ABSTRACT
A nickel-functionalized activated carbon (AC/Ni) was recently developed for microbial electrolysis cells (MECs) and showed a great potential for large-scale applications. In this study, the electroactivity of the AC/Ni cathode was significantly improved by increasing the oxygen (16.9%) and nitrogen (124%) containing species on the AC using nitric acid oxidation. The acid-treated AC (t-AC) showed 21% enhanced wettability that consequently reduced the ohmic resistance (6.7%) and the charge transfer resistance (33.3%). As a result, t-AC/Ni achieved peak values of hydrogen production rate (0.35 ± 0.02 L-H2/L-d), energy yield (129 ± 8%), and cathodic hydrogen recovery (93 ± 6%) in MECs. The hydrogen production rate was 84% higher using t-AC/Ni cathode than the control, likely due to the enhanced wettability and a higher fraction of N on the t-AC. Also, the increases in polyvinylidene fluoride (PVDF) binder loadings (from 4.6 mg-PVDF/cm2 to 7.3 mg-PVDF/cm2) demonstrated 47% higher hydrogen productions rates in MECs.
Subject(s)
Bioelectric Energy Sources , Nickel , Charcoal , Electrodes , Electrolysis , Hydrogen , WettabilityABSTRACT
Ammonia (NH3) recovery from used water (previously wastewater) is highly desirable to depart from fossil fuel-dependent NH3 production and curb nitrogen emission to the environment. Electrochemical NH3 recovery is promising since it can simply convert aqueous NH4+ to gaseous NH3 using cathodic reactions (OH- generation). However, the use of a separated electrode and membrane imposes high resistances to the cathodic reaction and NH3 transfer. This study examined an activated carbon (AC)-based membrane electrode functionalized with nickel to electrochemically recover NH3 from synthetic anaerobic centrate. The membrane electrode was fabricated using nickel-adsorbed AC powder and a polyvinylidene fluoride (PVDF) binder, and the PVDF membrane layer was formed at the electrode surface by phase inversion. The NH3-N recovery flux of 50.3 ± 0.4 gNH3-N/m2/d was produced at 17.1 A/m2 with a recovery solution at pH 7, and NH3-N fluxes and energy consumptions were improved as the recovery solution became acidic (62.2 ± 2.1 gNH3-N/m2/d with 16.0 ± 1.6 kWh/kgNH3-N at pH 2). Increasing PVDF loadings did not impact the electrochemical performances of the Ni/AC-PVDF electrode, but slightly lower (7%) NH3-N fluxes were obtained with higher PVDF loadings. Ni dissolution (3.7-6.0% loss) was affected by the recovery solution pH, but it did not impact the performances over the cycles.
