Anodic deposition of CoOOH films with excellent performance for electrochemical capacitors

Amorphous CoOOH films were fabricated on hexagonal graphite substrates in 0.2 M CoSO4 at a constant anodic deposition potential of 1.60 V vs Ag/AgCl (3 M KCl) under different deposition temperatures, and their electrochemical behaviors in 1 M NaOH and 1 M NaCl were systematically studied. The results showed that the deposition temperature had a significant effect on the electrochemical behaviors of the CoOOH films. For the four CoOOH films prepared under different deposition temperatures, when tested either in 1 M NaOH or 1 M NaCl, their area specific capacitance (C-A) and cycle stability increased monotonously, their mass specific capacitance (C-M) first increased and then decreased, while their bulk resistance (R-bulk) and charge-transfer resistance (R-ct) first decreased and then increased with increasing deposition temperature. In addition, the CoOOH films had high CM, good electrical conductivity, low faradic charge-transfer resistance, and low diffusive resistance. Among the four CoOOH films fabricated under different deposition temperatures, the film prepared under a deposition temperature of 45 degrees C (Sample 3) had the highest CM, the lowest R-bulk, the lowest R-ct, and good rate capability which can be ascribed to its structure with nanoparticles and nodules on its surface as well as its appropriate thickness. As a result, the CoOOH film fabricated by anodic deposition is a very promising electrochemical capacitor material for applications.