Abstract
Energy efficient water desalination processes employing low-cost and earth-abundant materials is a critical step to sustainably manage future human needs for clean water resources. Here we demonstrate that porous silicon – a material harnessing earth abundance, cost, and environmental/biological compatibility is a candidate material for water desalination. With appropriate surface passivation of the porous silicon material to prevent surface corrosion in aqueous environments, we show that porous silicon templates can enable salt removal in capacitive deionization (CDI) ranging from 0.36% by mass at the onset from fresh to brackish water (10 mM, or 0.06% salinity) to 0.52% in ocean water salt concentrations (500 mM, or ~0.3% salinity). This is on par with reports of most carbon nanomaterial based CDI systems based on particulate electrodes and covers the full salinity range required of a CDI system with a total ocean-to-fresh water required energy input of ~1.45 Wh/L. The use of porous silicon for CDI enables new routes to directly couple water desalination technology with microfluidic systems and photovoltaics that natively use silicon materials, while mitigating adverse effects of water contamination occurring from nanoparticulate-based CDI electrodes.
Highlights
Electrodes compatible with large-scale manufacturing, and controlling the electrode structure to inhibit fouling or deactivation[19]
Unlike other routes to produce CDI electrodes, this material has a pore architecture controlled by the silicon electrochemical etching process, a structure that is tethered to a solid surface to inhibit particulate removal, and a stable interface for salt removal that is mediated by the carbon passivation layer
The performance of porous silicon based CDI electrodes over this range of concentrations supports the principle of a multi-cell CDI system based on porous silicon materials that can maintain high efficiency in converting ocean water to fresh water
Summary
Electrodes compatible with large-scale manufacturing, and controlling the electrode structure to inhibit fouling or deactivation[19]. The porosity, thickness, and feature size (surface area) can be varied over orders of magnitude[27,28,29] enabling a level of control that can mitigate fouling, optimize durability under flow, and efficiently enable salt removal without the release of free particulates into the flow As this material has promise to overcome many of the key problems facing current CDI technology, our results indicate salt removal performance up to 0.52% by mass with performance maintained across the whole range of brackish water conditions, which is comparable or better than other state-of-the-art carbon particulate-based electrodes. This gives promise to this material for CDI applications, but opens new routes for integration into systems such as microfluidics[30] or solar cells[31], that are synergistic with desalination technology and rooted in silicon processing architectures
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