Multifunctional B/N/O-co-doped porous spherical carbons to achieve superior capacitive performance with OER activity†

A series of B, N and O-co-doped samples, CPFP-3/1, CPFP-2/1 and CPFP-1/1, with spherical morphological features have been synthesized by carbonization of a polymer obtained by co-condensation of 1,4-phenylenediamine/formaldehyde/phloroglucinol (PFP) in the presence of tetraethyl orthosilicate. Boric acid (H₃BO₃) has been used here as an external doping agent to introduce B into the frameworks. To distinguish the properties of the B-doped samples from their undoped counterpart, another sample has been synthesized without the addition of H₃BO₃ (CPFP-1/0). The materials have been thoroughly characterized by powder X-ray diffraction, nitrogen adsorption/desorption studies, scanning electron microscopy and X-ray photoelectron spectroscopy. All the samples possess a high specific surface area and are predominantly microporous in nature. The electrochemical behaviour of the samples has been studied thoroughly using cyclic voltammetry, galvanostatic charge/discharge studies and impedance spectroscopy in 1 M H₂SO₄ electrolyte. The specific capacitances of all the samples are high with the values improving as the number of B-atoms (total heteroatoms) increases from CPFP-1/0 to CPFP-3/1, CPFP-2/1 and CPFP-1/1 introducing pseudocapacitive behaviour. CPFP-1/1 with 1 : 1 doping of the polymer with H₃BO₃ is the best performer showing a specific capacitance of 977 F g⁻¹ at 1 A g⁻¹ and 700 F g⁻¹ at 30 A g⁻¹ with a high discharge time. It has a notable specific energy density of 110 W h kg⁻¹ at a specific power of 449 W kg⁻¹ at 1 A g⁻¹, performance-wise bridging the gap between supercapacitors and batteries. Additionally, beyond the potential window of supercapacitance (0–0.9 V), at higher voltage the material shows water splitting activity through the oxygen evolution reaction.