Neutralization Pseudocapacitors: An Acid–Base Machine

Abstract

This study proposes a thermodynamic machine that operates between acid and basic reservoirs in four stages. Two of these stages are buffered isothermal steps. The other two stages constitute an open system and allow the passage of acid and base. The machine consists of a neutralization pseudocapacitor that, after a full cycle, carries out work generated from partial change in entropy associated with a change in the hydrogen potential after the neutralization process. Thermodynamic formalism is presented under reversible stages. This presentation enables determination of the maximum efficiency, related to the difference between the hydrogen potential of the acid reservoir and of the resulting solution after neutralization in the machine. Hence, the hydrogen potential scale can be defined as a function of the efficiency of the reversible acid−base machine regardless of the electrochemical cell composition. Electroactive thin films formed from phosphomolybdic acid and poly(3,4ethylenedioxythiophene) have been investigated as proof of concept in electrolytic solutions at several pH values; their efficiency was close to the efficiency predicted by the thermodynamic approach. Therefore, this model allows one to estimate the maximum energy harvesting of neutralization pseudocapacitors and financial return for the treatment of acid wastewater, contributing to sustainable growth.

Electrochemical Systems for Renewable Energy Conversion from Salinity and Proton Gradients

“…Natural . Adapted from Morais et al 40 processes like the global hydrological cycle ensures the viability of these technologies by maintaining the salinity concentration difference of natural water reservoirs, e.g., river water and seawater. Also, concentration gradients resulting from human actions could be used for energy conversion purposes.…”

“…23,39 NB can be understood as an idealized acid-base machine, which is similar to the concept of thermal machines. 40 In an ideal acid-base machine, matter flows between the acidic and the basic reservoirs, to provide maximum work. Figure 7 shows a schematic representation of the working principle of this idealized machine.…”

“…The most common strategy to overcome this problem is to prepare organic-inorganic hybrid composites. To reduce the solubility of phosphomolybdic acid in aqueous medium, Morais et al 40 coupled PMA with the polymers poly(allylamine) (PAH) and poly(3,4-ethylenodioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) by the layer-by-layer (LbL) method, to obtain self-assembled films. Electrostatic interactions between the PMA oxygen atoms, the PAH protonated amine groups, and the PSS sulfonic groups allowed the film to grow.…”

“…Moreover, the intimate contact between the materials promoted by the LbL method elicited a synergistic effect that improved the specific capacity and ensured the practical reversibility of the electrochemical process. 23,39,40 An experimental proof of concept of the acid-base machine was carried out by using a three-electrode cell consisting of PMA/PAH/PEDOT-PSS as the working electrode, a platinum sheet as the counter electrode, and an Hg/Hg 2 SO 4 electrode as the reference electrode. Figure 10a shows the electroreduction, at pH 0, and the electrooxidation, at several pHs, of the PMA host matrix in a process that simulated H 2 SO 4 neutralization with KOH.…”

“…79 Aiming at its applications as the positive electrode in NB cells, an electro-synthesized PEDOT film was used to intercalate/deintercalate sulfate anions during the charge/ discharge processes; a PMA/PAH/PEDOT-PSS film was used as the negative electrode. 40 In these experiments, a 0.05 M H 2 SO 4 aqueous solution was neutralized with KOH. For this cell, the charge process was performed at several pHs, and the discharge process was carried out at pH 6, as seen in Figure 12.…”