Green synthesis of CoWO4 powders using agar-agar from red seaweed (Rhodophyta): Structure, magnetic properties and battery-like behavior

This work reports a proteic sol-gel green method that uses agar-agar from red seaweed (Rhodophyta) for synthesizing cobalt tungstate (CoWO4) powders for battery-like electrodes. For comparison, CoWO4 is also prepared by a similar proteic chemical route that uses flavorless gelatin. The as-prepared powders were calcined at 800 degrees C for 2 h and further characterized by XRD (with Rietveld refinement), SEM/EDS, FTIR/Raman/UV-Vis-NIR spectroscopies, VSM, and various electrochemical techniques for assessing the battery-like behavior in alkaline media (3 M KOH). The results indicate that samples produced by gelatin show average particle size of 150 nm and crystallite size of 68 mn, against 284 nm (particle) and 84 nm (crystallite) for agar-agar processed materials. Magnetic assessment at 300 K showed a paramagnetic behavior for both samples. The analysis of these curves showed an effective magnetic moment per cobalt atom of 4.908 mu(B) and 4.926 mu(B) for samples prepared using gelatin and agar-agar, respectively. The performance of CoWO4 as battery-like electrodes is ascribed due to a surface faradaic redox reaction mechanism related to reversible valence state between Co2+ and Co3+. Discharging curves indicate no substantial difference of electrochemical performance, with maximum specific capacity of 77 C g(-1) at a specific current of 1 A g(-1). The long-term stability of electrodes is confirmed by a capacity retention of around 98% over 1000 charge-discharge cycles at 1 A g(-1).