Combined production of hydrogen and electricity in electrochemical cell with soluble anode

This study addresses the important problem of energy saving in electrochemical hydrogen production by replacing the anodic oxygen evolution reaction (OER) in water electrolysis with a reaction occurring at less positive potentials. Thermodynamic and kinetic analyses show that the OER accounts for up to 85% of the total activation losses in industrial water electrolyzers, which require an operating voltage of 1.8–2.0 V. Replacing the OER with the dissolution of sacrificial aluminum anodes in an alkaline medium made it possible to substantially reduce the energy consumption for hydrogen production. Moreover, coupling an anode made of aluminum scrap with a nickel cathode, where hydrogen is evolved, creates an autonomous chemical power source. The theoretical potential of the Al/Al(OH)₄⁻ system is −2.31 V versus that of the standard hydrogen electrode (SHE). Depolarization due to hydrogen evolution on the aluminum surface shifted the measured anode potential to approximately −1.5 V vs. SHE. The hydrogen evolution potential in an alkaline medium is approximately −0.8 V; therefore, an electromotive force (EMF) of approximately 0.7 V is generated. Depending on the temperature and electrolyte concentration, the system can deliver a short-circuit current density of up to 0.3 A cm⁻². Experiments showed that the specific power density of this chemical power source can reach 10 mW cm⁻². The sodium aluminate produced during anode dissolution can be used as a raw material for the aluminum industry after hydrolysis and heat treatment or as a coagulant for wastewater treatment after treatment with sulfuric acid.