible metal-coated nanostructured silicon anodes for Li-ion microbatteries have been studied. The one-dimensional nanowires on black silicon (nb-Si) were prepared by inductively coupled plasma (ICP) etching and the metal (Au and Cu) coatings by successive magnetron sputtering technique. The Cu-coated nb-Si show the most promising electrochemical performance enhancements for the initial specific capacity as well as their cyclability compared to pristine nb-Si. The electrochemical and microstructural properties before and after cycling of the metal-coated nb-Si compared to their pristine counterparts are discussed in detail.

Automated spray coating process for the fabrication of large-area artificial opals on textured substrates.

3D photonic crystals, such as opals, have been shown to have a high potential to increase the efficiency of solar cells by enabling advanced light management concepts. However, methods which comply with the demands of the photovoltaic industry for integration of these structures, i. e. the fabrication in a low-cost, fast, and large-scale manner, are missing up to now. In this work, we present the spray coating of a colloidal suspension on textured substrates and subsequent drying. We fabricated opaline films of much larger lateral dimensions and in much shorter times than what is possible using conventional opal fabrication methods.

Upgraded silicon nanowires by metal-assisted etching of metallurgical silicon: a new route to nanostructured solar-grade silicon.

Through metal-assisted chemical etching (MaCE), superior purification of dirty Si is observed, from 99.74 to 99.9884% for metallurgical Si and from 99.999772 to 99.999899% for upgraded metallurgical Si. In addition, large area of silicon nanowires (SiNW) are fabricated. The purification effect induces a ∼35% increase in photocurrent for SiNW based photoelectrochemical cell.