Improving Atmospheric Water Harvesting in Carbon-Based Sorbents Through CO2 Activation

Abstract

Atmospheric water harvesting (AWH) can serve as an alternative fresh water source in regions with scarce access to drinking water. While many techniques are geographically or seasonally limited, sorbent-based AWH shows the potential for wider application. Low-cost, carbon-based sorbents named nanoporous sponges (NPS) are recently developed, exhibiting fast and repeatable water uptake of 0.14 g g−1 at 90% relative pressure. While useful from a cost and daily water yield point of view, there is room for improvement. This article presents an improved production process combining pyrolysis and activation under CO2 in a single step, yielding improved NPS capable of reproducibly reaching a water uptake of 0.47 g g−1 at 95% relative pressure while maintaining fast sorption rates. The NPS show significant endurance and are able to maintain stable performance over numerous humidity cycles. An unexpected time-dependant sorption behavior is also identified for NPS produced with a modified synthesis formulation, due to an increase in sodium carbonate residual content.