From Surface to Bulk Activation: Tailoring the Porosity and Surface Chemistry of Resorcinol‐Formaldehyde Carbon Sorbents for Atmospheric Water Harvesting

Sorbent‐based atmospheric water harvesting (SAWH) offers a promising route to decentralized water production. However, low‐cost, carbon‐based sorbents generally show insufficient water uptake in arid environments. We introduce a bulk activation strategy to synthesize carbon‐based sorbents, incorporating KOH during the polycondensation of resorcinol‐formaldehyde (RF). This approach utilizes the basic environment to promote a homogeneous distribution of the activating agent throughout the precursor, yielding BET surface areas and pore volumes up to 1704 m 2 g −1 and 0.65 cm 3 g −1 , respectively. XPS shows bulk‐activated samples retain more surface oxygen (13.4–17.7 at%) than conventionally surface‐activated carbons (9 at%). The activation route governs surface chemistry, the KOH/C ratio dictates porosity, and activation temperature affects both. Bulk‐activated sorbents exhibit earlier adsorption onset and kinetics. Sorbents treated at 500°C with a 4.5 KOH/C ratio delivered the best performance under arid conditions (10%–30% relative humidity), with a daily water yield of 15–18 L kg −1 day −1 , while the same sample activated at 600°C performed best at 60% RH, reaching 23 L kg −1 day −1 at a low regeneration temperature of 30°C. Sorbent performance remained stable for 400 h of cycling. These results establish bulk activation as an efficient strategy for tailoring porous carbon sorbents for SAWH across diverse humidity conditions.