Reduced graphene oxide–bismuth oxide composite as electrode material for supercapacitors

We have reported a new reduced graphene oxide–bismuth oxide composite that can be used as a supercapacitor electrode. Bi 2 O 3 was synthesized from bismuth nitrate pentahydrate and oxalic acid as a precipitating agent using a hydrothermal process in an aqueous graphene oxide suspension. Instead of mixing graphene oxide with bismuth oxide, we have developed a bismuth oxalate precipitation between the layers. As prepared, composite of hydrated bismuth oxalate and graphene oxide was converted to bismuth oxide and reduced graphene oxide by thermal decomposition in a muffle stove. The material exhibited the specific capacitance of 94 F/g at current density 0.2 A/g. Using the cyclic voltammetry, the specific capacitance was as high as 55 F/g at scan rate 5 mV/s over the potential range 0–1 V. The material exhibited long-term cycle stability retaining 90 % specific capacitance after 3,000 cycles. Except Bi 3+ ions present in Bi 2 O 3 , some amount of higher energy Bi 5+ was confirmed.