Bi-phasic BiPO4 prepared through template-assisted hydrothermal method with enhanced electrochemical response for hybrid supercapacitor applications

We report the structural evolution of BiPO4 prepared in aqueous under different synthesis conditions viz., templates and temperatures to explore their electrochemical performance for supercapacitor applications. The templates [(hexadecyltrimethylammonium bromide (CTAB)), sodium dodecyl sulfate (SDS)] were added in bismuth precursor solution at 60 degrees C, alternatively ethylene glycol (EG), a less toxic additive was incorporated at 90 degrees C. BiPO4 exhibits a monoclinic phase, whereas a hexagonal structure was observed with the addition of the templates SDS and CTAB. Interestingly, both monoclinic and hexagonal phases were obtained by the addition of EG. The presence of mixed phase was thoroughly validated through Raman spectra, where vibrational modes for both monoclinic and hexagonal phases of BiPO4-EG were witnessed. The effect of template was clearly seen through electron microscopy with a rod-like morphology with (no template) and unfaceted (template). The electrochemical behavior of the synthesized materials was investigated, and it was found that the mixed structure of BiPO4-EG exhibited the highest specific capacity (167.15 C g(-1)) at a scan rate of 5 mV s(-1), good capacitance retention at high current densities of up to 10 A g(-1) and the lowest electrochemical series resistance (ESR) of 57 Omega. [Graphical abstract]