Modeling and Experimental Analysis of Polarization-Induced Hydrogen Evolution and Electrode Dissolution in the Electrocoagulation Process

Electrocoagulation (EC) is a sustainable electrochemical water-treatment process in which contaminants are removed by generating coagulant species in situ through anodic metal dissolution, while hydrogen evolves at the cathode. Aluminum electrodes are widely used because they produce effective coagulants, but their performance is often constrained by surface passivation and apparent departures from ideal faradaic behavior. “Super-faradaic” hydrogen production is frequently inferred from electrical measurements alone, even though additional hydrogen can arise when electrochemical charge is coupled with chemically assisted aluminum corrosion and oxide-film disruption; therefore, hydrogen evolution and aluminum loss must be quantified together to close the mass/charge balance. In this thesis, hydrogen evolution and aluminum dissolution were measured in aluminum-based EC systems operated under direct current (DC), polarity reversal (PR), and linear sweep voltammetry (LSV) in sodium chloride (NaCl), sodium sulfate (Na₂SO₄), sodium nitrate (NaNO₃), and synthetic groundwater (SGW). Hydrogen was quantified using an electrode-resolved gravimetric method and dissolved aluminum by ICP-OES, with gas chromatography confirming the evolved gas was predominantly H₂, enabling direct evaluation of non-ideal behavior across electrolytes and operating modes. Under DC operation, hydrogen evolution was strongly electrolyte-dependent because dominant anions regulate passivation, depassivation, and competing cathodic pathways. Chloride-containing solutions produced the highest hydrogen generation and the strongest super-faradaic response, reaching a hydrogen faradaic efficiency of 259 ± 6% in 0.3 M NaCl at 1 mA·cm⁻², consistent with chloride-assisted destabilization of the surface film. In contrast, passivating media suppressed hydrogen evolution and aluminum release, yielding efficiencies closer to ideal values (106.6 ± 8% in Na₂SO₄ and 103.5 ± 6% in SGW under comparable conditions). In NaNO₃, hydrogen evolution was strongly inhibited because cathodic charge was largely consumed by nitrate reduction; anodic hydrogen was near the detection limit (0.3 ± 0.15%), and total hydrogen evolution remained extremely low. LSV trends supported the DC findings. PR (half-cycle durations 0.5–10 min) produced electrolyte- and PR interval-dependent responses. In Na₂SO₄, long half-cycles increased hydrogen efficiency from 106.6% (DC) to 190% (PR-10) and increased aluminum dissolution efficiency from 71.8% to 97.0%, indicating disruption of stabilized oxide/hydroxide layers on a timescale of minutes. In NaCl, PR reduced hydrogen efficiency (from ~259% to ~230%). A physics-based numerical model for DC operation coupled electrochemical kinetics with ionic transport and represented bubble effects through a reduction in fluid density and effective electrolyte conductivity. For a geometry-matched Al–Al cell under potentiostatic polarization (0.3–0.9 V), the gas-coupled model matched experiments within a few percent, whereas a single-phase no-gas model overpredicted current at high voltage (up to ~30% at 0.9 V). Overall, the combined measurements and experiment-constrained modeling support improved EC operation and scale-up by enabling more reliable prediction of voltage demand, energy efficiency, and electrode lifetime in gas-evolving regimes.