Bio-extract mediated green synthesis of bi-functional ammonium cobalt phosphate nanoflakes electrode/catalyst for supercapattery and ethanol oxidation

Abstract

The present study proposes a low-cost, green technique to the synthesis of bi-functional ammonium cobalt phosphate for energy storage and conversion applications. The comprehensive physiochemical investigations are carried out using various spectral-analytical techniques. The results of phase and surface morphology confirm the formation of an orthorhombic crystal structure with flakes-like microstructure. With a maximal specific capacity of 448.3 mAhg−1 at 2 mAcm−2, bio-solvent driven NH4CoPO4·H2O with graphene oxide (GO) nanoflakes demonstrates exceptional battery-type energy storage capabilities. As constructed supercapattery device exhibits a high specific energy of 85.4 Wh kg−1 at power output of 1283 W kg−1 and 81 % stability after 5000 cycles. Further exploration as a non-precious metal-based catalyst for ethanol oxidation reaction (EOR), NH4CoPO4·H2O /GO showed a high peak current density of 83.4 mAcm−2 at 20 mVs−1. Coupled oxygen/hydrogen evolution processes are investigated in 1 M KOH in order to acquire a better understanding of the catalyst's EOR activity. The NH4CoPO4·H2O/GO sample exhibited the lowest overpotentials of |ηOER@10| = 420 mV, and |ηHER@10| = 112 mV, with Tafel slopes of 169.8 mV dec−1 for OER and 132.8 mV dec-1 for HER, respectively. This is due to the catalyst's slow OH adsorption during OER and the limited H*recombination during HER. Therefore, this approach provides a green and cost-effective method to synthesis efficient bi-functional electrode/catalysts for supercapattery and alkaline fuel cells.