Asymmetric hybrid energy conversion and storage cell of thin Co3O4 and N-doped reduced graphene oxide aerogel films

Abstract Although batteries and supercapacitors can store electrical energy, they cannot convert energy like solar cells. Here, we introduce a new asymmetric hybrid energy conversion and storage (HECS) cell consisting of thin photoactive cobalt oxide (Co 3 O 4 ) film with a thickness of 1 μm coated on the fluorine-doped tin oxide (FTO) glass as the positive electrode and thin N-doped reduced graphene oxide aerogel (N-rGO AE ) film with a thickness of 10 μm coated on the FTO glass as the negative electrode. The HECS cell can convert light to electricity, which is subsequently stored within its electrode materials. The as-fabricated asymmetric HECS cell of Co 3 O 4 //N-rGO AE thin films exhibits 140% higher specific capacitance under red LED light illumination than that under dark condition and provides a specific energy and a specific power of ca. 3.5 Wh kg −1 and ca. 7000 W kg −1 , respectively. The Co 3 O 4 can absorb all visible light spectrum and excite its valence electron to the conduction band via its indirect band gap (1.45 eV) so-called the photovoltaic effect. Whilst, the N-rGO AE can balance all charges generated at the Co 3 O 4 positive electrode via the electrochemical double-layer capacitance. The asymmetric HECS of Co 3 O 4 //N-rGO AE may be an ideal solution for future renewable and sustainable energy.