Biomass-based N/P co-doped hierarchical porous carbon fabricated by a facile dual physico-chemical activation strategy for efficient capacitive deionization

The preparation of heteroatom-doped hierarchical porous carbons (HPCs) possessing both high-performance and cost-effective is advantageous for the advancement of capacitive deionization (CDI). Biomass, which is abundant and inexpensive, has been widely utilized as a precursor for carbon electrodes. However, the simple pyrolysis of a single biomass typically leads to insufficient porosity with narrow surface area, along with poor wettability and conductivity, thereby resulting in limited desalination performance. Therefore, we employ ammonium dihydrogen phosphate (NH4H2PO4) and potassium carbonate (K2CO3) as chemical and physical activators, respectively, to co-activate lotus petiole (LP) for the preparation of N/P co-doped hierarchical porous carbon (NPHPC). In comparison with conventional single K2CO3 activation, NPHPC prepared through dual physico-chemical activation exhibits exceptional specific surface area (SBET, 2170.00 m2/g), excellent pore volume (Vpore, 1.16 cm3/g), outstanding mesoporosity (Vmeso/Vpore, 72.41 %), superior hydrophilic performance (contact angle: 39°), high specific capacitance (221.86F/g), moderate N-doping (3.1 %) and P-doping (0.4 %). When assembled for desalination, the synthesized materials demonstrate a fabulous electroadsorption capacity of 21.85 mg/g together with notable cycling stability, highlighting their excellent application prospects. In summary, this work presents innovative ideas in proposing a facile synthesis of high-performance heteroatom-doped HPCs for CDI desalination.