Preparation of boron-containing carbons from glucose–borate complexes and their capacitive performance

Abstract

Hydrothermally synthesized glucose-borate complexes (mole ratio 1/1 and 1/2) were carbonized at 800–1200℃ for 1 h in argon, followed by boiling in water to remove borate byproducts. Formed boron-containing carbons (B-carbons) contained 1–3.4 mass% boron and, by XPS, boron was present mainly as a form of C-B-O bonding and not as the substituted boron. The specific surface area by N2 adsorption, SBET, was 850–1360 m2 g−1, and decreased with raising heat treatment temperature. The 1/2 complex provided larger SBET than the 1/1 complex. Pore width was less than 3 nm except for the products at 1200℃. The cyclic voltammograms (CVs) at 2 mV s−1 in 1 mol dm−3 Na2SO4 were rectangular and the specific capacitance normalized by SBET, CA, was 0.05–0.1 F m−2, indicating the electric double layer capacitance. In 1 mol dm−3 H2SO4, CVs showed broad redox peaks in a potential range of 0–0.6 V vs. SCE and CA was 0.13–0.2 F m−2:the pseudocapacitance is attributed to more than two types of oxygen-containing functional groups and one of them might be =B-OH type. The electrode capacitance, CM in F g−1, in the H2SO4 solution was more than twice of the CM in the Na2SO4 solution. It may be mainly due to the difference between Na+ and H+ ions, though a certain level of pseudo-capacitance is contributing to CM. Carbons derived from a mixture of poly (vinyl alcohol) and boric acid were SBET<50 m2 g−1, suggesting that the large SBET of B-carbon is owing to the thermal decomposition behavior of glucose-borate complexes, which is different from the pore formation mechanism of the MgO template method reported.