Improving atmospheric water harvesting in carbon-based sorbents through CO₂ activation

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.