Extended Data Fig. 9: CO₂ capture by PCS-OH at various relative humidity conditions.

(a) Quantitative ¹³C solid-state NMR spectra of sorbents with ¹³CO₂ gas dosing at 0.9 bar, acquired at a MAS rate of 12.5 kHz. Prior to ¹³CO₂ dosing, the sorbents were pre-humidified using saturated salt solution (approximately 53% RH at 25 °C). (b) CO₂ uptake of sorbents via chemical and physical adsorption calculated from resonances at 156 ppm and 119 ppm of (a), respectively. Shown in (c) and (d) are data analogous to (a) and (b), except with a relative humidity level of approximately 85% at 25 °C. CO₂ uptake of PCS-OH in various relative humidity (RH) at (e) direct air capture conditions and (f) 0.9 bar CO₂. The analysis in part (e) is from the sealed-container experiments presented in Fig. 4f of the main text, while the analysis in (f) is from solid-state NMR experiments shown in (a) and (c). (g) H₂O adsorption (filled circles) and desorption (open circles) isotherms of the PCS-OH at 298.15 K. (h) Specific heat capacity measurements from differential scanning calorimetry for PCS-OH, using a DSC2500 from TA instruments. Data is shown for the sample heated from 25 °C to 90 °C after an initial heating and cooling cycle from 5 °C to 200 °C and back to 5 °C. The mass of PCS-OH used was 2.7 mg. The average specific heat capacity between 25 °C and 90 °C is 0.62 J/(gK), and this value was used to estimate the minimum energy required for heating PCS-OH from 25 °C to 90 °C during regeneration, with a value of 40 J/g (see main text).