Energy harvesting in the course of acid solution neutralization

This work investigates electrodes consisting of phosphomolybdic acid/reduced graphene oxide (PMo12/RGO) and copper hexacyanoferrate (CuHCF) for proton adsorption/desorption and alkali metal ion intercalation/deintercalation, respectively. These electrodes can be used to harvest the energy resulting from the difference in ion concentrations during acid solution neutralization. H3PMo12O40 clusters were uniformly anchored on RGO sheets to ensure large electrode surface area and to facilitate proton access to the polyoxometalate elec-troactive sites. On the other hand, compared to iron ions in Prussian Blue, copper ions in the hexacyanometalate structure provided higher potassium ion intercalation/deintercalation rate. The experiments were performed in the time and frequency domains, and thermodynamic and kinetic models were proposed to improve our understanding of how the electrochemical system behaves with respect to energy harvesting. The reactions presented low energy dissipation due to low charge transfer resistance and diffusion impedance. The predicted energy harvested by the electrochemical full cell was 13.5 and 10.7 kJ per mol of adsorbed proton at 0.1 and 1.0 mA cm(-2) in acidic (pH = 2) and slightly acidic (pH = 6) media, respectively, which included acetate buffer and the feedback of the saline solution resulting from neutralization. The electrodes used here provided increased energy harvesting and power density compared to other electrode materials employed for the same purposes. Indeed, energy harvesting from acidic wastewater treatment can be a profitable and sustainable practice mainly for industries that generate enormous amounts of wastewater. (AU)